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Discussion Starter · #1 · (Edited)
Greetings Forum
I have a 250Kva genset that malfunctioned and my service contractor found some problems, including the shaft was way out of true. Does anyone know the typical tolerance % for this. I know this shaft should be 100% but does anyone know the ISO or NEMA design standard which these units are typically designed too?

What would be the typical damage from this alignment problem?

I appreciate your input in advance.
Thanks
 

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What would be the typical damage from this alignment problem?
Anything from a minor seal leak to braking the crankshaft at the rear journal.
Is this a direct mount with flex plate's, a close coupled two bearing, or some type of stub shaft/coupling device?
No matter what the coupling on anything over 50KW, you should drop the engine pan (resip's only) and check the crankshaft deflection, with the correct dial indicator system. Every engine mfg will list that spec or you can call them and get it. If the person that answers does not know what your talking about, bypass them and get to someone that Knows engines.


Many times if the crankshaft brakes from excessive deflection, it will wipe out the cranks line bore as well, which is very costly to correct, not counting the down time and maybe a rental machine as well.
Do it right from the gate, and be done with it. Face run out first, then lateral second, end play third, and deflection last. If all are within spec (I always shot for and corrected to mid spec myself) you will never have an issue.

Hope this helps.
Kenneth
 

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Discussion Starter · #3 ·
Thanks Kenneth
I appreciate it. I had it dialed and it shows 14/1000 out of alignment. Now my output voltage is way out of wack, Ive got broken magnets all over the place, and my irregular wear on my exciter/alternator. I'm not sure if just replacing the PME assembly is going to do it. Any recommendations to be sure I get this thing back up to full reliable performance for the long term?
 

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Who made the generator? By you saying PME I am assuming you meant PMG which has a permanent magnet exciter for open loop power, to the voltage reg, is that correct?
Is the runout your talking about at the drive end or the exciter end? If exciter end, have you checked the rear bearing and the clearance between the rotating fields and stator?

On the drive end you are allowed 0.00025-0.0005 per inch of diameter, be it lateral or face. If it has thrown the magnets out most of the time there will be other damage.

Is this unit paralleled with the utility or another gen set? If so you could have a voltage reg droop issue, if with another genset or power factor control issue if your tying to the mains.

Kenneth
 

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Discussion Starter · #5 · (Edited)
You mentioned "you are allowed 0.00025-0.0005 per inch of diameter, be it lateral or face". Is this from a typical spec or from some manufacturing Standard?

The unit is stand-alone..No syncing to other generators.

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Don't think Generac makes a generator end that big, unless things have changed in the last few years sense I retired from EPG (Electrical Power Generation) They will put their name on it, but they did not make it. If the rotating rectifier is almost square and on the very end of the shaft outboard of the exciter, it most likely is a Marathon. Which is very good quality, Unless it is one of the units that are now made in China.

Where are you measuring the run out? If it threw the magnets it could have bent the shaft, which would require major repairs or replacement. I've seen a few chi-com units throw the magnets. Can you post photos of the exciter area?
 

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Forgot to add the run out numbers are ind stds which exceed many mfg'ers specs. Get much over them and then add a very minor balance issue and things will go south quicker than 0.3-0.5 LCD (1/3-1/2 Life Cycle Design)
 

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