Ultra-wide Band Modeling and Over-voltage Analysis of High Altitude Nuclear Electromagnetic Pulse on Transformer

High altitude nuclear electromagnetic pulse (HEMP) can induce a steep pulse voltage with a peak value of up to thousands of kilovolts on an overhead power line, and the frequency is up to 100MHz, which is far beyond the amplitude and frequency range of traditional steep pulse voltage. Therefore, it is necessary to establish a ultrawide band model of the transformer to evaluate its insulation ability to HEMP. Firstly, a frequency-dependent distribution parameter model is established based on the skin effect of conductor and dielectric properties of oiled paper. Secondly, the ultra-wide band fractional multi-conductor transmission line model is established considering frequency-dependent distribution parameter model, and solved through the finite difference time domain (FDTD). Then, a simple model is taken as an example to compare the results of the electromagnetic simulation software with the model to verify the feasibility of the model. Finally, an oil-immersed transformer is modeled and calculated to obtain the law of voltage distribution. The current research on HEMP does not consider enough frequency-varying characteristics, the model can produce a more accurate database for the design of the transformer anti-HEMP system.