Breakdown and Partial Discharge in Dry Air under Non-uniform Electric Field for MVDC Applications

Medium and high voltage gas insulated switchgear (GIS) are key installations in the electrical power transmission and distribution network. The equipment in these substations are insulated with pressurized gas in order to guarantee their proper functioning. This work aims to investigate the performance, in DC, of dry air under non-uniform electric field conditions for medium voltage switchgear applications. Experimental investigations have been carried out to assess the breakdown and the partial discharge inception voltages as function of the electric field non-uniformity and dry air pressures. The experimental work has been compared with numerical study of the breakdown electric field based on streamer criterion using COMSOL Multiphysics numerical software. The results show that the breakdown maximum field decreases as a function of the utilization factor till 0.3, then it stabilizes for weakly non-uniform electric field. The breakdown maximum field is not dependent on the polarity of the DC voltage for utilization factors higher than 0.2. Otherwise, the breakdown maximum field seems to be lower under positive DC voltage for utilization factors under 0.2. Simulation results of the maximum field obtained using the streamer criterion are in good agreement with the experimental partial discharge results.