Effect of mineral charge with high relative permittivity in impregnation varnish on the life expectancy of electrical machines

The aim of this paper, is to test new ways in order to improve the lifespan of electrical machines fed by PWM inverters. The tested method consists in increasing the turn-to-turn capacitance in order to reduce the electrical stress applied to the turn-to-turn insulation. The difficulty is to keep this stress under the partial discharge inception voltage (PDIV). The proposed paper focuses its investigations on the nature of mineral charges and their ratios (5 vol%, 10 vol%, 20 vol%) in impregnation varnishes used to build motor windings. With such solutions, it is possible to obtain a significant reduction of the turn-to-turn stress. The research work consists in performing capacitance measurements on elementary twisted specimens made with various diameters (0.5mm, 0.85mm, 1.25mm) of enameled wires and several varnishes charged with alumina or barium titanate at micro-scale.