US3855437A

US3855437A - Electric compressed-gas circuit breaker

Info

Publication number: US3855437A
Application number: US00344043A
Authority: US
Inventors: H Goedecke; K Rolff; F Richter
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-02-22
Filing date: 1973-03-22
Publication date: 1974-12-17
Anticipated expiration: 1991-12-17
Also published as: DE2220897B2; CH554596A; DE2215656B2; FR2177804A2; DE2209287A1; DE2215656C3; NL173576C; CH544999A; DE2215656A1; US3854019A; FR2177804B2; FR2181860A2; FR2172980A1; NL7217042A; US3789175A; NL173576B; DE2220897A1; FR2172980B1; DE2209287C3; GB1394547A

Abstract

In order to avoid flow stagnation near the sliding contact ring of arc-resistant material, auxiliary flow passages are provided to pass at least a portion of the quenching gas flow across the contact ring during a breaker opening motion. The auxiliary flow passages can be formed to bypass a gas flow between the sliding bridging switching element and the downstream contact, e.g. through holes in the contact downstream of the nozzle or through passages in the nozzle. The auxiliary flow passages can also take the form of radial holes through the bridging switching element and contact ring itself.

Description

United States Patent 9 Goedecke et al.

[451 Dec. 17,1974

[ ELECTRIC COMPRESSED-GAS CIRCUIT BREAKER [75] Inventors: Heiko Goedecke; Klaus-Peter Rolff;

Friedrich Richter, all of Berlin, Germany [73] Assignee: Siemens Aktiengesellschaft, Munich,

Germany [22] Filed: Mar 22, 1973 [21] Appl. No.: 344,043

[30] Foreign Application Priority Data 7 Mar. 27, 1972 Germany 2215656 [52] US. Cl 200/148 R [51] lntLCl. HOlh 33/82 [58] Field of Search 200/148 R, 148 B, 148 BV, 200/148 A, 150 G [56] References Cited FOREIGN PATENTS OR APPLICATIONS Germany 200/148 R Primary Examiner-Robert S. Macon Attorney, Agent, or FirmKenyon & Kenyon Reilly Carr & Chapin [57] ABSTRACT ln order to avoid flow stagnation near the sliding contact ring of arc-resistant material, auxiliary flow passages are provided to pass at least a portion of the quenching gas flow across the contact ring during a breaker opening motion.

The auxiliary flow passages can be formed to bypass a gas flow between the sliding bridging switching element and the downstream contact, e.g through holes in the contact downstream of the nozzle or through passages in the nozzle. -The auxiliary flow passages can also take the form of radial holes through the bridging switching element and contact ring itself.

22 Claims, 7 Drawing Figures ELECTRIC COMPRESSED-GAS CIRCUIT BREAKER FIELD OF THE INVENTION The invention relates to an electric compressed-gas circuit breaker.

BACKGROUND OF THE INVENTION I-Ieretofore, various types of electric compressed-gas circuit breakers have been known. For example, one type has been constructed witha blasting device consisting of a piston and cylinder, with two stationary nozzle-shaped contacts, and with a bridging switching element surrounding these contacts and connecting the contacts in a closed breaker position. This circuit breaker is usually equipped with a sliding contact ring constructed of arc-resistant material and spring loaded contact fingers ln order to improve the arc commutation during a breaker opening process, it has been proposed in pending US. patent application Ser. No. 334,934, filed'Feb. 22, 1973. and entitled Electric Compressed-Gas Circuit Breaker, corresponding to German patent application P 22 09 287.1, filed Feb. 22, 1972 to have the bridging switching element carry the sliding contact ring with an electrically insulating layer interposed therebetween and to have the sliding contact ring and the contactfingerselectrically connected at the time .of separation of the contact fingers from'the one stationary contact.

However, in high-power breakers, due to the required large cross-section, the bridging switching element, which surrounds one of the stationary contacts even during thebreaker-opening motion can require a construction of the contact arrangement which causes the gap between the'two contacts to be at least partially the breaker-opening motion permits avoidance of flow separation areas in the quenching gas flow. By application of the invention, a path of flow is produced in the gap between the two stationary contacts, which has favorable quenching and cooling properties, and therefore accomplishes an increase in the circuit-breaking capabilities.

