By Mike Howell
EASA Technical Support Specialist

Manufacturers deploy various external connection schemes to produce three-phase induction motors for multiple voltages and/or starting methods. Be sure to follow the relevant connection diagram, which is usually affixed to the motor or contained in its manual. If the diagram is lost, damaged, or ignored, you could find yourself dealing with a costly rewind.

The tips in this article apply to connections commonly encountered on machines with one speed at power frequency. If the external connection information isn’t available, ask your local service center for assistance, especially if several lead tags are missing or there are multiple nameplate speed ratings at power frequency. The service center can also help with unconventional numbering or cross-referencing IEC and NEMA numbering.

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By Jim Bryan
EASA Technical Support Specialist (retired)

The effects of excessive temperature on motor performance are notorious. After moisture, they are the greatest contributor to bearing and winding failures. Understanding the source of increased temperature is key to correcting the problem and improving the reliability of your facility’s motor fleet.

Topics in this article cover:

• Overload and service factor
• Ventilation
• Voltage variation
• Electrical steel
• Current density
• Circulating currents
• Harmonics

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By Mike Howell
EASA Technical Support Specialist

Too often, replacement specifications for three-phase squirrel-cage induction motors cover only basic nameplate data such as power, speed, voltage, and frame size, while overlooking other important performance characteristics such as the design letter. This can lead to misapplication of a motor, causing poor performance, inoperability, or failures that result in unnecessary downtime. To avoid these problems, familiarize yourself with the following speed-torque characteristics and typical applications for design letters that NEMA and IEC commonly use for small and medium machines (up to about several hundred kilowatts/horsepower).

• NEMA Designs A and B, IEC Design N
• NEMA Design C, IEC Design H
• NEMA Design D

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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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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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By Jane Alexander
Managing Editor of Maintenance Technology

According to EASA’s technical experts, changes in motor/system vibration readings provide the best early warning of developing problems in a motor or system component. Other parameters to monitor may include operating temperature of critical components, mechanical tolerances, and overall system performance, including outputs such as flow rate, tonnage, and volume.

Motor-specific baselines incorporate records of electrical, mechanical, and vibration tests performed when units are placed in operation or before they’re put in storage. Ideally, baselines would be obtained for all new, repaired, and in situ motors, but this may not be practical for some applications. These baselines typically include some or all of the following:

• Load current, speed, and terminal voltage
• Motor current signature analysis (MCSA)
• Mechanical tests
• Vibration
• Infrared thermography
• New motor baselines
• Repaired motor baselines

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