Because of the growing harmonic distortion and pollution of the electrical power networks, in particular in those areas with high concentration of industrial facilities, reactive power compensation equipment may experience voltage and current harmonics over load which will ultimately result in capacitor failures and can no longer be used with acceptable life expectancy unless it is protected by detuning & tuning reactors.
Air core filter reactors have two functions, namely to produce capacitive reactive power at basic frequency and to filter out harmonics.
Asset high voltage filter reactors are designed to have small impedance between phase and earth, or between the phases at required harmonic frequency. Therefore the harmonic current will flow into the filter and not into the network. Normally each harmonic frequency required has a separate filter circuit. For higher harmonic frequencies, a wide-band filter is used.