Chuck Yung
EASA Technical Support Specialist

One of the unique motor applications we’re often called upon to service is the “shaker screen duty”or vibrator motor. See Figure 1. These are mechanically robust electric motors, fitted with large eccentric weights, designed to deliberately vibrate – a lot. The unusual application calls for some special considerations when repairing these motors. This article is intended to consolidate those tips in one place.

When dismantling the motor, the first step is to document the position of the eccentric weights on both ends, relative to each other, so the performance characteristics remain unchanged. Note that many of these are fitted with two weights on each end and that only one of the weights is keyed. The second weight can be shifted relative to the first to allow adjustment of the unbalance to suit the application. In some applications, for example, when shaking a product through a hopper, the weights might be adjusted to different settings to move materials of different density. See Figure 2.

David Sattler
L&S Electric, Inc.

A no ser que se tenga mucho cuidado, tirar del alambre magneto al desmantelar el estator de un motor a menudo deforma o dobla los dientes de las laminaciones. Estos dientes deformados comprometerán la calidad de la reparación y hay estudios que demuestran que este problema puede reducir la eficiencia del motor. Sin embargo, aunque esta reducción puede ser pequeña, genera altos costos y desperdicio de energía.

Aunque los clientes rara vez notan la merma del rendimiento, nuestro objetivo durante la reparación de los motores es siempre llevar a cabo rebobinados de la más alta calidad posible. Por lo tanto, hemos diseñado e implementado el uso de discos (platos) retenedores para mantener los dientes del estator en su lugar mientras se saca el alambre magneto de las ranuras. Los discos que se ven en las fotografías nos han ayudado a evitar y garantizar dañar los dientes del estator al sacar el alambre del estator.

Mike Howell
EASA Technical Support Specialist

The two primary reasons for performing stator core testing in the service center are (1) to verify that the stator core is acceptable for continued use and in the event of a rewind, (2) to verify that the repair process has not adversely changed the stator core condition. This testing can be done using a commercial core loss tester or a manual loop test using an appropriate AC source, cables and meters. Some typical reasons a manual loop test may be performed are: 

• Customer or service center preference / specs 
• Commercial core loss tester not available 
• Stator size is inappropriate for available commercial core loss tester 

Additionally, some service centers have forgone core loss testing on small stators for various reasons including difficulties with test configuration, calculations, cost or even appearance. The purpose of this article is to explore a low-cost test setup for loop testing small stators.

A special discounted collection of 11 webinar recordings focusing on AC motor electrical procedures.

Once purchased, all 11 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

The Basics: Motor Repair Burnout Procedures
Presented October 2016

• Interlaminar insulation materials / properties of AC stators
• Core testing before and after
• Processing equipment, controls and records

The Basics: The Why and How of Core Testing
Presented October 2016

• The reasons for performing core testing and why they are important
• An explanation of the two core testing methods:
• Loop testing
• Use of a core tester
• How to properly perform a core test
• How to assess the results
• Stator Core Testing: Know What You Have Before You Wind It

Stator Core Testing: Know What You Have Before You Wind It
Presented April 2017

This presentation covers:

• The importance of the stator core test 
• Simple theory to share with technicians and customers 
• Practical approach for testing small stators demonstrated 
• Eliminating pen + paper; loop test calculations for any device 
• Assessing the results

High Potential Testing of AC Windings
Presented December 2019

High-potential testing is routinely used to assess the ground insulation of AC stator windings in-process, after completion of a rewind and post-delivery. This webinar covers:

• Differences between AC and DC high-potential tests
• Sizing AC test sets when testing large windings
• What relevant standards address (and what they don’t)
• Communicating test requirements to all stakeholders
• When to test and at what levels
• How to evaluate results

Target audience: Beneficial for service center managers, supervisors and technicians responsible for high-potential testing.

Squirrel Cage Rotor Testing
Presented October 2014

Determining whether or not a squirrel cage rotor is defective is an issue that is a challenge to every service center as there is often no simple way to determine the integrity of a rotor. The primary focus of this session is to describe many of the available tests that can be utilized in the service center or at the motor installation site. In addition to conventional squirrel cage rotor testing methods such as the growler test, techniques that will also be covered are the use of a core loss tester, high current excitation, and spectrum analysis of vibration.

Target audience: This presentation will be most useful for service center and field technicians with at least 2 years experience, service center supervisors and managers, engineers, or anyone with previous experience dealing with suspected open rotor issues.

Evaluating High No-Load Amps of Three-Phase Motors
Presented December 2011

This presentation focuses on the steps to take before rewinding to avoid the undesirable situation of high no-load motor amps after the rewind.

The presentation covers the following steps that should be performed on every AC stator rewind:

• Inspect the stator bore and rotor outside diameter for evidence of machining or damage
• Record the original winding data exactly as found
• Verify the winding data
• Test the stator core before and after rewinding removal

Target audience: This is most useful for service center mechanics and winders with any level of experience, and service center supervisors and managers.

Insulation Technology Improvements and the Repair Market
Presented July 2019

Most modern rotating electric machines operate on the same principles their predecessors have for 100+ years. However, improvements in materials technology over that time have allowed for increasingly greater power density in machine design.

There is a natural time lag between OEM technology improvement and repair of equipment containing that technology. This session will explore some of these improvements and their implications for service centers attempting to provide a quality repair.

Target audience: This webinar will be appropriate for service center managers and technicians responsible for rewind activities.

Motor Temperature Rise and Methods to Increase Winding Life
Presented December 2018

This webinar discusses:

• Temperature rise: Method of detection, Insulation class, Enclosure, and Service Factor
• Increasing winding life: Insulation class, Cooling system, and Winding redesign

Target audience: This will be most useful for service center engineers, supervisors, managers and owners. The content will also be beneficial for mechanics and winders.

Air Gap: What It Is, What Does It Do, and Why Is It Important?
Presented October 2019

The physical air gap between the rotor or armature and the stator or field frame is complex and plays a critical role in the performance of AC and DC machines. Most repairers do not realize how little they understand about this subject.

This webinar explains the role air gap plays in AC motor performance, how to recognize the symptoms of an uneven air gap, and share corrective measures. For DC machines, this webinar will cover the distinctly different role of the field air gap as opposed to the air gap of the interpoles.

• Air gap tolerance of AC machines
• Air gap tolerance of DC fields and interpoles
• Allowable runout of rotor / armature
• Recognizing the signs of air gap anomalies
• Corrective actions

Target audience: This webinar recording is of benefit to managers, supervisors, winders, mechanics and field service personnel.

Troubleshooting AC Generators & Alternators
Presented May 2015

This recording covers theory of operation, inspection, operation and troubleshooting tips for AC generators and alternators. For the supervisor, field service technician or service center personnel, generators can present unique challenges. Topics covered include:

• Theory of operation
• Testing tips
• Stator winding cautions
• How to interpret the exciter motor connection
• In-shop and on-site testing methods
• How to test the voltage regulator
• How to test a generator without a regulator

Core Repair and Restack Techniques
Presented April 2014

This webinar teaches:

• How to repair damaged stator cores and how to know when a restack is necessary.
• There are often cases when repairs can be accomplished without a labor intensive restack.
• When a restack is required, there are pitfalls to watch out for to avoid problems with geometry, vibration and core losses.

Target audience: This presentation is useful to the supervisor, winder and sales personnel who interact with the end user.

Gene Vogel
EASA Pump & Vibration Specialist

Proper alignment of direct-coupled machinery is an essential element in reliability of a new or repaired machine (motor, pump, gear case, etc.). One common impediment to achieving proper alignment and smooth opera­tion is a “soft foot” condition. 

A soft foot occurs when all the feet of a machine case do not sit flat on the supporting base so that tightening the foot bolts causes distortion of the ma­chine case. The source of the soft foot could be a baseplate which is not flat or machine feet which are distorted. Not only does this make it difficult to align the machine, but the casing distortion may add additional load to the bearings and create internal mis­alignment between the rotating and stationary elements of the machine resulting in poor performance and increased vibration.

The webinar covers:

• How to set brush neutral in DC machines.
• Several methods of setting brush neutral along with the benefits and drawbacks of each.
• Tips for permanent magnet and series-would machines.
• Tips on how to recognize problems and settings that affect brush neutral, and what to check if the neutral adjustment seems higher than usual.

Target audience: This presentation is most useful for service center and field technicians involved in the repair of DC machinery, service center managers engineers, or anyone involved in DC motor or generator repair, as well as those who are simply looking to expand their understanding.

This video walks through the steps to adjust and set end play on a typical vertical hollow shaft pump motor. Proper end play adjustment is important to keep the lower bearing from supporting the weight of the rotor and to allow for thermal growth within the motor.

The motor in this video has a thrust bearing in the top and a standard ball-type guide bearing in the bottom, which is typical of vertical pump motors. There are other bearing arrangements with somewhat different procedures for setting end play, but here we’ll be working with the most common arrangement and procedure. There are variations of this process, and some vertical pump motor bearing arrangements require special procedures, especially those with springs mounted under a spherical roller thrust bearing.

Topics covered include:

• Tools and supplies needed
• Basic principle of end play adjustment
• How to adjust end play
• How to measure and verify proper end play

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Cuando se rebabitan o se reemplazan cojinetes de deslizamiento, un paso importante durante el montaje consiste en verificar el contacto entre el cojinete y el muñón del eje que monta sobre el. El uso de cojinetes de deslizamiento auto alineables (también denominados esféricos o de ajuste esférico) hace que este paso sea casi innecesario. Aun así, los cojinetes de deslizamiento cilíndricos se deben inspeccionar para verificar que haya suficiente área de contacto.

Los cojinetes de deslizamiento, también conocidos como cojinetes de babbitt, de metal blanco o cojinetes lisos, han sido utilizados por más de 150 años. Para una explicación detallada sobre el diseño y funcionamiento de los cojinetes de deslizamiento solicite a EASA el documento de la convención del 2007: “Sleeve Bearing Repair Tips,” o el libro Mechanical Repair Fundamentals of Electric Motors, 2nd Edition.

Este es un artículo específico para verificar y corregir el patrón de desgaste al momento de instalar cojinetes nuevos en un motor eléctrico. Ajustar cojinetes no es difícil, solo se requiere algún conocimiento básico, Un parte interesante de la historia es el kit de herramientas suministrado con el antiguo automóvil Ford -Modelo A, que incluía un cuchillo para babbitt para rascar los cojinetes del cigüeñal. Imagine desmontar el motor de su auto en el camino, para retirar y ajustar los cojinetes de babbitt.

Tom Bishop, P.E. 
EASA Technical Support Specialist

There are certain repair processes that can impact the efficiency and reli­ability of electric motors. Prudent repair practices must not increase overall losses, and preferably should maintain or reduce them. In some cases, repairers can also employ the principles applied by the motor designers and further reduce losses and enhance efficiency. Most of the following material is taken from, or based on, the “The Effect of Repair/Rewinding on Motor Efficiency; EASA/AEMT Rewind Study And Good Practice Guide to Maintain Motor Efficiency.” 

Stator core processing and repair 
Concerns about the possibility of core degradation during the rewind process have been expressed since at least the early 1990s. Higher tempera­ture rated core plate insulation mate­rial greatly reduces the possibility of core degradation during the burnout process. However, a best practice approach is to avoid the possibility of core damage no matter what type of core plate is used. 

The key steps to take during the burnout process are to set the burnout temperature to no more than 680° F (360° C), and use a temperature-sensing device attached to the core being processed to control the oven temperature. Further assurance that degradation will not occur is to use an oven equipped with a water suppression system. If an over-temperature condition is detected, the water spray is immediately activated. This method is highly effective because water changing from a liquid to a gas (steam) absorbs a tremendous amount of heat energy; much more than if simply changing tem­perature by absorbing heat energy. That is, water absorbs as much energy in changing from liquid to steam as it would in theoretically increasing temperature by 540° C (970° F). 

Prior to and following the burnout process the core should be tested, as illustrated in Figure 1. The core can either be loop tested (see Tech Note 17) or tested with a commercial type core tester. Both methods are effective. The watts per unit of weight core loss and temperature rise of the core during the test should be compared to each other (pre-and post-burnout process) and to typical limits. Typical limits for core loss are about 4 watts per pound (9 watts per kg) and for temperature rise about 15° C rise (27° F). Further, the watts loss per unit of weight should not increase more than 20% during the process, and best practice would be for neither temperature nor watts loss to increase at all. 

If the core test or visual inspection reveals core damage, the core should be repaired prior to winding. Minor defects such as splayed or flared laminations should be tamped back in place. A technique that is usually effective for flared laminations is to bend the teeth at the end of the slot at the vertical middle. That is, create a bowed effect, with the center bowed away from the core.

Tamping the teeth (by striking with a slight down­ward angle at the top of the teeth) back to the core causes the bowed teeth to act as a clamping mechanism. 

If lamination material has been eroded but the extent of the damage is minor, the laminations can normally be un-stacked in the affected area and restacked after repositioning the laminations to fill in the area that was missing lamination material. Removal of complete laminations should be avoided. As a guide to determining the limit of “minor” missing core ma­terial, it should not exceed 2% of the length of the core, or not affect more than 10% of the number of teeth. If damage is more extensive than these guidelines, best practice action steps would be to replace the damaged laminations with new laminations, restack the core with all new lamina­tions, replace the core, or replace the entire motor. New laminations can be obtained through firms that specialize in laser cut laminations, using a good original lamination as a template. 

Following core repair, always retest the core before proceeding with the rewind. The watts loss and tem­perature rise should both be less than prior to repair of the core damage; and the watts loss and temperature rise levels should be within the typi­cal limits given above. 

Winding practices 
The best practice goals in winding are to maintain or reduce the winding resistance and to maintain or improve the motor performance characteristics. The winding resistance is maintained by using the same size wire area, and the same mean (average) length of turn. Increasing the wire size area, reducing the mean length of turn, or doing both, reduces winding resis­tance. That reduces the stator winding I²R losses as the winding resistance is the “R” in the I²R equa­tion. Reduced losses mean that efficiency increases and heating is reduced, which length­ens the thermal life of the insulation. 

Reducing the length of the coil extensions is the only method of re­ducing the mean length of turn (MLT – the av­erage length of a single turn of the winding, as depicted in Figure 2) during rewinding. The core length is fixed, thus the only variable is the length of the end turns. The end turn length can be reduced to the point that any further reduction will result in a side force between the coil and the end of the slot. Going beyond that point can result in a winding ground fault due to the coil pulling against the slot cell extension and eventually breaking through it. 

Another consideration with coil extension length is that by reducing it, the surface area exposed to cooling air is also reduced. Although this would rarely be a significant pos­sibility, it should be kept in mind especially when there appears to be an opportunity to significantly reduce the coil extension distance. An example would be the pos­sibility of being able to reduce an approximately 4-inch (100 mm) coil extension to just less than 3-5/8 inches (90 mm). The 10% reduction in exposed length could increase heating due to less heat transfer from coils to cooling air. The effect of a +/- 10% change in MLT for a variety of motor power ratings is illustrated in Table 1. 

Increasing wire area is possible if slot space is available. A benefit of increasing slot fill is that there will be less space between wires, mak­ing varnish penetration and bonding more effective and resulting in better heat transfer as air pockets (voids) are reduced. However, making the wires fit too tightly in the slot can result in damage to the wire insulation as the winding is tamped in place with excessive force; the slot liner can also be damaged. It can also increase the time required to insert the coils. The increased wire area reduces copper (I²R) losses and reduceswinding tem­perature. The effects of these changes are increased efficiency and longer winding thermal life. 

Mechanical repairs 
Replacement bearings should be equivalent to those provided by the motor manufacturer. Selecting an incorrect bearing, such as changing from an open to a sealed bearing, will increase friction losses in the bearing, thus reducing efficiency. Incorrect in­stallation of a bearing—for example, driving it on by pressing against the outer race—can damage the bearing and cause rapid failure. Even a slight amount of damage can result in a noisy bearing. 

Bearings of C-3 internal clearance are the standard for most electric motors. A contact-type sealed bearing can create more friction than a shielded, open or non-contact sealed bear­ing. The increased friction results in a slight drop in efficiency. To avoid degrading efficiency and reducing reliability, it is good practice to remain with the open bearing style installed by the manufacturer. 

Fill the grease reservoir cavity to about one-third to one-half full. Over greasing a bearing, even by a small amount, increases friction losses. This not only reduces ef­ficiency (by 500 watts in one case cited in the EASA/AEMT study); it also causes local overheating, which can seriously reduce bear­ing life. Allow the motor to oper­ate unloaded long enough for the bearing temperature to drop. The drop in temperature indicates that the bearing has expelled excess lubricant and seated itself into a stable position. In essence, this denotes the bearing “break-in” period as shown in Figure 3. 

When application and environment dictate the installation of sealed bearings for reasons of reliability, some increase in bearing temperature and friction losses should be expected. A better alternative is to consider the installation of non-con­tact seals or bearing isolators, which exclude contaminants without causing friction. Some bearing manufacturers also offer non-contact sealed bear­ings. 

Ventilation issues 
Unfortunately, there is little op­portunity to improve efficiency by changing fans or ventilation, except in rare cases where a large increase in wire current capacity is possible, such as when converting from aluminum to copper wire. In such a case the fan size can be reduced if the aluminum wire is replaced with the same size copper wire. Reducing fan size or airflow reduces windage losses at the expense of increased winding heating. The converse also applies; increasing fan size or airflow reduces winding heating at the expense of increased windage losses.

Although we may not have opportunities to reduce losses with ventilation issues, good practices will result in maintaining the original efficiency. 

Installing an incorrect fan, or locating the fan or fan cover in the wrong position (improper clearance between the fan and fan cover), can affect windage. A fan that moves more air, i.e., has higher flow, inher­ently increases windage loss and reduces efficiency. Conversely, a smaller or lower flow fan (see Figure 4) reduces windage but also reduces cooling due to the lower airflow. If a fan has a broken blade or blades, it should be replaced. The miss­ing blade(s) reduce airflow and may increase vibration due to mechanical unbalance. 

