Effect of Residual Charges on Lightning Impulse Voltage Testing in Insulation Gaps

In this article, the effect of residual charges on the lightning impulse voltage testing in the air insulation gap and the hybrid gas–solid insulation gap within the range of 30–50 cm gap distances was studied using the modified up-and-down test (UDT) method. The impulse voltage testing was performed by changing the gap distance, the resting time, and the initial voltage. Experimental results show that the residual charges cause continuous breakdown and withstand during the testing when the gap distance is 30 cm, which cannot be considered by the standard UDT. When the residual charges are removed after the gap breakdown, the continuous breakdown and withstand phenomenon is disappeared, and the 50% impulse breakdown voltage
${U}_{50}$
is decreased under different gap distances, resting times, and initial voltages. The effect of the residual charges is strengthened with the decrease in the gap distance. When the breakdown path length is close to 30 cm in the air insulation gap and the hybrid gas–solid insulation gap, the effect of residual charges is significant. The modified UDT method is recommended when residual charges are present during impulse testing, which can be indicated by the number of tests.