Analysis and improvement of transformer overvoltage protection under high altitude electromagnetic pulse

Power system security is directly related to political, economic and social security. As one of the key equipment of the power system, the safe and stable operation of the transformer is the basis of the safety and stability of the power system. However, the high altitude electromagnetic pulse (HEMP) can induce a steep pulse voltage with a peak value of up to thousands of kilovolts on the overhead line, and the frequency is up to 100MHz, which is easy to damage the transformer and seriously threaten the power system. At present, the existing transformer protection schemes are mainly aimed at microsecond pulses such as lightning electromagnetic pulse, which is difficult to resist the invasion of HEMP. Therefore, it is necessary to analyze and improve transformer over-voltage protection under HEMP. In this paper, a transformer protection system model under the action of HEMP E1 is established, and the protection effect of existing protection scheme is analyzed combined with the multi-conductor transmission line model. The inverter over-voltage is suppressed by adding an arrester on the low voltage side. At the same time, the effect of series capacitance, parallel inductance and reducing ground resistance on the overshoot of arrester is also analyzed. The results show that the improved protection scheme can effectively resist the invasion of HEMP E1.