Windage varies among fan designs, depending on factors such as diameter, the number and size of blades, mate­rial, and surface finish. The single most important variable is fan diameter. All else being equal, a smaller diameter (D1) trimmed fan moves considerably less air than the larger original diameter (D2), by the ratio: [(D2 / D1)³]; and symmetrical fans of different diameters vary by [(D2 / D1)⁴]. Thus a propor­tional replacement fan that is 5% larger in diameter compared to the original requires 22% more power to drive the fan. That diverted power is lost power, which reduces motor efficiency. 

An incorrect fan cover may reduce air flow; an example is where the open­ings in it are smaller than the original. Location of the fan relative to the cover is also important. If the fan is too close to the fan cover, cooling air flow will be reduced. A damaged fan cover may result in reduced air flow, as the air may “leak” through the cracks or become turbulent due to a section that has broken off. Even with the correct fan cover, air flow will be reduced if it is not free from dirt or other material that blocks or restricts the vent open­ings. 

Motor design aspects 
Increasing magnetic flux increases core losses and therefore heating of the windings. The results are reduced ef­ficiency and winding life, and reduced reliability. Reducing the number of turns or changing the coil span or connection can increase magnetic flux. Doing the opposite, e.g., increasing turns, reduces magnetic flux. However, the reduced flux reduces torque capa­bility and typically results in higher current for a given load. The higher current means increased I²R losses, reduced efficiency and increased heating. Thus to maintain efficiency and reliability it is best not to change the magnetic flux level of the wind­ing. All else equal, a slight increase in magnetic flux density is preferable to a slight decrease. That’s because a magnetically stronger design has less slip, reducing the rotor losses. 

Repairers of­ten prefer to use lap windings be­cause all coils are the same. This is acceptable provided that the new winding is chosen such that the flux per pole is not changed. Single-layer lap windings are sometimes used motors, because the coils are easier to insert and no separators are required, thus allowing more room for copper. Double layer lap windings give a better flux distribution in the core than single layer windings, and in no circum­stances should a double layer winding be replaced by a single layer wind­ing. To do so will reduce efficiency. 

Conversely, changing from a single- to a double-layer lap winding may reduce losses and improve efficiency slightly. 

If the stator core is partially or fully restacked, a reduction in the total number of laminations reduces the core iron volume, effectively increasing magnetic flux densities. The higher flux levels increase core losses and heating. Improper restacking, such as by not compressing the core tightly enough, or by over-tightening the core, can lead to increased core and stray load losses. A key to a successful restack is to assure that the original core length is maintained and that all of the removed laminations, or equivalent replace­ments, are installed in the core. 

The rotor I²R losses can be in­creased by reducing the end-ring cross-section or by increasing the resistance of the rotor bars and end-rings. The repair process does not normally affect the rotor resistance, unless the rotor is rebarred. If the rotor is rebarred, it is critically important to have the bars and end ring materials tested to determine, and duplicate, the material resistance (or maintain the opposite characteristic, conductivity.) 

If the rotor surface must be cleaned up by machining, a sharp cutting tool is a necessity. The usual reason for need­ing to machine the core is to correct smearing caused by a stator to rotor core rub. Grinding the rotor surface, or machining the rotor core with a blunt tool or at an incorrect surface speed, can result in smearing the laminations together. The smeared laminations probably will not become hot at running speed due to the low rotor frequency of only a few hertz. How­ever, the warmer core area can create a thermal bow, resulting in vibration and an unequal air gap. 

An unequal air gap can cause circulating cur­rents in the stator wind­ing, resulting in increased I²R losses. Repairs to the stator frame or end bracket rabbet/spigot fits that reduce stator-rotor concentricity increase air gap eccentricity, and can result in circulating currents that increase I²R losses. 

An excessive air gap will increase magnetizing current and also increase I²R losses. Machining the rotor diameter to increase air gap can reduce losses at the expense of power factor; however, too great an increase in air gap will increase losses. This should only be done when the manufacturer’s design air gap tolerance is known to the service center. 

Stray load losses, illustrated in Figure 5, are typically 10-20% of total motor loss. Stray loss can increase if the air gap surfaces of the laminations are smeared together. Stray loss will also be increased if the air gap is un­even (i.e., stator and rotor not concen­tric) and may be increased if a wrong replacement rotor is installed. 

Closing comments
Of the things that affect efficiency, a typical repair only influences the core, winding (I²R), and friction losses. These and other key topics have been addressed in these best practices. Documenting the before and after core loss, comparing winding resistance to the manufacturer’s re­cords, and confirming the bearing type provide assurance to you and to the customer that the motor’s efficiency was maintained during the repair.

Tim Browne
Industrial Electric Motor Service, Inc.

Sospecho que casi todos en nuestra industria alguna vez han tenido el placer de reparar un motor “fabricado con requisitos especiales”. Este tipo de motor está construido para un propósito específico y tiene características que le pueden permitir funcionar bajo condiciones no habituales. Debido a la información limitada que algunos de ellos muestran en su placa de datos, la reparación de estos motores puede resultar un reto.

Tom Bishop, P.E. 
EASA Technical Support Specialist
 
Have you ever had to deal with a rewound motor that had high no-load amps? That is almost a rhetori­cal question as most of us have experienced this situation. The focus of this article will be on steps to take before rewinding in order to avoid the condition of high amps after the rewind. 

Steps that should be performed on every AC stator rewind: 

1. Inspect the stator bore and rotor outside diameter for evidence of machining or damage. 
2. Record the original winding data exactly as found. 
3. Test the stator core before winding removal. 
4. Verify the winding data. 
5. Test the stator core after winding removal and cleaning. Applying these five steps will help avoid the vast majority of situations where a rewound motor will exhibit high no-load current. If these steps were not all followed and a motor has high no-load current, if possible, perform any steps above that were omitted. 

Gene Vogel
EASA Pump & Vibration Specialist

This paper covers:

• How to set a balance tolerance
• Balancing machine setup, special fixtures and choice balancing speeds
• When to use single-plane, two-plane or static-couple methods
• Is it unbalance?
• How to get the right transducer and phase measurement setup
• Safe balance weight attachment techniques
• The ABCs of calculating balance corrections

Electric motor repair report form to collect basic motor, bearing, shaft, coupling information.

Kirk Kirkland
Electrical Repair Service Co. 
Birmingham, Alabama
Technical Education Committee Member

Many progressive end users require validated precision in the manufacturing of new motors they purchase as well as with the motors they have serviced.

As repair service providers to these end users, EASA service centers are often required to comply with the standards as implemented by the original equipment manufacturer. This holds true for the most basic components of an electric motor: the bolts.

The basic motor assembly and the integral parts are normally secured via a specific type and grade of bolt. Therefore, validated bolt torque procedures and referenced bolt torque values are necessary to address general compliance issues.

Robert Giesen 
B & B Electric Motor Co. 
Wichita, Kansas 
Technical Education Committee Member 

Editor's Note: The procedures outlined in this article exclude explosion proof motor end bracket rebuilding.  

Many motor service centers bore and sleeve end brackets (end bells) in machine lathes. When using a lathe you need one large enough to swing the outside diameter of the end bracket and the large mass is hard to indicate true. Many times it is difficult to clamp onto the lathe chuck or faceplate. 

When rotating a large mass there is always a chance of the part coming loose and causing damage to the end bracket or injury to the machine opera­tor. We have bored and sleeved end brackets for more than 25 years in a vertical milling machine. We find the mill is a more useful machine; it is faster and more accurate to indicate in and set up. 

The boring of the diameters are true and concentric and it is much safer to rotate a cutting tool and not the part. Following is a step-by-step procedure to bore and sleeve end brackets in a verti­cal milling machine. 

Kent Henry 
Former EASA Technical Support Specialist

In the power transmission indus­try, a fair amount of cast iron is used. Whether it’s for motors, pumps, or gear reducers, many use cast iron for the bulk of their structure. This variety of usage results in service opportunities involving the repair of cast iron components. 

Cast iron has a very high carbon content, so much so that the concen­trations of carbon form graphite flakes that result in a high resistance to wear. The drawback of cast iron is that the high carbon content also makes castings brittle. Examples of brittle castings are terminal boxes and fan covers. If a forklift operator rounded a corner a little wider than normal and bumped into the terminal box and fan cover of a Totally Enclosed Fan Cooled (TEFC) motor made from steel, the impact would bend the steel components. Steel is a fairly ductile material. The repair of these parts may Figure 1. Example of crack prepared for welding. and fully weld this side of the be limited to hammering out dents in the terminal box and fan cover. If the same collision happened with cast iron components, the damage would be quite different. They would likely be cracked or even break into pieces due to the brittleness. 

Gene Vogel
Especialista de Bombas and Vibraciones de EASA

En el principio, Dios hizo circular el agua libremente por toda la tierra. Entonces el hombre hizo las bombas para hacer fluir el agua donde él quería. Entonces Dios creó las fugas y el hombre creó los sellos de las bombas. Dios sonrió. El hombre continuó luchando contra las fugas en los sellos.

Para aquellos que son nuevos en el negocio de la reparación de bombas, los sellos pueden resultar intimidantes, sin embargo, es bien conocido que los sellos mecánicos de las bombas son dispositivos temperamentales que fallan con frecuencia. El hecho es que los sellos mecánicos son dispositivos simples que a menudo son utilizados de forma inadecuada, algunas veces instalados incorrectamente o tal vez montados en bombas que no son aptas para la aplicación. En la mayoría de las aplicaciones, los sellos mecánicos son lo suficientemente macizos para tolerar condiciones de operación y de manejo menos óptimas. Para aplicaciones exigentes todo debe estar bien.

Gene Vogel
EASA Pump & Vibration Specialist

In the beginning, God made water to run freely over the earth. Then Man made pumps to make water run where he wanted it. Then God made leaks. Then Man made pump seals. God laughed. Man continues to struggle with leaking pumps seals.

For those new to pump repair, mechanical seals can be intimidating. It is commonly known that pump mechanical seals are temperamental devices that fail frequently. The fact is, mechanical seals are simple devices that are often misapplied, sometimes installed incorrectly, or perhaps installed on pumps that are not well suited for the application. For many applications, the mechanical seal is robust enough to tolerate less than optimal handling and operating conditions. For more demanding applications, everything must be right.

Mike Howell, PE
EASA Technical Support Specialist 

The insulation system chosen for any rewind should be suitable for the application, the voltage class, and the winding process capability of the service center. In most cases, adherence to “equal to or better than” selection is a good practice.

By Chuck Yung
EASA Senior Technical Support Specialist

Existen beneficios e inconvenientes al usar circuitos en paralelo en un bobinado trifásico. Sea que estemos hablando de un bobinado de alambre redondo o de pletina (solera), algunas de las consideraciones se comparten. Comencemos con lo básico: Entre más alta la potencia y/o más bajo el voltaje nominal, menos vueltas por bobina se utilizan. Debido a que un devanado trifásico tiene grupos por fase y por polo que alternan ABC, ABC, ABC, etc., los puentes entre grupos podrían ser 1-4, 1-7, 1-10, 1-13, etc., o cualquier combinación de ellos, siempre y cuando se conserve la polaridad alternada de los grupos y que las fases no se crucen entre sí.

Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar recording discusses the equalized connections found in an increasing number of factory windings, explains why they are used, and addresses whether or not they are needed when converting a concentric winding to a lap winding. Alternatives, such as changing the number of circuits, or the special extra-long jumpers, are also compared.

The webinar recording covers

• Explanation of why machine-wound concentric windings use equalizers
• Effect of unbalanced voltage
• Role of air gap in causing circulating currents
• Labor involved and risk of failures due to increased complexity
• How to properly locate the equalizers

This webinar is useful for engineers, service center managers, mechanics and sales representatives.

Chuck Yung 
EASA Technical Support Specialist 

There are times when a winding cannot be processed through the burn­out oven, so it must be removed “cold.” The bond strength of most resins is approximately 8-10 psi (55-70 kPa), which means that a fairly large coil might have nearly 3,000 pounds (1350 kg) of bonding force with the slot. 

In those cases, there are some use­ful tips that can be used to reduce the difficulty in removing the coils. Many of the techniques in this article can be adapted for open slot wound rotors and armatures. 

Tom Bishop, PE
EASA Senior Technical Support Specialist

Three of the most common three-phase motor problems we receive inquiries about are:

1. “The motor is drawing high no-load current.”
2. “The current of the three line leads is not balanced.”
3. “The motor is running hot.”

Even if you have never faced one of these issues, read on because it is almost inevitable that you will, and you will want to know what to do about it.

Gary Braun
Brehob Corp.
Indianapolis, Indiana
Technical Education Committee Member

When servicing DC motors, one of the many tests we do to determine the condition of the commutator is to check it for loose bars.

We check for loose bars by lightly tapping the face of the commutator with a very small hammer. Then we check for suspicious sounds and move­ment or vibration of the bars as they’re struck. A loose bar will have a dull thud while tight bars will have more of a crisp “peck.” You should not feel any movement of the bar with respect to adjacent bars. 

Chuck Yung
EASA Senior Technical Support Specialist

One of the least understood parts of a DC motor is the commutator. With a little understanding and some helpful tips, commutator life can be maximized.

Commutators are made of copper bars* separated by insulation from each other and from the steel hub. Viewed from the end, each bar is wedge-shaped, tapered radially with the thickest portion towards the outside. The insulation material most often used is segment mica because it remains stable at the temperature and pressure required during assembly and operation. By alternating copper bars with mica segments, each bar is isolated electrically from the other bars. The resulting cylinder of bars and mica is mounted on an insulated steel hub.

Two-pole motors present special rewind issues, especially when converting them from concentric to lap windings. The pitch is especially important as certain coil pitches will cause harmonics that have a negative impact on performance. Optimum pitches are often very difficult to wind and shorter pitches result in sacrificed conductor area.

This presentation explores sample redesigns and present some guidelines to assist in deciding between the concentric and lap winding.

Target audience: This webinar will be most useful for service center winders, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons.

Chuck Yung
EASA Senior Technical Support Specialist

While manufacturers use concentric windings due to their ability to wind the coils directly into a core, many repairers convert them to lap windings to take advantage of the superior MMF (magneto-motive force) curve.

Although the former Tech Note 12 (see page 2-187 of the EASA Technical Manual), and the AC Motor Verification and Redesign Program, Version 4 allow us to convert a concentric winding to a comparable lap winding, there are still some winders using “shortcuts” they have learned over the years.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Mientras los fabricantes usan devanados concéntricos por su capacidad para bobinarlos directamente dentro del núcleo, muchos reparadores los convierten en bobinados excéntricos para aprovechar su curva FMM (fuerza magnetomotriz) superior.

Aunque la antigua Tech Note 12 (vea la página 2-187 del Manual Técnico de EASA), y la versión 4 del AC Motor Verification and Redesign Program, permiten convertir un bobinado concéntrico en un bobinado excéntrico comparable, aún existen algunos bobinadores empleando “atajos” que han aprendido con el tiempo.

Steven Carbone
Technical Education Committee Member
Industrial Electro-Mechanics

In today’s ever-increasing competitive environment, end users are looking for rotating apparatus service centers to increase their offering of value-added support. One of the easiest ways for a service center to achieve this is through a thorough and detailed inspection of items in the shop requiring repair. The results of this type of inspection allow for improved reliability achieved through the results of the evaluation and recommendations the service center offers to prevent reoccurring failures and improve mean time between failure.

Jacob Snyder
Evans Enterprises, Inc.

When a modern temperature controlled (i.e., controlled pyrolysis) burnout oven is not available, the method described here can be used to process aluminum frame motors.

Gene Vogel
Especialista de Bombas & Vibraciones de EASA

Esto sucede en casi todos los centros de servicio de EASA, aparece una máquina para reparación, con cables y un motor, pero es una bomba. A menudo es una bomba sumergible o de acoplamiento cerrado. Si su respuesta es: “Aquí no reparamos estos equipos” y está pensando: “Nosotros no sabemos nada sobre reparación de bombas” puede que le esté dando la espalda a un trabajo muy rentable.

Como ya detallé en mi artículo publicado en Febrero en la revista Currents, la reparación de bombas puede ser un área de expansión muy rentable para los centros de servicio especializados solo en la reparación de motores eléctricos. Si usted está de acuerdo en que la reparación de bombas sería una buena opción para su negocio, el próximo paso consiste en evaluar qué cambios necesita en sus instalaciones para incluir la reparación de bombas. Encontrará que ya tiene gran parte del equipo necesario. Las características de los motores y de las bombas centrífugas son muy similares y dependiendo del tipo de bomba, puede que necesite muy poco equipo adicional.

Mike Howell
EASA Technical Support Specialist

La precisión y exactitud de los equipos de prueba & medida (M&TE) han sido tratadas en artículos previos de Currents (noviembre y diciembre de 2014). Un tema relacionado que no fue cubierto en dichos artículos es la resolución. El documento JCGM 200:2012 del Joint Committee for Guides in Metrology define resolución como: “El cambio más pequeño en una cantidad medida que causa un cambio perceptible en la indicación correspondiente”. Simplificado, es la diferencia más pequeña que puede ser medida por el equipo en cuestión. La exactitud de la M&TE debe ser mayor (menos exacto) o igual a la resolución. Es decir, durante la calibración, el M&TE debe ser capaz de indicar el valor comparado con el estándar.

Precisión y exactitud
Repasemos brevemente la importancia de la precisión y exactitud. Al recoger la información de las medidas, los técnicos del centro de servicio obtienen datos con dos componentes: El valor auténtico de la medida (valor real) y el error asociado a la medida (componentes de precisión y exactitud). Así mismo, entre más pequeño sea el error de medida, más se acerca la indicación o valor medido a la medida real. Como lo muestra la Figura 1, a menudo los términos precisión y exactitud se demuestran y diferencian gráficamente utilizando el ejemplo de la diana.

La precisión se refiere al grado de repetibilidad y reproducibilidad en el sistema de medida, Repetibilidad es la capacidad que tiene un técnico para obtener la misma medida varias veces midiendo el mismo elemento con el mismo M&TE. Reproducibilidad es la capacidad de varios técnicos para obtener la misma medida midiendo el mismo elemento con el mismo M&TE. Normalmente, la precisión del M&TE es evaluada con estudios de repetibilidad & reproducibilidad (R&R).

La exactitud es el grado en el que la medida concuerda con el valor real. La exactitud de un M&TE es evaluada por calibración.

