Reactive Power and Its Control in a Large Metropolitan Electric Supply System

In large metropolitan systems, the magnitude of reactive power can become so great that controlling it and system voltage demands more than the ordinary requirements in equipment and operating techniques. On the Consolidated Edison system, one of the major problems concerns an excess of charging Mvars from high-voltage cables during light load periods. At the outset this would seem to indicate that, with such excesses of capacitive Mvars, few capacitors would be required in the distribution area of the system. This unfortunately is not the case, since it is desirable and economical to have the reactive power for distribution located as near the load as possible, to maintain the megawatt capability of distribution stations and equipment at their maximum values. Additional capacitance is therefore required in the form of switchable capacitor banks at strategic locations, even though there may be an excess of charging Mvars on the high-voltage systems at the same time. Also, voltage control is usually held within relatively narrow limits in metropolitan areas and this aggravates the overall problem. On the system discussed here, a very large change has come about in the last two years with installation of approximately 65 miles of 345-kV cable. These situations and ways of handling them are discussed.