Ever had a customer return from camping and complain of a distinct odor of burnt electronics filling the air? The next thing that RVer knows, the water pump quits and the AC stops working. The consumer flips the switch for a circulating fan, but nothing happens. Even the stabilizer jacks will not operate.

If so, the culprit may be voltage variation from the incoming power source, which sometimes is hundreds of feet from the distribution transformer that supplies the varying demands of all the RVs connected to it. While that prime campsite might be perfect for the user, voltage variation can be hazardous for the RV’s electrical devices—especially its electric motors.

This article covers:

• Voltage variation
• High and low voltage effects on motor performace and reliability
  • Energy efficiency
  • Current
  • Temperature rise
  • Overload capacity
• Imporatnce of checking service voltage

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By Chuck Yung
EASA Senior Technical Support Specialist

Downtime is costly, so it pays to have spare motors for critical applications. But unless they are stored properly, those spares may not perform reliably when needed.

Storage requirements generally depend on motor size and expected length of storage, so some measures may be impractical for smaller, readily available motors. The recommendations in this article cover most cases, but factors like heat, humidity and ambient vibration may dictate different schedules or procedures. It's important to recognize that some long-term storage procedures must be undone before the motor is placed in service.

See Page 12 of the December 2015 issue for the complete article.

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Storing an electric motor for more than a few weeks involves several steps to ensure it will operate properly when needed. For practical reason's, these are governed by the motor's size and how long it will be out of service. Factors like temperature, humidity and ambient vibration in the storage area also influence the choice of storage methods, some of which may be impractical for smaller machines or need to be reversed before the motor goes into storage. This article covers.

• Keeping good records
• Storage conditions
• Shafts and machined surfaces
• Bearing protection
• Special care for windings
• Carbon brushes

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By Gene Vogel
EASA Pump & Vibration Specialist

Vertical turbine pumps (VTPs) are workhorses in the petrochemical, power generation and manufacturing industries, and prolific in municipal water applications that handle the primary intake load. The ability to develop high head with multiple impeller bowls—coupled with the ubiquity of standard vertical motors that can support heavy pump shaft loads—makes VTPs a good choice. Although these machines are ruggedly built, abrasive sediments in the pumpage take a toll, particularly on line shaft and pump bowl bearings, so periodic overhauls are often necessary. Rather than simply replacing the bearings, however, it is important that repairs address all of the issues needed to restore maximum operating life.

This article covers:

• Common repairs
• Fit and alignment
• Bearing-to-shaft clearances
• Primary repair concerns

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

Most plant engineers and maintenance staff can attest to the reliability of standard-efficiency motors that have been repaired or rewound using industry best practices. They also know repair can cost far less than replacement, especially when the motor has special features. Despite this, some of them hesitate to have failed energy-efficient motors (NEMA Premium models, in particular) repaired because they’ve heard it degrades efficiency.

So, what’s the right answer? Is the decision to repair, rewind or replace a failed energy-efficient motor as simple and straightforward as you may have heard?

Topics in the article include:

• What makes a motor more energy-efficient?
• Repaired motor efficiency
• Review the motor application
• Catastrophic failure (present)
• Catastrophic failure (prior)
• Rotor condition
• Mechanical parts condition
• Higher-efficiency motors

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By Mike Howell
EASA Technical Support Specialist

Motors that meet the requirements of NEMA: MG1 Part 31 are designed for use with variable-frequency drives (VFDs). Motors that meet the requirements of NEMA: MG1 Part 30 may be suitable for inverter duty if appropriate measures are taken such as line conditioning. End users desiring speed and/or torque control often procure and install VFDs to modify existing applications where a standard-induction motor is in place. Frequently, they try to control costs by using the existing motor. There are a few areas of concern involving misapplication of a standard induction motor.

Topics covered include:

• Speed-torque characteristics
• Shaft currents
• Installation

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Mike Howell
EASA Technical Support Specialist

End users desiring speed and/or torque control often buy variable-frequency drives (VFDs) to modify existing applications where a standard induction motor is in place. Frequently, they try to control costs by using that existing standard induction motor. Before taking that path, however, it is best to consider a few areas of concern with the approach.

Topics covered in this article include:

• Speed-torque characteristics
• Shaft currents
• Installation

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By Chuck Yung
EASA Senior Tecnical Support Specialist

The evolution of electric motor design as it pertains to cooling methods provides insights about better ways to cool machines in service. The array of methods engineers have devised to solve the same problems are fascinating yet reassuring because many things remain unchanged even after a century of progress. This article discusses how motors are cooled and how heat dissipation can be improved for applications that fall outside the normal operating conditions defined by the National Electrical Manufacturers Association (NEMA) Standard MG 1.

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Until now, governmental and market forces have tried to reduce electrical energy usage in industry primarily by targeting electric motors. While these “green” initiatives have often raised concerns for manufacturers, repair facilities and end users, they have also spurred innovation.

