US2955182A

US2955182A - Contact cooling means for recirculating gas blast interrupters

Info

Publication number: US2955182A
Application number: US667203A
Authority: US
Inventors: Arthur S Caswell; Joseph D Wood
Original assignee: ITE Circuit Breaker Co
Current assignee: ITE Circuit Breaker Co
Priority date: 1957-06-21
Filing date: 1957-06-21
Publication date: 1960-10-04
Anticipated expiration: 1977-10-04

Description

Oct. 4, 1960 A. s. cAswELL ETAL 2,955,182

CONTACT COOLING MEANS FOR RECIRCULATING GAS BLASTl INTERRUPTERS Filed June 21, 1957 3 Sheets-Sheet 1 WN wn nb A NN Oct. 4, 1960 A s, CASWELL ETAL 2,955,182

CONTACT COOLING MEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS Filed June 2l, 1957 3 Sheets-Sheet 2 BY ZQM/ 9%", /W f' l/h Oct. 4, 1960 A. s. cAswELL ETAL 2,955,182

CONTACT COOLING MEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS Filed June 2l, 1957 3 Sheets-Sheet 5 MEI United States Patent C) CONTACT COOLING MEANS FOR RECIRCULAT- ING GAS BLAST INTERRUPTERS Arthur S. Caswell, Glenside, and Joseph D. Wood, Wayne, I a., assignors to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed .lune 21, 1957, Ser. No. 667,203 Claims. (Cl. 200--148) lThis invention relates to circuit interrupters of the gas blast type and more particularly to a circuit interrupter having a recirculating gas system wherein the cooperating contacts are subjected to a flow of gas, regulated 1n magnitude by a therrnostatically controlled orice, which cools the contacts thereby increasing their current carrying capacity.

When a circuit interrupter protecting Ia current carrymg l1ne 1s opened, an electric current arc is drawn between the parted contacts. At this time rapid interruption of the arc and the prevention of restrike once interruption hastaken place are of prime consideration.

A gas blast directed at the arc hfastens the deionization thereof by cooling the are and exhausting the hot arcing products from the region between the parted cooperating contacts. All other factors being equal, the larger the gap between the parted contacts the lesser the likelihood of `arc restrike. But a llarger gap necessarily means a greater overall size for the interrupter. However, by raising the pressure of the gas in the gap, the separation distance between the parted contacts may be reduced w1thout danger of restrike at a given voltage. That is, the ability of fa dielectric gas to resist breakdown at a given voltage gradient increases as the gas pressure in-A creases except at pheric pressure.

It has been found that the so called electronegative gases, such as sulphur hexauoride (SFS), peruoropropane (C3138), periluorobutane (C4F10), and sulphur monoiluoride (S21-T2) are superior to air in their deionizing and dielectric properties thereby making them particularly useful in arc interruption. When dielectric mediums other than air are used -a recirculating system should be ernployed because of the high costof these gases. Further, a recirculating system prevents the external introduction of contaminants into the gas and includes filters to remove arcing products thereby assuring a continuous suppressures considerably below atmosply of gas in which the dielectric strength, cooling properties, and interrupting ability is at a maximum.

Gas blast interrupters of the prior art usually stored high pressure gas in a tank forming part of the interrupter structure. At the instant -of contact separation, or immediately prior thereto, a value operatively connected to the contacts was opened to introduce the high pressure gas in the gap between the parted contacts. The introduction of high pressure gas was accompanied by turbulence which decreased the gas ilow rate along the arc stream thereby preventing a rapid arc extinction. In interrupters employing a bridging member moving transversely with respect to the stationary contacts, the initial gas blast was required to transfer the arc from the bridging contact to a stationary contact rather than cool the arc thereby further delaying arc extinction.l

Part of the blast gas was diverted to open an isolating switch when interruption was complete. The contacts were reclosed by springs as the blast pressure dropped. Closing the isolating switch once again completed the circuit. Y

2,955,182 Patented Oct. 4, 1960 ICC The circuit interrupter of the instant invention includes a separate interrupter unit for each current carrying line of the electrical system being protected. Each interrupter unit comprises a tank having stationary contacts entered through the opposite ends thereof and a movable contact structure positioned between the stationary contacts in axial alignment with the stationary contacts to bridge a gap therebetween. The movable contact structure comprises a cylinder having two pistons slideably disposed therein. Movable contacts are carried by each of the pistons and are biased out of each end of the cylinder so that the movable contacts are in engagement with the stationary contacts when the interrupter is closed.

