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.