Use of power electronics equipment (HVDC, SVC etc.) with technological developmentsand non-linear loads such as arc and induction ovens have caused to the harmonics ( magnitudes different than the network frequency) and have decreased the power quality. This issue affects other linear loads which do not cause harmonics and causes overheating, insulation problems, short operating life and significant loss of efficiency. Harmonics do not result in any benefits but cause significant power losses at the network.

Passive harmonic filtration is the most efficient and cost-effective method to eliminate harmonics. The harmonic filter systems can in principle only consist of capacitor and reactor (LC). However, in this case, a change in the value of the capacitor or reactor due to manufacturing defect, aging or temperature can affect the filtering very seriously and may even cause the parallel resonance to increase even more harmonics. This sensitivity can be controlled by adding resistance to the filter circuit and the harmonic filter system can continue to work with the same efficiency for a long time.