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UPS Failure on Generator Switching

09/05/2008 2:10 AM

We have a UPS (1ph, 120V) connected to a back up generator through an ATS. The UPS has operated normally on commercial power for a long time but on 2 occasions, when UPS switched to generator power it failed and encountered an internal fault, that required the unit to be sent back to the manufacturer for repair. On a generator load test run we checked the generator voltage before switching the UPS, found it normal and still the UPS encountered Fault. We are presently working out with the UPS supplier to investigate cause. The generator is 25KW 3ph 208/120V parallel wye, would grounding the neutral help?

Any feedback from similar experience will be appreciated.

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#1

Re: UPS Failure on Generator Switching

09/05/2008 3:35 AM

Hello crvsam

You have not advised the Make/Model of your UPS, which would need to be known before a proper answer could be given.

Does the UPS have an "always-on with brownout/over-voltage filter network" before supplying the battery bank and inverter unit?

Cheaper UPS units are just that, you don't get the useful extra protection.

Please reply, with

Kind Regards....

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#2
In reply to #1

Re: UPS Failure on Generator Switching

09/05/2008 4:13 AM
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#3
In reply to #2

Re: UPS Failure on Generator Switching

09/05/2008 5:45 AM

Hello Kilgore Trout

from me

Excellent reference paper.

Kind Regards....

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#4
In reply to #3

Re: UPS Failure on Generator Switching

09/05/2008 11:47 AM

We have been looking into getting a back-up gen set for a remote location that loses power regularly and has a computer system that needs to stay running--My master has exclaimed that gen-sets are no good for that--at least small ones. We ran ones as small as 20kw on the boats I fished on and never had any problems, so I don't know what size the problems with UPS and computers begin and end and have never seen it myself--But I believe it. I always had the feeling that they were heartier than this as we would lose and gain time and need to adjust the frequency setting and it was always changing with the load--True happy mediums, there.

Anywhoooo, Thanks Sparkstation!

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#5
In reply to #2

Re: UPS Failure on Generator Switching

09/05/2008 12:57 PM

Thanks for a good ref.

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#12
In reply to #2

Re: UPS Failure on Generator Switching

09/22/2008 2:35 AM

Thanks for the Cummins literature.

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#6
In reply to #1

Re: UPS Failure on Generator Switching

09/06/2008 1:31 AM

have you already check the Frequency from the generator? I think may be the freq from the generator, but also possible that the THD(total harmonic distirtion) cause your UPS fail

Thank's

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#11
In reply to #1

Re: UPS Failure on Generator Switching

09/22/2008 2:26 AM

Thanks for your reply Sparky.

Sorry I was not able to reply to you earlier as I was out for 2 weeks and was not able to access my emails.

Yes, our UPS has an EMI Filter before the battery bank and inverter unit.

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#7

Re: UPS Failure on Generator Switching

09/06/2008 3:20 AM

It is a synchronising problem between UPS oputput voltage and Generator output voltage. Voltage and Frequency of both the supplies may not be matching( i.e not within tolerences permitted by UPS manufacturer). Synchronising circuit in UPS ( synchronising card) may be faulty. Please check voltage and and frequency of generator also.

Regards

Bhushan

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#9
In reply to #7

Re: UPS Failure on Generator Switching

09/12/2008 11:05 PM
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#14
In reply to #7

Re: UPS Failure on Generator Switching

09/22/2008 2:45 AM

Appreciate your reply.

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#8

Re: UPS Failure on Generator Switching

09/06/2008 4:01 PM

Hi all,

The excellent reference fished out by Kilgore trout (sorry!) actually doesn't address the problem faced by CRVSAM. He (states that he) has a failure on the UPS after being connected to the generator. If this is so then feedback from the manufacturer about which circuit component has failed will give a much better idea of the root cause.

I would have thought that with a wye configuration it would be mandatory to ground the neutral. If the generator set or one of it's other loads has an earth leak then the result will be that L-N voltages on the other phases will be higher. If the UPS is connected to one of these then is the 208V causing an input circuit failure?

in the words of Sparky " a little more feedback"

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#10
In reply to #8

Re: UPS Failure on Generator Switching

09/13/2008 12:15 AM

No problem--I don't know why(still) there are issues with(small) generators and UPS systems--I have heard(not seen) that there are. We have more UPS failures than I care to deal with, when they are supplied by utilities--Usually we find space heaters and other elective feet warming apparatus plugged into them under office personnels' desks.

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#13
In reply to #8

Re: UPS Failure on Generator Switching

09/22/2008 2:44 AM

We have returned the defective unit to the UPS manufacturer and still waiting for feedback.

On the generator side, yes we too are confused why the generator supplier did not ground the neutral. We were advised that it was their standard connection (neutral with out grounding). The UPS is connected to a leg (120V) of the generator through an ATS.

We are suspecting this to be a cause as we are getting a neutral to ground voltage.

Thanks for your feedback.

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Anonymous Poster
#15
In reply to #13

Re: UPS Failure on Generator Switching

01/24/2010 12:26 PM

Hello crvsam,

do you mind updating us on the status of this issue.

typically when we've come across such problems it's because the UPS has a very small tolerance window for their input frequencies. tweaking the generator governor typically solves this issue.

appreciate some feedback!

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Anonymous Poster (4); bhushan (1); crvsam (4); Kilgore Trout (3); nesubra (1); Sparkstation (2)

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