The interior of the interrupter tank is at all times directly connected to a high pressure reservoir so that the movable and stationary contacts are always immersed in high pressure gas. A chamber positioned in the centerl of the cylinder between the two pistons is at the same high pressure as the interior of the tank when the interrupter is closed.

To open the interrupter a blast valve is operated to interrupt the connection between the chamber and the tank and to connect the chamber to a low pressure reservoir. Since the pressure behind the pistons is now very low the high pressure gas in the tank acting on the front of the pistons is sufficient to overcome the biasing forces, causing the pistons to converge and thereby separate the movable contacts from the stationary contacts opening the circuit.

The movable contacts have central openings therethrough which, together with openings in the chamber, provide a continuous gas passage between the chamber and tank while the movable contacts are moving away from the stationary contacts. In this manner the arc drawn as the cooperating contacts are parted will immediately be acted upon by a smooth flowing blast of gas which rapidly deionizes and cools the arc and exhausts the arc products to the low pressure reservoir. When the movable contacts have reached their most fully converged position they will be forced against seats projecting from the chamber walls to thereby seal off the gas passage between the chamber and tank to prevent the pressure in the tank from dropping to too low a value. Since there is hign pressure surrounding the parted contacts, the gap length therebetween necessary to prevent restrike will be smaller than if the parted contacts were surrounded by gas at atmospheric pressure. The cooperating contacts are brought into engagement by connecting the chamber to the tank which equalizes the pressure on both sides of the pistons to permit the biasing means to urge the `movable contacts to diverge and engage the stationary contacts.

Filters are provided between the low pressure reservoir and the compressor to remove the arc products and thereby assure a supply of clean gas for subsequent interruptions.

Since high pressure gas always surrounds the engaged cooperating contact-s, a smooth gas flow will act on the this manner the cooperating contacts, when engaged, are

subjected to a ow of gas from the interrupter tank, through the central openings in the movable contacts, through the chamber, through the gas line having the will not be suflicient to overcome the force of theclosing.

springs.

The gas flow acts as a forced convection cooling means for the cooperating contacts enabling smaller sized contacts to carry the same magnitude of current formerly carried by larger sized contacts. Since the parts arenow smaller, the speed of the moving parts is increased thereby achieving improved arc interrupting performance.

Further compactness of construction is achieved by storing the dielectric medium ina liquid or semi-solid state. The gas is liquied by means of a compressor or refrigerating unit and the storage tank therefore is providedA with a heater to maintain adequate gas pressure in the high pressure reservoir and to maintain the dielectric medium in the low pressure reservoir in a gaseous state at low ambient temperatures.

Accordingly, a primary object of the instant invention is to provide a circuit interrupter of the gas blast type wherein the cooperating contacts are refrigerated or cooled to thereby achieve increased current carrying performance.

Another object is to provide a forced convection cooling means for the cooperating contacts of a gas blast circuit interrupter.v

Still another object is to provide a thermostatically controlled orifice for controlling the degree of forced convection cooling.

A further object is to provide a gas blast circuit interrupter wherein the dielectric medium is stored inV a liquid or semi-solid state.

A still further object is to provide, a circuit interrupter ofthe recirculating gas blast type wherein the cooperating contacts are always immersedin high pressure gas thereby permitting smaller creepage distances, better heat transfer, and faster arc interruption.

Another object is to provide a gas, blast circuit interrupter wherein the arc drawn betweenV the cooperating contacts on opening is subjected to a smoothly flowing gasr blast from the moment of arc inception to achieve rapid arc, interruption.

Still another object is to provide a: gas blast circuit interrupter wherein the contact carrying pistons serve as valve members to turn off the gas blast when the movable contacts have reached their fully disengaged positions and thereby maintain a high pressure in the gas between the parted contacts.

