February 6th, 2019, 04:53 AM  #1 
Member Joined: Feb 2018 From: England Posts: 61 Thanks: 0  Total Power in 3 phase system.
Hi All, How do I calculate the total power by a 3 phase electrical supply when the rms input voltage = 350v? The power is delivered along a wire with a resistance of 0.170 ohm. Am I correct in saying V^2 / R = P = 720588.2353. MW megawatts answer. Any help would be much appreciated. Last edited by skipjack; February 6th, 2019 at 05:19 AM. 
February 6th, 2019, 05:17 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 20,746 Thanks: 2133 
A 3phase supply would be delivered via 3 transmission wires  one for each phase. Hence the wording of the question is a bit confusing. Multiplying your figure by 3 would give 2.16 MW after rounding to 3 significant figures.

February 6th, 2019, 08:12 AM  #3 
Banned Camp Joined: Mar 2015 From: New Jersey Posts: 1,720 Thanks: 125 
If the voltage drop were 350 the voltage at the end of the line would be zero and the entire output of the power plant would be consumed in the line. I don't know how to do it. Couldn't find it in old EE book or online. 
February 6th, 2019, 08:48 AM  #4 
Member Joined: Feb 2018 From: England Posts: 61 Thanks: 0 
Hi Skipjack, What is the correct way to perform this calculation? 
February 6th, 2019, 11:58 AM  #5 
Global Moderator Joined: Dec 2006 Posts: 20,746 Thanks: 2133 
The question doesn't really make sense, but calculating 2.16 MW, as I suggested, seems to be all that you can do.

February 7th, 2019, 08:25 AM  #6 
Banned Camp Joined: Mar 2015 From: New Jersey Posts: 1,720 Thanks: 125 
I have a generator with 120v at the terminals. Two 10ft wires leading from the generator are open at the ends, ie, the voltage across the ends is also 120v. The wires have a resistance of .170 ohms. Is the total power V^2/r? Power loss due to resistance in a supply line is an i^2r loss. 

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phase, power, system, total 
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