Calculation of inlet capacitance for long-duration induction voltage test of single-phase three-winding converter transformers

The converter transformer is one of the core equipment in the high-voltage DC (HVDC) transmission project. The capacity of the converter transformer is much larger than that of an ordinary AC transformer, and its main function is to convert the AC system voltage to the phase change voltage required by the converter. The long-duration induction voltage test is an important technical means to assess the insulation strength of electrical equipment, and the calculation of the inlet capacitance of the converter transformer in the test design is extremely critical. This paper conducts circuit and mathematical modeling based on the structure of a single-phase three-winding converter transformer, calculates the equivalent capacitance between each winding of the converter transformer and each winding to ground by the model, and uses each equivalent capacitance to calculate the voltage added inlet capacitance, then obtains the appropriate compensation inductance. Moreover, the calculated inlet capacitance is verified by using the field test data, and the verification results show the reasonableness of the model. Finally, the calculation results are analyzed for errors and possible sources of errors are pointed out. This inlet capacitance calculation method has some universality and is expected to be promoted and applied in this field.