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Topic Title: kVA - Amps, Three phase - Formula
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Created On: 02 October 2013 09:06 AM
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 02 October 2013 09:06 AM
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paultrimble

Posts: 19
Joined: 22 March 2008

Hi all

I have been asked to advise on supply conductor size for a sub distribution supply. The power I have been told is 10kVA, 400V.
I am used working with Kw power but not really for kVA.

Can someone clarify if my formula is correct please?

I(A) = 1000 × S(kVA) / (?3 × VL-L(V) )

Therefore - 1000 x 10kVA = 100000 / (1.732 x 210V)
= 27.49Amps?


This is where I get a little confused, if I transpose kVA to KW my result is different ; -
P(kW) = S(kVA) × PF
10*0.95 = 9.5kW

Therefore using formula for 400V kW - Amps I get 14.43Amps?

Hopefully that's not to confusing,

Cheers
Paul
 02 October 2013 09:07 AM
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paultrimble

Posts: 19
Joined: 22 March 2008

Just noticed a typo - 10000 not 100000
 02 October 2013 09:59 AM
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AJJewsbury

Posts: 11769
Joined: 13 August 2003

As a sanity check, I tend to think about it the other way around - 10kVA from a 400/230V 3-phase supply is the same as three 3.33 kVA single phase loads - so 14.49A per phase (at 230V).

- Andy.
 02 October 2013 10:03 AM
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paultrimble

Posts: 19
Joined: 22 March 2008

Cheers Andy, I noticed I used 210 line voltage instead of 400V for some daft reason

Your reasoning makes perfect sense
 02 October 2013 11:04 AM
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Parsley

Posts: 1090
Joined: 04 November 2004

I divide KVA/692 if using 400V (1.73 x 400) and by 718 (1.73x 415)for 415V to get current.

10000/692 =14.45A

Regards
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