DC conduction current, dielectric strength and electroluminescence of standard, nanofilled and microfilled polyetherimide varnishes

Results of DC conduction, breakdown strength and electroluminescence of standard (PEI), nanoscale-fllled and microscale-fllled 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 the dielectric properties of the nanofilled varnish, which exhibits the higher PD lifetime under a PD stress, are not highly affected by the fillers. On the contrary, the microfilled varnish properties are strongly modified.