Thyristor Controlled Series Compensator

The effective reactance is the parallel combination of a fixed capacitor and variable reactance. Parallel resonance may occur at certain values of firing angle. The characteristics of a TCSC are given on the right. Why cannot we increase the effective reactance of the parallel combination to much larger values say upto the parallel resonance point?

One of the major consideration of any series connected device is the need to bypass the device when faults occur nearby. Faults cause large overcurrent in a line, which in turn results in overvoltage across a capacitor. Therefore, Metal Oxide Varistors (which are nonlinear devices which have very low resistance when voltage magnitude is greater than a particular value) and circuit breakers are generally connected across series connected devices. Note that during faults, a series connected device is bypassed. However, immediately after the fault is cleared, it is necessary to insert maximum capacitive reactance in order to improve the stability of the rotor angular deviations which occur due to the fault.

Examples of controlled series compensation installations in India are the Raipur - Rourkela TCSC and the Kanpur Ballabhgarh TCSC. Details of the Kanpur-Ballabhgarh installation are given in the next module.

You may simulate the working of a TCSC using the MATLAB/SIMULINK file (TCSC3.mdl).