Power Electronics and Electrical Insulation Systems - Part 1: Phenomenology Overview

It is well known that the wide use of power electronic converters (PEC) is one of the main causes of current and voltage distortion in the electrical networks [1]?[7]. These converters generate harmonic components propagating toward the supplynetwork side and nonsinusoidal voltage at the load side. Significant reliability reduction of equipment insulation experiencing distorted voltage/current waveforms has been observed in the ac network in the past. Thus, limits for power quality were fixed by IEEE and IEC standards [1], [2]. Most emphasis was placed on current distortion because accelerated aging can result from overheating originating in power loss increase [3]?[7]. However, in recent years, the effect of voltage distortion on insulation system performance has also been investigated [8]?[11], with the focus mainly on cables and capacitors. The recent popularity of adjustable speed drives (ASD) has highlighted another possible cause of reduced insulation reliability, i.e., the impulsive waveforms generated by power converters using fast electronic switches [12]?[21]. These PEC generate width-modulated impulses with very high slew rate (up to 50 kV/μs) and repetition frequency (10?50 kHz). Electrical machines designed for power frequency (50?60 Hz), having organic-insulated wires, have shown premature breakdown due to these repetitive, impulsive waveforms. Thus, work has been done to develop solutions, e.g., filters, winding techniques, and new materials. In particular, the endurance of the so-called corona-resistant materials, i.e., wires having organic/inorganic insulation designed to withstand partial discharge (PD) activity at high frequency, has been investigated [11], [19], [22]. Partial discharge, triggered by the repetitive, impulsive nature of the voltage waveform, is claimed to be the main cause of insulation failure. © 2006 IEEE.