Behavior of Switching Arc in Low-Voltage Limiter Circuit Breakers

The noteworthy increase in the present low-voltage circuitbreaker capacity implies that these products must be able to dramatically reduce the short-circuit currents in electric installations. This important current limitation can only be obtained by rapidly inducing an arc voltage in the circuit breaker, that opposes the mains voltage. A preliminary computer calculation shows that the arc voltage, and in particular the immobility time of the arc on the contacts, is very important for the quality of the limitation. Electric tests, carried out with constant or alternating current, made with an experimental device, clearly show the influence on the stagnation time of the contact opening speed and of the nature of the contact materials. The speed during breaking, which is constant, ranges between 2 m/s and 13 m/s (current publications are limited to 5 m/s). The contact materials under survey have been copper and silver, taken as references, and for the first time silver cadmium oxide as breaking material in circuit breakers. Tests have resulted in a semiempiric arc voltage model, deducted from a Cassie equation, extended to an arc being stretched. Solving by means of a computer the equation governing a break, for this arc voltage model, makes it possible to know beforehand with great precision the performances of a product.