US3333077A

US3333077A - Compressed-gas circuit breaker having contacting interrupting and isolating contactswith sequential operation

Info

Publication number: US3333077A
Application number: US412354A
Authority: US
Inventors: Jr William A Fish
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1964-11-19
Filing date: 1964-11-19
Publication date: 1967-07-25
Anticipated expiration: 1984-07-25
Also published as: GB1080269A

Description

July 25, 1967 w. A. FISH. JR 3,333,077

SSEDGAS CIRCUIT BREAKER HAVING CQNTACTING INTERRUPTING AND ISOLATING CONTACTS COMPRE WITH SEQUENTIAL OPERATION 2 Sheets-$heet 1 Filed Nov. 19, 1964 NF a EP mommumaioo cub zu- 024 W fr- ATTORNEY y 1967 w. A. FISH. JR 3,333,077

COMPRESSED-GAS CIRCUIT BREAKER HAVING CONTACTING INTERRUPTING AND ISOLATING CONTACTS WITH SEQUENTIAL OPERATION Flled Nov 19, 1964 2 Sheets-Sheet 2 9 mfg United States Patent 3,333,077 COMPRESSED-GAS CIRCUIT BREAKER HAVING CONTACTING IN TERRUPTING AND ISOLATING CONTACTS WITH SEQUENTIAL OPERATION William A. Fish, Jr., Wilkins Township, Pittsburgh, Pa.,

assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 19, 1964, Ser. No. 412,354 12 Claims. (Cl. 200-148) This invention relates, generally, to circuit breakers and, more particularly, to circuit breakers of the gas-filled dual-pressure type in which a blast of high-pressure gas assists in arc interruption during opening of contact members of the breaker.

Prior dual-pressure gas-filled circuit breakers have been operated by a pneumatic operating mechanism located externally of the breaker and connected to the contact members through a mechanical linkage. The flow of gas from the high-pressure chamber for are interruption has been controlled by a mechanically operated blast valve. A gasoperated control system using the pressure differential between the high and low pressure chambers, thereby eliminating the need for a separate pneumatic operating mechanism and compressed air system, is disclosed in a copending application, Ser. No. 419,044, filed Dec. 17, 1964 by G. J. Easley, and assigned to the Westinghouse Electric Corporation.

In order to secure fast interruption of a circuit, it is desirable to open the contact members of a breaker and provide the contact separation required for most efficient arc interruption as quickly as possible. Accordingly, an object of this invention is to increase the speed of opening of a gas-operated circuit breaker.

It is also desirable to provide additional contact separation after interruption has occurred to prevent flash-over due to surge voltages. However, increasing the contact separation beyond that required for efficient interruption before a current zero, and thus an opportunity to interrupt occurs, can result in undesirably high are voltage and are energy. Therefore, another object of the invention is to provide delayed additional contact separation in a circuit breaker.

A further object of the invention is to provide a simplified gas-operated control scheme for a circuit breaker.

Still another object of the invention is to incorporate the blast valve of a circuit interrupter in the operating cylinder that withdraws the interrupter contact.

A still further object of the invention is to utilize the hollow contact member of an interrupter of the orifice type as part of an isolator assembly, which is operated after arc interruption.

Another object of the invention is to utilize the isolator to disconnect a resistor which parallels the interruper contacts of the interni-pter.

Other objects of the invention will be explained fully hereinafter, or will be apparent to those skilled in the art.

In accordance with one embodiment of the invention, two movable interrupting and isolating contacts are combined into one pair of contact members which are operated in sequence by pistons in two cylinders pressurized by gas from the high-pressure reservoir of a dual-pressure gas-filled circuit breaker. The sequence of operation is such that the movable interrupter contact is withdrawn first, separating the contacts and permitting high-pressure gas from a blast tube to flow through the interrupter and the hollow section of the isolator piston rod. At full travel of the movable interrupter contact, the interrupter contact and are horn provide the necessary separation for eflicient interruption. After a short delay to permit completion of the interruption, the movable isolator piston rod is withdrawn to increase and maintain contact separa- 3,333,077 Patented July. 25, 1967 tion, and the movable interrupter contact and are horn are returned to the initial or closed position, thus stopping the flow of gas. The operation of the two pistons is controlled by gas operated valves which, in turn, are con trolled by electrically operated valves.

