US2872550A

US2872550A - High voltage circuit interrupting and isolating apparatus

Info

Publication number: US2872550A
Application number: US610933A
Authority: US
Inventors: August C Schwager
Original assignee: SCHWAGER WOOD CORP
Current assignee: SCHWAGER WOOD CORP; SCHWAGER-WOOD Corp
Priority date: 1956-09-20
Filing date: 1956-09-20
Publication date: 1959-02-03
Anticipated expiration: 1976-02-03

Description

Feb. 3, 1959 A. c. scHwAGER 2,872,550

HIGH VOLTAGE CIRCUIT INTERRUPTING AND ISOLATING APPARATUS 2 Sheets-Sheet 1 Filed Sept. 20, 1956 BY WLM/ffy Feb. 3, 1959 A. scHwAGER 2,872,550

HIGH VOLTAGE CIRCUIT INTERRUPTING AND ISOLA'IING APPARATUS Filed sept. 2o, 195e 2 Sheets-Sheet 2 INVENTOR. z/wf C.' Sam/maa?.

BY i

JWM/IV United States Patent HIGH VOLTAGE CIRCUIT INTERRUPTING AND ISOLATING APPARATUS August C. Schwager, Portland, Oreg., assigner to. Schi/'vager-Wood Corporation, Portland, Greg., a corporation of Oregon Application September 20, 1956, Serial No. 616333 8 Claims. (Ci. Zitti-45) The present invention relates to a high voltage circuit interrupting and isolating switching apparatus and more particularly to a novel operating arrangement in which a high voltage arc quenching circuit ybreaker' of special construction is employed in series circuit with an isolating air break switch blade.

The principal object of my invention is to provide a ew and novel arrangement in which a high voltage arc quenching circuit breaker of the vacuum insulated type may be mounted upon and/0r operated in series circuit with a cooperating circuit isolating switch blade of conventional design in a practical, efficient and effective manner.

Another object of the invention is to provide a high voltage circuit interrupting switch having circuit inter rupting contacts enclosed in an arc quenching vacuum which can be mounted upon an air break circuit isolating switch blade and operated in series circuit relation with said switch blade to produce an arc free interruption of the circuit established by the air break switch blade.

Another object of the invention is to provide a high voltage circuit interrupting circuit breaker having relatively movable contacts enclosed within an evacuated envelope with terminal connections and an operating means hermetically sealed in and extending through the walls of said envelope which can be mounted on an air break circuit isolating switch blade and operated in series circuit therewith in response to the circuit controlling movements of said switch blade,

A further object of the invention is to provide a means by which switching operations comparable with those now generally employing large oil or iluid blast arc quenching circuit ,breakers may be controlled by a circuit isolating air break switch blade of conventional design in conjunction with a vacuum insulated arc extinguishing breaker of novel construction and operated substantially simultaneously with and by the circuit closing and circuit interrupting operations of the air break switch blade.

Ano-ther object of the invention is to pro-vide a new and novel mounting for a vacuum insulated circuit breaker having cooperating circuit controlling contacts enclosed in a sealed glass envelope which can be mounted for operation in conjunction with a relatively movable circuit isolating switch blade of conventional design in such a manner that the circuit controlling movements of said circuit isolating switch blade are relied upon to control the circuit opening and closing operations of the enclosed contacts of said vacuum insulated circuit breaker.

A further object of the invention is to provide an operating means for the circuit controlling contacts of a vacuum insulated circuit breaker having an encapsulation such as is illustrated in a zo-pending application, Serial Number 606,265 tiled August 27, 1956 and entitled, Encapsulated Vacuum Insulated Circuit Breaker.

Another object of the invention is to provide an operating arrangement for an encapsulated vacuum inice sulated circuit breaker operating in series circuit with a cooperating movable circuit completing conductor such as a conventional switch blade or the like, by which a relatively high contact pressure is established with the cooperating movable Contact or circuit isolating switch blade while at the same time the contact pressure at the contacts of the vacuum insulated circuit breaker will be limited to a substantially lower value as the difference in these contact pressure values will be borne by the encapsulating enclosure of the evacuated envelope withinA which the circuit breaker is supported.

