Electrical System Redundancy
- Thread starter gregdzip
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D
dewd
N stands for needed. If it takes 2 generators for needed back-up, N+1 would be 3 generators. Similarly, 2N would be 4 generators.
D
dewd
Uhhh... If your question is what the definition of those things are, there is nothing more to it. If you want to know how to apply that definition to a data center installation, I suggest you contact a qualified electrical engineer or read one of the thousands of articles written on the subject.
G
grover
That's pretty much to it. N is defined as the number of (whatever) you need to run the site. If you have a 300kWload and use 200kW generators, you need 2 generators running to carry the load and N=2. It's all written alegbraically, nothing tricky about it.
Note that this refers generally only to the generators and UPS, and not to the switchboards, as N+x generators often tie back into a single switchboard.
Personally, I don't like anything less than N+2 for critical loads- allows 1 down for maint (scheduled or not) with N+1 running to allow for failure. Gives a nice comfort buffer for unplanned growth, too! At least for generators- UPSs not so much, as you can always run the generators while one of the UPSs is down for maint. NEC only requires N+0 generators for emergency power though... boggles the mind
Note that this refers generally only to the generators and UPS, and not to the switchboards, as N+x generators often tie back into a single switchboard.
Personally, I don't like anything less than N+2 for critical loads- allows 1 down for maint (scheduled or not) with N+1 running to allow for failure. Gives a nice comfort buffer for unplanned growth, too! At least for generators- UPSs not so much, as you can always run the generators while one of the UPSs is down for maint. NEC only requires N+0 generators for emergency power though... boggles the mind
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T
twada
T
twada
Check www.apc.com
G
grover
APC's Symettra series doesn't really do true N+ redundancy, though, they have a quasi-internal redundancy which does offer redundancy, but not in the conventional sense. It offers some advantages at a reduced cost, but lacks some of the advantages of a true N+1 system; namely that you can secure one half of a parallel-redundant UPS for maint while the other assumes the load. They have some excellent white-papers on their website though.
N+1 UPS and N+2 Generators are generally sufficient for tier-4 quality power. Ideally, N is as small as possible, generally 1 unless your datacenter is so ginormous you can't find one large enough.
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