In a first embodiment of the compressed circuit breaker, according to the invention, the auxiliary passage means is in the form of at least one passage which begins in the region of the gap between the two stationary'contacts and terminates behind a nozzle located in the end of one of the contacts. Here, the auxiliary passage can run between the outer surface of one nozzlecontaining contact and the bridging switching element surrounding the contact. In this case, the outlet of the auxiliary passage is formed of at least one radially oriobstructed during breaker opening. This can cause hot quenching gas to collect in aregion of flow stagnation in frontof the sliding contact ring.

' OBJECT OF THE INVENTION I It is an object of the invention to eliminate the region of flow stagnation'in' electric compressed-gas circuit breakers in'order to achieve improved circuit-breaking capability. I l t SUMMARY OF THE INVENTION The invention provides an electric compressed-gas circuit breaker having two hollow contacts disposed in spaced relation, means including a bridging switching eIement-slidably surrounding the contacts for selectively electrically connecting the contacts in a closed breaker condition, a contact ring of arc-resistant material mounted on the bridging switching element, and means defining a chamber about the bridging switching element for a pressurized quenching gas with an auxiliary passage means for passing at least a portion of the quenching gas from the gas chamber across the contact ring during a breaker opening operation.

The auxiliary passage means is closed in the closed breaker position and is automatically opened during the breaker-opening motion. The auxiliary passage means is disposed in the usual gas flow channel between the means which defines the quenching gas chamber and the hollow contacts.

The component of quenching gas flow fed to the sliding contact ring by the auxiliary passage means during ented continuous hole in the hollow contact, located behind the nozzle in the direction of flow. Alternatively, insofar as there isa decrease in contact crosssection where cavities are placed in the contact which is undesirable for electrical reasons, the cavities can be placed in the nozzles for example by milling cuts running parallel to the nozzleaxis.

In both cases, several passages or cavities can advantageously be distributed around the circumference. In the embodiment with holes in the hollow contact, the nozzle connected with the contact becomes a simple structure of circular symmetry, which permits the use of, for example, graphite as the arc-resistant material.

Also, in both embodiments, the flow of quenching gas is branched in the outflow directionb ehind' the sliding contact ring; the main flow branch flowing through the interior of the nozzle of the one stationary contact while the other branch flows through the auxiliary passage. The dimensions ofthe branches can be made so that the flow of quenchinggas driving the are into the center of the gap between the stationary contacts is decreased only slightly or not at all.

In a further embodiment, the auxiliary passage means I is formed by drilling at least one hole transversely to the axis of the bridging switching elementQand passing through the switching element, an insulating layer between the switching element and the contact ring and the sliding contact ring itself. Here, too, several drill holes can be distributed over the circumference. In this embodiment, the quenching gasflow is branched in the outflow direction before the sliding contact ring is reunited behind the sliding contact ring, which is advantageous in some cases.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates a fragmentary crosssectional view of an electric compressed-gas circuit FIG. 5 illustrates a view similar to FIG. 3 of a modified circuit breaker in accordance with the invention;

FIG. 6 illustrates a view taken on line 6-6 of FIG.

and

FIG. 7 illustrates a view similar to FIG. 3 of a further modified circuit breaker according to the invention.

' PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. .1, the pressurized-gas circuit breaker, such as for a high voltage line carrying, for example, 110 kilovolts (KV), uses sulfur hexafluoride as a quenching and insulatingmedium. For the sake of simplicity, only those parts of the circuit breaker necessary for an understanding of the invention are shown.

. are connected in a closed breaker position by a tubular bridging switching element 6. The bridging switching element'6 has a pluralityof spring-loaded contact fingers 7 mounted on the inside. Each finger 7 has a contact surface 8 at each opposite end which exerts a predetermined contact pressure against the respective

stationary contact

3, 4. The bridging switching element 6 also carries asliding contact ring 9 consisting of areresistant, electrically conductive material, with an interposed electrically insulating layer 10. Thebridging switching element 6 is screwed into a coupling structure 18, connected by mounting hardware 19 to an insulating tube 20 which forms a blast cylinder. The upper edge 21 of the blast cylinder 20 carries a nozzle which slidably surrounds the stationary contact 3. The blast cylinder 20 isco'nstructed in one piece,"e .g. of fiber-reinforced plastic.

