Phase window analysis of partial discharges in an oil pressboard insulation system

Partial discharge (PD) distributions have been studied in a representative oil-pressboard insulation system using a phase resolved PD analyzer built for the purpose. The system divided a cycle of the applied voltage, starting from the zero of positive half cycle, into sixteen equal phase windows (Φ₁ to Φ₁₆) to determine the discharge magnitude in each phase. PD data are recorded according to their phase of occurrence with respect to the power frequency cycle, their magnitude and number over a period of time. The effect of different test procedures, stress levels and its duration on the ensuing PD patterns have been statistically studied. The results of the analysis help in identifying the probable phase windows which have significant contribution towards overall aging and the ensuing PD distribution patterns