Transformer Effiecieny calculations

[Mikeymike]

Hey guys

Just doing a few calculations on transformer effieciency but have I got the correct formula for this?

1: A transformer is rated at 10kW but is only delivering 9.8kW. Copper losses are 0.33kW and Iron losses are 0.2kW. Calculate the efficiency of the transformer.

Ok so our formula for this is

n = Output Power/Input power + losses

0.33KW + 0.2KW = 0.53KW losses

n = 9.8KW/10.53KW = 0.93

n = 0.93 x 100 = 93%

a 99%

b 98%

c 90.4% This is the answer but don't understand how it can be?

d 88.6%

---------- AUTO MERGE Post added at 14:49 ---------- Previous post was at 14:29 ----------

2: A 100KVA Transformer is fully loaded. A circuit having a power factor of 0.95 if losses in this transformer is 2.5KW copper & iron is combined. What is the percentage effieciency of the transformer?

Output power = KVA x p.f

Output power = 100 KVA x 0.95 = 950KW

n = Output power/Output power + losses

n = 950KW/950KW + 2.5KW = 0.97.7

n = 0.97.7 x 100 = 99.7%

a: 99.7%

b: 98.2%

c: 90.2%

d: 94.8%

That one I can work out