Grid Stability: Gas Turbines for Primary Reserve

Abstract

Power grids are continually subjected to variations in load demand, leading to imbalances between generation and consumption. Such imbalances have an impact on the frequency level, requiring ongoing frequency control. Timely response of sufficient magnitude is critical to ensure grid stability. Without appropriate controls, variation in frequency levels can compound, leading to trips or even blackouts. Primary Frequency Control (PFC) and Regulation Margin Control (RMC) have recently become a requirement for gas turbine generators (GTG) by many transmission grid authorities. PFC provides grid stability by allowing the gas turbine to automatically increase (or decrease) load when a grid frequency deviation occurs outside of a frequency band, and maintains this increased (or decreased) load while the deviations persist. RMC is used to ensure that a percentage of the GTG generating capability is reserved for use when grid frequency excursions occur. There are different grid control regulations for different countries and regions. For example, the European Grid Code requires enough Primary Reserve set aside to support a +/−200 mHz grid frequency deviation with associated response times. The GTG must keep a percentage of the unit’s power capacity, or Primary Reserve, available for this purpose. The size of Primary Reserve power contributed by the grid frequency deviation is determined by the RMC Margin and PFC Droop settings, and must be managed under a wide range of operating and ambient conditions. This paper reviews field test results and lessons learned in developing an approach to meeting the grid requirements. This includes the PFC reserve power response to frequency deviations, associated tolerances, and additional controls required to optimize the spray-intercooling power augmentation system.