Field-Validated Induced-Voltage Testing and Power-Supply Capacity Calibration for Converter Transformer Systems Considering Parasitic Capacitance

Abstract

Field voltage testing after the maintenance of large converter transformers requires high-voltage response verification while preserving the restored equipment boundary. However, conventional direct voltage application on the grid side usually requires the disconnection of high-voltage leads and auxiliary devices, which may alter the original electrical boundary and increase field disturbance. To address this issue, this study develops an integrated framework with three core contributions: a minimal-lead-disconnection induced-voltage testing topology, a boundary-specific engineering-equivalent parasitic-capacitance model, and a terminal-referred phasor-based power-supply capacity-calibration method. Under the proposed testing topology, single-phase power-frequency excitation is applied on the valve side, and the induced-voltage response is established at the grid-side bushings while some of the restored auxiliary-equipment connections are retained. Considering the parasitic capacitance introduced by valve towers, tubular busbars, grading fittings, and grid-side auxiliary devices under the minimal-lead-disconnection boundary, an engineering equivalent model for extracting the valve-side stray capacitance is developed based on quasi-static electric field theory, geometric-envelope dimensional reduction, and conformal-mapping-based edge correction. The grid-side equivalent capacitance is further obtained using equipment parameters. On this basis, the induced-voltage distribution under the interconnection of multiple converter transformers is analyzed, and a power-supply capacity-calibration method considering the phasor relationship between inductive excitation current and capacitive current is established. Pre-test calculations yield a valve-side stray capacitance of 0.96 nF and a grid-side equivalent capacitance of 1.27 nF. When the grid-side induced voltage of phase C reaches 9.90 kV, the induced voltages of phases A and B are 4.56 kV and 5.14 kV, respectively, while the apparent power calculated from the field-measured RMS voltage and current is 1.34 kVA. The results verify the effectiveness of the proposed method for low-disturbance field testing and portable test-power-supply configuration.