TURBINE-GENERATOR SHAFT TORQUES AND FATIGUE LIFE EXPENDITURE PREDICTED BY FREQUENCY DOMAIN AND TIME DOMAIN METHODS FOLLOWING SEVERE DISTURBANCES ON THE SYSTEM SUPPLY

ABSTRACT

This paper examines precision of predicting time responses for torque in turbine-generator-exciter shafts together with fatigue life expenditure of shafts by frequency domain analysis not analysed in the literature heretofore following incidence and clearance of worst-case disturbances on the electrical supply system. Effect of both governor and avr action following a range of disturbances is also illustrated. The effect of steam and electrical viscous damping on maximum and minimum shaft torques predicted by frequency domain analysis for a range of disturbances as a function of the fault clearing time is also depicted

The analysis is based on Fourier analysis of generator airgap torque following incidence and clearance of a severe supply network disturbance or following mal-synchronisation to obtain torque excitation which acts on the generator rotor corresponding to each modal vibration. Amplitude and phase of each modal 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 modal vibration. These time responses are compared with those obtained by solution of more than 50 differential equations which simulate the shaft train, turbine, generator, governor and avr

It is shown that time responses for transient turbine-generator-exciter shaft torques together with maximum shaft torques and fatigue life expenditure of the shaft can be predicted faithfully by frequency domain analysis taking due account of magnitude and phase of each modal vibration, and damping, following (i) worst-case Line-Line-Line, Line-Line, and Line-Ground disturbances from full-load to no-load with clearance, and (ii) mal-synchronisation. Simulation of damping of rotor swing, together with governor action, is important in making precise assessments of transient turbine shaft torque (and fatigue life expenditure of the shaft) at shaft locations which are close to die generator

660 MW, 1000 MW and 1300 MW two-pole Machines are analysed.