US2281042A

US2281042A - Circuit interrupter

Info

Publication number: US2281042A
Application number: US313430A
Authority: US
Inventors: John B Macneill; Benjamin P Baker; Andrew H Bakken
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1940-01-11
Filing date: 1940-01-11
Publication date: 1942-04-28
Anticipated expiration: 1959-04-28
Also published as: BE483191A; CH218492A; GB544755A; FR943606A

Description

Pl'l 28, 1942. J. B. MacNElLL. ETAL 2,281,042

CIRCUIT INTERRUPTERA y Filed Jan. ll, 19510 3 Sheets-Sheet l M @WVM April 28, 1942.

J. B. MacNElLL ET AL 2,281,042'

CIRCUIT INTERRUPTER 3 Sheets-Shee't` 2- Filed Jan. 11, 1940 WITNESSES:

3 Sheets-Sheet 3 April 28, 1942. J. a. MacNElLL. ETAL CIRCUIT INTERRUPTER Filed Jan. 11, 1940 Wwf-M Patented Apr.l 28, -1 942 UNITED STATES PATENT OFFICE CIRCUIT INTEBRUPTER John B. MacNeill, Wilkinsburg, Benjamin P. Baker, Turtle Creek, and Andrew H. Bakken, Edgewood, Pa., assig'nors to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 11,1940, serial N0.- 313,430

` (c1. zoo-14s) 12 Claims.

also adapted to circuit nterrupters other than the air blast type.

It is now the general'practice to house circuit interrupting apparatus for indoor use in cells or metal cubicles in order to provide a high degree of safety to operators and adjoining apparatus.l

Heretofore, the oil circuit breaker Was almost universally used in installations of this kind. However, due to the fire hazard accompanying oil breakers, power companies have given more and more consideration to oilless breakers and particularly breakers of the air break type. Circuit breakers employing a blast of compressed air to extinguish the arc have been developed which have an interrupting capacity comparable to that of oil circuit breakers in the same voltage class.

It is an object of our invention to provide a compressed air breaker structure that is compact in design, simple and rugged in construction and which will readily adapt' itself to mounting in` spaces such as cells or cubicles formerly housing oil circuit breaker equipment.

It is the usual practice in the operation of a plurality of compressed air vbreaker units to provide a central compressed air system feeding the individual units. In order to insure reliability of operation, each unit is provided with a separate 4or auxiliary pressure tank'of capacity sufcient to operate the individual breaker at least once in the event the main or central supply of.

air is made unavailable. Our invention contemplates using the auxiliary pressure tank as a support upon which the circuit interrupting elements and operating mechanism are mounted, thereby affecting economy in space required to house the breaker.

A more specific object of our invention is to provide a circuit breaker with the pressure tank and the operating and control mechanism grouped as aunit all at ground potential with the contacts and arcchamber supported on-the tank by means of insulating material which includes an insulating conduit for conducting gas from the tank to the arc chamber.

A further object of our invention resides-in the provision of a simplified moving contact structure f or a polyphase circuit breakerand proposes uniting the'moving contact .members in a single unitary structure including a single uid pressure operated piston for moving the contact members to open and closed circuit positions.

It is also an object of `our invention to provide an improved control system applicable-for controlling in proper sequence the opening and closing operation of a gas blast breaker and the admission of an arc extinguishing blast of gas to the breaker arc extinguishing means.

It is an object of our invention to provide an improved circuit breaker and operating mechanism having a piston for operating the contacts to open and closed positions when pressure is admitted to opposite sides of the piston, with means automatically operable when the contacts reach closed position to hold them closed against any opening. force applied to the contacts and arranged so that the application of pressure to the opening side of the piston causes the contacts to be moved to open position.

A further object of our invention is directed to control means for a gas pressure actuated operating mechanism for gas blast interruptels which prevents actuation of the contact mechanism if there is insufficient gas pressure available to move the contacts promptly to the open or to the closing position and if the gas pressure is invsuilicient to extinguish the arc.

