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• Testing methods for induction motors for use in VFD-powered applications

  No-load testing of repaired motors is common in most if not all repair service centers. ANSI/EASA AR100-2010 Recommended Practice specifies, “for AC motors, no-load running tests should be made at rated voltage and rated frequency.” For sine-wave powered motors, this statement is straightforward. For motors used on variable frequency drives (VFDs), there are a number of possibilities service centers may employ with the motor supplied by line (utility) power, and in some cases the tests may be less than ideal. 

• Selection and use of a VFD for service center testing

  With the growing popularity of variable frequency drives (VFDs), it is likely almost every EASA service center has repaired motors powered by one in a customer’s installation. For these motors, it is best that after repair they are tested using a VFD, typically at no-load. This will provide operation mimicking the actual customer application, at varying speeds, and will help ensure proper mechanical operation throughout the speed range. This will include detecting vibration problems, identifying any resonant speeds within the operating range, and more. Also, if the motor is used above utility line frequency (i.e., 50 Hz or 60 Hz), it should be operated up to top speed for vibration measurement and a good break-in of the bearings.

  Topics covered include:

  • Selection challenges
  • Voltage, power rating and frequency
  • New or used VFDs for testing?
  • Operating parameters