Thyristor controlled reactors mainly consist of reactor L located in the series with the thyristor valve. It is also the controlled element of the thyristor controlled reactors, plus it controls and limits the thyristor valve. The TCR comprises two opposite poled thyristor that controls each and every alternate half cycle of the reactor supply. Moreover, the duration of current flowing through the reactors is then controlled by the firing angle of the thyristor, and therefore, for every alternate half cycle, the thyristor is given a pulse by the controlled circuit. Besides, it is also used in Extra High Voltage (EHV) lines for the purpose of offering VARs during the load rejection or low load.
Thyristor Switched capacitor:
The thyristor switched capacitor is basically utilized in EHV lines for the purpose of providing VARs during heavy loads. The current passed through the capacitor can be featured by controlling the firing angles of thyristor connected in the series with the capacitor.
The main equipment of Thyristor controlled reactors:
The thyristor controlled reactors consist of two main pieces of equipment namely the reactor itself that is usually air-cored or iron cored, and the thyristor valve. Additionally, an intermediate power transformer may also be needed to set up with the use of voltage that is handled by the thyristor and the transmission system voltage.
What is a thyristor valve?
The thyristor valve basically comprises of 5 to 20 inverse parallel-connected sets of thyristors connected together in series. There is an absolute need for this inverse parallel connection because the higher voltage rating of commercially present thyristors that is approximately up to 8.5 kV is not enough for the voltage at which the TCR is connected. So, for some low voltage applications, it may also be possible to ignore the series connection of thyristors, and for such cases, the thyristor valve simply acts as an inverse parallel connection of the two thyristors.
Additionally, with the thyristors themselves, each of the inverse parallel pair of the thyristor reactors has a resistor-capacitor circuit that is well-connected across it so that it forces the voltage across the valve to separate uniformly amongst the thyristors as well as to damp the commutation that occurs when the valve switches off.
In some cases, the Thyristor connected reactors have to have some amount of control system that evaluates the gating instants, and which issues the gating pulses to the thyristors. While in some designs the control system acts to a signal which directly represents the expected susceptance, in others, the control processes multiple measured parameters of the compensated system. And it also generates the gating pulses that too without using any type of explicit signal.