What will happen when the harmonic distortion reaches its peak?
Sep 19, 2025| In an ideal power system, the voltage and current should be perfect and smooth sine waves. However, in the real power grid, it is filled with various nonlinear loads (such as frequency converters, rectifiers, LED lights, UPS power supplies, etc.), which act like rough "editors", distorting and cutting the smooth sine waves, generating a large amount of noise with frequencies that are integer multiples of the fundamental frequency - these noises are called harmonics.
Total Harmonic Distortion (THD) is a quantitative indicator used to measure the degree of waveform distortion. When the THD rate suddenly rises to its peak, it is not merely a simple numerical change; it indicates that the entire power system is facing an all-round "distortion storm", with consequences that are severe and multi-faceted.
1. The direct impact on power equipment and lines
⑴ Transformer and Cable: Harmonic currents will cause significant skin effect and proximity effect, causing the current to flow more concentratedly on the surface of the conductor, resulting in an increase in effective resistance. At the same time, high-frequency harmonics will cause additional iron loss in the core. The increase in resistance and the increase in loss jointly lead to a sharp rise in the temperature of the transformer and the cable. In mild cases, this may accelerate insulation aging and shorten the lifespan; in severe cases, it may cause insulation breakdown and fire. A transformer operating normally under full load at the power frequency may already be in a severely overloaded state in a harmonic environment.
(2) Rotating machines (generators/motors): The harmonic currents flowing into the motor will generate a reverse rotating magnetic field, resulting in braking torque, reducing the motor efficiency, and causing overheating of the windings and mechanical vibration. For generators, the harmonic load will cause additional heat to be generated in the rotor, which may exceed the capacity of their cooling systems, leading to rotor damage.
⑶ Capacitors and reactive power compensation devices: This is the area most prone to harmonic problems. Capacitors have extremely low impedance to high-frequency harmonics, absorbing a large amount of harmonic current, which can lead to severe overcurrent. What's even more dangerous is that they may form a parallel resonance with the system inductance, amplifying the harmonic current by several times or even dozens of times. This can easily cause the capacitor fuse to blow, the capacitor to bulge or even explode, making the reactive power compensation cabinet unable to function properly.