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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Determining the source of noise in a motor is often much more challenging than correcting it. However, a methodical approach to investigating noise can narrow down the possible causes and therefore make resolution easier. This webcast addresses the causes and characteristics of the primary sources of noise in AC motors.

Learning objectives include the following:

• Possible sources of motor noise
• How to investigate motor noise
• Nature of magnetic, mechanical and windage noise
• Reducing noise intensity.

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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

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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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Contrary to popular opinion, bigger isn’t always better—especially when it comes to electric motors. Plant maintenance and engineering departments like having a little extra power available “just in case,” so they sometimes specify larger motors than applications require. But oversized motors cost more to operate—sometimes a lot more. Fortunately, there’s a simple procedure for determining the actual hp required by a load, without expensive equipment or engineering. Bear in mind that loads should be determined when the motor is operating at its maximum load. Loads that vary widely are good candidates for variable-frequency drives (VFDs), which offer the added benefit of controlling rate of production.

• Topics covered include:
• Estimating actual load
• Cost of "safety margin"
• Real life example
• Power factor and efficiency

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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 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 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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Gene Vogel
EASA Pump & Vibration Specialist

When machinery vibration becomes severe, resonance is often at work. Methods of testing machines for natural frequencies that cause resonance have been discussed in prior presentations. This presentation will first focus on identifying resonance and then move to methods that help visualize the vibratory motion, helping to identify solutions. Two methods will be discussed- traditional Operating Deflection Shape (ODS) analysis and video motion magnification.

Learning objectives:

• Review of testing methods
• How to visualize vibratory motion
• Operating deflection shape analysis
• Understanding video motion magnification

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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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