The electricity supply can be affected by various types of disturbances, one of the most peculiar of which is harmonics. Harmonics differ from other disturbances caused by electricity generation in that they originate from the electrical loads themselves, or rather, from some of them.
Harmonics originate specifically from non-linear loads, where there is no proportionality between current and voltage, resulting in harmonic distortions consisting of sinusoidal waves whose frequency is an integer multiple of the fundamental signal. The combination of harmonics with the fundamental signal distorts the resulting waveform, which can negatively impact the operation of installed equipment.
Harmonics primarily originate from widely used devices such as variable frequency drives (VFDs), induction motors, switched-mode power supplies, and various other types of electronic devices, to name the most common. The widespread use of these electronic devices in all types of installations has significantly contributed to harmonics issues, as they typically convert AC to DC, often operate at high switching frequencies, and exhibit non-constant impedance.
Broadly speaking, harmonics reduce efficiency by increasing apparent power rather than actual power, which means that electrical installations have to be oversized, resulting in additional costs. They can also overheat equipment such as motors, cables, capacitors and transformers, shortening their useful life and increasing costs and downtime.
Another unwanted effect of harmonics is reduced power factor, which entails disproportionately high current consumption relative to actual power usage, and can lead to financial penalties imposed by the electricity supplier. Additionally, sensitive equipment may misinterpret signals and be affected by electromagnetic interference, which can lead to more inaccurate and less reliable results.
One of the most visible effects of harmonics is flickering, i.e., variations in lighting intensity that are noticeable and sometimes annoying to people.
The long list of problems caused by harmonics also includes the inappropriate tripping of protective devices such as circuit breakers, differential switches and relays. This can result in unwanted shutdowns and may create conditions like amplification or resonance, phenomena that occur when harmonic frequencies coincide with the operating frequencies of the loads, potentially leading to further overheating issues and severe faults.
Of course, the best way to deal with harmonics is to stop them from happening in the first place. This can be done by using converters and rectifiers with a configuration that prevents or minimises the generation of harmonics. Modernising old uninterruptible power supply (UPS) systems by replacing them with low-distortion models equipped with advanced digital control and topologies that cancel out harmonics while offering excellent performance is another recommended solution.
Whenever harmonics are an issue in an installation, we also recommend adding anti-harmonic filters, which can compensate for the reactive power factor of inductive loads and prevent resonance.
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