Our invention also has for its object theimprovement of ythe opening operation of gas pressure actuated operating mechanisms by holding the contact structure in the closed position until substantially full operating pressure has been applied to the gas pressure operated piston and thereafter-'releasing the contact structure so as to obtain opening movement of the contact structure with a snap action.

Other objects and advantages will be apparent from the following description when read in connection with the accompanying drawings, in which: v

Figure 1 is a front elevational view' of a cir cuit interrupter illustrating our invention;

Fig. 2 is a side elevational view of the interrupter lshown in Fig. 1;

Fig. 3 is a schematic illustration of the operating mechanism of our circuit interrupter and the control system therefor; and

Fig. 4 is a schematic development -of the auxiliary switch used in the control system of our invention, showing the relative positions of the contact structure for both the open and closed positions of the circuit interrupter.

Referring to the drawings, the reference numeral 5 designates a pressure tank for storing gas, such as air, which is preferably supplied from a central source of pressure, not shown. Secured to the upper side of the tank 5 is a framework composed of transverse bars 'I joined by longitudinal extending support bars 9, II, I3 and are similarly arranged and supported upon the bars I3 and I5. The insulators l1 and I9 are grouped .in pairs and provide the support for three the contacts and the air chutes.

identical circuit interrupting units generallyindicated at 2|. Each circuit interrupting unit 2| comprises a stationary contact assembly 23 anda coacting movable contact 25. The

contacts

23 and 25 when in the closed circuit position are surrounded by an arc chute 21 of insulating material. The moving contacts 25 are preferably of bladelike construction and operate into and out of engagement with the'stationary contacts 23 through a relatively narrow throat-like portion 29 of the arc chute 21. Each contact blade 25 is guided in its reciprocating movement by a support arm 3| mounted upon the insulator I9. The support arms 3| are provided'with yielding contact fingers 33 which bear on opposite sides of the contact blade 25 so as to establish a good electrical conterminal 31, stationary contact 23, moving contact blade 25, contact iingers 23, guide bracket 3| and terminates at the terminall 35. Each oi the moving contacts 25 is secured at its lower end to an'insuiator 39 which, in turn, are rigidly mounted at their lower-.ends to a transversely ex- The beam Il is provided with tending beaml 4|. an operating rodl3 associated with a piston 45 movable in an air actuated operating cylinder I1 which is preferably supported from a bracket. 49 secured to the side of the pressure tank 5. It will thus be seen that by reciprocating the piston 45, the moving contacts'25 will be moved to open and closed circuit position as a unit. In thefull open circuit position the moving contacts 25, as shown by dotted line position 25a in Fig. 2, are completely removed from the arc chutes 21 to provide visible air gaps 4between the upper ends of In order to arrest the motion of the moving contact assembly at the end of either its opening cylindrical construction ahd provide a passage 1| through which air from the valve 53 may be dlrected to the arc chutes 21. Each of the throatlike portions 29 through which the moving contacts 25 operate communicate with a passage 13 which, in turn, is arranged `to form a coextensive passage with vthe opening 1| in the insulators i9. Itv is thus seen that upon opening of the valve 93 at a time when an arc is drawn between the

contacts

23 and 25, a. blast of -gas from the tank 5 will pass through the valve 63, the conductor 61, manifold 99, the three passages 1| to the respective arc chutes 21 where the three individual blasts are deflected to pass crosswise of the arc between the

contacts

23 and 25 thereby causing the arcs to be extinguished.

The

valves

5i, 51 and 93 are preferably controlled by electromagnetlcally actuated pilot valves 15, 11 and 19, respectively. The operation of the pilot valves 15, 11 and 19 are controlled by an auxiliary switch 9| suspended from the support bars 9 and The auxiliary switch 9| is provided with an actuating arm 83 operatively coupled to the beam 4| at 85. Further details of. the auxiliary switch 9| and the operation thereof in controlling the circuit interruptor will appear hereinafter in connection with a description of the control system. I

In order to operate the circuit interrupter to open and closed positions, a control system has been devised, as more clearly shown in Fig. 3.

