ABSTRACT
Numerous aspects of feedback control systems are applied to electric power system operation. For instance, local controls are used at generator units and at controlled buses, whereas central controls are employed at area control centers to monitor area frequency, power flow to interconnected areas, and generating unit outputs. A number of automatic controls are used in present-day power systems. These include devices that control the generator voltage, the turbine governor, and the load frequency; there are also computer controls to ensure economic power flow and to control reactive power, among other power-system variables. Generator voltage control is accomplished by controlling the exciter voltage. Within a power plant, a number of ac generators generally operate in parallel. For the economic operation of the plant, the total load must be appropriately shared by the generating units. In a plant having two operating units, generally the incremental fuel cost of one unit will be higher than that of the other.
