# NEW NCEES PROBLEM 533



## jcreit (Mar 30, 2009)

Can someone refer me to a link where I could get some more information about harmonics, or formula for harmonic problems.

Thanks in advance


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## niurou (Mar 30, 2009)

jcreit said:


> Can someone refer me to a link where I could get some more information about harmonics, or formula for harmonic problems.
> Thanks in advance


In general, if you understand Fourier transformation and Fourier series, you know non sinusoidal periodic wave can be decomposed to a series of sinusoidal waves with different order of frequency. perfect sinusoidal wave will not have other high order sinusoidal wave other than itself.

For a three phase system, if the load is balanced and linear(current is proportional to the voltage). the neutral will carry zero current, since the three phase currents cancel themselves.

if the load is non-linear, that means, although the voltage is sinusoidal, the current will not be. so the current will have some high frequency sinusoidal wave component. For a three phase system, at base frequency, phases are 120 degree apart, and they cancel out. But for third order harmonic current, the frequency is 3 times of 60hz, and the angle between them is 120x3=360 degree. 360 degree is essentially 0 degree, which means they are in phase. so now you have 3 vectors that are in the same direction. they will not cancel out, instead they will add up. The result is neutral will carry a large current if the third order harmonic component is big.

These are just from my own understanding, it could be wrong.


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## tuki (Apr 12, 2012)

Niurou you are totally right there is a section on Power Qualit by C Sankaran book. The expressions for the third harmonics show that they are in phase and have zero

displacement angle between them. Figure 4.7b shows the third harmonic phasors.The third harmonic currents are known as zero sequence harmonics due to the zero

displacement angle between the three phasors .


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