It will, of course be understood that the illustration in Fig. 3 is merely schematic f or the purpose of clarifying the operation and function of the apparatus.

With particular reference to Fig. 3, the pilot valves 15, 11 and 19 are provided, respectively,

with actuating coils 91, 89 and' 9I.- 'I'hese coils` are adapted to be energized from a' suitable source of electrical potential indicated by the

conductors

92 and 93. One terminal of each

coil

91,19 and 9| is connected by'a conductor 95 to the potential or closing'stroke, shock absorbers, 'as shown at valve-5|. 'I'he control'valve 5| is connected with the pressure tankV 5 through a conduit 53 and connects'with the cylinder" .by-Way of conduit 55. Closing movement of the m'ovable contact 25 is accomplished by admitting air under pressure from the tank 5 through the gontroi valve.

51. The'control valve 51 is similar to the vvalve struction having a rotatable drum, not shown, l

5| and'connectswith the pressure tank n5y through l cylinder 41 through thev conduit 5|. An -ai'c es# 'a conduit 5 9 and delivers air underpress'ure to tablished betweenthe stationary contact 23 and Y 'themoving contact`25`is adapted to 'be extin- 2 guished by a blast of gas delivered fromfthe pressure tink 5 to the arcy chute v21. For this pur-: posefar air blast valve 53 is supported by and connected to the tank 5 by a connection 95. The

valve 53 is'connected to an outlet pipe 91 whichl connects withla manifold 59 having three outlet branches terminating, respectively, at the basesource 92. The other side of coil 91 is connected by conductor 91 through terminals b--a of the auxiliary switch 9| to conductor 99. Connection from the conductor 99 to the-conductor 93 of the source may be made either through the conductors |0| and |03 through the relay |95 or through the conductors|91 and |59 through the pushbutton switch The

actuating coil

9,9. for controlling the pilot valve I1 is yconnected by means of conductor H3 through the terminals dF-c of the auxiliary switch 4|, conductor' H5 to the push-button switch and iinally through conductor |59 to the conductor 93 of the source ot control potential. The actuating coil 9| of the pilot' valven19 is'connected by conductor ||1 through the terminals f--e o i the auxiliary switch 9| and conductor I9 to the line 93 of the contrat potential source.

VThe auxiliary switch 9| is of the usual concarried by the Vshaft`|2 I` which, in turn, supports the actuating arm 93 pivotally coupled to the f' moving contact structure at I5. The rotatable drum within the switch 9| carries'a plurality-'ot` contact 'segments schematically shown in' Fig. i.

A'fFor examplewhen-the circuit interruptor is in the 'closed circuit positiongthe auxiliary switch Atakes afposltio'n such that a pairof connected Y contact segments, |23on the drum bridge the terminals a and l.v A pair of segments |25 are out of contacting vengagement with the terminals of, each insulator I9. lThe insulators I9 are '0515 c` and d. The contact segments |21 and I29-are also out of contacting engagement respectively gagement to engaging position with respect to' terminals c-d. The segmentsv |21 will have moved from a position out of engagement to one of engagement and ilnally take a position out of engagement with the'terminals e-f. The segments |29 will have moved from a position normally out of engagement to one of bridging engagement with the terminals g-h Whereas the bridging segments |3| will have moved from a position of engagement to one out of engagement with the terminals i-:i.

