Solution for NCEES sample prob # 533

[visu212]

For the 3-phase Y connected system with perfectly balanced single-phase loads
an assumption is made that fundamental and third-harmonic
components are present. Summing the currents at node N, the
fundamental current components in the neutral are found to be zero,
but the third-harmonic components are 3 times those of the phase currents
because they naturally coincide in phase and time.
When the currents are balanced as given in the problem, the triplen harmonic currents behave
exactly as zero-sequence currents, so these triplen harmonic currents in the neutral conductor are 3 times Io.

So, the answer is 3 *3 = 9 Amps

The solution given in the back of the sample questions book do not give complete picture so I thought I would post the complete theory behind it so it would be useful for my fellow PE takers.

Good luck!!!

 

[cabby]

Just a note-

if you have the McGraw Hill 15th edition, "Handbook for Electrical Engineers", page 23-38 talks about Triplen Harmonics. Also, if you have Theodore Wildi's book "Electrical Machines, Drives, and Power System" he talks about it in Chapter 30, Harmonics. That is in the International Edition of Wildi's book. May be slightly different in other releases.