Magnetic Field Simulation of Grounding Conductor Current of Oil-Paper Capacitive High Voltage Bushing

Ground current serves as a crucial assessment parameter for evaluating the operational condition of capacitive high-voltage bushings in power transformers. Given its typically low magnitude, ground current is directly exposed to the intense electromagnetic environment on the high-voltage side of the transformer. Consequently, precise measurement of ground current has consistently posed a challenge in transformer condition assessment and a comprehensive evaluation of ground current and its associated magnetic field distribution is imperative for enhancing the accuracy of ground current measurements. This study establishes a three-dimensional magnetic field simulation model for oil-paper capacitive transformer bushings. A multilayer capacitor series circuit model is employed to represent the cylindrical capacitor core of the bushing, while the field-circuit coupling method is utilized to compute the magnetic field distribution surrounding the grounding wire of the bushing end screen and analyze its influencing factors. The simulation conducted on a 126kV/630A high-voltage bushing reveals a magnetic field intensity of approximately 480 μT in the measurement area around the grounding wire, primarily originating from the operational current in the bushing conductive rod. In contrast, the magnetic field generated by the grounding current amounts to only about 3.38 μT. The study indicates that the measurement error resulting from magnetic field interference of the drainage line may exceed 3%. Furthermore, the impact of the dielectric coefficient of the insulating material of high-voltage bushing on the end screen current with variations in ambient temperature is examined through simulation. The findings suggest that the influence of ambient temperature on the end screen current can be considered negligible.