Yet another object is to provide a gas. blast interrupter having smaller parts than former constructions thereby achieving faster contact movement.

These and other objects of this invention. shall becomeV more apparent after reading the following description of the accompanying drawings in which:

Figure 1 is a schematic representation of a three conductor system protected by the circuit interrupter of the instant invention.

Figure 2 is a side elevation of a single interrupter unit, partially cut away-V to show the internal construct-ion thereof, with the circuit closed.

Figure 3 is a section taken through line 3-3 of Figure 2 looking in the direction of arrows 3 3.

Figure 4 is a fragmentary view of the interrupter unit of Figure l with the circuit open.

Figure 5 is a section taken through line 5-5 of Figure 1 looking inthe direction of arrows 5 5.

Referring to the figures, interrupter unit comprises an elongated tank 11 which, together with its internal and external components, is symmetrical about the transverse center line of Figure 2. Only one half of the interrupter unit 10 will he described in detail, it being 4 understood that the other half is merely a mirror image thereof.

Tank 11 comprises two cylindrical shells 12 joined at their first ends and having end plates 13 covering their second ends. Either or both shells 12 and end plates 13 may be constructed of insulating or conducting material as design considerations may dictate. Cover 14 fits over maintenance opening 15 in shell 12 with window 16 in cover 14 permitting a view of the interior of tank 11.

Stationary contact 17 is mounted to the end of stud 18 andV is positioned within tank 11. Stud 18 passes through opening 19 in end plate 13l and is centered therein by insulator 20. Annular member 21 is secured to the end plate 13 outside of tank 11 to serve as a seal between insulator 20 and end plate 13. Corrugated bushing 22 lengthens creepage path between stud 18 and the outside of tank 11.

Movable contact structure 25 is positioned i-n axial alignment with stationary contact 17 by means of insulator standolfs 26-29 which have their first ends abutting the outside of cylinder 30 and their second ends resting in outer ring 31 which is positioned between the end flanges 32 of shells 12 to provide a seal between the sections of tank 11 when they are joined as by bolts 33. A passage 34 extends through standol 26, outer ring 31, and a fitting 35 secured to outer ring 31 for a purpose to be hereinafter fully explained.

Piston assembly 36, slidably mounted in cylinder 30 comprises a piston 37, a movable contact 38 secured to piston 37, and a plurality of circularly arranged contacts 40 urged into wiping contact with the inside wall 39' of cylinder 30. Ring member 43 is force fitted to movable contact 38 to be in good electrical contact therewith while fastening means 58 secures plate ring 44 to ring member 43 to provide a guide for contacts 40 as they are biased radially outward from movable contact- 38 by compression. springs 41 which abut opposite ends of adjacent contacts 40.

Closing springs 45 bear against piston 37 and baflie 46 positioned near the transverse center line of cylinder 30 to urge movable contact 38 out of cylinder 30 and into engagement with stationary contact 17 (Figure 2) and thereby close interrupter unit 10. Batiie projection 47, piston opening 48, and piston depression 49 act as longitudinal guides for closing spring 45. Thus a` complete electrical path is formed between stud 18 on one side of interrupter unit 10 to stud 18 on the other side ofv interrupter unit 10 through stationary contact 17, movable contact 38, contact 40, cylinder 30 and the mirror image of theseparts housed. in the adjacent shell- 12.

Baffles 46 are spaced to form chamber 50, at the center of cylinder 30, which communicates with passage 34 through opening 51 in the wall of cylinder 30. Movable contact 38 is a hollow member having a central passage 54 extending through the complete piston assembly 36. Batiie openings 55 provide a gas passage from contact passage 52 to chamber 50 except when piston 37 is driven against seal 56 as in the open position of interrupter unit 10 (Figure 4). Slots 53. are cut in the face or matingl surface ofv movable contact 38 and/or the face of stationary contact 17 to assure equal pressures on both sides of piston assembly 36 when interrupter unit 10 is closed even though the opening. or

blast valve 60 may leak and for another purpose to be hereinafter explained.

