A Study of Thyristor Controlled Series Capacitor Models for Power System Stability Analysis

A thyristor-controlled series capacitor (TCSC) is expected as a powerful device to make power transfer capability and transient stability increase. The basic configuration of the TCSC consists of a series of capacitors connected in anti-parallel with thyristorcontrolled reactors, so that the 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 the enhancement of the power transfer capability and transient stability in transmission lines. Two relationship equations for TCSC fundamental reactance have already proposed. One is the relationship equation derived from TCSC circuit, source of which is voltage. The other is the relationship equation derived from TCSC circuit, source of which is current. For the case of installing TCSC in the transmission line, it is not clarified that which equation is adequate to analyze power system stability. In this paper, the authors developed whether either of the equation is valid to analyze power system stability. 1. In the steady state, TCSC fundamental reactance is analyzed, and compared with two equations and EMTP. It is clear that TCSC reactance based on current source is adequate. 2. Swinging angle of a generator when the firing angle is stepped up is analyzed with EMTP and analytical model using TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis.