Power transformer monitoring using UHF sensors: site trials

Abstract

Sensors operating in the ultra-high frequency (UHF) band have been used to detect internal discharges during site testing of a 1000 MVA oil-filled transformer. The transformer was operated at voltages exceeding normal levels by up to 15%. Two discharge sources were detected at both sensors using UHF test equipment. Discharge signals are analyzed in phase-resolved form and time-of-flight measurements are used to provide further information regarding their origin. The results indicate that the UHF method could prove very effective for transformer testing and online PD monitoring.