UPS Rating
UPS Rating
(OP)
Hi,
I have a 3phase 208V 15KVA ups rated for 0.8 p.f. This is an older unit (1994) and the manfacturer was bought out by another company and I am unable to get any support on it.
Does this rating mean I can supply a 0.8 PF load up to 15KVA and a 1.0 PF load up to 12KW? I'm assuming that the unit is only rated to supply 12KW of real power and anything above that could lead to overheating.
I have a 3phase 208V 15KVA ups rated for 0.8 p.f. This is an older unit (1994) and the manfacturer was bought out by another company and I am unable to get any support on it.
Does this rating mean I can supply a 0.8 PF load up to 15KVA and a 1.0 PF load up to 12KW? I'm assuming that the unit is only rated to supply 12KW of real power and anything above that could lead to overheating.






RE: UPS Rating
RE: UPS Rating
Who is the manufacturer? There have been a lot of buyouts but most of the companies will support the legacy products. Often it is little more than a rebranding exercise when the original company gets absorbed by the multinational.
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Sometimes I only open my mouth to swap feet...
RE: UPS Rating
For a UPS it is possible that it may handle 15 KVA at 100% PF, but have commutation problems with a load of any magnitude at less than 80% PF. The implications of poor power factor, and the supply of real power are quite different between generators and UPSs.
The KVA rating of a generator is determined by the maximum allowable current times the rated voltage(over 1000). It is the limit of acceptable heating. The KW rating is limited by the available power of the prime mover. If the prime mover is over powered, it can safely deliver KWs equal to rated KVAs into a unity power factor load.
I'm hoping for more comments here. I may be on the verge of learning something new.
respectfully
RE: UPS Rating
waross - I'm not sure I'm understanding your statement "the supply of real power are quite different between generators and UPSs." Are you saying the main difference is due to the commutation problems? I agree with your comments about generators. Additionally, generators have a power factor capability curve which takes into effect stator and rotor heating effects.
RE: UPS Rating
Example;
A three phase set rerated for single phase:
3 PH. 1 PH
75 KVA 50 KVA
PF 0.8 PF 1.0
60 KW 50 KW
The prime mover has enough power to supply 60 KW, whether on three phase or single phase. The alternator can only safely supply 50 KW on single phase.
In a UPS, the real power output is dependent on the allowable discharge rate of the batteries. The other components are current limited.
This is the basis of my comments regarding real power from a generator versus a UPS.
There are others on this forum who are better qualified than I to comment on commutation issues with a poor power factor.
I hope to hear from them soon.
respectfully
RE: UPS Rating
Crest factor is something which is definitely worth looking at if the UPS will be working at the top end of its capacity. A CF lower than 3 would set alarm bells ringing for me - if the UPS can't deliver the high peak current which typically occurs just before the voltage crest then the voltage distorts.
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Sometimes I only open my mouth to swap feet...