For a better understanding of the nature and objects of the invention, reference may be had to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a diagrammatic vieW of one pole unit of a circuit breaker and control system embodying principal features of the invention, the contact structure being shown in the closed-circuit position;

FIG. .2 is a view, in section, of the interrupter, the interrupter, the interrupter operating cylinder and the isolator utilized in the circuit breaker, again the contact structure being shown in the closed-circuit position; and,

FIG. 3 is a view, in section, of a modified interrupter and shunting resistor which may be utilized in the circuit breaker, the contact structure again being shown in the closed position.

Referring to the drawings, and particularly to FIG. 1, there is shown therein a diagrammatic view of one pole unit and the associated control apparatus for a circuit breaker 1 embodying the present invention. It will be understood that additional pole units, similar to the one shown, may be provided. The structure shown in FIG. 1 comprises a generally cylindrical tank 2, a pair of terminal bushings 3 extending through a wall of the tank 2, a movable interrupter contact operating means or motor 4, an interrupter unit 5, an isolator device 6, a high pressure gas reservoir 7, a compressor and filter 8 and an auxiliary switch operating cylinder 9. As shown, control valves A, B and C are mounted inside the tank 2. A close valve 11 and a trip valve 12 are mounted externally ofthe tank 2.

The tank 2 contains an interrupting gas, such as sulfur hexafiuoride (SP gas, at a relatively low pressure, for example 40 p.s.i.g. The reservoir 7 contains SP gas at a relatively high pressure, for example 230 p.s.i.g. The gas in the reservoir 7 is maintained at the high pressure by the compressor 8, which is connected between the tank 2 and the reservoir 7 to form a closed system and returns gas from the tank 2 to the reservoir 7 after an interrupting operation. The high-pressure gas reservoir .7 is

connected to the operating cylinder 4 through an insulating blast tube 13.

The bushings 3 may be of any suitable construction, each bushing having a supporting plate 14 attached to the lower end of a terminal stud 15 which extends through the bushing. A current transformer 16 may be mounted around each bushing externally of the tank 2. The control valve A is a three-way, normally-closed, pressure-pilot-operated valve. The valve B is a three-way, normally-closed, pressure-pilot-operated valve with an internal bleed between the pilot section and the outlet as indicated by the dotted line b. The valve C is a straightway, normally-closed, pressure-pilot-operated valve. The close valve 11 is a straight-way, solenoid-operated, normally-closed valve of adequate capacity to pressurize the small pilot line 10 to valve B. The trip valve 12 is a threeway, solenoid-operated, normally-closed valve of :adequate capacity to pressurize or to exhaust the small pilot lines 20, 20a to valves A and C. One each of the close and the trip valves is required per breaker. One each of valves A, B and C is required per pole. i

As shown, a piston 17 is disposed inside the auxiliary switch operating cylinder 9. Contact members 18 and 19 are carried by a piston rod 21 attachedto the piston 17. The lower end of the cylinder 9 is connected to the high pressure reservoir 7 through a line 22. The upper end of the cylinder 9 is connected to a port K' in the isolator cylinder 57 through a line 23. When hgih pressure gas is admitted to the upper end of the cylinder 9, the piston 17 is retained in its lowermost position, as shown in FIG. 1, in view of the difference in area of the two sides of the piston 17. When the high pressure gas is exhausted from the upper portion of the cylinder 9, the piston 17 is raised by the pressure of the high-pressure gas in line 22. The function and operation of the auxiliary switch 24, which is Operated by the piston 17, will be described more fully hereinafter.

