# ZigZag transformer and harmonics

1. Nov 10, 2016

### KraakeCrest

Hi again,

Can/are zig zag connections used on the secondary side to avoid triplen harmonics flowing further up the power system? Lets say 3rd harmonics are flowing up the power system from some loads connected to phases a,b,c and the neutral. Since 3rd harmonic are all in phase, the ampere-turn created will cancel in a zig zag connection and thus not couple to the primary and further up the power system?

This pdf: http://static.schneider-electric.us...ansformers/Harmonic Mitigating/7400DB0301.pdf says on page 12 and 13:
"With all of the triplen harmonics in phase with each other, by vector analysis, the triplen harmonic currents produce ampere-turn fluxes that cancel each other such that no currents are induced in the primary winding. For this to work, the triplen harmonics must be real currents and not mere mathematical identities derived by the Fourier Transformation."

The last sentence in bold kind of confuses me.

2. Nov 11, 2016

### jim hardy

3. Nov 12, 2016

### KraakeCrest

Nice post @jim hardy , so from that post if I understand correctly, you can use a zig zag connection as secondary in a transformer to prevent triplen harmonics from coupling magnetically back to the primary.

But I am still alittle confused about the sentence in the PDF: "For this to work, the triplen harmonics must be real currents and not mere mathematical identities derived by the Fourier Transformation."

So if the current caused by the load contains fundamental + 3rd AND 5th harmonic, this would not work because the waveform is not a pure 3rd harmonic waveform? Hmm..