UPS, Generator and POCO

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brandon2177k

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Not really an NEC issue, but here goes it. We installed large UPS in an IT room. The UPS is fed via 480/277 three phase, and the output is 208/120 three phase which feeds a 208/120 three phase 200A panel in the IT. This supplies power for all equipment in the IT room. The UPS will run fine off the POCO power, however, in the event of a power outage, when the Generator kicks on, the UPS will not accept generator power, and will run only on its batteries. The UPS calls for clockwise rotation, which has been verified from both sourced, POCO and generator, using a rotation meter. We believe the problem is that the POCO power and generator power are not in sync together, L1 Poco and L1 generator ans L2 and L3 of each separate paths, probably at the transfer switch. So you may actually have L1 POCO and L2 generator, L2 Poco and L1 Generator, and maybe L3 and L3 are the same. You could still read clockwise rotation from each but phases could be in a different order. We have a 480 volt disconnect on the line side of the UPS and plan to swap leads there, keeping clockwise rotation, but hopefully syncronizing POCO and generator power. Hope that all makes sense! Anyone ever run into this problem before or have any suggestions??
 
Is the ATS sw. a "make before break: or a "break before make"? I have seen a UPS not accept power from a Generator before in a "break before make" senario. It was do to the Generator not suppling clean enough power. The ATS would not transfer because of this. Some UPS's have setting that can be adjusted to meet the output power of the Generator. Good Luck! Work Safe!
 
Brandon,

This is just an opinion,I think your problem lyes eleswhere. Most likely in the

ups paramitars such as high/low voltage cut out points,like I said JMO.

Just for goofs,I tried to keep CW rotation and swap phases around,using

your example, and I couldn't get to match!!
 
We had the same problem when we installed our genset. The ups would not snyc with the genset and would shut down. It almost became an allout brawl between the genset folks and ups folks. After much tweaking and reprograming of the ups, it worked in the test mode.
Power has never been lost long enought to see if it still works!
Based on what I saw for several weeks, I would think it might be the ups.
 
Thanks for the replies. I'm not sure of the rating of the UPS. I do know that the output load of the UPS on any one phase is no more than 15 Amps, at this point. Great article too, definantly some food for thought.
 
Brandon
We have found that UPS units require larger generator units than normal for the load. Most UPS units produce line side electrical "dirt" that must be absorbed and overcome by the power source. Most utility transformers can overcome this problem, but most generator heads are much smaller than their utility transformer counterparts. If you are not able to adjust the sensitivity settings of the UPS enough to allow the generator power to be accepted, then you may need a larger generator alternator. Here where I work, we have never been unable to fix the problem with UPS sensitivity adjustments. But our generator suppliers have told us multiple horror stories of their bad experiences with UPS units. They always end up having to supply a larger generator or at least a larger sized alternator.
Good luck!
 
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