Solving measures of Electric Harmonic Hazard(1)

What are harmonics?

The  main cause of harmonic generation is caused by the non-linear load. When the current flows through the load, there is no linear relationship between the current and the applied voltage, so that the non-sinusoidal current is formed and the harmonics are generated. The harmonic frequency is the integral multiple of the fundamental frequency in number, which is confirmed by the analytical principle of French mathematician M. Fourier. Any repeated waveform can be decomposed into sinusoidal components containing fundamental frequencies and a series of harmonics that are fundamental multiples. Harmonics are sine waves, each harmonic has a different frequency, amplitude and phase angle. Harmonics can be divided into even and odd harmonics. The third, fifth and seventh order harmonics is odd harmonics, while the 2, 14, 6 and 8 harmonics are even harmonics. If the fundamental wave is 50 Hz, the second harmonic is lOOHz. The third harmonic is 150 Hz. Generally speaking, the damage caused by odd-order harmonics is more and more serious than that caused by even harmonics. In a balanced three-phase system, due to the symmetry, even harmonics have been eliminated, only odd harmonics exist. For the three-phase rectifier load, the harmonic current is 6n ±1 harmonics, such as 5, 7, 11, 13, 17, 19, etc. The frequency converter mainly produces the fifth and seventh harmonics.