A study of thyristor controlled series capacitor models for power system stability analysis

The thyristor-controlled series capacitor (TCSC) is promising as a powerful device to increase power transfer capability and transient stability. The basic configuration of the TCSC consists of a series of capacitors connected antiparallel with thyristor-controlled reactors, so that firing angle control of the thyristors makes the TCSC capable of achieving impedance control in a wide range with quick response. It is important to clarify the relationship between the fundamental reactance of the TCSC and the firing angle of the thyristors, thus leading to practical applications of the TCSC for enhancement of power transfer capability and transient stability in transmission lines. Two relationship equations for the TCSC's fundamental reactance have already been proposed. One is the relationship equation derived from a TCSC circuit whose source is a voltage. The other is the relationship equation derived from a TCSC circuit whose source is a current. For TCSC installed in a transmission line, it is clear which equation is more adequate for analyzing power system stability. In this paper, the authors determine whether either of the equations is valid for analyzing a power system stability. 1. In the steady state, the TCSC fundamental reactance is analyzed and compared with the two equations and EMTP. It is clear that the TCSC reactance based on current source is adequate. 2. The swing angle of a generator when the firing angle is stepped up is analyzed with EMTP and an analytical model using the TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 20–28, 1999