Interference rejection 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 mainly emanated from the carrier communication and thyristor switching. This paper will focus attention on how to use software to suppress these interferences. A multi-bandpass digital filter based on FFT has been developed to suppress continuous periodic interference. It is better than other digital filters. The authors also developed a new pulse recognition method to suppress the periodic pulse interference effectively.