One of our 150 MW Generators is converted to run as synchronous condenser in summer. This summer we had replaced the coupling between the generator and the Pony motor. The old coupling was a limited end float coupling with a 3/16 in float. The present coupling is a shear pin gear coupling with a 1/4 inch float. It is not a limited end float coupling. When we ran up the Synch Condenser(Gene4ator) to 3600 rpm by the pony motor the vibrations were about 40 microns . But when we synchronised the Synch Cond the vibrations increased to 200 microns. The Synch Condenser(Generator) does not have a thrust bearing. We noticed that the Synch Condenser shaft (Generator shaft) moved 1/2 in towards the pony motor when we synchronized. Therefore we increased the float to 3/4 inch. The sych condenser ran with 80 microns for a month. We find the vibration steadily increasing to 160 microns now. The question is what has caused the vibration to increase?