Capability charts for combined cycle power plants

Thermal power plants, based on combined gas and steam turbine cycles, are now worldwide. In a competitive generation market, power plants are required not only to inject active power but also to support secure operation of the transmission system, providing adequate ancillary services. To determine power plant capability for supporting voltage/reactive power regulation of the power system, the active and reactive powers that a combined cycle power plant can inject into the power system must be evaluated. The concept of capability charts is therefore extended from synchronous generators to the whole combined cycle power plant, including the effects of the operating conditions of the thermal and electrical components of the power plant, as well as of the plant connection to the electrical power system. Steady-state mathematical models are presented and a modular algorithm is proposed to evaluate the power plant capability charts numerically. Some numerical results are presented to show the effective synthetic information that can be obtained by adopting the proposed approach in practical cases