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KVAr and capacitance
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| colinstone@hotmail.com 2007-08-17, 5:25 pm |
| What is the difference??
I have a table that tells me that I need 3 x 55uF to correct the power
factor of a 5.5kW motor and www calculators come up with 3 KVAr??
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| Paul Hovnanian P.E. 2007-08-17, 5:25 pm |
| colinstone@hotmail.com wrote:
>
> What is the difference??
>
> I have a table that tells me that I need 3 x 55uF to correct the power
> factor of a 5.5kW motor and www calculators come up with 3 KVAr??
At 220V 3ph 60 Hz, 3 55µF capacitors will draw 3 KVAr.
--
Paul Hovnanian mailto:Paul@Hovnanian.com
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On a clear desk, you can sleep forever.
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| colinstone@hotmail.com 2007-08-17, 5:25 pm |
| > > I have a table that tells me that I need 3 x 55uF to correct the power
>
> At 220V 3ph 60 Hz, 3 55=B5F capacitors will draw 3 KVAr.
>
Thanks - and at 400v 50Hz - UK 3 phase??
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| daestrom 2007-08-17, 8:25 pm |
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<colinstone@hotmail.com> wrote in message
news:1187385539.909839.213840@o80g2000hse.googlegroups.com...
>
> At 220V 3ph 60 Hz, 3 55µF capacitors will draw 3 KVAr.
>
*>Thanks - and at 400v 50Hz - UK 3 phase??
Xc = 1/(2*pi*F*C) = 1/(2*3.14*50*55e-6)= 57.9 ohms
Placed across line-line of 400V, Ir=400V/57.9ohms = 6.91 amps
VAR = 400V*6.91A * 3 = 8.29 KVAR
So you see the trouble with pf correction is you have to know how many VAR
you need to correct the motor and then figure out the capacitance needed to
'generate' that VAR based on Voltage and frequency.
daestrom
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