The movable interrupter contact operating means 4, is the interrupter unit 5 and the isolator operating device 6 are shown in more detail in FIG. 2. The movable interrupter contact operating means 4 comprises a base 25, a cylinder 26, a piston 27, a spring 28, a piston head 29 and a valve seal 31. As shown in FIG. 1, the base 25 is attached to the supporting plate 14 on the right-hand terminal bushing 3. The cylinder 26 is divided into two

compartments

32 and 33 by a partition 34. The compartment 33 is closed by a cylinder head or cap 35 removably attached to the right-hand end of the operating cylinder 26. The piston 27, which is disposed in the compartment or entrance chamber 32, has an integrally formed stem 36 which extends through the partition 34 into the compartment 33. The piston head 29 is attached to the end of the stem 36 by a nut 37. An O-ring seal 38 is provided around the stem 36 in the partition 34. A similar seal 39 is provided at the joint between the cylinder head 35 and the cylinder 26. Likewise, a seal 41 is provided at the joint between the cylinder 26 and the base 25. The piston 27 also has an integrally formed movable contact rod 42, which extends through the base 25 into an interrupting chamber 43 enclosed by an interrupter hood, or orifice member 44. The spring 28 surrounds the stem 36 in the compartment 32 between the partition 34 and the piston 27. An opening 45 through the base 25 connects the interrupting chamber 43 with the region 47 between the lefthand side of the piston 27 and the valve seal 31. Small bleed holes 46 extend through the piston head 29.

A normal condition of the movable interrupter contact operating means 4 is the closed contact position as shown in FIGS. 1 and 2. The front compartment, or chamber 32 formed by the cylinder 26, the partition 34, the piston 27 and the seal 31 is at high gas pressure, which is maintained through the blast tube 13 from high-pressure gas reservoir 7. The

regions

33a, 33b on both sides of the piston head 29 in the compartment 33, and the region 47 between the piston 27 and the base 25 are at low or tank pressure. Thus, the piston 27 is held closed against the valve seal 31 by the force of the high-pressure gas acting on the right-hand face of the piston 27 combined with the force of the compression spring 28.

As shown, the interrupter unit 5 comprises the orifice member 44 and a cluster of movable contact finger members 51 having a base 52, which is attached to the lefthand end of the piston rod 42 by means of an arc horn 53. Contact fingers 54 are attached to the base 25 to slidably engage the contact rod 42. The orifice member 44 is preferably composed of a suitable high-temperature material, such as polytetrafluoroethylene. The orifice nember 44 is removably attached to the base 25 by a :lamping ring 55.

The isolator operating device 6 comprises a base 56, a. cylinder 57, a cylinder head or cap 58, and a piston 59. kn O-ring gasket 61 seals the joint between the cylinder vall 57 and the cap 58. A seal 62 at the left-hand end of he cylinder chamber 60 is engaged by the piston 59 when he piston is at the left-hand end of the cylinder chamber 50. The piston 59 has an integrally formed isolator rod 53 which extends through the base 56. An O-ring seal 64 s provided around the rod 63 at the opening through the use Contact fingers 65 are attached to the base 56 to :lidably engage the piston rod 63. As shown in FIG. 1, the iase 56 is attached to the supporting plate 14 on the leftland bushing 3.

As shown, the right-hand end of the isolator piston rod 63 has a hollow or tubular portion 66, which substanitally fills an opening 67 in the interrupter orifice member 44 and is engaged by the contact fingers 51 when the circuit breaker 1 is in the closed position. Interrupting openings or vents 68 are provided in the wall of the tubular portion 66 of the isolator contact member to accommodate exhausting of the arc-extinguishing gas.

The region or chamber between the right-hand side of the isolator piston 59 and the base 56 is permanently connected to the blast tube 13 and hence to high pressure through a port L. Thus, the isolator is closed or opened by pressurizing or exhausting the region or chamber 60 formed by the cylinder cap 58, the cylinder 57 and the left-hand side of the piston 59.

