Evaluation of motor winding insulation performance under pulse waveforms through electrical measurements

This paper analyzes the main factors which can lead ac-motor wire insulation to premature failure when supplied by power electronic converters. In particular, experimental results show that the presence of partial discharge activity is able to accelerate insulation ageing particularly of organic insulated motors with respect to sinusoidal conditions. Peak-to-peak voltage together with pulse repetition frequency are observed to be the main factors accelerating wire insulation ageing. Different testing techniques, proposed by the authors and included in the recent IEC standards on this topics, are here discussed.