On-line Partial discharge (PD) measurement is very important for insulation monitoring of high-voltage equipment. One of the biggest challenges performing on-line monitoring is discrimination between PD detect signals and external noises. Experimental results using high frequency CT sensor show that the current waveforms associated with various PD signals are all damped cosine waveforms, and have unique frequency and decay times of damped oscillation. Therefore we focused attention on the damped oscillation waveform of the PD current, especially damped cosine waveform having a different number of oscillations. In addition to this, the noise discrimination method using wavelet transform or short-time Fourier transform is effective. Those noise discriminating process are applicable to on-line PD current measurement system.
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