actually rating of the machine (kva or kw) depends upon the
power factor since the load power factor to which
transformer is supplying power is not known , it may be
capacitive ,inductive , or resistive that is why its rating
is in kva and not in kw
The unit of voltage in Volts
The unit of current in Amperes
When the energy transfer from primary ciruit to secondary
circuit power is constant. there is no involvement of power
factor. Due to this transformer rating in KVA not in KW
Since Transformer is a Static device and it is having two
losses namely core loss and Cu loss. The core loss depends
on the Voltage (V) only, where Cu loss depends on Current
(I) only.So for this purpose the transformer always called
its rating in apparent power only(VA).
Because transformenr is used for converting voltage level
only and nothing therefore its rating is in KVA i.e. KV x
Amp It gives us rating/capacity of transformer how power it
The equipments not meant for consuming power are rated in
KVA units & those consuming power are rated in KW.
The leading/lagging power factor has
magnetizing/demagnetizing effect on armature reaction in a
rotating electrical machine. Hence the losses depends on
the load power factor. Unity PF has neither magnetizing nor
Whereas in a transformer, the power factor doesn't play any
role in machine losses i.e. Cu & core losses are
independent of power factor.
Hence the rating of transformer is always given in KVA and
the rating of generators is given in kW at certain pf i.e.
usually at 0.8 lag.