High Vibration Problem in 125 mw KN Series Steam Turbine

Something broke/shifted/whatever and it is now out of balance?

Machine is hot and on barring gear.So inspection can not be done.

Please explain why this problem is being offered to an bunch of anonymous strangers from all over the planet, and not to the turbine's original manufacturer, which is the correct place for it?

Hopefully it's your bearings and not an out of round turbine shaft. Neither one of those things will necessarily affect bearing temp, oil temp, or oil pressure.

It sounds like you're saying that 3 sets of bearings are showing high vibration. That's not a good sign.

We get so many complaints about vibrations, it seems like it would be easier to buy a new turbine, and purchase the extended warranty.

One of the squirrels that's turning the wheel has a broken leg.

Is it a new installation and you are rolling the turbine for the first time? At higher speeds, vibration may be high due to unbalance but high vibration at barring speed is beyond my understanding. Are you sure, the vibration probes are ok? Have you taken casing vibration with accelerometers? Have these values also gone on the higher side? Pl send the orbit, polar plot, shaft centerline plot and spectrum at .... It is not that easy to predict the cause without knowing the sequence of events and alot about the machine.

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Probes are checked and found correct only.Bearing housing vibrations are 0 at barring speed 123 rpm.Only shaft vibrations are high(150 microns p-p) at barring speed.

First you need to let us know if you are starting up after a major inspection or if new installation or it just occurred. In all instances it sounds like you rolled the unit for too long of a period at 3000 rpms and overheated the unit and got into a packing rub. If the vibration started and then increased drastically, it is a packing rub. If you had decreased the speed to 1000 rpms prior to it reaching trip limits you would have seen the vibration decrease to normal and then you could have went back to 3000 rpms. The other question I have is why were you setting at 3000 rpms for that long of a time.

This was new installation and machine was rolled first time.machine was at 3000 foe electrical testing.Vibrations were incresed very quickly and we had no time to reduce speed.

If it's new why are you asking here?

Tell the manufacturer to get it working to an acceptable standard. I think that would be reasonable to ask for 125MW turbine, or am I unreasonable.

Since this was a new installation, I have another question. Does this unit have a gearbox between the driver and the driven equipment? Was it preassembled at the factory prior to installation, (already set on a skid for installation)? If it was then I can almost guarantee that it is an internal rub. I have seen this on many of this type of installations.

First roll of a new turbine and you're getting high vibration? Not a good sign.

Was the turbine inspected prior to installation? There could be any number of things wrong here, poor handling during shipping and unloading, blocking material still in shipping position, poor bearing alignment, poor foundation/grouting, etc.

During commissioning was the turbine rolled to check clearances, critical frequencies, expansion of the bearing supports, etc.? During startup was the proper heatsoak procedures followed, were critical frequencies passed through at the right rate during the roll, was the unit allowed to cool at the right rate, was the barring gear engaged at the proper times, was shaft bowing due to differential heating accounted for, etc.

If you don't have answers to all these easy questions, or don't know the terms, you better get a real commissioning engineer out there who does. While you're waiting for him to arrive I suggest that do an internal inspection of both the turbine and the generator to find out where the rubbing took place.

Inexperience was most likely the cause of your problems.

Misalignment - Inadequate allowance for thermal movement of turbine components.

Shaft droop - Inadequate "heat soak" time prior to startup.

Packing rub - Improper installation, component failure, ?

Water Droplets present in HP section inlet steam

Barring gear not fully disengaging

Have you checked the thrust detectors yet?