Investigation of partial discharge activity of conducting particles in liquid nitrogen under DC voltages using uhf technique

In recent times, liquid nitrogen (LN₂) is used as an insulant as well as coolant in high temperature superconducting power equipments. One of the major problems in the liquid insulation is the particle contamination, which can generate incipient discharges that can lead to complete failure of the insulation system during operation. An attempt has been made in the present study to understand the feasibility of using ultra high frequency (UHF) sensors for identification of partial discharge formation due to particle movement in liquid nitrogen under dc voltages. It is observed that partial discharge formed in LN₂ radiates UHF signal. For the purpose of comparison, the studies were also carried out with air as an insulating medium. The UHF signal generated under dc voltage characterized by measurement of its amplitude, rise time, duration of signal and through frequency domain analysis. It is observed that intensity of partial discharge due to particle movement in liquid nitrogen is high under negative dc voltage compared to positive dc voltage. Also, the frequency content of UHF signal generated due to particle movement in liquid nitrogen lies in the entire bandwidth of 1-3 GHz.