Study on the current differential protection for half-wave-length AC transmission lines

Half-wave-length AC transmission technology is getting more and more attention due to its excellent characteristics such as large transmission capacity and long transmission distance. Traditional current differential protection is not applicable for half-wave-length transmission lines because of the influence of distributed capacitance current. Even if capacitance current compensation algorithm is considered, current differential protection still cannot satisfy requirements. Therefore, algorithms which are immune to capacitance current should be used. Travelling wave differential protection is based on distributed parameter model and is not influenced by capacitance current in theory, but power-frequency component should be used to discriminate internal fault with external fault for half-wave-length transmission line. Simulations verify that in all cases differential current during internal fault is much larger than that during external fault, so travelling wave differential protection is applicable for half-wave-length transmission line.