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

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

Determining the source of noise in a motor is often much more challenging than correcting it. However, a methodical approach to investigating the noise can narrow down the possible causes and therefore make it easier to resolve the noise issue. In this session we will address the causes and characteristics of the primary sources of noise in AC motors. Specific topics to be addressed:  

• Magnetic noise (aka “electromagnetic noise” or “electrical noise”) 
• Mechanical noise 
• Windage noise 
• Guidance for reducing or eliminating the intensity of these noise sources

This webinar recording is intended for mechanics, supervisors and testing technicians.

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. 

Neville Sachs, P.E.
Applied Technical Services, Inc.,
Syracuse, NY

This technical paper, presented at the 2014 EASA Convention, will help you understand how and why shafts and fasteners fail. This paper covers:

• Discussion of material properties typically found in motor shafts, machine shafts and common fasteners
• Differentiating between overload and fatigue failures
• Understanding and identifying the difference between ductile and brittle materials, and how their fracture appearances differ
• A detailed explanation of how to identify fatigue failures, including the rate and direction of force application and the effect of stress concentrations
• Examples of several failure analyses

Austin Bonnett
Austin Bonnett Engineering LLC

La finalidad de este artículo es proporcionar fundamentos suficientes sobre los rodamientos para que los responsables por la aplicación, operación, mantenimiento y reparación de los motores eléctricos puedan tomar las medidas necesarias para minimizar los fallos prematuros y mejorar la posibilidad de que de los rodamientos duren hasta el “final de la vida útil”, que normalmente se denomina L10.

Chuck Yung
EASA Senior Technical Support Specialist

There are times when a DC motor or generator experiences a catastrophic failure and the customer wants to know why it happened. One type of failure that seems to stimulate lively conversation is when the failure involves dramatic damage to the brushholders and commutator. The term “flashover” describes the appearance of the failure; the very name conveys an accurate mental image of the failure.  See Figure 1.

The questions that arise next are predictable: “What caused this?” and ”What can be done to prevent a recurrence?” Or, if the motor was recently repaired: “What did you do to my motor to cause this?!” The purpose of this article is to help you answer those questions.

The causes of a flashover can be partially explained by the insulating properties of air, and Ohm’s Law. Air is an electrical insulator, although the dielectric breakdown voltage of air is low compared to the insulating materials we use in electric motors. Inside an operating DC motor, we find heat, carbon dust and other contaminants, and perhaps even humidity. Each of these will reduce the dielectric strength of air.

As for Ohm’s Law, E/R = I; winders use this frequently to evaluate shunt fields and to extrapolate the temperature rise of those fields. But it also applies to the armature circuit. 
At the moment a DC motor is energized, before the armature starts to rotate, the armature current is limited only by the available kVA of the power supply. 

Consider the example of a 500 hp motor, with a 500V armature circuit. Static resistance of the armature-interpole circuit measured only 0.02 ohms, so the short circuit armature current could reach 25,000 amps if the drive has sufficient kVA: 500/0.02  = 25,000 amps.

Effects on armature
Fortunately, drives ramp up the armature voltage, rather than applying it instantly. As soon as the armature begins to rotate, the inductance provided by the armature becomes a factor in suppressing the armature current. Paraphrasing the now-defunct IEEE Standard 66: When voltage E is applied across a circuit consisting of a resistance and inductance L in series, the maximum rate of rise is given by the equation di/dt = E/L amperes per second; where E equals volts, and L equals henrys. In other words, the armature current decreases rapidly as the armature speed increases.

Every DC motor can be used as a generator, by driving it mechanically and applying current to the fields. When operating as a motor, there are times where the motor might be driven by an overhauling load (e.g., a loaded conveyor running downhill; or a hoist lowering a heavy load). When that happens, the counter-emf (electro-motive force) produced overcomes the applied emf, and flashover is likely. In layman’s terms, operating conditions cause the armature current to increase rapidly, and generated voltage/current trigger the flashover. 
A list of operating events that can cause a flashover is included in Table 1.

If the interpoles are not correctly adjusted to maintain brush neutral throughout the operating load range, the shifting neutral results in arcing as the load increases outside the black band region. That can, in and of itself, trigger a flashover. (The black band region can be described as this: Weakening / strengthening the interpoles, independent of all else, until the brushes begin to spark produces a band within which no sparking occurs. That band is referred to as the “black band.” For more information, see the Assembly and Final Test section of Fundamentals of DC Operation and Repair Tips.)

Preventive measures
Working to help your customer understand the basics of how a DC motor operates can go a long way towards helping them avoid problems. One of my most vivid “triggers” of a flashover is the customer who installs a newly rebuilt compound motor with more than 50% compounding. (The percent compounding describes the percentage of total field flux contributed by the series fields, at full load.) They check rotation and discover that the motor needs to be reversed. We all know that the correct way to do this is to swap the A1 and A2 leads (the large wires that are thoroughly taped). But, says the customer, it is so much easier to swap the shunt field leads (they are smaller, and probably held in a terminal strip by screws) instead. That shortcut has worked in the past — on straight shunt motors.

