We run a 60MW range steam turbine generator which is having closed air cooling system. This machine has a high shaft vibration problem that is occurring when high reactive power is transferred. Due to this problem, maximum reactive power that can be transferred to the system was gradually reduced with time. This issue is occurring only at the generator shaft, but not at generator bearings. Can anyone tell me the issues for this problem???

 

Kasun... can you provide some corroborating parameters such as Volts, Amps, MW, MVAr, Field Volts, Field Amps, vibration, temp, etc!

Regards, Phil Corso

 

I've seen this problem twice before; once it resulted in a fire when the Customer refused to reduce the reactive load on a hydrogen-cooled generator and the vibrations increased to the point that the hydrogen seals were damaged, hydrogen leaked out and caught fire. Very nasty situation.

In both cases the problem was with the "wedges" that were used to keep the rotor windings in the slots (of a non-salient pole rotor) which had become loose. Increased rotor current caused the windings to shift (because of heating) and cause an imbalance which caused the vibrations.

 

Generator Vibration

Shaft currents could also be a reason for the high vibration in generator bearing. please read the following thread

http://www.control.com/thread/1302754593

though i do not have any personal experience, i have read a report of a site where they had a similar problem, and kept reactive power within limits. during a overhaul they found severe damage in the generator bearings. they changed the bearings and the bearing insulation and voila at startup they did not have any problems with high reactive power output.

you can give it a look. you do need to test the rotor and you can add this as a test during that.

 

Kasun... another possibility! Same symptoms... different cause.

A cylindrical-rotor for a large turbo-generator was being off-loaded from its transport carrier. As it was being lowered onto chocks positioned at each end of the rotor-shaft, the supervising turbine engineer, ordered the chocks be relocated to a position directly under the end-winding retaining-ring enclosure.

From my position several stories above the operation I yelled "STOP!" Skipping ensuing details, I was asked to leave the premises.

Several weeks later, I returned to the site and noticed the rotor being lifted onto a transport carrier. It was being returned to the maintenance shop, because the shaft was "vibrating" during start-up!

Regards, Phil Corso

 

Dear Kasun

may i know the report of the below said problem at your site, what are the solutions provided to overcome the issue at your site.

Your earlier query

> We run a 60MW range steam turbine generator which is having closed air cooling system. This machine has a high
> shaft vibration problem that is occurring when high reactive power is transferred. Due to this problem,
> maximum reactive power that can be transferred to the system was gradually reduced with time. This issue is
> occurring only at the generator shaft, but not at generator bearings. Can anyone tell me the issues for this problem???