Resolución
De nuevo, podemos simplificar la resolución como la diferencia más pequeña que puede ser medida con nuestro M&TE. Aunque para cualquier medida la exactitud de nuestro M&TE se debe comparar con nuestro rango de tolerancia aceptable.  Tendemos a ver rápidamente la resolución de un indicador o medidor solo por observación. Por esta razón, la resolución es un buen “primer paso” cuando se selecciona un M&TE para una tarea específica. Es decir, si usted tiene una herramienta con una resolución de 1 cm y necesita medir algo con un diámetro nominal de 1 mm+/-0.1mm, ya debería saber que tiene la herramienta incorrecta para el trabajo. 

Existen algunos ejemplos obvios de malas elecciones que podemos identificar en un típico centro de servicio. Nunca pensaríamos utilizar una balanza industrial para pesar los pesos de balanceo o una regla para medir el diámetro de un alambre magneto. En estos dos casos, sabemos que la resolución de un M&TE probablemente es más grande que el valor medido; si la resolución no está ahí, seguramente la exactitud deseada no estará ahí. La selección del M&TE apropiado depende del propósito de la medición. Para balancear, muchos pueden considerar apropiada una balanza con una exactitud de 0.1 gramos que pese hasta 100 gr. Pero, los centros de servicio que balancean rotores de husillos o conjuntos extremadamente largos pueden necesitar algo diferente. 

Para el alambre magneto, la precisión y exactitud requeridas para identificar simplemente un calibre durante la toma de datos pueden ser muy diferentes a las requeridas para determinar si las dimensiones de una muestra de alambre magneto están dentro de la tolerancia de fabricación de las normas NEMA o IEC. Además, una galga para alambres nunca es una buena opción para medir alambres magneto.

Los M&TE escogidos por cada centro de servicio variarán de acuerdo con los requisitos de diferentes fuentes como clientes y entes reguladores o de certificación. Siempre deben evaluarse primero los requisitos de los clientes antes de tomar cualquier decisión sobre el proceso de negocios. Un centro de servicio cuyo cliente más importante es un lavadero de vehículos puede tener requisitos muy diferentes a uno que repara motores relacionados con la seguridad de una central nuclear. Sin embargo, todos los centros de servicio deben escoger los M&TE adecuados para darles una seguridad razonable en las actividades de seguimiento del proceso e inspección y pruebas que realizan.

Cuando se trata del seguimiento de procesos, para la mayoría de parámetros existen muchos medidores y sensores que varían ampliamente por rango, resolución y exactitud. Por ejemplo, si se usa un manómetro en un sistema VPI donde el proceso está calibrado a 80±5 psi (5.5±0.3 bar) y el manómetro tiene un rango de 0-150 psi (0-10.3 bar), es razonable tener una calibración limitada, tal vez de 70-90 psi (4.8-6.2 bar). La Figura 2 muestra un manómetro que puede usarse de esa forma.

Ahora, veamos un parámetro diferente que debe ser controlado durante el ciclo de vacío-VPI. Durante un proceso de impregnación global-VPI, existe una fase de vacío seco y algunas veces también una fase de vacío húmedo. Normalmente, los niveles de vacío seco deben estar por debajo de los 5 Torr (0.007 bar) y es deseable alcanzar un nivel menor o igual a 1 Torr (0.001 bar), especialmente en estatores con bobinas de pletina. El manómetro de la Figura 2 sirve para algún proceso industrial simple pero no es adecuado para las mediciones de vacío en el proceso VPI de un centro de servicio. Examinemos la resolución de la porción de vacío de la escala, desde 0 hasta 30 pul-Hg. La Tabla 1 muestra las unidades para convertir pul-Hg en Torr. Si estamos interesados en niveles de vacío seco menores o iguales a 5 Torr, resulta evidente por que el manómetro de la Figura 2 es inadecuado. No se puede diferenciar un vacío de 0.5 Torr de un vacío de 10 Torr.

Esto no significa que si su centro de servicio tiene un manómetro de vacío inadecuado, no esté logrando niveles de vacío aceptables- esto solo significa que usted no tiene un control de proceso adecuado y no sabe el nivel de vacío que está obteniendo. Una opción más razonable para medir el vacío en un sistema VPI se muestra en la Figura 3. Un manómetro similar a este puede tener un rango de 0.2 a 20 Torr y una exactitud del 20%.

Los centros de servicio deben evaluar cada medida que afecte la calidad del servicio o producto suministrado. Para cada uno, considere el rango de valores posible, así como también la precisión y exactitud de los M&TE necesarios para realizar el trabajo. incluso para los técnicos más calificados y experimentados, contar con los M&TE es crítico para la disposición adecuada de cualquier máquina o componente.

Gene Vogel
EASA Pump & Vibration Specialist

Una de las reparaciones más comunes en las bombas centrífugas consiste en reemplazar los anillos de desgaste deteriorados o dañados. En las bombas con impulsores cerrados (con una cubierta frontal como se describe más adelante), habrá un anillo de desgaste en la carcasa y posiblemente un anillo de desgaste en el impulsor, que se ajusta al diámetro exterior (OD) del ojo de succión. Los impulsores también pueden tener anillos de desgaste traseros que son importantes para controlar el empuje axial. Las bombas con impulsores abiertos generalmente no tienen problemas con la tolerancia del anillo de desgaste del ojo de succión, pero a menudo tienen anillos de desgaste traseros. Las holguras entre el anillo de desgaste de la carcasa estacionaria y el anillo de desgaste del impulsor rotativo son fundamentales para un adecuado funcionamiento de la bomba. Aunque muchos fabricantes de bombas proporcionan tolerancias y dimensiones correctas, otro no lo hacen; en la actualidad existen una gran cantidad de bombas de fabricantes antiguos que ya han desaparecido, donde los datos de las dimensiones simplemente no están disponibles.

By Mike Howell
EASA Technical Support Specialist

Accuracy and precision of measuring & test equipment (M&TE) have been topics of previous Currents articles (November and December 2014). A related topic that was not covered in the previous articles is resolution. The Joint Committee for Guides in Metrology document JCGM 200:2012 defines resolution as “the smallest change in a quantity being measured that causes a perceptible change in the corresponding indication.” Simplified, it’s the smallest difference that can be measured by the subject equipment. The accuracy of the M&TE must be greater than (less accurate) or equal to the resolution. That is, the M&TE must be able to indicate the value that is compared to the standard during calibration.

Jacob Snyder
Evans Enterprises, Inc.

El método aquí descrito se puede utilizar para procesar motores con carcasa de aluminio cuando no se tenga un horno moderno de quemado con temperatura controlada (es decir de pirolisis controlada).

Gene Vogel
EASA Pump & Vibration Specialist
and
Don Scaturro
Illinois Electric Works, Inc., Granite City, IL

Pump packing is a high maintenance item for any centrifugal pump so equipped, and unacceptable for chemical pumping applications. This paper covers how service centers can convert a pump from packing to mechanical seals to:

• Eliminate a maintenance issue for customers
• Allow an available pump to be put into alternate service requiring mechanical seals

This paper is an overview of such a conversion on a 50 hp split-case pump.

This webinar teaches:

• How to repair damaged stator cores and how to know when a restack is necessary.
• There are often cases when repairs can be accomplished without a labor intensive restack.
• When a restack is required, there are pitfalls to watch out for to avoid problems with geometry, vibration and core losses.

Target audience: This presentation is useful to the supervisor, winder and sales personnel who interact with the end user.

Ron Rapa
Rapa Electric, Inc.

At Rapa Electric, we’ve had a number of “opportunities” to remove a blind pinion from a motor shaft.

Sometimes, if we’re lucky, the pinion may have a push-off bolt to facilitate removal. And at other times, there may be a through-hole in the rotor shaft so that we can use a push-bar to shove the pinion out of its hole. If we’re not so lucky, we have to use a more creative method.

David Sattler
L&S Electric, Inc.

Unless great care is taken, pulling magnet wire from a motor stator often bends or splays the lamination’s end teeth. Bent teeth, or teeth that have been splayed outward at the ends of the core stack, will likely compromise the quality of the repair job. Studies¹ show that motor efficiency may be reduced by splaying end teeth. Even if that reduction in efficiency is slight, any reduction in efficiency results in higher costs and wasted energy.

Even though these performance reductions are seldom noticed by customers, our goal in motor repair is always to produce the highest quality rewind possible. Therefore, we have designed and implemented the use of disc clamps to hold the stator tooth tips in place while pulling magnet wire from the slots. The clamping fixtures described in the photos have helped ensure that we avoid damaging the stator teeth during the stripping process.

Chuck Yung
EASA Senior Technical Support Specialist 

Historically, one emergency repair used for large, low-speed machines (motors as well as generators) was to remove the damaged/failed coils from the circuit. Cutting out a single damaged coil permitted the machine to be quickly returned to service with minimal disruption.

As long as some basic principles are followed, this method can be safely used. It is still popular with operators of large, low-speed synchronous ma­chines. One common application for such machines is hydro power stations. There are many old hydro generators operating with a dozen or more coils bypassed. The underlying goal when cutting out coils is to minimize the negative side effects and keep coil groups intact for future removal.

WARNING: This procedure is not recommended for 2-pole machines. The odds of success are slim.

This inspection report helps record a DC motor's connection as it enters the service center. It is intended for use with 2-, 4- and 6-pole DC machines and includes space to:

• Draw and number the leads and jumpers
• Number of poles in series or in parallel
• Number of interpoles
• Number of series fields

This incoming inspection report provides a place to record basic DC motor conditions and test values, including:

• Customer information
• Armature voltage and amps
• Field voltage, amps ,etc.
• Electrical test information for the armature, fields, interpoles and series windings
• Brush and brushholder information

Mike Howell
EASA Technical Support Specialist

When rewinding the shunt fields of a DC machine, it is important to avoid making changes that could negatively impact performance. The recommended practice is to maintain the manufacturer’s winding configuration during the repair. That is, the field circuit connection, turns per coil, mean or average length of turn (MLT) and wire size should not be changed. However, service centers do sometimes encounter issues around wire size availability. The purpose of this article is to provide some guidance for making wire size substitutions when the original size is unavailable.

Presented by Chuck Yung
EASA Senior Technical Support Specialist

This webinar explains the DC redesign process along with the other factors often overlooked that should first be considered before a redesign.  As DC machines become difficult to source it’s not uncommon for an end user to ask about redesigning a DC motor that they have in storage, including changes in voltage for the shunt field and armature circuit.  Topics include:

• Shunt fields
• Reconnection for voltage change
• Change limitations
• Series fields  
• Cautions about circuit change
•  Armature circuit voltage change  
• Interpoles
• Brushes, boxes and current density
• Armature redesign considerations

This webinar is intended for winders, shop supervisors and engineering staff. 

Chuck Yung
EASA Senior Technical Support Specialist

Flooding in the aftermath of tropical storms (hurricanes, monsoons and cyclones) with heavy rainfall will often shut down hundreds of plants along the Gulf Coast from Florida to Texas and other places around the world.

To get them up and running again, maintenance departments and motor repairers face the daunting task of cleaning muck and moisture from many thousands of electric motors and generators. See Figure 1. The process in such situations can take weeks, if not months, and requires special clean-up procedures for motors contaminated by saltwater.

Although the problems are huge, affected plants can get back in production more quickly by working closely with service center professionals and following a few tips that will make the cleanup more manageable. These include prioritizing motors and generators for repair or replacement, storing contaminated machines properly, and using proven methods to flush away saltwater contamination. Constructing temporary ovens on site or at the service center can also add capacity for drying the insulation systems of flooded motors.

Cyndi Nyberg 
Former EASA Technical Support Specialist

There are a number of ways that the shaft of an electric motor can become magnetized in service. The most likely culprit is electric current through the motor and shaft, either from internal dissymmetry, welding or from a variable frequency drive. It can also be caused by electrical faults in the system, or even a lightning strike. 

We of course know that shaft voltages and the associated currents can cause bearings to fail. A typical ball bearing failure from shaft currents is shown in Figure 1. when a shaft is magnetized, it can further lead to bearing failures, unless something is done to elimi­nate the residual magnetism. The first reason for bearing failures is that the residual magnetism can cause shaft currents, which can quickly lead to bearing failures. But in addition, a magnetized shaft will attract bits of metal to the bearings. This reduces bearing life because it damages the bearing surfaces. 

The magnetism in the shaft may be strong enough that a screwdriver that sticks to the shaft. In fact, this is the most simple test to check for a magnetized shaft. 

Benny G. Darsey
Tampa Armmature Works, Inc.

There are several reasons that random wound electric motors have premature electrical failures. There have always been concerns of crossovers in the slot section and end turns. Crossovers create unfavorable conditions such as keeping the varnish or resin from bridging the magnet wires and bonding them together. Crossovers also create pressure points. Pressure points, combined with the condition of poor bridging of the varnish and the line frequency vibration, will cause the magnet wire insulation to abrade, causing a short circuit.

Gene Vogel
EASA Pump & Vibration Specialist

Whether it is a simple re-application of a pump from 50 Hz to 60 Hz (or vice versa), the repurposing of an existing pump, or the application of a new pump to an existing application, determining the proper trim for an impeller can be challenging. This presentation reviews: 

• Basic impeller design criteria 
• Methods of evaluating the head and flow and power implications of trimming impeller outside diameters

This recording will benefit pump technicians, engineers and sales personnel.

Steve Skenzick
HPS Electrical Apparatus Sales & Service

En mi centro de servicio hemos visto problemas en ejes previamente reparados que fueron metalizados. En estos casos recibimos motores para revisión. Después de la inspección y de medir los ajustes de los rodamientos en el eje, encontramos algo que simplemente no se “sentía” bien. Podríamos decir por la apariencia que los ejes habían sido reparados antes de la revisión actual.

This presentation focuses on:

• How to use basic design rules to verify data for fields, interpoles and armatures
• Verifying the correct armature coil pitch
• Special cases where you can improve on the original armature design
• What to do when the armature was received stripped, and the manufacturer no longer exists

EASA announces the publication of an update to AR200, now titled the Guide For The Repair Of Dry-Type Transformers. This guide outlines best practices for the repair of dry-type transformers.

EASA members adopt a customer service-centered mission encompassing various electrical apparatus repairs such as electric motors, transformers, controls, electrical troubleshooting and construction. EASA’s Technical Services Committee recently reviewed and extensively edited the AR200 guide in support of transformer repair services.

The previous version of AR200 (published in 2011) was titled Guide For The Repair Of Power And Distribution Transformers. Like preceding versions, it embraced a broad scope of transformer repair that included liquid-filled distribution or power transformers up to 10 MVA and 69 kV and dry-type distribution and power transformers up to 5 MVA and 25 kV.

In preparing this update, the Technical Services Committee chose to narrow the scope to the types of transformer repair activities usually found in EASA service centers (i.e., non-liquid-filled distribution dry-type transformers with high voltage windings up to 69 kV and rated less than 15,000 kVA). After all, liquid-filled transformer repair and service is a specialty few members offer, with many standards and best practices differing from those for dry-type transformers. In recognition of EASA’s international membership, the updated procedures in the new version now reference both IEEE and IEC standards.

Besides being helpful to the transformer repair and service efforts in many EASA service centers, it continues to position EASA as the definitive source for best practices in the electrical apparatus repair industry.

While the AR200 guide was an effort of the AR200 Task Group and EASA’s Technical Services Committee, thanks also go to EASA members who offered their comments and expertise. With a view of continual improvement as industry standards evolve, we welcome your feedback.

Table of Contents Summary

• Section 1 General
  • 1.1 Purpose
  • 1.2 Scope
  • 1.3 Identification
    • 1.3.1 Records
    • 1.3.2 Nameplate
    • 1.3.3 Service center labels
  • 1.4 Condition assessment and failure analysis
  • 1.5 Cleaning
  • 1.6 Terminals
    • 1.6.1 Leads
    • 1.6.2 Connections
    • 1.6.3 Enclosures
  • 1.7 Accessories
  • 1.8 Painting
  • 1.9 Packaging and transportation
• Section 2 Testing Transformers
  • 2.1 Safety considerations
  • 2.2 Instrument calibration
  • 2.3 Insulation condition test
    • 2.3.1 Insulation resistance test
    • 2.3.2 Polarization index test
    • 2.3.3 Insulation power factor test
  • 2.4 Other tests
    • 2.4.1 Winding resistance test
    • 2.4.2 Transformer turns ratio (TTR) test
    • 2.4.3 Polarity test
    • 2.4.4 No-load loss test
    • 2.4.5 Load loss test
    • 2.4.6 Single-phase impedance test
  • 2.5 High-potential tests
    • 2.5.1 50/60 Hz high-potential test
    • 2.5.2 DC high-potential test
    • 2.5.3 High frequency induced potential test
    • 2.5.4 Test levels, windings
• Section 3 Rewinding Transformers
  • 3.1 Investigation
  • 3.2 Gathering data
  • 3.3 Winding coils
  • 3.4 Core laminations
    • 3.4.1 Stacked cores, disassembly
    • 3.4.2 Stacked cores, assembly
    • 3.4.3 Wound cores, disassembly
    • 3.4.4 Wound cores, assembly
  • 3.5 Connections
    • 3.5.1 Connections in the winding
    • 3.5.2 External connections
    • 3.5.3 Insulating connections
  • 3.6 Leads
• Section 4 Transformer Repair
  • 4.1 Checking for service suitability
    • 4.1.1 Tests
    • 4.1.2 Equipment checks
    • 4.1.3 Summary of results
    • 4.1.4 Preparation for shipment
  • 4.2 Rewind
    • 4.2.1 Inspection, test and estimate
    • 4.2.2 Dismantle
    • 4.2.3 Winding new coils
    • 4.2.4 Reassembly
    • 4.2.5 Final tests
    • 4.2.6 Preparation for shipment
• Appendix A Electrical Testing Safety Considerations
  • A.1 Personal safety
    • A.1.1 Training
    • A.1.2 Personal protective equipment (PPE)
    • A.1.3 Supervision
    • A.1.4 First aid and CPR
  • A.2 Test area
    • A.2.1 Enclosure
    • A.2.2 Gates
    • A.2.3 Signs
    • A.2.4 Lighting
    • A.2.5 Safety equipment
    • A.2.6 Test unit clearance
  • A.3 Unit under test
    • A.3.1 Suitability for test
    • A.3.2 Exclusive attention
    • A.3.3 Grounding (earthing)
    • A.3.4 Base
  • A.4 Test panels
    • A.4.1 Construction
    • A.4.2 Voltages
    • A.4.3 Warning lights
    • A.4.4 Disconnect
    • A.4.5 Safety switch
    • A.4.6 Leads
  • A.5 High-potential ground (earth) test
• Appendix B Reference Information
  • Table b-1. Insulation resistance test voltages
  • Table b-2. Temperature correction factors for dry-type transformer insulation resistance tests
  • Table b-3. Recommended minimum insulation resistances for dry-type transformers
  • Table b-4. Recommended test levels for dry-type transformer new windings
• Bibliography
• Standards Organizations & Other Resources

EASA's Warranty Report Forms provide the ideal way to record your warranty service accurately. Many manufacturers request that warranty work be documented on this form. These forms were extensively reviewed and updated by EASA's Technical Services Committee with input and guidance from motor manufacturers. You may download this form for free to use in your service center. Both forms are provided with the ability to be filled out electronically using Adobe Reader. Although you may not have a warranty or repair report pending that might require use of one of these forms, we encourage you to download the forms. And don’t overlook the potential for using the Warranty Repair Report for internal warranty issues in order to improve your repair procedures.

