Accumulative Effect of Bipolar Oscillation Impulse Voltage on Interturn Insulation of Transformer Winding

When the external overvoltage impinges the oil-immersed transformer winding, the interturn insulation of the winding mostly withstands bipolar oscillation impulse voltage. There is currently a lack of basis for assessing the danger of the accumulative effect of bipolar oscillation impulse voltage. This article uses an experimental platform that can generate bipolar oscillation impulse voltage with different waveform parameters to study the accumulative effect of bipolar oscillation impulse. The experimental results show that under bipolar oscillation impulse voltage, the accumulative effect on interturn insulation weakens with the increase of damping factor and oscillation frequency, among which the damping factor has a greater impact. When the oscillation frequency of the impulse voltage is higher than 79 kHz and the damping factor is greater than 0.53, the threat of the accumulative effect of bipolar oscillation impulse voltage is less than that of standard lightning impulse. Combining the changes in the relative dielectric constant, dielectric loss, and surface morphology of oil-impregnated insulating paper under the accumulative impact of impulse voltage, this article proposes that accumulative damage mechanism of interturn insulation can be explained from two aspects: the production of strongly polar and highly conductive substances and the growth of “wormholes.” The research is of great significance for reasonably selecting the insulation margin of interturn insulation and improving insulation design.