Analysis of Effect Damper Circuit Modelling and the Fault Clearing Process has on Amplitude and Decay of Torsional Vibrations in Turbine-Generator Shafts Following Severe Disturbances on the Grid Supply

Abstract

Analyses on response torque and stressing of turbine-generator shafts following severe system events in the past have usually assumed simultaneous interruption of all three phase currents. From past theoretical investigations, it can be said that the alternating component of airgap torque following clearance at fault current zeros would vary only insignificantly, while if simultaneous interruption is assumed, the resulting unidirectional field gives rise to a resultant pulsating electrical torque. That is, maximum and minimum values of both the unidirectional field and amplitude of pulsating generator airgap torque will occur for a fault clearing time t_c+ △t, where 0< △ t<1/f seconds. This implies the pattern of pulsating airgap torque obtained following fault clearance where simultaneous interruption is assumed is incorrect. As excitation of torsional vibrations in machine shafts due to supply system disturbances is dependent on both the pulsating component of airgap torque following fault incidence and on that following fault clearance, torsional response will differ when the exact and approximate fault clearing processes are employed.