During normal operation of a power system, such as a transmission line, distributor, generating plant, or other, it is often necessary to switch the various circuits on or off in both normal and abnormal conditions. In older power systems, this function was carried out by a series of fuses within the circuit. However, this method of control brought multiple disadvantages. For one, when a fuse blows out, it can take a great deal of time to replace it and restore the system. Second, fuses are not capable of interrupting heavy fault currents that result from faults on modern, high-voltage, large capacity circuits. Because of this, fuses’ uses are limited to low-voltage and small capacity circuits where only intermittent operation is expected.