The Characteristics Of Creeping Discharge Of Oil-Impregnated Paper Under DC Voltage

HVDC transformer is an important part of power networks and its safe operation directly regulates the consistency of power supply.A large amount of data on transformer's fault statistic shows that the transformer insulation system is one of the weak links and the creepage flashover of insulation is the main cause of transformer's failure.Therefore,it is important to understand and evaluate the different parameters which realize the behavior of creeping discharges.The understanding of creeping discharge phenomena is necessary to guarantee a level of electrical insulation in the design of power transformers and reduce the failure rate of transformers under high electrical stresses.The discharge patterns analysis is the most widely used approach aiming to identify the root cause of insulation failure in electric power equipment's.These extensive patterns analyses help in order to classify the type of defects.This present work is intended to characterize the spectrum of creeping discharges in oil-pressboard insulation under different DC voltages by the using of a point-plane electrode configuration model.Hereby,the efforts were made to obtain the creeping discharge patterns and explored the contrivances of voltage on characteristics of creepage discharge under applied DC voltage 60kV,80kV,100kV respectively.The analyses were carried out on the basis of number of discharges(count),amplitude of discharges,time interval At and average value of discharges.A strong correlation of creeping discharges with the applied test voltage is found which is due to the increase of the discharged area with higher voltage.It is found that the amplitudes of discharges are not the same at all instants of time and voltages confirming that the partial discharge activity in the oil-pressboard insulation is a highly intermittent process.The experimental results show that the interval time between two discharges decreases with a higher DC voltage stress,whereas the number of discharges increases with a higher DC voltage stress.The Average value of discharges decreases because the number of discharges dramatically increases with the higher voltage.The test results indicate that the charge carriers can easily accumulate before discharging and quickly migrate along the direction of electric field after discharging with higher voltage.