Chuck Yung
EASA Senior Technical Support Specialist

Redesigning electric motors has become commonplace for motor repair service centers. By changing one or more motor characteristics, service centers often can adapt motors to meet new requirements faster and more economically than they can obtain new ones.

This paper explains how to make any changes in the ratings of AC electric motors that are possible within design limitations. Examples of each redesign are included as a guide for making your own redesigns. Besides mathematical formulas, this section provides guidelines on the limitations for each type of redesign. These guidelines will also help you determine whether a desired new rating is possible before you strip a motor.

In most service centers, there are rules regarding what winding changes can be made, who can make them, and who must approve them. Make sure that redesigns are not made without going through the proper channels.

This paper gives a brief review of AC motor theory and operation that includes flux pattern, types of losses, NEMA design designations and test procedures. It also covers:

• Design considerations for slip-ring and synchronous motors
• Requirements for reduced starting voltage
• Formulas for redesigning polyphase and single-phase AC equipment.

Chuck Yung
EASA Senior Technical Support Specialist

This paper covers:

• Interpreting AC and DC drop test results (Is that coil really shorted?)
• Differentiating between interpole and armature problems
• Locating an armature short/ground
• Locating shorted/open equalizers in an armature
• Working neutral: Did that motor arc when it left the factory? Let’s cure that problem!

Bill Finley and Tyler Gaerke
Siemens Industry, Inc., Norwood, OH

There is always a need to push to higher and higher efficiencies. This can be seen in the revisions to IEEE 841 which pushed efficiencies up to NEMA premium levels. DOE has continued to pass legislation increasing efficiencies to higher levels up to 500 HP. There has also been action recently to establish higher minimum efficiency levels on machines as large as 2500 HP. Motor manufacturers have been motivated to find creative ways to increase efficiency levels through optimization of manufacturing processes, designs, active material increase and better more efficient materials such as magnetic sticks.

To better understand the steps required, it is helpful to understand, how losses are generated and to identify the levers that reduce these significantly, all at an acceptable cost for the investment of the motor. Life cycle costs should also be investigated. 

This paper investigates the impact on the motor performance during starting and normal operation by employing magnetic wedges versus non-magnetic wedges and other potential design changes. The type of induction motor, open (ODP, WPII) or enclosed (TEFC), along with the number of poles, influences the effect on the motor these design changes may have.

Magnetic forces (stresses) acting on the wedges are also investigated in this paper. This paper also discusses qualification processes that are necessary in order to avoid failures and ensure reliable magnetic wedge systems.

This paper covers:

• Designing and testing for NEMA and IEC premium efficiency levels
• History of high efficiency standards activities
• Industrial facility opportunities
• Magnetic wedges (purpose)
• Impact of magnetic wedges on motor performance
• Experimental data for different magnetic wedges
• Qualification of magnetic slot wedges
• Designing with magnetic wedges

Gene Vogel
EASA Pump & Vibration Specialist
and
Walter Barringer
Mobius Institute, Knoxville, TN

Temperature is hot or cold, pressure may be high or low and a tank may be full or empty. But vibration cannot be adequately described by a single parameter. Vibration is composed of amplitude, frequency and phase. Overall amplitude may be used as a simplistic indicator of machinery condition; much like a noise could be described as loud or soft, even though there is a big difference between the scream of a siren and the roar of a train. And so it is with vibration.

The siren sounds different than the train because they are different frequencies. In the same way, the vibration from a failing rolling element bearing can be distinguished from coupling misalignment. This combination of vibration amplitude and frequency is the most common and useful vibration data for determining machinery condition, and analyzing machinery vibration problems. The phase angle of the vibration plays an important role in dynamic balancing and advanced analysis. The analysis of vibration amplitude and frequency as represented in the vibration spectrum, is the topic of this paper.

This paper covers how to get the vibration spectrum and what it means, including:

• Wave form
• Displacement
• Velocity
• Demodulation

Adam Willwerth (deceased)
AEGIS, Electro Static Technology, Mechanic Falls, ME
and
Hilton Hammond
Fluke Corporation, Everett, WA

Get a better understanding of the working principles of motor and drive measurements with test equipment, analysis tools and best practices. This paper presents valuable services you can incorporate to increase services and profits. It also covers:

• Safety practices related to test equipment
• Overview of the system drive train covering measurement protocols for:
  • Drive input and output
  • Motor and drive
  • Shaft voltage measurement and assessment

Not only is the measurement protocol explained but also the technology behind the systems under discussion, such as the inverter and motor. Measuring devices discussed will include:

• ScopeMeter
• Shaft voltage test kit
• Vibration analyzer
• Insulation tester
• Thermal imager

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 – and PD was a common consideration for machines rated 11 kV and higher. Since the advent of variable frequency drives (VFDs), PD activity is a major contributing cause to winding failures in 460v and (especially) 575v motors. This paper will describe PD, explain how to detect it, and offer repair solutions.

Topics covered include:

• Explanation of partial discharge (PD)
• Description of damage mechanism
• PWM drive and PD
• How to evaluate PD
• Repair tips

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

For most service centers the traditional repair services such as electric motor rewinding have been and will continue to be in a state of decline over time. Among the factors leading to this reduction in business are conversions to more efficient motors, improved maintenance of existing motors, incentives to replace with more efficient motors and in some regions a reduction in the industrial customer base. A consequence of this is that there is more competition for a “shrinking pie”. Service center reaction can be to make a comparable reduction in size or become pro-active and seek new business. The objective of this paper is to suggest and detail some of these alternatives, namely value-added repair and service opportunities for service centers that carry with them the added benefit of contributing to optimizing motor reliability.

The opportunities for value-added repairs and services are ever-increasing. Topics covered here are:

• Bearing isolators, increased winding wire area, ball-to-roller/roller-to-ball bearing conversions
• Preventive and predictive maintenance (PM & PdM) services: vibration analysis, condition monitoring, bearing lubrication, electrical testing (IR, amps, volts, kW)
• Motor management
• New premium efficient motors vs. repair and retrofitting of existing motors