Add individual phase kw or kva to get total

[Wireit]

I am working on a problem regarding a 208/120 volt wye 3phase panel in which I have the data showing the individual kw per phase. Can I add all three phases and get the total kw for the panel?

I am also applying the power factor to the kw in order to get the kva, once I have that number can I add all three of those phases to get the kva on the panel?

Example:
phase A=6.0kw
phase B=7.0kw
phase C=8.0kw
Total kW=21.0kW
PF .97
Total kVA=21.64 (Is this the total kVA for the panel?)

 

[charlie b]

Yes, it works that way. However, I would not expect to have the same power factor for each phase. I would expect to take the KW of each phase, divide it by the power factor for that phase, to get the KVA for each phase. Then you add the results to get total KVA.

 

[dbuckley]

Just a cautionary note; this approach does not necessarily work upstream; for example, if you have loads of 25/10/10 KVA, total load is 45KVA, so you may assume you could use a 50KVA supply transformer, but you cant, as the 50KVA transformer can only do (gets calculator...) about 16KVA per phase. In this scenario one phase would be overloaded, and thus although the transformer as a whole is not overloaded, and wont overheat, the wire that comprises one of the three windings is significantly overloaded, and will get hot and fail prematurely. Of course, the transformer protection breakers/fuses should kick in and save the transformer well before bad things happen, but you'll still be replacing the tranny for a bigger one.

 

[charlie b]

. . . for example, if you have loads of 25/10/10 KVA. . . .

All true. And that is the reason that we share the duty of making sure the load is more nearly balanced among the phases.