Sometimes a network with low power factor, contains harmonic generators, the harmonic frequencies take the form of nxf where n=2,3... etc and f is the fundemental frequency of the network. if a capacitor bank is installed, the capacityr of this bank and the reactance of the line form a parrallel resonance with resonating frequency = 1/sqrt(LC) .
if one of the harmonic frequencies is equal to the resonating frequency, and knowing that the harmonic generators are current sources, then this current source acts on an infinite impedence which ma cause a very dangerous voltage which may cause damage of the network .
The detuned reactor is chosen in a way to regulate the resonance impedance not to coinside with any of the harmonic frequencies.

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