Partial discharge characteristics leading to breakdown of GIS spacer samples with degraded insulation performance

We have developed partial discharge current pulse waveform analysis (PD-CPWA) method in order to assess insulation degradation of solid insulators with degraded insulation performance. PD-CPWA focuses on the time transition of individual PD waveform parameters such as peak value, rise time, di/dt in a single PD current pulse waveform and time interval Δt of sequential PD pulses. In this paper, PD-CPWA was applied to two types of epoxy spacer samples with degraded insulation performance; delamination and thermal degradation. Experimental results revealed that the delamination sample and the thermal degradation sample exhibited discrete PD generation characteristics from PD inception to breakdown (BD) and resulted in BD with a drastic increase in di/dt and decrease in Δt at immediately before BD.