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Abstract

An electrical power distribution system of an industrial plant or a commercial building and having a capacity for delivering at least 500 KVA, includes a voltage step-down transformer connected between an AC source of electrical energy and a pair of power distribution line conductors across which there is connected a pulsed inductive load, such as a motor with a thyrister speed controller. The power factor of the system is corrected by a power factor correction capacitor connected directly across the system power distribution line conductors. Pulsed inductive loads tend to excite large harmonic currents in such systems having both a transformer and a power factor correction capacitor directly across the distribution line conductors. A filter, made up of a filter capacitor and a filter inductor tuned exactly to one harmonic, are connected in a series circuit branch that is connected directly across the system power distribution line conductors. The name plate KVAR rating of and capacitance of the filter capacitor is chosen to be much smaller than corresponding KVAR rating and capacitance of the power factor correction capacitor in order to make the function of the power factor correction capacitor and the function of the filter essentially independent of each other. This independence is attributable to the substantially no current flow of frequency of the AC power source through the filter capacitor and substantially no current at the harmonic frequency to which the filter is tuned flows through the power factor capacitor.

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