Tek-Tips is the largest IT community on the Internet today!

Members share and learn making Tek-Tips Forums the best source of peer-reviewed technical information on the Internet!

  • Congratulations strongm on being selected by the Tek-Tips community for having the most helpful posts in the forums last week. Way to Go!

Strange problem with Geny/UPS setup

Status
Not open for further replies.

progless

Technical User
Oct 22, 2007
39
US
Hi pros,

I'm trying to figure out a problem I'm having with the following setup. I can't seem to find out if it's the geny or the UPS at fault. Here's the setup.

I have a 12KW Generac 4456 unit. It is dedicated to powering a Powerware Plus 12/12 UPS.

The UPS has about 5Kva load on it. It's output is around 40AMPS.
I have the UPS set to +/-3Hz fluctuation for testing. The range can be 1 to 3. The 3 setting is not a good idea, but I have it for testing only.

Powerware tells me that the generator cannot power this UPS, or at least, is having a problem syncing up to it as it's power source when the utility kicks out. When the utility kicks out, the UPS, which has at most, 2 minutes of backup battery power, goes to it's batteries until the geny kicks in about 30 seconds later.

For about 10 minutes or so, the UPS keeps trying to sycn with the geny, lasts a few seconds, then goes to it's batteries. Oddly enough, it lasts long enough on the geny to actually charge the batteries a little, hence the reason that my testing seems to last up to about 10 minutes.

The UPS keeps going back to it's batteries displaying that it is using it's inverter. The UPS folks tell me that it's the genys faullt yet it seems to keep the UPS going for longer than it's batteries could possibly do on their own.

The UPS folks are also telling me I should double the size of the geny for this UPS load. I feel they are wrong since the geny does seem to be able to power the UPS, and the problem appears to be that the UPS does not seem to be able to sync to the geny.

So, I've looked at both sides as well as I can.
I've set the UPS to +/-3Hz in the hopes that it might sync to the geny.
I've followed the manual for the geny as best I could to set it up and am not clear on some things.

The manual says that I need to have 63/63.5Hz output with no load. I can't seem to get it any better than 62/63 but I've not yet touched the governor setting which I guess could give me that extra bit I need.

I also set the voltage as close to the manual suggestions by removing the panel and adjusting the small potentiometer on one of the modules. I can't seem to get it to the right settings.

Also, and this is the weirdest part. Once I set all these things up, I tested it's output again to be sure and it was stable, fluctuating around 62/63Hz. I then cut the utility and allowed the geny to power the UPS without a load on it and for some darn reason, the Hz setting was 130Hz or so. Made no sense to me at all. Since then, I've been rather confused so wanted to ask the folks who work on these things more than I do :).

Sorry for the long message, just wanted to give all the info I could.

Mike
 
Hi,

The problem you are having is a sycronisation fault between the the UPS rectifier and alternator of the generator what is happening is that the UPS it partially sycronising with the Gen supply and then losing it again. This is why you are getting the extra minutes from your tests the rectifier is running the battery charger and it is charging the batteries.
The real problem is that the switch mode power supply of the rectifier is distorting the generated sinewave from the generator this is called harmonic distortion and the usual way to get round this is by oversizing the generator by the ratio 1:3. I think the solution would be either use a smaller UPS 6KVA or use a bigger generator 20KVA.

In effect the UPS is distorting its own input.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor

Back
Top