Karan Sorout

• Jul 21st, 2006

 

Hi all,

The 'SUM' of the instataneous value of voltage in a 3-phase circuit (Means at neutral point for balanced load) is used to be 'ZERO'.

But, For individual phases this voltage is equal in magnitude but symmetrically 120 degree out of phase to each other.

Now, anyone can imagine that 'why 3-phase sytem is used in transmission' not 4-phase or any other system is preferred; as it doesn't need the return wire... Isn't it?

If you feel otherwise then please let me know at karan.sorout@gmail.com 

Vineet

• Oct 5th, 2006

 

Your reasoning is not perfectly correct.1. You don't need return wire only when the 3-phase load is perfectly balanced, which is hardly a case in practical scenario. In practical senario transmission system earth is used as return path.2. If system is balanced, any n-phase system would not need the return conductor. If you take example of 4-phase system, the voltages need to be 90 deg phased in consecutive phases and the sum of voltages across all phases will still be zero and return conductor is not needed. So thats not the reason why 3phase system is used for transmission systems.

abhishek katkar

 Profile Answers by abhishek katkar 

• Mar 6th, 2007

 

what happened when we use 2 phase system is their any need to give extra return wire

cvk

• Oct 6th, 2007

 

The instantaneous voltage at time instant 't' in a three phase balanced circuit assuming that the voltage is applied at reference time ZERO and phase sequence to be +ve ( anti clockwise rotation of vectors) , is Em SIN(wt) for R phase, Em SIN(wt+120) for Y phase and Em SIN9wt-120) for B. Em is the peak value of the sinusoidal voltage wave.

raj

• Dec 4th, 2011

 

3 Phase sys is preferred because of least amount of CU material required.