They are used for improvement of power factor and part elimination of harmonics. They are combination of reactors and capacitors, suitably detuned. They are useful when distortion is 15 to 40 %.

Advantages of Harmonic Filters :

• Protect capacitors from Harmonic overloading.
• Eliminate 20 to 50% predominate Harmonics.
• Avoid harmonic amplification in the system.
• Improve power factor.