As shown in Fig. 3, the movable contact; memder .to eiect a closing of the interrupter contacts by manual control, the control button |33 of the push-button switch I is depressed so as to bers 25 lare in the open circuit position. In orcomplete the circuit from conductor 93, conductor |09 tothe conductor l I5, terminals c-d of the auxiliary switch 8| which, for the open circuit position of the breaker, are bridged by the segments |25, the conductor H3, coil 89 of the pilot.` valve 11, and back to the source of control potential through the conductor 95. It will be noted that for this position of the auxiliary switch, the terminals a-b in circuit with the coil `81 as well as the terminals e-f in circuit with the coil 9| are in open circuit position. Upon Y energization of the coil 89, the pilot valve 11 is opened, admitting air under pressure from the tank 5 to the upper end 'of the control valve 51 which causes the valve to open and admit air through conductor 5| to the lower end of the operating cylinder 41. The air thus admitted reacts against the piston 45, `driving it upwardly so as to actuate the rod 43 and the beam 4| carrying the contact members 25 to the'closed circuit position.

It will b'e noted that as the moving contact assembly moves toward the closed circuit position, the auxiliary switch 3| is also moved. towards the closed position and thail when the closed circuit position has been reached, the terminal c-d of the auxiliary switch will nolonger be bridged by the segments |25 and the control circuit to the Vcoil 89 will be opened. However, during movement from the open to the closed circuit position.

segments |21 of the auxiliary switch 8| will have passed over the terminals 'e-f so as to close the circuit to the coil 9| of the pilot valve19. Thus when the pilot valve ,19 is'open, compressed air from the tank 5 is admitted throughthe pipe 55 to the upper end of the controlvalve 93, there'- by opening the control valve 53 to'permit air to passfthrough\ the conduit 61, manifold 99 and ture is in the closed circuit position. The latch |35 and notch |31 forms a locking means for positively mechanically holding the contacts in closed position against any force applied to the contacts acting in a direction to open the contacts.

If it is desired to open the interrupter by manual control, the bottom |39 of the push-button switch Hi is depressed so as to connect the line 93 of the control potential source through conductor |09, to conductor |01, conductor 99, to the terminals a-b of the auxiliary switch 8i which, for this position of the interrupter are bridged by the segments |23 and thus complete the circuit to the conductor 91 which, in turn, is connected to the coil 81 ci' the pilot valve 15. Since the other terminal of the coil 81 is permanently connected by the conductor95 to the line-92 of the potential source, the circuit through the potential source of the control system is completed and the coil 81 is energized. Energization oi the coil 81 causes pilot valve 15 to be' opened. thereby admitting air from the pressure tank 5 through the conduits 53 to the upper endof control valve 5| which causes air under pressure to be admitted through conduit 55 to the operating cylinder 41. Air from the conduit 51 does not pass directly to the piston chamber within the operating cylinder 41`but is directed to ai valve chamber I4| which has access to the upper side of the piston 45 through a valve |43. Valve |43 is biased to the closed position `by a spring |45 which may be pretensioned so that the valve |43V will not open to admit air to the piston 45 unless thel pressure in the tank 5 is suillcient to promptly move the piston 45 to the open circuit position and to deliver a blast of compressed air suflicient to extinguish .the arcs in the circuit interrupting units 2|.

Assuming that the air pressure is sufficient to permit prompt movement' of the conhct structure and also extinction of the arcs, the valve |43 is raised permitting air to flow to the upper side of the piston |45l which tendsto urge the piston downwardly in a direction to move the moving contact structure to the open circuit position..

This movement, however, will not take place 'immediately since the operating rod 43. is latched in the closed circuit position by the latching member |35 engaging the notch |31. 'I'he valve |43, however, is coupled by a link |41 to the latching Y lever |35 so that following a' predetermined movement of the valve |43, the latch |35 will rethe passages 1|Yto the arc extinguishing units 2| where it is directed in a blast between the

respective contacts

23 and 25. Thus should a spark jump between the contacts during the closing operation, a blast of air is available to quickly extinguish the arc.

