Static synchronous series compensator: a solid-state approach to the series compensation of transmission lines

This paper describes an active approach to series line compensation, in which a synchronous voltage source, implemented by a gate turn-off thyristor (GTO) based voltagesourced inverter, is used to provide controllable series compensation. This compensator, called Static Synchronous Series Compensator (SSSC), can provide controllable compensating voltage over an identical capacitive and inductive range, independently of the magnitude of the line current. It is immune to classical network resonances. In addition to series reactive compensation, with an external dc power supply it can also compensate the voltage drop across the resistive component of the line impedance. The compensation of the real part of the impedance can maintain high X/R ratio even if the line has very high degree of series compensation. Concurrent and coordinated modulation of reactive and real compensation can greatly increase power oscillation damping. The paper discusses the basic operating and performance characteristics of the SSSC, and compares them to those characterizing the more conventional compensators based on thyristor-switched or controlled series capacitors. It also presents some of the results of TNA simulations carried out with an SSSC hardware model.