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# 5th and 7th Harmonics

## 5th and 7th Harmonics

(OP)
I fail to understand how introducing 30-degree phase shift can entirely eliminate the 5th and 7th harmonics.
I understand that in a wye-delta connection, a 30-degree phase shift is introduced. However, to completely eliminate the 5th harmonic (for 6 pulse rectifier), we require a phase shift of 180/5 = 36 degrees, and for the 7th harmonic, we need 180/7 = 25.71 degrees. Given that 36 and 25.71 degrees are close to 30 degrees, it's reasonable to assume that they are significantly reduced.
Is my understanding right? Some text books mention that by introducing 30-degree, 5th and 7th harmonics are cancelled.

### RE: 5th and 7th Harmonics

Yeah, shift of a harmonic is the fundamental shift plus the transformer shift times the harmonic number times the sign of the sequence. It seems weird but it does work.

5th harmonic - fundamental has a -30 shift and then add 5 * 30 * -1 = -150. Those two make -180. With no shift on the D-D side, the D-Y side cancels the D-D side.

7th harmonic - fundamental has a -30 shift and then add 7 * 30 * 1 = 210. Those two make -180. Same result as the 5th.

When one this sentence into the German to translate wanted, would one the fact exploit, that the word order and the punctuation already with the German conventions agree.

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