We are facing this problem for over 3 years. In normal operation all parameters of the turbine including vibration and all other temperatures are within limits. But when we shut down the machine for any maintenance activity for 10 days or for 3 days. The machine does not start normally, but with the ratchet plate. The day before yesterday; after 3 days of cool-down mood, we made lube oil system in service 2 hours ago and tried to crank the machine. It did not take crank so we needed to use the ratchet plate. I want to know the reason behind it or to find a solution for a normal start-up.
How old is the unit
What kind of cooldown scheme does the unit uses? Slowroll (which uses the torque converter to maintain 30-50 RPM? Turning gear? Hydraulic ratchet?
Does the unit have Bearing Lift Oil (sometimes called 'jacking oil)?
(Bearing Lift Oil will usually only be necessary for the generator bearings, and usually only if the generator is air_cooled.)