1456 IEEE TRANSACTIONS ON POWER SYSTEMS, VOL. 20, NO. 3, AUGUST 2005 The Impact of Combined-Cycle Gas Turbine Short-Term Dynamics on Frequency Control Gillian Lalor, Student Member, IEEE, Julia Ritchie, Damian Flynn, Member, IEEE, and Mark J. O’Malley, Senior Member, IEEE Abstract—A model suitable for studying the short-term dynamic response of a combined-cycle gas turbine (CCGT) to a system fre- quency deviation is developed. The model is used in conjunction with a larger system model to study the impact of increasing levels of CCGT generation on frequency control of a small island system. The study considers single contingencies and does not consider se- vere cascading-type events. A consequence of the results is that as the number and proportion of base-loaded CCGTs increases, fre- quency control may become more challenging. The results indicate that with additional CCGTs on the system large frequency excur- sions will be more likely, and the transmission system operators on the island of Ireland should review their frequency control strate- gies in the future to avoid the shedding of customers. Index Terms—Combined-cycle gas turbine (CCGT), frequency control, power generation control, power system security. I. NOMENCLATURE Scaling factor for frequency sensitivity of gas turbine exhaust temperature calculation. Constant, such that . Inlet guide vane angle ( ). 1/Droop. Inlet guide vane controller constant (s). Inlet guide vane position (per unit). Speed (per unit). Ambient pressure (mbar). Gas turbine power output (per unit). Set point (per unit). Ambient temperature ( ). Compressor discharge time constant (s). Gas fuel time constant (s). Inlet guide vane controller integration rate (s). Inlet guide vane actuator time constant (s). Rated turbine exhaust temperature ( ). Speed controller time constant (s). Temperature controller integration rate (s). Valve positioner time constant (s). Exhaust gas temperature ( ). Fuel flow (per unit). Exhaust gas flow (per unit). Manuscript received January 21, 2005; revised March 17, 2005. This work has been conducted in the Electricity Research Centre, University College Dublin, which is supported by the Electricity Supply Board (ESB), ESB National Grid, Commission for Energy Regulation (CER), Cylon Controls, and Enterprise Ireland. Paper no. TPWRS-00036-2005. G. Lalor and M. J. O’Malley are with the Electricity Research Centre, De- partment of Electronic and Electrical Engineering, University College Dublin, Dublin 4, Ireland (e-mail: gill.lalor@ee.ucd.ie; mark.omalley@ucd.ie). J. Ritchie and D. Flynn are with the School of Electrical and Electronic En- gineering, The Queen’s University of Belfast, BT9 5AH Belfast, U.K. (e-mail: j.a.ritchie@qub.ac.uk; d.flynn@qub.ac.uk.) Digital Object Identifier 10.1109/TPWRS.2005.852058 II. INTRODUCTION T HE DYNAMIC characteristics of combined cycle gas tur- bines (CCGTs) have become an issue of considerable in- terest over the last ten years. This is due to the increasing pro- portions of CCGT plant that are being brought online in the majority of electricity systems worldwide. Higher efficiency, greater flexibility, and lower emissions than many conventional thermal generators, combined with progressively shorter instal- lation times and reducing installation costs, are the basis for this move toward CCGT generation. Understanding the dynamic be- havior of CCGT units is crucial to maintaining system reliability and security in electricity systems. This is particularly true as the move toward competitive markets means system operators now have little or no control over the type and location of new plant investment. Maintaining the standards of security and quality of supply of any electricity system are of utmost importance to the system operator. Recent system blackouts in countries such as the USA, Canada, the United Kingdom, and Italy highlight the impor- tance of system security and reliability [1]–[3]. When an inci- dent occurs on the system, maintaining the system frequency within the stipulated limits is a major priority, and if these limits are breached, then the magnitude of the excursion needs to be restricted and the frequency returned to within the limits as quickly as possible. Of particular relevance to this study is the August 1996 blackout of Peninsular Malaysia that occurred as the result of a serious generation loss. The electricity system in the Peninsular and Sahab regions of Malaysia, operated by the Tenaga Na- sional Berhad (TNB) power utility, has a peak load approaching 14 000 MW, with approximately 29% of the generation con- sisting of CCGT and gas turbine units [4]. The behavior of gas turbines and CCGT units in response to the frequency disturbance contributed significantly to the severity of the event [4]. As a consequence of the incident, several modifications to improve the response of both gas turbine (GT) and CCGT controllers to large-frequency excursions were incorporated. In large, interconnected electricity systems, frequency devi- ations from nominal tend to be small. This is due to the rela- tively high inertia of the system and the fact that any sudden supply/demand imbalances are generally small in comparison with the total size of the system. The largest infeed in a small electricity system is likely to be a much higher proportion of the total generation while the system inertia is considerably less. Consequently, the effect of an incident, such as the loss of gen- eration, on the system frequency is much more notable. An un- derstanding of the response characteristics of CCGT generators 0885-8950/$20.00 © 2005 IEEE