Sensitivity verification and application of UHF sensor for partial discharge measurement in high voltage power transformer

UHF method is one of the well-known PD measurements and has been applied widely to PD diagnostic system of gas insulated switchgears (GISs). Recently, UHF method is also being applied to power transformers. This paper presents the UHF sensor for PD diagnosis of power transformers. To measure the PD inside of a power transformer, the UHF sensor is mostly mounted inside the oil drain valve of exterior walls in a power transformer. However, the size of the oil drain valve is too small to design sensors which have sufficient sensitivity and wide-band. The proposed UHF sensor has a structure of multi-resonance for high sensitivity and wide-band (300~1500MHz) measurement. The computer simulation was used for evaluating the UHF sensor´s performance. The sensitivity of the proposed UHF sensor was verified using simulated partial discharge sources in Laboratory and a 154kV power transformer. From experimental results, the proposed UHF sensor has enough high sensitivity performance to detect PD in power transformers.