Accumulative Effect of Oil-Paper Insulation System under Multiple Lightning Impulse Voltage

Insulation system of power transformers endures power frequency alternating voltage as well as switching impulse voltage and lightning impulse voltage, which may bring potential risk to the insulation system. Therefore, it is of great necessity and importance to study the influence of lightning impulse on the oil-paper insulation system. In this paper, the accumulative effect of multiple negative lightning impulses is evaluated in oil-paper insulation systems. To investigate the dielectric characteristic variation of oil-paper insulation model under lightning impulse voltage, an impulse voltage generating test platform is set up, which can simulate multiple lightning impulses imposed on the oil-paper insulation. At first, multiple lightning impulses were exerted on the oil-paper insulation system through the electrodes. Then, to find the difference between oil-paper insulation samples under lightning impulse impact or not, frequency domain dielectric spectroscopy measurements were carried out on oil-paper samples. Specifically, accumulative breakdown test was performed to demonstrate the existence of accumulative effect of multiple lightning impulses. At last, because of the importance of dielectric loss angle, as a non-destructive diagnostic method, the variation of dielectric loss angle of samples under different times of lightning impulse voltage was also investigated. And the comparison of dielectric loss angle can be an assertive evidence to reflect the deterioration processes due to multiple lightning impulses.