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My question is about phasing?

Why phasing is needed in power line? Can't we just use one conductor instead of two or more conductors? I already searched for it, but couldn't get any relevant answer.

Transistor
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ALAUDDIN PIAL
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  • Utility power is generated, transmitted and distributed as three-phase power. Three-phase power is used for industrial equipment. When used for three-phase motors, the motors will run in the reverse direction if two phases are interchanged. That may answer your question, or you may need to study more about what three-phase power is. It is not clear from your question what you don't understand. –  Jul 26 '17 at 23:22
  • Your title should be a preview of the question. – Jashaszun Jul 26 '17 at 23:23
  • Please help me out is not a question, write a clear specific question and a few paragraphs of your understanding and background of the topic. The better the question, the better the answers you'll get, if you really want help, then put some thought into writing a question. – Voltage Spike Jul 27 '17 at 05:50
  • You were searching for the wrong term. "Phasing" is generally not used. Search for "three-phase power distribution" instead. Also you don't need to put "My question is about" in your title. We know it's a question - just put the topic or actual question. – Transistor Jul 27 '17 at 08:43
  • Possible duplicate of [Why 3 phase and not 1 phase power transmission?](https://electronics.stackexchange.com/questions/255536/why-3-phase-and-not-1-phase-power-transmission) – Dmitry Grigoryev Aug 04 '17 at 11:34

3 Answers3

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Why at least 2 conductors? Because the power company must deliver the power into your loads (motors, clothes dryers, etc). The power company does not get paid for heating up the earth (the return path).

analogsystemsrf
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Firstly current flows in loops, so there always need to be at least two conductors. Sometimes the earth is used as one of the conductors (Google single wire earth return) but that creates problems so it's rare outside of relatively low power rural systems.

However in practice it is common to use a three phase system, this uses more wires but it offers several significant advantages.

  1. Currents in the neutral conductor generally cancel out, so the neutral conductors can be significantly smaller than in a comparable single ended single phase system and somewhat smaller than in a comparable split single phase system. In some cases the neutral conductor may be omitted altogether and loads connected between phase conductors.
  2. It delivers power continuously, unlike a single phase system where the power rises and falls through the waveform cycle. This makes motors and generators run smoother.
  3. It can easily create rotating magnetic fields. This avoids the need to use tricks that reduce motor performance.
Peter Green
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Minimum two conductors are required as Neutral is required to close the current path So if you don't connect neutral circuit will not work as no current will flow from it

enter image description here

For heavier load more than two conductors are required.

What if your load is 500 HP motor. So your Power consumption of that motor will be 372kW. Now for that much power if you connect single conductor your current from that conductor will be (V = 240 volts for Indian systems)

I = P/V = 372000/240 = 155 Amp

and this will generate plenty amount of heat which means more power loss in the conductor because of heat and also it is difficult to handle such a high currents.

If you use three phase system your current will be divided into 3 phases and it will be 51.66 Amp.

Hence for industries or heavy loads three phase is used and for home appliances single phase is good enough

Also power is constant throughout the cycle and that direction is given by the phase sequencing. enter image description here

I think now it will be pretty much clear let me know if there is still something unclear

Thanks

Abhishek Parikh
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    I didn't downvote but you have missed the main point of three-phase power which is that power is constant throughout the cycle and that *direction* is given by the phase sequencing. – Transistor Jul 27 '17 at 07:47
  • Yes I've missed that.. Edited now Thanks to pointout @Transistor – Abhishek Parikh Jul 27 '17 at 08:25