Three phase Harmonic Filter Reactor
Three phase Harmonic Filter Reactor - May be single phase or three phase units. Mostly used together with capacitors to filter certain harmonic frequencies. Usually iron cored.

A reactor will attenuate voltage spikes and notches on the waveform, in addition to providing a reduction in the level of harmonics.
When used in a filter circuit comprising a reactor and capacitors, the inductance and capacitance values are selected so that the circuit is tuned to the particular frequency of the harmonic which needs to be eliminated.