High-speed control scheme to prevent instability of a large multi-unit power plan

Abstract

Unintended loss of a major power plant can cause substantial strain on the remaining generating resources and lead to local system instability and/or generate oscillations with impact to the overall bulk power system. In the continuing quest to improve the availability of the generation supply and in order to meet the more stringent electric coordinating council reliability criteria, power companies and grid operators are focusing on System Integrity Protection Schemes (SIPS) that can detect and react on events leading to potentially unstable power system conditions. One such situation occurs when severe disturbances occur on transmission line exits from large multi-generator power plants. Based the disturbance severity, the typical results are intensive swings or loss of plant synchronism which will lead into loss of the entire generation complex either by out-of-step protection, or unit shutdown by protective devices reacting to voltage dips at auxiliary buses. By quickly detecting the destabilizing conditions, preemptive actions can be taken to preserve the plant and minimize the extent of the disturbance and subsequent effect on the power grid. Such SIPS offer added advantages under normal operating conditions for scheduled transmission line outages, and allow full power operation with a line out of service. This paper discusses a control solution based on implementation of high-speed SIPS. The control strategy results from transient stability analysis for various types of transmission line faults, including delayed faults caused by complete and partial breaker failures. Different types of faults and transmission outlet line outage conditions for various system and plant initial conditions are investigated and options for mitigation are recommended. The discussion includes stability requirements, alternative actions and algorithms, SIPS components, the methodology for obtaining arming settings, interaction with the existing protection schemes, and effect of a switchyard topology. Technical implementation considerations such as system design, architecture, measures for reliable and secure operation, synchrophasor capture, event capture, performance under missing or conflicting information, and testing are discussed.