Computer-based multi-terminal partial discharge measurements of transformers

Noise is probably the most difficult problem with online partial discharge (PD) measurements. This problem could be alleviated by the proposed multi-terminal measurement method. With a suitable frequency band, the first peak ratios of terminal signals resulting from a discharge may uniquely determine its position. PDs at different positions in the winding and external noise can then be distinguished. The discharge pulses from each PD source may be extracted and averaged for signal enhancement. The geometric mean of terminal signals can also be used to reduce the effect of PD pulse attenuation along the winding so that the measurement accuracy of apparent charges can be improved. Test results on power transformers at industrial sites are promising indicating the possible applications of this method for online PD measurements.