Electric

In the context of this forum, I guessed you are asking about the harmonics in power system. There are many threads available on this topic. You can search for them. In addition, there are thousands of links shows up in Google search for power system harmonic, however only few are the good documents for the beginners to understand it. Here are the links for some of the good ones. The last one is more elaborate and mathematical but it is the best one though. In fact, the concept of harmonics comes from the mathematics 'Fourier Series'. So, the better understanding of harmonics requires the good concept of 'Fourier Series'. The chapter 2 of the last link has pretty detail about it.

http://www.rose-hulman.edu/class/ee/HTML/ECE471/PDFs/Lect15.pdf

http://www.we-energies.com/business/energyeff/harmonics.pdf

http://www.powerstudies.com/articles/Harm_Intro.pdf

http://www.wmea.net/Technical%20Papers/Power%20System%20Harmonics.pdf

The method for measuring the harmonics is some kind of confusing especially to the beginners, because there are three different methods used for measuring the harmonics. The three methods are:

(1) Crest Factor (CF): It is ratio of the Peak of wave form to the rms of wave form, a true sine wave has its value 1.414. A wave having the CF less than 1.414 tends to be flat-tapped, while a CF greater than 1.414 indicates a voltage that tends to be pointy. CF is also called Peak Factor. This method is generally used for the measuring of harmonics contained in the UPS output.

(2) Total Harmonic Distortion (THD): The total harmonic distortion is the square root of the sum of the squares of the harmonic voltages divided by the fundamental voltage. A true sinusoidal wave has this value 0. This method is used for measuring the harmonics introduced by the non-linear loads in power system.

(3) K-Factor: It is a weighting of the harmonic load currents according to their effects on transformer heating. A K-factor of 1 indicates a linear load (no harmonics), while K-factor 20 indicates large amount of harmonic content. This method is used to measure the thermal effect of harmonics on transformers.

- MS