Other objects and advantages of my invention will be in part evident to those skilled in the art and. in part pointed out in connection with the accompanying draw-l ing, wherein there is shown by way of illustration and not of limitation a preferred embodiment of the invention. in the accompanying drawing wherein like gures refer to like parts throughout the several views:

Figure l is a composite external view showing two distinct types of encapsulation that may be used as a protective enclosure for a vacuum insulated circuit breaker and as a support for my improved operating mechanism,

Figure 2 is a sectional View taken in a vertical plane extending centrally through the encapsulation and circuit breaker as shown in Figure l, and

Figures 3, 4, 5, 6, 7, 8 and 9 illustrate arrangements wherein the encapsulated vacuum insulated circuit breaker is employed in a new and novel manner in conjunction with one o-r more circuit isolating switch bladesv and operated in series contacts. Circuit breakers of this type are not only extremely expensive, but they are bulky and require considerable space at the point of installation. When circuitbreakers of this type are used upon high voltage power line transmission systems, it is the practice to also employ a relatively long circuit isolating of an arc between the separating oil immersed contacts of the circuit breaker due to charging currents and/or other conditions upon the power line.

As distinguished from the above, the present invention contemplates the employment of a vacuum insulated circuit breaker which has Ibeen found to have a current interrupting capacity and arc extinguishing character` istics which when used in conjunction with an air break circuit breaker, as here proposed, can be relied upon to interrupt and isolate high voltage power transmission line circuits with operating results comparable, if not better than those now obtained under the same load conditions with a conventional oil circuit breaker operating in series circuit with` an air break circuit isolating switch blade.

For a detailed description of the invention reference is now made to the accompanying drawings wherein I have illustrated a vacuum insulated circuit breaker of the type described in United States Patent No. 2,740,869 and manufactured by Jennings Radio Manufacturing Corporation of San Jose, California. Circuit breakers of this type have been found to have an interrupting capacity of approximately 30,000 volts with a contact separation' of lV16 of an inch and a current rating in the neighbor- Y asiasst Patented Feb. 3, 1959` blade in series circuit: therewith to insure against a restrike or re-establishment' aevaeeo hood of 2500 amperes. It has also been found by actual tests on a commercial high voltage power transmission line that by employing four of these vacuum insulated units arranged in series circuit with the contacts operating substantially simultaneously, it is possible to interrupt a 120,000 volt power line circuit carrying 2590 amps. Recent tests have also shown that these vacuum insulated circuit breakers are capable of interrupting a current ilow of several thousand amperes. With this, their performance is considered to be equal to the interrupting performance of present day power line circuit breakers. As a result, it is conceivable that their use will not be limited to the interruption of load currents, but will be found practical as power line circuit breakers.

Vacuum insulated circuit breakers of the type hereinabove referred to and requiring as they do a vacuum retaining envelope of glass are of an extremely fragile character and, therefore, up until recently their use has been limited to indoor installations where they are generally mounted upon a panel or like support and used for the control of circuits Ioperating at factory voltages which may run from 110 to possibly a maximum of 1100 volts. Because of their fragile character these circuit breakers, insofar as I am aware, have not found an acceptance in connection with the control of outdoor power line circuits as is here proposed and made possible by the present invention.

Figure l of the drawings is a composite View illustrating the external appearance of a vacuum insulated circuit breaker having an encapsulation and an operating means by which the contacts of the circuit breaker are controlled when employed for the purpose of interrupting and isolating power line circuits operating at the voltages generally prevalent in high conventional power line transmission systems. In this showing, the encapsulation, designated by the numeral 10, is in the form of a casting formed of any suitable insulating and hard setting material which can be cast completely around the circuit breaker as a unit. I here show an encapsulation of an epoxy resin that extends between terminal forming llanges 11 and 12 which, as will hereinafter appear, are connected respectively to the stationary and movable contacts of the circuit breaker. The terminal flange 1l is shown as having a cylindrical extension 13 which when inserted into the end of a tubular air break circuit isolating switch blade, here indicated by dot and dash lines, will provide an electrical connection therewith. At the other end of the encapsulation 10 and mounted upon the terminal flange 12 there is an outwardly extending contact guide or sleeve 14 into which there is a movable and `outwardly biased circuit establishing contact 1S, which will, when brought into engagement with a cooperating contact or circuit completing terminal with surticient contact pressure, operate in a novel manner lo( close the contacts of the encapsulated circuit breaker. In order to provide a good current conducting path between the contact guiding sleeve 14 and the contact I have shown a seriesV of flexible jumpers 16 as connected therebetween. Considering this further, and as shown in Figure 1 of the drawings, it will be noted that the differently shown lower half of the encapsulation is in the form of a porcelain shell 17 of tubular construction into which the circuit breaker is inserted for encapsulation. In this instance the porcelain shell 17 is centered and clamped in position between

clamping rings

13 and 19 that are carried respectively by the terminal lianges 11 and 12 of the circuit breaker assembly.

