Effect of high frequency cable attenuation on lightning-induced overvoltages at transformers

The high frequency attenuation of XLPE and EPR cables differ substantially. The absorption of high frequency energy between the cable termination at an overhead line and cable-connected transformers can reduce substantially lightning-induced turn-to-turn overvoltages at the top of the transformer primary winding. This is especially true when the lead lengths of the arrester across the cable termination are longer than desirable, resulting in greatly increased lightning induced voltages across the cable termination. The computed data presented in this paper indicate that the arrester lead length, lightning rising time, the type of cable, and the length of cable have substantial impact on the overvoltage to which a transformer is subjected and the voltage across the top few turns of the transformer winding. The greater high frequency losses of EPR cable can increase substantially the risetime of lightning induced overvoltages. This results in much lower overvoltages in the first few turns of distribution transformers connected to the underground cable.