Study on UWB frequency characteristics of partial discharge as a criterion of aging degree of stator winding insulation

Since the introduction of partial discharge (PD) detection, the majority of conventional electrical measurement of PD has been performed with detectors operating in narrow bandwidths from 10 kHz to 1 MHz for several decades. In the past decade, advances in electronic instrumentation have permitted the measurement of PD with bandwidths up to 1 GHz. Since PD pulses are fundamentally events with duration as low as a few nanoseconds which have a very wide frequency spectrum, comparing with narrow band PD detection, PD measurement with such ultra-wideband (UWB) detection methods can provide more information on the deterioration of stator winding insulation subjected to combined stresses. A UWB PD measuring technique with bandwidths from 20 kHz to 1 GHz is presented, and some waveforms of UWB PD signals of stator bar specimens in different aging periods both in time domain and frequency domain are given in this paper. It has been found that the ultra high frequency components contained in PD pulse increase and the rise-time of the pulse decrease gradually with aging time. It would be suggested that the ultra high components of PD pulse may be used to characterize the aging degree of stator winding insulation