Harmonics in industry: A to apprehend common issue

Harmonics are sinusoid signals that are multiples of the primary signal frequency in power systems. These signals combine with the primary signal, which is then classified as contaminated. Harmonics are present in both voltage and current signals at the same time. They have an impact not just on power lines but also on neutral conductors with particular third harmonics from single phase loads.

Example of harmonic distortion

Harmonics are tolerable within specific boundaries. However, when such limitations are exceeded, harmonic repercussions become an issue. Harmonics raise the RMS value of the signal, causing current and heating to rise in conductors with time. It causes extra losses and accelerates thermal deterioration. In addition to the basic zero-crossings, the ensuing signal distortion might cause high-frequency peak values. Harmonics can create short-term disruptions to devices that employ rms, peak values, and zero-crossing triggering. Harmonic high frequency signals cause vibrations in spinning machinery and transformers, accelerating mechanical aging. As we may see, the concrete implications are numerous, with huge ramifications. It broadly encompasses process operation, overall system maintenance, and electrical distribution, with significant cumulative cost implications.

Harmonic effects and consequences

Harmonics are caused by non-linear loads that consume harmonic currents. Those loads are said to generate or inject harmonics into the network by convention. These currents travel via system impedances (source, transformers, cables) and produce harmonic voltages via Ohm’s law. Harmonic voltages cause a distortion in the supply voltage waveform throughout the network, whereas harmonic currents primarily affect the local network from which they originate. Resonance can also be used to amplify harmonic events. Standard power factor correction capacitors that are sensitive to harmonic voltages are likely to increase harmonic currents, necessitating derating or properly detuned reactors.

The fundamental interplay between harmonic current and voltage

Rectifiers are common harmonic sources. Variable Speed Drives (VSD) are the most popular and powerful devices embedded with it in industry, and Low Voltage VSD have a greater influence due to standard design. In industrial motor controllers, the VSD percentage might differ from the Direct On Line operation. Harmonic global pollution is affected by such load mix, as well as the associated loading. In any scenario, as soon as an LV VSD is present, the harmonic influence must be addressed.

The most prevalent harmonic mitigation technologies are Low Harmonic specialized LV VSD and Active Filters. The Low Harmonic (LH) option directly and significantly minimizes the harmonic influence of the LV VSD under consideration. An active filter (AF) is an electrical device that injects adaptative counter-harmonics to neutralize specified harmonics caused by one or more loads. The choice of a mitigation solution, either constant and devoted LH VSD or adaptative and mutualized AF, or finally a combination of both, is a balance between performance and investment throughout the process operation.