Comprehensive Research and Measurement on the Influencing Factors of Grounding Current of Converter Transformer Core and Clamp System

The influencing factors and generation mechanism of grounding current of converter transformer core and clamp system are still unclear. It is difficult for on-site operation and maintenance personnel to make timely and accurate judgments when they encounter related problems. In this paper, the influencing mechanism behind grounding current generation in the converter transformer core and clamp is analyzed through theoretical analysis, equivalent parameter calculations, experimental measurements, finite element method (FEM), digital simulations, and experimental verification. Factors such as grounding path, core type, connection type, voltage harmonics, coil arrangement and insulation parameter are considered. To simplify the calculation, a method for calculating the equivalent relative permittivity of insulation materials is proposed, supported by experimental measurements. Additionally, parasitic capacitance between components is calculated based on FEM. A model of the grounding current system is established to calculate and analyze the grounding current. The findings reveal that harmonic voltage from converter valve operations is the primary cause of elevated grounding currents. Excluding harmonic factors, the influence of temperature on the dielectric parameters of insulating materials is the second main factor in the change of grounding current. When the converter transformer is heated from 0 ° to 80 °, the grounding current will increase by 41.11%. Finally, on-site measurements of grounding current from a 412.3MVA converter transformer are compared with calculated results to validate the proposed study, providing a theoretical basis for establish future standard. And according to the results of this paper, the operation and maintenance personnel will not misjudge the grounding current due to excessive voltage harmonics or temperature fluctuations, and avoid to carry out power outage maintenance, affecting the power system.