KVA for installation

havo one · Apr 1, 2018

hi, being a bit rusty on my calculations i thought id ask.
I have to apply for alteration to supply as building is being extended.
the building was once 3 seperate buildings and over the years have become one. however there are 3 seperate supplies within which fed various parts of building. now with new extension the supply company has indicated they want to have one supply into building. thats fine as im rewiring the lot anyway. my loading is aprox;
heating/aircon 3ph: 147kw
heating/aircon 1ph: 10kw
lighting : 5kw
E7 : 9kw
instantaneous heat : 8kw
cooking : 40kw
water heating : 8kw
gaming machines : 60kw Total 287kw

I have applied 3% diversity to cooking and no other as installation operates virtually 24/7 /7 days.
I did apply a power factor of .9 as i didnt have any info on heating/air con.
so my calculation was KVA= square root of 3 x I x VL-L / 1000
KVA= 1.73 x 446 x 400 / 1000 = 308 KVA

I asked for this as 308kva total or 102kva per phase .

like i say im rusty on my calculations go easy on me. lol

plugsandsparks · Apr 1, 2018

Re - the a/c is that the output of the a/c units, or is it the electrical load as it is rather high. Also heating/ac is that the same thing or is there a separate heating system, if so what is the source, gas, oil ?

plugsandsparks · Apr 1, 2018

As these number are quite high, even for an industrial unit, it may be worth getting a sparkie to measure the real load you are taking, just in case you are adding up all the rating plates of the devices which will always give a spectacularly high reading and if you are on 3 phase for the new installation some calcs need to be done to see how well balanced you can make it.

havo one · Apr 1, 2018

the heating/air con units are the only source of heat for the building and yes ive just taken the plate ratings some of which are old and have a high rating of 21kw each . we have measured the current and at present am pulling 65/70 amps per phase. however i expect that to increase to aprox 120amps when new kitchen and extension is built. i know the supply company would give me 100A per phase supply but id rather make sure i get 125/150A supply

havo one · Apr 1, 2018

im just revising this.... if i want 130A per phase and work that out per phase (IxV/1000) = 30kva x 3 that would mean i ask for 90kva total supply.

but if i work it out at 390A total and work that out over 3 phases
(square root3 x I x vL-L/1000) i get 269kva so i ask for 90kva per phase supply...... this is where im getting mixed up!!!

plugsandsparks · Apr 1, 2018

Work out or measure the highest loaded phase current in amps and X 700 to get VA, divide by 1000 to get KVA. Its near enough for your purposes. 100A fuses get you a 70KVA supply, 200A fuses 140KVA etc.
As for a/c units the KW heating is the output and is roughly 3.5 times higher than the KW electricity usage. If you can get the manuals or specs for the a/c units it will give you the running current in amps.
cheers