Effect of Temperature on Space Charge Distribution in Two Layers of Transformer Oil and Impregnated Pressboard under DC voltage

The space charge accumulation is an important factor to design the oil-pressboard composite insulation of convertor transformer, which is greatly affected by the temperature. In this paper, the space charge accumulation and attenuation in the two layers and single layer under DC voltage were studied by the Pulsed Electro-Acoustic Method from 20°C to 60°C, and the electric field distribution was calculated by the space charge distribution. The studied results have indicated that the distributions of space charge and electric field in the test results do not follow the Maxwell-Wagner polarization. The space charge distribution is affected by the surface trap, bulk trap, charge migration and electric field. The temperature affected the polarity and amount of the charge at oil-pressboard interface. The space charge accumulation of the two layers is more complex than that of the single layer, and the space charge accumulation and attenuation of two layers need longer time to reach the stable stage. The space charge accumulation in the single layer is largest at 40°C, whereas the space charge accumulation in the two layers is largest at 20°C. Moreover, the increase in the temperature increases the attenuation amplitude and speed of space charge.