With the interrupter unit 10 in the closed positionY of Figure l, high pressure gas is present on. both the front 58 and back 59 faces of piston assembly 36 so that closing springs 45 are free to urge the piston assemblies 36 in diverging directions. into high pressure contactwith'` stationary contact' 17. To open interrupter unit 10' blast valve 60 is opened by applying power to coil 61 whichI attracts plunger 621 to the left with respect to. Figure 4 and thereby moves valve disc 64 off seat 63, against the force` of spring 66.

Chamber 50 now communicates with low pressure reservoir 65 through gas line 67, connected between fitting 35 and blast valve 60, and gas line 68, connected between blast valve 60 and low pressure reservoir 65.

Now the pressure on front face 58 is high and the pressure on back face 59 is low so that the piston assemblies 36 will be driven to a converging position where they will rest on seats 56 (Figure 4). As soon as an arc is drawn between movable contact 38 and stationary contact 17 it will be subjected to a smooth flowing gas blast, flowing from tank 11 toV low pressure reservoir 65, which cools and deionizes the arc bringing about its rapid extinction. The arcing products are rapidly moved from the arcing gap by the gas blast and carried through the movable contact passage 54, chamber 50, passage 34, and gas lines 67, 68 to low pressure reservoir 65. Slots 53 enable the gas blast to be initiated at the moment blast valve 60 is opened even though the movement of movable contact 38 will necessarily be delayed after opening blast valve 60 due to inertia and friction effects.

By the time piston assembly 36 rests -against seat 56 the arc is extinguished and the gas blast is shut off since seat 56 now seals off chamber 50 from contact passage 54. VPacking 42 in peripheral groove 42 serves as a gas tight seal between piston 37 and the inside wall 39 of piston 30. High pressure gas is present in the gap between cooperating

contacts

38, 17 since tank 11 is connected through fitting 70 and gas line 69 to high pressure reservoir 71 thereby preventing arc restrike.

When blast valve 60 is closed by deenergizing coil 61, interrupter unit will not close immediately since chamber 50 is not as yet filled with high pressure gas. Closing valve 72 must first be opened by energizing coil 73 which attracts plunger 74 and moves valve disc 75 downward off seat 76 against the force of biasing spring 77. At this time high pressure gas line 69 is connected to pistonchamber 50 thus bringing both sides 58, 59 of piston assembly 36 to the same pressure level and permitting closing springs 45 to expand and bring cooperating

contacts

38, 17 into engagement.

Separate cooling lines 101 for each in interrupter unit 10 are connected between gas lines 67 and 68 to bypass blast valve 60. Thermostatically controlled orifices 102 are positioned at intermediate points in cooling lines 101 to control the rate of gas flow through cooling lines 101. When cooperating

contacts

38, 17 are inengagement there will be a slight flow o f gas from the interrupter tank 11 to low pressure reservoir 65 by means of slots 53, movable contact passage 54, chamber 50, passage 34, and cooling line 101. This gas slight flow is effective to provide sufficient convection cooling of the cooperating contacts 38, 177 more particularly movable contact 38, so that a reduction in size of the moving parts or an increased current carrying capacity for the interrupter unit 10 is achieved.

Thermostat 130 is mounted inside of tank 11 and is positioned to be predominantly affected by the radiant heat from

contacts

17, 38. When the upper temperature limit, approximately 90 C., is exceeded due to excessive current flowing through

contacts

17, 38 radiant heat therefrom will actuate thermostat 130 to complete circuits through a suitable power supply 131 to orifice 102 and normally open valve 132.

l Thermostatically controlled orifice 102 will open wide to permit a greater flow of gas from tank 11 to pass over contact 17, through-contact 38, passage 54, space 50, passage 34, and by bleeding through orifice 102 vby-pass blast Valve 60 and return to low pressure reservoir 65. In this way greater than rated currents may safely be carried for extended periods of time.

A separate check valve 133 in parallel with a normally open valve 132 is associated with each of the temperature controlled orices 102. Check valve 133 will only permit gas flow in the direction indicated by arrow A.

