Shaft alignment - why is angled?? 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 slighly angled downward towards one another at the coupling? If this is so why is it done?

Many thanks to all in advance who humor a somewhat mystified electrical person.

 

[MachineryWatch]

If you observed this condition in when the machine was not operating and cold, it may be that this condition goes away when the machine comes up to normal operating temperature. In other words, thermal growth brings the shafts into alignment, but results in misalignment when the machine is at ambient temperatures.

Skip Hartman

http://www.machinerywatch.com

 

[sms]

Most large steam turbines generator sets (above say 250 MW) are aligned to what is called the catenary curve. The rotors are so heavy, that there is a significant sag between bearings, either cold or hot. The couplings between casings are typically solid bolted joints, so for the coupling hubs to line up, and in order to minimize reversal stresses on the bolting, the sag of one rotor is matched to the sag of the next. The result is that the governor end bearing on the turbine is way high, while the LP turbine may be significantly lower, and the the outboard generator bearing is at about the same elevation as the governor end bearing. If you had a side view drawing of the bearing elevations, and the rotors installed you would see a nice smile...

 

[Rob45]

What kind of coupling do you have?
If it's a universal-joint type coupling, a little angle would be built-in to provide some rotation of the joint and avoid hammering the needle bearings to dust.

 

[byrdj]

I agreement with sms. refer to thread666-104515