Statistical properties and test analysis of the measured lightning invasion waves in a substation

A standard wave shape of 1.2/50 μs is often used for the insulation design and experimental researches of transformers. However, research achievements on the actual lightning invasion waves are much few, which is not good for the reasonable insulation design and assessment for transformers. In order to provide the technical basis and support for the insulation coordination of transformers, the statistical regularity of time parameters is achieved, based on the measured lightning data of an 110 kV substation. Then the breakdown characteristics of oil-paper are studied by contrast under both measured waveform and the standard one. Statistics show that the measured front time is mainly within a few microseconds, while the tail time is within a few hundred microseconds. Far different from the standard lightning wave shape of 1.2/50 μs, the front time and the tail time with 50% statistical probability of the lightning invasion waves in the substation are 20 μs and 198 μs respectively. The experimental results explain that the 50% breakdown voltage U50 and 50% voltage-time characteristic curves of oil-paper are both much different with two overvoltage waveforms. The U50 of oil-paper with the wave shape of 20/198 μs is over 10% higher than that with the standard wave shape, and the 50% voltage-time characteristic curves are above the standard ones. It is indicated that the best insulation coordination of transformers are needed to take a large number of the actual lighting data in consideration synthetically. ©, 2015, Science Press. All right reserved.