With a compound-wound machine, this time-saving shortcut changed the motor from a cumulative connection to differential. The motor runs fine unloaded, and even with a moderate load. But when the load is increased to the point that the series overpowers the shunt fields, catastrophe occurs. Since this is a newly rebuilt motor, there is a very good chance that your customer will blame you. After all, you just rebuilt the motor. So it is important to educate the customer to avoid just such a situation. (And yes, I have had many, many calls where a newly installed motor failed exactly as just described.)

If someone blames a flashover on “drive settings,” that implies that the drive is accelerating or decelerating the motor too rapidly. If so, a competent drive technician should be able to adjust that to reduce the chance of flashover. Blaming the drive may instead mean that the motor is in an application calling for a regenerative drive, but the customer replaced the drive with a less expensive model that cannot handle the regenerative mode. (And the customer might not admit having done so until you press the issue.) One example would be a compound wound motor driving a roller coaster. When the cars are coasting downhill, the regenerative mode is used to prevent dangerous over-acceleration.

A compound wound motor, in such an application, requires a drive that has connection points for the shunt, armature and separate series field leads. This is to permit the motor to operate with a cumulative connection in both directions of rotation. If a compound wound motor is operated from a drive with only shunt- and armature circuit leads, in a reversing application, it will be cumulative in one direction but differentially compounded in the opposite direction. The higher the percent compounding, the greater the risk of speed instability and/or flashover. See Table 2.

Specific to any DC motor, there are several preventive measures to reduce the chance of a flashover. The first of these is to simply chamfer the end of the commutator bars. Voltage stress varies exponentially to the inverse of the radius. Chamfering the customary square corner at the end of the commutator to a 1/16” (1.6 mm) radius reduces the voltage stress to approximately 15%, significantly reducing the opportunity for flashover to occur. See Figure 2.

Add flashover protection
If a customer has chronic issues with flashover, take a lesson from the traction motor industry and add flashover protection. Install four equally spaced short lengths of angle iron in line with the end of the string band area. The bolted connection must be electrically sound and the edge closest to the commutator must be bare metal (no paint or other coating). The bare metal provides a reliable path to ground, if an arc is to occur, thus minimizing damage to the costly brush boxes and commutator. See Figure 3.

Flashover detection is commercially available and reliable. It has long been known that, at the moment a flashover begins, the field polarity reverses. Automated instrumentation, by monitoring the polarity of the field current, can shut the motor down before the fault current causes damage.

If the application is a fan, blower or downhill conveyor, where the motor might start while the load is free-wheeling in reverse, the solution could be a brake – either mechanical or otherwise, interlocked with the drive to release the brake when the motor starts. One option the end user might consider is to use the shunt fields as the dynamic brake. If they do so, the field current should not exceed 1/3 of the rated shunt field current. Otherwise, the shunt fields might overheat and fail prematurely.

The manufacturer has more latitude than we do as repairers, so it is common to see larger machines designed with a compensating winding (a.k.a. “pole face bars”), imbedded in the face of each field pole to effectively extend the influence of the interpoles. Those compensating windings, just like interpoles, must be connected correctly so as to yield the correct interpole strength. Misconnected interpoles or compensating windings (i.e., the wrong number of circuits) radically change performance and are much more likely to spark and/or flashover.

This book ws developed in conjuction with EASA's two-day Fundamentals of DC Operation & Repair Tips seminar.

This book is not meant to replace the many good texts that cover the theory and design of DC machines, but to supplement them. Its purpose is twofold: to help the technician understand DC machine theory without complex formulae; and in a larger sense, to record in one place the repair procedures and tips usually learned the hard way during a long career of DC machine repair. It may take a decade or longer for a technician to become proficient and knowledgeable. We hope this book will cut many years from that timeline.

The text begins with DC theory (no math, we promise!), and then follows the logical progression of a DC machine through the service center. Disassembly, inspection and testing are covered in the initial chapters. 

Subsequent chapters are organized around the main parts of a DC machine. The final chapters cover assembly, final testing and application issues. Sections focusing on components explain how those parts work, how they are made and how they can best be repaired.

Repair tips gleaned from EASA members’ decades of experience are liberally sprinkled throughout the book. While many texts about DC machines explain how they should work, this is the first (to our knowledge) to discuss all the exceptions that a repairer is liable to run across during a lifetime of working with DC machines. These might otherwise be labeled “lessons learned the hard way,” except that the reader can benefit from having all these special cases collected in one source. When possible, it is better to learn by reading than by trial and error; otherwise, the first encounter with a unique design can result in a painful “learning experience.”

A DC machine can be used interchangeably as a motor or generator, simply by changing the connection. Any DC motor can be driven and used to produce power, and any DC generator can be motorized to provide mechanical power. Although this text predominately refers to “motor;” the material applies to both motors and generators.

As with the other EASA publications—Principles of Large AC Motors, Mechanical Repair Fundamentals of Electric Motors, and Root Cause Failure Analysis—each section is designed to stand alone. The small amount of duplication is intentional, to save the reader from flipping back and forth between sections.

