*4.1. Case A) 940 MVA Combined-Cycle Power Plant*

The combined-cycle power plant is composed of two identical groups, where each one has a synchro generator-gas turbine (300 MVA) and a synchro generator-steam turbine (170 MVA).

The considered power plant is connected to the Italian 400 kV transmission grid, whilst its topology is depicted in Figure 6. The effectiveness of the control (essentially a PI) is checked by analyzing the step response on the controlled variable reference (the reactive power level, *qliv*). The obtained results are reported in Figures 7–12. Particularly, the correspondence between the simulated trends and the trends measured in the real plants can validate the proposed mathematical model. Such a correspondence between simulation and experimental data accredits the suitability of the adopted mathematical model.

By observing the last figures, it is possible to see the different level of reactive power reached by the groups two and four; this aspect obviously depends on the different size of groups two and four (170 MVA) in respect of the two twin gas generators of 300 MVA. Particularly, the SART system reactive requests are proportional to the reactive power capability of each generator. Each group changes its generated reactive power according to its capability curve and its generated active power (not shown). In the simulation, a little difference has been considered in the capability of groups one and three, while all active powers are kept constant during the simulations.

**Figure 6.** The topology of plant A.

**Figure 7.** Generators reactive powers response (in p.u.) to a step in the reactive power level reference (experimental data).

**Figure 8.** Generators reactive powers response (in p.u.) to a step in the reactive power level reference (simulated data).

**Figure 9.** Voltage profile (in p.u.) at the different nodes of generation (experimental data).

**Figure 10.** Voltage profile (in p.u.) at the different nodes of generation (simulated data).

**Figure 11.** Voltage profile (in p.u.) at the POC (experimental data).

**Figure 12.** Voltage profile (in p.u.) at the POC (simulated data).

#### *4.2. Case B) Synchronous Condenser of 160 MVA*

This case considers a synchronous condenser rated 160 MVA, whose aim is mainly the reactive power production to compensate for voltage perturbations in the transmission network. The plant topology is depicted in Figure 13.

**Figure 13.** The topology of plant B.

The obtained results are reported in the Figures 14–17. In this case, the mathematical model is very simple. Experimental data and simulations are shown both for voltages and reactive powers. The correspondence between experimental data and simulations is shown as a proof of the correctness of the proposed mathematical model.

**Figure 15.** Reactive power profile (in p.u.) of a generator (simulated data).

**Figure 16.** Voltage profile (in p.u.) at the POC (experimental data).

**Figure 17.** Voltage profile (in p.u.) at the POC (simulated data).
