Evaluation of rotating machinery insulation by partial discharge pulse testing

For years, measuring the dissipation factor tip-up has been a recognized criterion for stator coil insulation acceptance testing and evaluation. Additional information on the insulation quality can be gained using hf-methods to determine and indicate voids in the insulation. Investigations showed that weak spots hidden in the cumulative measurement of the power factor tip-up are found by selecting the highest partial discharge pulses. Correspondence with big voids is demonstrated by x-ray testing and opening of the models and the original winding elements. Breakdown voltage and voltage endurance have been found to be lower with high energy pulses. This method was introduced and is now being used successfully as an additional quality test for stator winding phase connectors with T-shaped leads and narrow bends which are difficult to insulate, and under high electrical stress with a grounded surface.