Partial discharge characteristics of long-term operated 550kV GCB epoxy spacer

We developed partial discharge current pulse waveform analysis (PD-CPWA) method in order to estimate insulation degradation of solid insulators. Focusing on the time transition of sequential PD pulses from their inception to breakdown (BD), PD-CPWA was applied to epoxy samples cut from an actual 550kV GCB spacer which had been used in a substation for 25 years. PD parameters such as peak value I, rise time tr, di/dt in a single PD current pulse waveform and time interval Δt of sequential PD pulses were analyzed. Experimental results revealed that PD generation until BD was not continuous, but disappeared frequently. tr increased drastically and Δt shorter than 1 msec appeared at about 0.4 sec before BD, which might be prediction parameters of BD.