The UHF method for measurement of partial discharge in oil-impregnated insulation

In recent years, the ultra high frequency (UHF) method is employed to suppress the interferences during the partial discharge (PD) measurements with the detecting frequency range from 300 MHz to 1.5 GHz. However, with such width of frequency range, the interferences, sometimes, can not be avoided. In order to suppress the interferences for on-line PD detection of a power transformer effectively, a narrow band UHF method is put forward in this paper. The fundamental works have been carried out in high voltage laboratory to confirm the frequency range for PD detection with UHF method. To suppress the continuous and random UHF interferences, the envelope detection technique is introduced in the paper too. The experimental results show that the frequency of the UHF signals radiated from PD sources in oil-impregnated insulation is mainly concentrated on the range from 0.4 GHz to 0.8 GHz. The envelope detection can not only suppress the continuous high frequency interferences, but also reduce the sampling rate of PD measuring systems.