I would appreciate if someone with expertise could confirm or correct my calculations.
45 KVA 600/120/208 volt dry type distribution transformer
97.7% efficient (therefore losses are 2.3%)
.023×45 = 1.035 KW loss
1.035 KW x 24 hr x 30 days x $.20 kwhr = $149.04 per month
15 KVA 600/120/208 volt dry type distribution transformer
97% efficient (therefore losses are 3%)
.03×15 = .45 KW loss
.45 KW x 24 hr x 30 days x $.20 kwhr = $64.80 per month
Best Answer
You have assumed each transformer is connected to a load and that load is at the rated VA of the transformer. This may not be true. If it is true then the efficiency figure can be used to calculate the approximate losses for a load that has a power factor of unity. At very low power factors in the load this assumption may be a little inaccurate.
If the transformer Is not constantly delivering full VA the losses will be less. Consider the losses when the transformer is disconnected from a load. There will be minimal copper loss but there may be a slight increase in iron loss, but, overall I would suggest the no-load losses are significantly less. This must be factored in if the load is variable or intermittent.