Adding shaft angle measurement to generator protection and monitoring

Traditional protective relays for generators have used electrical quantities (current and voltage) to measure the condition of the machine. It has long been recognized that information about the machine can also be used in protection. New technology makes it possible to combine mechanical and electrical inputs. This paper examines the use of rotor shaft angle measurement in a generator combined with the electrical angle of the output voltage. This provides for the direct measurement of system conditions that could only be estimated or approximated with earlier technologies. Some of the protection, control, and situational awareness applications now possible include the following: • Subsynchronous resonance detection and mitigation • Out-of-step detection • Machine parameter estimation and validation • Transient stability control One significant improvement over previous applications that provided these functions is that no physical connection or significant modification of the shaft is necessary. As power grids operate closer to critical stability limits, the ability to measure and control precise shaft angle will provide the high reliability necessary for electric power.