By now referring to Figure 2 of the drawings, it will be seen that in this instance for weather proong, the porcelain shell 17 is shown as provided with` a mastic seal 20 at the ends thereof by which it is rmly secured between the clamping rings l and 19.

As indicated above, the particular vacuum circuit breaker shown for purpose `of illustration, forms no part of my present invention except insofar as its construction l tact 21 and the movable contact 22 is produced.

and general outline lends itself to the particular form of encapsulation here described. However, it should be pointed out that this particular vacuum circuit breaker has a stationary contact 21 that is connected directly to the terminal flange 11 at one end of the circuit breaker. Operating in axial alignment with the stationary contact 21, there is a movable contact 22 that is electrically connected with the terminal Contact flange 12 as will presently appear. ln this particular arrangement, the relatively

movable contacts

21 and 22 are shown as enclosed within an evacuated glass envelope 23 that is closed at its ends by metallic seals formed as a part of the terminal contact flanges 11 and 12. To permit the required circuit controlling movements of the movable contact 22,

evacuated envelope 23 is shown as sealed by a exible bellows 24 which as is well understood will permit movement of the contact 22 toward and away from the stationary contact 21 without danger of breaking the vacuum seal of the envelope 23. This movement of the contact 22 is accomplished through the medium of an extending stud or operating member 25 which has a sliding nt through the seal at this end of the evacuated envelope 23.

It will be here noted that the extending stud or operating member 25 of the movable contact 22 is threaded and adjustably mounted thereupon there is a spring seat forming member 26 against which a compression spring 27 |operates as a means for biasing the movable contact Z2 of the circuit breaker into an open circuit position. At the other side of the spring seat forming member Z6 and operating in a reverse direction there is a compression spring 23 through which a circuit closing movement is imparted to the contact 22 of the circuit breaker when the exposed movable circuit controlling contact 15 moves into the guiding sleeve 14 within which it is slidably mounted. This compression spring 28 is so calibrated and adjusted by means of the spring seating cup Z6 that a limited contact pressure suicient only to form a good electrical connection between the stationaryI ognt as been found that a contact pressure of no more than five pounds is quite suicient for the successful operation of the

circuit breaker contacts

21 and 22 asV here operating in a vacuum. However, to establish a suflicient contact pressure between the exposed circuit completing air break -contact 15 and a similar contact or with a cooperating relatively movable circuit completing contact means, a contact pressure in the'neighborhood of 50 pounds is required. Therefore, in order to differentiate between these two contact pressure requirements and avoid the possibility of destructive pressure between the

contacts

21 and 22 of the circuit breaker, I have shown the movable circuit completing contact 15 as biased outwardly by a relatively stronger compression spring Z9 that is adapted and arranged to transmit this difference in the contact pressure requirements between the vacuum insulated

contacts

21 and 22 of the circuit breaker and the exposed air break contact 15 directly through the encapsulating means lll -or 1-7, as the case may be, to the circuit breaker supporting terminal 11 at the other end of the encapsulation.

With the above described multiple contact arrangement with vacuum insulated contacts operating in series circuit with air break contacts, it will be seen that when the vacuum insulated circuit breaker unit with its air reak contact terminal 15 is brought into engagement with a cooperating relatively movable contact or circuit completing terminal the outer or heavier contact biasing spring 29 will be iirst subjected to compression and establish a high contact pressure. `During this period the weak or lighter compression spring 2S will also become operative and exert a lesser pressure on the spring seating cup or collar 26 which, as noted above, is adjustable along the threaded end of the operating rod 29 whichl operates the movable contact 22 of the vacuum insulated circuit breaker. The adjustment of the spring seat 26 is such that when the required pressure is established at the contact 15 a substantially lower contact pressure will be produced between the

