Today's industrial conditions force the manufacturer to increase the efficient use of electrical energy.Therefore reducing the reactive current component by PFC correction has become inevitable.The increasing usage of the modern power electronic apparatus(drives, UPS,etc) in systems cause nonlineer current influences and undesirable harmonics.And as a result a lot of network problems are faced. In such a situation the power factor correction or capacitance of the power capacitor and the feeding transformer of the system together constitute a resonance circuit.The self-resonant frequency of this circuit varies between 250Hz. and 500Hz. and it lies in the region of the 5th and 7th harmonics. The main harmful results of these resonance effect are: Overloading of capacitors,transformers and the other possible transmission equipments, Interference with metering and control systems , computers and electrical gear, Amplification of harmonics which causes resonance elevation and voltage distortion. This disturbing resonance phenomenon can be prevented by connecting compatible capacitors in series with the correct filter reactors.Detuned systems are scaled so that the self-resonant frequency is below the lowest line harmonic.The detuned PFC system is seen purely inductive by harmonics above this frequency.For the 50Hz. line frequency the detuned system acts purely capacitively,thus correcting the reactive power.