UPS Design Question

Dear,

Not exactly true for designing a system with all the equipments of same rating.

WE must consider the performance of each equipment individually to take up the full load of 40kva continuous without de rating. at max. ambient temp. / humidity / geographical height / nature of load .... inductive, heating, max. 3rd harmonics , continuous , etc...

Further, in cases of short circuits or over voltages, other equipments should not blow off along with the faulty one.

Isolator carries a high reactive currents , i.e. arcing currents. So, they will be derated more.

So, if you design accordingly,

When Inverter is of 40 kva, Transformer feeding to it will be 20% more. i.e. 48 kva

Making & breaking current duty selection, by pass Isolator shall be 50% more i.e. 60 kva

Normally we design as follows:

for 40 kVA load ,taking inverter efficiency to 90%, we select inverter of 40/.9=44.44, rounded off to 45 kVA, since the market does not provide 45 kVA,we go in for 50 kVA rating.

The neutral to be rated for double the phase current,therefore we select the switchgear 4 pole,rated for 2 times the phase current,inthis case 50 *1.4*2=140 amps,standard rating of switchgear available is 160Amps,so select 160 Amps.

Alternatively you can select 100 Amps 3 pole switchgear and 160 Amps nutral link.

Bypass arrangement can be rated for 40 kVA.