Measurement of PD in Operating Motors Fed by Voltage Source PWM Drives

Published Jun 17th, 2015 Nordic Insulation Symposium NORD-IS - H. G. Sedding, I. Culbert, S. R. Campbell

On-line partial discharge (PD) measurement is now widely applied to motors rated 6 kV and above that are fed from the 50/60 Hz power system. However, many motors are being powered from invertors which facilitate variable speed motors to improve process efficiencies. One of the most common drives now being used is of the voltage source, pulse width modulation (VS-PWM) type. Such drives generate high voltage spikes in the kV range with risetimes in the sub-microsecond range. These high voltage spikes are a form of severe electrical interference which render the detection of PD (with magnitudes 1000 x smaller) difficult, due to the overlapping frequency content in PD and the spikes. Thus PD detection on VS-PWM has been a challenge, in spite of the serious insulation aging that such drives may cause. This paper will outline the challenges in measuring the stator winding PD in motors fed by VS-PWM drives and describe a measurement system that is often effective. Results from measurements obtained using this system will be presented.


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