The method of arc interruption is similar to that described in US. Patent 3,154,658, issued Oct. 27, 1964 to R. G. Colclaser and R. N. Yeckley and assigned to the Westinghouse Electric Corporation. High-pressure gas is blasted into the hollow contact member 66 and out through the vents 68 into the low pressure tank. The contact finger members 51 are sepaarted from the isolator contact member 66 by moving the piston 27 to the right. When the piston 27 moves to the right, high pressure gas from the reservoir 7 flows through the blast tube 13 into the compartment 32 of the cylinder 26 and out through the openings 45 into the interrupting chamber 43 and thence into the hollow contact member 66 to extinguish the established arc.

Thus, the hollow contact 66 is part of the isolator assembly 6 and the blast valve is incorporated in the operating means 4 that withdraws the interrupter contact member 51 to the open position. The sequence of operation is such that the interrupter contact 51 is first withdrawn, separating the contact fingers 51 from the isolator cnotact member 66, and permitting high pressure gas from the blast tube 13 to flow through the interrupter unit 5 and the hollow section 66 of the movable isolator contact 63. At full travel, the interrupter contact 51 and are horn 53 provide the necessary sepaartion for efiicient arc interruption. After a short delay to permit completion of the interruption of the arc, the movable isolator contact 63 is withdrawn toward the left to increase and maintain contact separation, and the piston 27 and the interrupter contact 51 return to their initial or closed position, thereby stopping the flow of high pressure gas.

The opening, or interrupting operation is initiated by admitting high pressure gas to port F. This pressurizes the chamber 33a in front of the piston head 29 and drives the piston and the interrupter contact 51 to the open position. This separates the contact members 51 and 66 (which remains stationary) and opens the blast valve, permitting gas to flow through the interrupter orifice 44 and the hollow end of the movable isolator contact to interrupt the resulting are. The small bleed holes 46 in the piston head 29 permit the pressure on the two sides of the piston head to equalize and the interrupter contact 51 to return to the initial or closed position under the action of the spring 28. The size of the bleed holes 46 will determine the length of time the interrupter contact 51 and blast valve 27 remain open, and will be selected to permit reclosure as soon as possible after allowing adequate time for interruption of the arc to be completed. When port F is again reduced to the low pressure, the chamber 33a will exhaust and the interrupter operating piston 29 will remain in the normal closed position. A check valve 69 (FIG. 1) between ports F and G also quickly exhausts the chamber 33b behind the piston head 29 so that the opening operation can be repeated quickly if desired.

As shown in the drawings, the breaker is in the closed circuit position. The close valve 11 and the trip valve 12 and the valves A and C are deenergized and closed. The isolator chamber 60 is pressurized and the pilot 71 of valve B is maintained at high pressure by the internal bleed connection b, thus holding this valve in the open position and admitting high pressure gas to maintain the pressurized condition of the isolator operating device 6. The low pressure condition in the compartment 33 of the interrupter operating cylinder 26 is maintained through the open exhaust port of the normally closed valve A.

Energizing the solenoid 72 of the trip valve 12 admits high pressure through the pilot line 20' to the pilot 73 of the valve A which opens and admits high pressure to the interrupter operating chamber 33a through the port F. The

interrupter contacts

51, 66 then separate permitting gas flow through the interrupter unit and the contact 51 recloses after a short delay as previously explained. The trip valve 12 also admits high pressure through the pilot line 20a to the pilot 74 of the valve C, which opens and exhausts the pilot 71 of valve B to low pressure. This permits valve B to close moving upwardly under the influence of spring 71', thus exhausting the isolator cylinder 60 to low or tank pressure through exhaust opening 71". The piston 17 in the auxiliary switch operating cylinder 9 is operated by the pressure change at port K of the isolator chamber 60, thus opening the contact members 19 of the auxiliary switch 24 and deenergizing the solenoid 72 of the trip valve 12. The trip valve 12 returns to its normally closed position, exhausting the pilots of valves A and C which return to their normally closed positions. This exhausts the interrupter operating chamber 33a and isolates the pilot 71 of the valve B except for the internal bleed connection b which is connected to the isolator chamber 60 (now at low tank pressure). The compression spring 71 of valve B will now maintain the valve B in its upwar-d position (not shown) exhausting the isolator chamber 60 through exhaust opening 71".

