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In my book I have following task that actually has a solution. However I do not understand the solution idea and that's why I'm asking you guys to help me understand that if possible. enter image description here enter image description here enter image description here

Why I do not understand are following:

  1. Why do we have a \$U_a'\$, \$U_b'\$...?
  2. Do we in the end use \$U_a\$,\$U_b\$,.... or \$U_0\$?
  3. How they calculate the \$I_1\$ or \$I_2\$? Why do they use \$U_0\$ when calculating the current but do not use \$Z_{L0}\$.
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  1. The U' voltages supply the electric radiators. They can be used to calculate the power of the electric radiators, but the current can be calculated and the load power calculated using the current and load resistance.

  2. The voltage at the source end of the transmission line must be used to calculate the current since the impedance and losses in the transmission line are part of the problem.

  3. The currents are calculated using the line to neutral voltages from the source end of the transmission line and the transmission line plus load resistances. Since the system is completely balanced, the neutral voltage and current are zero.

I believe that sufficient information is given to work the problem more than one way, but I have not looked at it thoroughly since the question didn't really ask about that.

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  • \$\begingroup\$ Do you mean that the U' is the voltages to the radiator and not U_a for instance? is there a transformer there that down gains the voltage? \$\endgroup\$ – Payam30 Nov 7 '17 at 15:03
  • \$\begingroup\$ Yes. U' is less than U because of the voltage drop in the transmission line. \$\endgroup\$ – Charles Cowie Nov 7 '17 at 15:49
  • \$\begingroup\$ Why isn't mentioned that there is a transformer? would an ideal transmission line contain any losses of voltage? \$\endgroup\$ – Payam30 Dec 7 '17 at 8:26
  • \$\begingroup\$ @Payam30 The stated problem is concerned only with the transmission line and the load. The voltage at the secondary of the transformer is given. Since no information is given about anything "upstream" from that point, it must be assumed that any effect due to upstream components is negligible in comparison to the transmission line impedance. \$\endgroup\$ – Charles Cowie Dec 7 '17 at 14:01

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