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I am really confused with the above problem. I can also solve the problem taking an AC supply across a 20ohm resistor and end up getting like

P = 100^2/20 = 500W

I am not able to digest the solution provided to me by my coaching institute and think that my solution is correct. Please help me with the above problem.

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    \$\begingroup\$ add up 2 phasor voltages between R&Y using trig. then try again. The vague question means 100V Phase to neutral for each phase, not phase to phase \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Jan 25 '18 at 20:52
  • \$\begingroup\$ Am I correct in thinking that the calculation assumes a neutral connection at the star point when the schematic doesn't show one? This would change the result. \$\endgroup\$ – Transistor Jan 25 '18 at 21:03
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    \$\begingroup\$ No further comments on your question. I think your answer is correct for the schematic given. \$\endgroup\$ – Transistor Jan 25 '18 at 23:25
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Given the circuit diagram you have provided with the B(lue) phase disconnected and no neutral shown then your answer of 500 watts is perfectly correct with a line voltage of 100 V.

The written solution to this problem will only be "correct" if a neutral line was present because then you can see that each load resistor will receive a phase voltage of 100/\$\sqrt3\$ = 57.74 volts and, using voltage squared divided by resistance for power, you get 333.33 watts per resistor making 666.66 wats in total.

I will also add that the "correct" answer of 666.54 watts is naive and that the way the solution calculates current is also naive. The way the written solution rounds the correct phase voltage of 57.735027 to 57.73 is very careless.

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