EMC & Circuit Protection


Harmonic currents do not exist in isolation. Transformers, generators, cables, capacitors and other equipment can all influence the behaviour of the electrical network. This is why a filter that works effectively in one installation may not necessarily be the correct solution for another. Harmonic mitigation is sometimes approached primarily as a compliance exercise; however, the benefits can extend much further. Reducing harmonic distortion can help reduce losses and unnecessary heating, improve power quality and support more reliable operation of connected equipment.


● Increased operating temperatures ● Premature equipment failure In industrial environments, the consequences can lead to increased maintenance requirements, unexpected downtime and higher operating costs. The challenge is that harmonic problems are not always immediately obvious. A system may appear to operate normally while components are subjected to additional thermal and electrical stress.


Total Harmonic Distortion — what does THD mean?


One of the key measurements used when assessing harmonics is Total Harmonic Distortion (THD). THD provides an indication of the level of harmonic content compared with the fundamental component. For current, this is commonly expressed as THDi, while voltage distortion is expressed as THDv.


A simplified representation of current THD is: where I1


represents the fundamental current and the other terms represent harmonic currents. The higher the THDi, the greater the harmonic distortion present in the current waveform. However, selecting a filter should not be based on a THD figure alone. The characteristics of the complete electrical installation, load profile, supply impedance and operating conditions all need to be considered. This is where technical advice becomes particularly valuable.


The art of harmonic filtering Harmonic filtering is about more than simply installing a device into a circuit. The filter must be correctly selected for the


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application, electrical characteristics and required performance. There are two principal approaches: passive harmonic filtering and active harmonic filtering.


Passive harmonic filters


Passive filters use combinations of inductive and capacitive components to provide a path for unwanted harmonic currents, reducing the amount of harmonic distortion seen by the supply. They can be an effective solution for applications with relatively predictable loads and are particularly suited to individual drives and defined applications.


Enerdoor’s FINHRM range provides passive harmonic filtering designed to attenuate current harmonic distortion and overvoltage spikes. The FINHRM5 range can reduce current THDi to below 5 per cent under specified conditions and is available across a broad current range. The range is suitable for applications including variable frequency drives, HVAC systems, industrial equipment, pumps and UPS systems.


Active harmonic filters Active harmonic filters take a different approach. Rather than relying solely on passive components, they actively monitor the electrical system and inject compensating currents to counteract unwanted harmonic currents. This can make active filtering particularly attractive where loads are variable, multiple loads contribute to harmonic distortion or where a more flexible solution is required.


Enerdoor’s active harmonic filters operate in parallel and can compensate current for single or multiple load applications operating under varying load conditions.


Choosing the right harmonic filter One of the biggest mistakes when approaching harmonic mitigation is selecting a filter merely according to the equipment’s rated current. An in-depth technical assessment should consider several factors. 1 Identify the source


First establish which equipment is generating the harmonics. Is the problem associated with one large VFD, multiple drives, a UPS system or a combination of non-linear loads?


2 Measure the installation Where possible, measure the electrical system under representative operating conditions. Measurements of current, voltage, THDi, THDv, load profile and individual harmonic orders can provide valuable information.


3 Understand the load profile A system operating continuously at a relatively stable load presents a different filtering challenge from a facility where loads vary significantly throughout the production cycle.


4 Consider the required performance The objective may simply be to reduce distortion to an acceptable level, or it may involve achieving a specific power quality target.


Enerdoor offers solutions designed to reduce harmonic distortion to low levels, with certain filter ranges specified for THDi below 5 per cent under defined operating conditions.


5 Look at the complete system


Enerdoor’s FINHRM5C passive harmonic filters are designed to reduce current THD to below 5 per cent under specified conditions while also improving flicker and power factor. The manufacturer identifies applications including compliance with IEEE-519 and IEC 61000-3-12 requirements.


Technical advice matters Harmonic filtering is an area where engineering support can make a significant difference. At GD Rectifiers, we understand that customers don’t simply need a catalogue part number. They need to know which technology is appropriate, how it should be specified and whether it will achieve the required result. GD Rectifiers provides access to Enerdoor’s range of active and passive harmonic filters and helps customers identify a suitable solution for their application. Enerdoor brings extensive experience in EMC, power quality and CE certification, with dedicated expertise in harmonic measurement, analysis and solutions. Filters can be supplied for individual applications or wider facility requirements, with Enerdoor solutions available across a broad range of current and voltage ratings.


As industrial electrical systems become increasingly dependent on power electronics, harmonic distortion will continue to be an important consideration for designers, engineers and maintenance teams. For engineers looking for technical advice on harmonic mitigation, GD Rectifiers can help assess the application and recommend an appropriate Enerdoor solution. From passive filters for individual drives through to active solutions for changing and multiple loads, the combination of Enerdoor technology and GD Rectifiers’ technical support provides a practical approach to improving power quality.


www.gdrectifiers.co.uk Components in Electronics September 2026 43


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