Rejection of narrow-band noise and repetitive pulses in on-site PD measurements

This paper deals with the possibilities of noise suppression in partial discharge (PD) measurements under on-site conditions. After the presentation of previous work, a new concept of designing a digital FIR filter with a fixed order to suppress narrow-band disturbances is presented. The method is compared to a design using adaptive filters. A filter device, which was developed as an extension for a conventional PD detector, is presented. In the second part of the paper, a method for suppressing pulse shaped noise synchronous to the test voltage is discussed. The disturbing pulses are detected automatically in a PD signal by comparing several recorded cycles of the test voltage. There are two possibilities to suppress the pulses. The first one is an off-line method that allows attenuation degrees up to 30 dB, the second one works on line, and can process continuous PD signals. For the latter case a suppression of 14 dB for worst case pulses is possible with the developed hardware. In order to demonstrate the abilities of the filters, several measurements are shown.>