Protection coordination
Protection of low-voltage public distribution networks

Network structures (lines, cables, transformers, etc.) can withstand overcurrents for shorter periods of time, the higher the amplitude of the overcurrents (inverse-time withstand characteristics).

Protective devices (fused circuit-breakers, circuit-breakers) are themselves designed to interrupt currents all the faster, the higher their amplitude (inverse-time operating zones). Such a protective device must be installed upstream of the installations causing the overcurrent, i.e. generally upstream of the protected structure; however, other possibilities exist, such as protecting transformers against overloads by means of a circuit-breaker placed on the secondary side. Protection is verified by the relative position of the operating zone of the protective...