In AC (alternating current) power systems, harmonics refer to the additional frequencies that are integer multiples of the fundamental frequency of the power supply. The fundamental frequency is the primary AC waveform, which is typically 50 or 60 Hertz (Hz) depending on the region. Harmonics are created when nonlinear loads are connected to the power system. These nonlinear loads, such as electronic devices, power electronics, and certain types of lighting, draw current in a non-sinusoidal manner.
The presence of harmonics in the power system can lead to several issues, including:
Increased losses: Harmonics cause additional heating and losses in electrical equipment, such as transformers, motors, and cables, reducing their efficiency and potentially shortening their lifespan.
Overloading of neutral conductors: In three-phase systems, harmonics can cause imbalances in the neutral current, leading to overloading of the neutral conductor.
Voltage distortion: Harmonics can distort the voltage waveform, resulting in poor power quality and affecting the operation of sensitive equipment.
Resonance: Harmonic frequencies can coincide with the natural resonant frequencies of the power system, leading to excessive voltage and current levels and potential equipment damage.
To mitigate harmonics in AC power systems, various methods and technologies can be employed:
Passive filters: These are tuned LC circuits that act as low-pass filters, diverting harmonics away from the power system.
Active filters: Active power electronic devices can generate counteracting harmonic currents, canceling out the effects of harmonics in the system.
Transformers with low harmonic content: Special transformers designed to handle harmonics can be used to reduce their impact.
Multi-pulse converters: These converters use multiple sets of diodes or thyristors to rectify the AC power, reducing the generation of harmonics.
Phase-shifting transformers: By introducing phase shifts between different transformer windings, harmonics can be mitigated.
Use of harmonic-resistant equipment: Selecting electrical equipment designed to handle harmonic loads can minimize issues related to harmonics.
Load distribution: Distributing nonlinear loads across multiple phases can reduce the negative impact of harmonics on individual phases.
Power factor correction: Improving the power factor of the system can also help reduce harmonic levels.
It's important to note that the specific mitigation techniques depend on the nature and severity of the harmonic issue in a particular power system. Harmonic analysis and modeling are often conducted to identify the sources of harmonics and determine the most appropriate mitigation methods for a given situation.