Suppressing Transient Shaft Stresses of Turbine-Generators using a Static Phase-Shifter

A novel approach for damping transient oscillatory stresses of the shaft segments of large steam turbine-generators, based on the application of static phase-shifters is presented. The supplementary damping is obtained based on the active power modulation characteristics of static phase-shifters, by injecting lead-lag quadrature phase voltage, using the rotor speed deviation from the synchronous speed as the control signal. A detailed digital simulation study, using the BPA´s EMTP, is conducted to reveal the damping effect of static phase-shifters under different operating points, system configurations and switching time intervals. Emphasis is placed on the most severe disturbances, e.g., three-phase faults and automatic reclosures. The simulation results indicate that injection of 7% of the system phase voltage, in 4 discrete steps of 1.75%, can effectively reduce the peak torque and life-times of the shaft system oscillatory stresses.