Research on the Effect of Nonlinear Variation in Insulation Resistance on the Voltage Divider Ratio of 2 × 550 kV DC Voltage Proportional Standard Device

This paper investigates the effect of nonlinear changes in insulation resistance on the accuracy of a 2 × 550 kV DC voltage scaling standard device. As the voltage and electric field strength increase, the insulating material exhibits nonlinear conductivity characteristics, leading to a decrease in the insulation resistance value, which in turn affects the potential distribution and the partial voltage ratio and thus reduces the measurement accuracy of the standard device. In order to study this problem in depth, this paper builds a nonlinear resistance measurement platform for insulating materials, and it fits and analyzes the experimental data using an NCIR neural network (Neural Network for Nonlinear Characteristics of Insulation Resistance). In addition, in this paper, the finite element model of the standard device was established by ANSYS simulation, and the equivalent resistance network model was established by applying MATLAB in order to calculate the variation in the voltage dividing ratio under different voltages. The results of the study showed that the nonlinear variation in insulation resistance significantly affects the voltage division ratio of the standard device, especially at high voltage conditions. Addressing the issue, this paper proposes to optimize the electric field distribution by optimizing the structure of the grading ring and adding a shielding resistor layer to reduce the influence of nonlinear effects. Simulation results show that the addition of a second layer to the shielding resistor can effectively improve the measurement accuracy of the device, and the reduction in voltage division ratio error is significant. Compared with the case of a shielding resistor with only one layer, the voltage divider ratio was reduced from 109,998.203 to 109,998.994, and the relative error was reduced 44%, changing from 1.634 × 10−5 to 9.15 × 10−6. The above study provides an optimized solution for achieving high-precision DC voltage measurement.