A 6 MW Turbogenerator suffered a catastrophic failure on 26th December 1999 due to a ground fault in the line. The turbine along with the transmission unit and both the couplings failed in this accident.
The turbogenerator set is modeled for torsional vibration analysis as a multi degree of freedom system. The natural frequencies and mode shapes are obtained. The system is next modeled as an equivalent four rotor system and a short circuit analysis is made to determine the magnification factor in this period. A complete gear box analysis has been made for its fatigue life and it was shown that it is just not capable of withstanding even a single alternating stress arising from the short circuit. The pinion will fail under short circuit condition.