In addition, the coupling structure 18 is connected to a plurality of tension rods 12, each of which is pivotally secured to the coupling structure by a pin 13 integral with the coupling structure 18. A drive member (not shown) is coupled to the tension rods 12 and moves the circuit breaker from a closed breaker position, shown on the right as viewed, to an open breaker position, shown'on the left. as is known. A stationary piston 24 is also mounted, as is known, in sealed slidable relation between the bridging switching element6 and the blast cylinder 20.

The switching chamber is totally filled with a quenching. gas, such as sulfur hexaflouride, at a pressure of, e.g. 4 atmospheres.

When the breaker opens, the bridging switching element 6 together with the blast cylinder 20 moves against the fixed piston 24 in the downward direction. This causes the sulfur hexafluoride present within the blast cylinder 20 to be compressed, since the gas cannot flow out at the beginning of the breaker-opening motion. Only when the blast cylinder 20 has completed approximately one-half of a stroke do the contact fingers 7 of the bridging switching element 6 and the sliding contact ring 9 slide off the stationary contact 3. As a result, an electrical separation occurs between the

contacts

3, 4 as well as the formation of a clearance, or gap, for gas outflow. The previouslycompressed sulfur hexafluoride then flows through this gap into the

outflow nozzles

3a, 4a mounted on the

stationary contacts

3, 4. This causes the arc to be commutated from the sliding contact ring 9 over the outflow nozzle 4a on the stationary contact 4, and then quenched.

In the open breaker condition, the electric field in- .tensity in the gap is kept as small as possible by appropriate design of the large-surfaced nozzles 3a, 4b which act as electrodes.

Referring to FIG. 2, for high required breaker power with a correspondingly strong flow of quenching gas and comparatively high cross-sections of the sliding contact ring 9, a flow stagnation, asshown, can form in the quenching gas flow between the bridging switching element 6 and the nozzle 4aof the stationary contact 4. Thus, under certain circumstances the arc is not sufficiently blasted in the region of the sliding contact ring 9, and the heated and ionized quenching gas present there flows out only after a delay.

Referring to FIGS. 3 and 4, wherein like reference characters indicate like parts as above, in order to avoid any flow stagnation, an auxiliary passage means in the form of a passage or bypass 40 is added to the flow'channel between the bridging switch element 6 and the

hollow contacts

3, ,4 to feed quenching gas to the sliding contact ring 9. This passage or bypass 40 is closed to the flow of quenching gas in the closed breaker condition of the bridging switching element 6, and is automatically opened during the breakeropening motion. The passage 40 terminates in a plurality of radially disposed holes 42 in the contact 4 behind the nozzle 4a. When a breaker-openingmotion occurs, a quenching gas flow 41 is branched in the direction of flow behind the sliding contact ring 9, so that one flow portion 41a flows through the interior of the nozzle 4a, while another flow portion 41b flows through the auxiliary passage. 40 to the holes 42 and then into the nozzle 4a. P

'Referring to FIGS. Sjand 6, wherein like reference characters indicate like parts as abov9, the auxiliary passage means can also be formed by cavities in the nozzle 4a of the stationary contact 4 so that quenching gas is fed to the sliding contact ring 9. Here, too, the auxiliary passage means 50 is closed in the closed breaker condition of the bridging switching element 6, and is automatically opened during the breakeropening motion.v

As may be seen in FIGS. 4 and 6, several passage means 40, 50 respectively are distributed overthe cir-.

cumference of the nozzle 4 in order to achieve a quenching gas flow that is evenly distributed over the circumference of the sliding contact ring 9.

Referring to FIG. 7, wherein like reference characters indicate like parts as above, an auxiliary passage means is formed by at least one drill hole disposed transversely to the axis of the bridging switching element 6 and passing through the element 6, the insulating layer 10 and the sliding contact ring 9. This auxiliary hole 60 is closed until the sliding contact ring 9 is lifted off from the nozzle 3a of the stationary contact 3, and is automatically opened as the breaker-opening motion of the bridging switching element 6 proceeds.

Several drill holes 60 are advantageously distributed over the circumference of the element 6 to obtain a quenching-gas flow that is evenly distributed over the circumference of the sliding contact ring 9.