But the commercial and regulatory landscape continues to evolve, and the horizon coming into view includes a new focus on pumps and pump systems. Starting in January 2020, the U.S. Department of Energy (DOE) will begin implementing the first ever energy efficiency standards for freshwater rotodynamic (centrifugal and axial flow) pumps. These standards will directly affect pump manufacturers and, to a lesser extent, the pump repair market, while ultimately benefiting end users if the new focus can reduce their energy costs.

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

Determining the source of noise in an electric motor is often more challenging than correcting it. A methodical investigative approach, however, can narrow the possibilities and make it easier to resolve the issue—with one caveat. If the noise is due to something in the motor design (e.g., a manufacturing defect or anomaly), a solution may be impossible or impractical. With that in mind, let’s review the primary sources of noise in electric motors—magnetic, mechanical, and windage—as well as their causes and ways to reduce or eliminate them.

Areas examined in this article include:

• Magnetic noise
  • Slip noise
  • Skewing
  • Unequal air gap
• Mechanical noise
  • Loose stator core
  • Bearings
  • Airborne noise
• Windage noise

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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

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

It’s a striking fact that operating a three-phase induction motor at just 10°C above its rated temperature can shorten its life by half. Whether your facility has thousands of motors or just a few, regularly checking the operating temperature of critical motors will help extend their life and prevent costly, unexpected shutdowns. This article will show you how to go about it.

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

The International Electrotechnical Commission (IEC) standard 60529, “Degrees of protection provided by enclosures (IP code),” addresses the degrees of protection for electrical machines (motors and generators). The “IP” acronym means “international protection” but is sometimes referred to as “ingress protection.” The IP code is commonly displayed on the nameplates of metric machines that are manufactured to IEC standards.

The NEMA MG1 Motors and Generators standards have adopted the IEC standards for IP designations. Although not prevalent on NEMA machine nameplates, the inclusion of the IP marking is becoming more common. In light of this, this article reviews IP code designations and examples of the IP codes for common electrical machine enclosures.

• IP characteristic letters
• IP characteristic numerals
• Typical IP codes

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Gene Vogel
EASA Pump & Vibration Specialist

Vertical turbine pumps (VTP) commonly have rotors with multiple mixed-flow impellers (sometimes 12 or more) that are supported by a vertical pump motor. Such designs offer a lift adjustment for raising or lowering the pump rotor to properly position the impellers within the bowl. Depending on the type of pump, this may be critical for maximizing pump efficiency and could have a significant impact on motor load (current) and reliability. Given the importance of VTP lift adjustments, it is necessary to recognize that procedures vary with the characteristics of the pump and motor.

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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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By Mike Howell
EASA Technical Support Specialist

For many industrial plants, maintenance strategies and decisions relating to the electric motors in use are among their most critical. Without question, motors are the primary workhorses for many of these plants—driving machinery, pumps, conveyors, and other vital equipment. So when they don’t work properly or fail, the impact on regular plant operations can be enormous.

When faced with an ailing or failed motor, plant operators typically consider whether to repair or replace it. According to a 2014 study conducted by Plant Engineering magazine for the Electrical Apparatus and Service Association (EASA), just more than one-half of plants have a policy of automatically replacing failed electric motors below a certain horsepower rating. While that horsepower rating varied depending upon the plant’s installed motor population, the average rating was 30 hp.

While such policies address a portion of the motors used at most plants, they do not cover what occurs with those motors. That question was addressed in a more recent research project commissioned by EASA that focused on the disposition of electric motors considered for repair. The research showed that just over three-quarters (79%) were repairable, with the remainder (21%) replaced. Within the repaired electric motor group, mechanical repairs were the most common (49%), compared with electrical rewinds (30%). Further, over the past three years, mechanical repairs are trending higher, while the electrical rewinds are declining.

The article looks at some of the reasons for these motor repair trends:

• Availability of a suitable replacement
• Cost of repair vs. replacement
• Repair provides opportunity to determine (and address) root cause
• Regular preventive and predictive maintenance practices can provide “early warning”
• ANSI/EASA standard establishes motor repair best practices
• EASA accreditation provides third-party assurance of motor repair practices

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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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By Jim Bryan
EASA Technical Support Specialist (retired)

The Institute of Electrical and Electronics Engineers (IEEE) has published a new standard: IEEE Std. 3004.8-2016, “Recommended Practice for Motor Protection in Industrial and Commercial Power Systems.” If you’re an electrical professional who deals with a broad spectrum of motor protection schemes, including low- and medium-voltage AC and DC motors, then you need to become familiar with this standard.

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Gene Vogel
EASA Pump & Vibration Specialist

Service centers are often called on to provide replacement pumps or pump motors or to advise on pump retrofit and re-application projects. A good understanding of the parameters that govern pump performance is essential to help customers with these opportunities. The information here relates to rotodynamic pumps (centrifugal and axial flow impellers) and not to positive displacement pumps.

