A thyristor-controlled reactor (TCR) is a reactance, which is connected in series with a bidirectional thyristor valve. The thyristor-controlled reactor is an important component of a Static VAr Compensator.
The thyristor valve is phase-controlled. In parallel with the circuit consisting of the series connection of the reactance and the thyristor valve, there may be an opposite reactance, usually consisting of a permanently connected, mechanically switched or thyristor switched capacitor. By phase-controlled switching of the thyristor valve, the value of delivered reactive power can be set. Thyristor-controlled reactors can also be used for limiting voltage rises when circuits are open. Another device used for this purpose is a transducer, magnetically controlled reactor (MCR)