This paper presents a newly developed voltage and reactive power control device, the coordinated Q -V controller (CQVC), for a multimachine steam power plant (SPP). The requirements for the new controller are defined based on identified inadequacies of manual Q-V control. The controller uses a feed-forward correction signal based on the application of the sensitivity matrix at a power plant level. It is designed and its performance initially assessed using the Matlab/Simulink environment. The performed simulations show that all the primary design objectives are met. The Q-V controller maintains the voltage at the SPP busbar with a certain droop characteristic during slow voltage changes in the power system whilst also maintaining equal per unit reactive power sharing among the SPP generators. This ensures that the power system fully benefits from all generating units during system perturbations. The performance of the designed CQVC is validated by comparing simulation results with measured responses obtained from a real CQVC installed at a SPP.