Partial Discharges in Insulating Systems of Low Voltage Electric Motors Fed by Power Electronics—Twisted-Pair Samples Evaluation

Abstract

Power electronics switching devices currently represent the dominant technology for supplying low voltage (LV) electric motors. The fast switching processes exert a different class of stress on dielectric insulating materials than standard sinusoidal excitations. Such stresses result in an increase in the dynamic activity of the working electric field, which in turn lead to an increased likelihood of partial discharges (PD). The stator design of low voltage motor is often in form of random-wound windings, where the magnet wires (copper or aluminum round wires coated with thin layer of insulation) form a common system of coils with not precisely defined mutual position of particular turns, resulting in various turn-to-turn and coil-to-coil voltage distributions. Pulse Width Modulated (PWM) voltage waveforms from modern electronic inverters are characterized by very short rise times and presence of repetitively occurring overvoltages that can significantly stress the insulation of feeding cables and motors. These factors influence the inception and dynamics of PD and processes of space charge accumulation in electrical insulation. In this paper investigations performed on round magnet wire twisted-pair samples representing LV motor random-wound winding elements are presented. Special attention was afforded to the twist configurations, observed breakdown voltage and PD activity. To describe the field conditions for the formation of PD in the turn-to-turn insulation system, the results of numerical simulations of electric field distributions for winding wires with different diameters, modeled using the COMSOL program, were analyzed. PD created in the insulating systems of model twisted-pair systems were registered and analyzed using the phase resolved partial discharge analysis (PRPDA) method.

Performance Analysis Based on Thermal Aging Tests of Sol-Gel and Polymer Insulated Wires by Enameling and Extrusion Technology

“…For the partial discharge phenomena observed on twisted-pairs samples [42], some works [40,41] show that PDIV decreases during the thermal degradation of the insulation, as the results obtained in this experience.…”

Modeling of high frequency high voltage of waveforms on life of enamel insulation

“…It is also reported that the breakdown strength of composites is lower compared to unfilled polypropylene. Researchers reported that the failure of twisted pair insulation is due to high repetition frequency initiating the partial discharge [17]. It is also reported that through the simulations the PD arises in the micro gap between the twists using the COMSOL software.…”

Accumulative effect of partial discharges at impulse voltage wave tail

“…The electrical exposure on the insulation system caused by such distorted supply voltage may lead to the degradation and the breakdown of powertrain devices (i.e. motors, cables) [10,[20][21][22][23][24][25].…”