Chuck Yung
Especialista Sénior de Soporte Técnico

Solía bromear con que si mencionas la palabra armónicos, los ingenieros se emocionan mientras que los ojos de los que no lo son se nublan. La verdad es que los armónicos se pueden entender fácilmente cuando se explican en términos sencillos. Estos son simplemente múltiplos de la frecuencia fundamental, con secuencia positiva, cero o negativa. La frecuencia fundamental es la frecuencia de línea, también llamada armónico de primer orden, que es de 60 Hz en América del Norte o de 50 Hz en la mayor parte del resto del mundo.

Otros armónicos (quinto, séptimo, etc.) se pueden ver como ese orden multiplicado por la frecuencia fundamental, o visualizarse como si tuvieran ese número de formas de onda en la misma distancia que una sola forma de onda de la frecuencia fundamental. Entonces, en un sistema de 60 Hz, el quinto armónico es 5x60 o 300 Hz. Habrá 5 formas de onda completas en el lapso de una sola forma de onda de 60 Hz. Cuando las porciones positiva y negativa de la onda sinusoidal son simétricas, los armónicos de números pares no existen.

Cualquier armónico que sea múltiplo de tres, en el mundo trifásico, es un armónico de secuencia cero; y, cuando estamos considerando un sistema de potencia sinusoidal, se cancela (a excepción de los alternadores síncronos, que están fuera del alcance de esta discusión).

Chuck Yung
EASA Senior Technical Support Specialist

I used to joke that if you mention harmonics, engineers get excited while the eyes of non-engineers glaze over. The truth is that harmonics can be easily understood when explained in layman’s terms. Harmonics are simply multiples of the fundamental frequency, with positive, zero or negative sequence. The fundamental frequency is line frequency – also called the first order harmonic -- that being 60 Hz in North America or 50 Hz in most of the rest of the world.

Other harmonic numbers (5th, 7th, etc.) can be viewed as that order times the fundamental frequency, or visualized as having that number of waveforms in the same distance as a single waveform of the fundamental. So in a 60 Hz system, the 5th harmonic is 5x60 or 300 Hz. There will be 5 complete waveforms in the span of a single 60 Hz waveform. When the positive and negative portions of the sine wave are symmetrical, even number harmonics are non-existent.

Any harmonic that is a multiple of three, in the three-phase world, is a zero-sequence harmonic; and, when we are considering a sinusoidal power system, cancels out (except for synchronous alternators, which are outside the scope of this discussion).

El Efecto de la Reparación/Rebobinado en la Eficiencia del Motor: Estudio de rebobinado realizado por EASA/AEMT y la Guía de Buenas Prácticas, ilustran que cuando la reparación/rebobinado de un motor eléctrico se realiza de forma correcta, no se degrada su eficiencia! y que esta tampoco se reduce después de varios reparaciones/rebobinados.

Basado en un estudio realizado en conjunto por EASA y la Association of Electrical and Mechanical Trades (AEMT) del Reino Unido, esta publicación concluye que empleando las mejores prácticas de reparación/rebobinado la eficiencia del motor se conserva. Además de una Síntesis, el informe proporciona todos los datos de prueba, mucha información relacionada con procedimientos de prueba y metodología, información de los procedimientos que utilizan buenas prácticas, lecturas complementarias y un capítulo entero sobre las consideraciones para reparar/reemplazar un motor.

This PowerPoint presentation is available for members to use to present the factors that should be considered when customers are faced with making the difficult decision to repair their existing motor or purchase a replacement.

The presentation is designed to help service center sales and marketing personnel answer these difficult questions for their customers:

• Is it better to repair or replace an electric motor that has failed?
• Will a repaired motor retain its efficiency?

Members are welcome to customize the presentation with their company logo, contact information and anything else that might help better inform their customers.

With this presentation, you will be able to discuss the complete repair/replace decision-making process from reviewing the application demands, failure assessment, factoring in efficiency, and motor repair/rewinding good practices.

The presentation also is helpful in explaining the value of working with an EASA accredited member (if you are accredited). If you’re not an EASA accredited member, you may remove this portion of the presentation.

A special discounted collection of 7 webinar recordings focusing on various aspects of electromechanical repair.

Once purchased, all 7 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

Time-Saving Repair Tips
Presented August 2014

This webinar shares:

• The secrets used by other service centers to gain a competitive edge in the repair process.
• Mechanical, winding and machining tips reduce repair time, help avoid unnecessary rework, and decrease turn-around time.

Target audience: Supervisors, machinists, mechanics, winders, and sales personnel who interact with the end user.

Repair Best Practices to Maintain Motor Efficiency
Presented June 2012

There are certain repair processes, such as winding removal and replacement, that can impact the efficiency and reliability of electric motors. Prudent repair practices must not increase overall losses, and preferably should maintain or reduce them.

This presentation explains how those repair processes affect efficiency and reliability, and gives the best repair practices in order to maintain or improve efficiency.

Target audience: This presentation is most useful for service center inside and outside sales representatives, customer service personnel, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons.

Practical Problem Solving for the Entire Service Center
Presented August 2013

This presentation focuses on a report format developed by Toyota for a simple, yet methodical approach to document improvement. Whether you're dealing with problems related to sales, purchasing, repair or testing, if all team members can learn to speak the same, simple problem-solving language, they can tackle problems efficiently and effectively.

Target audience: This presentation is best suited for executives, managers, team leaders and front line supervisors from the office and service center who want to understand and implement such a program.

Induction Motor Speed Control Basics
Presented March 2019

Induction motors are most often applied to what are essentially constant speed drive applications. However, the use of induction motors in variable speed applications continues to grow, primarily due to technology advances in power electronics. This webinar will review speed control basics for induction machines.

• Wound-rotor motor speed control
• Squirrel-cage speed control by pole changing
• Squirrel-cage motor speed control by variable voltage, fixed frequency
• Squirrel-cage speed control by variable voltage, variable frequency

AC Motor Assembly and Testing
Presented August 2018

This webinar recording focuses on:

• Motor assembly issues
• Electrical and mechanical inspection
• Static and run testing
• AC motors with ball, roller and sleeve bearings

Target audience: This webinar recording is most useful for service center mechanics, supervisors and engineers. The content will also be beneficial for machinists, managers and owners.

On-Site Testing & Inspection of Electric Motors
Presented July 2015

This webinar covers electrical testing and inspection of installed electric motors, including:

• Condition assessment for continued service
• Diagnostic fault testing and interpretation
• Physical inspection key points

Selecting Replacement DC and 3-Phase Squirrel Cage Motors
Presented September 2019

On many occasions, a different motor type is desired or needed. In these cases it is essential that the replacement motor provides the required performance, and do so reliably.

This presentation focuses primarily on the electrical aspects of selecting replacement motors. It also addresses speed and torque considerations.

• DC motor to DC motor
• DC motor to 3-phase squirrel cage motor
• AC motor to 3-phase squirrel cage motor

Target audience: Anyone involved with selecting replacement motors or diagnosing issues with replacement motor installations.

Global vacuum pressure impregnation is the most common insulation system processing method utilized for form wound stators today. A successful VPI depends on several variables including materials, methods and maintenance. This recording will provide information to assist the service center with ensuring success with form wound VPI projects.

Target audience: This recording will be most useful for service center winders, engineers, supervisors and managers. The content will be beneficial for beginners through highly-experienced persons.

Mike Howell, PE
Especialista de Soporte Técnico de EASA 

El sistema de aislamiento escogido para cualquier rebobinado debe ser el adecuado para la aplicación, el voltaje y la capacidad del proceso de rebobinado del centro de servicio. En la mayoría de los casos, seleccionar una opción "igual o mejor" es una buena práctica.

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

As much as we all try to “make it right the first time,” invariably there will be times when a repaired machine is returned with a customer request for a warranty repair. This article will focus on three-phase squirrel cage induction motors. However, much of it can also be applied to other rotating apparatus. Prior to evaluating a motor for warranty status, you should familiarize yourself with the EASA Limited Warranties. Topics covered include: Scope of work performed Physical condition of motor Assessing failures: technical aspects Winding failures Mechanical failures Ball bearing failures

Presented by Tom Bishop, PE
EASA Senior Technical Support Specialist

This recording covers the broad topic of high no-load current with 3-phase motors and the issue of high current with load with 3- phase motors. Also covered are the cases of lower than expected no-load current. 

Primary topics are:

• High no-load current – motor not rewound
• High no-load current – rewound motor
• High current with load

This presentation is intended for mechanical technicians, winders, supervisors, engineers and managers. 

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

Service centers routinely check the shaft extension runout of motors and generators. When there are issues associated with them, or when applicable, the coplanarity of the mounting feet and the amount of end foat of horizontal sleeve bearing motors and generators are checked. A common point about all three of these dimensions is that they are checked with the machine assembled; that is, no disassembly is required. There are many other mechanical tolerances associated with motors and generators, such as bearing fits. However, the focus of this article will be the three tolerances just mentioned. Rather than referring to both electric motors and generators, for brevity the term “machine” will be used.

Topics covered include:

• Shaft extension runout tolerance
• Coplanarity of mounting feet tolerance
• End float

Chuck Yung
EASA Senior Technical Support Specialist

When sleeve bearings are rebabbitted or replaced, an important step during assembly is to check the contact between the sleeve bearing and the journal which rides in it. The use of self-aligning sleeve bearings (also called spherical or ball fit) renders this step almost unnecessary. Still, cylindrical sleeve bearings should be inspected to make sure the contact area is sufficient.   

Sleeve bearings, also known as babbitt bearings, plain bearings or white metal bearings, have been in use for over 150 years. For a detailed explanation of sleeve bearing design and operation, request the EASA 2007 Convention paper, “Sleeve Bearing Repair Tips,” or see Mechanical Repair Fundamentals of Electric Motors, 2nd Edition.  

This article is specific to checking and correcting the wear pattern when installing a new sleeve bearing in an electric motor. Fitting a sleeve bearing is not difficult; it just requires some basic knowledge. An interesting bit of history: the toolkit provided with the old Model A Ford automobile included a babbitt knife for scraping crankshaft bearings. Imagine dismantling your engine alongside the road to remove and fit the babbitt bearings.

Chuck Yung
EASA Senior Technical Support Specialist

When rewinding field coils, there are a couple of common problems that make life difficult for the service center. One problem occurs when the newly rewound set of shunt fields is returned to the service center, roasted again. What causes this, and whether we can improve our winding proce­dure, has been the subject of much discussion. 

We all realize that something caused that first failure. If the subse­quent failure looks a lot like it — the shunt fields were charred in both cases — then it seems logical that the underlying cause could be the same. Sometimes it is. 

Let’s look at why the coil is burnt. Well sure, it got too hot. But why? Is it because the shunts are energized when the machine is otherwise shut down? If so, the fields can be automatically de-energized after “x” minutes of machine inactiv­ity. Installing a timed relay in the controls will avoid future problems. It may be that the customer is able to trace the problem to a new operator, who needs more training. 

Chuck Yung 
EASA Technical Support Specialist 

When repairing slip-ring machines, it is sometimes necessary to re-insulate the collector rings from the hub. In these cases, some proce­dural guidelines may be helpful. Specifics such as interference fit, type of insulating material, and type of ring material require careful attention.

By Chuck Yung
EASA Technical Support Specialist 

Most EASAns are familiar with the basics of rotor rebarring.  We know that the endrings and bars are not always the same material, and understand the importance of maintaining the cage resistance.  For those of us who only occasionally rebar rotors, here are a few tips to assure a quality repair. 

Chuck Yung
EASA Technical Support Specialist 

When rewinding motors rated 6 kV and above, there are certain steps beyond the normal rewind procedures used for 2.3 kV/4 kV machines. Whether a machine is to be VPI processed makes a difference in how the winding should be treated. 

Aside from the obvious issues of insulation and higher voltages, there is also the possibility of partial discharge (PD), which brings its own unique set of problems. Air is an electrical insulator, albeit one of inconsistent quality. Increased humidity lowers the dielectric breakdown voltage of air, so an air gap that might be adequate under dry conditions may prove inadequate when the humidity is high (Table 1). Even though a form coil is fully taped, sealed and processed, the presence of air in voids within the coils, or between the coil and ground (i.e., in the slot) can cause problems with PD. 

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA 

Todos nosotros tenemos ese cliente ocasional que compró “una ganga” en una subasta, como un compresor, un torno o una máquina para trabajar madera y que solo descubre al comenzar a instalarlo que ese equipo tenía un motor trifásico y que él dispone únicamente de energía monofásica. Posiblemente sea su vecino o un amigo de la iglesia. En cualquier caso, usted está a punto de ser contactado para “convertir” esa parte del equipo y probablemente piensa que eso le va a costar más de lo que el puede gastar.

En toda reparación mecánica, la capacidad para desmontar, reparar y volver a montar el motor de forma apropiada sin dañar innecesariamente ninguna de sus piezas es fundamental. Esto suena sencillo, sin embargo, durante el proceso de desarme se cometen demasiados errores costosos.

Si todos los motores entraran “como nuevos”, la tarea sería más simple, aunque esto no sería garantía de que el montaje del motor fuera adecuado.

Cuando un centro de servicio recibe un pago por reparar un equipo, quiere que este permanezca en funcionamiento, ya que, si el equipo falla dentro del período de garantía, deberá asumir el costo de volver a repararlo. Por lo que tiene sentido realizar la reparación correcta la primera vez.

Los procedimientos de reparación, así como los propios motores, son afectados por los cambios en la tecnología. Este libro intenta incluir las últimas tecnologías comprobadas. En muchos casos, los métodos de reparación tradicionales aún pueden ser la alternativa más práctica. Las opciones presentadas a lo largo de este libro están destinadas a ayudar a los técnicos a seleccionar el método de reparación correcto, reconociendo que la decisión final recae en el propietario del equipo.

Algunas veces los métodos de reparación pierden popularidad, no porque aparezcan métodos mejores sino debido a técnicas deficientes. Otros métodos de reparación son adecuados para algunas aplicaciones, pero no para otras. Es trabajo del reparador decidir cuál será el mejor método para cada caso.

Este libro se encuentra dividido en secciones para los componentes básicos del motor con métodos de reparación y consejos dispersos por todas partes. Donde resulte práctico, se discuten también las causas de fallo. Esto ayudará a los técnicos a seleccionar el método de reparación más apropiado para cada aplicación en particular. La información presentada se basa en publicaciones de EASA y en revistas técnicas y literatura suministrada por fabricantes de motores, proveedores y centros de servicio establecidos.

COMPRAR DESCARGAR COMPRAR VERSIÓN IMPRESA

Tabla de contenido

• Terminología del motor
• Aplicaciones del motor y encerramientos
• Procedimientos de inspección y prueba
• Consejos para desmontar motores
• Rodamientos
• Alojamientos de rodamientos, orificios de eje, sellos y ajustes
• Ejes
• Rotores
• Ensamble del motor
• Accesorios y cajas de conexiones del motor
• Dinámica del motor
• Vibración y geometría del motor
• Corrientes por el eje/rodamientos
• Consideraciones especiales para motores a prueba de explosión
• Fallos en las componentes mecánicas
• Reparaciones misceláneas

Esta obra contiene muchas sugerencias sobre el manejo apropiado de las diferentes partes de un motor para minimizar los daños durante el proceso de reparación. Sin embargo, es imposible desarrollar un listado que las incluya todas.

En cambio, el principio básico de tomarse el tiempo para usar la herramienta adecuada y por lo general el procedimiento apropiado guiará a los técnicos por el camino correcto.

By Mike Parsons
Hupp Electric Motors Co.

The purpose of this article is to provide the information you need to get the most effective and useful information from EASA’s Technical Support Department. This in turn helps you serve your customers quickly and efficiently.

Most of the information provided here is based on my own experience. I hope you find it beneficial.

Keep in mind that the quickest and most efficient way for members to contact EASA Technical Support is through EASA’s website by going to www.easa.com/resources/tech_support. You can submit an online general technical inquiry or data verification and redesign request through the website. Or if you prefer, you can fax in your technical support request by downloading and competing the appropriate forms.  

But when you need to make a technical inquiry by phone, the first step is to have your company identification number ready. When the EASA receptionist answers the phone, you’ll be asked to provide that number before being connected to one of EASA’s technical support staff. 

All questions are important
When making a technical inquiry, it’s important to feel comfortable. Don’t feel like your questions lack importance or the technical support staff has better things to do. I remember the first time I contacted EASA Senior Technical Support Specialist Chuck Yung. I had a question that I asked one of the employees in our service center.  He said, “Mike, contact Chuck Yung at EASA and see what he thinks.” I responded, “I will look stupid asking this.” He smiled and replied, “Mike, the only stupid question is the one you don’t ask.”

I shook my head, went to computer and forced myself to type out my question and hit send. 

Chuck answered me within the hour with an answer and I was able to take care of my customer much quicker than thumbing through manuals or searching for a white paper on the subject.  I learned a lot that day. 

As a member, you are entitled to technical support. Asking for help before you take action just once may save you enough money to pay your annual dues — and maybe more.

