KVA calculation

Discussion in 'Electricians' Talk' started by Bewlec, Oct 24, 2013.

  1. Bewlec

    Bewlec Member

    What would be the total KVA for a commercial premise with a 3 phase supply
    I have worked the total current required, which would be 300 amps (72kw in total circuits and appliances,) this includes two fryers 1 at 22kw 1 at 24kw and other cooking appliances.
    Last edited: Oct 24, 2013
  2. Caddy

    Caddy Active Member

    its about 210KVA @ 400V..

    I assume that you got to the 300A Figure with 72KW worth of appliances + Other circuits? I only ask becuase 72 Kw 3 phase is only around 120A
  3. Lectrician

    Lectrician Screwfix Select

    I make it 104 Amp per phase.
  4. Caddy

    Caddy Active Member

    Sorry Lectrician i'm missing something. What do you make to be 104A per phase?
  5. Lectrician

    Lectrician Screwfix Select

    You say 72kw is 120A. I make it 104A.
  6. Bewlec

    Bewlec Member

    my workings out are based on the follwing rating of appliances
    1x fryer 24kw
    1x fryer 22kw
    1 x griddle 6kw
    1 x water heater 3kw
    1 x coffee/grinder machine 5kw
    plus other kitchen type appliances.
    also
    2 x ring circuits
    1 x cooker circuit (30amp)
    1x lighting circuit (2o x 2' grid light flourescents)
    three convector heater at 2kw

    After diversity was applied I had just under 300 amps (100 amps per phase) which I belive equals to around 72kw
    Last edited: Oct 24, 2013
  7. Lectrician

    Lectrician Screwfix Select

    Those fryers seem large. Are they the type with several baskets? Are you sure that's correct?

    Your question: "what would be the total KVA for a commercial premises?"

    That depends on what is there!

    For WPD, it is usual to see a standard supply of 80amp per phase (55KVa).
    WPD will also supply 100amp per phase via a larger head with standard metering.
    Above this is CT metering, and could be 150/160, 200, 250, 300, 500, 630, 800.

    Have you seen the site? Have you seen the incomer? You need to ask for the "Agreed Capacity" or "Agreed Maximum Demand" from the supplier or DNO.
  8. Caddy

    Caddy Active Member

    Thats because it is 104A I had worked it out on 82KW rather then the 72KW
    Lectrician likes this.
  9. Bewlec

    Bewlec Member

    what formula did you use to get your result
  10. Bewlec

    Bewlec Member

    one of the fryers is a lincat twin basket model OE7108 and the spec sheet says 22Kw (31.8amps per phase)
    http://www.lincat.co.uk/products/type/category/free-standing2

    Also how are you working your KVA value out (which formula)
  11. Caddy

    Caddy Active Member

    For single phase

    S(kVA) = I(A)× V(V)/ 1000

    The apparent power S in kilovolt-amps is equal to current I in amps, times the voltage V in volts, divided by 1000:

    Three Phase

    S(kVA) = 3 × I(A)× VL-L(V)/ 1000

    The apparent power S in kilovolt-amps (with balanced loads) is equal to square root of 3 times the current I in amps, times the line to line voltage VL-L in volts, divided by 1000:
  12. Lectrician

    Lectrician Screwfix Select

    The simplest way for three phase:

    72000 devided by 3, devided by 230.
    (72000 / 3) / 230 = 104.35A
    The DNO's will work it out this way too.

    OR, the correct way (but longer winded):

    72000 / (3 * 400) = 103.92A



    That linkat model can be connect in two ways - three phase (31.8amp per phase) or two single phases (47.8amp per phase). If you have three phase, obviously the three phase connection would be the one you choose.
    Do you actually know the size of the supply on the site?
    Last edited: Oct 26, 2013
  13. Caddy

    Caddy Active Member

    Bewlec was asking how to calculate KVA. Which in this case would be

    S(kVA) = 3 × I(A)× VL-L(V)/ 1000

    1.73 x 300 x 400 / 1000 = 207 KVA
  14. Lectrician

    Lectrician Screwfix Select

    He also said: "what formula did you use to get your result".

    And as he had the KVA, and was looking for amps, you were going the wrong away (although I'm sure he can transpose the formulae).

    When working out max demands, it makes sense to do it the same way the DNO do.
  15. Caddy

    Caddy Active Member

    Thats the question I responded to with the KVA Calculation.. Since his Original question was how to caculate 3 phase KVA from a 300A Supply. But regardless I think his working is a little out to start with as he said a total loading of 300A (72KW) on a 3 phase supply.

    To start with 72kW 3 phase would only be 104A as you correctly corrected my mistake of 120A. It would be some 315A single phase but then that's unlikely to be the case. so really if he wants a 72kW loading over a 3 phase supply it would be a 75Kva ish supply.
  16. sinewave

    sinewave Screwfix Select

    Those are big feckin Fryers OP??

    I'd double check that!
  17. Lectrician

    Lectrician Screwfix Select

    They do do em that big Sine, and larger too. Linkat is pretty defacto these days. The link does show the ratings.
  18. sinewave

    sinewave Screwfix Select

    TBH we don't have a lot to do with Retail premises, so not that genned up on Maccy Dee gear!

    Now if we're talking Air-handling units or VRF A/C units......................................... :D
  19. Lectrician

    Lectrician Screwfix Select

    Rare to see them installed this size, its usually gas. Where gas is unavailable, it's a toss up between lecky and bottled/tanked gas.
  20. Bewlec

    Bewlec Member

    Thanks lads for your replies. there is three phase in the property but this is split over three floors (1 phase used per floor), All were office space (2 floors still are) The customer wants to make the ground floor into a cafe so a new three phase board will have to be installed, but not sure if existing supply cable will be sufficient , due to around 250-300 amps extra due to the equipment she is looking at. I could not beleive the power rating of some of the equipment (ie 22KW Fryer)

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