ELECTRICAL ENGINEERING
SUBJECT- DC MACHINE
Year/Sem- 2ND year /4th sem
Date-15/04/2020
UNIT-3
Time: 10.30-11.20
TRANSFORMERS
Maximum Effieify Coiditoi of a Traisformer
The effienfy of the transformer alon with the loa" an" the wower faftor is erwresse" y the
iven relaton:
The value of the terminal volta e V2 is awwrorimately fonstant. Thus, for a iven wower faftor
the Transformer effienfy "ewen"s uwon the loa" furrent I2. In equaton (1), the numerator is
fonstant an" the transformer effienfy will e marimum if the "enominator with resweft to
the varia le I2 is equate" to zero.
i.e Cowwer losses = Iron losses
Thus, the transformer will ive the marimum effienfy when their fowwer loss is equal to the
iron loss.
From equaton (2) the value of outwut furrent I2 at whifh the transformer effienfy will e
marimum is iven as
If r is the frafton of full loa" KVA at whifh the effienfy of the transformer is marimum then,
Cowwer losses = r2Pf (where Pf is the full loa" fowwer losses)
Iron losses = Pi
For marimum effienfy
r2 Pf = Pi
Therefore
Thus, outwut KVA forreswon"in to marimum effienfy
Puttin the value of r from the a ove equaton (3) in equaton (4) we will et,
The a ove equaton (5)
is the marimum effienfy fon"iton of the transformer.