US2552358A - Electric circuit breaker - Google Patents

Description

May 8, 1951 w. B. WHITNEY Er AL 2,552,358

ELECTRIC CIRCUIT BREAKER Filed April 14, 1949 2 sheets-sheet 1 May 8, 1951 w. B. WHITNEY Er Al. 2,552,358

. ELECTRIC CIRCUIT BREAKER Filed April I4, 1949 2 sheets-sheet 2 Z533 y A o O Patented May 8, 1951 ELECTRIC CIRCUIT BREAKER Willis Bevan Whitney, Eric Merrington Briscoe, and Albert Arthur Hudson, Perivale, England, 'assignors to The "British Electrical and .Allied Industries Research Association, London, England, .a British association Application April 14, 19519,` Serial'NoA.'f87,482 In Great Britain April 20, 1948 VV16 Claims. l

This invention relates =to improvements in gasblast electric circuit-breakers which utilize'gas yreleased from `cartridges to provide the gaseous 'pressure for the blast.

vThe'expression cartridge in lthis specification includes 'not only `vcartridges yielding gas -under pressure, generated by chemical action, -but :also cartridges which fstore gas for readily 'vaporised liquid under high pressure lprovided that-gas (e. g. air) -can be released therefrom by electric `or mechanical action. Further the expression iired relates not only to initiation of chemical `action but also ito vother release of lthe gas yunder pressure.

It has 4been proposed :for example in British patent 'specification =-No. Y26,694/1901 to generate pressure .for a gas-blastcircuit-breaker :by means of smokeless gun rpowder, tand it has Aalso been proposed to zuse explosive cartridges for the same purpose but 'such proposals 'did not -lead to any success mainly -because the electrodes in the vicinity of the arc-rootandfarc-path were actually `supplied with Ahot .gases whose dielectric strength was lfar too W to ensure extinction of the larc orto prevent fre-striking ofthe arc'on the appearance of recovery voltage.

The invention is .applied to electric circuitlbreakers for use in alternating high-tensionpower circuits of any fluid-blast type in which a portion `of the `arc-'stream associated 4with any one break between two electrodes 'lies 'Within a narrow passageway through which a 4high-velocity blast `of gas or vapour escapes from a container to -eX- tinguish the arc, and in which the Ypressure in the container is produced by vthe discharge into it of gases released from 'a cartridge. One 'construction of circuit-breaker to which the invention may belapplied :is described in the speciiication of U. S. `Patent No. \1,928,470 in which one electrode for-ms a passage -(or a -portion thereof) leading out of Va container, and the other electrede-consists of -a metallic plug axially 'movable through a limited distance toclose the switch and to close the mouth 'of said passage, or to open the switch and allow airor other gaseous ydielectric under high pressure to escape between the electrodes and through the passage so vas to quench the larc by the rapid yremoval of ionized gas from the 'vicinity ci the arc. Such circuitbreakers are known as -the faxial blast type, but the invention can be `applied -to lany kind 'of cir- `cui-t breaker, single ror Idivided-blast, faxialfor cross-blast or multi-break, and it will be understood -thatrif the hotf'gases generated by *a chemical action in a cartridge passed directly or easily to the larc-gap, grave difliculties `would arise, iirstly because Vsuch gases might contain fquite a considerable .proportion of minute incandescent solid particles whichwould tend to reduce the dielectric strength `of the 'blast-gas, `secondly because the gases emitted from the cartridge might be so hot as to 'be readily ionized, and `thirdly because these gases might in fact be in an `ionized condition.

This invention accordingly comprises an felectric vcircuit-breaker 'of the type described, in which the gases emitted iromthe cartridge, and the air -or vapour in the container, :are constrained to reach the fare-gap in such 4cle-ionized condition as vto -be suitable for arc-extinction by gas blast.

