Distribution Characteristics of Slightly Uneven Electric Field in Oil of Oil-Pressboard Insulation Structure Under DC Voltage

Nowadays, the converter transformer has become one of the key equipment in the High voltage direct current (HVDC) transmission system. Due to factors such as the interface charge in the insulation structure of the oil-pressboard, the internal electric field is uncertain. Considering that the internal structure of the transformer is relatively complicated, it is necessary to perform non-contact measurement of the uneven electric field and interface charge of the oil-pressboard composite insulation structure under DC voltage. In this paper, based on the Kerr effect, a liquid dielectric photoelectric field measurement platform is established. By actually measuring the electric field in oil and calculating the charge on interface between oil and pressboard, the distribution characteristics of the electric field and the interface charge can be obtained under the condition that the DC electric field is non-uniform. The experimental results show that as the pressurization time increases, the space electric field has a decaying trend, and the interface charge has an upward trend. The electric field decay and charge accumulation are more obvious under negative voltage. As the measurement position under the upper electrode deviates from the center more and more, the spacial electric field in oil becomes smaller and smaller, but the accumulated charge on the oil-pressboard interface shows an upward trend.