Synchronous Compensator

a synchronous electric motor that operates without an active load; it is used to improve the power factor (cos Φ) and regulate the voltage in power lines and power distribution networks. Voltage at the point of consumption (at the terminals of a transmission line) varies with the magnitude and nature of loads in the distribution network (inductive or capacitive loads).

If the load carried by a distribution network is high and inductive, a synchronous compensator operating in the overexcited mode is connected to the network, which is equivalent to connecting a capacitive load. If power is transmitted over long, lightly loaded lines, the distributed capacitance of the line has a marked influence on the operating conditions of the distribution network. In this case the capacitive current in the network is compensated by connecting a synchronous compensator operating in the underexcited mode. A constant line voltage is maintained by controlling the excitation current according to the regulator voltage. A synchronous compensator is started in the same way as conventional synchronous motors; the starting current of a synchronous compensator is 30–100 percent of the nominal current value. Synchronous compensators are manufactured with power ratings up to 100 kilovolt-amperes; high-power synchronous compensators are cooled by hydrogen or water. Synchronous compensators are used mainly in electric power substations.