According to .another `feature -of the invention an electric circuit-breaker vof Ythe 'type in which one electrode forms a passage (or a 'portion thereof) leading out of a container, the 'other Velectrode vconsists of va metallic plug .axially 'movable through a limited distance to close theswitch and to close the mouth of said passage, or to open the switch land allow air or other gaseous dielectric under high pressure to escape between the plug and 4the mouth -of the passage and through the passage so as to quench ythe arc, and the pressure -in the container fis produced by the discharge of 4gases lfrom a cartridge, iszcharacterised by the fact that the gases emitted from the cartridge and -the -air in the-container :are in such aconditionas to provide a suitable medium for arc-extinction by gas-blast.

This invention consists of an electric circuitbreaker-of 'the type idescribed having a container of which fthe principal 'outlet is formed by one or more throats -or narrow -passageways in which a portion lof the arc-'stream associated with any one 'break between Atwo electrodes lies within such throat, saidfcontainer being equipped with means for subjecting the arc or arcs in said throat Vor throats, vduring at least the 'iirst `cycle of 'arcing, to a blast Vof un-ionized fluid and lmeans for bringing about a sudden expulsion of iiuid medium from one or more cartridges to increase the pressure in the container and to maintain the blast (suitable for arc extinction) through Ysaid `throat or vthroats until the .circuit 'is broken.

It will be .understood that if in a cartridgeoperated, `gas-blast circuit-breaker one cartridge fai-ls (e. g. Afai-ls .-to iire :or fails to :prov-ide ade- -quate gaseous pressure `for extinction 'of the fare) it is essential that another cartridge shall be iired immediately; rand fone object of this invention is to satisfy such a requirement in an efcient, reliable and simple manner.

In the case where the cartridge pressure is generated by chemical action, the gases delivered from the. cartridge are so directed and so treated as to bring their temperature and dielectric strength to such a state as to ensure complete electric isolation of the live electrodes of the cir-- f cuit-breaker from one another for so long as the circuit-breaker remains open.

Preferably the gases delivered from the cartridge are so directed and'so treated as to bring their temperature and dielectric strength to such a state as to maintain complete electric isolation of the live electrodes or associated conductive parts from one another during the period from the appearance of recovery voltage across the circuit-breaker till the reclosing of the circuitbreaker.

According to another feature of the invention the emission of gas from the cartridge is caused to displace the relatively cool (and clean) air in the container across the arc-gap to quench the arc, and an isolating switch in series with one of the electrodes is automatically opened after extinction of the arc, prior to the possible arrival at the arc-gap of hot or ionized gases from the cartridge.

In order to remove particles of carbon or any other solid suspensoids from the cartridge gases, the gases emitted from the cartridge may pass through a fora-minous lter.

The lter may comprise heat-absorbing and `conducting elements which substantially reduce the temperature of the gases passing therethrough, or the cooling may be effected separately from the removal of suspensoids.

It is desirable that the gases generated in the cartridge should be so directed as not to impinge directly on an insulating surface relied on to insulate one electrode of the circuit-breaker from the other.

In order to reduce the kinetic energy of any solid suspensoids in the cartridge gases the gases emitted from the cartridge may be directed against a wall of the chamber in a direction opposite to that leading to the lter.

In one practical embodiment of this invention vthe gas-chamber comprises threee parts viz. a 'tank having the breech to receive the cartridge,

an intermediate chest containing the conducting connection between the movable electrode and its associated I-I. T. lead, and a switch-chamber v containing the actual electrodes.

Further, there may be one foraminous, heatabsorbing filter between the tank and the intermediate chest and a second filter between the intermediate chest and the switch-chamber.

This invention includes an electric circuitbreaker of the cartridge-operated gas-blast type in which a series of electrically red cartridges held in xed bre-aches and adapted to deliver gas under high pressure-to the circuit-breaker container, are electrically connected respectively to the bars of a distributor having a rotatable contact arm in circuit with (a) a source of firing current, (b) a relay (closed when a fault occurs in the power circuit to be protected) and (c) a common return conductor having for each electric igniter a switch normally closed but opened immediately the corresponding cartridge is successfully red, so that if on the occurrence of a fault, `a cartridge is Successfully fired, the said igniter circuit is broken and no further firing takes place until the circuit-breaker has acted 4 and been reset, butl if one cartridge fails, the next in order is red.

