Directly connected static VAr compensation in distribution system applications

Many types of industrial loads on utility distribution systems adversely affect power quality on the distribution line. Large power supplies, motors, welders, and arc furnaces, for example, cause voltage flicker which is experienced not only by the offending industrial power user, but also by any other utility customers receiving power from the same distribution feeder. In addition, the typically poor displacement power factors of these loads result in higher fundamental line currents which must be supplied by the utility. One way to alleviate these problems is to provide static VAr (volt-amperes reactive) compensation in shunt with the distribution line. This paper discusses the advantages of applying this compensation directly to the distribution line using high voltage semiconductors versus VAr compensation at industrial voltage levels (such as 480 volts) either via a dedicated step-down transformer or on the customer 480 V plant power. Power system analyses of loads with and without compensation are described and compared to demonstrate the effects of static VAr compensation on flicker, voltage support, power factor, and system harmonics.