It should also be noted that the operating cylinder 41 is provided with a latch |35 adapted to engage a suitable notch |31 formed in'the op-V erating rod 43 whenthe moving contact struclease the operating rod 43 to permit the contact come its static friction as soon as the valve |43 begins Ato move, and continues to move while the gas is flowing from the valve |43 to the upper .side ofA piston 45. This movement of the holding means begins before appreciable force is applied.

to the moving contact tending to move it open. so that the static friction of the holding means which has 'to be overcome is-much smaller than if opening forcewere applied to the moving contact prior to or at the same time as the beginning' of the releasingmovement of the holding means.'r

It will also be seen that a certain amount of time delay is obtained between the initial opening of the.valve |43 and the final release of the latch |35. The amountv of time delay that is desirable depends upon the time required to substantially build up -full operating pressure above the piston- 45 prior to final release ofthe latch |35. Under these conditions, nal release of the latch |35 causes a rapid opening movement of the moving contacts which in effect takes place witha snap action. I i

It is also seen that in the eventl the pressure in the tank 5 is insufcien; toppen the valve |43 or is insuflicient to raise the valve |43 anamount necessary to unlatch the operating rod 43,the moving contact structure of the interrupter remains in the closed circuit position. Thus the auxiliary control switch8l also remains in the closed circuit position and the electromagnet 9| of the circuit interrupter at such time when an over- Y pilot valve 19 remains deener'gized so as not to t further deplete the supply of gas stored in the pressure tank 5.

Under the conditions where suilicientpressure existsA in the tank 5 to permit opening of the interrupter, immediately following initial movement of the contacts iitoward the open circuit load or fault condition exists on the connected circuit, relay |05 will be immediately energized to bring about opening of the interrupter in the manner previously described.

Although we have shown and described a specificcircuit interrupting structure and control means therefor, it is to be understood that the same was for the purpose of illustration and that changes and modifications may be made by those skilledin the art without' departing from the spirit and scope of the appended claims.

We claim as our invention:

1. In a gas blast circuit breaker, separable contacts for establishing an arc, asource of gas under pressure, means for directing a blast of gas from said source against the arc to extinguish `the arc, operating means actuated by gas under pressure from said sourcefor moving said contacts4 to closed position, means for positively mechanically holding said contacts in the closed position, and said holding means being operated mechanically by thev pressure of said source 4for releasing said contact means to move to open position withI the pressure from said sourcefor releasing the` holding means applied prior to the application of tacts af-b so as to deenergize the coil 81 of the pilot valve 15.

It will be understood that push-button switch may be of any well known type used for the remote control of the electrical Aapparatus butv preferably is of the type'which assumes a neutral, position following the completion of the switchingV operation initially controlled by operation thereof. In order to indicate the position of the circuit interrupter at a remote point, we provide signal lamps |49I and |5| which are controlled by the segments |29 and' |3| of the auxiliary switch 8|. Forexample, indicating lamp |49 preferably shows a red signal when the breaker is'A in the closed circuit position, whereas the lamp |5| is energized and shows agreen signal when the breaker is in the open circuit position. The specic method of connecting the signal lamps |49 and |5| to the control potential source 92T' ,force to the moving contact tending to move it in opening direction. t

2. In a gas blast circuit breaker, separable contacts for establishing an arc', a source of gas under pressure, a piston actuated by gas under'pressure from said source for moving said contacts to open and closed positions, means for holding said between said valve and'said vpiston operative to contacts in the closed position, a valve for admitting gas under pressure from said source to said piston to operate said contacts to open circuit position, and pressure responsive means'disposed release said holding means and admit gas to said piston only upon the delivery of gas by said valve ci. predetermined pressure.

' 3. In a'gas blast circuit breaker, separable con.. 'l

' tacts for establishing an arc, a source of gas unand 93 is well known in the art and need not be' further described.

