Series Reactor

(also current-limiting reactor), a high-voltage electrical apparatus designed to limit the current of a short circuit and maintain adequate voltage on the buses of distribution switchgear during a short circuit in a network. It consists of an inductance coil, on which the principal voltage drop occurs during the short circuit. Such reactors are also used to limit the starting currents of synchronous electric motors and to compensate reactive power in order to improve the transmission capacity of power lines. For voltages up to 35 kilovolts in indoor installations, series reactors are in the form of coils whose turns are cast in concrete columns; for voltages of 35 kilovolts and higher, the coils are mounted in steel drums filled with transformer oil.

The principal technical parameters of a reactor are the nominal voltage and current, together with the relative inductive reactance—the percentage ratio of the voltage drop on the reactor at the nominal current to the nominal phase voltage of the network. In order to reduce the voltage loss in a reactor when a load draws current through the reactor, double reactors are used, consisting of two coils wound in opposing directions with each coil connected to its own line. When both lines have the same load, the magnetic fluxes of the coils practically compensate each other so that the inductive reactance and voltage loss are small. During a short circuit in one of the lines, the resultant magnetic flux in the reactor increases sharply because the magnetic flux created by the coil with nominal current is much less than the magnetic flux of the coil with the short-circuit current. The inductive reactance increases, and the magnitude of the short-circuit current is limited.