The effect of voltage distortion on ageing acceleration of insulation systems under partial discharge activity

Abstract

Power electronic equipments are the main responsible for harmonic pollution of AC-electrical plants. In particular, Adjustable Speed Drives (ASD) affect both the AC-supply network and electrical motor supply voltage. A significant reliability reduction of equipment insulation fed by distorted voltage waveforms has been observed since 1950, but only recently voltage distortion effects on insulation have been deeply investigated. However, it is doubtful that the limit for power quality fixed by IEEE and IEC standards [1-3], which regard voltage and current rms distortion, can really improve electrical insulation reliability. Mostly, emphasis is put on current distortion, since accelerated aging is related to overheating caused by power loss increase [4][5][6][7][8]. Only recently the effect of voltage distortion on insulation system performance has been highlighted [9-12], focusing on cables and capacitors.Historically, investigations of the effect of voltage and current distortion on insulation degradation started from the harmonics injected in the AC distribution network by distorting loads [13], typically low-order harmonics (from 3 rd to 21 st order, i.e. having frequency from 3 to 21 times the fundamental one). Most of the work of the previous decade, in fact, was referred to transformers, rotating machines, cables and capacitors subjected to supply voltage distortion [5,6].The recent large diffusion of Adjustable Speed Drives (ASD) has brought significant attention to another possible cause of loss of insulation reliability, i.e. the steep waveforms generated by AC/AC converters using fast electronic switches (as MOS-FET or IGBT), e.g. [14][15][16][17][18][19][20][21][22][23]. These inverters generate width-modulated pulse trains with very high slew rate (up to 50 kV/us) and frequency (10-50 kHz). Electrical machines with insulation designed for supply frequency (50-60 Hz) have shown premature breakdown due to these periodic supply pulses, so that work is being

The effect of DC superimposed AC voltage on partial discharges in dielectric bounded cavities

“…The VSC will produce a high DC voltage with an overlaid AC ripple, and little is known about the influence this kind of voltage distortion has on the insulation found in HVDC systems. It is known that partial discharges (PD) with a repetition rate higher or proportional to the AC power frequency can lead to a significant reduction of life time in polymeric insulation systems [1]. The PD occur in small voids in the insulation, e.g.…”

Diagnostics of Insulation Condition and Risk Evaluation of Electrical Machines Employed in Mining Application

“…Voltage distortion gives another acceleration factor for aging of insulation under partial discharges activity, [3]. Electrical configurations with long cables can produce reflections and harmonic resonance causing spikes and overvoltages with added stress to the insulation, as shown by [4].…”

Analysis of overvoltage on motor winding insulation fed by PWM pulses

“…1) [1][2][3][4][5]. They are discussed particularly from the point of view of partial discharges mechanism, which may be in these conditions of another form than in the case of AC voltage [2,4,[6][7][8][9].…”