Turbine vibration

[Dave001]

on a turbine data sheet , the maximum vibration amplitude at stabilized conditions is 34 micron , so I have a question does the vibration normally increase when we increase the load of turbine from 1 MW to maximum load 250 MW or it should be constant in all cases ? Also if the value of amplitude on a polar plot is increasing and decreasing is that normal if it is within the range of 34 micron or not normal ?

 

[racookpe1978]

Every turbine will behave slightly different during each startup. Each has resonance zone that need to be avoided at EVERY startup, but no two turbines will have the same resonances.

You MUST call your turbine-generator vendor and get their specific limits, or risk losing their warranty immediately.

2580 Megwatts?

 

[byrdj]

Given I haven't comissioned a new unit in decades now;
besides being shocked that steam turbines are now up to 2580 MWs, the fact that expected vibrations is less that 1 mil (34microns) is even more so

 

[spciesla]

byrdj - 1 mil is 25.4 micron, nevertheless, the specification of 34 microns seems pretty tight. I haven't heard of a 2580 MW steam turbine either.

It is typical for vibration on a turbine to change with load. This can be related to thermal affects, a change in forces on the rotor (how steam is admitted), etc. If you are looking at the 1X vectors on the polar plots, you can expect to see some movement. I would be concerned if you see loops on the Polar, which may be an indication of a rub.

 

[Dave001]

sorry the turbine is 250 MW

 

[byrdj]

normally I observed, for a unit in proper alignment, the vibration would slightly reduce as load increased. mainly due to foundation and elements "growing" to design conditions. a turbine is in an offset when cold and would excite the normal unbalance vibration.

things like internal elements making contact (rubbing) can and do cause significant vibration increase. Most rubbing is encountered during roll up and low load.

some other design features that may cause undesired vibration increase with loading would be the inlet steam that could "lift" the rotating element and cause instablity.

I did observe that normal vibration levels were decreasing with the new units. the units I worked during the 70-90's, a 5 mil running on a 3600 rpm was Good Enough. shut down level was up to 10 mils. Oh, these measurements were shaft absolute displacement. other measurements locations like bearing displacement were much low.

Polar plots were mentioned
I never liked, nor reviewed bearing orbital data. I got by nicely just by using magnitude and phase angle.
Taken the bearing locations magnitude and phase, I would do a polar plot of vector addition across a span. This would give me the simple model of the rotor’s unbalance for its static and coupled components