Table of Contents - (Download the complete Table of Contents)

• Nomenclature and Nameplate Information
• DC Motor Theory
• Disassembly and Inspection
• Testing
• Armatures
• Commutators
• Frames
• Ventilation and Accessories
• Motor Assembly and Final Testing
• On-Site Troubleshooting
• Failure Analysis

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The repair of the various types of pumps represents an important segment of the service center repair market. Electric motors and pumps are the two most widely used industrial machine components.

Although there are two principle pump types (dynamic and positive displacement), this manual focuses on dynamic pumps and the fundamentals of dynamic pump repair. The information it contains will be helpful to both novice and experienced pump repair technicians, to supervisors and managers of pump repair operations, and to customer service and sales personnel who communicate with customers about pump repair issues.

Section 2 covers repair concerns and techniques common to most pumps, while the following sections focus on specific pump types and the unique concerns associated with repairing them. These sections include submersible pumps, vertical turbine pumps, end suction pumps and split case pumps. Where appropriate, these sections may reference the general repair information in Section 2.

Table of Contents- (Download the complete Table of Contents)

1. Nomenclature
2. General Pump Repair Procedures
3. Submersible Pumps
4. Vertical Turbine Pumps
5. End Suction Radial Split Pumps
6. Axial Split-Case Pumps
7. Seals
8. Pump Reliability
9. Glossary and Standards Organizations

Por Tom Bishop P.E.
Especialista Sénior de Soporte Técnico de EASA
 
Algunas veces, los cables de salida de los motores no se encuentran  identificados o sus marcas no  son legibles, por lo que se hace necesario  marcarlos para poder  conectar el motor adecuadamente  a la línea de alimentación. Este artículo se ocupará de cómo identificar  los cables de los motores eléctricos con 9 cables de salida y se  basa en la premisa de que ninguno de los  cables se encuentra marcado. Si alguno de ellos estuviera identificado, el procedimiento es el mismo, pero se requerirán menos pasos. Nota: Vea el artículo publicado en  mayo de 2008, en la revista Currents de EASA, titulado “Identifying Unmarked Leads Of 6-Lead Motors With 1 Or 2 Windings”.

Chuck Yung
Especialista Senior de Soporte Técnico de EASA

Un requerimiento frecuente al personal de soporte técnico de EASA es la solicitud de ayuda para la identificación de los cables de salida que no están marcados. Este artículo establece una serie de procedimientos para identificar los cables no marcados en motores con 1 ó 2 bobinados que tienen 6 cables de salida. Para identificar la mayoría de las conexiones, los únicos instrumentos necesarios son un óhmetro y un equipo de onda de choque. (surge tester)

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

The markings on the external leads of a motor sometimes become defaced or are removed, which makes it neces­sary to identify and mark them before the motor can be properly connected to the line. This article will address lead identification of three-phase motors with 9 leads, based on the premise that none of the leads are marked. If some of the leads are marked, the process is the same, but may require fewer steps. Note: See the May 2008 issue of Currents for the article “Identifying Unmarked Leads Of 6-Lead Motors With 1 Or 2 Windings.” 

Pat Douglas Kirby Risk
Mechanical Solutions & Service

Shaft currents have always been a concern for large motors due to magnetic asymmetries within the motor. Manufacturers strive to keep these to a minimum.

With the widespread use of Variable Frequency Drives (VFDs), shaft current issues have become a concern in all sizes of motors. If these currents are discharged through the bearings, electrical discharge machining (EDM) occurs. Proper installation of VFDs can play a large part in mitigating issues with shaft currents. 

Many end users are not aware of shaft currents or their destructive paths. All too often they think that the motor bearings keep failing because the motor repair was not completed properly. 
Service centers need to be on the lookout for these issues when repairing a customer’s equipment. Many repairs arrive at the service center with no history and no hint of what the problem with the motor might be. The technicians have to do an “autopsy” of the motor to be sure the causal problem is repaired and not just the symptom.

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

Steps to determine characteristics needed for finding a replacement A motor is received from a customer with the request that it be replaced. However, it does not have a nameplate. The steps to determine the motor characteristics needed for identifying a replacement will be described here. These same steps can also be used in the case of repair of a motor without a nameplate, so that a new nameplate with key identification characteristics can be made and attached to the repaired motor. The focus of this article will be NEMA or IEC horizontal motors in standard frame sizes.

Chuck Yung 
EASA Technical Support Specialist

One frequent request of EASA’s technical support staff is for help in identifying unmarked motor leads. This article introduces a set of proce­dures for identifying unmarked leads of 6-lead motors with 1 or 2 wind­ings. For most connections, the only tools required for these procedures are an ohmmeter and surge tester. 

An additional benefit is that these procedures can be used to identify the type of connection (Table 1); for example, when a motor is received without a nameplate. With 6 leads, the motor connection could be part-winding start, wye-delta, or a 2-speed design. 