The isolator region 60 thus remains exhausted through valve B to low tank pressure, and the isolator contact 66 remains in its leftward fully open position. Since the interrupter operation is initiated by pressurizing a very small volume 33a between the one side of the piston head 29 and the partition 34 in the cylinder 26, and the isolator contact opening is initiated by exhausting a relatively large volume 60 in the cylinder 57 between the piston 59 and the cylinder head 58, the interrupter contact 51 will open sooner than the isolator contact 66. The desired time sequence and time intervals of interrupter open, isolator open and interrupter reclose can readily be obtained by selection of the proper size of gas passages.

Energizing the solenoid 75 of the close valve 11 admits high pressure through the pilot line 10 to the pilot 71 of valve B which opens, moving downwardly and admits high pressure to the isolator chamber 60 through pressure line 30, thus closing the isolator contact 66. The pressure change at port K operates the auxiliary switch 24 to open its contact members 18 and hence deenergize the solenoid 75 of the close valve 11. The pilot 71 of valve B is maintained at high pressure by the internal bleed connection b to the now pressurized isolating chamber 60 and the breaker stays closed.

The gas flow capacity of valve C should be greater than that of the close valve 11 to assure pneumatically trip-free operation of the isolator contact 66. Any standard, non-pumping electrical control scheme which provided seal-in on both closing and opening operations is applicable to this circuit breaker although not shown in the drawings.

A well known principle in circuit interruption is that performance can be improved and ratings can be increased by adding a shunt resistor in parallel to the main separating contacts while interrupting the main fault current, and then opening the resistor circuit to interrupt the residual resistor current. In the modification shown in FIG. 3, a resistor 76 is wound around the interrupter orifice member 44' and is connected across the interrupter contact member 51 and the isolator contact member 66 by means of a spring-biased contact member or, probe 77, which engages the isolator contact member 66 when it is in the closed position, as shown in FIG. 3. As shown, contact member 77 is slidably disposed in an enlarged end portion 78 of the insulating orifice member 44' and is biased into engagement with the isolating contact member 66 by a spring 79. Contact member 77 is connected to one end of the resistor 76 by a connector 81. The other end of the resistor 76 is connected to the base 25 by a connector 82. If desired, resistors of other types, such as carbon block or disc resistors, may be utilized in place of the wire resistor 76.

Interruption of the main fault current is accomplished, as hereinbefore described, by the flow of high-pressure gas into the hollow isolator contact member 66 when the main interrupter contact member 51 and the arc horn 53 are withdrawn to the right. The resistor interrupter probe 77 remains in contact with the isolator contact member 66, thus shunting the current through the resistor 76 when the arc has been extinguished. When the isolator piston rod 63 is withdrawn toward the left, the

residual current arc is drawn between the interrupter probe 77 and the isolator contact member 66, and is interrupted by the continued flow of high-pressure gas out through the orifice opening 40. The movable isolator contact 66 continues its movement to the open position, thus maintaining contact separation, and the main interrupter piston 27 returns to the leftward closed position over the valve seat 31, thus stopping the flow of gas.

The closing operation of the modified-type interrupting unit 50 is the same as hereinbefore described in connection with the interrupter of FIG. 2. The isolator contact 63 is moved to the closed position and contact is made by engaging first the resistor interrupter probe 77 and then the main interrupter contact 51, thus completing the circuit.

