Model-based relaying supervision for mitigation of cascading outages

Abstract

Several major outages have been traced to the failure of remote backup protection elements in distance relays. Experience has shown that coordination of remote backup zones in stepped-distance protection can be vulnerable during stressed conditions. Furthermore, relay settings are typically biased for high dependability, resulting in lower security especially when several unexpected events coincide. An incorrect response by a relay during such a condition can trigger or propagate the disturbance. Therefore, a new framework for Model-Based Relaying is introduced to supervise and secure the operation of remote backup protection elements, such as Zone 3. The framework utilizes the fact that while a single relay can observe a 3-phase fault or stressed system condition with similar apparent impedances, other system parameters will be significantly different. Therefore, the framework proposes to include the capability in relays to quickly run circuit model simulations at the relay level. The proposed method aims to work in parallel with and supervise the conventional distance relay's zone 3 for discrimination between 3-phase faults and stressed conditions using the output of local circuit model simulations. Several case studies are evaluated to demonstrate that dependability is not degraded for true fault conditions and security is enhanced for stressed system conditions.