Using TCSC scheme for SSR mitigation in a radial transfer corridor

The thyristor controlled series capacitor (TCSC) has been well known as a potential countermeasure against SSR since it was introduced. This paper uses a real case, a local power plant connected to a remote load center through a series compensated radial transfer corridor, as an example to illustrate the capability of TCSC to mitigate SSR. The TCSC uses a special patented control scheme called synchronous voltage reversal (SVR). The paper is organized into three parts. Firstly, modal analysis is applied to obtain the natural torsional modes of the shaft spring mass model. Secondly, simulation of the generator and the connected electric network is performed, when a small modulation of the generator shaft speed within the SSR frequency range has been applied. As a result the electrical damping can be obtained from the calculated electrical torque. The scanning results under different scenarios show that the units using a fixed series compensation scheme are highly exposed to SSR risk. A novel scheme with TCSC is proposed and the result of frequency scanning shows very good SSR damping performance, where SVR counteracts the most part of the electrical damping of the modes at risk. Furthermore, an add-on control strategy can be easily introduced to pull the remaining slight portion into a secure range. Simulation results with detailed shaft spring-mass model validate TCSC control effect and the feasibility of such transmission schemes.