Experiment and Simulation of Air Gap Breakdown Characteristics Under Short-tail Impulse Waveform

To investigate the overvoltage during direct lightning strike,models on PSCAD/EMTDC platform were designed to simulate the transients during lightning direct strike on transmission tower and impulse voltage waves imposed on insulators According to the simulation results,the actual impulse voltage is not same as standard one.And the differences may cause errors in the evaluation of lightning performance.The breakdown characteristics of air gap under short-tail impulse,which is similar to actual waveform,were experimentally investigated.In the experiment,the impulse wave featured a reduced wave-tail time which was less than 10μs.It would cause equivalent effects to the air-gap with actual lightning strike.The air gap under study was a rod-plane gap with the length ranging from 0.5 ～ 1.4 m.The experimental result indicates that the breakdown voltage of air gap under short tail impulse is significantly higher than that of standard wave,about 40% higher for positive impulses,implying that previously-used methods may yield much lower withstand lightning current and consequently causes an over-investment on insulation.Finally,the parameters of Leader Propagation Model were studied and their effects on the simulation results were illustrated.Experimental data shows that the LPM can be applied to calculate the breakdown characteristics of short-tail waveform with good accuracy,and a set of parameter suitable for short-tail impulse is acquired.