Harmonic Filtering

Passive or Active Harmonic Filtering

When it comes to mitigating harmonics to compensate for harmonic distortion, the two main technologies commonly used are passive harmonic filters (PHF) and active harmonic filters (AHF). With such effective options at our disposal, the frequently asked question is "which one should I use?" How would you answer this question? As with most things in life, there is no definitive answer... it depends on several factors.

Using passive harmonic filters or active harmonic filters is all about how to win the project and balancing a combination of technical and business considerations. How many VSDs and where are they located? If harmonic mitigation is provided for a frequency converter, a PHF would be the logical solution due to the lower cost. However, as soon as you work with more than one VSD, an AHF becomes more profitable. Maintenance As a passive device, a PHF on each unit can be a less intrusive method of compensation as no ongoing maintenance is required.

PerformanceA PHF is specifically designed to mitigate VSD harmonics. Although most PHFs go as low as 10%, an AHF with 5% THDi can perform better over the full load range and also improve the power factor if needed and balance the load across all three phases. An AHF mitigates all types of harmonics from VSDs, lighting, switching power supplies, thyristor circuits to data centers and does it anywhere within the facility. Is this a new "greenfield" site or an existing
site? Another consideration is the ability to compensate at the frame or at the individual harmonic source.

This decision between group payment and centralized payment depends on the nature of the site or project. If you are considering a new possibility, the harmonic mitigation strategy can be implemented at the design stage. If you are working with an existing website, the solution provided must be sent to the & Limitations of the existing system. Perhaps the most important decision: dimensioning. The types of loads in a system must be considered in order to achieve the best value for money
. There are often many possible combinations of AHF & PHF solutions that can be used for an application and the important consideration is to choose 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 point load in a system, such as a chiller, the correct solution could be a PHF on the chiller and an AHF on the main switchboard, or an AHF on the chiller and an AHF on the switchgear. In both cases, size matters...because size determines cost. In other applications, a cumulative VSD load distributed over many different floors of a commercial building can be serviced
by an AHF at the switchgear or motor control center on each floor.

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