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

This webinar recording reviews the failures associated with 3-phase motors on Variable Frequency Drives (VFDs) and how to rewind to limit future failures. The transient over-voltages produced by the VFD can cause the winding insulation to break down. Motor manufacturers and service centers have recognized that the winding insulation system must be enhanced to help withstand the effects of being used on a VFD. Topics include:

• Brief overview of the transient voltage phenomena
• Materials for an inverter-duty winding system
• Processes for an inverter-duty winding system
• Other considerations: cables, VFDs

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

Gene Vogel
EASA Pump & Vibration Specialist

When machine vibration increases, one of the first questions asked is: "Is a failing bearing causing the vibration?" In the case of rolling element bearings, it is not difficult to separate vibration caused by a failing bearing from other common faults such as unbalance, misalignment, looseness, etc. But sorting out vibration from a failing rolling element bearing (here-after called "bearing vibration") from process sources such as flow induced and background vibration can be more demanding. The secret is to identify the frequency at which a flaw on a roller or raceway will impact the mating bearing component. These are commonly known as bearing fault frequencies.

Topics covered include:

• Simple to complex steps in identifying bearing vibration
• "Locate rpm" function
• Occurance of sidebands

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.

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.

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

In a previous article in Plant Engineering ("A systematic approach to AC motor repair," Plant Engineering, April 2015), EASA highlighted the good practices for electrical repair found in ANSI/EASA Standard AR100 Recommended Practice for the Repair of Rotating Electrical Apparatus, and the significant impact they can have on motor efficiency and reliability. But that was only part of the story, because mechanical repairs—and even documentation, cleaning, and inspection—can also markedly affect motor reliability and efficiency.

This latest article focuses on the mechanical and "other" repair good practices prescribed by AR100 that are mandatory in EASA's motor-repair accreditation program, including lubrication, bearings, and repair of frames, shafts, and bearing fits.

Items discussed include:

• Identification and labeling
• Identification of cause of failure
• Cleaning and inspection
• Cooling system check
• Exterior finish
• Packaging and transportation
• Mechanical repairs including items such as shafts, bearings, lubrication, frames, etc.
• Mechanical tests and instrument calibration

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Presented by Ashutosh Kumar
Karsten Moholt AS

Learn how a fellow EASA service center interpreted different maintenance philosophies and put their own development in that curve. Their evolution has gone from workshop to predictive maintenance and beyond–to proactive maintenance, including 3D scan/print and the Internet of Things (IoT)

This recording addresses how the modern toolbox has changed–from an adjustable spanner (wrench) to sophisticated sensors. IoT is just a new tool in the box.

Rick Hoadley
ABB

Whenever an application engineer is planning on installing adjustable speed drives for AC motors, line current harmonics and reflected waves are two factors that need to be addressed. Four basic questions should be answered in order to successfully commission the drive system:

1. What is my power system like today
2. What impact will the additional drives have on the power quality for the other equipment
3. If needed, what harmonics mitigation method should be used
4. How long and what type of cable is used between the drive and motor

This paper, presented at the 2013 EASA Convention, deals with understanding IEEE Std 519 and various mitigation methods in order to meet those recommendations. It also reviews the types of filtering that is available to reduce the reflected waves seen at the motor terminals.

Topics covered include:

• Overview of drives topologies
• The differences between 6,12,18 pulse and active front end drives
• How the differences in drives relate to harmonics generated
• Filters on either end of the drive to mitigate the effects of harmonics, as well as voltage spikes and other potential damaging effects on the motor

Joe Junion
L&S Electric,Inc.

Electrical bearing damage has become a very common issue in electric motors. This is not a new problem, but awareness has put the spotlight on this important reliability factor and industry has stepped up to deal with it.

Let’s keep it simple though. Voltage is induced on the rotating member of an electric motor. If the voltage level gets high enough, it will discharge across the thin lubrication film of a bearing and cause damage.

Topics covered in this article include:

• Effects of arcing
• Detecting shaft voltage
• Preventing damage
• Shaft grounding products
• Identifying and assessing damage

Austin Bonnett
Austin Bonnett Engineering LLC

The purpose of this article is to provide enough rolling element bearing fundamentals so those who are responsible for the application, operation, maintenance and repair of electric motors can take the necessary steps to minimize premature bearing failures and enhance the possibility of bearings lasting until the "end of life" predictions, which is normally referred to as L10 bearing life.

Gene Vogel
EASA Pump and Vibration Specialist

When a motor is test run in the service center, the two most common vibration frequencies that occur are at 1x rotating speed (1x rpm) and at 2x line frequency (2x lf). High 1x rpm is often corrected by balancing, and the 2x lf is traditionally attributed to air-gap anomalies or voltage or winding unbalance. However, there are those cases where the traditional approaches are unsuccessful and technicians and managers are left scratching their heads. In these difficult cases, there is often a combination of electrical and mechanical vibration. Being able to separate electrical and mechanical vibration is necessary to efficiently arrive at a solution.

By Mike Howell
EASA Senior Technical Support Specialist

Process downtime is expensive—even more so when it’s unexpected. So, when an electric motor fails, we tend to pull, repair, or replace it, and move on as quickly as possible. In doing so, however, we may miss an opportunity to capture basic information that could help improve the reliability of the application. With a little planning, these data can be gathered with no delay in startup.

Topics covered include:

• Collect initial data
• Don't destroy two motors
• Help your service center

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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

Mike Dupuis
Monelco, Ltd.

Our service center location in Southern Ontario, Canada, is considered ground zero for automotive stampings. One of the more common prime movers employed on stamping presses in our area is the dependable eddy current drive. Most units our technicians encounter are in the 50 hp plus category, which makes for a large piece of equipment. 

