Answer / gajanan

there are two losses occure in transformer viz. Cu loss and
iron loss.
Cu loss depends on current & iron loss depends
on voltage and not affected by power fector hence always
transformer ratting defined in KVA not in Kw.

Answer / prabahakaran

WE know the relation of power in three phase =
√3VIcosØ.hence we can say that the load is not constant it
very accordingly. So power factor is also get vary with
load it is hard to define the power of transformer so it is
rated in KVA.

Answer / gaurav bhardwaj

Rating is any device,s power capacity..so if u know how much useful power u can get then only it will be in kW..bcz power factor plays role in useful power then we can say that if a transformer has 20kva rating then it will deliver 20,kw at pf=1..Nd as we don't know the load which is to be supplied that's y rating in kva ,as kW=kva*pf

Answer / eng. d

I like the answer which is talking about the cu losses and
characterstic of the transformers.

let me drive the answer from differint angle.

let us assume that we told you that, the transformer is 20
MW, and now you want to connect motor of 15 MW to this
transformer, are you able to start this motor from this
transformer before the protection setting trip the circuit
breaker of the transformer?

I don't really know!! because I don't know how much
reactive power in this transformer, in other words, I don't
know how much losses in this transformer, then I can't do
prpoer analisys of the motor starting without knowing the
MVA rating.(which will include active and reactive power)

my advice, please try to do motor starting analysis on ETAP
or Matlap or any electrical softwaer and play with the
reactive power and see the differance and you will be clear
more ^_*
good luck

Answer / chinna

trf rating in KVA,current measures in amps&voltages
measures in volts.thats trf rating in kva.

in a 740 kw dc seperately excited motor field voltage is constant about 17.4 volts and armature voltage is500 volts dc. how it is possible to have two different voltages from single transformer of output voltage 500 volts? if any difficulty in question contact ajitsingh.kadian@gmail.com

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