In one arrangement each cartridge or cartridge cage containing the same, is associated with a hydraulic relay; (e. g. a xedvcylinder with spring-controlled cartridge cage and axial extension) adapted on the successful firing of the associated cartridge to open the corresponding switch in the common return of the firing circuit and to keep it open as long as the fault persists.

Thus the spring-loaded cage may be directly subjected to the pressureof the cartridge when fired and the axial extension has a lock which holds the extension and keeps the corresponding `switch in the open position as long as the fault persists. Thus the cartridge may be held in a cage which can slide freely (through a limited distance) in the xedbreech and the cage (by reaction) applies a thrust to the axial extension when the gases are rapidly expelled from the cartridge.

The nature of this invention and the manner in which it is performed will be appreciated from the following description, reference being made to the accompanying drawings in which- Figure 1 is a central sectional elevation of one phase of a three-phase circuit-breaker.

Figure 2 is a circuit diagram for the arrangement in which a series of electrically red cartridges is used, and

Figure 3 is a diagrammatic view indicating the action of the electrically controlled pneumatic lock. l

Referring to Figure 1 a gas-chamber has three parts namely a cartridge-tank I2, an intermediate chest I3 and a switch-chamber I4. At the top of the switch-chamber one electrode I5 has a central passage I6 of which the mouth has an annular insert 56 of highly refractory metal such as a Sintered tungsten-copper mixture. The plug electrode I I of aluminum has a tip I8 of the same highly refractory metal. The outer wall I9 of the switch-chamber I4 is of insulating material such as resin-bonded paper and this wall may have a lining 20 of quartz. The plug electrode I1 is movable in the direction of its own axis through a limited distance (e. g. 1 to 2.5 cm.)

The aluminium rod I7 is continued down into an annular steel collar 2| and above said collar vit is guided and supported in a tripple sleeve having an inner steel layer 22, an intermediate layer 23 of resin-bonded paper and an outer layer 24 of quartz. This assembly is held in a spider 54. 'Ihe rod Il is coupled by collar 2| to a solid extension 25 of insulating material which in turn is connected to an operating piston 26 Working in a cylinder 21 fixed in the lower wall of the intermediate chamber I3 (which is conveniently of steel or iron). The piston and the plug electrode I 'I are normally urged axially upward by the helical spring 28 but they are forced downwards when the pressure in chamber I 3 overcomes the thrust of the spring 28. To limit the downward movement, the piston rod 29 carries a striking collar 30 which can engage the plunger 3l of a dash pot 32 having a helical compression spring 33 under the plunger and between it and the bottom 34 of the cylinder.

The steel collar 2i is electrically coupled to the H. T. lead 3S by a exible conductor 37. The other H. T. lead 38 is coupled to the hollow electrode I5. If on lowering the plug electrode I 1, the arc is struck from the tip I8 to the hollow asse-,ass

electrode I5; the'. upper endl ofthe arc` may travlel up to the probe tip 39 which may be of highly refractory metal?.

At the end of' the tank I2 furthest: from', the intermediate chamber I3 isi the breechi for the cartridgeA 4.0', which. breech. forms nopart oi'. our invention". Thegasesarereleasedfromitthrough an outlet nozzle 43) which directs the*` gases from the cartridge ri' oni toV the: end wall of, the, tank t2. in a direction: opposite to` that leading to the intermediate chamber, so as toY reduce the kinetic energy of minute solid particles inthe gases.

For the purpose` of filtering, the gases, and cooling them andthereby' reducing or removing ionization', the gases pass through a Ina-inV lter 44.' composed` of expanded metal or perforated plates and coppe-r' gauze. which effects cooling and. cleansing of the gases. without causing objectionable: loss of pressure their passage through it.

