why transformer ratings in kva?




Answers were Sorted based on User's Feedback



Answer / r. anand

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

Is This Answer Correct ?    841 Yes 97 No

Answer / siva

because,ironloss is depends in voltage and cu_loss is
depends in current.so the transformer ratings in kva

Is This Answer Correct ?    676 Yes 217 No

Answer / senthil kumar.a

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
knowledge only

Is This Answer Correct ?    291 Yes 50 No




Answer / gk

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
power factor.

Thumb Rule - all AC power sources - Generators,
Transformers, UPS etc. are rated in KVA and all loads are
rated in Watt or Kilowatt.

Is This Answer Correct ?    246 Yes 41 No

Answer / chiya

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┬ź 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.

Is This Answer Correct ?    147 Yes 37 No

Answer / ankaraju.k

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

Is This Answer Correct ?    72 Yes 24 No

Answer / pradeep kumar rawat

transformer is static device there is no any rotating part
so there is no any friction losses, only iron loss and cu
loss in transformer, iron loss depend upon the voltage and
cu loss depend upon the current, there in no any loss which
depend upon power factor,so rating of transformer only in
kva.

Is This Answer Correct ?    35 Yes 11 No

Answer / dhanraj kolambe

1. The core losses of the transformer is depend upon
the voltage while the copper losses depends upon the
current.

2. The load which is connected on the transformer is in the
terms of Kw. That's why the rating of the transformer is in
KVA.

Is This Answer Correct ?    28 Yes 7 No

Answer / j naveen kumar

the taransformer is a static device which converts one form
of voltage to another form of voltage wuthout changing the
frequency,the two losses i.e,copper losses and iron losses
are depends upon current and voltage respectively.there is
no losses depending upon power factor.since the power factor
is constant,that's why the transformer ratings is on kva but
not in kw.

Is This Answer Correct ?    28 Yes 10 No

Answer / saravanan

the losses in the transformer is dependent upon the voltage
and current i.e cu and iron loss

Is This Answer Correct ?    78 Yes 61 No

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