GB837825A - Improvements relating to air-blast electrical circuit-breakers - Google Patents

Abstract

837,825. Gas-blast switches. ETABLISSEMENTS MERLIN & GERIN. July 8, 1957 [July 10, 1956], No. 21511/57. Class 38 (5). A pneumatically opened air-blast circuitbreaker has its contacts pressed together by pneumatic means at the start of an opening operation. In Fig. 1, the pressure in the arc extinction chamber enters cylinders 7, 10 through orifices 9, 11, to act on the pistons 3, 2 of the moving contact 1. Although the cylinder 7 has a small orifice 8 open to the atmosphere the orifice 9 is so related to the orifice 11 that the initial effect is to urge the contact 1 upwards until the pressure above the piston 2 builds up so as to overcome the opposing air pressure and spring force and open the contacts. As the piston 2 moves downwards it uncovers further orifices 14 allowing greater air flow into the cylinder to accelerate the movement. During the latter part of its movement the piston 3 closes the orifice 9 so as to form an air buffer in the bottom of the cylinder 7 since air can only escape slowly through the orifice 8. On closing the air can escape from the cylinder 10 through non-return valves 16, 17. The fixed contact 4 is hollow and vented to the atmosphere. In Fig. 2, the hollow moving contact 1 is vented to atmosphere via holes 18, passage 19 and an orifice 20 which is sealed after arc-extinction by a slow-acting valve 21, 22, 23 operated by the arc-chamber pressure. In Fig. 3, the hollow stem 36 of the moving contact 1 is vented to atmosphere through holes 41, 20, and the cap 21 is arranged to seal the hole 20 in the circuit-open position. The moving contact 1 passes through a fixed cap 37, preferably of insulating material, and a second fixed cap 38 of metal, which acts as an arcing tip and electrostatic shield. In Fig. 4 (not shown) the orifice 9 is at the lower end of the cylinder 7 and has a non-return valve. Specification 837,824 is referred to.