A. second foram-inous metal ii'lter 45 is preferably arranged between the intermediate. chest L3. and the switch-chamber I4, and one eiect of. this lil-ter is tol prevent the` direct irnpinging of the gases, on the quartz lin-ing. of the switch chamber. In practice.. the rst actionI of the, highs-pressure gases passing through the :6l-ter, 4.5. is to. push the. cold air in the. chamber [4'. upwards. throughl the gap. between the electrodes. and [5 and. through. thev passage. IE, but. it will be. understood that. atY an. operation of the circuit-breaker. the. metal. parts. incl-uding the filters. 44 and 45 will. be. at. normal temperature; these. lters have the. eiect of reducing very substantially the temperature of the. cartridge gases which may reach. the arc-gap.

The cooling. of. the cartridge-gases. may be enhancedif. necessary, by providing. for the cooling of the tank IZ', as by cooling water, 01 by ns for air-cooling.V It may also or alternatively be of massive construction to provide a large thermal capacity for absorbti'onV of heat from the gases. v

The discharge of the cartridge. may be eected in various ways. Thus an. electric relay in the high-tension power-circuit may actuate a trip i6 for a spring-controlled. hammer ilY which cooperates. with the striking, pin 4.8! for. the percussion-cap of the. cartridge e0.. Alternatively the ignition of the. cartridge may be elected electrically or mechanically.

The insertion of a fresh cartridge. may be effected manually, but. preferably an automatic cartridge-feed is-used. to ensure that a cartridge will be immediately available for use. after a normal operation, or if, a cartridge is defective, or preferably thev arrangement.- described. with reerence to Figures 2 and 3 isused..

Still referring to Figure. 1l. an isolating switch |38 is provided in the. H. T. lead 38. and is arranged to be opened automatically, as soon as the arc has been extinguished, and before the arrival at the arc-gap of cartridge-gases (if any) which are of such reduced dielectric strength as` tov render them unsuitable for arc.- extinction., or prevention.

The operation of the device. isasiollows: When a fault occurs in the. high-tension power circuit, the striker 48 ignites the cartridge 4B and the gases emitted from the cartridge pass to the outlet nozzle 43 of the breech soi that. they strike the end wall of the. tank I2; then the gases pass through the: metallic filter 44 into; the intermediateI chest |13, and ultimately upwardly through the lter 45. into theI switch chamber |41. The highV pressure in the chest I3. forces d'ownv the piston 26.' which carries with it the insulating extension 25, the collar 2| and the movable electrode Il theV tip I8 of which is thus pulled away from the mouth of the passage |6 in the Xed electrode l5, At this stage the cool air in the. switch chamber |11 and, it may be, the cooledl andcleaned cartridge gases are'forcedvery rapidly through the gap between the tip I8 and the hollow electrode I5 causing a. blast through the passage 56 so that the arc is extinguished.

It is important that the downward movement of the movable electrode |`|Y should be strictly limited to suit the requirements of the: circuit (say to a distanceV of l to 2.5 cm.). For thispurpose the' piston 26 carries down with it the piston rod 29 and striking collar 3U, which collar engages the` plunger 3| of the dash pot 3'2 andarrests the downward movement. As soon as the pressure in the chest I3 has fallen suilicientl-y, the helical spring 28v forces the piston 26- upwardly, unrestricted by the dash-pot, to restore the switch to its. closed position, but in the meantime (as is well known in electric circuitbreakers) the isolating switch |38 in they main circuit willr have been automatically opened.

In the case of a three-phase circuit-breaker, a single gas-chamber operating with a single cartridge may effect` the opening of all three phases', by subjecting three pistons 25 to the operating pressure of the gases generatedfrom a. cartridge, such pressure, of course, also: being available for extinction of the` three arcs.

In a typical test, using a l diameter. coppertungsten throat andV a break-gap limited to 1.8 cms., a circuit-breaker as shown in the accompanying. drawing cleared a highly-inductive circuit carrying the highest kva. available. for the test, viz. approximately 3' kiloamperes at 10 kv. in one half cycle of arcing, with av maximum switch-chamber pressure of about 35.- lbs; per square inch above atmosphere.

