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.

Reliable Remote Relay Protection in Smart Grid

As the false trips of remote protection relays are among the main reasons behind cascading blackouts, it is critical to design reliable relay protection. Even though common protection schemes on traditional power systems have been investigated for a few decades, cascading failures in recent years indicate more research needed in this area. Consequently, researchers have proposed agent-based methods on the Smart Grid （SG） to address this issue. However, these existing agent-based methods simply use TCP protocol without considering real-time communication requirements （such as bandwidth and delay）. To deal with this issue, several methods for efficient network resource management are proposed. Furthermore, these existing methods do not consider the potential issues in practical communication networks, which may result in delay violation and trigger relay false trips. We have discussed simple backup solutions in the previous work. In this paper, in addition to network efficiency, we focus on improving the system reliability by exploring known power system information and minimizing the chances of false trips of important remote relays, e.g., defining power line priorities based on their importance. Moreover, to further improve the. system reliability, we also in- vestigate the peer-to-peer protection approaches to address the single point of failure of centralized control center.

Preventing False Trips of Zone 3 Protection Relays in Smart Grid

While remote zone 3 protection relays are essential to power systems, their false trips are also one of main causes related to cascading blackouts. Although many methods have been developed on traditional power systems to address this issue, the past cascading failure events showed the ineffectiveness of these methods. With the development of Smart Grid （SG）, new agent-based methods have been proposed to address this issue by utilizing SG real-time communications. We found that these solutions simply assume ideal communication networks and do not consider the effect of practical network constraints and resource management. In this paper, we propose several solutions to address practical network resource management and constraints, and further improve the agent-based solutions in order to prevent the false tripping of zone 3 relays in various conditions. We also analyze the potential issues of these solutions, and point out the future investigation in this direction.