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3 phase step down tranformer

  1. Sep 17, 2012 #1

    I have one question. Assume a source of about 20KV and 4 Amps. This source needs to be connected to a transformer in order to vary the voltage and current into desirable amounts. The ideal transformer takes the input power and gives out the same power as output. My question is: I know that the voltage comes out of the "pole pig" tranformer outside our houses is 240 V, how much is the current? 20A ? Where does the line go after that? into the switch board of each house? Is there any other transformation made within the house?
  2. jcsd
  3. Sep 18, 2012 #2


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    Staff: Mentor

    Most electronics gadgets have a transformer to change the 240 V to a much lower value, somewhere around 6 V to 25 V.
  4. Sep 18, 2012 #3


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    Gold Member

    If your in the US your HV supply to the pole xfmr is usually 2K, 4160, or 13.2K.
    Your secondary is 120/240V. In a residential situation you cannot have 3 phase. It is usually
    only available in commercial residential situations (large apt complex), but no individual unit will have 3 phase, only 120/208 or 120/240 single phase depending on the supply xfmrs. Agriculture, commercial, and industrial areas can have 3 phase.
    As for the current it depends on the size of the supply wire to the house, it could range from 30 A (very very old) to 60 A(pretty old- pre 1990's) to 100 A (smallest legal service as per NEC now) to as much as 400A + (very rare but still possible). The current is limited by fuses or circuit breakers.
    There are calculations in the NEC to figure this.
    Before you play with mains power please consult someone who is trained and educated in the safety procedures if you aren't.
    remember if you make a mistake it only hurts 'til you stop breathing.
  5. Sep 19, 2012 #4
    20KV is seriously high voltage! If you make a mistake with a 20 KV source that gives 4 amps you will kill yourself.
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