Extending the Use of Shunt Capacitors by Means of Automatic Switching

It generally is recognized that the kilowatt loading on distribution circuits or plant feeders may be increased substantially by using capacitors to supply the kilovar load and relieve the current-carrying system of this burden. The use of capacitors to boost voltage or actually to regulate voltage has increased during recent years. Automatic switching of capacitors makes it possible to obtain the benefits of adding capacitors to take care of the full load kilovars without the objection of excess capacitor kilovars at light loads. It also makes it possible not only to apply capacitors in the most effective manner from the standpoint of meeting power-factor limits established by the utility, but also to regulate voltage in the plant or on the system. Capacitors may be switched automatically by the same switching means controlling the load, or they may be switched in response to changes in circuit conditions such as voltage, current flowing, or the reactive kilovars drawn by the load. The advantages of the various types of control and the choice of the number and size of capacitor steps to be switched are discussed fully.