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The rated quantities of a transformer, its power, voltage, frequency, etc. are given in Manufacturer’s name plate, which should always be arranged so as to be accessible. But the term ‘rated’ can also be applied to quantities not indicated on the name plate, but relating to the rated duty, as for example, the rated efficiency, rated temperature conditions of the cooling medium, etc. :

  • The rated duty of a transformer is determined by the quantities given in the name plate,
  • The rated power of the transformer is the power at the secondary terminals, indicated in the name plate and expressed in kVA.
  • The rated primary voltage is the voltage indicated in the .transformer name plate; if the primary is provided with taps, the rated tapped voltage is specially noted.
  • The rated secondary voltage is the voltage across the transformer secondary terminals at no-load and with the rated voltage across the primary terminals; if the secondary winding has taps, then their rated voltage is specially indicated.
  • The rated currents of the transformer, primary and secondary, are the currents indicated in the name plate of the transformer and calculated by using the corresponding rated values of power and voltage.