From the foregoing description, it is apparent that the invention provides a circuit breaker in which fast contact separation required for two or three cycle interrupting time is readily obtainable. The physical disturbance on interruption of the arc is kept to a minimum by completing the interruption with an ideal contact separation distance, after which the separating distance is increased by the operation of the isolator device 6 to prevent flash-over due to surge voltages. The gas blast time is reduced to a minimum, thus reducing the amount of gas reservoir volume and the amount of time during which the compressor 8 is required to operate and maintain high pressure in the high pressure reservoir 7. The combining of the interrupter and isolator contacts and incorporating the blast valve in the interrupter operating cylinder reduces the number of parts and simplifies the breaker structure, thereby decreasing the cost, improving the reliability and reducing maintenance requirements.

Since numerous changes may be made in the above described constructions, and diiferent embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all subject matter contained in the foregoing description, or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A circuit breaker of the compressed-gas type including, in combination, means defining an orifice member having an orifice opening therein, a movable interrupting contact disposed within said orifice member, a movable isolating contact movable through said orifice opening during the closing operation and into contacting closed engagement with said movable interrupting contact, means defining an entrance chamber filled with high-pressure gas disposed on one side of said orifice member, said entrance chamber having a blast opening leading into said orifice member, blast-valve means including a movable blast valve responsive to movement of said movable interrupting contact for controlling a flow of high-pressure gas out of said entrance chamber and into said orifice member, first operating means for causing an initial retraction of said movable interrupting contact away from said movable isolating contact within said orifice member while the movable isolating contact is stationary during the initial portion of the opening operation, said retracting separating movement of the movable interrupting contact effecting opening of said blast-valve means for causing a blast of high-pressure gas to flow through said blast opening from the pressurized entrance chamber into said orifice member for arc-extinguishing purposes, and second operating means for subsequently effecting isolating movement of said movable isolating contact out of said orifice opening to interpose an isolating gap into the circuit.

2. The compressed-gas circuit breaker according to claim 1, wherein a tank at relatively low pressure is provided, two terminal bushings extend into said tank, the orifice member and first operating means are supported at least partially by the inner end of one terminal bushing, and the movable isolating contact and second operating means is at least partially supported by the inner end of the other terminal bushing.

3. The compressed-gas circuit breaker according to claim 1, wherein the first operating means comprises a pneumatic operating cylinder and a first piston member movable therein and secured to the movable interrupting contact.

4. The combination of claim 3, wherein means are provided to bias the movable interrupting contact to the closed-circuit position.

5. The combination according to claim 1, wherein means are provided to bias the movable interrupting contact to the closed-circuit position.

6. The compressed-gas circuit breaker according to claim 1, wherein the second operating means comprises a pneumatic operating cylinder and a second piston member movable therein and secured to the movable isolating contact.

7. The compressed-gas circuit interrupter according to claim 3, wherein the second operating means comprises a pneumatic operating cylinder and a second piston member movable therein and secured to the movable isolating contact.

8. The combination according to claim 2, wherein a high-pressure blast tube extends from the tank wall to the entrance region at high pressure to maintain the same pressurized at high pressure.

9. The combination according to claim 3, wherein the region (33b) within the operating cylinder on one side of the first piston member is generally at low pressure, the region (33a) within the operating cylinder on the other side of the first piston member is alternately pressurized and exhausted, and conduit means and unidirectional valve means (69) interconnect the two regions for rapid reopening operations.

10. The combination according to claim 1 wherein a resistance contact member (77) is supported in the orifice member and bears against the movable isolating contact, and a resistance is connected between said resistance contact member (77) and the movable interrupting contact.

11. A circuit breaker comprising a tank containing an interrupting gas at a relatively low pressure, a reservoir containing the same kind of gas at a relatively high pressure, an interrupting chamber disposed inside the tank, a movable interrupting contact member and a movable isolating contact member engaging within the chamber, a first piston disposed in a first cylinder for withdrawing the movable interrupting contact member, a second piston disposed in a second cylinder for withdrawing the movable isolating contact member, valve means for controlling the admission of gas into said cylinders from the high pressure reservoir first to withdraw the interrupting contact member in one direction and then to withdraw the isolating contact member in the opposite direction, auxiliary switch means for controlling the operation of containing the same kind of gas at a relatively high pressure in said second cylinder for operating the auxiliary switch means.

