Insulation evaluation for electrical rotating machines

A research project developing testing methods for machine insulation condition monitoring has been carrying out by Industrial Research Ltd. for about three years. The paper reviews off-line testing methods and then focuses on the introduction of new on-line partial discharge measuring methods. The off-line method combines tan delta, capacitance and partial discharge vs voltage measurements simultaneously which provides more informative and accurate insulation test results and condition evaluation. Additionally a parabolic ultrasonic detector can be used at the same time to correlate with electrical partial discharge measurements for PD position location and noise suppression. For on-line or live-line PD measuring, a high voltage high frequency current transformer has been developed and incorporated with a high voltage capacitor low frequency PD coupling device for noise suppression and PD position location. The principle of the method, laboratory and field test results of electrical machines are presented. To overcome PD measuring calibration problems for the machines, an on-line or live-line PD calibration device has been developed. This allows quantitative on-line measurements to be made and the PD measurements of different machines to be compared, which facilitates insulation condition evaluation