Removal of these units from a stamping press is no small task, so taking steps to more positively identify a problem with the actual drive unit as opposed to the controller or load is highly advisable. Our company provides on-site service and troubleshooting to our customers, which allows us to inspect the application firsthand before removal of the unit is performed.

Chuck Yung
EASA Senior Technical Support Specialist

Concerns about partial discharge (PD) used to be limited to repairers and users of machines rated over 7 kV. PD is a common consideration for machines rated 11 kV and higher. This article will describe PD, explain how to detect it, and offer repair solutions.

What is partial discharge?
Air, like Nomex^®, Mylar^®, mica and Dacron^®, is an insulator. Like any insulation, it will break down electrically if subject to too high an im­pressed voltage. Air is capable of with­standing approximately 75 volts/mil (3000 volts/mm), as compared to mod­ern insulating materials rated many times higher. (See Table 1.)

Gene Vogel
EASA Pump and Vibration Specialist

When a motor fails to perform, we know what to check: the voltage, whether it’s balanced, the current, whether there is a ground, etc. When a pump fails to perform, many service centers are at a loss on how to troubleshoot it. If the pump has just been repaired and fails to perform, it will be hard to convince the customer that the pump is not the problem. The fact is, there are three areas of possibilities: It could be the pump, or it could be the fluid that is being pumped (the pumpage), or it could be the system of vessels, pipe and fittings connected to the pump (the system).
Understanding a little bit about pump curves and pump performance parameters, and using the process of elimination, will allow the service center technician to narrow the possibilities — especially those that are pump related.

Jim Bryan (retired)
EASA Technical Support Specialist

Voltage surges come in many forms, all of which can be devastating to an electric motor. Transient conditions, rapid bus transfer, ungrounded systems, reclosure, improperly located power factor correction (PFC) capacitors, accidental connection of a new dual-voltage motor for the wrong voltage, and lightning are all sources of damaging surges. Here, we would like to discuss two of these sources: rapid bus transfer and reclosure.  Rapid bus transfer occurs when the voltage source is changed from the primary to a secondary source or back. This might occur when an automatic back-up source is brought on line during a power outage. Reclosure is similar but may include the automatic reclosing of an overcurrent device or “chatter” in a switch or circuit breaker.

By Gene Vogel
EASA Pump & Vibration Specialist

An important step when selecting a centrifugal pump and an electric motor for an application or when troubleshooting operation issues is to determine how much power the pump should be using. The “by-the-book” approach references the pump curve, which shows the power requirement for the pump’s range of operation (head and flow rate). While that’s the best approach, a simple, universal formula based on the relationship of power, head, flow rate, and efficiency can provide realistic estimates for general planning or primary troubleshooting.

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This version of Principles of Medium & Large AC Motors manual is now available to address applicable IEC standards and practices. This 360-page manual was developed by industry experts in Europe along with EASA's engineering team. (The "original" version of this book based on NEMA standards remains available as a separate document.)

This manual includes drawings, photos and extensive text and documentation on AC motors, including how they work, information on enclosures, construction on components and applications. Many of the principles included apply to all AC motors, especially those with accessories that are associated with larger machines in the past (such as encoders, RTDs, thermostats, space heaters and vibration sensors).

While the manual covers horizontal and vertical squirrel-cage induction motors in the 37 to 3,700 kW (300 to 5,000 hp) range, low- and medium-voltage, most of the principles covered apply to other sizes as well. 

This valuable instructional/resource manual is available in printed and downloadable versions, and focuses primarily on IEC motors.

Sections in the manual include:
(Download the PDF below for the complete Tables of Contents)

• Motor nomenclature & definitions
• Motor enclosures
• Typical motor applications
• Safety & handling considerations
• Basic motor theory
• Motor standards
• Stators
• Squirrel cage rotors
• Shafts
• Bearings & lubrication
• Motor accessories & terminal boxes
• Test & inspection procedures
• Motor alignment, vibration & noise
• Storage procedures
• Synchronous machines

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This book is also available focusing on NEMA Standards — in both English and Español.

NEMA - English NEMA - Español

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

Reclosure occurs when power to a motor is briefly interrupted and restored before the magnetic field has fully collapsed in the motor’s winding. If this occurs while the applied power is out of phase with the collapsing field, significant damage can result. This webinar will address how this can happen and what measures can mitigate damage potential.

Topics covered include:

• Reclosing a switch or breaker before the magnetic field collapses
• Utilities’ automatic reclosure
• Contactor “chatter”
• Determining the time constraint
• Remedies: Time delay; Zero crossing

Jim Bryan
EASA Technical Support Specialist (retired)

Reclosure occurs when power to a motor is briefly interrupted and restored before the magnetic field has fully collapsed in the motor’s winding. If this occurs while the applied power is out of phase with the collapsing field, significant damage can result. This paper, presented at the 2014 EASA Convention, addresses how this can happen and what measures can mitigate damage potential. Topics covered include:

• Reclosing a switch or breaker before the magnetic field collapses
• Utilities’ automatic reclosure
• Contactor “chatter”
• Determining the time constant
• Remedies
• Time delay
• Zero crossing

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.

