Vibration in No-1 bearing increases incessantly above 12 mm/s when the load increase above 25 MW and I don’t know the ending of the increase of vibration as I can’t let the GT to trip. However, we have experienced 14.1 mm/s at 27MW load in 49.5 Hz, whereas, below 23 MW the GT is operating smoothly without any anomaly. Moreover, it has been observed that the vibration in No.-1 bearing is relatively higher when GT is running at low frequency (<50Hz) and other bearing vibrations are more or less same. The table below shows data of vibration at different loading condition-


MW------Hz--------Bearing 1------Bearing 2-----Load Gear-------Generator
-----------------(Comp. side)----(Tur. side)-----Bearing--------Bearing
-----------------BB1-----BB2----BB4----BB5-----BB7----BB8-----BB9
15------49.2----5.1-----5.8-----3.6-----3.7-----0.1-----4.6-----5.8
18.5----49.2----4.5-----4.8-----3.5-----3.6-----0.2-----4.4-----5.9
20.5----49.2----4.8-----5-------3.6-----3.6-----0.2-----4.8-----5.8
22------49.2----5-------5.4-----4.1-----4.2-----0.2-----5.1-----5.8
23------49.2----5.8-----6.2-----4.5-----4.6-----0.2-----5.6-----5.6
23.5----49.2----7.6-----7.3-----5.8-----5.8-----0.2-----6.1-----5.5
24------49.2----8.8-----8-------6.1-----6.2-----0.2-----6.4-----5.5
29------51.1----8.2-----9.3-----5.9-----5.9-----0.4-----8.5-----5.3


The particulars of the GT is simple cycle GE Frame-6, PG 6541B, running on natural gas, base load operation, no steam injection, supply power to 33kV distribution line which is connected to the national grid. Running hours more than 102000 hrs, which was under shutdown for the last 8 months. Before long term shutdown the GT was operated on 32-34 MW and the maximum vibration was below 7 mm/s, moreover, the temperature at different point before and after the maintenance is almost same. The last maintenance activities, within the shutdown period, were- Changing of Inactive thrust bearing, Disassembling and assembling of Compressor upper shell casing (up to 11th stage), Prosthesis in generator stator winding, disassembling and assembling of Rotor, dismantling of retainer ring and wedges, and assembling of those. However, before changing the inactive thrust bearing the axial movement of the prime mover was 0.61 mm, whereas, after changing the thrust bearing it came to 0.42 mm.

Presently the GT is operating on 22-23 MW. Can anyone please suggest us how to find and solve the problem? Please give us some idea about the cause of the problem?

Waiting for your valuable suggestions. Thank you.

 

Dear Pirate,

what you do operation in 49.2Hz?
what is normal operation speed & HZ in your machine?

 

I'm earnestly requesting experts to give us some suggestions...

 

Machine rated frequency is 50 Hz. However, Grid frequency varies from 51.2 Hz to 48.8 Hz.

 

And the rated speed of the Turbine is 5135rpm and Generator rotor speed is 3000rpm.

 

Accurately analyzing vibration events requires a lot more data than you have provided, and possibly even more that you have access to without additional instrumentation.

But, based on the information you provided, the Number 1 Bearing cover was disassembled and reassembled to replace the thrust bearing. A lot of things can go wrong, such as bearing alignment, turbine-to-Accesory Gear alignment, seal installation/wear, etc. Since the difference in vibration started after the machine was mechanically disassembled and reassembled, it's a good bet the problem is something to do with reassembly or alignment.

I don't know what the specification is for thrust travel with a new bearing, but I would suspect that if the thrust bearing was replaced it was done so because the thrust travel was excessive indicating some wear of the bearing surfaces, and simply installing new bearings would therefore reduce the thrust travel simply due to the thicker thrust pads.

We have a lot of experience here at control.com, but it seems not too much with vibration and mechanical issues such as this one.

 

It seems that alignment issue or bearing worn out, please check the alignment datas before and after the turbine maintenance.

 

Much more data is needed AND an experienced vibration professional is needed to help you pinpoint your problem. You may have enough equipment on site to gather the data, but you need the proper type of data and details. Then this needs to be presented to somebody that can interpret the data.

The other option is to go back into what you had apart on and double check all the work done including clearances and alignment.

Regardless, the numbers presented to the operator are useful for monitoring, but not much more.