The lightning impulse breakdown characteristics of oil gaps between wire-disks in 500 kV transformer windings

The experiment and research results of lightning impulse breakdown characteristics of oil gaps between winding disks of a 500 kV power transformer is described in this paper. Based on the analyses of the electric field of the interleaved type disks the test models which reflect the feature of combined electric field were designed and the step up test method was used to test the models. The research of probability distribution showed that the lightning impulse breakdown voltage of oil gap between winding disks is distributed as the normal distribution and the experimental data were processed according to the maximum likelihood principle to obtain the 50% breakdown voltage and the standard deviation of some models with various sizes. The research results showed that the narrow oil gaps between wire-disks could be used to replace the wide one and the axial height of the windings might be decreased about 10%