12. A circuit breaker comprising a tank containing an interrupting gas at a relatively low pressure, a reservoir containing the same kind of gas at a relatively high pressure, an interrupting orifice member disposed inside the tank, an interrupting contact member and an isolating contact member engaging within the orifice member, a first piston disposed in a first cylinder for withdrawing the interrupting contact member, a second piston disposed in a second cylinder for withdrawing the isolating contact member, valve means for controlling the admission of gas into said cylinders from the high pressure reservoir to operate said pistons in sequential relation, and resistance means including a resistance contact supported in said orifice member connected in parallel circuit relation with said contact members.

References Cited UNITED STATES PATENTS 2,447,656 8/1948 Ludwig et al 200-148 X 3,164,705 1/1965 Cromer 200148 FOREIGN PATENTS 512,623 9/1939 Great Britain. 546,399 7/1942 Great Britain.

267,793 7/ 1950 Switzerland.

ROBERT K. SCI-IAEFER, Primary Examiner. R. S. MACON, Assistant Examiner.

Claims

1. A CIRCUIT BREAKER OF THE COMPRESSED-GAS TYPE INCLUDING, IN COMBINATION, MEANS DEFINING AN ORIFICE MEMBER HAVING AN ORIFICE OPENING THEREIN, A MOVABLE INTERRUPTING CONTACT DISPOSED WITHIN SAID ORIFICE MEMBER, A MOVABLE ISOLATING CONTACT MOVABLE THROUGH SAID ORIFICE OPENING DURING THE CLOSING OPERATION AND INTO CONTACTING CLOSED ENGAGEMENT WITH SAID MOVABLE INTERRUPTING CONTACT, MEANS DEFINING AN ENTRANCE CHAMBER FILLD WITH HIGH-PRESSURE GAS DISPOSED ON ONE SIDE OF SAID ORIFICE MEMBER, SAID ENTRANCE CHAMBER HAVING A BLAST OPENING LEADING INTO SAID ORIFICE MEMBER, BLAST-VALVE MEANS INCLUDING A MOVABLE BLAST VALVE RESPONSIVE TO MOVEMENT OF SAID MOVABLE INTERRUPTING CONTACT FOR CONTROLLING A FLOW OF HIGH-PRESSURE GAS OUT OF SAID ENTRANCE CHAMBER AND INTO SAID ORIFICE MEMBER, FIRST OPERATING MEANS FOR CAUSING AN INITIAL RETRACTION OF SAID MOVABLE INTERRUPTING CONTACT AWAY FROM SAID MOVABLE ISOLATING CONTACT WITHIN SAID ORIFICE MEMBER WHILE THE MOVABLE ISOLATING CONTACT IS STATIONARY DURING THE INITIAL PORTION OF THE OPENING OPERATION, SAID RETRACTING SEPARATING MOVEMENT OF THE MOVABLE INTERRUPTING CONTACT EFFECTING OPENING OF SAID BLAST-VALVE MEANS FOR CAUSING A BLAST OF HIGH-PRESSURE GAS TO FLOW THROUGH SAID BLAST OPENING FROM THE PRESSURIZED ENTRANCE CHAMBER INTO SAID ORIFICE MEMBER FOR ARC-EXTINGUISHING PURPOSES, AND SECOND OPERATING MEANS FOR SUBSEQUENTLY EFFECTING ISOLATING MOVEMENT OF SAID MOVABLE ISOLATING CONTACT OUT OF SAID ORIFICE OPENING TO INTERPOSE AN ISOLATING GAP INTO THE CIRCUIT.