Thank you very much for the quick response. Will revert soon after collecting necessary data and other information's as desired.I concur--this should be a completely separate thread as it really has little or nothing to do with the original post. And bhilal.bhatti should explain his TLA (Three-Letter Acronym).
That being said, I have seen this once. The shear strength of the coupling bolts was calculated incorrectly--or that's what the steam turbine-generator set packager said (actually, it wasn't probably calculated at all--the packager bought a steam turbine from one manufacturer, a generator from another manufacturer and a coupling from a third supplier). The coupling manufacturer said the bolts are designed to shear primarily based on torque-based calculations (but also includes other electrical phenomenon, PhilCorso) to protect the turbine and the generator from serious damage in the event of pole slippage or similar occurrence. The bolts that were supplied weren't the right bolts for that particular application. (The coupling bolts kept shearing when lightning strikes in the area caused utility breakers to open in an incorrect order and greatly increase the load on the steam turbine-generator at one small biomass plant.) The local utility had to get involved to develop a different breaker tripping scheme than the one which was put in place when the biomass was being built and tied to the utility because the load "throw-on" was definitely going to break even the proper coupling bolts. This problem took over a year-and-a-half to sort out. The PLC being used to control the steam turbine had been improperly programmed and was annunciating a misleading alarm from the AVR. Four sets of coupling bolts were sheared before involving the coupling manufacturer and the STG supplier to solve the problem and obtain the proper bolts for the application and getting the utility to review and revise their protection scheme in the event of a fault or lightning strike near the plant.