# harmonic currents

Discussion in 'Homework Help' started by amilton542, Nov 28, 2010.

1. ### amilton542 Thread Starter Active Member

Nov 13, 2010
496
64
what are harmonic currents, are they excessive currents travelling down the neutral from unbalanced loads? and why do they have effects on the wave cycle?

2. ### mik3 Senior Member

Feb 4, 2008
4,846
70
Harmonic currents are currents which have different frequency and amplitude than the mains frequency and they distort the pure sinewave current that is supposed to exist on the lines.

3. ### Cerkit Senior Member

Jan 4, 2009
286
3
How do they distort the pure sinewave if they are at different frequencies?

4. ### mik3 Senior Member

Feb 4, 2008
4,846
70
They will be added to the 50/60Hz sinewave that is expected to exist on the mains lines. It will be a high amplitude 50/60Hz sinewave with small amplitude sinewaves around it.

Here is a picture of a sinewave under low distortion:

The distortion can be as high as the resulting wave will not be a sine wave anymore.

Have a look at fourier series to find more about harmonics.

5. ### amilton542 Thread Starter Active Member

Nov 13, 2010
496
64
ive done some research, and have looked up about current distortion, voltage distortion, non linear loads and stuff but now , 3rd harmonics,4th harmonics,5th harmonics etc are poppin up, whats this tellin me? i thought there was only one type of harmonic current

6. ### amilton542 Thread Starter Active Member

Nov 13, 2010
496
64
its ok i think i got it, i think its how many cycles of the harmonics fit into the fundamentals complete cycle, so if there were 3 cycles of harmonics in the fundamental it would be 3rd harmonics

7. ### mik3 Senior Member

Feb 4, 2008
4,846
70
Exactly! A 3rd harmonic has 3 times the fundamental frequency and so on.