At present, in China's industrial enterprises, the harm of harmonics is mainly manifested in the following aspects:

(1) Cause voltage distortion

Because the power system has internal impedance, harmonic load currents will cause harmonic voltage distortion of the voltage waveform (which is the source of "flat-top" waves). This impedance has two components: the impedance of the cable routing inside the electrical installation after the power interface (PCC) and the impedance within the power supply system before the PCC. The distorted load current caused by the nonlinear load creates a distorted voltage drop across the impedance of the cable. The synthesized distortion voltage waveform is added to all other loads connected to the same circuit, causing harmonic currents to flow through, even if these loads are linear.

(2) Cause the power cable to heat up

When the high-frequency current passes through the wire, the current has a skin effect, obviously the presence of high harmonic current aggravates the skin effect of the line, and the current density on the outer surface of the line increases, resulting in the heating of the line (phase line and neutral line).

(3) Electric motor

The harmonic current generated by the harmonic voltage on the short-circuit impedance of the motor and the negative sequence fundamental current of the motor together make the equipment produce additional heat loss, and it is easy to develop into interference torque when the motor starts, resulting in difficulty in starting the motor and reduced operating efficiency. Too high a harmonic content can cause damage to the motor.

(4) Capacitors

Due to the parameter coordination of ICs in the power grid, capacitors inevitably have an amplifying effect on some harmonics. If the capacitor parameters are not properly selected, the capacitor is used for reactive power compensation, and the fundamental reactive current is greatly reduced, there may be a large increase in the harmonic and fractional harmonic currents in the supply current and the capacitor current, resulting in overtemperature and overvoltage of the capacitor, and then damage. In recent years, the service life of reactive power compensation capacitors in industrial enterprises has been greatly shortened by this.

(5) Relay protection

Harmonics can cause relay protection and automatic device malfunction, and will make the measurement of electrical measuring instruments inaccurate, which is a major hidden danger in the stable operation of the power grid.

In addition, the harm of harmonics to electronic equipment and the impact on communication are also obvious. Harmonic pollution generated by power electronics has become a major obstacle to the development of power electronics technology itself. For the power system environment, no harmonics is one of the main signs of green environmental protection.