Partial discharge characteristics of enameled wire of electric machine winding under exploitation stresses

In applications where power electronic converters are used, the voltage stress has a form of fast switching pulses composing of repetitive sequences. Such conditions have influence on inception and development of partial discharges in insulating systems of electrical machines subjected to non-sinusoidal waveform. The paper presents the dependence of partial discharge parameters and partial discharge patterns upon kinds of magnet wires used in twisted pair samples. The mechanism of discharges is explained on the basis of electric field simulations and partial discharge measurements, especially surface discharges generation on wires contact. They are the main cause of erosion processes on the surface of enameled wires. The long tests with fast switching pulses revealed the influence of diameter of wires on time needed to breakdown of enameled magnet wires.