Chuck Yung
EASA Senior Technical Support Specialist

Have you ever had a curing issue with your DAP monomer (diallyl-phthalate ) solventless resin (hereafter referred to as resin for simplicity)? If you haven’t, read on for guidance on preventing issues in the future. If you have, this article provides guidance on correcting the issues as well. 

As expensive as resin is, all service centers should be diligent about the care of their resin dip tank and VPI (vacuum pressure impregnation) systems.

Joe Junion
L&S Electric, Inc.

El daño eléctrico de los rodamientos se ha convertido en un problema muy común en los motores eléctricos. Este no es un problema nuevo, pero la concientización ha arrojado luz sobre este importante factor de confiabilidad y la industria ha dado un paso adelante para afrontarlo.

Sin embargo, hagámoslo simple. Se induce voltaje en una parte rotativa de un motor eléctrico. Si el nivel de voltaje sube lo suficiente, se descargará a través de la fina película de lubricación de un rodamiento y causará daños.

Los temas incluyen:

• Efectos del arco eléctrico
• ​Detectando el voltaje en el eje
• Previniendo el daño
• Productos para la puesta a tierra del eje
• Identificando y evaluando el daño

This book was developed to help electric motor technicians and engineers prevent repeated failures because the root cause of failure was never determined. There are numerous reasons for not pursuing the actual cause of failure including:

• A lack of time.
• Failure to understand the total cost.
• A lack of experience.
• A lack of useful facts needed to determine the root cause.

The purpose of this book is to address the lack of experience in identifying the root cause of motor failures. By using a proven methodology combined with extensive lists of known causes of failures, one can identify the actual cause of failure without being an “industry expert.” In fact, when properly used,  this material will polish one’s diagnostic skills that would qualify one as an industry expert.

The book is divided into the various components of an electric motor. In addition to a brief explanation of the function of each component and the stresses that act upon them, numerous examples of the most common causes of failure are also presented.

For this second edition, the manual has been reorganized and updated with new information including a new approach to methodology, new case studies and a new section covering synchronous machine failures. This could not have been done without many contributions from EASA members and the Technical Education Committee. 

The all new “Root Cause Methodology” section goes into great detail explaining that effective root cause failure analysis must take place within the context of a practical problem-solving methodology or framework. It covers a modified Plan-Do-Check-Act process that emphasizes the importance of planning and the related problem-solving methodology components. This section also explains A3, a high-level reporting tool that is very effective for problem solving.

In addition, besides a systematic approach to problem solving, root cause failure analysis of motors and motor systems requires familiarity with contributing factors attributable to various kinds of applications, environments and industries. This includes how various stresses can affect motor components and the reciprocal impact the motor system may have on the motor. This section includes a table with a detailed summary of motor stresses. 

There also is a new section on “Synchronous Machine Failures” and an expanded “Case Studies” section. Readers are guided through eight case studies.

With 328 pages, the book provides extensive information, including a wide range of failures, the likely causes listed, and the methodology for confirming the probable cause of each failure. 

Members may purchase a printed manual and/or a PDF download. The printed manual is in black and white, while the download shows most of the failure photos in color.  

Sections in the manual include:

• Root Cause Methodology (all new)
• Bearing Failures
• Stator Failures
• Shaft Failures
• Rotor Failures
• Mechanical Failures
• DC Motor Failures
• Synchronous Machine Failures (all new)
• Accessory Failures
• Case Studies (expanded)
• References

This book is available as part of EASA's Root Cause Failure Analysis seminar.

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This webinar recording covers:

• Starting torque
• Breakdown torque
• Full load torque
• Speed current curve
• Load torque curve
• Impact of reduced voltage start (autotransformer, PWS, wye-delta)
• Slot combination problems (noise, torque cusp, cogging)

It is very important to understand speed/torque curves and how they impact motor operation.

Target audience: Engineers, mechanics, winders and sales persons with fundamental knowledge of motor operation. 

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

Three of the most common motor problem calls received from members by EASA’s Technical Support Department 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.”

If you have ever faced one or more of these issues, and it’s almost certain you have, read on.

Gene Vogel
EASA Pump & Vibration Specialist

Increasingly, it is not enough to just “fix” that pump. Customers want and need to understand the “why” behind the failure. This pump failure case study looks at:

• Failure methodology and how it was used
• The possible causes of failure
• The final analysis
• How the analysis impacted the repair approach

This presentation covers: 

• What is classic pump cavitation?
• The NPSHA – NPSHR relationship
• How to identify the evidence of cavitation
• Other types of cavitation

Matthew Conville, MBA, PE
EASA Technical Support Specialist

Balancing plant maintenance costs and activities with the need to achieve production goals is a daily challenge for most maintenance professionals. Since the motor-driven system is often a critical component in this dynamic, let’s look at some best practices to help it achieve those goals and meet customer demands.

To plant maintenance pros in most industries, these are familiar questions:

• “How do we improve reliability within our plant?”
• “How can we reduce unplanned downtime, so our production stays more consistent?”
• “How can we decrease our total cost of ownership of our equipment?”

