LV breaking by current limitation

Principles

This “Cahier Technique” provides a simple introduction to the principles of low voltage current limitation, a technique developed by Merlin Gerin in direct current as early as 1930 and in alternating current in 1954.

It simplifies understanding of the advantages gained by using limiting circuit-breakers in electrical installations.

Definition

A device is said to be limiting when the current passing through it during a short-circuit has an amplitude considerably lower than the prospective current. In the case of limiting circuit-breakers, this reduction in amplitude is accompanied by a reduction in the current flow time T compared with the short-circuit current flow time of a nonlimiting circuit-breaker.

Why limit?

To make more cost effective circuit-breakers, especially in low rated current ranges. Only the limited current, far smaller than the prospective current, flows through the limiting device, which then has only to break this limited current.
To minimise fault current effects in electrical installations.

AUTHOR: Schneider Electric expert | Pierre SCHUELLER