In the event that it is desired to trip or to open the circuit interrupter automatically, as for instance, in response to an overload or fault oci cuzring in the circuit in which the interrupter is cf-.inected we provide a trip coilrcircuit (not shown) which'is connected'to the coil |53 ofthe der pressure, a piston actuated by gas underpressure from said source for moving said contacts tov open and closed positions,.means for latching said contacts inv the closed positiona valve for admitting gas under pressure from said source to said piston to operate said contacts to open circuit position, a valve member disposed between said valve and said piston movable'to open and closed positions for controlling the ow of gas to said piston, resilient means biasing said valve member relay |05. Upon'energization of the coil |53 in response to an overload, the "relay |05 closes a i circuitl from the line 93 through the conductorV N3, and ||l| to the conductor 99 which is in circuit withv the terminalsc-b of the auxiliary switch 8| which, in iturn, completes the circuit Ythrough the conductor 91 to the coilv 81 of the pilot valve 15, which doll is energized as a' result of being connected to the line 92 of the control potential source by the conductor 95. Energiz'ation of the coil Il' causes' actuation of the pilot valve 15 in the manner previously described Vso as to effect operation of the contact structurev to the open circuit position as well as to cause an arc extinguishing blast of gas to flow lbetween the separating contacts and extinguish the arcs.

It will be understood that suitable circuii-l connections vcan be made to the conductor ||5 for Y automatically reclosing the circuit interruptor.

It will also be apparent that ifoupon' closing the' to the closed position, said resilientI means enabling said valve member to open in response to a flow of gas from said valve of Vpredetermined pressure, and means operable in response to movement of said valve member to the open position for releasing` said latching means to enable said piston to 4move said contacts to the open circuit position.

r- 4. In a gas blast circuit breaker, separable contacts for establishing an are, a source of gas under pressure, a piston actuated by gas under pressure .from said source'or moving said contacts to open and closed positions, means for latching said contacts in the closed position, a valve for admitting gas under, pressure from said source to said piston to operate said contacts to open circuit position, anda pressure responsive member v disposed between said Vvalveand said piston operative in response to gas at a predetermined pressure from said source to admit gas Vto said piston and to release said latching means, said. -pressure responsive member delaying release. of'

erating pressure is available at said piston toV cause said piston to open said contacts with a snap action.

5. In a gas blast circuit breaker, circuit interrupting means including a moving contact structure, a uid pressure-actuated piston for moving said contact structure to open and closed positions, a source of gas under pressure, a control valve arranged to admit gas under pressure from said source to said piston to operate said contact structure to open circuit position, a gas blast valve arranged to.admit an arc extinguishing blast from said source to said circuit interrupting means, electromagnetic means for controlling said valves, means for energizing said control means for operating said control and gas blast valves in the order named, means for positively mechanically holding said contact structure in the closed position, and pressure responsive means for releasing said holding means only when sufcient pressure exists at said source to extinguish the arc.

6. In a gas blast circuit breaker, circuit interrupting means including a movingcontact structure, a iiuid pressure actuated piston for moving said contact structure to open and closed positions, a source of gas under pressure, means directing an arc-extinguishing blast from said source to said circuit interrupting means, a control valve operative to 'admit gas under pressure from said" source to said piston to operate said contact structure to the open circuit position, a pressure responsive valve between said control valve and said piston for controlling the iiow of gas to said piston, and means holding said contact structure in the closed position against movement to the open position until a predetermind pressure is available at said piston,

7. In a gas blast circuit breaker, circuit interrupting means including a moving contact structure, a fluid pressure actuated piston for moving said contact structure to open and closed positions, a source of gas under pressure, means directing an arc-extinguishing blast from said source to said circuit interrupting means, a control valve operative to admit gas under pressure from said source to said piston to operate said contact; structure to the open circuit position, a pressure responsive valve betwwen said control valve and said piston for controlling the 'ilow of gas to said piston, latch means for normally holding said contact structure in the closed position against movement to the open position, and means actuated by said pressure responsive valve for releasing saidlatch means only when substantially full operating pressure is available at said piston to cause said piston to 'open said contact structure with a snap action.