Since valve 132 is closed when thermostat 130 is actuated, cooling or bleed-off gas from one interrupter unit 10 will be prevented from passing through any orifice 102 other than its associated one. It should be apparent to those skilled in the art that thermostatically controlled orifice 102 may be completely closed when interrupter unit 10 is operating below the upper temperature limit and only open when the upper temperature limit is exceeded. Also, thermostatically controlled orifice 102 and thermostat 130 may be of a construction such the size of orifice 102 will gradually increase as the temperature to which thermostat 130 is subjected to increases.

Shell 12 may be connected to ground potential so that the secondary wiring, such as the wiring to power supply 131, orifice 102, and valve 132, is not exposed to primary potential.

The size of thermostatically controlled orifice 102 var- `ies as the temperature of the gas flowing therethrough to thereby increase the flow of cooling gas as the temperature of

contacts

38, 17 rises. However, when on'- fice 102 is opened to a maximum, the net force on piston assembly 37 due to tank 11 gas pressure will be less than the force being exerted by closing springs 45 so that the interrupter unit 10 will not be opened.

The dielectric medium is passed in a gaseous state 110 from low pressure reservoir 65, through filter unit 83 to remove arcingproducts from the gas after it has interrupted a first arc and before it will be played on a second arc. From filter unit 83 gas 110 passes through a compressor 84 or refrigerating unit where the dielectric medium is transformed to a liquid or semi-solid state 111 and thereafter passed through check valve 85 and stored in high pressure reservoir 71.

High pressure reservoir 71 is positioned Within low pressure reservoir 65 with a heater unit 112, having a thermostatic control (not shown) being secured to the out-,

side of high pressure reservoir 71. Being so positioned, heater unit 112 is effective at low ambient temperatures to maintain a minimum gas pressure in high pressure reservoir 71 and maintain the dielectric medium in low pressure reservoir 65 in a gaseous state.y

Reducing valve S8 maintains a uniform gas pressure in interrupter tanks 11 while safety valve 82 bleeds excess pressure in tank 11 back to low pressure reservoir 65. Pressure switch 113 is closed, when the pressure in low pressure reservoir 65 exceeds a predetermined value to start up refrigeration unit 84 to replenish the supply of gas in high pressure reservoir 71 and prevent too high a back pressure from the low pressure reservoir 65 to slow interrupter opening.

Control cabinet houses pressure gauge 91 and operation counter 94 which is operated by means of an extension from the auxiliary switch operating arm 93 which is` operated to the right by the air valve 92 connected to gas line 39 and returned to the left by the spring 149 when the pressure in line 39 is released.

The three interrupter units 10 `of Figure 4 may each be connected to a separate current carrying line to provide a double break in each line. However, for severe interrupting conditions two `or more interrupter units 10 may be serially connected to produce four, six, eight, etc. breaks in the line.

Thus an interrupter unit of the gas blast type has been provided which is of an especially compact 'and simplified construction achieved by:

(l) Subjecting the cooperating

contacts

38, 17, when in engagement, to a flow of dielectric gas,

(2) Refrigerating the dielectric gas,

(3) Storing the dielectric medium in a liquid or semisolid state,

(4) Positioning the movable contact structure 25 between two spaced stationary contacts 17 in axial alignment therewith and providing axially movable contacts 7. 38 which converge to open the circuit and diverge to close the circuit,

Having the pistons 37, which carry the movable contacts 38, acted upon directly by high pressure gas to effect circuit opening and also act as valves to stop gas flow out of tank 11 when the cooperating

contacts

38, 17 are fully separated,

(6)- Filling the gap between the cooperating

contacts

38, 17 under open circuit conditions, with high pressure gas which is ia more effective insulator than gas at atmospheric pressure, and

(7) Submerging the cooperating contacts 38, i7, under closed circuit conditions, in high pressure gas which is a more effective heat conductor than gas at atmospheric pressure. Furthermore, the presence of high pressure gas at the junction of the cooperating contacts 3S, 17 assures .a smooth fiowing gas in the larcing gap at the moment the arc is first drawn.