They phrase it differently, but ultimately each of these questions is about improving the efficiency and reliability of the motor-driven system. Although that encompasses a wide range of components including fans, pumps, and drives, here we’ll focus on the electric motors.

READ THE FULL ARTICLE

Cyndi Nyberg 
Former EASA Technical Support Specialist 

NEMA MG-1-12.45 states that motors shall operate successfully under running conditions at rated load with a variation in the voltage or the frequency up to the following: 

• Plus or minus 10 percent of rated voltage, with rated frequency. 
• Plus or minus 5 percent of rated frequency, with rated voltage. 
• A combined variation in voltage and frequency of 10 percent (sum of total values) of the rated values, provided the frequency variation does not exceed plus or minus 5 percent of rated frequency. 

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

Two of the most important expecta­tions informed end users (customers) have of service centers are consistent best practice repairs and root cause failure analysis (RCFA). Following best practices helps ensure reliable repairs and maintenance of motor efficiency; and RCFA identifies the cause to help prevent a recurrence of the failure. 

Service centers can meet these expectations by performing repairs in conformance with ANSI/EASA AR100 Recommended Practice for Repair of Rotating Electrical Apparatus; and by providing RCFA in accordance with a proven methodology such as that in the EASA Root Cause Failure Analysis seminar reference manual. 

Chuck Yung
EASA Senior Technical Support Specialist

This paper, presented at the 2014 EASA Convention, covers theory of operation, inspection, operation, and troubleshooting tips for AC generators. 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 rotor connection
• In-shop and on-site testing methods
• How to test the voltage regulator
• How to test a generator without the regulator

Chuck Yung
EASA Technical Support Specialist

When an armature is rewound, there is always a slim chance that it may be connected incorrectly. If two coil leads are switched, or if the error results in an armature where each coil closes on itself, normal tests will detect the problem. The trouble arises when the misconnection results in a uniform winding. When that happens, the result may be—in effect—an accidental redesign for a different voltage.

The number of parallel circuits in an armature winding can be changed simply by shifting the top lead position. As with a 3-phase winding, doubling the circuits halves the design voltage. If a wave-wound armature is rewound with the same data but connected lap simplex, or if a lap simplex armature is connected lap duplex, the circuits have been doubled. The same is true of a wave simplex armature reconnected wave duplex.

George Stratton 
G.E. Jones Electric Co., Inc. 
Amarillo, Texas 
Technical Education Committee Member 

Before I get started with this rambling about variable frequency drives (VFDs), I wish to ex­plain that this technical article is definitely NOT intended for the “drive techs” out there among you. It is intended to educate that poor, confused soul who might be timid when it comes to dealing with these high tech appliances…just as I once was. I hope that this helps you. 

Is anyone sleepy? Then welcome to VFDs 101! I’ve always said that if anyone has a problem sleeping, just tune in the History Channel. Well, here’s another sure cure. Let’s learn about VFDs! 

Tom Bishop, P.E.
EASA Technical Support Specialist

Unbalanced voltages are unequal line-to-line voltage values on 3-phase circuits that can exist anywhere in a power distribution system. Unbalanced voltages can cause serious problems, particularly for motors and other inductive devices. Perfectly voltage-balanced circuits are not possible in the real world. Typically, the circuit line-to-line voltages may differ by a few volts or more. It’s when voltages differ by more than 1% that problems tend to occur.

Cyndi Nyberg
Former EASA Technical Support Specialist 

Shaft failures are not an everyday occurrence, but when they come in, it can be an interesting challenge to determine the cause of failure. Regardless of what caused the shaft to fail, what actually happens when it bends or breaks? 

Nitin Kulkarni
Miembro del Comité de Servicios Técnicos
Helwig Carbon Products, Inc.

La cara desgastada de una escobilla de carbón indica las condiciones de funcionamiento. Por lo tanto, los expertos en escobillas pueden utilizarla como una herramienta de diagnóstico muy eficaz para la resolución de problemas y determinar la causa de fallo raiz. Si estas señales de advertencia que se muestran en la cara de la escobilla pueden identificarse y solucionarse proactivamente de manera oportuna, entonces se pueden evitar fallos catastróficos costosos e inesperados, como flameos o la reparación de la superficie de contacto.

Con mucha frecuencia, cuando un motor o generador deja de funcionar o se envía a reparar, las escobillas usadas se consideran inútiles como elemento emplazable. A medida que se pasan por alto las señales de advertencia en las superficies de las escobillas y no se aborda la causa raíz, los fallos pueden volver a ocurrir y el mantenimiento será costoso.

Nitin Kulkarni
Technical Services Committee Member
Helwig Carbon Products, Inc.

The worn carbon brush face indicates the operating conditions. Therefore, it can be utilized by brush experts as a highly effective diagnostic tool for troubleshooting and determination of root causes. If these warning signs shown at the brush face can be identified and proactively addressed in a timely manner, then major unexpected expensive catastrophic failures like flashover or repair of the contact surface can be avoided.

Far too often when a motor or generator comes out of service or is sent in for repair, the used brushes are considered worthless as a replaceable item. As warning signs at brush faces are missed with root cause left unaddressed, there can be a repeat of failures and high-cost maintenance.

