Thyristor controlled reactor (TCR) mainly consists of a bi-directional thyristor switch and an inductance connected in parallel. The firing angle control of the thyristor switches, on the other hand, regulates the time for which the inductance is included in the circuit line, furthermore which controls the average value of the required inductance. Besides, the continuity regulated inductance can be used for short circuit current reduction, as well as, for line flow regulation. It can also be used for series compensation when the thyristor controlled reactor is connected in a series with the fixed capacitor and when both the combination is inserted in series with the transmission lines.
The use of thyristor controlled reactors in series capacitors offers some crucial advantages, such as:
• Continuous and rapid control of series-compensation and transmission-line level.
• It offers suppression of oscillations and at subsynchronous frequencies, it also presents a resistive inductive reactance. These oscillations cannot be sustained in the situation and as a result, they rapidly get damped.
• It also prevents the loop flow of power supply as the control of power flow in the transmission lines within the network enables the optimal power flow, and thus prevents any type of loop flow of power.
• It offers great voltage support. The thyristors in conjunction with the series capacitors can make reactive power that enhances with line loading and further aids the regulation of local voltages and alleviates voltage instability.
• It increases the level of protection for the series capacitors. A bypass of the capacitors can easily be achieved through thyristor controlled reactors when large voltages build across the capacitors following different errors and faults. In the same way, the capacitors can be instantly reinserted by the thyristor action after clearing all the faults in order to support system stabilization.
• The use of thyristor controlled reactors in series capacitors also reduces the short circuit current. During high short circuit current, the thyristor can switch from the capacitance to the inductance mode, wherein limiting the short circuit currents.
• It decreases the dc-offset voltage. The dc offset voltage that comes as a result of the insertion of capacitors can further be made to decay very instantly from the firing limit of the thyristor controlled reactors.
So, these are a few major benefits that come with the use of thyristor controlled reactors in series capacitors.
Moreover, when it comes to the equipment of thyristor controlled reactors, note that it has two major ones: the reactor that is usually iron cored or air-cored and the valve. In addition to these two, an intermediate power transformer may also be required to set up with the voltage that is controlled by the transmission system voltage, as well as, the thyristor.