340 IEEE TRANSACTIONS ON ENERGY CONVERSION, VOL. 27, NO. 2, JUNE 2012 Modeling Combined Cycle Power Plants for Power System Restoration Studies Stefano Barsali, Antonio De Marco, Giorgio Maria Giannuzzi, Franco Mazzoldi, Andrea Possenti, and Roberto Zaottini Abstract—This paper presents a dynamical model for simulating combined cycle power plants to be used for assessing the plant be- havior during large transients and for restoration procedures. The 80th dynamic order model considers the complex structure of the heat recovery steam generator and calculates the main variables that are critical during these transients. The model has the double purpose of studying both the plant behavior under the usual con- trol systems as well as innovative logics and control strategies for increasing its performances in terms of regulation and emergency services. The possible use of combined cycle power plants for sup- plying a restoration area is finally investigated adopting different control strategies that also involve the regulating capacity of the steam turbine. Index Terms—Boilers, power generation, power system model- ing, power system restoration, turbines. NOMENCLATURE Variables Q ex [kW] Heat released by exhaust gases. q [kg/s] Mass flow. T [ ◦ C, K] Temperature. σ [kJ/kg/K] Heat transfer coefficient. c [kJ/kg/K] Specific heat capacity. v [m 3 ] Volume (banks, drums, etc.). ρ [kg/m 3 ] Density. P [bar] Pressure. h, H [kJ/kg] Enthalpy, saturation enthalpy. M [kg] Mass. L [m] Height (risers). S D [m 2 ] Drum cross section. y [m] Drum water level. l w [p.u.] Fraction of risers with liquid water. Ψ [kg/s] Steam production in the risers. g [m/s 2 ] Gravity acceleration. k fd , k fr [m −2 ] Friction factors. η, η c , η t [p.u.] Efficiency, compressor and turbine. Manuscript received June 21, 2011; revised October 27, 2011 and December 30, 2011; accepted February 10, 2012. Date of publication March 16, 2012; date of current version May 18, 2012. Paper no. TEC-00307-2011. S. Barsali is with the Department of Energy and Systems Engineering, Uni- versity of Pisa, I-56122 Pisa, Italy (e-mail: barsali@dsea.unipi.it). A. De Marco, F. Mazzoldi, and A. Possenti participated as consultant of the University of Pisa, I-56122 Pisa, Italy (e-mail: antoniodemarco65@gmail.com; franco.mazzoldi@tin.it; andreapossenti@tiscalinet.it). G. M. Giannuzzi and R. Zaottini are with TERNA SpA, 00156 Rome, Italy (e-mail: giorgio.giannuzzi@terna.it; roberto.zaottini@terna.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TEC.2012.2188406 r, r c [p.u.] Compression ratio, critical comp. ratio. γ c p /c v . ϑ [p.u.] Valve position. A n [kg/s/bar] Rated valve admittance. LHV [kJ/kg] Lower heating value. HP, MP, LP High, medium, and low pressure. Subscripts in, out Variable value at input and output section. ex Exhaust (e.g., q ex = exhaust mass flow), q fl Flash (e.g., q fl = flash mass flow). l, g Liquid, gas (e.g., h l = liquid enthalpy). ls, gs Saturated liquid, saturated gas. d Downcomers (e.g., h d = enthalpy in down- comers). D Drum (e.g., M D = mass of water in drum). m Metal (steel of banks, e.g., M m = mass of bank steel). sat Saturation condition (e.g., T sat = saturation temperature). ac Compressed air. a Ambient. fm Flame (e.g., T fm = flame temperature). fu fuel. For vaporizer nomenclature, see Fig. 2. I. INTRODUCTION I N recent times, worldwide power systems have experienced a strong increase in the number of combined cycle power plants (CCPP) installed for satisfying the electricity demand. These plants show high efficiency thanks to improvements in the gas turbine technology, which enable reaching very high temperature at the combustor outlet, and low emissions through advanced combustion techniques. At the same time, system operators needed to adapt the way they used to manage the whole system for coping with the spe- cific dynamic performances of this new class of plants. Com- pared with classical oil or gas fired steam plants, CCPPs have a limited regulating capacity, which needs to be considered when stating the operating rules. Grid codes clearly define the regulating performances each plant must show, and CCPPs ac- tually comply with such requirements in normal operating con- ditions [1]. Each regulating event is supposed to be activated with the plant running in a steady-state condition with all the variables within very narrow ranges. But, when the system ex- periences very large disturbances, or even a blackout, each plant has to face a sequence of cascading events which demand a larger 0885-8969/$31.00 © 2012 IEEE