Both the losses of the transformer is independent of the
power factor (cos phi), which means a transformer would not
make any change in the power factor, since both the losses
viz copper loss(depends on current) and iron loss(depends
on voltage) are independent of power factor, that is why a
Transformers rating is not on kW, but on KVA
adding to above answer Transformer is not a load and having
no effect on P.F and it only transfer the constant power
from one voltage level to another voltrage level without
changing frequency thats why transformer are rated in KVA
transformer has two major losses one is copper loss it
depends upon the current , the current unit is Amps ans the
core loss depends upon the voltage it unit is Voltage, so
VA the k mantion for the capacity
why transformer capacity not say in KW?
becaz watts is unit of power already we know the formula of
power, it is current x voltage x cos phi. but the two
losses not depends upon the power factor, incase we r say
in KW it makes a error in calculation. because the KW
include the power factor. I hope that it is correct upto my
kVA is the unit for apparent power. Apparent power consists
of active and reactive power. Active power is the share of
the apparent power which transmits energy from the source
(generator) to the user. Reactive power is the share of the
apparent power which represents a useless oscillation of
energy from the source to the user and back again. It
occurs when on account of some »inertia« in the system
there is a phase shift between voltage and current. This
means that the current does not change polarity synchronous
with the voltage. But the heat generated in a winding as
well as the eddy current losses generated in a transformer
core depend on the current only, regardless of whether it
aligns with the voltage or not. Therefore the heat is
always proportional to the square of the current amplitude,
irrespective of the phase angle (the shift between voltage
and current). So a transformer has to be rated (and
selected) by apparent power.
The difference is that, even though both are electrical
equipments, transformer is considered as a power source
while the Induction motor is considered as a load.
In the case of a power source, you cannot predict the type
of load (resistive, Capacitive or Inductive) that will be
connected to it. Hence the actual usable capacity rating
depends on the power factor of the load.
Power = Voltage x Current x Power Factor
If the load is resistive, PF is 1 (unity) and if the load
is inductive, it will be less than unity.
In the second case (Load), the motor manufacturer gives the
rated voltage and full load current taking into account the
Thumb Rule - all AC power sources - Generators,
Transformers, UPS etc. are rated in KVA and all loads are
rated in Watt or Kilowatt.
At the designing of transformer you can not predict which
type of load is placed on thatone i.e; the power factor is
unknown.under no load conditions thhe transformer losses is
depend on nearly sqare of voltage.under load condition the
losses depends on sqare of current.So overall losses in
transformer is depends on voltage and current only,so yhe
rating is inKVA
1.What is the proper definition of power system stability?
2.some times a blue spark is visible in the secondary side
of a distribution transformer at the contact position of
bushings and fuse wire,why?