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3 phase kVA to amps per phase query #137473
07/09/03 01:23 PM
07/09/03 01:23 PM
S
Steve|Uk  Offline OP
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Hi all. Call me noobie [Linked Image] Been reading for a few days, and like it.

Long story short, I'd like a refresher on how to ascertain the amps per phase if given a kVA / 3 phase rating.

For instance, an appliance is 75 kVA three phase. What is the current per phase ?

I've seen various (differing) answers on websites, which in turn give different results; Only one can be correct.

Would anyone be so kind as to refresh my memory - I'm due to start a job in industrial electrics; I've spent the last 15 years house bashing :-)

TIA

Steve|Uk

Test Equipment:
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Re: 3 phase kVA to amps per phase query #137474
07/09/03 02:11 PM
07/09/03 02:11 PM
C
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Welcome to ECN! I like your use of the | divider.

The kVA is the easy one:

current = VA/(phase-to-phase voltage x square root 3 )

or in another form

current = VA/(phase-to-neutral voltage x 3)

75kVA on a 230/400V system is

75000/(230 x 3)= 109 Amps


[This message has been edited by C-H (edited 07-09-2003).]

Re: 3 phase kVA to amps per phase query #137475
07/09/03 02:14 PM
07/09/03 02:14 PM
S
Steve|Uk  Offline OP
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Hi. Thanks for the welcome.

Yeah I did think it was that, but was getting all sorts of confuzzled input.

Just as you replied, I found this helpful page right here at electrical-contractor.net
https://www.electrical-contractor.net/ubb/Forum15/HTML/000043.html

I can see me liking this place [Linked Image]

Bye for now.

Steve

Re: 3 phase kVA to amps per phase query #137476
07/09/03 02:38 PM
07/09/03 02:38 PM
P
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Hi Steve, and welcome to ECN.

I see you've already gotten a really quick answer to your question so there's nothing I can add there.

I reckon the industrial side will be quite different to what you've been doing. I've not been inivolved in that side of the job either; I do mostly residential with just a little very light commercial from time to time. That being the case, even where 3ph supplies are involved it's mostly single-phase loads, so it's so easy to forget those forumlas if you're not using them regularly.

Re: 3 phase kVA to amps per phase query #137477
07/09/03 04:24 PM
07/09/03 04:24 PM
B
Bjarney  Offline
Moderator
Joined: Apr 2002
Posts: 2,527
West-Southern Inner-Northeast ...
For 400V 3ΓΈ, a rule of thumb is 1.4(4) amperes/kVA.

600V >> 1A/kVA
480V >> 1.2A/kVA
240V >> 2.4A/kVA
208V >> 2.8A/kVA

Re: 3 phase kVA to amps per phase query #137478
07/09/03 06:30 PM
07/09/03 06:30 PM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
Gidday there Steve,
Welcome along to ECN, mate!. [Linked Image]
The other guys have just stolen all the thunder out of this one, no worries though.

Re: 3 phase kVA to amps per phase query #137479
07/10/03 12:45 AM
07/10/03 12:45 AM
O
old Appy  Offline
Member
Joined: Mar 2001
Posts: 118
Auckland, New Zealand
Very easy to forget if you aint using it!! even when you have just learnt it all again.
CW

Re: 3 phase kVA to amps per phase query #137480
07/10/03 04:53 AM
07/10/03 04:53 AM
Trumpy  Offline

Member
Joined: Jul 2002
Posts: 8,231
SI,New Zealand
Appy,
You've got that right!. [Linked Image]
When I last went to do a Refresher Lines Course at the Power Board, we were ALL handed an exam paper, made up by one of the Inspectors, in things like 3P theory, Neutral Currents in Star systems, etc.
I had an OK time with it all, but some of the old Lineys, really kicked up a stink about it and they also failed miserably.
They thought that they were just there to wear some gloves and do a few Pole Top Rescues.
Was good to give the Grey matter a good work out though! [Linked Image]
[Steve, sorry about the threadjack!]

[This message has been edited by Trumpy (edited 07-10-2003).]

Re: 3 phase kVA to amps per phase query #137481
07/10/03 05:24 AM
07/10/03 05:24 AM
S
Steve|Uk  Offline OP
Member
Joined: Jul 2003
Posts: 18
Horley, Surrey, UK
Jack away!!!!

I've said it once, and I'll say it again. I think I'm going to like it here [Linked Image]

Steve

Re: 3 phase kVA to amps per phase query #137482
07/10/03 08:58 AM
07/10/03 08:58 AM
L
lyledunn  Offline
Member
Joined: Jun 2002
Posts: 159
N.Ireland
Remember, it is usual to mark plant such as generators and transformers in kva and plant which "consumes" energy in kw. Thus a piece of piece of equipment requiring 30 kw at a power factor of 0.5 would need to be fed from a source that could deal with the current associated with 60kva.


regards

lyle dunn
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