Which of the following is true for a 3-phase unbalanced load?a.Neutral current is the algibric sum of all phase currents..b.Neutral current always is zero.c.Neutral current is the vector sum of all phase currents.d.Neutral current is the vector difference of all line currents.

Answered: Which of the following is true for a…

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter8: Symmetrical Components

Section: Chapter Questions

Problem 8.13P

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Which of the following is true for a 3-phase unbalanced load?

Neutral current is the algibric sum of all phase currents..

Neutral current always is zero.

Neutral current is the vector sum of all phase currents.

Neutral current is the vector difference of all line currents.

Expert Solution

Step 1

Balanced load

In 3 phase system is a condition where all three phases (lines) take same magnitude of current, with evenly spaced phase difference.

If the load is star connected, with neutral as return path, this neutral will carry no current. That's why vector sum of all three phase currents meeting at common neutral point is zero.

Which eventually means that magnitude of currents in all three phase are equal & are displaced from each other by 120 degrees and thus adds up to zero. Hence, zero neutral current

Step 2

. A unbalanced 3 phase load is one which is not equally distributed among all three phases.

Thus the current in 3 phases are unequal which leads to a non—zero neutral current

Since the load is unbalanced, the line currents will be different in magnitude and displaced from one another by unequal angles, The current in the neutral wire will be the phasor sum of the three line currents i.e. $I_{N} = I_{R} + I_{Y} + I_{B}$

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Which of the following is true for a 3-phase unbalanced load? a. Neutral current is the algibric sum of all phase currents.. b. Neutral current always is zero. c. Neutral current is the vector sum of all phase currents. d. Neutral current is the vector difference of all line currents.