Why Transformer Rating In kVA, Not in KW?
There are two type of losses in a
transformer;
1.
Copper Losses
2.
Iron Losses or Core Losses or
Insulation Losses
Copper losses ( I²R) are variable losses
which depends on Current passing through transformer windings while Iron Losses
or Core Losses or Insulation Losses
depends on Voltage.
So the transformer is designed for
rated voltage (iron loss) and rated current (copper loss). We can't predict the
power factor while designing the machine, because power factor depends upon the
load which varies time to time.
When manufacturers design the
transformer, UPS etc, they are never able to predict the exact type of load
that would be used and consequently rate the device based on its maximum output
of current that can be safely carried by the conductors (at unity Power Factor)
as well as the conductors' insulation rating (Voltage & temperature). That
is why the transformer rating can be in kVA, and not in kW.
