Real time test system and method of conduction characteristics of oil-paper insulation

It is necessary to consider the conduction characteristics of oil-paper insulation when designing valve windings of converter transformers. However, current test methods of conductivity cannot simulate DC electrical stress directly. Therefore, we proposed a real-time test system and a method for testing conduction characteristics of oil-paper insulation, and used them to test the conductivity of a 8 mm-long transformer oil gap and a 6 mm-thick impregnated pressboard, respectively, under different field intensities and temperatures. The test results show that the proposed system can measure volume conductivity of oil-paper insulation directly, so it can be applied to study conduction characteristics in uniform electrical field. The volume conductivity of the 8mm oil gap presents an obvious temperature effect when the electrical field intensity is less than 3 kV/mm, but it presents an obvious field effect when the electrical field is more than 3 kV/mm. The volume conductivity of the impregnated pressboard is stable and within the range of 10^-16~10^-17 S/m. These test results can be used to optimize the valve-side insulation design of convertor transformers.