Calculating Transformer load - Contractor Talk - Professional Construction and Remodeling Forum

daiashi · 02-04-2007, 05:06 PM

Any understand how to properly calculate primary and secondary
overload protection.Or links to a know how.A little rusty in that
area at best.Thanks.

RobertWilber · 02-05-2007, 09:50 AM

try mike holt's site
http://www.mikeholt.com/code_forum/
lotsa lotsa there

Sparky Joe · 02-05-2007, 08:04 PM

How about; kVA secondary equals kVA primary?

What size panel do you intend to install on the secondary times how many volts the panel is equals your transformer.(perhaps 1.73 comes in somewhere, I'm not sure)

srwhitus · 02-05-2007, 09:26 PM

Single Phase when KVA is known:
(kva x 1000) divided by (voltage) = amps

Three Phase when KVA is known:
(kva x 1000) divided by (voltage x 1.732) = amps

Sparky Joe · 02-05-2007, 10:10 PM

Quote:

Originally Posted by srwhitus

Single Phase when KVA is known:
(kva x 1000) divided by (voltage) = amps

Three Phase when KVA is known:
(kva x 1000) divided by (voltage x 1.732) = amps

I think "kVA" is what's trying to be found.

Does anyone know of a 'buffer' they would add when sizing a transformer once they know their load demand and of course load volts? (load = secondary)

For example; calulated load would equal 46 kVA though instead of a 50kVA xfmr you'd install a 75kVA. Just curious if this sort of thing comes into play? Or does one just figure the amps of panel dictates the amps of the transformer?

srwhitus · 02-05-2007, 11:35 PM

Hummm...I thought the question was to find overload protection for a transformer. Since you want to know the kva it is as follows:

Single Phase:
(Volts) x (Load Amps) divided by (1000) = kva

Three Phase:
(Volts) x (Load Amps) x (1.732) divided by (1000) = kva