By Chuck Yung
EASA Senior Technical Support Specialist

It’s fair to say that one’s outlook on life is colored by experience. A good example of this with sleeve bearing motors is the question, “What’s the proper clearance between a shaft and the sleeve bearing it rides in?” Chances are each of us has a rule of thumb for this, probably related to shaft diameter. Some of these may look familiar:

• One thousandth, plus 1 per in. of diameter
• Two thousandths, plus 1 per in. of diameter
• 0.0015 in. per in. of diameter
• 0.002 in. per in. of diameter

They can’t all be right, yet many of us may have used one of these rules (probably not the same one, either!) with great success. Which one, if any, is correct? The answer depends on the application.

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By Gene Vogel
EASA Pump & Vibration Specialist

High vibration is a common problem for motors that are installed on top of vertical pumps. Its source can be a mechanical issue with the pump, motor or coupling or even hydraulic forces from the pump. Structural issues involving “reed frequency” resonance often amplify the problem, but effective diagnosis must begin with an understanding of the underlying vibratory forces. Although the general vertical pump category includes submersibles, this article focuses solely on the ones that most commonly exhibit high-vibration conditions: surface-mounted pumps with the motor bolted to a pedestal on top.

Topics covered in this article include:

• Mass unbalance
• Coupling type and alignment
• Mechanical action of pump shaft & impeller
• Hydraulic action of fluid
• Resonant frequencies
• Basic frequency analysis
• Trim balancing
• Other possibilities
• Vertical pump troubleshooting checklist

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By Gene Vogel
EASA Pump & Vibration Specialist

If you work with electric motors and pumps, you’ll eventually encounter a pump curve and one of its key parameters — best efficiency point (BEP). The BEP is the point on the curve where the pump operates most efficiently. Unique to each pump, the BEP is a product of both impeller design and several related pump curve parameters.

This article covers:

• Pump efficiency
• Effect of flow rate
• Effect of impeller design on BEP

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By Jim Bryan
EASA Technical Support Specialist (retired)

Much has been said and done to produce the "perfect" fit for rolling element bearings in motors and other rotating equipment. Assembly of these machines requires that either the inner fit to the shaft (journal) or the outer fit to the housing (bore) is able to slide; so if one fit is tight, the other must be loose. While "tight" and "loose" are relative terms that must be defined in the quest for the perfect fit, any fit that's too loose or too tight can lead to early bearing failure and costly downtime.

A tight (interference) fit is usually recommended for motor bearing journals. Standard fits for radial ball bearing journals range from j5 to m5; the standard housing fit is H6. These are the "standard" fits and may be different depending on the machine designer's understanding of the application.

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By Mike Howell
EASA Technical Support Specialist

Suspect a three-phase motor is running hot? If you’re right, the unit is either producing more heat than it’s designed for or dissipating less. With excess heat, the main concerns are typically the health of the bearing-lubrication and the winding-insulation system.

Before incurring the expense of pulling the motor, evaluate its winding temperature. This article explains how.

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Gene Vogel
EASA Pump & Vibration Specialist

One of the most common repairs on centrifugal pumps is replacing worn or damaged wear rings. To restore efficient, reliable operation and prevent catastrophic pump failure, it is critical to restore proper clearances between the stationary casing wear ring and the rotating impeller wear ring. Although many pump manufacturers provide clearances and dimensions, some do not. There are plenty of aging pumps around from now-defunct manufacturers for which dimension data is simply not available.

In such cases, the rule of thumb that follows provides some guidance for acceptable running clearances, or the minimum running clearance chart in American Petroleum Institute (API) Standard 610 can be used as a guide.

• Suction side wear rings vs. rear wear rings
• Open vs closed impellers
• Wear ring clearances & specific speeds
• Wear ring clearance guide

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By Jim Bryan
EASA Technical Support Specialist (retired)

Whether you're selecting a motor for a new application or a replacement for one that has failed, you need a reliable way to match the capabilities and performance characteristics of various motors with the requirements of the application.

Fortunately, motors that conform with NEMA Std. MG 1-2016 or IEC Std. 60034-8:2007 must include all nameplate data that the respective standards require. What this entails will vary with motor type and size, so for example, rated field and armature current data would be required for direct current (dc) motors but not for alternating current (ac) motors. The focus here is on how the required nameplate data for NEMA and IEC motors can be helpful for selecting the right motor for an application.

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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

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

Those familiar with industrial electric motors have heard “DC is dead” for decades as advances in variable-frequency drive (VFD) technology for AC squirrel cage induction motors (SCIMs) seemed destined to replace their DC counterparts in every conceivable application.

But just as DC’s demise was greatly exaggerated, so too is the prospect of successor technologies replacing the installed base of SCIMs any time soon – whether for new applications or replacement motors. Still, it’s wise to recognize that change is coming, and that two of the newer technologies are already in common use – permanent magnet motors and reluctance motors.

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