Analysis and suppression of continuous periodic interference for on-line PD monitoring of power transformers

The key to on-line partial discharge (PD) monitoring of power transformers is how to suppress interference effectively. This paper reports an interference qualitative and quantitative analysis on site using a fast Fourier transform (FFT) technique. Various periodic interferences have been found, which emanated from the carrier communication, thyristor switching, and high frequency protection signals of power system as well as radio broadcasting signals. LMS adaptive digital filter and FFT threshold digital filter can be used to eliminate continuous periodic noises for on-line PD monitoring. However, they suffer from their own intrinsic weaknesses. Therefore, a multi-band-pass digital filter based on FFT has been developed. It is a much better method for the purpose of suppressing continuous periodic interference.