ABSTRACT
Short-circuit protection is the selection of equipment, placement of equipment, selection of settings, and coordination of devices to efficiently isolate and clear faults with as little impact on customers as possible. All circuit interrupters—including circuit breakers, fuses, and reclosers—operate on some basic principles. Circuit breakers are often used in the substation on the bus and on each feeder. Circuit breakers are available with very high interrupting and continuous current ratings. Several types of relays are used to control distribution circuit breakers. When an electrical distribution system energizes, components draw a high, short-lived inrush; the largest component magnetizes the magnetic material in distribution transformers. Expulsion fuses are the most common protective device on distribution circuits. Fuses are low-cost interrupters that are easily replaced. Engineers most commonly pick fuse sizes for distribution transformers from a fusing table developed by the utility, transformer manufacturer, or fuse manufacturer.