contacts

21 and 22 of the circuit breaker. From experience, it has been determined that a contact pressure of not more than tive pounds between the

contacts

21 and 22 is generally sucient, whereas at the contact of the air break terminal contact 15 a pressure up to as much as 50 pounds may be required. With this higher contact pressure requirement, it will be readily seen that the vacuum maintaining envelope 23, which up to the present time has required a construction of glass, some means must be provided to protect the vacuum sustaining envelope against any such force. YThis feature is disclosed in part and claimed in the above copending application. Whether the enclosure is in the form of the cast encapsulation or the insulator unit with its supporting

rings

18 and 19 vthe arrangement is such that the entire pressure force exerted or required upon the exposed operating contact will be transmitted through this encapsulation to the supporting switch blade or other means upon which the encapsulated unit is mounted. Under these conditions, the lighter compression spring 28 will become operative and establish a lower contact pressure between

thecontacts

21 and 22. Upon release of this pressure upon the air break contact 15, the lighter compression spring 27 operating on the opposite side of the adjustable spring seat 26 will move thecontact 22 of the circuit breaker out of engagement with the stationary contact 21 a distance sutiicient to interrupt the circuit.

With the vacuum insulated circuit breaker unit encapsulated as described above and with the contact operating mechanism operating in series circuit with an air break switch blade for the purpose of establishing an air break circuit isolating contact separation in series circuit with the vacuum insulated arc

free contacts

21 and 22, there is provided a unit which lends itself to many applications in switching on high voltage transmission lines. Therefore, and as a further aspect of this invention, I hav'e shown in the remaining figures of the drawings several illustrative embodiments thereof.

Figures 3 and 4 show two circuit breaker units, designatedby the

numerals

30 and 31, mounted respectively upon and as an extension of two cooperating air

break switch blades

32 and 33. In this instance the

switch blades

32 and 33 are mounted upon rotatable insulator stands 34 and 35 that are mounted upon a suitable support 36 in a conventional manner. As shown the rotatable insulator stands 34 and 35 are connected by atie rod 37 in such a manner that when one or the other of these insulator stands is rotated, the other stand will be caused to rotate in the opposite direction. For this purpose, I have shown the insulator stand 34 as having an operating lever arm 38 that is connected to an operating rod 39 which may be employed to operate a gang or number of these units in unison as on a multiphase circuit.

With the switch blades 32 -and 33 in circuit completing engagement with each other, as here shown, it will be seen that if the rotatable insulator stand 34 is rotated counter-clockwise by the operating rod 39, the insulator stand will rotate clockwise. When the circuit is finally and fully opened, the

circuit breaker units

30 and 31 will assume a position as here indicated by dot and dash lines. As a means for completing a circuit the

switch blades

32 and 33 are shown as having terminals 40 to which the conductors of the power line are secured. From the foregoing description, it will be understood that when the cooperating contacts 15 of the

circuit breaker units

30 and 31 have engaged with suicient movement the circuit will be completed through the

movable contacts

21 and 22 of the circuit breaker. With the two

circuit breaker units

30 and 31 operating as here shown in series circuit the voltage interrupting capacity of the assembly will be double that of a single unit. The circuit isolating characteristics of the apparatus may be determined for any degree of contact separation by the length of the

switch blades

32 and 33.

In Figures 5 and 6 of the drawing, there is shown a single vacuum insulated circuit breaker unit, designated by the numeral 41, mounted in a iixed position upon an insulator stand 42 for engagement by a circuit isolating switch blade 43 that extends laterally from a vertically disposed rotatable insulator' stand 44. IIn this instance, the rotatable insulator stand 44 has an operating arm 45 to which an operating rod 46 is connected for operating a plurality of these switch blades in unison. The full circuit open position of the switch blade 43 is shown by dot and dash lines. As in the previous instance, the insulator stands 42 and 44 are mounted upon a support 36 and carry power line terminals 40.

