Transformer are rated in kVA instead of kW because

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UKPSC JE Electrical 2013 Official Paper I (Held on 7 Nov 2015)
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  1. Load power factor is often not known
  2. KVA is fixed while kW depends on load pf
  3. Total transformer loss depends on volt – ampere
  4. All of the above

Answer (Detailed Solution Below)

Option 4 : All of the above
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Detailed Solution

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Reason for kVA rating of Transformer:

Reason 1:

  • The losses in a transformer include copper losses and core losses or iron losses. Core losses depend on voltage whereas copper losses depend on the current which passes through transformer winding.
  • The total losses depend on volt-ampere.
     

Reason 2:

  • When the transformer is designed the manufacturer does not know which type of load will be connected in the future. And the power factor depends upon the load.
  • Since kVA is fixed and kW depends on the power factor.
     

Hence, the rating of the transformer is mentioned in kVA but not in kW

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