Ultra-wide band Detection of Pulse Current in DC Withstand Voltage PD Test, Part 2: Waveform transformation

Based on the definition of measuring instrument of ultra-wide band (UWB) partial discharge (PD) in Part 5.5 in GB/T 7354-2018 High-voltage test techniques—Partial discharge measurements and the lack of related information, a preliminary study was conducted on UWB detection technology of on-site voltage withstand PD test of converter transformers. Various transformations were carried out on pulse current waveforms on the basis of PD pulse current waveforms of oil-paper insulation defects under DC obtained by UWB detection and the requirement of fast extraction of characteristic parameters of pulse current waveforms. The waveform transformations include the fast Fourier transformation (FFT), Hilbert transformation (HT), fast Mellin transformation (FMT) and short-time Fourier transformation (STFM). The PD pulse current waveforms of four typical defect models (needle plate, internal air gap, surface, and suspension) obtained by UWB detection show different distribution characteristics under corresponding waveform transformations. This study provides a variety of fast extraction methods of characteristic parameters of pulse current waveforms for the UWB detection technology based on pulse current waveform-time series.