Accumulative effect characteristics of transformer oil impregnated paper under repeated lightning impulses

Oil-paper insulation, as a common insulation mode used in power transformers, is continuously and unavoidably subjected to repeated lightning impulses, which may cause irreversible damage to the insulation system. Therefore, by using a repetitive impulse accumulating test platform, we applied repeated lightning impulses to the oil paper insulation model to simulate the accumulative effect of transformer invading lightning impulse on the oil impregnated paper (OIP). Then a systematic approach was carried out to obtain the U-N characteristics (the relationship between the amplitude of lightning impulse and impulse number when OIP is broken down) of oil impregnated pressboard model under standard lightning impulse voltages. And the U-N characteristics were mathematically analyzed using a modified Weibull distribution model. The atomic force microscope (AFM) observation was carried out on OIP samples before/after the accumulation of repeated lightning impulses. The results indicate that, with the increase in the amplitude of applied lightning impulses, the impulse number before breakdown occurring becomes increasingly smaller, which confirms the existence of accumulative effect. The roughness will increase by 0.61 times, 2.80 times, 5.97 times, and 11.76 times for OIP samples subjected to 200, 400, 600, 800 times of lightning impulses, respectively, compared with that of original OIP. © 2016, High Voltage Engineering Editorial Department of CEPRI. All right reserved.