Waveform analysis of partial discharge current in liquid nitrogen immersed insulation

This paper deals with the partial discharge characteristic in liquid nitrogen immersed insulation using high frequency detection system. AC voltage of 3-6 kV were applied on a needle-plane electrode system in which a polyethylene terephthalate film was inserted. Partial discharge detection was carried out using a wide band current detection system that has a frequency range up to 250MHz. Frequency analysis was done in both low and high frequency bands. It was found that the signal component within 150-250MHz had a correlation with the discharge mode. The signal component within 1-10MHz had a correlation with PD charge magnitude. Based on the above results, the partial discharge measurement with high frequency range is suggested to be effective for the monitoring of discharge mode.