The `recirculating gas system also contributes in part to ythe compact construction by supplying non-contamin-ated gas to the interrupter. Because of this, the safety factor used in calculatingl creepiage distances within the tank 11 of the interrupter unit 10 may be kept to a minimum since dirt and arcing products are not likely to build up on the insulating surfaces to impair their effectiveness as insulators.

It should be lapparent to those skilled in the art that a suitable construction of piston assemblies 36 will eliminate the necessity of forming chamber 50 by means of bafiies 46. Instead, the back faces 59 of the newly designed pistons will form chamber S0 and in the 1open position of the circuit interrup-ter, the newly designed piston assemblies will be positioned back to back and carry suitable formations whch cooperate to act as a closed valve between passage 34 of insulator 26 and central passage 54 of movable contact 38.

In the foregoing, we have described our invention only in connection with preferred embodiments thereof. Many variations and modifications of the principles of our invention within the scope of the description herein are obvious, Accordingly, we prefer to be bound not by the specific disclosure herein but only by the appending claims.

We claim:

1. A gas blast type circuit interrupter unit comprising a tank, a first and a second stationary contact; a movable Contact structure; said first and second stationary contacts being disposed within said tank and positioned with a gap therebetween; said tank being connected to a high pressure source of dielectric gas; said movable Contact structure comprising `a cylinder and two piston assemblies slidably disposed in back to back relationship within said cylinder; each of said piston assemblies including a movable contact; said piston assemblies being movable between a converged and a diverged position; said gap being open when said piston assemblies are in said converged position; said stationary contacts being engaged by said movable contacts and said gap being bridged by said movable contact structure when said piston assemblies are in said diverged position; first means for maintaining said contacts in engagement; a first and a second gas line communicating with the inside of said cylinder; means selectively connecting said first gas line to a low pressure source )of dielectric gas and to said high pressure source; said piston assemblies being operated to said converged position by gas pressure when said first gas line is connected to said low pressure source; said second gas line being connected to said low pressure source; each of said movable contacts having a passage communicating with said second gas line and said tank when said gap is bridged; said second gas line being of a size sufficiently smaller than the size of said first gas line so that said movable contacts will be subjected to a cooling flow of dielectric gas when said gap is bridged without overcoming said first means so as not to cause said piston assem-Y blies to move toward their diverged position.

2. A gas blast type circuit interrupter unit comprising a tank, a first and a second stationary contact; a movable contact structure; said first and second stationary contacts being disposed within said tank and positioned with a gap therebetween; said tank being connected to a high pressure source of dielectric gas; said movable Contact structure comprising a cylinder and two piston assemblies slidably disposed in back to back relationship within said cylinder; each of said piston assemblies including a movable contact; said piston assemblies being movable between a converged and a diverged position; said gap being open when said piston assemblies are in said converged position; said stationary contacts being engaged by said movable contacts and said gap being bridged by said movable contact structure when said piston assemblies are in said diverged position; a first and a second gas line communicating with the inside of said cylinder; means selectively connecting said first gas line to a low pressure source of dielectric gas `and to said high pressure source; said second gas line being connected to said low pressure source; each of said movable contacts having a passage communicating with said second gas line and said tank when said gap :is bridged; a thermostatically controlled orifice positioned in said second gas line to regulate the magnitude of a cooling flow of dielectric gas to which the contacts are subjected when said gap is bridged.

3. A gas blast type circuit interrupter unit comprising a tank, a first and a second stationary contact; a movable contact structure; said first and second stationary contacts being disposed within said tank and positioned with a gap therebetween; said tank being connected to a high pressure source of dielectric gas; said movable contact structure comprising a cylinder and two piston assemblies slidably disposed in back to back relationship with said cylinder; each of said piston assemblies including a movable contact; said piston assemblies being movable between a converged and a diverged position; said gap being open when said piston assemblies are in said converged position; said stationary contacts being engaged by said movable contacts and said gap being bridged by said movable contact structure when said piston assemblies are in said diverged position; first means for maintaining said contacts in engagement; a first and a second gas line communicating with the inside of said cylinder; means selectively connecting said first gas line to a low pressure source of dielectric gas and to said high pressure source; said piston assemblies being operated to said converged position by gas pressure when said first gas line is connected to said low pressure source; said second gas line being connected to said low pressure source; each of said movable contacts having a passage communicating with said second gas line and said tank when said gap is bridged; said second gas line being of a size sufficiently smaller than the size of said first gas line so that said movable contacts will be subjected to a cooling fiow of dielectric gas when said gap is bridged with-out overcoming said first means `so as not to cause said piston assemblies to move toward their diverged position; said high pressure source comprising a first reservoir and said low pressure source comprising a second reservoir; a compressor unit being operatively connected between said first and second reservoirs; said compressor transforming the dielectric gas of the second reservoir to a semi-solid state and depositing it in said first reservoir.

