redudant UPS in data center

[gabeNC]

Howdy gents,

Sorry about the long post and hopefully I can articulate the issue.

Just wonder if anybody here has experience with large UPS's in data centers. We've been having a discussion / argument about what happens when redundant power supplies fail. Ideally we would want the load evenly distributed across each UPS in the event of either a loss of power at the power supply, PDU or a UPS. (In the event of commercial power loss, a generator will be online within a couple of minutes).

so the question is... does power on a redundant power supply split across both (load balanced) or a hot standby? If it is considered a hot standby i would imagine there would be at least some current draw on the secondary so there would not be a noticeable hic-up. One idea I had was to put one of those "kill-a-watt" meters and measure each PSU. (shrug).

The next question is that if one UPS was to fail would the other one's load double? My fear is that if one died, the other one could not sustain the entire load. I guess the answer to this question probably lies within the answer of the first one.


thanks!

 

[smanches]

You are correct, it all depends on if they are both active or one is failover.

Is the datacenter big enough for DC UPS's? Those are cool.

 

[gabeNC]

I guess "big" is relative. But I've had no complaints so far... oohh you're talking about the data center. oops.

Seriously though...

I wouldn't consider it big compared to banks (they are friggin huge), but it's effective and the servers are managed well. Years ago, I think size used to be considered in square footage but with all the virtualization you can do now, a DC with alot of "computers" doesn't need to be a huge building anymore. We've got 40+ lpars (AIX partition, independent O/S) running on a 16 way box with 256GB of ram. All that in half a rack. Now add a bunch more racks, 80TB sans, a robotic tape library, wintel racks etc.

Someone on my team has taken over the management of our DC after the previous guy got sacked. We've found all kinds of wiring issues, PDU's daisy chained instead of direct runs to circuit breakers, poor record keeping etc. We are suspecting that at least two of the UPS's have been oversubscribed.

 

[OutToLunch]

from what i recall, redundancy in the UPS world isn't really true redundancy. true redundancy would mean you have twice the UPS you need so that if UPS1 fails UPS2 can take the entire load. UPS redundancy is viewed in terms of modules that can support the load in a distributed manner such that if n modules can service the load you would install (n+1) or (n+2) modules so that if a single module were to fail, the technician would come in with a new module and hot swap it with the failed module so the load is protected at all times with at least n modules.

 

[Chippie]

true redundancy would mean you have twice the UPS you need so that if UPS1 fails UPS2 can take the entire load. UPS redundancy is viewed in terms of modules that can support the load in a distributed manner such that if n modules can service the load you would install (n+1) or (n+2) modules so that if a single module were to fail, the technician would come in with a new module and hot swap it with the failed module so the load is protected at all times with at least n modules.

Agreed, and that is what we have where I work...We have a 110v ac system that has 2 invertors; 1 duty, other standby....Maintenace can be carried out on the standby without affecting availability...

 

[Leftyretro]

The UPS installations for control house use in process plants in the refinery I worked at were indeed 100% redundant. Takes a ton of money but here is the setup. Two UPS units were powered from seperate AC input power coming from seperate substation power (there were 4 substation power sources avalible to the refinery). Each UPS was sized to be able to handle 100% of the load if needed and normally sized to run around 25-30% load. Each UPS outputs wired to seperate 120vac distrubution panels and the control systems used power supplies designed to have two independent AC power sources and/or were using redundant DC power supplies (diode isolated) to power their circuitry). This setup allowed any given UPS to be taken out of service for normal PM or battery replacement without having to power any equipment down. These were continous type UPSs where the input ac was converted to DC and powered an output invertor, so that the batteries just floated on the DC buss. It all worked very well but did take a lot of money and floor space to implement. However when large plant outages can reach $1M a day it was justified.

Lefty

 

[gabeNC]

Sounds like some neat stuff Lefty, makes our stuff pale in comparison.

Had a meeting with the electrician today to educate us on the UPS config. Looks like we have 4 UPS boxes with 80kva capacity each. They are then paired up to provide redundancy across the entire floor. We need to keep the load under 50% on each pair in case of a lose of a UPS and I suppose ideally maybe around 40%.

So once again, you guys nailed the solution.