The research on testing technique of conductivity of oil-paper insulation

It is necessary to consider the DC electrical stress when designing the valve winding of converter transformer, which makes it important to understand the conduction characteristics of oil-paper insulation deeply. The test methods of volume conductivity are generally according to broadband dielectric method or IEC method, which remain problems that it could not simulate the actual conditions of the DC electrical stress on the main insulation directly. As a result, a kind of testing system and method on conduction characteristics of oil-paper insulation is set up and proposed. Moreover, the conductivity of transformer oil with 8mm gap and impregnated pressboard with 6mm thickness are measured respectively under different electrical strength and temperature. On the basis of studying conscientiously, get the following conclusions: (1) Testing system provided direct way to measure the conductivity of oil-paper insulation, and could study the conduction characteristics under uniform electrical field of different temperature and field strength. (2) The volume conductivity of oil gap appeared temperature effect when the electrical field is less than 3kV/mm while field effect when the electrical field is more than 3kV/mm. (3) The volume conductivity of impregnated pressboard is stable and within the range of 10 ¹⁶-10 ¹⁷S/m.