Measurement and modelling of the DC dielectric strength of pure, nanofilled and microfilled polyetherimide resin

Results of DC breakdown strength of pure, nanoscale-filled and microscale-filled PEI varnishes are described and analyzed in this communication. Silica (10nm and 400nm) has been used as a filler to increase the lifetime of such varnishes submitted to a partial discharge activity (varnish to be used in rotating machines fed by inverters). Experimental results have shown that both dielectric strength and conduction current are affected by the fillers. The higher the conduction current, the lower the DC breakdown strength. The modelling has consequently been focused on the thermal breakdown theory to explain these experimental data.