Comparison of turbine-generator shaft torsional response predicted by frequency domain and time domain methods following worst-case supply system events

The paper examines precision of predicting time response for torque in turbogenerator exciter shafts by frequency-domain analysis following incidence and clearance of short-circuits etc on the electrical supply system. The analysis is based on Fourier analysis of generator air gap torque following incidence and clearance of a supply network disturbance or following worst-case mal-synchronisation to obtain torque excitation which acts on the generator rotor corresponding to each modal vibration. Amplitude and phase of each vibration is thereby determined. Using appropriate damping, time responses for shaft torque at each shaft cell is constructed by summing components which correspond to each frequency of modal vibration of the shaft. These time responses are compared with those obtained by solution of more than 50 differential equations which simulate the shaft train, turbine, generator, exciter, electrical supply system, the fault clearing process, the turbine governor, and the generator excitation system