GB675763A - Improvements in and relating to fluid control mechanism for electric circuit breakers - Google Patents

Abstract

675,763. Fluid-blast switches. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 18, 1948. [Nov. 18, 1947] No. 30022/48. Class 38 (v). [Also in Group XXIX] In a fluid-blast circuit-breaker having a series isolator, the blast valve is fully., opened to supply fluid to separate the contacts and extinguish the arc, and is then partially closed so as to supply a reduced amount of fluid to hold the contacts open until the isolator opens, when the valve closes completely so that the main contacts are allowed to reclose. The blast valve 12 is carried by a rod 72 and is normally held closed by a spring 82 acting on a piston 76 fixed to the rod and working in a cylinder 78. The opening of valve 12 is effected by closing a switch 44 to energize a coil 46 to operate a pilot valve 53 so as to connect the fluid container with the upper face of piston 76, thereby causing the valve 12 to open. The rod 72 has a hollow portion 101 terminating in radial ports 102, 104, the latter being uncovered after a small movement of the rod so as to supply fluid to a further cylinder 90 containing a second piston 88 which is slidable on rod 72. The piston 88 has holes 93 which are closed by a cap 96 on the rod 72 after the small movement of the rod has taken place, further movement of the rod causing the cap to push the piston 88 downwards against the action of a spring 92. Fluid passes into the lower part of cylinder 90 at a rate determined by a needle valve 106 which is so adjusted that when the contacts 30, 32 are open and the arc extinguished, there is sufficient pressure in cylinder 90 to move piston 88 back against a flange 91, as shown. This movement causes the valve 12 to move back to a partially-open position, with the cap 96 abutting the upper face of piston 88, the valve 12 being held in this position by the pressure on the upper face of piston 76. When the isolator is opened, the valve 53 is returned to its initial position by reopening switch 44, thereby venting the upper face of piston 76 to atmosphere through a hole 55 so that the spring, 82, recloses the blast valve and at the same time the cap 96 uncovers holes 93, to vent the cylinder 90 to atmosphere. In a modification, Fig. 2 (not shown), the piston 88 and its associated parts are omitted, and fluid is supplied to the upper face of piston. 76 through one pipe and to the under face thereof through a smaller pipe which may have a reservoir for delaying the pressure build-up beneath the piston. The valve 12 is fully opened as before,but when the pressure beneath it is great enough it is moved back until an escape hole in the cylinder is uncovered, at which point the piston is held in equilibrium, with the valve 12 partially open, by the fluid pressure above and the combined fluid and spring pressure below. Reference has been directed by the Comptroller to Specification 583,200.