Zone 3 Relay Blocking Scheme to Prevent Cascaded Events

Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events. Cascaded events can be attributed to improper operations of protective relays. The most challenging problem for the design and implementation of a defense system is the performance in accuracy and speed in a real time environment. Protective devices are normally designed to operate fast in order to isolate the fault（s）. This paper proposes a new methodology to distinguish line overloads from actual faults for distance relays. In order to distinguish between line flow transfers from a line outage and an actual fault, the line outage distribution factor （LQDF） and generation shift factor （GSF） based power flow estimation method, and a secure peer to peer （P2P） communication structure are adopted. Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.

Defense systems are needed to prevent catastrophic failures of a power grid due to cascaded events.Cascaded events can be attributed to improper operations of protective relays.The most challenging problem for the design and implementation of a defense system is the perform- ance in accuracy and speed in a real time environment.Protective devices are normally designed to operate fast in order to isolate the fault(s).This paper proposes a new methodology to distin- guish line overloads from actual faults for distance relays.In order to distinguish between line flow transfers from a line outage and an actual fault,the line outage distribution factor(LODF)and gen- eration shift factor(GSF)based power flow estimation method,and a secure peer to peer(P2P) communication structure are adopted.Computer simulations of cascaded events for a 6-bus system and the Korean power grid have been performed to establish the feasibility of the proposed scheme.