PD pulse burst characteristics in differently aged transformer oils under AC conditions

Partial discharge (PD) detection is a technique widely used for high voltage equipment insulation condition assessment. In such applications, an understanding of PD mechanisms, characteristics and development processes is important. In this paper, PD characteristics of three typical transformer oils, aged to different degrees, are examined under AC conditions, using a needle-to-plane electrode system. The PD activity in transformer oil is confirmed as appearing in pulse burst form. Pulse burst characteristics recorded in the study show that the transferred electric charge per PD pulse burst increases with the degree of aging. This increase is accompanied by an increase in the number of discrete PD pulses and by a decrease in cavity formation time. The experimental results of cavity discharge in differently aged transformer oils are discussed and their characteristics are explained in terms of the charge exchange mechanism.