Characterization of partial discharges in transformer oil insulation under AC and DC voltage using acoustic emission technique

Convertor transformer is the heart of HVDC power system network. The insulation of the transformer is stressed by AC and DC voltages. At the time of installation, AC and DC voltage tests are routine test to understand the withstand capability of the insulation structure for the rated voltage. The Acoustic Emission (AE) technique can identify any incipient discharges in the insulation structure generated by different voltage profiles. In the present work, a methodical experimental study was formulated to characterize the AE signals produced due to partial discharges under AC and DC voltages, in transformer oil insulation. It is realized that the AE signals generated due to partial discharges under AC and DC voltages are different. It is observed that an AE signal generated due to AC voltage is of long duration pulse compared to that generated under DC voltage. The amplitude, rise time, counts, duration and energy content of the AE signal produced, due to partial discharges under positive DC, are high compared to the negative DC voltages.