Investigation Of Breakdown Characteristics Of Oil And Pressboard Insulation In Converter Transformer Under Wide Temperature

As an indispensable part, the reliability of converter transformer play important roles in DC power transmission system. It is different in the excitation voltage of converter valve winding with traditional power transformer. The on-load voltage is more complex than traditional transformer, the major insulation of converter transformer facing a tremendous challenge. Temperature has a great influence in the property of oil-pressboard insulation, in order to optimize the structure of insulation and provide a guidance for the design of converter transformer that working under different temperatures, electric division need the relevant studies urgently.Temperature has a great influence in the electric field distribution between oil and pressboard under compound electric field, because of temperature change the dielectric parameter of oil and pressboard. For this purpose, this paper get the rules of the dielectric parameter of oil and pressboard with the temperature change by experiment. The result shows that: there is a huge difference between the dielectric parameter of oil and pressboard, lead to the great difference in electric field distribution under different temperatures.Because the electric field distribution effected by temperature and AC percent, and so does the breakdown strength of oil and pressboard. For this purpose, this paper get the breakdown voltage of this three insulation structures under compound voltage. This paper analyzed the breakdown mechanism and process of oil-pressboard insulation under different temperature and AC percent combined with the calculation of electric field distribution. The result shows that:in order to meet the demands of the dielectric strength of the insulation structures under limit operating temperature, the only method is increase the insulation margin. The insulation structures need specific design for the different operating condition.