When I need to contact EASA Technical Support, I look at it in the same way as when a customer contacts me. There is specific information I need to help them as quickly and efficiently as possible. That is no different from when I contact EASA. We all have had the customer who takes half an hour to describe to us what should have taken five minutes. Then there’s the guy who gives you details and it’s like pulling teeth. Let’s not be either of those guys. 

Benefits of technology
Technology today has made contacting EASA far easier than it once was. Years ago we only had the phone (a land line), the fax machine, and the postal service. Today we can call or email from practically anywhere in the world at any time. We can send pictures and/or test data from the service center floor or in the field. I find this extremely exciting and I wonder what it will be like 30 years from now.

Today, with digital cameras and smart phones it is possible to email photos of failures. This can be very nice when needing help with the root cause of a failure. Be sure to include the key details of the scenario leading to the failure and the nameplate data of the failed machine. When emailing pictures, it is helpful to send both a wide screen shot and a close-up of the failure. It is also helpful to include pictures of other conditions, e.g., if the motor has a rub, take a photo of the complete rotor; if the windings are blown, take a photo of the failure (include a close-up) of both ends of the windings, the stator core and the leads.  It would not hurt to take a shot of the grease and the bearings. Capturing everything helps in seeing the big picture and helps in determining the cause of a failure or explain an anomaly.

You’re not a bother!
When calling in with an inquiry, I find it helpful to have my questions written down. I use a notebook and will have all my data written down and hopefully ready to answer any question. If you need to leave a message, don’t speak too quickly. I know I’m guilty of this sometimes and it goes back to that old feeling that I was bothering them. I’ve learned to relax. We will be less of a bother if we slow down so we are understood the first time.

I know this because of my experience of being on the receiving end of that kind of message from others. I’ve learned that it actually helps if we speak slower than normal. Leave yourself a message sometime. It may sound strange, but it doesn’t hurt practicing. You will see what I mean. Be sure to leave your company ID number, full name, company name & city, phone number with area code, and your extension.

Describe the problem first and then the background data. When we give them the question first they know where we are going as we relay the background information. This saves time.
After leaving a message, remember to have patience. They will treat every call as an urgent one unless we say otherwise. The staff is busy; they receive 75-100 calls a day. 
When we are looking for help with winding data we need to be sure to state what it is we want. If we send data but don’t address what it is we need, that requires a followup call or email and delays the needed answer. On a rush overtime job when the customer is losing money per hour and you are doing everything possible to finish the job quickly, you can see how this could impact your company. 

Organization is the key
When you have a technical inquiry, it is important that we are organized before we make contact and tell staff what the facts are as we know them. They are here to help us. 
As I look back at that time when our employee first told me to contact EASA, I see that it still holds true today. Two heads are always better than one.

This 40-page booklet provides a great marketing tool for your service center! Use it to provide end users with information that will help them obtain the longest, most efficient and cost-effective operation from general and definite purpose electric motors with these characteristics:                                                                                                          

• Three-phase, squirrel-cage induction motors manufactured to NEMA MG 1 standards 
• Power ratings from 1 to 500 hp (1 to 375 kW)                                        
• Speeds of 900 to 3600 rpm (8 to 2 poles) 
• Voltages up to 1000V, 50/60 Hz 
• All standard enclosures (i.e., DP, TEFC, WPI, WPII) 
• Rolling element (ball and roller) and sleeve bearings

This booklet covers topics such as:

• Installation, startup and baseline information
  • Basic system considerations
  • Installation
  • Startup procedures
  • Baseline data
  • Total motor management
• Operational monitoring and maintenance
  • Application specific considerations
  • Preventive, predictive and reliability-based maintenance
  • Inspection and testing
  • Relubrication of bearings
• Motor and baseline installation data
• How to read a motor nameplate
  • Overview
  • Required information
  • Other terms
• Motor storage recommendations
  • Motor storage basics
  • Preparation for storage
  • Periodic maintenance

This resource is provided as a FREE download (use the link below). You can also purchase printed copies ready to distribute to your current or potential new customers. The cover of this booklet can also be imprinted with your company's logo and contact information (minimum order or 200). Contact EASA Customer Service for details.

READ MORE ABOUT THE FEATURES AND BENEFITS

The purpose of this guide is to provide repair/rewind practices and tips that will help service center technicians and motor winders maintain or increase the efficiency, reliability and quality of the motors they repair.

Some of the included procedures derive directly from the 2019 and 2003 rewind studies by EASA and AEMT of the impact of repair/rewinding on motor efficiency. Others are based on the findings of an earlier AEMT study [1998] of small/ medium size three-phase induction motors and well-established industry good practices . 

The procedures in this guide cover all three-phase, random-wound induction motors. Much of the guide also applies to form-wound stators of similar sizes. 

(Note: This guide provides many specific procedures and recommendations. Alternative practices may accomplish the same results but must be verified.)

Table of Contents Overview

• Terminology
• Energy losses in induction motors
• Motor repair processes
  • Preliminary inspection
  • Dismantling the motor
  • Removing the old winding and cleaning the core
  • Rewinding the motor
  • Reassembling the motor
  • Confirming the integrity of the repair

El propósito de esta guía es suministrar prácticas y consejos de reparación/rebo­binado que ayudarán a los técnicos y a los bobinadores del centro de servicios a conservar o aumentar la eficiencia, confiabilidad y calidad de los motores que reparan.

Algunos de los procedimientos incluidos derivan directamente de los estudios sobre el impacto de la reparación/ rebobinado en la eficiencia del motor realizados por EASA y AEMT en los años 2003 y 2019. Otros se basan en los hallazgos del estudio previo efectuado por AEMT [1998] en motores trifásicos pequeños/medianos y en las buenas prácticas industriales bien establecidas.

Los procedimientos de esta guía cubren todos los motores trifásicos de inducción de alambre redondo. Mucha información también aplica a motores con bobinas preformadas (pletina o solera) de tamaños similares.

(Nota: Nota: Esta guía proporciona muchas recomendacio­nes y procedimientos específicos. Se pueden lograr los mismos resultados con otras prácticas, pero deberán ser verificadas.)

Tabla de Contenido

• Terminología
• Pérdidas de energía en los motores de inducción
• Procesos de reparación del motor
  • Inspección inicial
  • Desmontaje del motor
  • Remoción del antiguo bobinado y limpieza del núcleo
  • Rebobinado del motor
  • Montaje del motor
  • Confirmando la integridad de la reparación

The challenge for every motor repair firm is twofold: to repair the equipment properly; and to demonstrate to their customers by means of adequate testing and documenta­tion that rewound motors retain their operating efficiency. Following the guidelines in the “DOs” and “DON’Ts” below will help you accomplish both.

Numerous studies have been done to determine the effect rewinding has on motor efficiency. These studies identified several variables that can impact the efficiency of a rewound motor, including core burnout temperature, winding design, bearing type, air gap and winding resistance. The following guidelines were developed as a result of those studies, which found that the efficiency of both standard and energy efficient electric motors can be maintained during rebuilding and rewinding. 

To ensure that motors retain their efficiencies when rewound, EASA also strongly recommends that electric motor repair centers comply with ANSI/EASA Standard AR100: Recommended Practice For The Repair Of Rotating Electrical Apparatus and strictly adhere to the “DOs” and “DON’Ts” that follow. These guidelines, which contain safe values (based on available data) and correct procedures, apply to both energy efficient and standard motors. Further study of the matter continues, and these guidelines will be revised if additional information warrants.

Gene Vogel
EASA Pump & Vibration Specialist

Service centers that provide field service for equipment removal and installation have little trouble handling most common horizontal pumps. However, vertical turbine pumps (and similarly mounted vertical pumps) present some additional challenges. Vertical pumps of this style use the discharge column to suspend the pump below grade from a grade mounted discharge casing. The casing provides the support for the pump, the pedestal for the vertical drive motor, and a 90 degree discharge elbow. The discharge elbow may be above or below grade.

The initial challenge for pump removal is presented by the length of the pump. Short set pumps range to about 50 ft. (15 meters) in overall length, minus the drive motor. Deep set pumps can extend hundreds of feet (or meters) into a well or sump. The designation as short set or deep set is somewhat arbitrary, depending on the working height of the available crane to lift the machine. A short set pump could be handled as a single piece (again, less the motor). But if the length of the pump exceeds the working height of the crane, then field disassembly is necessary – usually referred to as a deep set pump.

Topics covered include:

• Documenting the condition of the machine
• Overhead clearances
• Reinstalling the pump
• Tests

This presentation covers:

• An explanation of partial discharge
• Description of the damage mechanism
• PWM drive and partial discharge
• How to evaluate partial discharge
• Repair tips for dealing with partial discharge

Often an overhung fan is balanced in a single plane, only to find that the vibration has shifted to the outboard bearing. Attempts to use standard two-plane techniques may result in calculated correction weights that are very large and produce poor results. There are more effective ways to approach this common problem. This presentation shows a methodical approach and techniques for tackling this difficult balancing problem.

Target audience: This presentation is intended for field service balancing technicians, supervisors and managers.

This presentation demonstrates an easy-to-build temporary oven that can be constructed in the service center or in site. The recording covers:

• Materials to use and where to obtain
• Heating: electric, propane, or other?
• Measuring winding temperature
• Regulating oven temperature
• Storage of the parts when not in use
• Safety concerns and cautions

Target audience: This presentation will benefit service center supervisors and management.

Chuck Yung
EASA Senior Technical Support Specialist

Flooding in the aftermath of tropical storms, including hurricanes, monsoons and cyclones, and with their associated heavy rainfall can shut down hundreds of plants along the Gulf Coast, from Florida to Texas, as well as in other places around the world. And they are doing so more often.

To get them up and running again, maintenance departments and motor repairers face the daunting task of cleaning muck and moisture from many thousands of electric motors and generators. The process involved in such situations can take weeks, if not months, and requires special clean-up procedures for motors contaminated by saltwater.

Although the problems are huge, affected plants can get back in production more quickly by working closely with service center professionals and following a few tips that will make the cleanup more manageable. These include prioritizing motors and generators for repair or replacement, storing contaminated machines properly, and using proven methods to flush away saltwater contamination.

Constructing temporary ovens on site or at the service center can also add capacity for drying the insulation systems of flooded motors.

Topics covered in the article include:

• Understanding the problem
• Two ways to clean
• Saltwater flush procedure
• Temporary bake oven - eliminating the bottleneck
• How long to bake?
• How it works

READ THE FULL ARTICLE

Chuck Yung
EASA Technical Support Specialist 

Occasionally, someone asks how much current a squirrel cage rotor bar carries. That’s an interesting question, and the answer depends on several factors. The rotor kVA* of a wound rotor motor is typically about 0.8 times the stator kVA. 

The rotor rated voltage is open circuit—a condition than cannot exist in a functional squirrel cage rotor— and the amps are at rated-load; the two don’t “coincide,” thus the 0.8 factor. For a squirrel-cage induction rotor, a multiplier of 0.96 is used because the magnetizing current comes from the stator rather than from the rotor. 

By Tom Bishop, P.E.
EASA Senior Technical Support Specialist

The Electrical Apparatus Service Association (EASA) has published two documents to help users and service providers ensure that motor repairs performed reflect good practices that maintain or improve a machine's energy efficiency and reliability: ANSI/EASA Standard AR100-2015: Recommended Practice for the Repair of Rotating Electrical Apparatus and the "Good Practice Guide" of the 2003 study The Effect of Repair/Rewinding on Motor Efficiency, by EASA and the Association of Electrical and Mechanical Trades (AEMT). These documents serve as tools by which service centers and end users can speak the same language when it comes to level-setting service and performance expectations on motor repair and rewind.

Also, a little more than a year ago, EASA launched its electric motor repair accreditation program, based on AR100 and the "Good Practice Guide." The program benefits both end-users and service providers by ensuring that electric motor repairs conform to the good practices identified in the aforementioned documents."

Electric motor efficiency can be maintained during repair and rewind by following defined good practices. This article builds on my previous discussion of PM and PdM for three-phase squirrel-cage motors ("PM and PdM for electric motors") by outlining some of the expectations and good practices for repairs of these types of motors.

READ THE FULL ARTICLE

This video shows one step in collecting motor winding data: how to measure magnet wire. A service center could use this data to:

• Duplicate an original winding
• Verify that a previous rewind was done correctly
• Serve as a basis for redesigning a winding
• Store recorded data for future reference

Helpful tools

• EASA's magnet wire table can be found in Section 6 of EASA's Technical Manual and can be downloaded for free by EASA members.
  
  DOWNLOAD FREE PDF BUY LAMINATED WIRE TABLE
   
• EASA's polyphase and single phase winding data cards are available for purchase in EASA's online store.
  
  BUY WINDING DATA CARDS

By Chuck Yung
EASA Senior Technical Support Specialist

There are several methods to operating a three-phase motor using single-phase power to make what would be an otherwise expensive and arduous process a little easier.

So, you told a neighbor you work with electrical equipment and now he thinks you can solve his problem because he or she bought a three-phase motor that can't run on single-phase power. Being asked to convert this motor already sounds like more trouble than it's worth. That's not quite true though. There are some methods to make the process easier.

These methods include:

• The phantom leg method
• Rotary phase converter method
• Variable frequency drive method

READ THE FULL ARTICLE

This video shows how to adjust the brush neutral position of a DC machine to prevent sparking at the brushes at full load. An accurate neutral setting promotes good commutation and efficient machine operation. It also minimizes commutator wear while maximizing brush life. For this video, we’re using the AC method of setting brush neutral.

Chuck Yung
EASA Senior Technical Support Specialist

We all know that stator cores should be burned at a controlled temperature to prevent lamination deterioration that can lead to harmful eddycurrent losses. But what about armatures? While that DC machine is energized by direct current, it is also true that the armature itself sees alternating current as the current in each coil reverses while passing from pole to pole. 

A temperature-controlled burnout oven permits us to cremate a stator without worry, but an armature is another story. Because the commutator is integral to the armature, and cannot be easily removed, some repairers resort to a hand-stripping operation. Careful use of a torch to warm the windings accelerates the stripping job, but controlling the core tempera­ture can be difficult. And stripping a large armature without heat is all but impossible by conventional methods. 

Presented by Carlos Ramirez
EASA Technical Support Specialist

Is the motor drawing high no-load amps and winding data are correct? Are you experiencing unusual heating of the stator under load? Those common questions can be answered by checking the stator core condition. This presentation will discuss how to perform a stator core test using a loop test. It also will explain how to analyze the results, providing information about the associated equipment, tips for repairing core damage and explain other alternatives for stator core testing.

The presentation covers:

• Loop test theory
• Testing procedure
• Acceptable limits for losses and core temperatures
• Associated equipment
• Tips for repairing core damage
• Alternative stator core test

This presentation will be useful for supervisors, winders and test technicians.

This EASA software is a valuable interactive training tool ideal for training your novice(s). Even experienced winders will learn from it. The CD teaches how to wind in a richly detailed, step-by-step approach. It includes narrative, animations and video clips, with tests to assess student comprehension. The training, which is divided into 13 lessons, covers data taking, core testing, coil cutoff, burnout, stripping, core preparation, coil making, stator insulation, coil insertion, internal connections, lacing and bracing, inspection and test of untreated and treated windings, and winding treatment. Features include "Pro Tips" and "Drill Downs" that enhance the learning experience and assure that even the most experienced technician will learn from this product. The course is delivered as an interactive Adobe PDF file containing text, audio, video, supporting documents and quizzes.

LEARN MORE

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

When a shaft is in need of repair, often the first step is to determine the corrective method required. Econom­ics and best practices are typically sig­nificant factors in the decision-making process in selecting the method of repair. The types of shaft repairs that will be dealt with here are:  opposite drive end bearing journal, drive end bearing journal and a bent shaft. The objective is not to detail the repair processes, but to identify the most common methods appropriate to the types of repair and considerations associated with each method. Table 1 summarizes the methods for various load conditions.

Nota del editor: Este artículo técnico "repetido" fue publicado por primera vez en la edición de Currents de enero del 2012.

Eugene Vogel
Especialista de Bombas y Vibraciones de EASA

Cuando trabaje con bombas, seguramente encontrará instancias en las que se hace referencia a la curva de la bomba, junto con una serie de parámetros asociados con ella. Un parámetro clave de la curva de la bomba es el Punto de Mejor Eficiencia (BEP). Este concepto simple de un punto de operación que produce la operación más eficiente no es difícil de visualizar. Para motores eléctricos, la eficiencia varía con la carga; la mejor eficiencia está en alrededor del 75% de carga. Sin embargo, con las bombas rotodinámicas, que incluyen bombas centrífugas y de flujo axial, hay que considerar cuatro parámetros clave, uno de los cuales es la eficiencia. Estos cuatro parámetros son cabeza, caudal (también conocido como capacidad o volumen), potencia y eficiencia.

Gene Vogel
EASA Pump & Vibration Specialist

It happens to just about every EASA service center. A machine shows up for repair; it has leads, and there’s a motor, but the machine is a pump. Most often, it’s a close-coupled pump or a submersible pump. If your response is, “We don’t work on those here,” because you’re thinking, “We don’t know anything about repairing pumps,” you may be turning your back on some very profitable work.

As I detailed in my February Currents article, pump repair can be a very profitable expansion area for service centers that specialize in electric motor repair only. If you agree that pump repair would be a good fit for your business, the next step is to evaluate what changes your facility needs to accommodate repairing pumps. You will find that you have much of the necessary equipment from repairing electric motors. The mechanical characteristics of motors and centrifugal pumps are very similar. Depending on the type of pump, there may be very little additional that you need.

Chuck Yung
EASA Senior Technical Support Specialist

One of the more mundane things we as repairers must be concerned with is motor storage. For many of us, storing large motors for major customers is its own profit center. For all of us, being aware of how our customers store the motors we repair and send to them is critical to customer satisfaction. A poorly stored motor is likely to suffer winding or bearing failure, and we don’t want unrealistic warranty claims over something outside our control.

Our primary concerns when storing motors, especially long-term, are windings, bearings and shaft sag.

Tom Bishop, P.E., and Chuck Yung
EASA Senior Technical Support Specialists

The typical service center repairs at least 300 motors per technician annually. Saving 8 minutes (0.133 hours) per job equates to: 300 x 0.133 = 40 man-hours per year—a full week of labor per employee. It is not unrealistic to expect twice that much savings, just by implementing some of these timesaving tips.

