Absorption Filters are used when the main purpose is not the reactive power compensation at the fundamental frequency but the reduction of the TDH in the network distribution system. Harmonic absorption filters are usually designed with serial filters composed by reactors and capacitors, tuned at the harmonic frequency that should be eliminated. In the practice, filters are tuned at frequencies a little bit lowers than the harmonic to be eliminated. The rectifiers are the harmonic generators that more often could be found in the industry. The installation of these filters, produce a little modification on the input of the electrical system, so the design of this filters has to be done with an accurate analysis and complete study.