Analysis and simulation of sub-synchronous resonance in steam turbine on a series-compensated network

In series compensation networks (where capacitors are added to transmission lines to improve power transfer), transient events (such as faults or disturbances) can amplify the torque on the turbine generator shafts. Series capacitors are used to increase the power transfer capability by compensating for some of the reactance in the transmission lines. The use of series capacitors may cause the phenomenon of sub-synchronous resonance (SRR). This phenomenon may cause torsional oscillations in the turbine-generator shaft system and electrical oscillations with sub-synchronous frequency. In this paper, the objective is to study and analyze the phenomenon of sub-synchronous resonance in a steam turbine in a series compensated power system. The system has a synchronous generator connected to an infinite bus via two transmission lines, one with series compensation. A three-phase fault followed by fault recovery excites the torsional modes of the system, leading to a potential torque amplification on the generator shaft. The mechanical system is modeled as a three-mass system consisting of a generator, a low-pressure turbine, and a high-pressure turbine. The system starts in steady state. A three-phase fault is considered for 0.017 seconds (starting at 0.1 seconds). This excites torsional modes and leads to oscillations in the shaft torques. Increasing the compensation percentage reduces the series capacitor voltage and phase current, but increases the magnitude of the oscillations in the masses and mass velocities. The simulation results are shown using the MATLAB Simulink implementation of the studied system model.