Introduction to Circuit and Motor Protection – CIRCUIT PROTECTION (1)

The distribution of electrical power in a plant can be very complicated. In addition, the circuits that are receiving power are subject to destructive overcurrents and short circuits. To protect these circuits and power systems from blackouts, prolonged downtime, and fire hazards, fuses and circuit breakers are widely used. Let’s first define what an overcurrent is.

An overcurrent is the result of an overload current, a short-circuit, or a ground-fault current. An overload current is an excessive current, relative to the normal operating current, that is confined to the normal conductive path provided by conductors, other components, and loads, such as motors, that form part of the power distribution system (see Figure 1). A short-circuit or a groundfault current is an excessive current that flows outside the normal conducting path (see Figure 2).

While overloads are most often at no more than 6 to 10 times the normal current levels, shortcircuit currents can be hundreds of times that of the normal operating current. This high current, if not stopped in a few thousands of a second, can cause severe insulation damage. In addition, overloads can cause melting of metal and conductors, vaporization of metal, ionization of gases, and arcing, all of which can result in a fire.

to be continued……………

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