We all know that seemingly small time savings can significantly improve the bottom line. For a service center with a 12% return on investment (ROI), shaving a few minutes off each job is the equivalent of adding 2 manmonths of billing per productive employee.

For a 10-man service center, with a shop rate of $75 per hour, 20 man-months times 75 = $258,000. To add a quarter-million dollar account usually means adding personnel, sales maintenance, and risk of bad debt/warranty expense. However, steps that streamline efficiency continue to pay dividends.

Topics covered include:

• Layout and workflow
• Time killers
• Time: Is every hour on the job billable?
• Time-saving equipment
• Attitude and productivity
• Communicating effectively
• Training
• Lighting
• Calibration
• Storage/handling/procurement
• Parts storage
• Examples from real service centers

Doug Moore
Kentucky Service Co., Inc.

Many EASA members perform service on pumps of some type and have had the customer return the pump or call back to say it leaks or it still will not pump. We solved this by making a very inexpensive test center for all types of pumps: flooded suction, immersion lube, submersible, centrifugal, deep well and many others.

Jim Bryan
EASA Technical Support Specialist (retired)

En la edición de Febrero de nuestra revista Currents, Mike Parsons proporcionó excelentes consejos para contactar y formular preguntas al Departamento de Soporte Técnico de EASA. Mike hace parte de Hupp Electric Motors Co. en Marion, Iowa y es miembro del Comité de Educación Técnica y me gustaría resaltar una declaración que hizo: “¡Ustedes no son ninguna molestia!” De hecho, son nuestro sustento. 

Durante años, sus Juntas Directivas y Gerentes han asignado recursos para aumentar el número de especialistas de soporte técnico y en encuestas anteriores de evaluación de necesidades, los miembros han calificado al soporte técnico/ingeniería de EASA como el beneficio número uno de la membresía. Así que aprovechad esto por todos los medios. 

Para ayudarle a obtener el mayor beneficio, este artículo explicará la información requerida para llenar la Solicitud de Verificación de Datos & Rediseño. Puede completar y enviar su solicitud en línea en www. easa.com/resources/tech_support/ redesign_inquiry o descargarla en este link y enviarla por fax o correo electrónico. Ver Figura 1. En el caso que llene la solicitud a mano, asegúrese de escribir claramente. Por ejemplo, los números “1” o “7”, o “5” o “6”, se parecen cuando se escriben muy rápido.

Figura 1

Cuando esté llenando la solicitud impresa o en línea, verá que ciertos campos están marcados con un asterisco (*), esto implica que son obligatorios para poder completar la solicitud. Algunas veces toda esta información no está disponible por lo que se debe informar de esto en el campo apropiado. Entonces nosotros haremos lo posible para determinar lo que se debe hacer. 

Comenzando con la información de la empresa, los datos importantes son su número de identificación de EASA, su nombre y la información de contacto por si nos surgen algunas preguntas. Indique porque medio prefiere recibir su respuesta, proporcionando un número de fax, un correo electrónico o su número telefónico. Nosotros utilizamos los datos de placa y la información del fabricante para ingresarla en la base de datos de EASA. Aunque esta información será de ayuda para futuras consultas, en caso que falte, no impedirá que la solicitud sea procesada. 

Datos de placa 

*Hp o kW es la potencia de la placa de datos que determina la capacidad de carga de la máquina. Cuando existen opciones como esta, se debe encerrar dentro de un círculo la unidad correcta. Las rpm o el número de polos y la frecuencia determinan la velocidad de la máquina. La frecuencia, el voltaje y los amperios también son tomados de la placa de datos. Si existe más de un valor todos deberán ser reportados.

Datos y dimensiones del núcleo 

Uno de los puntos clave para evaluar o rediseñar un bobinado es verificar si las densidades de flujo magnético en el entre hierro y en el núcleo del estator son razonables. Estas se pueden expresar en miles de líneas de flujo por pulgada cuadrada (klíneas/ pul²) o Teslas (T) y se comparan con los valores máximos establecidos en el entre hierro (65 klíneas/pul² o 1 T), yugo (130 klíneas/pul² o 2 T) y diente (130 klíneas/pul² o 2 T). También son comparadas con motores de la base de datos de EASA con dimensiones y potencias similares. Podemos calcular el número de líneas de flujo por pulgada cuadrada utilizando el voltaje, la frecuencia, los datos del bobinado y las dimensiones del núcleo. Los cálculos requieren mediciones precisas de cada uno de los componentes así como también el número de ranuras del estator. La Figura 2 proporciona las directrices para tomar estas medidas.

Figura 2

El número de ranuras del rotor es opcional a no ser que se requiera un cambio de velocidad. Dependiendo del número de polos, ciertas combinaciones de ranuras rotor-estator producirán ruido, variación del torque a muy baja velocidad (cogging) o una reducción del torque cuando el motor comienza acelerar (cusp). Con el número de barras del rotor podemos verificar si esta combinación ocasionará problemas en su motor. Tenga en cuenta que si las ranuras del estator o del rotor son inclinadas, dicha combinación no deberá causar estos problemas. 

El largo del núcleo deberá ser la distancia total entre los dos extremos del núcleo. Si existen ductos de aire, el número y ancho de los mismos se deberán anotar en los campos provistos. Estos datos serán incluidos posteriormente en la evaluación. 

En los bobinados preformados (pletina) son necesarias las dimensiones de la ranura del estator. Las medidas exactas facilitarán el cálculo de los calibres o tamaños de alambre y del aislamiento, para que se ajusten adecuadamente en la ranura cuando se construyan las bobinas. 

Información del bobinado 

El número de grupos y bobinas se requiere para evaluar el bobinado. Aquí tenga cuidado con la matemática. Un ejemplo es un motor de 48 ranuras con 3 bobinas por grupo, en el cual el llenado de todas las ranuras es el mismo. Muchas veces este diseño se reporta como un bobinado concéntrico de 12 grupos y 4 bobinas por grupo con un total de 48 ranuras y tres pasos de bobina. Realmente existen 36 ranuras y la tercera bobina de cada grupo tiene el doble o casi el doble del número de espiras de las otras dos bobinas del grupo. En cada grupo de bobina, dos bobinas compartirán una ranura y la otra bobina llenará por completo una ranura. Esto puede causar confusión y muchas veces requiere de una llamada telefónica para aclarar lo que realmente hay ahí. 

La sección de los datos del alambre indica el número de alambres en paralelo y los calibres de cada bobina. Recuerde que el alambre redondo puede ser métrico o AWG. Si no está seguro, proporcione las medidas con micrómetro y nosotros tomaremos la decisión. Tenga en cuenta que si una máquina no está fabricada en Norte América, bien podría tener alambre métrico. Se debe evitar el uso de galgas ya que generalmente no cuentan con la suficiente precisión para poder determinar la diferencia entre los calibres medios o AWG versus los métricos. Incluso un alambre medio puede marcar la diferencia. Una mejor práctica consiste en medir el alambre con un micrómetro y utilizar la tabla de Alambres Redondos de EASA para identificar el calibre del alambre. 

Sin duda, la parte de este rompe cabezas que se reporta erróneamente con más frecuencia, es la conexión. Una buena regla a tener en cuenta es que si el motor tiene más de tres cables, existe más de una conexión. Una discusión acerca de esto y de cómo determinar la conexión, se encuentra en el artículo publicado en octubre de 2011 en la revista Currents titulado “Understanding three-phase motor connections.” 

Sera necesario contar las espiras en varios grupos de bobina ya que no es raro que exista un número de espiras diferentes en las bobinas de un mismo grupo o en grupos distintos. Algunas de estas pueden parecer impares, por lo que es bueno contar varios grupos de bobinas hasta que se identifique el patrón. El número de espiras será el número total de alambres dentro de la ranura dividido por los alambres en paralelo y el número de lados de bobina. Por ejemplo, en la ranura compartida de un bobinado excéntrico (imbricado) con 90 alambres dentro de la ranura y con 3#16, 2#17, el número de espiras es: 

90/2 = 9 espiras
( 3 + 2 ) 

El paso indica la ranura en la cual se aloja el primer lado de bobina y la ranura en la cual se inserta el lado opuesto. Ver Figura 3. Por lo que en un paso 1-8, el primer lado de bobina está insertado en la ranura 1 y el otro lado cae en la ranura 8. Un paso de bobina 1-8 abarca 7 dientes, por lo que la extensión de la bobina es igual a 7 (span). Todas las bobinas de ese grupo tendrán el mismo espacio entre ellas y a continuación comenzará la siguiente fase.

Figura 3

Los bobinados concéntricos siempre tendrán más de un paso, como 1-8, 10, 12. Éste es un grupo de tres bobinas que están concéntricamente anidadas como se ve en la Figura 4 a la derecha. No todas las potenciales combinaciones de paso permitirán una distribución equitativa de las bobinas y por consiguiente no se pueden utilizar. Por ejemplo, un motor de 4 polos con 48 ranuras y 36 bobinas no puede utilizar un paso 1-7, 9, 11 ya que la bobina a ranura llena caerá en la parte superior de la ranura de una bobina compartida y habrá ranuras vacías. 

Datos nuevos

Esta sección contiene las instrucciones de lo que usted desea obtener. Esto puede incluir cambios de potencia, velocidad, frecuencia o de voltaje. El motivo de la solicitud es muy importante ya que no necesitamos adivinar o suponer nada. Entre más detalles proporcione, especialmente en solicitudes complicadas, mejor serán los resultados. Si alguna información no está disponible, incluya una nota al respecto para que podamos hacer nuestro mejor esfuerzo para llenar los vacíos. 

Conclusión 

Entre más completa y exacta sea la información, recibirá una respuesta más rápida y precisa. Agradecemos mucho cuando nos envían al Departamento de Soporte Técnico de EASA sus solicitudes en línea o mediante los formatos que pueden descargar en la WEB. Al parecer cada centro de servicio tiene su propia forma de registrar esta información y esto es bueno. No obstante toma más tiempo encontrar la información cuando no estamos familiarizados con dichos formatos. Enviar la información en los formatos estandarizados por EASA acelera el proceso.

Jim Bryan
EASA Technical Support Specialist (retired)

In the February 2017 edition of Currents, Mike Parsons provided excellent advice on contacting EASA Technical Support with questions. Mike is with Hupp Electric Motors Co. in Marion, Iowa, and is a member of the Technical Education Committee. I would like to underline one statement he made: “You are not a bother!” In fact, you are our livelihood. 

Over the years, your Board of Directors has allocated resources to increase the number of technical support specialists. And in past Member Needs Assessment Surveys, members have consistently rated technical/engineering support as the number one benefit of membership. By all means, take advantage of it. 

To help you get the most from the benefit, this article will explain the information required to complete the Data Verification & Redesign Request form. You can complete and submit the request online or you may complete and fax or email the form that is available to download. See Figure 1. If the forms are filled out manually, be sure to write clearly. For example, numbers such as “1” or “7”, or “5” or “6”, can look the same if written too quickly.

Figure 1: EASA's Data Verification & Redesign Form

When completing both the printed and online forms, certain fields are marked with an asterisk (*) implying that they are required to complete your request. Sometimes all of this information is not available and should be noted so in the appropriate spot. We will then make every attempt to determine what should be done. 

Starting with the company information block, the important data are your company EASA identification number, a name and contact information in case we have questions. Let us know which medium you prefer to receive your response by filling in either the fax, email, or phone area. We use information in the manufacturer block to enter into the EASA database. While helpful for future reference, it will not impede the request if it is missing. 

Nameplate data 

*Hp or kW is the rating from the nameplate for the machine’s load capacity. When there are choices such as this, the correct unit should be circled. Entering rpm or poles and frequency determines the speed of the machine. Frequency, volts and amperes are also from the nameplate. If there is more than one of any of these values, all should be reported. 

Core data & dimensions 

One of the keys to evaluating or changing a design is to determine if the magnetic flux densities in the air gap and core iron are reasonable. This can be expressed in thousands of lines of flux per square inch (klines/in²) or Tesla (T). This is compared to the maximum values established for the air gap (65 klines/in² or 1T), core (130 klines/ in² or 2T) and tooth (130 klines/in² or 2T). They are also compared to motors with similar cores and ratings found in the EASA motor database. We can calculate the number of lines of flux per square inch using the voltage, frequency, winding data and core dimensions. The calculations require accurate measurements for each of the components as well as the number of stator slots. Figure 2 provides guidelines for these measurements.

Figure 2: Important information for taking measurements

The number of rotor bars is optional unless a speed change is requested. Depending on the number of poles, certain combinations of numbers of rotor bars compared to stator slots will produce noise, cogging or torque cusps. With the number of bars, we can check to see if the combination in your motor will be a problem. Note that if the rotor bars or stator slots are skewed, the combination should not cause these problems. 

The core length should be given as the overall distance from one end of the core to the other. If there are air ducts, the number and width of these can be reported in the spaces provided. They will then be included in the evaluation. 

For form coil windings, the stator slot dimensions are needed. Accurate measurements will facilitate designing the wire size and insulation to fit properly in the slot when the coil is made. 

Winding information 

The number of groups and coils is required for the winding evaluation. Be careful with the math here. An example is a motor with 48 slots with 12 groups of 3 coils, but all the slots are equally full. Many times this will be reported as 12 groups of 4 for 48 total coils with 3 pitches in the concentric winding. Actually, there are 36 total coils and the third coil in each group has twice or nearly twice the number of turns of the other two coils in the group. In each coil group, two coils will share a slot and one of the coils will fill the slot alone. It can be confusing and often require a phone call to clarify what is really there. 

The wire data section tells the number and size of the wires in hand for each turn. Remember the wire could be AWG or metric. If you are not sure, provide the micrometer readings for the wire sizes and we will make the determination. Note that if the machine is not made in North America, it well could be metric wire. Wire gauges should be avoided; they are generally not sufficiently accurate to determine the difference between half sizes or AWG versus metric sizes. Even a half wire size can make a difference. It is best practice to measure the wire with a micrometer and use the EASA Round Magnet Wire Data chart to identify the wire size. 

By far the most often misreported piece in this puzzle is the connection. A good rule to remember is that if the motor has more than three leads, there is more than one connection. A discussion of this and how to determine the connection is found in the October 2011 Currents article titled “Understanding three-phase motor connections.” 

Several examples should be taken to determine the number of turns in each coil; it is not uncommon for there to be different turns in the coils in the same group or for different groups. Some of these may seem odd, so it is good to count multiple coil groups until you recognize a pattern. The number of turns will equal the total number of strands (wires) in the slot divided by the number of wires in hand and the number of coil sides. For instance, in a shared slot lap winding with 90 total wires in the slot and 3#16, 2#17 the number of turns is: 

90/2 = 9 turns
(3+2) 

The pitch is the slot the first coil side falls in and the slot for the opposite side reached. See Figure 3. Such as in a pitch of 1-8, the first coil side is in slot 1 and the other side is in slot 8. A coil pitch of 1-8 spans 7 teeth, so the span = 7. All of the coils in that group will have the same space between them and then the next phase begins.

Figure 3: Coil pitch

Concentric windings will always have more than one pitch listed such as 1-8, 10, 12. This is a group of three coils that are concentrically nested as seen in Figure 4 at the right. Not all potential pitch combinations will allow the coils to be distributed evenly and therefore cannot be used. For instance, a 4-pole motor with 48 slots and 36 coils cannot use a pitch of 1-7, 9, 11; the full slot coil will fall on top of a shared slot coil and there will be empty slots. 

New rating 

This section contains the instructions for what you would like to accomplish. This may include changes in the horsepower, speed, frequency or voltage. The reason for the inquiry is very important so we do not need to guess. The more detail provided, especially for complicated requests, the better the results. If any of the information is not available, include a note to that effect so we can do our best to fill in the gaps. 

Conclusion 

The more complete and accurate the information provided, the more quickly and accurately the answer will be received. We very much appreciate when you submit your requests to EASA Technical Support online or using one of the downloadable forms. It seems that every facility has its own way to record this information and that is good. It does take extra time to find the information if you are not familiar with the format; submitting on standardized EASA forms expedites the process.

Tim Browne
Industrial Electric Motor Service, Inc.

I suspect that just about everyone in our industry at one time or another has had the joy of repairing a “purpose-built” motor. This kind of motor is built for a specific purpose and has characteristics that may allow it to operate under non-standard conditions. Due to the limited information that some of them display on the nameplate, the repair of these motors can be somewhat of a challenge.

Sometimes these motors possess differences such as the color of paint, the shaft size, the bearing size, or type. It can be the operating temperature and at times it can be the motor in its entirety. Following are a few useful tips we use when repairing a motor with so many question marks.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

A menudo, las inundaciones producidas por las intensas lluvias de las tormentas tropicales (huracanes, monzones y ciclones) colapsan cientos de plantas industriales a todo lo largo de la costa del golfo de México, desde la Florida hasta Texas y en otros lugares del mundo.

Para retomar las actividades productivas, los departamentos de mantenimiento y los reparadores enfrentan la difícil tarea de limpiar la suciedad y desalojar la humedad en miles de motores y generadores eléctricos. Ver Figura 1. El proceso en tales situaciones puede tomar semanas o meses y requiere procedimientos especiales para limpiar los motores contaminados con agua salada.

Aunque el problema es enorme, las fábricas pueden volver a producir más rápidamente aunando esfuerzos con centros de servicio profesionales y siguiendo algunos consejos que facilitan las tareas de limpieza. Estos incluyen, priorizar los motores que requieren ser reparados o reemplazados, almacenar adecuadamente las máquinas contaminadas y utilizar métodos contrastados para eliminar la contaminación con agua salada. Fabricar hornos provisionales in situ o en el centro de servicio también puede aumentar la capacidad de secado de los sistemas de aislamiento de los motores inundados.

Por Steven Carbone
Miembro del Comité de Educación Técnica
Industrial Electro-Mechanics

En el actual entorno competitivo cada vez mayor, los usuarios finales buscan centros de servicio de máquinas eléctricas rotativas que aumenten su oferta de valor agregado. Una de las formas más fáciles para que un centro de servicios logre esto es efectuando una inspección minuciosa y detallada de los equipos que reciben para reparación. Los resultados de dicha inspección permiten mejorar la confiabilidad de los equipos que se logra a través de los resultados de la evaluación y las recomendaciones que ofrece el centro de servicio para prevenir fallas recurrentes y mejorar el tiempo medio entre fallas.

