The Influence of Relative Humidity on Partial Discharge and Endurance Features under Short Repetitive Impulsive Voltages

Abstract

Partial discharge(PD) inception voltage (PDIV) and insulation lifetime (endurance) need to be performed on insulation of inverter-fed motors under repetitive impulsive voltages. We reported previously that the voltage parameters of repetitive impulsive voltage such as rise time, fall time, frequency and duty cycle can influence PD and endurance features significantly. Accordingly, when PDIV and endurance tests are carried out, close attention should be paid on these influences to evaluate the insulation system performance of inverter-fed motors objectively. It was well-known that higher environmental temperature will give rise to lower PDIV and shorter lifetimes at both sinusoidal and repetitive impulsive voltages. There is little evidence, however, on the effects of relative humidity (RH) on PD and lifetime statistical features (especially under impulsive voltage with short on-time). Therefore, this paper aims to report our preliminary results of the tests carried on twisted wires under repetitive impulsive voltages with short voltage duration at four RH (i.e. 30%, 50%, 70% and 90%). Experimental results show that higher humidity can influence PD features and insulation endurance significantly. Higher RH tends to give rise to PD with higher magnitude, shorter delay time (discharge time) and thus, shorter insulation endurance.