Characteristics of the Space Electric Field in Oil Under AC and DC Voltages in the Large-Scale Outlet Device Model of Converter Transformer

In DC transmission system, we must make the insulation design of converter transformer reliable, which is very important for the safe operation of transmission system. At present, the research on the space electric field of the oil-paper insulation structure is limited to the simple and equivalent flat electrode model, and there is a lack of research on the electric field characteristics of large-scale complex structures. In this paper, the internal electric field of the valve-side outlet model is measured and compared with the simulation results, and the distribution characteristics of the electric field and electric charge in different oil gaps are obtained. The experimental results show that: under AC voltage, the difference between the measured electric field and the simulated value in the inner oil gap is 1.73%. Under DC voltage, the electric field in the inner oil gap is 30.1% larger than the value in the middle oil gap and increase first and then stabilizes with time. The electric field in the middle oil gap is 51.3% larger than the value in the outer oil gap and increase first and then decrease with time and finally stabilize. The space electric field in the oil changes significantly, and there is a charge concentration on the oil- pressboard interface. By testing the space electric field in the oil under AC and DC voltages on the device based on the electric field equivalent model, the variation law of the space electric field has been obtained.