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Capturing generator rotor angle and field quantities - SDG&E experience and approach to using nontraditional generator measurements

Measurements of signals associated with a generator beyond the traditionally measured terminal voltage and current are receiving more attention recently due to their promise of increased insight into the operation of the machine and electrical system during transient conditions. Mechanical measurements such as speed, vibration, shaft strain, pressure, and other physical quantities are already used for turbine protection and monitoring, but the use of mechanical quantities for generator protection has not been investigated in detail. One promising measurement, rotor angle, has historically been of limited use due to a lack of synchronization of the measurement to electrical system events. Present data acquisition technology allows for the highly accurate measurement of machine rotor angle, and when coupled with IEEE C37.118 synchrophasors, such a measurement can be synchronized with other power system measurements to gain a broader understanding of the relationship between the electrical and mechanical systems. In addition, taking time-synchronized measurements of the field voltage and current allows us to gain greater insight into the operation of the machine and has implications beyond traditional generator protection. Such measurements bring greater insight into mechanical transients occurring within the machine during electrical system events and can provide us with a deeper practical understanding of the electromechanical relationship between the generator and the power system. This paper discusses a first-hand experience with the installation and commissioning of a rotor angle measurement system installed on the generators in a 740 MVA combined cycle plant. This installation provides real-time monitoring and recording of the generator rotor angle as well as field excitation quantities. This paper discusses the lessons learned and possible applications using these measurements.