Extraction of Partial Discharge Signal in Predominantly VHF Frequency Range in the Presence of Strong Noise in Power Transformer

Abstract

This paper provides a detailed analysis of the online detected partial discharge (PD) in the predominantly VHF range in the power transformer during normal operation in the thermal power plant. A standard UHF drain valve sensor is used with the ability to also capture VHF frequencies of received signals. If PD detection is performed during off-line testing, there are excessive costs proportional to the time during which the power transformers are disconnected from the network. For this economic reason, online PD detection techniques are more convenient. The UHF technique has a higher signal-to-noise ratio compared to IEC 60270 and the acoustic method. To accurately determine the strength and waveform of the PD signal, especially if the source position is far from the UHF sensor or if the signal is weak, it is necessary to properly separate the useful part of the recorded signal from the background noise. The criterion for this is that there are no time shifts of the first peaks of the most prominent PD. For that reason, the beginning and the approximate end of PD signal has to be determined. The results show some obvious similarities of PDs in the recorded signals, such as frequency range, duration, repetition rate and the same dominant frequency, which sufficiently indicates that it is the same type of PD.

Power Transformer Numerical Modeling to Locate Partial Discharge Source Using the UHF Technique

“…These changes travel through space as an EM wave along the x axis from the current source to the receiving antenna. Partial discharge (PD) detection by finding the released energy in the form of EM waves during PDs using an ultrahigh frequency (UHF) antenna is one of the methods for determining the level of quality of the insulation system of power devices [2,3]. The main advantage of the UHF PD detection system using an antenna is the possibility of finding the PD signal without first turning off the power apparatus [4].…”