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AS MACHINE TRAINS
In a typical coupling alignment, one machine is moveable and the other is stationary. Shaft alignment readings are taken at the coupling directly followed by "moves."
During a machine train alignment all the coupling alignment readings are taken first. Then a deliberate, "well thought out" approach is taken to determine what will be moved to correct the alignment.
Steam turbine coupling alignment is a machine train alignment. There is a basic step-by-step procedure to follow which will maximize all of the benefits of aligning a machine train. A machine train approach to steam turbine alignment can often be easier to accomplish than a one-coupling alignment.
The steps will ensure that the alignment obtained is better and takes less time. By using this approach to perform a machine train alignment, an "impossible move" may not be encountered. This means the alignment can be performed from start to finish at one time.
After the alignment is performed to acceptable alignment tolerances the machine train will run more efficiently. This will mean the alignment will have to be performed less often; the couplings, seals, and bearings will last longer; and there will be less power loss due to useless heat transfer.
Graphing it out
When the steam turbine is installed initially, each bearing is set to a specified elevation based on the machine's catenary curve (the shape of the shaft centerline under gravity when supported by the bearings). Setting the bearings to this elevation should achieve the target alignment at the couplings. Small bearing moves are made to align the rotors within tolerance. Installation is generally the last time bearing elevations are determined.
When a turbine is brought down for an outage, rotor position readings are recorded at the machine's oil bore or oil deflectors (an immovable point) to have a reference when the machine is put back together. As-found coupling alignment readings are also recorded.
The machine is reassembled after the outage by targeting the rotor into the same position as disassembly by using the rotor position readings. After the machine is completely assembled, small bearing moves are made to correct any coupling misalignment. This is how OEMs accomplish this task.
Steam turbines qualify as a machine train because they are more...