Partial discharge pulse phase patterns on operating motors and generators

Many hundreds of partial discharge test results on about 100 operating motors and generators have been reviewed. In the majority of results, the position of the partial discharges with respect to the 600 Hz phase angle was as expected from conventional partial discharge theory, as well as laboratory experiments. However, perhaps 25490 of the PPA plots were "abnormal" in some way. Yet these patterns are real, and are not due to noise, nor are they artifacts of the measurement system. Researchers developing pattern recognition techniques for PD pulses should be aware that patterns from operating high voltage equipment may be much more complex than the patterns obtained in laboratory apparatus.