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Transformer output current @ Different tap

MG
Hi all,


Say we have a distribution transformer which has a nominal current output. If this transformer is tapped at the primary should we assume that the power rating of the transformer is constant and as such the output current will change to satisfy the constant power rating?


I.E. 1MVA, 11kV/433V transformer has a nominal output current of 1333 A. If the primary is tapped at +5%, then to satisfy the transformer apparent power rating remaining constant means the output current now is increased by 5% at 1400A.


Thanks
  • 0
    Yes and no. The tapping is normally adjusted to compensate for the 11kV voltage, so a 1000 kVA is usually taken as 1333A and a 500 as 666A, as it is adjusted for 433V on no load. 


    Regards,


    Alan.
  • 0
    Thanks for the response Alan, I suppose I was looking at this from a different perspective.

    Perhaps taking the maximum nominal secondary current as the transformer output limit is the way forward since the tap is made at the primary as you described it is there to compensate and ensure pretty much steady secondary output close to the nominal
  • 0
    The rating plate on the transformer will give the currents at the nominal tap. For different taps it only details the percentage change in voltage. 


    Regards,


    Alan.
  • 0
    I think you will find that for a 1000 kVA transformer, the manufacturer will give its full load current as 1333A, regardless of its tap. 


    Regards,


    Alan.
  • 0
    I seem to recall the rating plate describes no load volts and full load current at normal tappings they assume  11000/433 volts

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