3 phase power formula

E

erthlink

Guest
the three phase power formula goes like this:

V * I * 1.732 * PF

where V - voltage, I - current, PF - power factor

a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
at each phase.. PF is 0.8

which V value should i use? do i take the average current (I) or do i add
them up?
 
erthlink wrote:
the three phase power formula goes like this:

V * I * 1.732 * PF

where V - voltage, I - current, PF - power factor

a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
at each phase.. PF is 0.8

which V value should i use? do i take the average current (I) or do i add
them up?
Click to expand...
If the three currents listed are the 3 line to neutral currents (not
line to line current) then you just use the single phase formula 3
times and add the results. 120V*A*PF

--
John Popelish
 
which brings me to another question.. what am i measuring when i use a
clamp-on ammeter? am i correct in stating this equation then?

P = V[phase-ground] * ( I[phase1] + I[phase2] + I[phase3]) * PF * 1.732

assuming i have the same phase voltages across the board of course..

If the three currents listed are the 3 line to neutral currents (not
line to line current) then you just use the single phase formula 3
times and add the results. 120V*A*PF

--
John Popelish
Click to expand...
 
which brings me to another question.. what am i measuring when i use a
clamp-on ammeter? am i correct in stating this equation then?

P = V[phase-ground] * ( I[phase1] + I[phase2] + I[phase3]) * PF * 1.732

assuming i have the same phase voltages across the board of course..

If the three currents listed are the 3 line to neutral currents (not
line to line current) then you just use the single phase formula 3
times and add the results. 120V*A*PF

--
John Popelish
Click to expand...
 
Lord Erdel wrote:
which brings me to another question.. what am i measuring when i use a
clamp-on ammeter? am i correct in stating this equation then?
Click to expand...
You are measuring the line currents (the same as the line to neutral
load currents.)

) * PF * 1.732

assuming i have the same phase voltages across the board of course..
Click to expand...
The square root of 3 factor is needed only if you are multiplying the
line to line voltage (208 in this case) times the line current (clamp
on meter around one line), and assuming that all line currents are
equal (or are using an average of each of the line currents). The
1.73 factor takes into account the fact that each line current split
into two line to line loads and that those load voltages are phase
shifted with respect to the line current and that there are 3 loads
represented by a single voltage and current measurement.

If you use the phase to ground voltage, you effectively have 3
independent single phase sources so you just all 3 line voltage *
current products. The two methods give the same answer, because the
ratio of (line to line voltage)/(line to ground voltage)=1.732.

Do it both ways and you should come out with the same answer.

--
John Popelish
 
"erthlink" <chaosghost@earthlink.net> wrote in message
news:DHS_b.20461$hm4.5791@newsread3.news.atl.earthlink.net...
the three phase power formula goes like this:

V * I * 1.732 * PF

where V - voltage, I - current, PF - power factor

a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
at each phase.. PF is 0.8

which V value should i use? do i take the average current (I) or do i add
them up?

If the currents are the same in all 3 phases then use the line to line
Click to expand...
voltage (208V). Otherwise use 120*I*pf 3 times and add them up as John has
indicated. Actually using 208*1.732*24A*pf will probalby be close enough for
government work.

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer
 
On Wed, 25 Feb 2004 01:16:19 GMT erthlink <chaosghost@earthlink.net> wrote:

| the three phase power formula goes like this:
|
| V * I * 1.732 * PF
|
| where V - voltage, I - current, PF - power factor
|
| a 3 phase generator set to 120/208 V with amperage values of 24A, 26A, 22A
| at each phase.. PF is 0.8
|
| which V value should i use? do i take the average current (I) or do i add
| them up?

Is that 0.8 PF the rating of the generator, or the actual load?

--
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| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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