Magnetohydrodynamic modelling of high-energy power-frequency arcs in transformer oil: Energy partition and impedance-plasma-property relationships

Abstract

Internal short-circuit faults in ultrahigh-voltage transformers can generate high-energy power-frequency arcs in transformer oil, creating substantial fire and explosion hazards. To investigate the coupled electrical, thermal, and fluid-dynamic behavior of these arcs and the influence of electrode geometry, a two-dimensional axisymmetric multiphysics magnetohydrodynamic (MHD) model was developed with temperature-dependent multicomponent plasma properties, copper-vapor transport, compressible flow, and radiative loss. An inductor-capacitor (LC) resonant high-current platform was also constructed to obtain synchronized electrical, high-speed imaging, and pressure measurements for several electrode configurations and gap lengths. The measured current waveform was prescribed as the electrical boundary condition, while the terminal voltage and voltage-derived channel impedance were used to evaluate the model. During high-current arc burning, the impedance comparison gave a root mean square error (RMSE) of 0.1357 Ω and a normalized root mean square error (NRMSE) of 29.02%. Near current zero, the model underestimated the impedance peaks associated with deionization and reignition, and the RMSE and NRMSE increased to 4.0113 Ω and 61.41%, respectively. Increasing the rod-to-rod gap from 5 to 25 mm reduced the non-radiative residual-energy fraction from 54.32% to 37.95%. Analytical and empirical relationships were further identified between channel impedance and plasma conductivity, equivalent radius, core temperature, and energy density. The results define the applicable range of the local thermodynamic equilibrium (LTE) magnetohydrodynamics model and provide arc-source and energy-partition information for subsequent pressure-response analysis.