Influence of frequency of impulsive square wave voltage on partial discharge characteristics and its mechanism

To probe into the influence of frequency of (impulsive) square wave voltage on partial discharge (PD) characteristics, a system for PD detection specially used at square wave voltage was designed by resorting to the ultra-high frequency (UHF) detection method and the IEEE 488.2 protocol. By utilizing this system, PD features of corona resistance enameled wires, i.e., magnitude, occurring phase and time/frequency characteristics, were investigated. The research results show that high-frequency (above 200 Hz) square wave voltage will make space charge decaying rate reduce to increase the probability of initial electrons for PD, decrease instantaneous voltage when PD occurs and result in PD events with voltage magnitudes below 200 mV. Under high-frequency square wave voltage, when PD occurs at the rise time of voltage, PD features will be changed to make energy components with 1 to 2 GHz frequency increase. So when PD of inverter-fed motors is detected on the basis of related standards, low-frequency (below 200 Hz) square wave voltage should be used to induce the PD of insulation weak points easily. Furthermore, to increase the signal-to-noise ratio, UHF sensor should have a better performance in the frequency range equal to and higher than 1.2 GHz, and 500 MHz high-pass filter ought to be adopted.