Online Application of Local OOS Protection and Graph Theory for Controlled Islanding

Abstract

Despite layers of protection at work, power systems have experienced major blackouts in the past due to cascading outages. Such outages can be prevented with controlled islanding, which consists of two problems: “when” and “where” to island. The majority of the existing offline and real-time methods for the “when” aspects are based on wide area measurement systems (WAMSs), which depend on the system topology to perform periodic offline simulations or real-time computation of dynamic system equivalents. In this paper, a simplified “when” approach is proposed based on local generator out-of-step (OOS) protection and generator coherency using fault location. The novelty of the work lies in the use of local OOS protection relays to identify the overall system instability, which eliminates the need for WAMS communication and the complex computation required in real-time methods to form dynamic system equivalents. As this approach does not require any equivalent networks, the methodology is independent of system topology. Unlike existing WAMS-based methods, the proposed methodology simplifies the communication between the central “when” unit and each generator's OOS protection relay using status flags communicated with the IEC 61850 R-GOOSE protocol. The proposed “when” methodology is combined with the “where” method based on graph theory to test the overall controlled islanding scheme in the IEEE 39-bus system using the real-time digital simulator (RTDS).