N THE PERIOD following World War II. shunt capaci tor banks totaling in capacity approximately 225,000 re lative kva were installed on the system of American Gas and Hectric Company. At distribution stations, 24 switched ind unswitched banks, ranging in voltage from 2.3 to 13.8 ;v and in size from 720 to 20,100 reactive kva, were proided. At transmission stations 12 outdoor capacitor tanks, ranging in voltage from 22 to 44 kv and in size from ),075 to 19,800 reactive kva, were installed.Most of the low-voltage installations are in two or more teps and are switched on and off under voltage control. \11 of the most recent units are of the housed-cabinet type, ince this arrangement is found to be most economical and provides advantages of prompt delivery, quick installation, md possibility of later relocation at small expense. The >enefits of providing reactive kilovolt-amperes in this man ner at distribution stations have become obvious to almost veryone in the last five years. The high-voltage banks uere found to be desirable for several reasons.
Lower cost when capacity is required in a large amount at a given location, as compared to the provision of -witched low-voltage banks at several locations in an area.2. W T fiere heavy power interchanges on the 132-kv system are causing low-voltage conditions at transmission nations, the use of large capacitor banks during these periods maintains reasonably satisfactory voltage levels.3. When used in conjunction with existing synchronous condensers or voltage-regulating transformers, high-voltage !>anks provide an increase in the voltage level necessary to permit the existing equipment to operate in its normal voltage-regulating range.In connection with high-voltage banks, capacitors of Figure 2. Oscillogram of energizing and immedi ate de-energizing of 9,900 -reactive -kva 45,700-volt capacitor bank at Sprig g Station of the Appalachian Elec tric Power Company 7m/+tyfif\^$\*+A^ [|g Figure 1. A 6,600-reactive-kva 45,700-volt capacitor bank at Mikcgrady Station (near Elkhorn City, Ky.) of the Kentucky and West Virginia Power Company, Inc. standard voltage ratings were used because there were considerable savings in cost and greater availability for quick replacement, as compared to special 6,900-volt units. For instance, for 44-kv operation, each phase in the bank is made up of four parallel groups in series, utilizing 7,200-volt capacitors in each of the first three groups and 4,800-volt units in the fourth group. The three groups of each phase are Y-connected, thus obtaining a voltage rating of 45.7 kv. A view of such a typical 45.7-kv bank connected to a 44-kv line in a remote location near Elkhorn City, Ky., is shown in Figure 1. A voltage limit of 110 per cent has been used to determine how many capacitors may be allowed to fail in a series group before automatically trip ping the bank out of service. Experience over several years has indicated that capacitor failures are quite rare; there fore, banks may be designed and control provided on the basis of staying in se...