The transformer ratings are usually expressed in terms of

The transformer ratings are usually expressed in terms of

Right Answer is:

KVA

SOLUTION

The rating of any electrical machine shows its ability to carry the mechanical load without showing any signs of overheating. The transformer ratings are usually expressed in terms of KVA.

There are two types of losses in a transformer

⇒ Iron Losses
⇒ Copper loss

  • Copper losses ( I²R) depends on the Current which passes through transformer winding.
  • Iron Losses (Core Losses or Insulation Losses) depends on Voltage.
  • This shows that the iron and copper losses depend only on the supply voltage and the current flowing through the winding respectively.
  • Since the power factor is dependent on the load which is not stable.
  • Since these losses do not depend on the phase angle between the supply voltage and the current, the transformer rating expressed as a product of voltage and current is called the VA rating of the transformer.
  • KVA tells you the current rating of the transformer, regardless of the power factor of the load.
  • Hence, total transformer loss depends on volt-ampere (VA) and not on phase angle between voltage and current

Therefore, the transformer rating is expressed as kVA and not as kW.

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