These filters are used when the main objective is not the reactive power compensation at the fundamental frequency, but to reduce the harmonic distortion in the supply system.Among the problems caused by harmonics and which may make their suppression necessary, are the following:

  • Interferences in telecommunications.
    Distortion on the mains voltage.
  • Disturbances in electronic systems.
  • Erratic operation of control and protection relays.
  • Failures in transformers and motors, due to overheating caused by losses on the core.
  • Overheating of protective fuses to the point where a minor spike on the line causes them to blow.

It should be pointed out that the impedance of all the filters is capacitive below its tuning frequency, whereby they also contribute, even if in a small scale, to the reactive power compensation at the fundamental frequency. Installation of filters produces a modification on the topology of the electrical supply system. For this reason, the design of filters must be done with regard to an accurate analysis and study of the whole system.

According to the application, there are different types of filters: