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Revisiting insulation resistance temperature correction

Publication date: 
July 2013
Mike Howell, EASA Technical Support Specialist
Type of media: 

Insulation resistance (IR) testing is performed on rotating machines for several reasons including evaluation of condition, suitability for service and suitability for additional testing. IEEE Std 43-2000 provides the industry recommended practice. It is well established that there is an inverse exponential relationship between IR and winding temperature. For this reason, minimum acceptable values of IR after one minute are specified at a baseline temperature of 40°C to which test values are corrected for evaluation and/or comparison with previous measurements. When using IR data for trending, industry recommended practice is that subsequent tests be performed when the winding temperature is near the same temperature as the previous test to minimize correction inaccuracies. Topics discussed include:

  • Why is IR temperature correction necessary?
  • How is IR temperature correction performed?
AC motors
Winding insulation
Motor testing