Research on Partial Discharge Detection Technique under Square Wave

The detection methods of partial discharge (PD) in power equipment insulation under square wave need to consider the displacement current and electromagnetic interference caused by the fast rising and falling edges of the power source. Therefore, there are some differences in PD measurements from those under power frequency sinusoidal wave. In this paper, a PD detection method based on super high frequency (SHF) signal and down-mixing principle is proposed, which suppresses interference through increasing the frequency band of the collected signal and shift the spectrum to lower frequency through down-mixing method to lower the requirements of the acquisition equipment. PD experiments are performed on epoxy specimen with needle-plate defect under the square wave and the SHF mixing method was compared with the pulsed current method and the ultra-high frequency (UHF) method. It is determined that, pulsed current method and UHF method were no longer applicable under the square wave with fast rising edge, while there are some advantages of SHF mixing method in anti-interference and feasibility. Especially for those PDs in solid materials with high insulation strength, it shows high sensitivity and good signal-to-noise ratio (SNR).