UPS Failure on Generator Switching

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....

Thanks for a good ref.

Thanks for the Cummins literature.

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

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.

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

Appreciate your reply.

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"

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.

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.

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!