Effect of thermal stress on partial discharge characteristics of oil impregnated pressboard

Power Transformer insulation system is part of protection scheme that acquired by the transmission and distribution transformer to ensure the reliability and safety operation of the power transformer. Partial discharge (PD) is one of the event that occurs within insulation material located adjacent to the conductor that needs to be taken care of during condition-based assessment monitoring. Temperature is among factors that are known to severely degrade the dielectric properties of transformer insulation. Power transformer cannot operate without energy losses, which lead to rises in temperature. Failing to identify the root cause results in premature aging and ultimately to failure of the equipment. This report discusses about the characteristic of PD with influence of thermal stress. The insulation material characteristics was tested and measured through PD activities using CIGRE Method II test to study the electrical performance of samples. Applied voltage was set at 3 kVrms for half an hour ageing time and PD characteristics were investigated using PD Detector as per IEC60270 standard. The test was conducted inside Thermal Tank to imposed the sample with real-time temperature setting along with high voltage application. The result revealed that PDIV (Partial Discharge Inception Voltage) value decreased because of the effect of high temperature to the sample and PD numbers and magnitude increased also contributed by the effect of high temperature