Load
Load
(OP)
Hi
I am doing a load survey for an office building for emergnency generator. The building is stuffed with computers and lot of unbalance as I can see when we measure current, here is an example:
Ia- 27.7 AMP
Ib- 9.25Amp
Ic- 15.25 Amp
120/208 V
I should go for load =Sqrt(3)* 208*27.7 cos(phi)
Now which current should I assume and what power factor .
One more thing to it, those duplex outlets, which are not being used right now, what load should I assign to them, as you know
each outlet is rated for (15 A, 120 V) and there are two receptacles in each outlet.
Thanks
I am doing a load survey for an office building for emergnency generator. The building is stuffed with computers and lot of unbalance as I can see when we measure current, here is an example:
Ia- 27.7 AMP
Ib- 9.25Amp
Ic- 15.25 Amp
120/208 V
I should go for load =Sqrt(3)* 208*27.7 cos(phi)
Now which current should I assume and what power factor .
One more thing to it, those duplex outlets, which are not being used right now, what load should I assign to them, as you know
each outlet is rated for (15 A, 120 V) and there are two receptacles in each outlet.
Thanks






RE: Load
power factor
displacement power factor
real, reactive and apparent powers...
harmonics up to the 50th...
Hope this helps
RE: Load
If you have unused receptacles, you could use 180VA (or some multiple of that you feel comfortable).
Add a fudge factor for future growth.
Generally don't plan to run the generator at 100%, 80% max is where I would consider.
RE: Load
I always ask to see the power bills for the last 6 or 12 months or more.
For a large building, they usually show maximum demand each month, as well a KVARHrs. which you can use to calculate power factor.
If you get lucky, more information may be available. In my area the utility is using electronic meters on more and more commercial buildings.
I had a building owner request a download of the meter history from the utility.
The utility sent a floppy disk with;
WHr
KVARHr
KW
KVA
KVAR
KW
PF
Volts "A" phase
Volts "B" phase
Volts "C" phase
Current "A" Phase
Current "B" Phase
Current "C" Phase
The readings were at 15 minute intervals for the last 7000 15 minute intervals.
Check to see what information is available from the office (old power bills) and the power utility.
RE: Load
I will procedd now with all the ideas and ask the client for billing and other details as suggested by you.
Before all this, based on your experiences,
what is the power factor of a lighting panel used for flourscent lighting. Please advise a value which I can consider.
What power factor should I consider for a panel hooked to a computer rooms.
Thanks
RE: Load
If the power factor is lower, in fact if it is lower than 90% you should be considering capacitors to avoid utility penalties on your power bill. This will also raise the power factor that the generator "Sees".
Remember, with computer loads, the neutral must be full size or larger.
RE: Load
When we have a 2 pole, 30 Amp breaker on a 120/208 V 3 phase 4 wire system , the power consumed by that load will be
This is what I think.= 30*208*cos(phi)
Am I correct?
Thanks
RE: Load
RE: Load
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Your body might be a temple. Mine is an amusement park...
RE: Load
I beleive , You guys missed my question:
What i want to know is is
the power formular ok or I am wrong:
as a 2 pole 30 Amp breaker has line to line voltage of 208 v and phase current of 30 A(Suppose it is )what will be the phase angle, between Ia or Ib as if the breaker for phase A and B.
The formula is V(Ph)I(Ph)cos (phi)
while I am using V(L-L)I(Ph)cos(phi).
Please advise now.
Regards
RE: Load
----------------------------------
Your body might be a temple. Mine is an amusement park...
RE: Load
Power factor is the cosign of the angle between the volts and the amps.
The volts will be 208 as you stated.
Another thing that is a little confusing is the 30 amp breaker. Use the actual amp draw of the load, not the breaker rating.
Use the power factor of the load, not the cosign of the phase angle between phases.
If the load is 22 amps at a power factor of .78 then the Watts are;
208 Volts x 22 Amps x .78 Power factor = 3569.28 Watts.
I agree completely with scottyUK on the power factor of the lights. I wanted to say the same thing but I didn't have the exact figures at hand.
Thanks scottyUK