Why is the rating of transformer written in VA, KVA, MVA?
We know that total
loss of transformer = core loss + copper loss. Core loss mainly depends on
voltage and copper loss depends on current. This means that the total loss
depends on the voltage and current (VI) but not on the phase angle between them
and the total loss has nothing to do with the power factor.
The power factor
largely depends on the load. The load can be of any type resistant, inductive or
capacitive. There are different types of loads with the transformer due to
which the power factor is different. Besides, power cannot be extracted without the power factor.
If we notice the
following equation, we will see:
W = √3VICOS∅ __ (I)
4 tests of current transformer
(i) Equation No. is the equation of power. The
value of W cannot be found because the value of COS∅ is not
known. So there is no unit of voltage (V), no unit of a current ampere (A), and no
unit of power factor.
So we get VA from the
equation (i), and if the value is greater then it will be KVA. Larger ones are
written in MVA.
Why is the rating of the motor written only in KW instead of VA, KVA, MVA?
We know that motors
are designed with specific power factors. Therefore its load size can be
determined. So in the nameplate of the motor the unit of power is W, if it is
big then KW is written.
We know that motor
converts electrical power into mechanical power. Mechanical power is active
power. What is written on the nameplate of the motor is the output or
mechanical power of the motor. And the unit of power in watts (W).
The answer is, here is Core & Copper loss. The core loss depends on Voltage & Copper loss current. So it is rated on KVA. But now if you are asked again that - 1) Generator, Inverter, why are they rated in KVA? 2) Generator is rated KVA but the Motor is rated KW? Now maybe you got a little worried? No worries, let's find the solution in the story.
Suppose you are going
to your village home by train. Get off at the station. But then at midnight.
Drizzle There are two ways to get to your home. He heard in people's mouths
that if they go one way, they can catch ghosts or not. Another way is
absolutely safe.
Which path would you
choose now? Surely the second way. Because there is no risk in that.
Similarly, when manufacturers make transformers, generators, inverters, they do
not know what kind of load consumers will use ????
They can use any
inductive, capacitive, or resistive load. And that's the problem. Power Factor
and Vary in Variations of Load. So they choose KVA tie from KVA and KW options.
Because there is no
uncertainty that there will be no trouble if you go this way. But the question
remains why? KVA means apparent Power which does not depend on Power Factor. So
whatever the power factor of the load, there is no problem and KW means Real
Power which depends on the Power Factor.
So think for yourself,
if Transformer, Generator was rated in KW then it would have to determine a
power factor. And then the problem was playing. Then there would be enough
mismatch of its power factor with the load.
Now let's come to the
second question. So why is the motor assigned to KW? We all know that motors do
not produce electricity. It generates Mechanical Power. And one of its power factors
is determined in the plate. And Motor Real Power does this. So Mr. was assigned
to KW.
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