7/8 – Electrical equipment: harmonic mitigation

How to achieve “harmonic mitigation” ?

Several different solutions are proposed for Harmonic mitigation. The right choice is always dependent on a variety of factors, such as the activity sector, the applicable standards, the power level …. Several solutions are relative to Variable Speed Drives, as this type of electrical equipment represents a large part of the installed power in industrial installations and the most significant power harmonic current generators.

  • AC-Line or DC-link chokes for Drives
    They are commonly used up to about 500kW unit power or 1,000kW total drives power. Depending on the transformer size and cabling, the resulting THDu will be ~ 5%, which is usually well accepted in industrial networks.


  • C-less technology Drives
    This technology applies to Variable Speed Drives and offers a reduced current distortion compared to traditional technology. Combined with an advanced control algorithm, this solution is suitable for applications with low over-torque requirements like centrifugal pumps, fans and HVAC machines.


  • Multi-pulse arrangement
    This solution includes a dedicated transformer directly supplied from the MV network. Standard is the use of a 3-winding transformer providing a 12-pulse supply for one or multiple rectifiers or drives. This limits the power harmonic emission considerably and usually no further mitigation is necessary. Besides, multi-pulse solutions are the most efficient in terms of power losses. This is usually used for drives above 400 kW, but could also be reasonable for smaller power ratings.


  • Active Front End (AFE)
    An Active Front End is a sophisticated electronic circuit connected on the supply side of a Variable Speed Drive. This is the best performing solution concerning harmonic mitigation, limiting the THDi below 5%. All the applicable standard requirements can be met. No detailed system evaluation is necessary, making this solution the easiest to implement.


  • Passive filter
    A passive filter consists of reactors and capacitors set up in a resonant circuit configuration, tuned to the frequency of the power harmonic order to be eliminated. A system may be composed of a number of filters to eliminate several harmonic orders.


  • Active filter
    An active filter is an electronic equipment which injects, in opposite phase, the same harmonic current as drawn by the load, such that the line current remains sinusoidal.


  • Hybrid filter
    A hybrid filter is a combination of a passive filter and an active filter in a single unit.

Jacques Schonek


  • Very informative post! I hope the local electricians know this. The transformer outside our house keeps shooting sparks. One time, it even burst into flames.

  • Hi, I am project engineer for one consultant company.

    Currently, I working on mitigating flicker issue in some steel manufacturing plants. After made some assessment we found that the problem comes from their loads (of course :-) ). One plant has big arc furnace. On another plant the culprit is billet-forming machine, another one is big DC drive. The common thing for all of these are; they are run on MV system (3.3 and 6.6 kV)

    We plan to use active filter like Accusine since it has fast compensation response, but unfortunately it only run on LV.

    Do anyone has experience how to overcome this issue?
    Could we use accusine on MV system by inserting step-up transformer?

    Thank you for any help provided.


    • Hello Abdalla!! the voltage flicker that you are talking about is that issue solved, by now or are you still looking for a solution?? if you have found a solution then please share what you did, if not then please provide some more details!!
      the flicker you are talking of , is that only a transient phenomenon, as in only during the starting or increasing the loading of the motors heavily, or is the flicker constantly happening, even after about 10-20 seconds of starting the equipment ??

  • I agree with Fred M., it is a good post but I am wondering what Fred is talking about when he refers to the transformer?

  • A very nice post Mr.Jacques Schonek, please provide some references online or books, which can provide deatails into these methods.. :)

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