8. In a circuit interrupter of the gas blast type.V

a reservoir for storing gas under pressure `arranged to be maintained at ground potential, an

arc-extinguishing device including separable 'contacts, at least one of which is movable, means at least partially o! insulating material for insulatranged to permit movement of said movable *contact with respect thereto and with respect to said arc-extinguishing device. y

9. In a gas blast circuit interrupter, a base structure including a tank at ground potential for storing gas under pressure, separable contacts, an arc chamber in which said contacts separate to establish the arc, means for insulating and supporting said arc chamber from said loase structureand tank including a conduit of insulating material for conducting gas from said tank to said arc chamber, a piston mounted at ground potential on said base structure and tank, an insulated operating rod extending from said piston to actuate said contacts, and control means also supported on said base structure and tank at ground potential for controlling the iiow of gas to said arc chamber and said piston.

10. In a gas'blast circuit lnterrupter, a base at ground potential, supporting means of insulating material eitending from said base; an arc chute, a contact and a terminal for the circuit interrupter connected to said contact all carried by said supporting means of insulating material and insulated from the base thereby; a second terminal for the circuit interrupter mounted on said supporting means of insulating material and ins'ulated thereby both from said base and from the iirst said contact and terminal, a movable contact connected to said second terminal and engageable with the rst said contact, and operating means at ground potential connected by means of insulating material to the movable contact, said operating means moving said movable contact through the arc chute from a position in engagement with the iirst said contact to a position out of the arc chute where there is a visible gap between the movable contact and the arc chute.

l1. In acircuit interrupter, separable contacts for establishing arf arc, a source of gas under pressure, operating means actuated by gas under pressure from said source for moving said contacts to closed position, mechanical means for rigidly holding said contacts in the closed po.` sition. and means operated by gas pressure applied thereto from said source prior to the application of force to said contacts tending to separate them for mechanically releasing said holding means and permitting movement of the contacts to open position.

l2, In a circuit interrupter, separable contacts for establishing an arc, a source of gas under pressure, operating means including aA piston actuated by gas under pressure from said source i or moving-said contacts to closed position when pressure is applied to one side of said piston and for moving said contacts to open position when pressure is applied to the other side of said piston, mechanical means operableautomatically upon said contacts reaching closed position for rigidly holding said contacts in the closed position against any force applied to the contacts tending to move them to open position, and means operated by the gas pressure admitted from said source to the opening side of the piston for automatically mechanically releasing said holding means and permitting movement of the contacts to open position bythe gas pressure admitted to the opening side of the piston, and said means acting to begin the release of the holding means prior to the application of force to the contacts tending to move them inthe opening direction.

- JOHN B. MACNEIIL BENJAMIN P. BAKER. ANDREW H. BAKKEN.

DISCLAIMER 2,281,042.J`ohn B. MacNe'ilI,y Wilkinsburg, Benjamin P. Baker, Turtle Creek nd Andrew H. Bakken, dgewood, Pa.. CIRCUIT IN'rmnnUmn. Patent ated A r. 28, 1942. Disclaimer filed Mar. 3, 1945, by the assignee, Westinghouse ectr: d: Manujactung Company. Hereby enters this disclaimer to claims 1, 11, and 12 in said spcification.

[Oicial Gazette April 8, 1.945.]

DISCLAIMER 2,281,042.Jbhn B. MacNeill- Wilkinsburg, Benjamn P. Baker, Turtle Creek v and Andrew H. Bakken, dgewood, Pa.. CIRCUIT INTEBRUPTER. Patent ated fr. 28, 1942. Disclaimer filed Mar. 3, 1945, by the assignee, Westinghouse ectr: cf: Manufactung Company. Hereby enters this disclaimer to claims 1, 11, and 12 in said spcification.

{Ocz'al Gazette April 3, 1945.1'