# NCEES #533



## Mahmoud (Oct 15, 2011)

Can someone please explain problem 533 of the NCEES book? also I would like to know where I can find more information about Harmonic Distrortion?

Thanks


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## kris7o2 (May 25, 2021)

Same question. I am also confused on this problem.




If anyone can point me in the right direction it would be much appreciated. Thanks


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## akyip (May 25, 2021)

Normally in a balanced 3-phase system, the phase currents - which are fundamental-sequence currents, also known as 1st harmonic positive-sequence currents - cancel out at the neutral connection point. This is because of the 120-degree displacement between each phase in a balanced 3-phase system.

1<0 + 1<-120 + 1<+120 = 0

But 3rd harmonic phase currents have the same phase angle, so the 3rd harmonic phase currents add up at the neutral connection point. 3rd harmonics are part of triplen harmonics. All triplen harmonic currents have the same phase angle and therefore will add up at the neutral connection point.

So in problem 533, the neutral conductor will have the following currents:

1st harmonic currents in neutral conductor:
60<0 + 60<-120 + 60<+120 = 0

3rd harmonic currents in neutral conductor:
3<0 + 3<0 + 3<0 = 9<0 A = 9 A

NOTE: The actual phase angle is arbitrary. What really matters more here regarding the different types of harmonics is the phase angular displacement between each phase.

Positive-sequence and negative-sequence phases have 120 degree displacement between each phase, so they will add up to zero at the neutral connection point.

Zero-sequence phases have 0 degree displacement between each phase. So they will be additive, and the magnitudes of each phase will add up at the neutral connection point.

I've attached my notes on the different harmonics - positive-sequence, negative-sequence, and zero-sequence harmonics - from studying off of Zach Stone's Electrical PE Review.


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## Zach Stone P.E. (May 26, 2021)

akyip said:


> Normally in a balanced 3-phase system, the phase currents - which are fundamental-sequence currents, also known as 1st harmonic positive-sequence currents - cancel out at the neutral connection point. This is because of the 120-degree displacement between each phase in a balanced 3-phase system.
> 
> 1<0 + 1<-120 + 1<+120 = 0
> 
> ...


Thanks for the mention, @akyip!


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## KY518 (Jun 16, 2021)

Which book is this? I thought the NCEES book only had 80 questions. If there are 500+ questions for $40, its definitely worth the price.


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## Dothracki PE (Jun 16, 2021)

KY518 said:


> Which book is this? I thought the NCEES book only had 80 questions. If there are 500+ questions for $40, its definitely worth the price.


It does only have 80 questions. But the numbering starts with 501. Just to make it confusing. It probably comes from a bank of questions they used to use on the exam and have been retired.


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## yaoyaodes (Aug 31, 2021)

Am I unders


akyip said:


> Normally in a balanced 3-phase system, the phase currents - which are fundamental-sequence currents, also known as 1st harmonic positive-sequence currents - cancel out at the neutral connection point. This is because of the 120-degree displacement between each phase in a balanced 3-phase system.
> 
> 1<0 + 1<-120 + 1<+120 = 0
> 
> ...


Thanks

Am I understanding correctly. 

First Harmonic is positive sequence, Second Harmonic is negative sequence, Third Harmonic is zero sequence.


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## Sam_ (Sep 1, 2021)

yaoyaodes said:


> Am I unders
> 
> Thanks
> 
> ...


Yes, that's correct


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