Can Prevent Cascade Tripping Of Wide-area Protection System

Recently, the consecutive whopping power failures in the world reveal the limitation of relaying protection and stability control measures. Wide area protection system has attracted the attention since it is proposed in the late 20th century. It makes relaying protection and stability control measures operate in a new way, and it is the direction of relay protection development.The relay protection system of electric grid in our country is adopted the main plus backup protection. The backup protection is depending on the single-end electric quantity to establish the multi-zone distance protection or the time-laddered over-current protection. This thesis illustrates the definition, functions, structures, communications schemes of wide area protection, and carries on a study to novel relay protection theory based on multi-quantity of wide area. It operates more reliably, quickly, and reduces blackout district.Conventional protection relays generally take actions to protect an electric component without considering the impact on the whole system. Once some key lines with heavy load are tripped because of fault, cascading trips, even catastrophic blackout are possibly triggered for the accumulative effect of flow transferring and irrational activation of backup protection. This thesis analyses the redistribution of load flow after the fault line is isolated. The definition of load flow transferring factor and relative cluster is brought forward. The method of judging the over loading lines of relative cluster because of load flow transferring is introduced.This thesis proposed a new wide area protection scheme which can prevent cascading trips. Different from conventional protection relays, wide area protection systems have wide view of the power grid. Protection relays and stability control measures take actions cooperatively. The emulator in IEEE-39 proves the proposed scheme is feasible.