ln Figures 7 and 8 of the drawings, there is shown a further variation of the invention in which a single vacuum insulated circuit breaker unit 47 is operated in combination with two

opposed switch blades

48 and 49 that move in opposite directions about a common axis. These

blades

48 and 49 are mounted upon

co-extending strain insulators

50 and 51. Switching apparatus of this particular character will be found particularly useful on the lower voltage distribution lines where a complicated and/or expensive operating mechanism is not justified. As here shown, the

switch blades

48 and 49 carried by oppositely extending strain insulator strings 50 and 51 are journalled for rotation upon a cross-arm assembly 52 as is commonly used upon transmission line supporting poles. The insulator string 50 has a blade carrying bracket 53 with a power line connecting terminal at its outer end and the insulator string 51 has a corresponding bracket 54. The switch blade 49 is here shown as having the vacuum insulated circuit breaker unit 47 at its end and extending in a line substantially tangent to the arc described by the end of the switch blade 49 and cooperating therewith the switch blade 48 has a circuit completing contact 55 which will operate to close the

contacts

21 and 22 of the vacuum insulated unit 47 when the

switch blades

48 and 49 are in their full circuit closed position. Conversely, when the

switch blades

48 and 49 are in their full open circuit position, the circuit will be interrupted at the

movable contacts

21 and 22 of' the circuit breaker unit 47 and isolated by the air gap between the blades.

As a variation of the last described apparatus, Figure 9A of the drawings shows a similar arrangement employing the oppositely extending insulator stands 50 and 51 upon which two similar circuit isolating switch blades 56 and 57 are provided with oppositely disposed vacuum insulated circuit breaker units 58 in such a manner that the cooperating air break contacts 15 thereof will meet in opposed relation when the circuit is closed. It is conceivable that circuit breaker unitshaving vacuum insulated arc extinguishing contacts and operating in the manner here disclosed will be found adapted to many other situations in which one or more of these assemblies may be employed as a substitute for the more expensive conventional circuit breakers of the type in which the current interrupting arc is suppressed or extinguished by submersion in oil or by a blast of tiuid.

By installing and connecting two or more of the above assemblies in series circuit, it will be understood that the voltage interrupting capacity thereof will be a multiple of the number of vacuum insulated circuit breaker units employed. In like manner, it is also conceivable that the current carrying capacity of any particular circuit so controlled might also be increased by operating two or more of the vacuum insulated circuit breaker units is parallel.

While I have, for the sake of clearness and in order to disclose my invention so that the same can be readily understood, described and illustrated a specific form and arrangement, I desire to have it understood that this inven- 7 tion is not limited to the specific forni disclosed, but may be embodied in other ways that will suggest themselves to persons skilled inthe art. It is' believed that this in'- vention is new and all such changes as come' within the scope of the appended claims are' to be considered as part of this invention.

Having thus described my invention, what l claim and desire to secure by Leters Patent is:

l. In a high voltage` arc interrupting and circuit isolating switch, the combination of pair' of sp ing insulators', a line terminal contact carried by cach cf said insulators for connection in a power line circuit to be interrupted, a circuit isolating switch blade mounted upon and extending from one' ofsaid supporting! insulators and movable relative' to the terminal Contact by the other or said insulators' upon rotation of said one iusu'- lator, a high voltage are interrupting vacuum insulated circuit breaker unit including an evacuated envelope mounted upon and in co-extcnding relation at the end of said circuit isolating switch bld'e, said circuit breaker unit having a xed contact enclosed Within said evacuated envelope electrically connected to said switch blade and a movable contact normally biased into an open circuit position with an operating` member sealed in and extending through a wall of said envelope, means disposed externally of said envelope forming an insulating support for an air break circuit controlling contact, an air break contact slidably mounted up'n said means, and means responsive to movement of said air break contact adapted and arranged to ov'ercome the bias upon the movable contact of said circuit breaker u'nit and establish a circuit through the contacts of said vacuum insulated circuit breaker when said air break Contact is brought into engagement with the line terminal contact carried by the other of said supporting insulators by a circuit closing operation of said circuit isolating switch blade.

