Port Conducted HEMP Environment of Distribution Transformers Considering Transient Response of Power Lines

High-altitude electromagnetic pulse (HEMP) poses a serious threat to critical equipment in power systems. Existing standard conducted environments, due to neglecting the transient response characteristics of actual lines, are difficult to accurately guide the effect testing and survivability assessment of power equipment. To address this issue, this article systematically investigates the transient conducted environment characteristics of transmission and distribution lines under HEMP by constructing a comprehensive simulation model that includes insulator flashover, surge arrester operation, and the broadband equivalent circuit of distribution transformers, combined with the finite difference-time domain (FDTD) field-line coupling algorithm and the Simulink simulation platform. The results show that: insulator flashover significantly limits the amplitude of conducted voltage, but retains the nanosecond-level rising edge characteristics; surge arresters cause waveform overshoot due to parasitic parameters; the waveform parameters of the distribution transformer port voltage are influenced by factors such as the angle of incidence and ground conductivity, with typical characteristics being a double exponential pulse with a rise time of 20 ns, a half-width of 500 ns, and a peak value of 440 kV; the conducted environment model established based on the actual transient response of the lines can provide input conditions that are closer to engineering scenarios for vulnerability assessment tests of power equipment. The research results overcome the scenario limitations of traditional standard conducted environments and provide theoretical support and a data foundation for HEMP effect threshold extraction and protection design of power systems.