4. A gas blast type circuit interrupter unit comprising a tank, a first and a second stationary contact; a movable contact structure; said first and second stationary contacts being disposed within said tank and positioned with a gap therebetween; said tank being connected to a high pressure source of dielectric gas; said movable contact structure comprising a cylinder and two piston assemblies slidably disposed in back to back relationship with said cylinder; each of said piston assemblies including a movable contact; said piston 'assemblies being movable between a converged and a diverged position; said gap being open when said piston assemblies are in said converged position; said stationary contacts being engaged by said movable contacts and said gap being bridged by said movable contact structure when said piston assemblies are in said diverged position; first means `for maintaining said contacts in engagement; a first anda second gas line communicating with the inside of said cylinder; means selectively connecting said first line to a low pressure source of dielectric gas and to said high pressure source; said piston 4assemblies being operated to said converged position by gas pressure when said first gas line is connected to said low pressure source; said second gas line being connected to said low pressure source; each of said movable contacts having a passage communicating with said second gas line and said tank when said gap is bridged; said-second gas line being of a size sufiiciently smaller than the size of said rst gas line so that said movable contacts will be 4subjected to a cooling flow of dielectric gas when said gap Vis bridged without overcoming said first means so as not to cause said piston assemblies to move toward their diverged position; said high pressure source comprising a first reservoir and said low'pressure source comprising a second reservoir; a compressor unit being operatively connected between said first and second reservoirs; said compressor transforming the dielectric gas of the second reservoir to a semi-solid state and depositing it in said first reservoir; one of said reservoirs being disposed within the other of said reservoirs; a heater unit secured to the outside of said inner reservoir to maintain sufficient gas pressure in said first reservoir and prevent liquification and solidification of the dielectric gas in said second reservoir under conditions of low ambient temperature.

5. A gas blast type interrupter unit comprising a tank, a stationary contact, a cylinder, a piston, a movable contact; all of said members being disposed within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder and movable between a first position, wherein said contacts are in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected to a high pressure source of dielectric gas; a first valve when opened operatively connecting said cylinder to a low pressure source of dielectric gas; said contacts being disengaged when said first valve is opened; ra second valve operatively connected between said high pressure source and said first valve; a gas passage operatively connected between said cylinder and said low pressure source; said movable contact including a passage communicating with said gas passage and said tank when said contacts are in engagement; said gas passage bypassing said first valve to thereby subject said contacts to a cooling flow of dielectric gas when said first value is closed and said contacts are engaged.

6. A gas blast type interrupter unit comprising a tank, a stationary contact, a cylinder, a piston, `a movable contact; all of said members being disposed within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder and movable between a first position, wherein said contacts yare in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected to a high pressure source of dielectric gas; a rst valve when opened operatively connecting said cylinder to a low pressure source of dielectric gas; said contacts being disengaged when said first val've is opened; a second valve operatively connected between said high pressure source and said first valve; a gas passage operatively connected between said cylinder and said low pressure source; said movable contact including a passage communicating with said gas passage and said tank when said contacts are in engagement; said gas passage bypassing said first valve to thereby subject said contacts to a cooling flow of dielectric gas when said first valve is closed and said contacts are engaged; a thermostatically controlled relay positioned in said gas passage to regulate the magnitude of gas flowing therethrough.

