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Decoding Detuned Reactors : What and Why

In this blog, I will acquaint you with Detuned Reactors and analyse their usage and benefits. Detuned reactors, that are three-phase inductors dedicated to attenuate the amplification of harmonics in harmonic rich networks,  protect the different components of the installation.

What are Detuned reactors?

Detuned Reactors prevent harmonic amplification caused due to RESONANCE and avoid the risk of overloading capacitors, thereby significantly reducing voltage and current harmonic distortion in the network. All connected equipment, and even remote substations are subject to voltage fluctuations which may result in equipment malfunction or failure. To avoid this problem, it is common to insert reactors in series with capacitor banks.

The reactor also by its nature will safeguard capacitor and associated switch gears against switching inrush, which other may damage capacitors, circuit breakers and contactors.

Why use Detuned reactor?

detuned reactorPresence of Harmonic distortion due to the  non-linear loads within the network or due to import of harmonic from grid or power source will increases the current flowing through capacitors as the capacitive reactance is inversely proportional to the frequency , consequently capacitors will be subjected to over load. The over load on capacitors can cause premature failure in capacitor due to increased voltage and thermal stress on dielectric.

detuned reactor On the other hand, the inductive reactance XL of a Reactor is directly proportional to frequency: The magnitude of inductive reactance will increase with high frequency harmonics thus blocking the harmonic current. Hence, use of detuned reactor in series with capacitor will offer higher impedance for harmonics, thus eliminating risk of over load in capacitors.

The inductance value of detuned reactor is selected such that the resonance frequency is less than 90% of dominant harmonic in the spectrum. For example: if 5th harmonic is dominant in the spectrum, any series LC circuit having resonance frequency 90% of 250Hz (for 50Hz system), i.e. if the natural resonance frequency of LC is less than 225Hz, it is categorized as detuned filters or detuned capacitors.

What are the benefits of using a Detuned Reactor?

The typical benefits of a detuned reactor are as follows:

  • It eliminates harmonic amplification
  • It enhances the life of capacitors by reducing voltage and thermal stress due to harmonics.
  • Prevents the constant nuisance of input fuse blowing or circuit breaker tripping
  • Reduces over heating of the transformer, busbars, cables, switchgear etc caused due to harmonic amplification.
  • Reduces the harmonic current in the electrical supply system
  • Addresses the harmonic problems created by non-linear loads.
  • Improves Power Factor in harmonic rich environment.

Technical data

They form a complete product range from  6 to 100 kvar and are available in the most common tunings like 135, 190 and 210 Hz for network voltage of 400/415V 50Hz. They must be chosen according to the capacitors they are associated with.

To prevent disturbances in a remote installation, select a tuning frequency that is at a lower value than the ripple control frequency (applicable for  networks having Remote Utility metering system). In a detuned filter application, the voltage across the capacitors will be higher than the nominal system voltage due to Vector sum of voltage drop, hence  the capacitors must be designed to withstand higher voltages. Typical capacitor voltages for 400/415V network are 480V, 525V etc.

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  • Jayaprakash Narayan

    7 years ago

    Very easy and precise explanation easy to understand, Thanks.

    • M R Srinivas

      7 years ago

      Thanks for the encouraging words, Mr. Narayan.

  • Amin Mosavi

    6 years ago

    Excellent article, I needed this information direly. Thanks.
    Could you please create an article and explain why tuned filters needed to be grounded but detuned filters don’t?

  • Chitta Ranjan Mishra

    6 years ago

    Very knowledgeable article . Excellant .

  • Thanks for the explanation M R Srinivas, very helpfull.
    I have a question, there are detuned filters with the next features :
    – 400V 50Hz Utility Voltage, 210Hz Resonance Frequency (p=%5,67)
    – 400V 50Hz Utility Voltage, 189Hz Resonance Frequency (p=%7)
    – 400V 50Hz Utility Voltage, 134Hz Resonance Frequency(p=%14)

    What means this p=5,67%, 7% or 14%?

    Thanks in advance

  • Sharad Gaitonde

    5 years ago

    Very good and precise explanation, thanks.


    4 years ago

    Excellent explanation even for professionals ,it really helps in sales speech for sales executives


    4 years ago

    Nice explanation…

  • Michael Messina

    4 years ago

    Very clear explanation. This article gave me a lot of insight into why a capacitor fuse may have failed severely without any apparent indication or location of a fault. The capacitor bank in question did not have any connected reactors to mitigate the harmonics, which I originally suspected as the culprit, and now this article confirms my suspicions.

    Thank you!

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