Experimental research on lightning shielding performance of large scaled UHV transmission line

In actual operation, the shielding failure rate of UHV transmission line is much higher than that in simulation, so it is crucial to study the lightning shielding performance by experimental research. The testing UHV transmission line model is scaled down in the ratio of 12.5 which is relatively large comparing to other testing models. Two kinds of negative switching impulse waveform were applied to HV rod to simulate the lightning descending leader. The probability of transmission line being stroked was calculated statistically by recording more than two thousand discharges and the factors that affecting the discharge probability were studied through contrast tests. The results show that the grounding condition, DC bias, the protection angle, the switching impulse voltages have an influence on the discharge probability, breakdown voltage and breakdown time. The spatial boundary of shielding failure area was determined in the middle of the span. The upper and lower spatial boundary and the distance between them increased with the increasing of the lateral distance between HV rod tip and transmission line model simultaneously.