Tracking resistance of organic insulating materials by merry-go-round test method

In order to investigate the deterioration of the surface of organic insulating materials for outdoor use, scaled-down equipment for the merry-go-round test was manufactured. The diameter of a rotating wheel on the test equipment is 60 cm. An AC voltage of 6 kV was applied to the sample. The surface stress for the sample is about 83.3 V/mm. The other conditions for the test are the same as for the usual merry-go-round test method. Epoxy resin (CT-200) (system-1) with silica flour was used as the sample. Three regimes in the behavior of the leakage current were observed during the tracking resistance test. The leakage current temporarily increases after the voltage is applied, and then it changes at a constant rate. Just before tracking breakdown the leakage current rapidly rises again. The changes correspond to the changes in the state of the surface. The rotating wheel´s speed had influence on the time to tracking breakdown. The required time for the three regions and the acceleration coefficient of the rotating wheel were established. The speed has great influence on the process until the initiation of carbon path (middle region)