Assessment of primary response capability of generating units for dynamic allocation of spinning reserves in the Cyprus power system

This paper describes a methodology to derive the primary response capabilities of generating units in the Cyprus TSO system. This is important from the standpoint of assessing the amount of operating reserve that will be available to support the system in the first few seconds following a disturbance. Conventional thinking is that the entire spinning reserve (maximum capability of the on-line units minus the outputs or dispatched MWs) is available for achieving frequency recovery (or load-generation balance). But the amount of additional output from each generating unit (within seconds) depends upon its primary response capability. Hence, operating a system with larger amount of spinning reserve, without considering primary response capability of the on-line units, may not prevent under-frequency load shedding. Furthermore, carrying more reserve than is needed also results in higher operating costs. Thus, knowledge of primary response capabilities of the generating units is essential for determining the primary operating reserve requirements both on systemwide level and on a generating unit level (for example, more primary operating reserve on units with high primary response capabilities). This is especially critical for islanded and small to medium sized systems where generation outages or loss of tie lines cause significant frequency excursions. Averting frequency collapse due to sudden generation outages by proper allocation of primary reserves among generating units have been demonstrated by actual case studies. The results of these studies are supported by interpretation of system behavior following actual system disturbances. The paper describes the results of these investigations.