The hazards of harmonics
Generally speaking, the impact of frequency converters on power systems with relatively large capacities is not very significant. However, for systems with small capacities, the interference caused by harmonics cannot be ignored. It is a form of pollution to the public power grid, and harmonic pollution poses a serious threat to the power system, mainly manifested in:
(1) Harmonics cause additional losses to power supply lines. Due to skin effect and proximity effect, the resistance of the line increases with frequency, resulting in energy waste. As the current flowing through the neutral line is very small during normal operation, its conductor is thin. When a large amount of third harmonic flows through the neutral line, it will cause overheating, insulation aging, shortened lifespan, and even damage to the conductor;
(2) Harmonics affect the normal operation of various electrical equipment, causing additional power loss, heat generation, mechanical vibration, and noise to rotating machines such as generators; For circuit breakers, when the current waveform crosses zero, the presence of harmonics may cause high dldt, which will make it difficult to disconnect and prolong the cutting time of fault current;
(3) Harmonics cause resonance in capacitors in the power grid. Under power frequency, capacitors installed for various purposes in the system have much larger inductive reactance than those in the system, and resonance does not occur. However, at harmonic frequencies, the inductive reactance value increases exponentially while the capacitive reactance value decreases exponentially. This may lead to resonance, which amplifies harmonic currents and causes equipment such as capacitors to be burned out;
(4) Harmonics cause local parallel and series resonances in the public power grid, thereby amplifying harmonics, greatly increasing the above-mentioned hazards and even causing serious liability accidents;
(5) Harmonics will cause misoperation of relay protection and automatic devices, and result in significant errors in instruments and energy metering; Harmonics also pose significant harm to other systems and power users; If there is interference with nearby communication systems, some may cause noise and reduce communication quality, while others may lose information, making the communication system unable to function properly, affecting the accuracy of electronic equipment, and reducing the quality of precision machined products; The lifespan of equipment is shortened, and the working conditions of household appliances deteriorate.