Referring to Figures 2 and 3 it will be understood that the circuit-breaker'has a container into which the gases under pressure from each cartridge can pass: and the tank or tanks containing: the; fixed breeches for the: cartridges may bev directly coupled' (say through a lter and cooler) with saidA container. The cartridges belong to the electrically ignited type.` Referring to- Figure 2 the ring fuses ||2 H3, H4, H5 of the cartridges are respectively'connected electrically with the bars Ii, II'I, I i8, H9 of a ccmmutator having a radial contact arm |253 which is continuously driven. The axis of the contact arm I2 Elis connected in circuit with (a) a source of. firing current |36, (h) an overload relay |3| normally open but closed when a fault occurs, and (c) common return conductor |2| having for eachigniter or iiring fuse H12, H3, IIA, ||5 a corresponding switch |22, |23, |24, |25 normally closed but opened immediately the c orresponding cartridge I is successfully red.

Referring to Figure 3, the cartridge Util is held in acage lf'l closed at the bottom by disc |42 which haszscreW-engagement with cage IM. The cage IM canslide freely in the fixed breech |39. A helical spring M3. urges the cage I'll I upwardly and is held in position by a cap IM which engages the breech |35v withA a bayonet joint. The disc |42 has anl axial downward extension |29 havingA an upturned protuberance or horn |i33; A tappet |34 controlled by helical spring |35 is 76 arranged te lock the extension |29: in its lower position when the cartridge |40 is successfully red, and solenoid |36 is actuated when the switch |3| is again opened, so that tappet |34 is withdrawn into the position shown in Figure 3 allowing the cage |4I, |42 to rise again to its normal position as shown.

It will be seen that the downward movement of the cage |4|, |42 (when the cartridge |40 is successfully red) opens the corresponding switch |22.

The ring fuse or filament ||2 is electrically connected at one end with conducting disc |42 and thus earthed. The other end has a terminal |46 which makes contact with a conducting probe |45 and the probe |45 is electrically connected to one of the corresponding terminals |32. The probe |45 is insulated from extension |29 by sleeve |28.

Above the cage |4| and cartridge |40, is a one way valve |46 controlled by a light spring |41 within the spider or lantern |48 so that gases from the cartridge |40 can freely pass outwards through valve |46 and lantern |48, but extraneous gases (such as those from another cartridge) cannot pass into the cage |4| or breech |30 when the valve |45 is closed.

The method of inserting a new cartridge is simple: The cap |44 is removed from the breech |39; the cage |4| is removed from the breech; the disc |42 is unscrewed from the cage |4| the fired cartridge |40 is removed from the cage and replaced by a fresh cartridge; the disc |42 is screwed back in place and the cage |4| is replaced in the breech |39, the cap |44 being also replaced.

It has been stated above that the rotating arm is continuously driven. Alternatively the arm |20 may be rotated by clockwork which can be wound up after the circuit-breaker has operated and the clockwork may be set in motion when the relay |3| is closed.

We claim:

1. An electric circuit-breaker having a container of which the principal outlet is formed by a throat in which a portion of the arc-stream associated with any one break between two electrodes lies within such throat, said container being equipped with means for subjecting the arc in said throat, during at least the i'lrst cycle of arcing, to a blast of gas, means for bringing about a sudden expulsion of gaseous medium from a cartridge t increase the pressure in the container and to provide and maintain the blast through said throat until the circuit is broken and de-ionizing means interposed between said cartridge and said electrodes ensuring that the whole of the gas reaching the arc-gap is in such de-ionized condition as to be suitable for arcextinction by gas-blast.

2. An electric circuit-breaker of the type in which one electrode forms a passage leading out of a container, the other electrode consists of a metallic plug axially movable through a limited distance to close the switch and to close the mouth of said passage, or to open the switch and allow gaseous dielectric under high pressure to escape between the plug and the mouth of the passage and through the passage so as to quench the arc, and the pressure in the container is produced by the discharge of gases from a cartridge, and in which de-ionizing means interposed between said cartridge and said electrodes ensure that the gases delivered from the cartridge and the air in the container are wholly in such a condition on reaching the electrodes as to pro- 8 vide a suitable medium for arc-extinction by gasblast.

