Silcon UPS - battery time expired?

[cctdiag]

I have had a recent situation where I have had a loss of mains and have been running on a single standby generator.
During a programmed switch of 1 of our 4 Silcon UPS systems the generator freq altered to such an extent all UPS modules went onto battery (supply freq out of tolerance). Our critical load can be spplied on batteries for about 15mins. We did manage to sort ourselves out with a few minuets to spsre, but i am not sure what would of happened if the battery capacity had run out (at approx 320v). Would it of switched to the out of spec supply without a break or shutdown with a total loss of supply? Any ideas.

Jeff

 

[mpparent]

I believe ups's typically have logic to determine if the source is "out of spec." If the source is not within tolerance, I believe in your case the UPS would dump the load, provided you lost battery. You can double check this with the equipment manufacturer.

 

[dydt]

The mains (utility or genset) and the inverter output of a UPS with static switch are synchronized. In this manner if you have an internal fault the bypass static switch kicks in uninterrupted to supply the critical load if it is within the specs. otherwise the battery will take over. Normally there is an alarm that tells you that you are on bypass and not on inveter.

If for example the genset output has an out of spec. frequency or a very low voltage during a mains failure, the UPS will react as if there is still a mains fault even if you are trying to connect on the genset manually via the static switch. Eventually, the battery will supply the load until it drains. But of course, there is a low battery indicator that gives you enough time to shut down your critical load safely and without loss of critical data. And once your loads are off, you can now shut down the UPS and wait for the utility supply restoration.

I hope this info will help you..

dydt

 

[cctdiag]

Thanks Guys for the input
They say 'lighting never strikes twice', but late last week we had the very same fault on our backup system but at a different site. I can cofirm by experience now that the UPS output breaker drops and you lose critical load.
We have altered the freq tolerance of the UPS from 0.5% to 2% to stop any further out of sync inhibits on freq, I guess we was running too tight.
The load was dropped because we are upgrading at the moment and were running our 2 x 320kva (paralleled system at 101% normally about 50% for redundancy purposes) and the batteries gave up immediately. Cost of down time? they are still trying to add it up. This was the last of 12 systems to be upgraded (total of 5.4MW of UPS thank god thats over)
Lets hope I have a job after the inquest.
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