Cihan Şenel  
Technical Sales Engineer  
Aktif Mühendislik

Despite being used extensively in the compensation systems of this type of reactor, which is defined by various names such as detuned reactor, passive harmonic filter, unsteady filter, low pass band filter, there is information pollution and misconceptions about what works. This article has been revised to remove this fallacy and information pollution.


Harmonics are unwanted electrical components that are most often spoken about in power quality parameters and cause problems when they exist over the limits set by the standards in the electrical system. n systems where harmonics are present, harmonic filter reactors are connected in series to the capacitors. The main purpose is to prevent the harmonic current flowing on the capacitor and to prevent the resonance of the system.

II. What is Harmonic Filter (Detuned) Reactor?

The harmonic filter (Detuned) reactor is a fixed impedance load in the structure of the coil calculated according to certain calculations.

III. Why Harmonic Filter (Detuned) Reactor is used ?

The harmonic filter (Detuned) is to limit the flow of harmonic current from non-linear loads on the reactor to the fixed impedance loads (eg capacitor).

Harmonik Filtre (Detuned) Reaktörü Nedir? 
Kompanzasyon sistemlerinde neden kullanılır?

Formula 1 - Calculation of Capacitor Impedance

If we look to the impedance equation of the capacitor, it is seen that the capacitor impedance decreases with the increase of the frequency. In this case, the current will flow at low impedance so that the total current on the capacitor will be equal to the sum of the nominal coupling current and the harmonic current. An unwanted state will occur on the capacitor due to the harmonic current.

Total Current = Nominal coupling current + Harmonic coupling current

To reduce the harmonic coupling current we need to increase the line impedance to which the capacitor is connected. As can be seen in Formula 2, the high impedance bobbin at high frequencies is possible by connecting the capacitor in series..

Harmonik Filtre (Detuned) Reaktörü Nedir? 
Kompanzasyon sistemlerinde neden kullanılır?

Formula 2 - Calculation of Coil Impedance

Harmonik Filtre (Detuned) Reaktörü Nedir? 
Kompanzasyon sistemlerinde neden kullanılır?

Formula 3 - Calculation of Total Equivalent Impedance

At this point the total impedance will be equal to the sum of the capacitor and coil impedance and the harmonic current flowing on this arm will be reduced to the lowest level.

Harmonic Filter (Detuned) Reactors can be manufactured as single-phase or three-phase, choosing the tuning frequency according to the dominant harmonic current order in the system according to the bus bar voltage and capacitor impedance / power.

Harmonic filter (detuned) reactors do not destroy harmonic components in the system. It only prevents the harmonic current from increasing in amplitude. It is a well-known misinformation to say that it destroys harmonics in the system.

IV. What are the advantages of using Harmonic Filter (Detuned) Reactor?

  • Prevents harmonic current and voltage amplitude from increasing in systems with non-linear loads.
  • Limits the harmonic current flowing on the capacitor. This prevents heat and high current stresses and allows the capacitors to have a longer operating life.
  • Prevents to overcurrent and heating problems on transformers, bus bars, cables, switchgear, protection equipment, etc…


Given the fact that almost every use of nonlinear loads increases day by day, it is important to use harmonic filter (detuned) reactors in compensation systems.