Discharge Characteristics of Needle Plate Electrode in Transformer Oil Under Low-frequency AC Voltage

Abstract

Low-frequency transformer is the key equipment of flexible low-frequency AC transmission systems for offshore wind power. As the low-frequency voltage is applied, the transformer has significantly different insulation characteristics from those of the conventional transformer, it is necessary to study the typical characteristics of partial discharge of oil-paper insulation under such voltage. In this dissertation, the characteristics of discharge of needle plate electrodes in transformer oil under power frequency to low-frequency voltage are experimentally researched by adopting the pulse current method, and the discharge statistics, discharge atlas as well as feature parameters are analysed. With the decreasing of voltage frequency, the inception voltage (IV) value of partial discharge slightly increases, the extinction voltage (EV) phases of positive half-cycle (PHC) voltage waveform, as well as negative half-cycle (NHC) voltage waveform appear earlier, and the maximum discharge (MD), average discharge (AD), and pulse repetition rate (PRR) all show a downward trend.