EMC & Circuit Protection
Understanding harmonics and the art of harmonic filters
Paul Bentley, GD Rectifiers’ managing director, speaks exclusively to CIE magazine about why understanding power quality matters and how the right harmonic filter can improve efficiency, reliability and equipment performance
M
odern industrial electrical systems are becoming increasingly efficient, automated and electronically
controlled. Variable frequency drives (VFDs), uninterruptible power supplies, switched-mode power supplies, EV charging equipment and other power electronic loads have transformed the way electrical energy is controlled. However, these technologies can introduce an often- overlooked challenge: harmonic distortion. For engineers responsible for power quality, understanding where harmonics come from, how they affect an electrical installation and how to select the right
42 September 2026
mitigation technology is becoming increasingly important. At GD Rectifiers, the UK’s exclusive distributor for Enerdoor harmonic filters, our technical team helps customers assess their requirements and identify appropriate power quality solutions.
What are harmonics?
In an ideal AC electrical system, voltage and current waveforms are sinusoidal. The fundamental frequency in the UK is 50 Hz, meaning the fundamental component of the waveform repeats 50 times per second. Harmonics are additional frequency components that occur at integer multiples of this fundamental frequency.
Components in Electronics
For example: ● 1st harmonic = 50 Hz fundamental ● 3rd harmonic = 150 Hz ● 5th harmonic = 250 Hz ● 7th harmonic = 350 Hz ● 11th harmonic = 550 Hz
Non-linear loads draw current in a way that is not proportional to the applied voltage waveform. This creates distorted current waveforms containing harmonic frequencies. Common sources include variable frequency drives, rectifiers, UPS systems, switched-mode power supplies, industrial automation equipment and other electronic power conversion systems. The increasing use of these technologies means harmonic distortion can become
a significant consideration in modern installations.
Why are harmonics a problem? Excessive harmonic currents can have huge consequences for electrical equipment and system performance. They can contribute to: ● Increased transformer and cable losses ● Additional heating in electrical equipment
● Reduced system efficiency ● Voltage waveform distortion ● Overheating of neutral conductors ● Increased stress on capacitors ● Interference with sensitive equipment ● Reduced power factor
www.cieonline.co.uk
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