UHF-based Measurement of Partial Discharge in an Oil-filled Tank from Outside

Abstract:
Within this contribution, an approach is investigated which uses external ultra-high frequency (UHF) antennas to detect strong Partial Discharge (PD) inside a transformer’s tank. The question how well radiated PD emissions are detectable outside the tank is discussed and the usability of graded bushings as waveguide for broadband signals is studied in a practical lab setup. Measurement results show that UHF signals from PD sources are significantly attenuated once they have traveled from inside the tank into the air space. Nonetheless, these weak signals can be detected and discriminated from superimposing disturbances, even if the latter are relatively strong. The approach is a first step to implement a non-intrusive PD on-line monitoring system based on radio frequency (RF) measurements.