Research on preventing zone 3 distance relays from operating incorrectly caused by non-fault overload

Transmission lines are operating close to their limit with the promotion of power networks interconnection. The possible non-fault overload caused by the transferred flow from a removed line may lead to incorrect operation of zone 3 distance protection, which is considered as the origin of several well-known cascading trips. Taking advantage of wide area measurement system (WAMS), a novel scheme is proposed to identify flow transferring to block the zone 3 distance relays which may operate incorrectly. The new voltage and current criteria to distinguish between internal short-circuit fault and non-fault overload caused by transferred flow are derived by use of power system fault modeling. The implementation process is also provided. The simulation results demonstrate the validity of the proposed scheme.