A tuned reactor connected in series with a capacitor (L-C-circuit) creates a resonance frequency "tuned" to a certain harmonic frequency of the mains. As the impedance of the L-C-circuit is very low at intended frequency, the harmonic current is absorbed ("filtered") by the circuit. The design of tuned reactors, as well as the corresponding filter capacitors, must consider the high currents occurring in the L-C-circuit.