Answer / shekhar

bcoz in most of the machines the current losses depend upon
current and iron losses depend upon voltage and they does
not depend upon the powerfactor

Answer / sugankumar

in ac machines the iron loss is depends on voltage(V)...
and the cu loss depends on current(I).... so the total
power depends on KVA.... in DC the voltage and current
depends on cu loss only so the DC power is calculated in
KW......

Answer / sugun

KVA is used to measure an apparent power on AC signals for
a m/c, with out any particular inductive/capacitive load
consideration.
But the power o/p is non-constant and it depends on the
type of load/ p.f of the load applied on the equipment(in
case of motor also it is applicable as by varying the
mechanical load on motor it's operating pf also be varied).

Before connecting load to the m/c type of load /pf of the
load con't be predected at the manufacturing end. Hence A.C
m/c always be rated in kva only.
So... AC doesn't have a constant power associated with it.
DC does.

Answer / manugirl

t is because machinery used on ac supply are transformer regulated and the certainty that transformers are rated in KVA so as machineries used on ac supply should be given contained by KVA rating.
AC supply machines are rate in KVA . The total power consumed or supplied by the system depend up on the power factor of the load. As you know KVA= KW / Power factor.KW will cash for power factor.

Also size of a AC system is depend up on the insulation requirement (depend upon voltage) and size of conducting material( depend upon the current) so Voltage x current will give VA or Size of AC system
All AC power sources like transformers, generators, inverters etc. are usually rate in KVA.

The reason is that surrounded by 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 size 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 nouns is inductive, it will be less than unity.

Answer / mani2089

kw = kva * power factor
The power factor affects the maximum demand component of
the network charges. Generally, kva demand tariffs are
structured to be revenue neutral compared with kw demand
tariffs at a power factor of 0.8

Answer / rod

AC has a component called VAR's, KVA takes into account
power factor KW does not, most machinery (motors) are rated
in KW or in the old language Horse power not KVA, KVA
relates to the supply.

Answer / sri

as transformers are independent of power factors so they
are rated in kva

Answer / bhanu pratap pal

Because the power factor of the machinery is not a constant
parameter i.e. it varies with the change in the supply,
hence the rating of machinery declares in KVA.

Answer / zahid noor

Question is wrong, Generators are rated in KVA, DO NOT
HAVE AC SUPPLY.

Answer / prabs

Depends upon load we are choosing the KVA & KW.
For Ex: Transformer we are call it as KW
But Generator we call it as KVA.

why ups rating in kva? and why ups are in parellel?.why isolation transformer is used in ups?

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