Simultaneous measurement of partial discharge using TEV, IEC60270 and UHF techniques

This paper explores a means of quantifying the relationship between transient earth voltage (TEV), ultra-high-frequency (UHF) and IEC60270 partial discharge (PD) measurements on a pulse-by-pulse basis for well-defined, laboratory-based discharge sources. Since each technique responds differently to the same PD event, there is no theoretical relationship between the measured quantities; TEV and UHF techniques respond to the rate of change of charge movement, while IEC60270 responds to its integral. Empirical measurement is therefore necessary. Discharge pulses for each system were captured simultaneously using a 3 GHz, 20 GS/s digital sampling oscilloscope. PD amplitudes recorded by the respective systems were analysed and their relationships evaluated. Although these relationships are complex and bear characteristics particular to the PD geometry, the order-of-magnitude variation in amplitude between the sources allows approximate linear interpolation of the relationships when pulses are plotted on a logarithmic scale. The TEV/IEC correlation approximated to 1 µV/pC. The TEV/UHF correlation approximated to 0.05 mV/mV (TEV/UHF). Using TEV data measured at various points at an on-line medium voltage substation, approximate corresponding pC levels have been estimated based on the above relationships. The implications for PD severity judgment are discussed.