Find out the efficiency at full load:
An open circuit test for core losses in a 10 kVA transformer [Example (1)] gives a reading of 70 W. If the PF of the load is 90%, find out the efficiency at full load.
Solution:
Eff. = VSIS x PF / (VSIS x PF) + Copper Loss + Core Loss x 100
VSIS = transformer rating =10kVA =10,000 VA
PF = 0.09; Copper loss = 100 W; Core loss =70 W
Eff. = (10,000(0.90)/10,000(0.90) + 100+70) x 100 - 99000/9170) x 100 - 98.2%