Patent GB-544017-A (GB)
Title: Improvements in fluid blast electric circuit breakers
IPC: H01H33/08
Filed: 1940-11-06
Abstract: 544,017. Gas-blast switches. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 6, 1940, No. 16162. Convention date, Nov. 6, 1939. [Class 38 (v)] A gas-blast switch comprises a slidably - movable contact blade 10 with an arcing tip, and a fixed contact 11a with arcing fingers 11' and a tip 11<SP>11</SP> of arc-resistant material. The blast of gas is admitted from a reservoir 12 of about 150 1bs. per square inch pressure, through manifold 15 to the individual phases by way of pipes 16 in which are orifices of such cross-section that a constant blast-pressure of about 50 1bs. is obtained for all back-pressures up to 53 per cent. of the reservoir-pressure. The arc chute comprises side plates 21 and a pair of tapering members 27, both of which, are grooved to receive transverse insulating partitions 32 defining, with the end walls of the chute, a series of flaring passages into which the arc is looped, and leading to an exhaust chamber 23 for the gases. The escaping gases are cooled by means of a series of metal plates 24 spaced by projections 25 and secured by bolts 26. Two of the plates have projections extending upwardly into the neighbourhood of the arc path in the third passage from the left, so as to serve as an auxiliary electrode, a resistance being, connected between it and contact 11a. The value of the resistance is determined from a formula given in the Specification, and depends on the rate of rise of recovery voltage for the particular circuit, the value and the electrode location being, however, such that no arcing to the electrode occurs prior to current-zero, but thereafter the gap between it and contact 10 breaks down due to the recovery voltage, the rate of riseof which is limited by the resistance. One partition 22<SP>1</SP> extends across the path of the movable contact and is apertured to slidably receive the latter. The arrangement is such that a current-zero occurs before the contact clears that partition 22<SP>1</SP>, and the aperture in the righthand end wall is long enough to ensure removal of all the arc gases through the chute before that aperture is opened, a dashpot being provided to slow down the contact 10 at this stage. The contact 10 is operated through a sliding crosshead 35 and arm 33 from a shaft 32 which is common to all the phases and rotated by a pneumatic motor 28, 29, 30. During anti-clockwise opening movement of 32, a lever 31 carrying a roller 40 engages a surface 41 on a lever 42. which is pivoted at 43 to a lever 44 which is thus rotated clockwise, so that a part 45 thereon drives rod 14 to the left and opens valve 13. This action is assisted by a spring 46 which holds the tail 42<SP>1</SP> of lever 42 against a stop 48. After, a certain rotation, roller 40 slips off surface 41 and spring 46 recloses the valve. During the closure of the switch, a surface 31' on lever 30 engages a roller 49 on pivot 43 and opens the valve 13 just before the arcing contacts engage. The blade 10 may be enlarged in width at the upper part of its cross-section (Fig. 9, not shown). A. suitable material for the partitions 22 is a hard white vulcanized fibre having a moisture content of 4 to 7 per cent. zinc chloride less than 0.2 pen cent ash-red 5 per cent., all other ash 1 per cent but methyl methacrylate and " certain urea resins " also are referred to. Specification 164,827, [Class 38 (v)], is referred to. The Specification as open to inspection under Sect. 91 states also that the invention is applicable to liquid-blast and plain-break oil-switches, and that axial gas-blast switches can be equipped with constant-pressure orifices and with an arrangement of auxiliary electrodes and shunt resistances. This subject-matter does not appear in the Specification as accepted.