Jun 02, 2020

**1. What are harmonics?**

Harmonics refers to the components of the order that are obtained by Fourier series decomposition of the periodic non-sinusoidal AC components and are greater than integer multiples of the fundamental frequency. They are usually called higher harmonics, while the fundamental wave refers to its frequency and power frequency (50Hz) The same component. The interference of higher harmonics is a major "pollution" that affects the quality of power in the current power system and needs to be reduced as much as possible.

Harmonic (harmonic wave), in a strict sense, harmonic refers to the electric energy contained in the current with an integer multiple of the fundamental wave, generally refers to the Fourier series decomposition of periodic non-sinusoidal electric energy , The rest of the electricity generated by the current greater than the fundamental frequency. Broadly speaking, because the effective component of the AC power grid is a single frequency of the power frequency, any component different from the power frequency can be called a harmonic.

The main reasons for the generation of harmonics are: due to the sinusoidal voltage pressurizing the nonlinear load, the fundamental current is distorted to generate harmonics. The main non-linear loads are UPS, switching power supply, rectifier, frequency converter, inverter, etc. Overtones are harmonics in physics, but the definition of order is slightly different. Audio with 2 times the fundamental frequency is called primary overtone, audio with 3 times the fundamental frequency is called second overtone, and so on.

The frequency of the harmonics must also be equal to an integer multiple of the frequency of the fundamental wave. A wave with a frequency three times the fundamental wave is called a third harmonic, a wave with a frequency five times the fundamental wave is called a fifth harmonic, and so on.

**2. IEEE 519 Standard Harmonics Limit**

**Voltage harmonic limit:**

**Current distortion limit:**

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