Breaking by auto-expansion

Breaking methods

The term «auto-expansion» is used to cover a variety of techniques or breaking methods according to technical documents and circuit breaker manufacturers. This «Cahier Technique» first points out the main differences concealed by this term, as regards both breaking principles and special features, and then presents breaking by autoexpansion in SF6. To date this technique is used solely by Merlin Gerin circuit-breakers.

Finally, three circuit-breaker models are presented, the performances of which are proof of the advantages of this breaking mode.

Special SF6 breaking techniques

Since the purpose of this “Cahier Technique” is to present the principle of breaking by auto-expansion, this principle must be situated among the other techniques using SF6 as a breaking fluid.

In the space of 30 years these techniques have evolved, moving progressively from arc blowing caused mechanically (double pressure, pistons) to blowing linked to the actual current (rotating arc, expansion). These terms are used to refer to actions on the arc, separate or combined, the main aim of which is to cool the arc. They in fact vary in meaning according to the manufacturers using them.

AUTHOR: Schneider Electric expert | Georges BERNARD