Analysis of differential protection response for cross-country faults in transmission lines

This paper studies impact of cross-country faults in double-circuit lines on current differential relay. The protection in case of double-circuit lines should trip faults only in protected zone and not overreact for outside disturbances. The problem is when cross-country faults occur, which means that fault is incepted in the protected zone and also outside at the same time or after short break. For such a situation the differential protection may trip external faults incorrectly or may not trip internal faults. This situation should be analyzed and suggestions for protection improvement proposed. Signals for tests originated from ATP-EMTP simulations.