TURBINE-GENERATOR SHAFT TORSIONAL TORQUES DUE TO NETWORK DISTURBANCES

In the past few years, there has been an increasing recognition of the potentially harmful effect of electrical network disturbances on turbine-generator shaft systems. These disturbances include transmission line switching, short-circuits that occur in the electrical network, out-of-phase synchronization accidents and circuit breaker operations following electrical system faults. All such events induce high torsional torques on the turbine-generator shafts. Depending upon many factors, the stresses induced by these torques may exceed the endurance limit of the turbine-generator shafts and thus cause shaft fatigue. The main purpose of this thesis is to investigate the effect of electrical network disturbances on the turbine-generator shaft torsional torques. To carry out these investigations, a digital computer program was developed to simulate in considerable detail the interaction of the turbine-generator shafts and the electrical network disturbances. The studies reported in this thesis have revealed that the turbine-generator under study is subjected to a potential problem due to the interaction between the electrical disturbances and its shaft mechanical system. The nature of this interaction is explained and the impact of the various types of system disturbances and loading conditions is presented. The thesis also presents a comprehensive study to investigate the possibility of damping turbine-generator shaft torsional torques following clearing a network fault by interrupting the generator excitation during the fault period and switching in a field discharge resistor. In this context, it has been found that the field discharge resistor has significantly reduced the peak amplitudes of the turbine-generator shaft torsional torques after the fault clearance