Research on the electric field distribution of multilayer dielectric under AC-DC Composite Voltage

Converter transformer, converter valve and bushing are the most important equipments in the valve hall of converter station. At normal working condition, these equipments will bear AC-DC composite voltage and current; at polarity reversal condition, they must endure a higher transient DC bias voltage, which will bring out serious electric field distortion of the multilayer dielectric in devices. In the type test process of converter transformer and bushing, the AC superposed DC voltage and transient DC bias voltage are also included, so researching the electric field distribution of multilayer dielectric in AC-DC composite voltage has great significance for the design of converter transformer, converter valve and bushing. In this paper, a double-layered dielectric model was put forward to analyse the law of electric field distribution under different voltage forms by using field-circuit coupled method, and the simulation results of the model under AC superposed DC and polarity reversal voltage were given via a finite element method (FEM) analysis software ANSYS. The simulation calculation method was proved to be correct in compared with the theoretical analysis result. Based on these studies, the electric field distribution of one ±800 kV converter transformer bushing outlet terminal under AC superposed DC and polarity reversal voltage were calculated and discussed. The above research results provide an important reference for the design of the converter transformer, converter valve and bushing.