Application of UHF partial discharge monitoring and expert system diagnosis

This paper handles the practical application of the ultra high frequency (UHF) partial discharge (PD) measuring technique in on-site tests using a resonant test set-up. Application during the service life of gas-insulated switchgear (GIS) is also addressed (on-line monitoring). Tests made during commissioning proved that even small PD defects can be detected. Even at a test voltage frequency of 122 Hz (produced by a resonant test system), the type of PD defect can be recognised on the basis of PRPD patterns from 50 Hz laboratory measurements. Furthermore, the application of PD expert system diagnosis is discussed in terms of reliability. Results based on more than a thousand measurements made at a 420/550 kV GIS laboratory set-up are presented