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Topic

Why the neutral current is zero in WYE configuration in balanced load while it is unbalanced?

Why the neutral current is zero in WYE configuration in balanced load while it gives some value of current in unbalanced load?

Please tell me and also explain about it ...

Comments

In a WYE 4 wire system the neutral, in theory, carries only the difference of current flow between the 3 phase conductors. So, when the current in phase A, B and C are equal, then there3 is no current flow in the neutral. When current flow in phase A only increases, then the neutral current will equal that increase.
However this is true only for purely resistive (linear) loads. Non-linear loads cause harmonics , some of which will add up on the neutral.
Because when you add all the currents together at the neutral they add up to 0 if they are balanced. If your balanced current was 10A/ phase then you would add 10cos(0) + 10cos(-120)+10cos(120) = 0 for a 3 phase system. If it's not balanced then when you add them all together you will have some current at some angle left over. 


Marvin R Hamon, P.E., MScEE

Principal,   Hamon Engineering, Inc,   www.hamonengineering.com