7. A gas blast type interrupter unit comprising a tank, a stationary contact, a cylinder, a piston, a movable contact; all of said members being disposed Within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder -and movable between a first position, wherein said contacts are in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected to a high pressure source of dielectric gas; a first valve when opened operatively connecting said cylinder to Va 10W pressure source of dielectric gas; said contacts being dissengaged when said first valve is opened; a second valve operatively connected between said high pressure source and said first valve; a gas passage operatively connected between said cylinder and said low pressure source; said movable contact including a passage communicating with said gas passage and said tank when said contacts are in engagement; said gas passage bypassing said first valve to thereby subject said contacts to a cooling fiow of dielectric gas when said first valve is closed and said contacts are engaged; said position, when in said second position serving as a valve to shut oli all gas flow from said tank to said low pressure reservoir.

8. A gas blast type interrupter unit comprising a tank, a stationary contact, a cylinder, a piston, a movable contact; all of said members being disposed within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder and movable between a first position, wherein said contacts are in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected to a high pressure source of dielectric gas; a first valve when opened operatively connecting said cylinder to a low pressure source of dielectric gas; said contacts being disengaged when said first valve is opened; a second valve operatively connected between said high pressure source and said first valve; a gas passage operatively connected between said cylinder and said low pressure source; said movable contact including a passage communicating with said gas passage and said tank when said contacts are in engagement; said gas passage bypassing said first valve to thereby subject said contacts to a cooling flow of dielectric gas when said first valve is closed and said contacts are engaged; said high pressure source comprising a first reservoir and said low pressure source comprising a second reservoir; a compressor unit being operatively connected between said first and second reservoirs; said compressor transforming the dielectric gas of the second reservoir to a semi-solid state and depositing it in said first reservoir.

9. A gas blast type interrupter unit comprising a tank, a stationary contact, a cylinder, a piston, a movable contact; all of said members being disposed within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder and movable between a first position, wherein said contacts are in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected t-o -a high pressure source reservoir of dielectric gas; a first valve when opened operatively connecting said cylinder to a low pressure source reservoir of dielectric gas; said contacts being disengaged when said first valve is opened; a second valve operatively connected between said high pressure source reservoir and said first valve; a gas passage operatively connected between said cylinder and said low pressure source reservoir; said movable contact including a passage which is operatively positioned, when said contacts are engaged, in communication with both said tank and said gas passage; said gas passage bypassing said rst valve to thereby subject said contacts to a cooling ow of dielectric gas when said rst valve is closed and said contacts are engaged; one of said reservoirs being disposed within the other fof said reservoirs; a heater unit secured to the outside of said inner reservoir to maintain suicient gas pressure in said first reservoir and prevent liquication and solidication ofthe dielectric gas in said second reservoir under conditions of low ambient temperature.

10- A gas blast type interrupter unit comprising a tank, a stationary contact, 'a cylinder, a piston, a movable contact; all of said members being disposed within said tank; said movable contact being operatively connected to said piston; said piston being slidably disposed within said cylinder and movable between a rst position, wherein said contacts are in engagement with each other, and a second position, wherein said contacts are disengaged from each other; said tank being connected to a high pressure source of dielectric gas; a first valve when opened operatively connecting said cylinder to a low pressure source of dielectric gas; said contacts being disengaged when said firs-t valve is opened; a second valve operatively connected between said high pressure source and said first valve; a rst means operatively connected between said cylinder and said low pressure source and by-passing said first valve; said movable contact including a passage com- References Cited in the le of this patent UNTED STATES PATENTS l901,967 Hewlett Oct. 27, 1908 2,459,600 Strom Jan. 18, 1949 2,611,846 Applegate Sept. 23, 1952 2,757,261 Lingal et al July 31, 1956 2,766,348 Forwald Oct. 9, 1956v FOREIGN PATENTS 151,019 Sweden Aug. 9, 1955 367,940 Great Britain Mar. 2, 1932 375,364 Great Britain June 27, 1932 533,476 Germany Sept. 19, 1931 582,299 Great Britain Nov. 21, 1946 593,230 Great Britain Oct. 10, 1947 652,721l Germany Nov. 9, 1937 727,258 Great Britain Mar. 30, 1955