In use, the drill holes 60 form nozzles directed toward the axis of the

contacts

3, 4, which feed additional quenching gas into the gap between the

contacts

3, 4 during thebreaker-opening motion. The drill holes 60 are arranged to feed the quenching gas into the gap in an essentially radial direction. As shown, the outlets of the nozzles 60 are located in that part of the electrode surface that is near theend face of the bridging switching element 6 It is possible within the scope of the invention, to add a guiding structure on the sliding contact ring 9 which acts as the arc electrode so that the guiding structure is at, or constitutes, the free upper edge of the bridging switching element 6 and can accommodate some of the nozzles 60 such that these would terminate in the guiding structure. The dimensions of the effective cross section of all nozzles are then advantageously made so that the quenching gas flow through the nozzles comprises only asmall part of the total flow of quenching gas through the outflow cross-section of the end face of the bridging switching element 6."At least some of these nozzles 60 would end at the surface of the sliding contact ring 9 that carries the arc.-

What is claimed is: t 1. ln an electric compressed-gas circuit breaker, a contact arrangement comprising: two stationary-mutually adjacentcontact pieces; a bridging switching unit movable between closed and open positions forelectriplurality of elongated contact elements disposed in said supporting body for electrically connecting said contact pieces when said switching unit is in the closed position, and spring means for spring loading said contact elements to displace the same into electrically conductive contact with said slide contact ring as said ring and said contact elements separate from said other contact piece when said switching unit moves into the open position. i

3. In an electric compressed-gas circuit breaker as set forth in claim 1 wherein said one contact piece has a of said one contact piece and said bridging switching unit.

5. The contact arrangement of claim 4, at least one radially directed bore formed in said one contact piece behind said nozzle, said bore communicating with said space and constitutingthe outlet of said passage to the hollow interior of said one contact piece.

from said region to'the interior of the hollow contact cally bridging said contact pieces in the closed position i and for electrically disconnecting said contact pieces in the open position whereby an arc develops when said switching unitis moved to the open positiomsaid switching unit being mountedon one of said contact pieces so as to define a'gap'betwe en said switching unit and the'other one'of said' contact pieces when said switching unit is moved to said open position; a slide contact ring of arc-resistant material mounted on said bridging switching unit for slideably engaging said other contact piece in the closed position andfo'r being in spaced relation to'said contact piece across said gap when said switching unit is moved to the open position; compressed-gas chamber" means for blasting compressed-gas through said gap when said switching unit separates from said other contact piece during the movement thereof to said open position; at least said one contact piece being hollow to define a flow path for conducting the gas away from the gap; said one contact piece and said switching unit conjointly defining, during the movement of said switching unit to said open position, a region at least partially shielded from the flow of thegasthrough said gap; and, auxiliary passage means communicating with said region for causing at least a portion of the compressed-gas to flow through said region when said switching unitseparates from said other contact piece during the movement thereof to said open position whereby flow stagnation of gas in said region is prevented.

2. The contact arrangement of claim 1, said switching unit including a supporting body, electrical insulation disposed at said supporting body, said contact ring being mounted on said electrical insulation, said insulation being disposed between said supporting body and said ring thereby insulating said ring from said body, a

piece. i 7. The contact arrangement of claim 1 wherein said one contact piece has a nozzle in the end thereoffacing said other contact piece, said auxiliary passage means being a plurality of cavitiesdistributed about the periphery of said nozzle, each one of said cavities extending from said region to the interior of said one contact piece.

passage means comprising at least one bore passing through said ring and said insulation and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said switching unit is in said closed position, said bore having an outlet at said interface whereby said bore is closed off in said closed position and during the opening movement of said switching unit until said contact ring separates from said other contact piece whereafter said bore is opened to communicate also with said gap and with said partially shielded region.

9. The contact arrangement of claim 2, saidauxiliary H passage means comprising a plurality of bores disposed about the periphery of said slide contact ring, each ofv 8. The contact arrangement of claim 2, said auxiliary to communicate also with said gap and with said partially shielded region.

10. The contact arrangement of claim 1, said auxiliary passage means comprising at least one bore passing through said ring and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said switching unit is in said closed position, said bore having an outlet at said interface whereby said bore is closed off in said closed position and during the opening movement of said switching unit until said contact ring separates from said other contact piece whereafter said bore is opened to communicate also with said gap and with said partially shielded region.

11. The contact arrangement of claim .1, said auxiliary passage means comprising a plurality of bores disposed about the periphery of said slide contact ring, each of said bores passing through said ring and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said'switching unit is in said closed position, each of said bores having an outlet at said interface whereby each'of said bores is closed off in said closed position and during the'openingmovement of saidswitching unit until said contact ring separates from said other contact piece whereafter each of said bores is opened to communicate also with said gap and with said partially shielded region.