Art Godfrey (retired)
Birclar Electric & Electronics

Mi primera experiencia con lubricantes sintéticos para rodamientos con elementos rodantes fue durante la reparación de dinamómetros para probar motores de automóviles de alta velocidad. Durante varios años nuestro centro de servicio había reparado máquinas similares con rodamientos con elementos rodantes, pero todas ellas estaban lubricadas con sistemas de bombeo de aceite con accesorios especiales cerca de los rodamientos para suministrar solo pequeñas cantidades de aceite por minuto.

Comenzamos a ver máquinas enviadas para reparación con rodamientos con elementos rodantes lubricadas con grasa y estas indicaban en la placa de datos una marca y tipo de lubricante específicos. Compramos lo que estaba especificado en la placa y todo salió bien. Con el tiempo, comenzamos a ver más máquinas que especificaban la misma marca de grasa, pero con un tipo o grado diferente y esto me condujo a comenzar a buscar las diferencias en los productos, ya que uno era muy costoso y tenía una vida útil limitada.

Gary Braun
Brehob Corp.

Repair and rewinding of table and chuck magnets requires the same skill set as winding field coils for DC motors. The testing is also similar. These magnetic chucks are primarily used on large grinders. DC electro-magnets seem deceptively simple. They operate on the same principles as the common bar electromagnet and horseshoe electromagnet. The strength of this magnet is proportional to the ampere turns of the coil. The coil will produce north and south poles just as in a DC motor frame.

Topics covered in this article include:

• Brief background of these types of magnets
• Tests with same standards
• Possible coolant leaks
• Identical field coils
• Lead failure is common
• Potting of the coils

Eugene Vogel
EASA Pump & Vibration Specialist

It is common for vertical turbine pumps (VTP) to be designed with mul­tiple mixed flow impellers (sometimes 12 or more) and for the pump rotor to be supported by the vertical pump mo­tor.

Vertical pump motors can be solid shaft or hollow shaft. Solid shaft motors have an annular keyway in the shaft that is engaged by a solid coupling that supports the pump rotor. 

Hollow shaft motors support and drive the pump rotor from the top by means of a head shaft fitted through the hollow motor shaft to the pump line shaft. In either case, there is an adjustment that lifts the pump rotor so it is supported by the motor shaft. This adjustment is obviously critical to the proper operation of the pump and motor and can have a significant effect on the motor load (current). Presented here are some of the main concerns for setting this pump lift ad­justment.

This video explains how to measure the diameter of a bearing journal accurately to within five hundred-thousandths of an inch or one-thousandth of a millimeter. This critical step will determine if the shaft needs any repairs for proper bearing fitment.

Topics covered include:

• Tools and supplies needed
• How to validate micrometer accuracy
• Minimum number of measurement locations
• How to measure a bearing journal

Fundamental to every good mechanical repair is the ability to disassemble, repair and reassemble the motor correctly without unnecessary damage to any of the motor parts. This sounds simple, and yet too many costly mistakes are made in this process of taking things apart. If every motor repaired was in “as new” condition, the task would be much simpler. But this would be no guarantee that the reassembly would be correct.

​There is usually an easy way and a hard way to remove and install parts. Brute force is seldom the easiest or the correct way. The old saying of “don’t force it, get a bigger hammer” is seldom the best way.

When a service center is paid to repair equipment, the service center wants it to stay in operation. If the equipment fails again—within the warranty period—the service center pays to repair it again. It makes sense to repair it correctly the first time.

In order to improve equipment, it is important to know how and where it operates. Without understanding why a motor fails, it is impossible to deliberately improve its mean time between failures.

To do this, there must be communication between the service center and the motor user. Not only does this help the repairer decide the best course of action, but it helps the user appreciate the professionalism of the service center.

Repair procedures, like motors themselves, are affected by changes in technology. This book attempts to include the latest proven technologies. Time-honored methods of repair, in many cases, may still be the most practical option. Options presented throughout this book are intended to help the technician select the appropriate repair method, recognizing that the ultimate decision rests with the equipment owner.

Repair methods sometimes fall into disfavor, not because better methods are introduced, but because of poor techniques. Other repair methods are well-suited to some applications but not to others. It is the job of the repairer to decide what is the best method for each case.

This book is divided into sections for basic motor components with repair methods and tips dispersed throughout. Where practical, reasons for failures are also discussed. These will aid the technician in selecting the most appropriate method of repair for each unique application.

The information presented draws from EASA publications, IEEE publications, technical journals and literature supplied by vendors, motor manufacturers and established service centers.

This book contains many suggestions on how to correctly handle the various parts of a motor during the repair process so as to minimize damage. However, it is impossible to develop an all-inclusive list. Instead, the basic principle of taking the time to use the correct tool and correct procedure will usually lead the technician down the right path. Always remember, if it has to be forced beyond reason, it might be that neither the proper tool or procedure is being used or something is wrong with the parts. Step back and ask “What am I overlooking?”

Table of Contents

1. Motor Nomenclature
2. Motor Applications and Enclosures
3. Test and Inspection Procedures
4. Motor Disassembly Tips
5. Bearings
6. Bearing Housing Repair, Shaft Openings, Seals and Fits
7. Shafts
8. Rotors
9. Motor Assembly
10. Motor Accessories and Terminal Boxes
11. Motor Dynamics
12. Vibration and Motor Geometry
13. Shaft/Bearing Currents
14. Special Considerations for Explosion-Proof Motors
15. Failures in Mechanical Components
16. Miscellaneous Repairs

This book is available as part of EASA's Fundamentals of Mechanical Repair seminar.

BUY A COPY
BOOK DOWNLOAD CD-ROM BOOK & CD-ROM

Chuck Yung
Especialista de Sénior de Soporte Técnico de EASA

Una de las cosas más mundanas de las que debemos preocuparnos como reparadores es el almacenamiento de los motores y para muchos, almacenar motores grandes para clientes importantes representa ganancias. Para todos nosotros, ser conscientes de cómo nuestros clientes almacenan los motores que les reparamos es crítico desde el punto de vista de la satisfacción del cliente. Es probable que un motor mal almacenado sufra fallos en el devanado o en los rodamientos, y no queremos reclamos por garantía poco realistas sobre algo que está fuera de nuestro control.

Nuestras principales preocupaciones al almacenar motores, especialmente a largo plazo, son los devanados, los rodamientos y el pandeo del eje.

This webinar presents a product quality planning process for industrial motor stator windings rated above 4 kV. Emphasis is placed on analyzing gaps between these projects and lower voltage rewinds as they relate to:

• Stator winding design
• Insulation system validation
• Process control

Target audience: This presentation is most useful for service center winders, engineers, supervisors and managers. The content targets beginners through highly experienced persons.

Chuck Yung
EASA Senior Technical Support Specialist

You've just dismantled a special motor for a customer, and the core test indicates the watts loss/pound is excessive.  The high core losses are caused by shorts between the laminations.  This may be the result of a ground failure.  Or excessive temperatures may have caused the deterioration of inter-laminar insulation (called coreplate.)

Whatever the cause, a replacement is 16 weeks away, and your customer wants his motor repaired.  This motor sounds like a prime candidate for a restack, but you are hesitant.  Your company has a reputation for quality, and the finished product has to meet your usual high standards. 

You want to know the best procedure for repairing this core.  Here are some guidelines to help you do the best possible repair. 

Tom Bishop, P.E.
EASA Senior Technical Support Specialist

Cleaning of electric motor parts is performed in every electrical apparatus service center. This begs the question of whether or not cleaning is being done productively and with minimal safety and environmental consequences.

This webinar recording addresses some of the more common conventional methods of electric motor cleaning and some alternative methods, including:

• Methods
  • Solvent
  • Aqueous (water-based)
  • Other more aggressive methods
• Selection factors
  • Size and quantity of parts to be cleaned
  • Type of part, e.g., stators, rotors, housings
  • Type of cleaning agent: solvent or aqueous
• Environmental and safety concerns

This webinar recording will benefit service center managers, supervisors and technicians.

By Tom Bishop, P.E.
EASA Senior Technical Support Specialist

It’s impossible to balance line-to-line voltages perfectly in three-phase circuits, so they typically differ by a few volts or more. However, if voltage unbalance exceeds 1%, it can markedly decrease the performance and energy efficiency of three-phase motors while increasing the likelihood of premature failure. Avoiding these issues requires a proactive approach that includes installing adequate protective devices and periodically checking for voltage unbalance at the motor terminals.

The article covers:

• What it is
• Common causes
• Effects of unbalanced voltage
• Testing for unbalanced voltages and single-phasing
• Ways to correct unbalanced voltages

READ THE FULL ARTICLE

​Este folleto de 40 páginas ofrece una gran herramienta de marketing para su centro de servicio! Lo utilizan para proporcionar a los usuarios finales con información que le ayudará a obtener la, operación más eficiente y rentable de propósito más larga de los motores eléctricos generales y definidas con estas características:

• Trifásica, motores de inducción de jaula de ardilla fabricados con las normas NEMA MG 1
• Los valores de potencia de 1 a 500 CV (1 - 375 kW)
• Velocidades de 900 a 3600 rpm (8 a 2 polos)
• Tensiones de hasta 1000 V, 50/60 Hz
• Todas las cajas estándar (es decir, DP, TEFC, WPI, WPII)
• Rodando elemento (bolas y ruedas) y los cojinetes de manguito

Este folleto cubre temas tales como:

• Instalación, puesta en marcha y la información de base
• monitoreo y mantenimiento operativo
• Datos del motor y la instalación de línea de base
• Cómo leer una placa de identificación del motor
• recomendaciones de almacenamiento del motor

Este recurso se ofrece como una descarga gratuita (utilizar el enlace más abajo). También puede comprar copias impresas listo para distribuir a sus actuales o potenciales nuevos clientes. La portada de este folleto también se puede imprimir con el logotipo e información de contacto de su empresa (pedido mínimo o 200). Póngase en contacto con Servicio al Cliente EASA para más detalles.

Tom Bishop, P.E. 
EASA Technical Support Specialist

Performing work at a customer site is often more challenging than service center work. The main reasons are that the personnel and material resources are limited to the person(s) sent to the site and the equipment they have brought with them. 

To put it another way, the on-site technician can't simply call another technician over from another part of the service center to assist (the service center may be a great distance away), and the service center stockroom is likewise not available. Plus there is the added pressure of having someone (or several people) looking over your shoulder. 

The following is a series of tips to help you when performing on-site ser­vices. While these will not completely overcome the challenge of working remotely, applying several of them may reduce some of the challenge in on-site service work. 

Mike Howell
EASA Technical Support Specialist

The open stator impedance test (a.k.a, ball test or dummy rotor test) is used by many service centers as a quality control check before winding treatment and/or a troubleshooting test. This webinar recording reviews test procedures, expected outcomes and incorporating thermal camera imaging. Topics covered include:

• Understanding the principles of the test
• Performing the test safely and consistently
• Expanding the value of the test with thermography 

This webinar recording is intended for personnel responsible for testing stator assemblies.
 

Chuck Yung
EASA Senior Technical Support Specialist

We all have that occasional customer who got a “deal” at an auction: a compressor, or lathe, or wood-working equipment, only to discover when he started to install it that this equipment has a three-phase motor and only single-phase power is available. Maybe it’s your neighbor or a friend from church. In any case, you know that you are about to be called upon to “convert” that piece of equipment, and you probably realize that it’s going to cost you more than you can charge.

Chuck Yung
EASA Senior Technical Support Specialist

There are benefits and drawbacks to the use of multiple circuits in a 3-phase winding. Whether discussing a random winding or form coil winding, some of the considerations are shared. Let’s start with the basics:  The higher the power rating, and/or the lower the voltage rating, the fewer turns/coil used. Because a 3-phase winding has pole-phase groups alternating ABC, ABC, ABC, etc., the intra-phase jumpers could be 1-4, 1-7, 1-10, 1-13, etc., or any combination of these so long as the alternating polarity of the groups is maintained and the phases are not cross-connected.

This video explains how to check the ground insulation of an AC motor winding using the insulation resistance (IR) test. The IR test is usually the first electrical test because it indicates if the motor winding can withstand further testing, or the machine can return to service. This video shows:

• How to select the megohmmeter and IR test voltage
• How to connect the megohmmeter to the winding and ground the leads
• How to perform the IR test and for how long
• How to safely discharge the winding
• How to correct the IR test result to the standard temperature of 40°C and determine if it is acceptable

We often hear the terms preventive maintenance (PM) and predictive maintenance (PdM) of electric motors, but far less often do we give consideration to the tasks associated with these methods of maintaining motor operation and extending operating service life. This article addresses some of the more common activities associated with PM and PdM, with the focus on three-phase squirrel cage motors.

Preventive maintenance:

• Insulation resistance (IR) test
• Polarization index (PI) test
• Motor current signature analysis (MCSA)
• Mechanical activities such as lubrication, lubricant level checks, and lubricant analysis
• Visual inspection
• Thermal scanning
• Ultrasonic testing
• Cleaning
• Belt tensioning
• Bolt tightness checks

Predictive maintenance activities:

• Trending and assessing most activities associated with preventive maintenance
• Vibration analysis
• Checking and adjusting alignment

READ THE FULL ARTICLE

Ron Rapa
Rapa Electric, Inc. 
Allegan, Michigan
Technical Education Committee Member 

Over the many years that I’ve been in the electrical and mechanical repair business, I’ve learned a number of tips and techniques to help me work more efficiently. Time is a precious commod­ity, so making the best use of it can help you provide the best possible service to your customers.

Gene Vogel
EASA Pump & Vibration Specialist

This presentation provides an overview of common predictive technologies and information about applying them correctly.  While providing break-fix service and analysis is not uncommon for a service center’s field service team, the industry is pushing more towards failure prevention methods and testing and this requires a shift in tools and thought processes. Topics include:

• Ultrasonic analysis
• Vibration analysis
• Oil analysis
• Thermography

This presentation is best for technicians, field service, shop managers and engineering staff.

Tom Bishop, PE
Especialista Sénior de Soporte Técnico de EASA

Tres de los problemas más comunes en los motores trifásicos por los que somos consultados son:

1. “El motor toma mucha corriente en vacío”
2. “La corriente en las tres líneas no está balanceada”
3. “ El motor trabaja caliente”

Incluso si nunca te has enfrentado a uno de estos problemas, sigue leyendo porque es casi inevitable que lo hagas y querrás saber qué hacer al respecto.

1. “El motor toma mucha corriente en vacío”
Esta llamada suele estar asociada a un motor que acaba de ser rebobinado. Las causas frecuentes de la alta corriente son un devanado con densidades de flujo magnético elevadas o un aislamiento de las láminas del núcleo dañado. Verificar las densidades de flujo magnético y probar el núcleo antes de rebobinar son buenas prácticas que pueden prevenir el problema de la alta corriente. El programa AC Verification and Redesign de EASA - Versión 4 calcula rápidamente los flujos magnéticos y la densidad de corriente e "indica" los valores que quedan fuera de los rangos de aceptación típicos. Una comprobación rápida de la densidad del entrehierro (AGD) consiste en utilizar la base de datos de devanados y buscar "HP (kW), polos, largo y diámetro interior del núcleo" y comparar las densidades con la de sus datos. Si sus datos dan como resultado un AGD de más de un 20 %, la culpa es de sus datos. Se puede utilizar un probador de núcleo comercial o una prueba de lazo ("toroide") para verificar la condición del núcleo laminado. Si utiliza el método de prueba de lazo, consulte la Sección 7 del Manual técnico de EASA para obtener una guía paso-paso de esta prueba.

Los valores de flujo magnético del devanado que son demasiado altos, o las pérdidas en el núcleo excesivas, a menudo resultan en una corriente sin carga más alta de lo normal. Al verificar las densidades magnéticas, los datos del devanado se pueden corregir antes de rebobinar el motor envés de hacerlo después de que se haya ensamblado por completo. Del mismo modo, un núcleo defectuoso se puede reparar o reemplazar como resultado de una prueba del núcleo en lugar de saber después del ensamblaje que el núcleo está defectuoso. Si no está seguro de un procedimiento o resultado de una prueba, comuníquese con nuestro departamento de soporte técnico: technicalsupport@easa.com o +1 314 993 2220.

La alta corriente en vacío podría tener causas distintas a los defectos mencionados anteriormente. Los motores de baja velocidad, normalmente de 8 o más polos, tienen una corriente sin carga relativamente alta. Consulte con el fabricante del motor, sus propios registros de reparaciones anteriores o contacte nuestro soporte técnico para evaluar la alta corriente antes de desmontar el motor, o tomar la decisión más costosa: Retirar los devanados. Además, compare el voltaje de línea aplicado con el voltaje nominal del motor. Otras posibles causas incluyen: Desalineación axial de los núcleos del estator y del rotor (deben estar alineados dentro del 3% de la longitud del núcleo del estator); un núcleo del estator en cortocircuito; Conexión o vueltas incorrectas.

La Tabla 1 es una adaptación y ampliación del artículo de Currents de febrero de 2005: “No-load Current Basics: Practical Guidelines for Assessment” y proporciona rangos típicos para las corrientes en vacío de los motores. A más número de polos, mayor será la relación entre la corriente en vacio y la corriente a plena carga. Las densidades de flujo magnético de los devanados, en particular las del entrehierro y el yugo (corona), también afectan la relación entre las corrientes en vacio y a plena carga. Cuanto mayor sea la densidad de flujo, mayor será la corriente sin carga comparada con la corriente a plena carga. Los motores de mayor potencia tienden a tener relaciones más bajas. Un voltaje de línea superior al nominal aumentará la corriente en vacio y un voltaje inferior al nominal la reducirá. Por muy obvio que parezca, es algo que a menudo pasamos por alto cuando probamos un motor, como un motor de 200 o 208 voltios que se prueba con 240 voltios o más, u otro de 380 voltios que se prueba con más de 415 voltios.

Nota: Puede encontrar información adicional sobre las corrientes en vacío en los siguientes artículos técnicos en easa.com/currents: "A Closer Look At The Sin-Load Current" en la edición de Currents de mayo del 2001 y "Avoiding High No-Load Amps" On Rewound Motors” en la edición de Currents de febrero del 2004.

