Control.com - Nerds in Control

Dear all,

Recently we have a problem with generator vibration. Turbine and generator are from altshom (Turco 119 and generator T190-240). When unit runs in FSNL the vibration in 3rd bearing (generator) is normal, about 0.25 inch/sec. But when the generator is synchronized, the vibration is high, at 5MW load the vibration is 0.7 inch/sec. and keeps rising until trip (setting 0.8 alarm, 0.85 inch/sec trip). The rated power is 12 MW.

Has anybody had the same experience? Please help.

Thank you.

We operate a 45MVA Frame 6B Gas Turbine (installed 1984). Since the generator rotor was removed for inspection two years ago we have had vibration issues (mainly axial). Most of the ventilation slots on the rotor windings were blocked so I requested that they were cleaned as best as possible very carefully so as not to damage the insulation.

I believe that since this cleaning, the air flow is better through some parts of the rotor windings than others and this is causing a non-uniform heat distribution and very slight bowing of the rotor.

We carried out a number of experiments by varying the VARS (excitation) at various fixed loads and noting the vibration readings. The vibration varies mostly with the VARS and not load. It is believed that the increased rotor excitation current is compounding the heat distribution issue.

I had three choices, rewind the rotor as the insulation was in such a fragile condition thus preventing thorough cleaning, trim balance the rotor to compensate for the bowing effect or operate with less excitation.

I have made the decision to operate with less excitation (0.97 PF, was previously 0.92 PF) and this is acceptable for me and the long term plan will be to rewind the rotor.

Not sure if you have this issue, but it is a fairly simple trial to carry out, providing that the machine does not still trip on high vibration even with reduced excitation.

Let me know how it goes.

Steve

Thank you Mr. Steve for your comment. We tried it but the vibration is still the same. When generator was synchronized with network the vibration increased, but when we opened the generator breaker, vibration went back to normal (less than 0.25 inch/sec). So we have a plan to pull out the rotor for more inspection.

Thank you for your comment.

Hartanto

Dear all,

Sorry for my english.

Two years ago I had the same problem on a GT EGT TB5000 N° 2 (Gas Turbine European Gas Turbines)
at one of our stations of compression.

After an overhaul of the GT, and on running, the generator vibration were normal before synchronized.

But when the generator is synchronized, the vibration on the 2 bearings of Generator were high, near Alarm, and it was a problem for us to continue the running or to stop the machine.

We kept the machine running and I proposed an idea for the operator.

1 - Start the GT TB5000 number 1
2 - Balance all the load from the Machine N°2 to the machine N°1. The machine N°1 were running with no vibration in spite of the maximum load.

3 - After 1 hour of time we did the opposite action. The operator balanced all the load from GT N° 1 to the GT N°2 gradually.

4 - We noted that: no vibration on the 2 bearings of generator (disappear).

Really what happened, nobody can explain this.

It happened only one time.

Thanks for believing me.