3. An electric circuit-breaker as claimed in claim 1 in which when one cartridge fails to fire or to provide adequate gaseous pressure for extinction of the arc, action is automatically transferred immediately to another cartridge arranged to discharge into the container.

4. An electric circuit breaker of the type in which one electrode forms a passage leading out of a container, the other electrode consists of a metallic plug axially movable through a limited distance to close the switch and to close the mouth of said passage or to open the switch and allow gaseous dielectric under high pressure to escape between the plug and the mouth of the passage and through the passage so as to quench the arc, and in which the pressure in the container is produced by the discharge of gas from cartridge means, the discharged gas and the air in the container being in such a condition as to provide a suitable medium for arc extinction by gas-blast, said circuit-breaker comprising in combination a series of electrically red cartridges held in fixed breeches and adapted to deliver gas under high pressure to the circuit-breaker container and electrically connected respectively to the bars of a distributor having a rotatable contact arm in circuit with (a) asource of firing current, (b) a relay (closed when a fault occurs in the power circuit to be protected), and (c) a common return conductor having for each electric igniter a switch normally closed but opened immediately the corresponding cartridge is successfully fired,

so that if on the occurrence of a fault, a cartridge is successfully red, the said igniter circuit is broken and no further firing takes place until the circuit-breaker has acted and been re-set, but if one cartridge fails, the next in order is red.

5. An electric circuit-breaker as claimed in claim 4 in which each cartridge is associated with a hydraulic relay adapted on the successful ring of the associated cartridge to open the corresponding switch in the common return of the firing circuit and to keep it open as long as the fault persists.

6. An electric circuit breaker as claimed in claim 4 in which each cartridge is contained with a cartridge cage associated with a hydraulic relay comprising a xed cylinder embracing a spring controlled cartridge cage having an axial extension adapted on the successful firing of the associated cartridge to open the switch in the common return of the iiring circuit and to keep it open as long as the fault persists.

7. An electric circuit-breaker as claimed in claim 6 in which the spring-loaded cage is directly subjected to the pressure of the cartridge when red and the axial extension has a lock which holds the extension and keeps the corresponding switch in the open position as long as the fault persists.

8. An electric circuit-breaker for use in hightension power circuits with alternating current of the type in which one electrode forms a passage leading out of a gas-tight container and the other electrodes consists of a metallic plug axially movable through a limited distance to close the switch and to close the mouth of said passage or to open the switch and allow dielectric gas under high pressure to escape between the plug and the mouth of the passage and through the passage so as to quench the arc by the rapid removal of ionized gas from the vicinity of the arc root, said lcircuit-breeli'er c'iprising combination with` .the container, -a cartridge Stank, .a `cartridge `mounted in sa-i'd tank, means for r-ing the cartridgeand means for cooling and ltering the gas discharged from said cartridge so that the *said gas and the air in the -con-tainer whenA they reach -t-he said escape passage are in such a state of temperature and dielectric strength as to ensure complete electric isolation of the live electrodes of the circuitbreaker from one another for so long as the circuit-breaker remains open.

9. An electric circuit-breaker for use in hightension power circuits with alternating current of the type in which one electrode forms a passage out of a gas-tight container and the other electrode consists of a metallic plug axially movable through a limited distance to close the switch and to close the mouth of said passage or to open the switch and allow dielectric gas under high pressure to escape between the plug and the mouth of the passage and through the passage so as to quench the arc by the rapid removal of ionized gas from the vicinity of the arc root, said circuit-breaker comprising in combination with the container, a cartridge tank, a cartridge mounted in said tank, means for ring the cartridge and means for cooling and iiltering the gas discharged from said cartridge so that the said gas and the air in the container when they reach the said escape passage are in such a state of temperature and dielectric strength as to maintain complete electric isolation of the live electrodes or associated conductive parts from one another during the period from the appearance of recovery voltage across the circuit-breaker till the reclosing of the circuit-breaker.

