Patent GB-512623-A (GB)
Title: Improvements in or relating to gas-blast electric circuit-breakers
IPC: H01H33/83
Filed: 1938-03-08
Abstract: 512,623. Gas-blast switches ; pneumatic actuation; switchgear structures. REYROLLE & CO., Ltd., A., ALLAN, A., SMALL, J., and ANDERSON, W. March 8, 1938, No. 7175. [Class 38 (v)] The co-operating contacts of a gas-blast switch are both movable, the first being arranged, on opening of the switch, to move at high speed through a short distance to form an initial gap of length suitable for gas-blast arc extinction, whilst the second is arranged to move after a brief time interval through a relatively long distance to provide the desired long final gap, after which the first contact preferably returns to normal position. Fig. 1 shows a switchgear structure employing a horizontally-withdrawable circuit-braker, shown in detail in Fig. 2, the outer metal casing A' of which is movable on rails A" and carries plug contacts B', B' for engaging socket contacts B', B' associated, respectively, with busbars B' and a transformer, feeder or other external circuit. The phases of a threephase gear may have separate casings A<1> or a common casing. The plugs B<1>, B<2> are connected by conductors C<1>, D' to metal housings C, D associated, respectively, with the first and second contacts, the conductors passing through an insulating tube A which is separated from A<1> by. insulating compound or compressed gas. When the gear is in operative position, nozzles F', F<2> engage orifices connected by pipes F<3>, F' to a gas reservoir through an electromagnetic valve casing F<5>, these pipes controlling the opening and closing operations, respectively, and providing the gas blast for the former. The first contact comprises an annular arcing piece C<6> carried on a combined piston C<4> and throat member C' slidable in a metal plug C<2> in housing C against the action of spring C'. The second contact comprises the arcing tip E', normally closing the orifice in arcing piece C', and the conducting rod E which is slidable in the spring contacts D<2> and connected by insulating part E' to the operating piston rod E<2>. To effect conjoint operation of all phases, a shaft E' carries pinions E<6> engaging racks on the piston rods. Opening-pressure is applied to the upper face of the piston E' through a narrow gap D<3> between the rod E<2> and cylinder E' the gap serving slightly to delay the effect of the pressure. The rod has also a locking projection E' engaged by a spring-latch G having a gas-pressure operated piston G', the full area of which is not exposed until the latch begins to move, thereby imparting a slight delay. When the operating pressure has built up sufficiently to overcome the springs G<2>, C<5>, the contact C<4>, C<6>, due to its low inertia, moves quickly to the desired small gap, thus opening the throat to the blast. After a suitable delay, the latch is released and the lower contact moves downwards to provide the final gap, whereupon the gas-supply ceases and spring C<5> restores the upper contact in readiness for the closing movement of the lower contact. In order to reduce the tendency of the upper contact to move prematurely due to the pressure having access to the full face of the piston, arrangements may be employed in which a reduced area is initially exposed, as by fitting in the housing C an internal flange against which a small auxiliary piston-like surface abuts, Figs. 3 and 4 (not shown). Fig. 5 shows a further arrangement in which the closed and open position are shown, respectively, on the left and right-hand side, and the piston K is separate from the arcing piece K'. A spring K' normally urges the piston K against an insulating flange K<3> so that only a small part of its face is exposed until upward movement begins. After a given travel, the piston engages and lifts the throat member K<4>, with the arcing piece, against spring-action until arrested by a stop K<6>. The piston K also houses contacts L engaging the sides of the arcing-tip E<1>. A heavier current-rating may be got by providing a number of parallel-connected annular contacts in the piston, each cooperating with a spring-contact on the rod E, Fig. 6 (not shown). Instead of a parallel connection, three groups of contacts may be connected in series, Fig. 7, by arranging two upper contacts P<2> (only one shown) in a metal plug P' in an insulating plug P<4> in the piston P. The arcing tips P<5> are mounted in an insulating head P<6> on the rod E, two being interconnected by a flexible lead P', while the other is connected to the rod E by a lead P<8>. Contacts.-Constructions suitable for the contacts L of Fig. 5 and for those D' of Fig. 1 are shown in Fig. 8. A number of tangential arms L are arranged with their inner ends L', forming the contact-surface, bearing against the cylindrical surface of the lower contact E or E'. whilst the outer end L<2> houses a spring L<3> acting on the inner end of the adjacent arm. Engaging faces L', L<5> on adjacent arms limit the inward movement of the arms when the contact E' is withdrawn.