Shaft torques during out-of-phase synchronization

As a consequence of shaft failures in two units in a Consumers Power gas turbine installation, a computer study was Performed to determine the torques In the turbine-generator shaft system during out-of-phase synchronization. Prior to this study, the possible occurrence of excessive torques in the turbine-generator shaft system without damage to the stator windings due to large currents was questioned. If the gas turbine-generator unit is designed to sustain the stator currents and the instantaneous shaft torques resulting from a three phase short circuit at the machine terminals, then the results of this investigation revealed that during out-of-phase synchronization the design torques may be exceeded by 2 to 3 times without exceeding the amplitude of the short circuit stator currents. From this it seems reasonable to infer that shaft failure could occur during out-of-phase synchronization without damage to stator windings due to excessive currents.