Effect of Humidity on Time Lag of Partial Discharge in Insulation-Gap-Insulation System

This paper deals with the discharge time lag of partial discharge in insulation-gap-insulation system with different levels of relative humidity. The sample was polymethylmethacrylate (PMMA) plate with 1 mm thickness. The PD patterns and the PD time lag with various levels of relative humidity were measured and discussed. The increasing of relative humidity brings significance change in PD time lag. The PD magnitude decreased by 50% when relative humidity changed from 33% to 98%. The change in relative humidity brought about 1.2 ms of characteristic time lag. In the vicinity of crossing point, 1.2 ms of time difference is equivalent to 0.5 time PD inception voltage. This can be an explanation that, PD intensity goes down as much as 50 %