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Passive Filter vs Active Filter. Which one to use?

Passive Filter vs Active Filter. Which one to use?


When it comes to mitigating harmonics to comply with Australian Standards for harmonic distortion, the two main technologies that are commonly applied are Passive Harmonic Filters (PHF) and Active Harmonic Filters (AHF).

With such effective options at our disposal, the common question asked is “Which one do I use?”

How would you answer that question?

Actually, as with most things in life there isn’t one definitive answer….it depends on a number of factors. Whether to use Passive Harmonic Filters or Active Harmonic Filters is largely a question of how to win the project and balancing a combination of commercial vs engineering considerations.

How many VSD’s and where are they located?

If you are providing harmonic mitigation for one VSD, a PHF would be the logical solution due to the lower cost. However as soon as you are working with more than one VSD, an AHF becomes more cost effective.


Being a passive device, a PHF on each drive can be a less intrusive method of compensation as it does not require any ongoing maintenance.


A PHF is designed specifically to mitigate the harmonics for VSD’s. Although most PHF’s achieve 6-8%, the MTE Matrix AP can reduce the THDi to 5% from 30%-100% of load and will also assist with the power factor. This is a great result but if you require even greater performance, you need to consider an AHF.

An AHF can produce a result better that 5% THDi across the load range and it can also improve the power factor and balance the load on all three phases if required. An AHF mitigates all types of harmonics from VSD’s, lighting, switch mode power supplies, thyristor switching to data centres and it will do it at any location within the plant.

Is it a new ‘greenfield’ site or an existing site?

Another consideration is the choice of compensating at the switchboard or at the individual source of harmonics. This group compensation vs centralised compensation decision depends on the nature of the site or project.

If you are considering a greenfield opportunity, the harmonic mitigation strategy can be implemented at the design stage. If you are operating with an existing site, the solution provided must adapt to the parameters & limitations of the existing system.

Perhaps the most significant decision – Sizing

The types of loads in a system need to be considered so that the optimum cost vs performance outcome can be achieved. Often there are many possible combinations of AHF & PHF solutions that can be employed for an application and the important consideration is choosing the combination that achieves the desired performance at the most economical cost.

If there are many and varied loads, an AHF would be the preferred method. However, if there is a significant single load in a system such as a chiller for example, then the correct solution could be a PHF on the chiller and an AHF on the main switchboard or an AHF on the chiller and AHF on the main switchboard. In both cases, sizing is important……as size dictates the cost. In other applications, a cumulative VSD load spread across many different floors of a commercial building can be catered for by an AHF at each floor’s switchboard or motor control centre.

Drawing on many years of experience with such calculations, Fuseco’s Power Quality engineers can assist you to achieve the optimum cost vs performance outcome for your project. We welcome you to contact Fuseco to organise a consultation to discuss your requirements.

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