Study on Partial Discharge Characteristics of Scratched EPR Cables Based on Pulse Sequence Analysis

The partial discharge of ethylene-propylene rubber cable insulation due to scratch defects may affect the normal operation of the cable. Based on the principle of pulse current method, the EPR cable sample discharge of simulated scratch defects is measured every 20 min at 35 kV, and at the same time, partial discharge pulse time domain spectrum is collected. The time domain characteristics of discharge pulse with discharge durations of 60 min, 140min, 220min and 300 min were analyzed separately. The discharge pulse oscillation wave extracted from the spectrums were analyzed, and the positive and negative pulse fall time $\mathrm{T}_{r}+(-)$ of each pulse oscillation wave was analyzed and rise time $\mathrm{T}_{f}+(-)$, pulse width $\mathrm{T}_{\mathrm{w}}+(-)$, duration Ti, pulse peak absolute value p, etc., respectively calculate the difference in the same characteristic quantity of the oscillation wave at different discharge times. In addition, the starting frequency, cutoff frequency and rms bandwidth of the oscillating wave power spectrum are studied. The results show that during a power frequency cycle, as the discharge time increases, the discharge pulse of the positive half cycle gradually shifts to the left; the oscillation attenuation rate is faster, and the discharge intensity is continuously enhanced; $\mathrm{T}_{r+}, \mathrm{T}_{\mathrm{w}+}, \mathrm{T}\iota$ and p have lager degrees of difference in different discharge times; the initial frequency, cutoff frequency and rms bandwidth of the power spectrum increase with the increase of discharge time, and the maximum increment is from 140 min to 220 min. Comprehensive analysis of the partial discharge pulse characteristics provides a basis for further evaluation of the EPR cable operating state.