Harmonic current direction

[ciy]

Hi,

I find an image in the website accidently about the harmonic issue.

This image mark the direction of triple order harmonic.

So, I curious and wonder to know their direction if lost the neutral line or add grounding wire.

Please find the five(5) schematic as attached and advise these triple order direction.

Thanks in advance.

 

[7anoter4]

In my opinion, roughly, you have only voltages full of harmonics. The current is the result of flowing in a suitable closed circuit provided with impedances. If no circuit is suitable for harmonics current circulation it will be not any draining current-the current per phase will be deformed-not sinusoidal form-and IA+IB+IC=0 always. It will not be filtered out.
Since between medium voltage side of transformer and low voltage side it is not a galvanic connection no current will flow through the grounding resistance-except capacitive current collected by medium voltage cables or overhead lines and medium-voltage transformer windings.

 

[electricpete]

I would add brief derivation of the assertion that triplen harmonics do not flow if there is no external path to the neutral.

ASSUME the three phase currents are perfectly balanced. That means they are the same magnitude and shifted by "120 degrees" of fundamental frequency F0.

How much time is this shift of 120 degrees of fundamental? It is Tshift=(1/3)*T0 where T0 is fundamental period (T0=1/F0).

How many degrees is Tshift compared to the 3rd harmonic frequency T3 = T0/3?

Tshift = T0/3 = (3*T3)/3 = T3. The phase shift of the 3rd harmonic is one full cycle (of 3rd harmonic). All three 3rd harmonic are in-phase. That is why they must sum to zero if no external path.

BUT we started with an assumption of balanced condition. It's unknown whether that assumption was stated in your reference.





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(2B)+(2B)' ?

 

[ciy]

7anoter4 and electricpete,

Thanks for your excellent opinion.

I also think that triplen harmonic current flow under a loop condition.

Again, please advise how to get the magnitude of neutral current under unbalance condition?

Should include triplen harmonic and unbalance current?

Regards,