Passive filters

The offer of FDUEG includes custom solutions to filter unwanted disturbances on the line, while also optimizing the power quality of the supply. The service is complete, from the electrical measurements on site, to the realization of any kind of filter needed with characteristics of compactness, efficiency and long service life. The whole design phase is custom, based upon a client’s request.

The need for filters is given by the presence, within industrial plants, of non-linear loads as inverters, LED lighting, soft starters, rectifiers, motor drives or machinery as welding equipment and presses.

These users may provoke a non-optimal operation of their systems, since, because of their response, they distort the current absorbed and hamper the overall efficiency. This is due to the introduction of current and voltage harmonics, which lower the global power factor.

Apart from increasing power consumption and, thus, costs, the non-optimized system behavior directly impacts on the services life of the devices installed along the line: from breakers to transformers, down to the very power electronic components. Moreover, the protection apparatus needs to be oversized and may not operate as desired. It might also be that a power supply, although designed in a correct way, is not able to deliver enough power to the load just because of the harmonic distortion induced on the waveforms.

Passive Filters FDUEG
Notch Filter made in Italy FDUEG

Active and Passive filters: Passive harmonic filters manufacturers. We offer customized solutions

Power systems which include a rectifier need passive filters for harmonics mitigation. Since, qualitatively, this kind of converters always produces the same harmonic content on the supply, an effective filter may be studied before the installation to deal with the principal harmonic components which disturb the power supply. The number of single harmonics that can be treated separately can be discussed with the customer in terms of cost-effectiveness, and has no upper bound. FDUEG harmonic filters remove most of the current noise on the line, improving as consequence the voltage sine wave.

If the passive filter is installed on a line whose power factor is too low and inductive, the reactor-capacitor coupling can be tailored by the Technical Department so that the required capacitive compensation power is supplied. If, conversely, the power factor is naturally capacitive, load reactors are inserted to adjust the power flow.

This way, the system’s power factor can be led back to unity, reducing the absorbed power and its purchase costs while attaining the same performances from the power line. Plants can be used at full capacity immediately after the filter has been installed.

FDUEG tackles the filtering issue with a modular approach, making its passive filters adaptive to load fluctuations. Among the advantages of this solution, one can list efficacy, reliability, compactness and efficiency. These come with all typical characteristics of modular solutions, like easy and fast maintenance, quick substitution of the components and precise management of the power flow.

The whole product is confined in a standard cabinet, without any special installation requirement, equipped with control logic and electrical protection devices. Since the amount of moving parts is limited to contactors, the durability of the filter is considerably enhanced.

The company supplies both passive (electrical) and active harmonic filters (electronic). Each solution is tailored upon the needs of the customer.




Passive notch filter

The Engineering Department designs and supplies filters to prevent some specific harmonics to access a particular network. The quality of this kind of application has to be kept considerable, in order to grant selectivity and avoid overvoltage induced damage on the apparatus: all components are optimized to reduced their resistive component, increasing the band and closing the passage to the considered harmonic component.

The filter remains transparent to low frequencies, so that the normal operation of the power line remains the same as before the filter insertion.

These products are characterized by compactness, efficiency and durability, even if they work with medium voltage and a considerable power. In fact, the quality of the filter and the absence of active and moving components reduce to the minimum the product overheating and degradation.

The solution is definitely solid also in medium voltage operations. FDUEG’s design guidelines aim at keeping small dimensions and stability with respect to important mechanical stresses. The composition of the capacitive bank, together with the precision in construction of the magnetic products, permits the minimization of the tolerance on the resonance frequency attained. The efficacy of the apparatus is insured by a precise test phase in the company’s test room, which includes resonance calibration.

Solutions mounting a combination of filters together allow to erase any number of specific harmonics from the system, or to filter the spectrum within a certain band.

Low pass LC filters

FDUEG manufactures low pass filters with passive components, able to withstand strong currents. They are ideal to be installed in service of converters as inverters or rectifiers, and they are studied to improve the power quality in input and output of the power electronics components by cutting the high switching frequency and disturbances that may appear on the line.

The system’s performance remains untouched for what concerns low frequencies, typical of the usual grid operations. The global frequency response of the filter can be adjusted to meet a customer’s necessities.

The internal expertise knows how important it is to keep the frequency response stable at the different load conditions present. Because of this, the effects that aging and mechanical stresses have on the long run are kept into consideration from the start. The design conditions are fully respected and studied to grant the best performance of the filter.

Filters with kA-range currents are available, with air cooling or heat exchange through demineralized water. Insulation classes up to 3,6 kV are easily managed. Moreover, FDUEG has the capabilities to produced higher power rating components, based on the incoming requests.


Technical data

Typer Power Features Cooling
Passive harmonic filter Up to
Up to 1.1  kV AN – AF
Passive notch filter Up to 20 MVA Up to 36 kV AN – AF
Low pass LC filter Up to
6 kA
Up to 3.6 kV AN – AF – ANWF


Industrial electric power supply
Public, Medical and Commercial Buildings
Renewable Energies
fdueg applicazioni steelworks
Data Centers


    Contact us
    +39 0321 824131

    Related products

    • Italian
    • English
    • French
    • German
    • Russian