Characterization of PDIV, PDEV, and RPDIV in Insulated Wires Under Unipolar Repetitive Square Wave Excitations for Inverter-Fed Motors

Abstract

The behaviour of partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV) and repetitive partial discharge inception voltage (RPDIV) as a function of exposure/poling time under unipolar repetitive square wave excitations at atmospheric pressure (1013 mbar) is experimentally measured and investigated. The partial discharge (PD) tests are performed on two commercially available insulated wires: Glass fibre as Type II and Polyether Ether Ketone (PEEK) as Type I insulated wires used in inverter-fed motors. The impact of excitation polarity, pulse repetition frequency and rise time on the PD quantities (i.e., PDIV, PDEV and RPDIV) is studied as a function of stressing duration. In addition, the trend of RPDIV and PDIV dispersion levels are compared as a function of poling time under positive and negative unipolar excitations with two rise times (i.e., 80 and 800 ns) and two pulse repetition frequencies (i.e., 50 Hz and 2.5 kHz), relying on the shape/slope parameter of the Weibull distribution. The collected data shows that the electric field induced by the interface charge deposited by PD occurring during consecutive pulses and the space charge accumulation in the insulation bulk plays a decisive role in PD quantities' variations under unipolar repetitive square wave excitations.INDEX TERMS Electric machines, partial discharges, pulse width modulation, space charge, variable speed drives.

Air Pressure Impact on the Avalanche Size for Turn-to-Turn Insulation of Inverter-Fed Motors

“…Therefore, it is suggested the measured voltage just before PD inception (i.e., during the waiting time) to be recorded as PDIV rather than the voltage after PD occurrence when the voltage drops more outside the insulation IEEE TRANSACTIONS ON DIELECTRICS AND ELECTRICAL INSULATION (i.e., in air) at low air pressures. Furthermore, it becomes evident from (14) and Fig. 7 that the diminished PDIV sensitivity to variations in enamel thickness leads to conspicuously comparable measured PDIV values for wires with different grades (i.e., insulation thicknesses) at reduced air pressures [21].…”

“…It should be noted that in practical applications where pollution is present, the first electrons to initiate discharges can be released by the insulating surface. Furthermore, bipolar excitations with polarity reversal (e.g., AC waveforms) are preferred over voltage waveforms with a DC component (e.g., unipolar excitations) in order to reduce the effect of space charge accumulation on both the field distribution in the air wedge and PDIV [14].…”

Temperature Impact on PDIV for Turn-to-Turn Insulation of Inverter-Fed Motors: From Ground Level to Cruising Altitude

“…As a result, the only way to initiate a discharge event is through air ionization [14]. Additionally, bipolar excitations featuring polarity reversal (e.g., AC) are preferred to voltage waveforms with a DC component (e.g., unipolar excitations) to avoid the impact of space charge accumulation on both field distribution in the air wedge and PDIV [15], [16], [17], [18].…”