A number of researches on the torsional vibration of vessel's propulsion shafting system have been conducted. But the research on shafting system of driven generator in a diesel engine has hardly been reported, because the system has been considered as less important. However, if the engine power is increased, the shaft can be easily broken down by the incorrect design without considering its excessive torsional torque.
In this study, the effect of the torsional vibration amplitude by increasing load of the driven generator was conducted on actual operation of diesel engine, and the result was that the increase of torsional vibration amplitude was very infinitesimal in proportion to the load increase. The reason is that the more increasing the load is the more increasing the exciting force, which results the torsional vibration increases. Moreover, the dumped force is increased due to the damper winding of the diesel engine driven generator.
The excessive torsional vibration in the shaft occures when generator's parallel operaton begins or when auxiliary machines suddenly start or stop while normal load operation, Through the experiment of the effects about the load variation on the vibration of a generator's shaft, It was found that the torsional vibration amplitude increased about 56% during the "ABC-on", and 44% during the "ABC cutoff", compared to the condition before "ABC-on". In addition to, when the load suddenly change, the torsional vibration amplitude increased about 138% compared to that of steady-state load.
It seams important that these results might be considerd for generator shaft designs and Register's approvals.