Field practices of UHF technique for on-line PD monitoring and site testing of power transformers

A field-oriented UHF system for on-line PD monitoring of transformers is designed, which has been installed inside the oil tank of a 220 kV transformer in a substation of Henan Province by two ways: on-line installing mode through the oil-valve and preinstalling mode through the man hole/hand hole cover. This system has successfully captured long intermittent discharge signals that hadn't been detected through conventional techniques, and solved the problem successfully. The results demonstrate that UHF technique has great advantages for on-line PD monitoring of transformers. By adopting the peak detection technique, it becomes easy and effective for the transplantation of the phase-resolved pattern recognition technique from conventional method to UHF method, and then to realize continuous on-line monitoring, source characterization and trending analysis.