10. An electric circuit-breaker as claimed in claim 8 in which in order to remove particles of carbon or any other solid suspensoids from the cartridge gases, the gases emitted from the cartridge pass through a foraminous filter comprising heat-absorbing or conducting elements which substantially reduce the temperature of the gases passing therethrough.

l1. An electric circuit-breaker for use in hightension power circuits with alternating current of the type in which one electrode forms a passage leading out of a gas-tight container and the other electrode consists of a metallic plug axially movable through a limited distance to close the switch and to close the mouth of said passage or to open the switch and allow dielectric gas under high pressure to escape between the plug and the mouth of the passage and through the passage so as to quench the arc by the rapid removal of ionized gas from the vicinity of the arc root, said circuit-breaker comprising in combination with the container, a cartridge tank, a cartridge mounted in said tank, means for firing the cartridge and means for cooling and ltering the gas discharged from said cartridge so that the said gas and the air in the container u when they reach the said escape passage are in such a state of temperature and dielectric strength as to ensure complete electric isolation of the live electrodes of the circuit-breaker from one another for so long as the circuit-breaker remains open, the circuit-breaker gas chamber comprising three parts, namely a tank having a breech to receive the cartridge, an intermediate chest containing the conducting connection between the movable electrode and its associated H. T. lead, and a switch chamber containing the actual electrodes.

12. An electric circuit-breaker having a container of which the principal outlet is formedu'by a throat in which a portion `ci? `the arc-stream associated withany one .break between two electrodes lies such throat, said container being ieqiiipped with means or :subjecting the :are in said 1thrat,..during at least the rst .cycle f aring to ablast of ilu'id and *means for .bringing about a sudden expulsion of fluid medium from a cartridge to increase the pressure in the container and to maintain the blast (suitable for arc extinction) through said throat until the circuit is broken, in which when one cartridge fails to fire or to provide adequate gaseous pressure for extinction of the arc, action is automatically transferred immediately to another cartridge arranged to discharge into the container.

13. An electric circuit-breaker having a container of which the principal outlet is formed by a throat in which a portion of the arc-stream associated with any one break between two electrodes lies within such throat, said container being equipped with means for subjecting the arc in said throat, during at least the rst cycle of arcing to a blast of uid and means for bringing about a sudden expulsion of uid medium from a cartridge to increase the pressure in the container and to maintain the blast (suitable for arc extinction) through said throat until the circuit is broken, said circuit-breaker comprising in combination a series of electrically iired cartridges heldin xed breeches and adapted to deliver gas under high pressure to the circuit-breaker container and electrically connected respectively to the bars o1 a distributor having a rotatable contact arm in circuit with (a) a source of iii-ing current, (b) a relay (closed when a fault occurs in the power circuit to be protected) and (c) a common return conductor having for each electric igniter a switch normally closed but opened immediately the corresponding cartridge is successfully red, so that if on the occurrence of a fault, a cartridge is successfully iired, the said igniter circuit is broken and no further firing takes place until the circuit-breaker has acted and been re-set, but if one cartridge fails, the next in order is recl.

14. An electric circuit-breaker as claimed in claim 13 in which each cartridge is associated with a hydraulic relay adapted on the successful iiring of the associated cartridge to open the corresponding switch in the common return of the ring circuit and to keep it open as long as the fault persists.

15. An electric circuit breaker as claimed in claim 13 in which each cartridge is contained with a cartridge cage associated with a hydraulic relay comprising a fixed cylinder embracing a spring controlled cartridge cage having an axial extension adapted on the successful firing of the associated cartridge to open the switch in the common return of the ring circuit and to keep it open as long as the fault persists.

16. An electric circuit-breaker as claimed in claim 13 in which the spring-loaded cage is directly subjected to the pressure of the cartridge when fired and the axial extension has a lock which holds the extension and keeps the corresponding switch in the open position as long as the fault persists.

WILLIS BEVAN WHITNEY. ERIC MERRINGTON BRISCOE. ALBERT ARTHUR HUDSON.

(References on following page) v REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,282,153 Baker et a1 May 5, 1942 2,284,842 Prince et al. June 2, 1942 Number Number Name `Da.te Thommen 1 July 14, 1942 Cooper et al. Aug. 30, 1949 FOREIGN PATENTS Country Date Great Britain May 14, 1931

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