2. “La corriente en las tres lineas no está balanceada”
La corriente desbalanceada se puede atribuir al motor o a la línea de alimentación. Para determinar la causa, marque arbitrariamente las líneas de alimentación como A, B y C, y las del motor como 1, 2 y 3. Conecte A con 1, B con 2 y C con 3, energice el motor y mida la corriente en las tres lineas. Apague el motor y reconecte A con 3, B con 1 y C con 2, opere el motor y mida las tres corrientes de nuevo, Si la corriente más alta y más baja siguen las mismas líneas, el problema está en la alimentación; pero si siguen las líneas del motor, está en el motor. Esto se ilustra en la Tabla 2.

Si la causa es la alimentación, se requiere balancear el voltaje de suministro. Las normas NEMA establecen un límite del 1% para este desbalanceo y remarca que el desbalanceo total de corriente esperado para el motor funcionando a velocidad nominal es de 6-10 veces el desbalance de voltaje. Si el desbalanceo de la fuente de voltaje excede del 1% o la corriente desbalanceada sobrepasa el 10%, se debe corregir el porcentaje de desbalanceo a menos del 1% o derratear el motor.

Si el motor es la causa, las vueltas por fase o los circuitos en paralelo probablemente están desbalanceados o el bobinado está mal conectado. Un error de fabricación puede conducir a que las bobinas no tengan las mismas vueltas dando como resultado vueltas por circuito/fases desiguales. Las vueltas desbalanceadas darán como resultado corrientes desequilibradas similares a las producidas por los voltajes de alimentación desbalanceados. Un bobinado desbalanceado o mal conectado normalmente se puede detectar con un probador de impulso (surge). Medir la resistencia entre fases con un microohmímetro (DLRO) también puede detectar vueltas desiguales. Estos valores deben estar dentro del 2 % para bobinados de alambre redondo o del 1 % para bobinados de pletina (solera). Nota: Algunos devanados concéntricos pueden exceder el límite del 2 %,

También puede ocurrir una corriente desequilibrada si el devanado tiene grupos desiguales con más circuitos de los permitidos. Otra fuente de desbalanceo es una secuencia de agrupación incorrecta de acuerdo a los puentes seleccionados (polo adyacente versus polo saltado). Además, aunque es poco común, si el entrehierro está excéntrico, pueden ocurrir corrientes desequilibradas. En ese caso, la “corriente más alta” permanecerá con el motor. Esto es particularmente cierto en un devanado cuyo número de circuitos es la mitad del número polos (por ejemplo, una conexión de 3 circuitos en un motor de 6 polos). Otra posibilidad es una conexión abierta que omita un circuito en un devanado con varios circuitos en paralelo. Un ejemplo de esto es una conexión delta en un motor de 4 polos en la que uno de los circuitos de una fase no ha sido conectado. El resultado es un devanado con tres circuitos en una fase y cuatro circuitos en cada una de las dos fases buenas. La medición de resistencia entre fases con un DLRO o una termografía durante una prueba de estator abierto a voltaje reducido detectaría esta condición.

Nota: Puede encontrar información adicional sobre desbalance de corriente (y voltaje) en easa.com/currents en el artículo técnico titulado: “Unbalanced Voltages and Electric Motors” en la edición de Currents de diciembre del 2007.

3. “El motor trabaja caliente”
¿Con qué frecuencia ha escuchado esto de uno de sus clientes? En algunos sistemas de aislamiento modernos, la temperatura de la superficie del motor podría ser lo suficientemente alta como para causar quemaduras si se posa un dedo o una mano sobre él. Por tanto, una advertencia: Nunca utilice una parte de su cuerpo para comprobar la temperatura de un motor. Utilice un sensor de temperatura. Las normas definen los límites de temperatura para los devanados, pero no para la superficie de un motor.

Si se puede alcanzar con seguridad el exterior del centro axial del núcleo del estator con un sensor de temperatura (ver Figura 1), se puede estimar la temperatura del devanado. Esto es que la temperatura del devanado será aproximadamente entre 5 °C a 10 °C (9 °F a 18 °F) más alta que la temperatura medida en el exterior del centro axial del núcleo del estator. Los límites de temperatura del devanado varían según el tamaño y el tipo de motor. Para determinar si el devanado está muy caliente, vea el artículo: “Understanding Motor Temperature Rise Limits” en la edición de Currents de noviembre del 2003 en easa.com/currents. Si la temperatura del devanado es mayor de lo esperado en comparación con la temperatura de la superficie de la carcasa, es posible que el núcleo esté suelto, lo que inhibe la transferencia de calor. Las causas del calentamiento excesivo del devanado pueden ser externas o internas al motor. Las externas incluyen temperatura ambiente alta, contaminantes, sobrecarga, cargas de alta inercia, voltaje de suministro alto o bajo o voltajes desequilibrados. La temperatura total del devanado es la combinación del aumento de temperatura del devanado más la temperatura ambiente. Si el ambiente es 10°C (18°F) más caliente de lo normal, el devanado en las mismas condiciones probablemente estará 10°C (18°F) más caliente y tendrá aproximadamente la mitad de su vida térmica normal. Los contaminantes que se acumulan en el motor o que bloquean los conductos de ventilación aumentan la temperatura del devanado y de otros componentes, como los rodamientos, lo que provoca fallos prematuros.

La sobrecarga simplemente significa que la carga impulsada excede la potencia nominal del motor. Una bomba o ventilador con una válvula de descarga o compuerta muy abierta puede aumentar la carga, al igual que poner demasiado peso en un transportador. Las cargas de alta inercia, como ventiladores o sopladores, requieren un tiempo de arranque prolongado, lo que aumenta el calentamiento del rotor y del estator. Los voltajes de suministro altos o bajos darán como resultado pérdidas en el núcleo excesivas o una capacidad de torque reducida, respectivamente. Los voltajes desequilibrados aumentan la corriente en al menos una fase, aumentando las pérdidas en el cobre del devanado (I²R). También producen corrientes de “secuencia negativa” (tema fuera del alcance de este artículo) que calientan la superficie del estator y del rotor al doble de la frecuencia de línea. Las causas internas del motor incluyen también contaminantes que se acumulan en el motor o que bloquean los conductos de ventilación, un núcleo del estator dañado o un devanado con datos incorrectos. Un núcleo de estator dañado puede aumentar considerablemente las pérdidas en el núcleo y provocar un calentamiento excesivo y una corriente elevada incluso sin carga. (Vea el problema Nº 1). Los ejemplos de datos de devanado incorrectos incluyen un devanado mal conectado, como un devanado conectado en delta envés de estrella, un bobinado con "menos" vueltas (la reducción de vueltas aumenta la densidad del flujo magnético y las pérdidas en el núcleo), o un voltaje incorrecto como un devanado de 200 o 208 voltios energizado con 240 voltios.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Existen ocasiones en las que una aplicación requiere que un motor soporte una carga radial para la que los cojinetes de deslizamiento no son adecuados. En casos como bajas revoluciones, carcasas inusuales, etc., puede ser conveniente convertir el motor del cliente montado sobre cojinetes de deslizamiento envés de obtener un motor de repuesto con rodamientos de bolas / rodillos. Este artículo contiene procedimientos sugeridos y advertencias sobre problemas potenciales relacionados con dichas conversiones.

Primero, inspeccione las tapas del motor para asegurarse de que tengan la rigidez mecánica suficiente para soportar la carga y suprimir la vibración (vea la Figura 1). Si las tapas carecen de rigidez, puede que sea necesario utilizar tapas nuevas fabricadas con un material más grueso. En otros casos, se puede utilizar un inserto para reforzar la tapa existente.

Chuck Yung 
EASA Technical Support Specialist 

We've all faced those rush jobs, where a cus­tomer is desperate to get his motor back faster than humanly possible. It is our nature to try to do the impossible that's why we are in this business.

We enjoy a challenge and the opportunity to help people. Turning a motor around quickly, when a customer is in need, is rewarding. One of the most time-consuming steps drying the windings after they have been cleaned Ð can be frustratingly slow when an anxious customer is calling. How long does that motor need to bake to be safe? 

Most service centers have built in a safety factor, based on some long-forgotten problem we had (or heard about) with a winding that was not properly dried. "Joe" opened the oven door right before lunch and left it open, then someone pulled a stator out a couple of hours later and it megged low. Maybe it failed on the test panel. Of course, "Joe" didn't fess up to what happened.  So you told everyone: "From now on, all windings bake 2 hours longer than we used to."

Chuck Yung
EASA Senior Technical Support Specialist

This presentation examines features, benefits and drawbacks of both conventional and alternative methods of cleaning electric motors.

Methods covered include:

• Immersion tanks
• Steam cleaning
• Parts-washing machines
• Pressure washers
• Abrasives
• Ultrasonic devices

Environmental options for handling waste by-products are also addressed. If you are considering changing your cleaning methods, this webinar is for you.

A special discounted collection of 8 webinar recordings focusing on various aspects of pump repair.

Once purchased, all 8 recordings will be available on your "Downloadable products purchased" page in your online account.

Downloadable recordings in this bundle include:

Troubleshooting Pump Performance Problems
Presented May 2017

This presentation covers:

• Not enough pressure (head) or not enough flow – how do you respond?
• How to determine if a pump is operating properly
• Differentiating a pump problem from a system problem
• Determining pump load and power requirements
• The effect of fluid parameters and cavitation on pump performance. 

Target audience: This will be most useful for service center technicians and engineers. The content will also be beneficial for supervisors and managers who are responsible for pump failure analysis and testing. 

Pump Failure Case Study
Presented December 2013

This presentation covers:

• Brief overview of disassembly and evidence of failure
• Discussion of possible failure scenarios
• Review of actual repairs, modification and reassembly
• Update of machine's present operation

Repair Tips for Submersible Pumps
Presented February 2013

This presentation focuses on:

• Types of submersible pumps
• Tips on seal arrangements
• Common repair procedures
• Cables and cable entries
• Testing submersibles in the service center

Assessing Impeller Damage
Presented May 2019

The impeller is generally the most difficult pump component to repair and the most expensive to replace. This session will look at case histories of failed pumps and the steps to determine the cause of failure. Topics covered include:

• Erosion, corrosion, cavitation or wear: What happened to this impeller?
• How to spot the tell-tale signs
• What operational conditions led to impeller damage

Repairing Impeller Damage
Presented May 2016

We’ve covered how to assess impeller damage. Now learn how to fix that damage. This presentation covers: 

• Replacing/repairing wear rings
• Repairing cavitation damage
• Impeller replacement options
• Dynamic balancing impellers

Techniques for Straightening Pump Shafts
Presented March 2011

The slender dimensions of many pump shafts make them susceptible to distortion, which affects pump performance and reliability. This recording presents a methodical approach and effective techniques for measuring and correcting shafts which are bent or twisted.

Target audience: This presentation is intended for service center supervisors, managers and machine shop technicians.

Vertical Turbine Pump Repair Tips
Presented February 2012

Vertical turbine pumps are used extensively in every segment of industry. Although they are not complex, repairing them in the service center can present a few challenges. This presentation gives some approaches and procedures that experience has shown will make the job easier.

Final Testing for Pumps - An Overview
Presented November 2014

The pump repairs are completed! Now the pump needs to be tested. This presentation discusses the procedures for the basic tests that can be performed on pumps that have been repaired in the service center.

Final testing of pumps can include:

• Operational tests
• Seal leakage test
• Motor chamber leakage test (submersibles)
• Casing pressure test

While some of these tests are not difficult to perform, knowing the methods and limits will help service centers to confidently deliver quality pump repairs.

This presentation focuses on:

• A review of seal basics
• Seal materials for primary and secondary seals
• How to determine spring tension values
• How to calculate PV values
• Seal flush plans

Eugene Vogel
Especialista en Bombas y Vibraciones de EASA

Es común que las bombas de turbina vertical (VTP) se encuentren diseñadas con varios impulsores de flujo mixto (algunas veces 12 o más) y que los rotores de las bombas estén soportados por los motores verticales. Los motores de las bombas verticales pueden ser de eje macizo o hueco. Los motores de eje macizo tienen una cuña o chaveta anular (en forma de anillo) en el eje, para asegurar un acoplamiento sólido que soporta el rotor de la bomba.

Los motores de eje hueco soportan y accionan el rotor de la bomba desde la parte superior, mediante un cabezal de eje que está asegurado al eje lineal intermedio (line shaft) a través del eje hueco del motor. En cualquiera de los casos, existe un ajuste que eleva el rotor de la bomba para que quede soportado por el eje del motor.

Obviamente este ajuste es crítico para el funcionamiento adecuado de la bomba y el motor y puede llegar a tener un efecto significativo en la carga del motor (consumo de corriente en amperios). En este artículo se presentan algunos puntos importantes para ajustar la elevación del eje de la bomba.

By Tom Bishop, P.E.
EASA Technical Support Specialist

Being accustomed to rewinding AC stators, we may not realize that there is an equivalent repair service that can be performed on some rotors…namely, rebarring. Our focus in this article will be the rebarring of fabricated copper squirrel cage rotors. Redesign of rotors is outside the scope of this article.

Chuck Yung
Especialista Sénior de Soporte Técnico de EASA

Muchos de sus clientes cuentan con buenos departamentos de mantenimiento predictivo propios y otros lo subcontratan con proveedores externos calificados. En ambos casos, ellos deben saber cuando un rodamiento presenta deterioro y sacar de servicio el motor antes que el fallo se vuelva desastroso. En términos de mantenimiento, esto ahorra mucho dinero, lo cual es excelente. Pero si el cliente se detiene ahí, sin descubrir por qué el rodamiento está mal, su motor puede regresar reparado de nuevo con el mismo problema. Los rodamientos defectuosos aportan una gran cantidad de evidencias, si solamente las buscamos.

La clave consiste en la comunicación con el cliente, dado que nosotros los reparadores, sabemos que el motor fue retirado del servicio debido a un fallo en los rodamientos, podemos ir un paso más adelante en el proceso de diagnóstico.

Especialmente debido al uso frecuente de los variadores de velocidad electrónicos (VFDs), las corrientes por los rodamientos causan un número considerable de fallos en los mismos. Si sabemos que el motor funciona con un variador de velocidad electrónico, existen medidas correctivas para prevenir fallos futuros del mismo tipo. Y esos pasos adicionales son facturación extra. Ignorar esos pasos de inspección adicionales, es como olvidar dinero encima de la mesa, tanto para el centro de servicios como para el cliente.

Chuck Yung
EASA Senior Technical Support Specialist

Many of your customers have good in-house predictive maintenance departments and others outsource that skill. Either way, they should know when a bearing is deteriorating and remove the motor from service before it turns into a catastrophic failure. That saves a lot of maintenance dollars, which is great. But if the customer stops there, without discovering why that bearing is bad, your repaired motor could be returned with the same problem again. Defective bearings often hold a great deal of evidence, if we only look for it. 

The key is communication with the customer so that we repairers know that the motor was removed for bearing faults, and so that we can go a step further in the diagnostic process. Especially with the prevalence of variable frequency drives (VFDs), bearing currents cause a significant number of bearing failures. If you know the motor is operating from a drive, there are corrective measures to prevent future failures of the same type. And those extra steps are billable extras. Neglecting these additional inspection steps is like leaving money on the table, for both the service center and the customer.

There are certain repair processes, such as winding removal and replacement, that can impact the efficiency and reliability of electric motors. Prudent repair practices must not increase overall losses, and preferably should maintain or reduce them.

This presentation explains how those repair processes affect efficiency and reliability, and gives the best repair practices in order to maintain or improve efficiency.

Target audience: This presentation is most useful for service center inside and outside sales representatives, customer service personnel, engineers, supervisors and managers. The content will be beneficial for beginners through highly experienced persons.

This presentation focuses on:

• Types of submersible pumps
• Tips on seal arrangements
• Common repair procedures
• Cables and cable entries
• Testing submersibles in the service center

Chuck Yung 
EASA Technical Support Specialist 

A good friend recently reminded me of a tip that can save you a lot of trouble when repairing motors with an aluminum frame: Never hot-dip a stator with an aluminum frame. 

In the bake oven, the aluminum frame expands faster than the encased steel stator core. The core is loose inside the aluminum frame and, if dipped hot, varnish seeps into the gap and cures.

That destroys the concen­tricity between the stator bore and the bracket fits. The critical airgap between the stator bore and rotor becomes eccentric, and the rotor might even drag on the stator bore. Even if it does not rub, the eccentric airgap is likely to cause electrical noise when the motor runs. 

That reminded me of other valuable tips worth sharing. So that is what this article is about: Tips to help you do your job faster with less effort and to avoid mistakes; and a few that you could classify as opportunities to improve a customer’s motors. 

Gene Vogel
EASA Pump & Vibration Specialist

Corrosion and/or erosion damage is inevitable for some pump applications. Pumps received for repair with significant damage may look like a candidate for the junk bin, but with proper repair techniques can often be restored to original performance – or perhaps better than original. Damage from corrosion and erosion (henceforth “damage”) can occur on stationary pump components as well as on the rotating impeller. Note: Cavitation damage is a form of erosion damage.

We’ve covered how to assess impeller damage in a previous presentation. Now learn how to fix that damage. This presentation covers: 

• Replacing/repairing wear rings
• Repairing cavitation damage
• Impeller replacement options
• Dynamic balancing impellers

Gene Vogel
Especialista de Bombas & Vibraciones de EASA

En algunas aplicaciones, los daños por corrosión y/o erosión de las bombas son inevitables. Las bombas enviadas para reparación que presentan daños significativos pueden parecer buenas candidatas para ser desechadas, pero a menudo con las técnicas de reparación adecuadas pueden restaurarse a sus condiciones originales o quizás a unas mejores. Los daños por corrosión y erosión (en adelante “daño”) se pueden presentar en las partes estáticas de las bombas, así como también en el impulsor rotativo. Nota: La cavitación es una forma de daño por erosión.

This presentation covers:

• Who can perform repairs on hazardous location motors?
• What does it take to be certified?
• UL Files: Manufacturer and Rebuild Class, division, group and zone
• Temperature codes CSA, IECEx, FM and other third parties

Target audience: This will benefit service center management for firms that are interested in learning more about servicing hazardous location motors.