The vibration measurement Of 100 MW Alsthom MS9001E gas turbogenerator was taken using Commtest VB3000 from Bently 3500 panel. Brg 1 at compressor, brg 2 and 3 at turbine and brg 4 and 5 at generator;

1. Why the phase at critical speed change 360 deg not 180 deg?

2. Pls comment on the orbit plot taken at 80MW load

3. Pls advise me what is recommended alarm and trip limit for the shaft displcement at the moment we only using seismic velocity casing vibration as a protection

Ahmad

GT3B.pdf (57 Kb, 112 downloads)

I will answer the 1st question, there are more authoritative folks here to answer the other 2.

180 and (-180) degrees are equal. Think of it as a circle. The plot ends at (-100) degrees, which is equal to 280 degrees.

quote:

1. Why the phase at critical speed change 360 deg not 180 deg?

Agree with Michael. Your software is not really the best for display phase angle

quote:

2. Pls comment on the orbit plot taken at 80MW load

Assuming the unit has reached full temperature and load, I offer the following comments (prox data should always be compensated, which this data appears not to be): Bearings 1, 2 and 5 are very well loaded. Bearing 4 is lightly loaded and bearing 3 is very lightly loaded. When viewing orbits, you need to be aware how compliant the bearing housings typically are on gas turbines.

quote:

3. Pls advise me what is recommended alarm and trip limit for the shaft displcement at the moment we only using seismic velocity casing vibration as a protection

On Gas Turbines, stick with the seismic for machine protection and use the prox data for diagnostics.

Just my 2 cents, but one must know the bearing type prior to deciding it is lightly loaded. I don’t remember on the 9E, but on the 7EA the number 3 bearing is a tiltpad. Generally, tiltpad bearings have less asymmetry than a fixed arc bearing.

Also, the 3 and 4 bearings are next to each other if numbered in the usual fashion. Thus, it would be difficult for both to be lightly loaded.

Look at ISO. It can give you guidance, but be a little more conservative in general. Prox. probes will prove more consistent machine to machine on these turbines.

9E bearing #3 is a tilipad. The orbits looks were usual for a 9E.

The load on the bearing depends of the thermal condition of the unit. The correct loading can also be checked by the beraing metal temperature if installed.

For the alarm setting take has reference ISO 7919-3.


Pierre