Research on the Water and Temperature Dependency of Oil-Immersed Pressboard Surface Conductivity

The valve side of converter transformer needs to bear DC electric field component, which makes it important to investigate the characteristics and the influencing factors of the conductivity of oil-pressboard insulation. Therein the surface conductivity of oil-immersed pressboard under the influence of water content, temperature and electric field strength were studied. Results showed that the surface conductivity of oil-immersed pressboard increases exponentially with the increase of water content and temperature. When the water content of the pressboard increases from 0.7 to 4.2%, the surface conductivity increases by about 5 times. When the temperature rises from 25 to 70 °C, the surface conductivity of the pressboard increases by 67 times. As for the electric field strength from 1 to 5 kV/mm, the surface conductivity changes insignificantly. The above results may provide theoretical references for the optimal design of valve side insulation of converter transformer.