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

Two common scenarios that service centers deal with regarding belt drive applications are failure of a motor drive end ball bearing or breakage of the shaft at the drive end bearing shoulder. The cause of these failures often is over-tensioning of the v-belts. However, there are many other faults or undesirable practices that can lead to premature bearing failure, belt wear and sheave wear. 

Due to practical space limitations, this article won’t be exhaustive in its coverage but will deal with common scenarios other than motor bearing failure and shaft breakage.

This 48-page manual was developed following EASA’s 12-part Vibration for Service Centers webinar series. It serves as an introductory training resource for service center technicians and supervisors involved in measuring, evaluating, and correcting vibration and balancing issues on machines under repair – as opposed to the in-plant predictive maintenance tasks covered in most general classes on the subject.

This document is intended as basic introductory training material for anyone who may be involved in evaluating or correcting vibration issues on machines repaired in the service center. Only certain sections may be of interest depending on the area and amount of involvement in vibration issues.

For a technician with responsibility for analyzing and correcting vibration and balancing issues, a general understanding of all of the information is essential. For technicians who will conduct field vibration and balancing services in customers' facilities, additional training is strongly recommended. A Level 1 vibration analysis class (usually 4 or 5 days) is a first step toward the competence needed for conducting field services. A Level 2 class is recommended. A number of providers offer ANSI-certified Level 1 and Level 2 vibration analysis classes, which normally include an opportunity for certification.

Major sections in the document include:

• Introduction and Overview
• Vibration Basics: Amplitude, Frequency and Phase
• Vibration Tolerances
• Basic Vibration Analysis
• Dynamic Balancing Basics
• Resonance
• Rolling Element Bearing Vibration
• Demodulation and High Frequency Band Measurements
• Field Analysis Techniques
• Field Balancing—Problems and Solutions

DOWNLOAD THE COMPLETE TABLE OF CONTENTS

LEARN MORE ABOUT THE COMPANION WEBINAR RECORDINGS

This presentation focuses on:

• Identifying belt vibrartion
• Identifying pulley pitch line run-out vibration
• Other vibration sources
• ODS analysis

When motors are installed on top of vertical pumps, high vibration is a common problem. The problem may be mechanical, hydraulic or structural.

This presentation provides an understanding of the nature of this style pump and the various forces essential to diagnosing and correcting vibration problems on vertical pump motors.

Gene Vogel
EASA Pump & Vibration Specialist

The most basic tool a vibration analyst uses is the vibration spectrum. The spectrum is a graphic illustration of the frequencies present in a vibration signal and their relative amplitudes. A good way to understand the spectrum is that it is a “bar graph” of the frequencies, with hundreds of individual vertical frequency “bars” across a range of frequencies. Most spectra are displayed with only a single dot for the highest amplitude in each frequency bar, so the graph appears as a jagged line reflecting those highest amplitudes for each bar. The highest frequency in the graph is called the fmax and the number of bars in the graph is known as the “number of lines of resolution.”

“We have rewound a motor, and now that it is back in service, our cus­tomer says it’s running hot. The frame is getting so hot that he can’t put his hand on it, and now he is blaming us for rewinding the motor incorrectly!” 

Has this ever happened to you? You have rewound a motor without changing the design at all; you tested the motor before you sent it out, and everything appeared to be fine. But now your customer wants you to fig­ure out what is wrong, or rewind the motor again. 

Before you consider this, there are a few things to check to see if the motor is, in fact, running properly. It is quite possible that the motor ran “hot” before it failed, but what are the chances that someone on-site put their hand to the frame before it had to be rewound? 

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

The most frequent concern about high current with a three-phase motor is high no-load current. But the broad issue of high no-load current isn’t the only three-phase motor issue to which plants should pay heed: High current with load and lower-than-expected no-load current are potential areas of concern, too. This article published in Plant Services explores the sources of all of these.

• High no-load current: Motor not rewound
• Motor with no nameplate
• High no-load current: Rewound motor
• High current with load

READ THE ARTICLE

Gene Vogel
EASA Pump & Vibration Specialist

Centrifugal pump failures are most commonly attributed to seal failure, impeller damage and bearing failures. A good understanding of failure modes for seals, impellers and bearings is essential to providing customers with reliable pump repairs. This presentation will explore various failure modes and provide some direction on ways to avoid them.  

• How mechanical pump seals operate, the importance of seal face material selection and proper installation techniques 
• Impeller damage examples and causes 
• General rolling element bearing failure modes 
• Bearing failure modes unique to vertical turbine pumps and associated vertical motors 

This recording will be useful for service center engineers, pump technicians and operations managers.

Chuck Yung 
EASA Senior Technical Support Specialist

Wound rotor (WR) motors represent only a small fraction of all electric motors in service. In reviewing the EASA Technical Support call logs, one would conclude that there are many more wound rotor motors in service. Because many of us do not work on wound rotor motors often, it is understandable that not everyone has a clear understanding of how they differ from a squirrel cage motor. The purpose of this article is to dispel some misconceptions about how they work and to offer valuable tips for failure analysis, repair and testing. Other topics covered include:

• Secondary voltage
• Crane applications
• Testing tips, after assembly