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| terryh@souzaconstruction.com 2007-08-15, 5:25 pm |
| OK...I know this is something I should know, but I don't. I have 4160
entering the site. I need a 480 3 phase at 200 amps, and a second
panel, 120/208 3 phase 125 amp.
How do I calcultae kVA on the 4160/480 xfmr? And how do I calculate
the kVa on the 480/208 xfmr?
| |
| Don Kelly 2007-08-16, 3:25 am |
| <terryh@souzaconstruction.com> wrote in message
news:1187216648.050103.163340@j4g2000prf.googlegroups.com...
> OK...I know this is something I should know, but I don't. I have 4160
> entering the site. I need a 480 3 phase at 200 amps, and a second
> panel, 120/208 3 phase 125 amp.
>
> How do I calcultae kVA on the 4160/480 xfmr? And how do I calculate
> the kVa on the 480/208 xfmr?
>
try volt-amps =voltage*current* root(3) in both cases.
1000volt-amps =1KVA
--
Don Kelly dhky@shawcross.ca
remove the X to answer
----------------------------
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|
|
> try volt-amps =voltage*current* root(3) in both cases.
> 1000volt-amps =1KVA
Huh?
Why the "root(3)?"
VA can be determine by taking each phase voltage to neutral and multiplying
by the current. If the phase currents are the same you just take one
current and multiply by 3.
>
> --
>
> Don Kelly dhky@shawcross.ca
> remove the X to answer
> ----------------------------
>
>
| |
| daestrom 2007-08-16, 5:25 pm |
|
<nni/gilmer@nni.com> wrote in message
news:tO2dnTyhwaOd0VnbnZ2dnUVZ_qmlnZ2d@nni.com...
>
>
>
> Huh?
>
> Why the "root(3)?"
>
> VA can be determine by taking each phase voltage to neutral and
> multiplying
> by the current. If the phase currents are the same you just take one
> current and multiply by 3.
>
If you have individual phase voltages and currents, that is perfectly true.
But if all you have is line-line voltage, then you'll find that phase
voltage is line-line/sqrt(3).
So...
3*Vphase*Iphase = 3*(Vline/sqrt(3))*Iphase = Vline*Iphase*sqrt(3)
That's for a wye connected load. You can do a similar calculation for
delta-connected loads but its the Iphase = Iline/sqrt(3)
daestrom
| |
| Don Kelly 2007-08-19, 8:25 pm |
| ----------------------------
<nni/gilmer@nni.com> wrote in message
news:tO2dnTyhwaOd0VnbnZ2dnUVZ_qmlnZ2d@nni.com...
>
>
>
> Huh?
>
> Why the "root(3)?"
>
> VA can be determine by taking each phase voltage to neutral and
> multiplying
> by the current. If the phase currents are the same you just take one
> current and multiply by 3.
>
I should have said root(3)* line voltage*line current
or 3*phase voltage* phase current
Both are valid for star or for delta.
Very often you only have access to 3 terminals so that only the line values
can be measured.
--
Don Kelly dhky@shawcross.ca
remove the X to answer
[color=darkred]
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