Clarification of the SSR mitigation mechanism of a TCSC

Abstract

A thyristor controlled series capacitor (TCSC) is considered to be effective not only for flow control and stabilization of power systems, but also for mitigation of subsynchronous resonance (SSR). This paper clarifies the SSR mitigation mechanism of a TCSC. First, using time simulations, we show that SSR appears and disappears depending on the firing angle of the TCSC. Next, we show that the frequency characteristics vary considerably with the firing angle. Further, we show that SSR occurs in TCSC-compensated systems as well as in conventional series-capacitor-compensated systems when 60 Hz minus the electrical resonance frequency of a transmission system coincides with the torsional oscillation frequency of a generator-turbine shaft. TCSC can avert SSR by changing the firing angle and by shifting the electrical resonance frequency. Next, we propose an equivalent circuit to TCSC which consists of a series capacitor in parallel with a resistor and a reactor. We adjust the parameters so that it shows the same frequency characteristics as TCSC. We apply it to time simulations to see if it is equivalent to TCSC. Finally, we perform an eigenvalue analysis on the equivalent circuit. We obtain results that correspond to the time simulations. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(4): 31–39, 1997