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I am currently studying "Principles of Power System by V. K. Mehta". I am stuck at a tutorial problem from chapter 13, which is as follows:

A 2-wire d.c. distributor, 500 m long is fed at one of its ends. The cross-sectional area of each conductor is 3·4 cm² and the resistivity of copper is 1·7 μΩcm. The distributor supplies 200 A at a distance of 300m from the feeding point and 100 A at the terminus. Calculate the voltage at the feeding end if the voltage at the terminus is to be 230 V.

Here is my solution:

handwritten solution attempt

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  • \$\begingroup\$ Possible duplicate of What is the voltage at the feeding end? \$\endgroup\$ – Harry Svensson Feb 18 '18 at 13:59
  • \$\begingroup\$ He has deleted it. \$\endgroup\$ – Leon Heller Feb 18 '18 at 14:46
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    \$\begingroup\$ @SamGibson: nice crop and contrast enhancement. Why didn't OP do this? \$\endgroup\$ – Transistor Feb 18 '18 at 15:07
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    \$\begingroup\$ Note the possible ambiguity or misreading in the question I read it as supplying 200A TO point C alone, PLUS 100A to point B. \$\endgroup\$ – Brian Drummond Feb 18 '18 at 15:26
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Work backwards:

Section C-B

  • You know what \$ V_B \$ and \$ I_B \$ are so you can work out what voltage is required at C to get that.

Section A-C

  • Now you know \$ V_C \$ and \$ I_A \$ so you can work out what voltage is required at A.
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  • \$\begingroup\$ That is a really good example of an answer - that leads the OP further! neat. \$\endgroup\$ – Solar Mike Feb 18 '18 at 16:44

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