Transient electric field analysis of 750 kV GIS breaker under lightning impulse delivery test

Ultra-high-voltage electrical equipment places stringent demands on electric field distribution. Traditional engineering calculations often assess the insulation performance of equipment using electrostatic field methods, neglecting the process of polarization establishment within the equipment. To address this limitation, this paper proposes a method that combines Variational Mode Decomposition (VMD) and Hilbert Transform to extract the instantaneous frequency of high-frequency voltage signals. The resulting instantaneous frequency, in conjunction with the dielectric spectrum of different insulating materials, is used to determine the transient electric field variation within key insulating components of the circuit breaker. Compared to the traditional electrostatic field method, the maximum insulator transient electric field strength inside the circuit breaker under lightning impulse voltage is 1.65 % higher, with the electrostatic field and transient field results being similar. However, when spherical metallic microparticles attach to the surface of the support insulator, the maximum field strength at the most distorted point is significantly higher than that predicted by the electrostatic field calculation. This finding is validated through lightning impulse experiments. This method provides a computational basis for insulation margin design and fault analysis of power equipment under high-frequency voltage conditions.