12. in an electric compressed-gas circuit breaker as set forth. in claim I wherein said auxiliary passage means includes a plurality of passages distributed over the circumference of'said one contact.

13. in an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to the other of said contacts, a contact ring of arcresistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion,

means defining a chamber about said bridging switching element for a' pressurized quenching gas to be flowed through said gap into said contact; and auxiliarypassage means for passing'at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means being between the outer surface of said one contact and said bridging switching element and being formed by at least one continuous radially oriented hole in said one contact behind said nozzle.

14. in an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to the other of said contacts, a contact ring of areresistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion, means defining a chamber about said bridging switching element for a pressurized quenching gas to be flowed through said gap into said contact; and auxiliary passage means for passing at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means being between the outer surface of said one contact and said bridging switching element and being formed by at least one cavity in said nozzle running parallel to the contact axis of said contact.

15. In an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to theother of said contacts, a contact ring of arcresistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion, means defining a chamber about said bridging switching element for a pressurized quenching gas to be flowed through said gap into said contact; and auxiliary passage means for. passing at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means including at least one hole disposed transversely to the axisof said bridging switching element and passing through said element and said contact ring.

16. In an electric compressed-gas circuit breaker as set forth in claim 8, a plurality of said holes distributed over the circumference of said contact ring.

17. In an electric compressed-gas circuit breaker as 7 set forth in claim 9 wherein said holes are in the form of nozzles.

18. In an electriccompressed-gas circuit breaker as set forth-in claim 10 wherein at least some of said nozzles terminate in the surface of said contact ring.

19. In an electric compressed-gas circuit breaker as set forth in claim 10 wherein at least some of said nozzles terminate near the end face of said bridging switching element. v

20. in an electric compressed-gas circuit breaker as set forth in claim 8 wherein the effective cross section of said nozzles is controlled by the motion of said bridg-' ing switching element. a

21. In an electric compressed-gas circuit breaker as set forth in claim 8 wherein said nozzles are radially disposed tosaid contact ring.

22. In an electric compressed-gas circuit breaker as set forth in claim 8 further including a guiding structure on said contact ring at the free end face of said bridging switching element and at least some of said holes terminate therein.

Claims

1. In an electric compressed-gas circuit breaker, a contact arrangement comprising: two stationary mutually adjacent contact pieces; a bridging switching unit movable between closed and open positions for electrically bridging said contact pieces in the closed position and for electrically disconnecting said contact pieces in the open position whereby an arc develops when said switching unit is moved to the open position, said switching unit being mounted on one of said contact pieces so as to define a gap between said switching unit and the other one of said contact pieces when said switching unit is moved to said open position; a slide contact ring of arc-resistant material mounted on said bridging switching unit for slideably engaging said other contact piece in the closed position and for being in spaced relation to said contact piece across said gap when said switching unit is moved to the open position; compressed-gas chamber means for blasting compressed-gas through said gap when said switching unit separates from said other contact piece during the movement thereof to said open position; at least said one contact piece being hollow to define a flow path for conducting the gas away from the gap; said one contact piece and said switching unit conjointly defining, during the movement of said switching unit to said open position, a region at least partially shielded from the flow of the gas through said gap; and, auxiliary passage means communicating with said region for causing at least a portion of the compressed-gas to flow through said region when said switching unit separates from said other contact piece during the movement thereof to said open position whereby flow stagnation of gas in said region is prevented.

2. The contact arrangement of claim 1, said switching unit including a supporting body, electrical insulation disposed at said supporting body, said contact ring being mounted on said electrical insulation, said insulation being disposed between said supporting body and said ring thereby insulating said ring from said body, a plurality of elongated contact elements disposed in said supporting body for electrically connecting said contact pieces when said switching unit is in the closed position, and spring means for spring loading said contact elements to displace the same into electrically conductive contact with said slide contact ring as said ring and said contact elements separate from said other contact piece when said switching unit moves into the open position.

3. In an electric compressed-gas circuit breaker as set forth in claim 1 wherein said one contact piece has a nozzle in the end thereof facing said other contact piece for the flow of the quenching gas therethrough, said auxiliary passage means including at least one passage extending from said region and terminating behind said nozzle.

4. In an electric compressed-gas circuit breaker as set forth in claim 3 wherein said auxiliary passage means includes a space conjointly defined by the outer surface of said one contact piece and said bridging switching unit.

