The occurrence of harmonic in power system is mainly caused by two factors:

(2) for the design of the equipment changes.In the past tended to adopt under the rated conditions work or margin larger design.Now in order to compete, to tend to adopt under the condition of critical electrical equipment design.For example, some design work in order to save material to make magnetic materials in deep saturation magnetization curve segment, and in running the segment will lead to serious distortion waveform excitation material.Figure 1 for three-phase six pulse rectifier device principle diagram of ac current of the Fourier series expansion is:

Visible containing the ac current harmonics, the harmonic number (6 k + 1) times, every harmonic contains at a rate of 1 / n.

                                                 Dingfeng Capacitor---The Cause of Harmonic Wave