Filter for harmonics
Filter for harmonics are necessary for the elimination of the harmonic waves and for the production of the necessary reactive power. At plants with six pulse inverters complex harmonic filters are necessary, because there are odd-number harmonics from the 5th order upwards. At 12 pulse static inverter plants, only harmonic waves of the order 12*n + 1 and 12*n - 1 (n = natural number) result. Filters are tuned to the expected harmonic frequencies and consist of series combinations of capacitors and inductors.
Beside the harmonic filters, equipment is also provided to eliminate spurious signals in the frequency range of power-line carrier equipment, in the range of 30 kHz to 500 kHz. These filters are usually near the alternating current terminal of the static inverter transformer. They consist of a series coil which passes the load current, with a parallel capacitor to form a resonant circuit.
