Electrical and Insulation Characteristics of Digital Twin Model of Valve Side Bushing for Ultra-High Voltage Converter Transformer Based on Field Circuit Coupling and Transient Lightning Impulse Simulation

This “field circuit coupling” model simulating the short-circuit condition at the outlet of the valve side winding of a converter transformer. Each wire cake element of the grid side winding and the external power supply voltage are connected in series to form the circuit. After 150 minutes, temperature growth rate decreases and stabilizes. Moreover, the valve side bushing current structure exhibits the inverted “U”-shaped distribution with low ends and high middle. For the DC polarity reversal test, according to the provisions of GB/T or IEC standards, voltage value for the DC polarity reversal test of the ultra-high voltage converter studied in paper is 970 kV, and the test time is $90 / 90 / 45$ minutes, with negative polarity applied first. During experiment, there were two polarity reversals, and it is required that duration of polarity reversal should not exceed the 2 minutes. The average value of the temperature physical quantity is around the 29.9° C, which is 303.05 K, and is similar to the temperature value at point after reduction, proving accuracy of method.