Mitigating SSR: The threat of hidden critical lines and WAMS as a solution

Abstract

Major incidents of dangerous Subsynchronous Resonance (SSR) have been caused by the loss of one or more lines causing the generator to come radial or partially radial with the series capacitor. Identification of such lines in a meshed multi-compensated power network is not possible through mere topological inspection. The paper presents a methodology for identifying Critical lines that may be hidden in meshed networks and can be used by the System Operator to raise EMS alarms against SSR threats in case of planned or unplanned outages. The paper also describes how Wide Area Monitoring Systems (WAMS) can be used to provide an economical alternative to existing SSR mitigation techniques by making best use of existing WAMS assets and minimizing further investment. To provide visibility of torsional oscillations (4–46 Hz), the paper describes a new Waveform Measurement Unit (WMU) that offers this additional functionality using a software update of a contemporary PMU, which is being trialed for the first time as part of the GB VISOR project. The potential opportunity and challenges of using WAMS for SSR mitigation is studied using the IEEE FBM. The methodology for identifying Critical lines and generators is demonstrated using the IEEE 68 bus model.