The growing use of modern electricity electronic apparatus (drives, uninterruptible power supplies, etc.) produces nonlinear modern and thus hundreds the community with harmonics. The capacitance of the power capacitor forms a resonant circuit at the side of the feeding transformer. Experience shows that the self-resonant frequency of this circuit is generally between 250 and 500 Hz, i.E. within the place of the 5th and seventh harmonics. Typical hundreds requiring harmonic filtering consist of 6 pulse drives (AC / DC), 3 section UPS, frequency converters
