The rigorous harmonic analysis gets involved because of interaction between harmonic-producing equipment and the power system, the practical limitations of modeling each component in a large power system, the extent to which the system should be modeled for accuracy and the types of component and nonlinear source models. The purpose of harmonic analysis is to ascertain the distribution of harmonic currents, voltages, and harmonic distortion indices in a power system. This analysis is then applied to the study of resonant conditions and harmonic filter designs and also to study other effects of harmonics on the power system, that is, notching and ringing, neutral currents, saturation of transformers, and overloading of system components. There are a number of methodologies for the calculation of harmonics and effects of nonlinear loads. One method uses harmonic sources on the ac network, and the other injects harmonic currents into the ac system using high-voltage dc converter.