A detuned reactor is a series-connected inductor in a power factor correction (PFC) system along with capacitors, forms a harmonic filter. By tuning the resonant frequency of the reactor-capacitor circuit below the lowest expected harmonic (typically the 7th harmonic), the detuned reactor prevents harmonic resonance and over currents in the capacitors, protecting them and other components from damage caused by harmonic distortion from non-linear loads. 

How it works:

• Series connection:
  The detuned reactor is connected in series with a capacitor bank, creating a parallel resonant circuit. 

• Tuning frequency:
  The reactor's inductance and the capacitor's capacitance are selected to set the series resonant frequency of the unit to a frequency lower than the lowest harmonic present in the power system. 

• Harmonic absorption:
  This low-frequency tuning creates a high inductive impedance for all harmonic frequencies, diverting harmonic currents to the mains and away from the capacitors. 

• Capacitor protection:
  By limiting the harmonic current, the reactor prevents the capacitor banks from being overloaded, which reduces heat and prolongs their lifespan. 

Benefits of using a detuned reactor:

• Prevents harmonic amplification:
  It stops harmonic distortions from increasing to damaging levels within the power system. 

• Protects equipment:
  It shields capacitors, switchgear, transformers, and cables from overcurrents and overheating. 

• Improves power quality:
  By reducing harmonic distortion, it enhances the overall quality and stability of the power system. 

• Enhances system reliability:
  It contributes to a longer operational life for power system components. 

• Power factor correction:
  While its primary function is harmonic filtering, it also supports power factor correction by ensuring the capacitor bank operates efficiently at the fundamental frequency.