2. In a high voltage arc interrupting and circuit isolating switch, the combination of a pair of spaced supporting insulators, a line terminal contact carried by each of said insulators for connection in a power lin'e circuit to be interrupted, a circuit isolating switch blade mounted upon one of said supporting insulators and movable relative to the terminal contact carried by the other of said insulators upon rotation of said one insulator, a high voltage arc interrupting vacuum insulated circuit breaker unit including an evacuated envelope mounted upon and in co-axial relation at the end of said circuit isolating switch blade. said circuit breaker unit having a fixed contact enclosed within said evacuated envelope electrically connected to said switch blade and a movable contact normally biased into an open circuit position with an operating member scaled in and extending through a wall of said envelope, an encapsulating insulator carried by said switch blade and disposed externally about said envelope to form a support for an air break circuit controlling contact, an air break contact mounted at the extending end of said encapsulating insulator, and :spring means responsive to movement of said air break contact adapted and arranged to overcome the bias on the movable contact of said circuit breaker and establish a circuit through the contacts of said vacuum insulated circuit breaker when said air break contact is brought into Contact with the line terminal contact carried by the other of said supporting insulators by a circuit closing operation of said circuit isolating switch blade.

3. In a combined high voltage are interrupting and circuit isolating switch means, the combination of a pivotally mounted circuit isolating switch blade, an enclosed arc suppressing circuit breaker unit having a fixed contact electrically connected to the outer end of said switch blade and a movable circuit interrupting Contact enclosed within an evacuated envelope, an operating member for the movable contact of said circuit breaker hermetic'ally sealed in and extending through a W'll of said evacuated envelope, an encapsulating protective enclosure mounted in co-extending relation upon the end of said switch blade forming a support for an exposed air break circuit controllingcontact for said switch blade, a circuit completing air break contact mounted upon the outer end of said encapsulating enclosure and electrically connected to the movable contact terminal of said circuit breaker, a rst spring means disposed between said movable circuit completing air break contact member and said encapsulating enclosure for establishing a predetermined contact pressure between the air break contact carried by said encapsulating supports when brought into engagement with a cooperating contact, and a second spring means disposed between said air break contact member and 'the operating member of' said arc extinguishing circuit breaker through which a yielding operating force is applied to the movable contact of said circuit breaker unit, whereby a circuit closing operation of said circuit breaker contacts will occur only after a predetermined relatively higher contact pressure has been established upon the exposed circuit completing air break contact carried by said cncapsulating support.

4. In a high voltage arc interrupting and circuit isolating switch means, the combination of a pair of spaced line terminal supporting insulator stands cach rotatable about a vertical axis, a circuit isolating switch blade extending radially at the upper ends of said insulator stands and connected to line terminals carried thereby, means for rotating said insulator stands to bring said circuit isolating switch blades into alignment between said insulator stands, an insulating support mounted in co-extending relation at the ends of each of said switch blades, an air break contact mounted at the outer ends of each of said insulating supports adapted and arranged to be brought into abutting relation and move co-axially with respect to said switch blades when said switch baldes are brought into alignment by rotation of said insulator stands, a high voltage vacuum insulated are interrupting circuit breaker unit mounted upon the ends of each of said switch blades having a stationary contact electrically connected to said switch" blades and a movable contact connected to and operable in response to co-axial movement of said air breakcontact, the stationary and movable contacts of said arc interrupting circuit breaker being normally biased into an open circuit position, and an operating connection between said air break contacts and the movable contacts of said vacuum insulated circuit breaker unit adapted and arranged to 'overcome said bias and close the contacts of said vacuum insulated circuit breaker units and thus complete a load carrying series circuit between the line terminals upon said supporting insulator stands through the contacts of said vacuum insulated circuit breaker units and said switch blades.

5. ln a vacuum insulated arc extinguishing and circuit isolating su-'itch means, the combination of a pivotally mounted circuit isolating switch blade, an arc suppressing circuit breaker unit having a stationary contact connected to the end of said switch blade and a movable contact enclosed within an evacuated envelope, an operating member for the movable contact of said circuit breaker unit hcrmetically sealed in and extending through a wall of said evacuated envelope, a reinforcing encapsulation of insulating material surrounding said evacuated envelope mounted upon the free end of said switch blade and forming a support for an exposed circuit completing air break contact, an exposed air break contact movably supported at the outer end of siad encapsulation, a first spring means for yieldingly biasing said exposed air break contact outwardly from said encapsulation to establish a predetermined relatively high contact pressure when engaged by a cooperating circuit completing contact, and a second spring means interposed between said exposed air break contact member and the operating member for the movable contact of said circuit breaker unit, said latter spring means being adapted and arranged to establish a limited contact pressure between the contacts of the circuit breaker as a relatively higher predetermined contact pressure is established between said exposed air break contact member and a cooperating circuit cornpleting contact by said first spring means.

