Turbine Balancing- Mechanical and Electrical Lag 1

[todcaesar]

We have a turbine for which we have, in the past, brought in an outside vibration firm to collect data during startup (phase angle and magnitude) to be used in the future for a balance shot. We would like to do this ourselves with equipment from another supplier.

My question is, how do we relate the data taken in the past from one set of equipment with data taken from the new equipment? I guess my concern deals with mechanical and electrical lag.

The turbine manufacturer and the outside vibration firm are owned by the same company; so, they are,understandably, not being terribly helpful. Is this info something I should expect from the new equipment supplier?

Thanks,

Tod

 

[sms]

What instrument are you buying, and what instrument did your vibration firm use? What kind of tranducers did your vibration firm use, and what kind of transducers are you planning to use?

If you are using proximity probes, and a permananently installed keyphasor reference, just about all modern turbine analyzers take the data in the same way, and will give you the same results. So electrical and or mechanical lag errors should not be an issue.

If you have questions, just ask. I used to be a service engineer for a vibration company that is now owned by a turbine manufacturer. But now I am an end user, so I would be happy to help!

 

[todcaesar]

Hey SMS,

We have used Bentley Nevada in the past with proximity probes. The phase reference is not permanently installed.

We are looking at a Maars system and considering using accelerometers. Balancing is probably secondary in importance(we may just bring Bentley Nevada in for balance shots), our main concern is watching for rubs on startup. We have a GE Turbine with a monoblock rotor and rubs during startups and shutdowns have been a problem.

 

[sms]

You need to take care about using accels to monitor for rubs on startup. The best way to see that is to look at orbits, and the bode/polar plots during run up. Most startup rubs are on the high pressure packing, or due to rotor long causing axial contact in the diaphragms, and basically induce a bow in the rotor. That kind of rub will not transfer much energy out to the case where an accel can measure it effectively. I would hook the MAARS system directly to the Bently rack and monitor both spectrums as well as 1X amplitude and phase during the startup process.

Also, you might review your startup procedure, you may be moving too fast. These big turbines need the time to heat up and stretch out. You should also look at retrofitting with retractable packing that helps a bunch. Also watch the temps on the back end of the machine, for instance insufficient condenser vacuum often heats up the back end and causes rubs.