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Transformer sizing calculations. Please help.

  1. Feb 3, 2014 #1

    I've just got into my electrical engineering course and I need some help with a question of mine here.

    During a site visit, we were shown a main LT panel which has switchgears, ammeters and different kinds of relays and the distribution network from that panel. In the main LT panel I've noted down the current readings as Ir - 163A, Iy - 150A and Ib - 147A. The Line to Line voltage is 415 V at 50 Hz and Line to Neutral voltage is 230V at 50 Hz.

    From the above details, how would I calculate the kVA rating of transformer? The primary side voltage of the transformer is 11 kV and the secondary side voltage is 415V and the frequency is 50 Hz.
  2. jcsd
  3. Feb 4, 2014 #2


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    Science Advisor


    You have recorded inconsistent voltages. The voltage between phases will be √3 = 1.732 times the neutral to phase.

    World standards have moved to 230V and 400V for single phase and three phase respectively.
    The 415V you report suggests distribution is still 240V.

    The transformer rating will need to be greater than the KVA observed.
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