6. Ina vacuum insulated arc extinguishing circuit breaker for operation in series circuit with an air break circuit isolating switch blade, the combination of a movably mounted circuit isolating switch blade, a vacuum insulated circuit breaker unit having an elongated contact enclosing envelope with a stationary and a Inovable contact operating in axial alignment therein, means at one end of said envelope for electrically connecting the stationary contact-of said circuit breaker' unit to the end of said circuit isolating switch blade, an operating rod for the movable contact of said circuit breaker unit hermetically sealed in and extending axially at the other end of said envelope, a reinforcing encapsulation of insulating material extending over said evacuated envelope and forming a support for an exposed air break contact, an exposed circuit completing air break contact mounted upon said encapsulation for movement relative thereto when engaged by a cooperating circuit completing contact, spring means for yieldingly biasing said exposed circuit forming air break contact outwardly f from said encapsulation to establish a predetermined relatively high contactv pressure and permit inward movement thereof when engaged by a cooperating circuit completing contact, and a second spring means interposed between said exposed air break contact and the operating rod of the circuit breaker unit for establishing a relatively lower contact pressure between the stationary and movable contacts thereof only after said predetermined relatively higher contact pressure has been established between the exposed air break contact carried by said encapsulation and a cooperating circuit completing contact.

7. In a vacuum insulated are extinguishing circuit breaker, the combination of an elongated evacuated envelope, a stationary contact mounted within and having an exposed terminal at one end of said envelope, a movable contact also enclosed within said envelope and biased into an open circuit position in axial alignment with said stationary contact, means at the stationary Contact end of said evacuated envelope for mounting same upon a movable circuit completing switch blade, an operating rod hermetically sealed for movement through the other end of said envelope for operating said movable contact against said bias and into engagement with said enclosed stationary Contact, a reinforcing encapsulation of insulating material forming a protective cover for said envelope and acting as a support for an exposed air break contact when mounted at the end of a switch blade, an air break contact mounted upon said encapsulation for movement relative thereto, a rst spring means biassing said air break contact outwardly from said encapsulation and establishing a high contact pressure upon said air break contact when in engagement with a cooperating circuit completing contact, and a second spring means forming a yielding connection between said exposed air break contact and the operating rod of said enclosed movable Contact adapted and arranged to establish a lesser contact pressure between the stationary and movable contacts within said envelope as said rst spring means operates to produce a relatively high contact pressure engagement between said air break contact and the cooperating circuit completing Contact.

8. In a vacuum insulated arc extinguishing and circuit isolating switch, the combination of a pivotally mounted switch blade, a circuit breaker unit comprising an evacuated envelope having a stationary contact mounted therein and connected to the free end of said switch blade, a movable contact operating in axial alignment with said stationary contact also enclosed within said envelope, means at the stationary contact end of said evacuated envelope for mounting said circuit breaker unit upon the end of said switch blade, a movable operating rod hermetically sealed in the end of said envelope and extending from said movable contact, a reinforcing encapsulation of insulating material forming a protective cover for said envelope and a support for an exposed air break contact when mounted upon the end of said switch blade, an exposed air break contact movably mounted upon said encapsulation for co-axial movement relative to said switch blade, a rst helical compression spring carried by said encapsulation for maintaining a high contact pressure bias upon said air break contact when in engagement with a cooperating circuit completing contact, and a second helical spring disposed concentrically within said rst spring forming an operating connection between said exposed air break contact and the operating rod for the enclosed movable contact of the circuit breaker unit adapted and arranged to establish a lower contact pressure between the stationary and movable contacts of said circuit breaker unit as said first helical spring operates to maintain said relatively higher contact pressure engagement between said exposed air break contact and the cooperating circuit completing contact.

References Cited in the tile of this patent UNITED STATES PATENTS 2,084,886 Biermanns June 22, 1937 2,353,729 Jensen July 18, 1944 2,419,446 Flurscheim Apr. 22, 1947 2,480,622 Warnock Aug. 30, 1949 2,706,742 Ehlers Apr. 19, 1955 2,740,869 Jennings Apr. 3, 1956 2,773,154 Williams Dec. 4, 1956 FOREIGN PATENTS 615,965 Germany July 17, 1935 699,367 Germany Nov. 28, 1940 530,338 Great Britain Dec. 10, 1940