Query: Third Harmonic And Zero Sequence

Third harmonics are sine-wave as any other frequency, so they have all three "components". If you are adding them to the fundamental, then that's another question. They make the waveform more square. Does that answer your question?

thanks for the answer but somebody told me that in unbalanced three phase system, second harmonic is negative sequence only, 3rd harmonic current is of zero sequence type only and then again 4th harmonic is positive sequemce and so on.. If this is true can anybody please explain it to me? Link to any literature would be helpful. for example if i connect a power analyser to an unbalanced 3 phase supply. then 2nd harmonic will contain only -ve sequence or it will have all three parts viz +ve, -ve and zero sequence. ?

Dear Mr. Muditmah,

The Third and Multiples of Third Hormonics will be NULLIFIED and DOES NOT EXIST.

RAJESWARI

The first harmonics are the positive sequence

2nd are negative

Third are zero sequence

Forth are again positive and so on

To understand this (mathematically) is easy

Say the Fundamantals are

I_a = I Cos(ωt), I_b = I Cos(ωt+120), I_c = I Cos(ωt+240) (rotation I_a,I_b,I_c)

The second harmonics would be

I_a2 = I' Cos(2ωt), I_b2 = I' Cos 2(ωt+120), I_c2 = I' Cos 2(ωt+240)

ie I_a2 = I' Cos(2ωt), I_b2 = I' Cos (2ωt+240), I_c2 = I' Cos (2ωt+480)

ie I_a2 = I' Cos(2ωt), I_b2 = I' Cos (2ωt+240), I_c2 = I' Cos (2ωt+120)

This you can see is rotating in opposite direction (I_a,I_c,I_b)

Similarly the third harmonics are

I_a3 = I'' Cos(3ωt), I_b3 = I'' Cos 3(ωt+120), I_c3 = I'' Cos 3(ωt+240)

ie I_a3 = I'' Cos(3ωt), I_b3 = I'' Cos (3ωt+360), I_c3 = I'' Cos (3ωt+720)

ie I_a3 = I'' Cos(3ωt), I_b3 = I'' Cos (3ωt), I_c3 = I'' Cos (3ωt)

all in phase with each other and hence the sum is non zero at neutral

You can now go to fourth, fifth etc and see.

thanks and GA. I got it now