5. The contact arrangement of claim 4, at least one radially directed bore formed in said one contact piece behind said nozzle, said bore communicating with said space and constituting the outlet of said passage to the hollow interior of said one contact piece.

6. The contact arrangement of claim 1 wherein said one contact piece has a nozzle in the end thereof facing said other contact piece, said auxiliary passage means being a cavity formed in said nozzle so as to extend from said region to the interior of the hollow contact piece.

7. The contact arrangement of claim 1 wherein said one contact piece has a nozzle in the end thereof facing said other contact piece, said auxiliary passage means being a plurality of cavities distributed about the periphery of said nozzle, each one of said cavities extending from said region to the interior of said one contact piece.

8. The contact arrangement of claim 2, said auxiliary passage means comprising at least one bore passing through said ring and said insulation and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said switching unit is in said closed position, said bore having an outlet at said iNterface whereby said bore is closed off in said closed position and during the opening movement of said switching unit until said contact ring separates from said other contact piece whereafter said bore is opened to communicate also with said gap and with said partially shielded region.

9. The contact arrangement of claim 2, said auxiliary passage means comprising a plurality of bores disposed about the periphery of said slide contact ring, each of said bores passing through said ring and said insulation and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said switching unit is in said closed position, each of said bores having an outlet at said interface whereby each of said bores is closed off in said closed position and during the opening movement of said switching unit until said contact ring separates from said other contact piece whereafter each of said bores is opened to communicate also with said gap and with said partially shielded region.

11. The contact arrangement of claim 1, said auxiliary passage means comprising a plurality of bores disposed about the periphery of said slide contact ring, each of said bores passing through said ring and extending transverse to the longitudinal axis of said switching unit so as to communicate at one end thereof with said chamber means, said contact ring and said other contact piece conjointly defining an interface when said switching unit is in said closed position, each of said bores having an outlet at said interface whereby each of said bores is closed off in said closed position and during the opening movement of said switching unit until said contact ring separates from said other contact piece whereafter each of said bores is opened to communicate also with said gap and with said partially shielded region.

12. In an electric compressed-gas circuit breaker as set forth in claim 1 wherein said auxiliary passage means includes a plurality of passages distributed over the circumference of said one contact.

13. In an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to the other of said contacts, a contact ring of arc-resistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion, means defining a chamber about said bridging switching element for a pressurized quenching gas to be flowed through said gap into said contact; and auxiliary passage means for passing at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means being between the outer surface of said one contact and said bridging switching element and being formed by at least one continuous radially oriented hole in said one conTact behind said nozzle.

14. In an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to the other of said contacts, a contact ring of arc-resistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion, means defining a chamber about said bridging switching element for a pressurized quenching gas to be flowed through said gap into said contact; and auxiliary passage means for passing at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means being between the outer surface of said one contact and said bridging switching element and being formed by at least one cavity in said nozzle running parallel to the contact axis of said contact.

15. In an electric compressed-gas circuit breaker having two hollow stationary contacts disposed in spaced relation, means including a bridging switching element slidably surrounding said contacts for selectively electrically connecting said contacts in a closed breaker position and being mounted on one of said contacts in an open breaker position in spaced relation to the other of said contacts, a contact ring of arc-resistant material mounted on said bridging switching element to be disposed in spaced relation to said other of said contacts across a gap when said bridging switching element is moved during a breaker opening motion, means defining a chamber about said bridging switching element for a pressurized quenching gas to be flowed through said gap into said contact; and auxiliary passage means for passing at least a portion of the quenching gas from said chamber across said contact ring during said breaker opening motion, said auxiliary passage means including at least one hole disposed transversely to the axis of said bridging switching element and passing through said element and said contact ring.

17. In an electric compressed-gas circuit breaker as set forth in claim 9 wherein said holes are in the form of nozzles.

18. In an electric compressed-gas circuit breaker as set forth in claim 10 wherein at least some of said nozzles terminate in the surface of said contact ring.

19. In an electric compressed-gas circuit breaker as set forth in claim 10 wherein at least some of said nozzles terminate near the end face of said bridging switching element.

20. In an electric compressed-gas circuit breaker as set forth in claim 8 wherein the effective cross section of said nozzles is controlled by the motion of said bridging switching element.

21. In an electric compressed-gas circuit breaker as set forth in claim 8 wherein said nozzles are radially disposed to said contact ring.