This paper presents a fuzzy logic switching for the thyristor controlled braking resistor to damp turbine-generator shaft torsional oscillations. Following a major disturbance in electric power system, variable rotor speed of the generator is measured, and then the current through the braking resistor is controlled by the firing-angle of the thyristor switch which is controlled by the fuzzy logic. Thus the braking resistor controls the accelerating power in generators and damps the shaft torsional oscillations. The effects of the fault occurring time on turbine shaft torsional torques have also been investigated. Simulations are performed by using EMTP (Electro-Magnetic Transients Program). Through the simulation results of various multi-phase faults in a single machine connected to an infinite bus system, the effectiveness of the proposed fuzzy logic controlled braking resistor in damping shaft torsional oscillations is demonstrated.
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