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Homework Help: High Power Transmission

  1. Jan 25, 2009 #1
    We are constantly told at school that in order to reduce power loss in overhead cables, high voltages and low currents are used as P = I squared R. This seems to make sense until you substitute I=V/R into P=VI and get P = V squared / R. Now if voltage is increased in the cable, and resistance is decreased, power loss is at its greatest, completely opposite to the other example. Am I doing something wrong?:confused:

    Many thanks

    Paul Harris
  2. jcsd
  3. Jan 25, 2009 #2
    What you're saying would be true if the high power line were shorted to ground and all the voltage were across the line. In practice the line feeds a transformer with an impedance much higher than the line. So in reality most of the voltage is across the transformer and the voltage across the line is very low.
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