Hydroelectric Generators and Mechanical Vibrations

Use VDI 2056 as a guide line for allowable vibrations.

Use a vibrometer to measure the vibration. Vibration is generally measured on the pedestal or on the bearing housing.

The vibration analysis will give the reasons of vibration and possible solutions.
You better hire an expert.

I am not aware of vibration limits on hydroelectric Generators, but you must install vibration monitorng units for Generators of 50 MW rating. There are many supliers for such systems. one of the reputed supplier is Bentely Neveda. In their system they will suppply panel & vibration sensors (which are to be insttalled on terbine & Generator both). This system will continouslt monitor vibration levels & also gives alarm & trip commands. Perhaps supplier of vebration monitoring systems or Gen-set manufacturer can help you for setting of Alarm & Trip limints.

As suggested by other friend, you must hire agency for such job. Since this is special work & should be done by proffessional experts only not in house.

I am simply amazed that anyone comes here for an answer to such a question as it does not matter if we answer correctly or not (and how will the OP know what is correct or not mostly!).

He should be employing a person with that knowledge and qualification(s).....onsie etc etc.

Getting this sort of thing wrong could in an extreme case ruin machinery big time AND maybe kill somebody.....

Is it only me who get worried about what is going on today in India and other countries in that region??? (according to the style of names of CR4 posters anyway....)

You are right. I am also concerned. I also agree you can tell by the name often where the question comes from and the lack of engineering is scary. Here in the US we have wind generators from India and the blades are breaking.

You appear to be the one person on this blog who understands the REAL problem(s) here (Sadly typical for CR4). Many thanks.

Back in the mid eighties I was consulting to the Navy for a Gas Turbine company as the FSR and we were taught to use the Bently Navada TK80 analyzer. Unfortunately it was looking for known frequencies only, as set up in our guide lines for vibration analysis. The problem with the gas turbines at the time is that they were only lasting 2000 hrs before being sent to overhaul. These units were going from 0 to 22,500 RPM in 15 seconds. (generators) I was suspect of what was being called a normal baseline for the ship board installations, especially when I had found that the same gas turbine gen sets were being dropped out of Hercules air craft and lasting 20,000 hours. So against my bosses wishes I brought vibration analysis specialist from the dockyard in to do a full spectrum analysis. The end result was amazing and lead me to rewrite the installation and alignment procedures and manuals and gave lectures to navy and dockyard techs. Within 6 months the so called average normal baseline established 10 years prior, of the entire fleet was significantly dropped after only 1/3 of the turbines being analyzed and being realigned. My boss was pissed because they were no longer getting the many overhauls at a 1/4 of mil per unit. I resigned after that, but got letters of recommendations from the Department of National Defense which I still have. (What the heck I was looking for a job when I found that one.)

My point is that you should bring a specialist in and do a complete full spectrum analysis and establish a baseline and strive to improve it if possible. Your boss might like it.

"Andy Germany" I thought the point of this board was to give proper direction to those in need of answers. Why the snide remarks? "There are no stupid questions only stupid answers"

SAFETY SAFETY SAFETY......

Nothing more, nothing less......I get the impression you did not understand me in the slightest......

You asked a couple questions,

1. Yes there are reference's for vibration, but if you have no metering they don't matter either. For that size hydro-gen set you should be able to put a small coin on its edge and it should stay in place thru all start-run-stop.

2. Displacement of the rotor is the proper measurement, normally neasured in two axes and electronicly plotted to see any shaft out-of-round action.

3. 4. Did the vibration suddenly happen while the turbine was running ? look for broken shear pins on wicket gate stems to see if something is lodged in the turbine, either causing the vibration or the wicket gate is flopping causing the vibration or generator output cycling. Have you changed the load ? does the vibration remain constant at different loads ? Some turbine runners have a "do not run here" band that may take time to find, where there are vortex's in the draft tube, need more info to understand what you have. Sometimes if the trash rack is plugged the water flow will be non-laminar and will cause vibration.

That large a generator is on an oil film on babbit bearings, the generator rotor contacting the stator windings could cause a vibration.

Hydro units are balanced as an assembly, usually the balance weights are in the rotor, did something move ?

Is this a new installation or first start-up after a rebuild ?

5. The excitation has no effect on vibration. Unless you are turning it on-off rapidly, which wouldn't matter anymore by the time you read this.

There are lots of good vibration analysts around and they are not very expensive. Just ask for and check references. They typically have the equipment with them and your generator is not that mechanically complex. If you know the dimensions and weights of the rotating parts it should be easy to get the numbers you want as part of an analysis. I have seen bearings fail, shafts crack, concrete break and large steel structures fail from imbrittlement because production overruled common sense. Don't wait too long. A few hours downtime compared to months of construction should be an easy choice.

Interesting,

I have similar vibration problem in my mill which is on third floor.

Actually it is a mixer tank which is driven by geared motor with gear.

If I used belt drive for the same will it reduce vibration.

Please let me know.

If the vibration is due to the gear mesh, replacing them will generaly solve your issue. This could include belt drives if the belts will do it. The trick to finding out is to determine the frequency of the vibration and find out what produces it by converting the frequency to it's equivalent rpm. If the rpm matches any object's rotating frequency you've probably found your source. If its the gears, it will be at the gear's rotating frequency times the number of teeth on that gear. If the frequency is lower than all rotations in the mixer, the problem gets tougher. Let me know.

The initial questions to answer are:

1. Is this a new installation or an existing plant ?

2. Was the plant running without vibration and all of a sudden the vibrations started ?

This has quite a range and can even be a broken turbine, i.e. a broken blade or bucket fractured due to metal fatigue.

I hope you can appreciate the humor of some who have not walked in your path and craft your response accordingly.

Dear Sir,

Thankyou for your response.

The generator capacity is 55 MW, 11 KV terminal voltage, Hydo electric.

The machine is installed very recently and put it into service. The vibration of the machine at that time is below 100 micron during turbine operation. The vibration is increased when loaded. Now our problem is during maximum load the vibration of the machine is above 200 in the LGB Y axis

What is the possible cause of this problem.

Rgds

BRN

If x and y are horizontal axes and z is vertical.

A horizontal vibration at the generator rotor would be imbalance or a looseness in the rotor, unlikely to be a "soft foot" in the bearing spider, lack of dowels?, was this a rebuild or new installation ?, some rebuilds the concrete has had "growth" due to chemistry.

Does the temperature of the generator guide and turbine guide bearing significantly increase from low load to full load ? Is the temperature rise of both bearings similar ?

Thankyou for your comment

The machine is reinstalled one. I will check the variations of vibration and mail to u.

Rgds

BRN

By growth in the concrete, I mean that when the weight of the turbine and generator was removed during the rebuild, the concrete "breathed" moisture into fractures and a chemical reaction takes place causing the concrete to expand. At one hydro site on a 10MW unit the vertical growth in less then 6 months was 3/8 inch I was told.

Sometimes the hydro unit vertical alignment changes due to the powerhouse structure itself "tipping".

Was the turbine runner repaired or replaced during the rebuild ?

Do you "motor" the generator and check for vibration ?