Investigation of the effect of layered structure on partial discharges in transformer pressboard insulator

The dielectric performance of pressboards impregnated with mineral oil is one of the key points in regard to the quality of the transformer’s working life. Partial discharges (PDs) occurring in the pressboard can cause some insulation defects which might be one of the major reasons for an electrical breakdown. Detection of the PDs in pressboards gives a chance to understand the dielectric behavior of the insulators, hence major defects can be prevented just in early stage. The main point of the study is to investigate the differences in dielectric performance of layered and non-layered pressboards in the presence of PDs. For this purpose, the PD behavior of a layered pressboard with three layers (each with a thickness of 0.5 mm) and of a non-layered (solid) pressboard (with a thickness of 1.5 mm) is examined for two different high voltage levels (20 and 30 kV). To detect the PDs, Hall Effect Sensors are employed, considering that PDs cause fluctuations in the magnetic field. To analyze the magnetic field measurements from a statistical point of view, the Kaplan–Meier method and the Weibull analysis are used.