In order to understand why there is a need for a harmonic solution guide, we need to go back to the end of the 19th century, when the increasing demand for electricity led to a requirement for public power supply. The conflict between the two concepts “AC” and “DC” led to the “war of currents” around 1890. Both technologies were promoted and installed, but finally the “war” was won by the supporter of the alternating current technology, against the supporter of the direct current led by Thomas A. Edison. The victory was mainly secured by the ability to transmit energy over long distances by using transformers. Recognizing the advantage of the alternating current, George Westinghouse bought patent rights of the transformer (1885 called “secondary generator”) from Lucien Gaulard and John Gibbs and the victory of the AC current took its course.