Turbo alternator alignment 1

[norske]

Hi everyone,

In a coupled steam turbine alternator arrangement (3000RPM, 10MVAe) should the DE bearings be slightly lower than the two NDE bearings? That is should both the turbine shaft and alternator shaft be slightly angled downward towards one another at the coupling? If this is so why is it done?

Many thanks to all in advance who answer.

 

[mc5w]

The only reason that comes to mind is that the turbine and generator sag differently when turning and when stationary. Most modern horizontal shaft machines have a gearmotor and clutch that keep the system turning at a low speed during shutdown so that gravity will not distort the shaft. There also may be some gyroscopic reaction due to gravity or the earth's rotation when the turbine is at full speed.

The first steam turbine generators were vertical shaft just like hydroelectric units for that very reason.

In a paperboard making machine the corrugating rolls are larger in diameter in the center so that when under pressure a flat surface is the result. We determine correct pressure by running carbon paper through the rolls at different pressures - the correct pressure results in uniform teeth marks from the rolls.

Mike Cole, mc5w@earthlink.net

 

[TheBlacksmith]

In our applications (Shipboard), we usually align the steam turbine slightly lower than the generator when cold. The turbine casing expands more in operation, raising the shaft slightly, bringing the unit into alignment under operating conditions. The difference is referred to as "cold offset".

Blacksmith

 

[mc5w]

I was also just thinking that stationary shafts will sit lower in a sleeve bearing than when the shaft is turning at high speed. The rotating shaft exerts a pumping force that makes the oil film thicker at the bottom of the bearing and possibly on one side. You probably would also have more oil pumps running when the shaft is running at high speed which would affect the thickness of the oil film - when turning slowly during shutdown you only need enough pumps to keep the bearing wet.

Mike Cole, mc5w@earthlink.net