US2936355A - Latch means for recirculating gas blast interrupters - Google Patents

Description

May 10, 1960 A. s. gAswELL LATCH MEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS Filed June 21, 1957 3 Sheets-Sheet 1 Div I:

u m mm mu y 1960 A. s. CASWELL 2,936,355

LATCH MEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS 3 Sheets-Sheet 2 Filed June 21. 1957 BY%W/=%' MK 4 May 10, 1960 A. s. CASWELL LATCH MEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS Filed June 21, 1957 3 Sheets-Sheet 3 United States Patent LATCH NIEANS FOR RECIRCULATING GAS BLAST INTERRUPTERS Arthur S. Caswell, Glenside, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application June. 21, 1957, Serial No. 667,202 5 Claims. 01. 200-448 This invention relates to circuit interrupters of the gas blast type and more particularly to a latch means for a circuit interrupter having a recirculating gas system where in the cooperating contacts of the interrupter are operated to the disengaged position, against the force of the contact closing springs, by high pressure gas and latched to remain in this position even though there is a subsequent loss of pressure.

When a circuit interrupter protecting a current carrying line is 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 has taken place are of prime consideration.

A gas blast directed at the arc hastens the deionization thereof by cooling the arch 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 larger 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 without danger of restrike at a given voltage. That is, the ability of a dielectric gas to resist breakdown at a given voltage gradient increases as the gas pressure increases except at pressures considerably below atmospheric pressure.

It has been found that the so called electronegative gases, such as sulphur hexafluoride (SP and sulphur monofluoride (S F are superior to air in their deionizing and dielectric properties thereby making them particularly useful in arc interruption. When gases other than air are used arecirculating system should be employed because of the high cost of 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 supply 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 valve 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 flow rate along the arc stream thereby preventing a rapid arc extinction. In interruptcrs employing a bridging member moving transversely with respect to the stationary contacts, the initial gas blast was required to transfer the are from the bridging contact to a stationary contact rather than cool the arch thereby further delaying arc extinction.

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.

In some prior art constructions, such as the gas blast 2,936,355 Patented May 10, 1960 ICC interrupter described in copending application Serial No. 667,201, filed June 21, 1957, and assigned to the assignee of the instant invention, the interrupter is opened by high pressure gas acting directly upon the cooperating con tacts. In other constructions the gas forces are transmitted to the cooperating contacts through mechanical linkages. Once opened, the continued presence of high pressure gas was relied upon to maintain the cooperating contacts disengaged.

Should a leak develop in the gas system or should there be a loss of control circuit power for energizing the control valve, or for any other reason a partial or complete loss of gas pressure should occur, the cooperating con tacts would move to their engaged position even though it was desired to have them remain disengaged.

The circuit interrupter of the instant invention includes a separate interrupter unit for each current carrying line of the electrical system being protected with each interrupter unit including means whereby the interrupter is latched open. Each interrupter unit also 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 slidably 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 or the output of a compressor so that the movable and stationary contacts are always immersed in high pressure gas. A chamber positioned in the center of the cylinder between the two movable contacts 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.

A latch means, including a latch member operatively connected at its center to a latch piston and having latch tips and cam surfaces at both ends thereof, is positioned with the latch tips projecting into the cylinder and being biased toward the longitudinal axis of the cylinder. As the pistons converge they engage the cam surfaces to force the latch tips out of the piston path and thereafter the latch tips are biased back toward the longitudinal axis into latching position.

If the gas pressure in the interrupter tank should drop significantly or should completely disappear the pistons in attempting to move in diverging directions will be engaged by the latch tips and be prevented from restoring closed circuit conditions.

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 sttaionary contacts. In this manner the arc drawn as the cooperating contacts are partedwill immediately be acted upon by a smooth flowing blast of gas which rapidly deionizes and cools the arc and exhausts the arch 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 high pressure surrounding the parted contacts, and the gap therebetwcen necessary to prevent restrike will be smaller than if the parted contacts were surrounded by gas at atmospheric pressure.

The interrupter is closed by connecting the chamber to the high pressure of the tank and simultaneously connecting one end of a latch cylinder to the low pressure reservoir. The latch cylinder has a latch piston slidably disposed therein which is operatively connected to the latch members. High pressure gas in the tank will now drive the latch piston away from the longitudinal axis which at the same time frees the pistons from the latch tips and permits the piston 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 are products and thereby assure asupply of clean gas for subsequent interruptions.

Since high pressure gas always surrounds the engaged cooperating contacts, a smooth gas flow will act on the are from the moment of its inception. Smooth gas flow assures maximum interrupting and dielectric properties since the arcing products are rapidly carried away from the arcing gap and a fresh supply of clean gas is being continuously introduced into the gap until interruption is completed.

Accordingly, a primary object of the instant invention is to provide a circuit interrupter of the recirculating gas blast type having a latch means to latch the interrupter open.

Another object is to provide a latch means whereby closing of a gas blast circuit interrupter is prevented if there is a loss of gas pressure.

Still another object is to provide a latch means whereby closing of a gas blast circuit interrupter, which is biased toward closed position, is prevented if there is a loss of control circuit power.

A further object is to provide a latch means, for a recirculating gas blast interrupter, which is uulatched by means of high pressure gas.

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

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

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

Figure 1 is a side elevation of a single interrupter unit, partially cut away to show the internal construction thereof, with the circuit closed.

Figure 2 is a section taken through line 2--2 of Figure 1 looking in the direction of arrows 2-2.

igure 3 is a fragmentary view of the interrupter unit of Figure 1 with the interrupter unit latched open.

Figure 4 is a schematic representation of a three conductor system protected by the circuit interrupter of the instant invention.

Figure 5 is a section taken through line 5-5 of Figure 1 looking in the 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 1. Only one half of the interrupter unit 10 will be described in detail, it being 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 per itting a View of the interior of tank 11.

Stationary contact 17 is mounted to the end of stud 1S and is positioned within tank 11. Stud 18 passes through opening 19 in end plate 13 and is centered therein by insulator 2i). Annular member 21 is secured to the end plate 13 outside of tank 11 to serve as a seal between insulator 2t) and end plate 13. Corrugated bushing 22 lengths creepage path between stud 18 and the outside of tank 11.

Movable contact structure 25 is positioned in axial alignment with stationary contact 17 by means of insulator standofiis 26-49 which have their first ends abut ting the outside of cylinder 36 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. The four insulator standolfs 26-29 may be replaced by a single ring-shaped insulator (not shown), in which event sealing between the sections of tank 11 will be simplified. A passage 34 extends through standofi 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 33 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 4-4 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 baffle 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 1) and thereby close interrupter unit ill. Baffle 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 of interrupter unit It through stationary contact 17, movable contact 38, contact 4% cylinder 30 and the mirror image of these parts housed in the adjacent shell 12.

Bafiles 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. Baffle openings 55 provide a gas passage of generous size from contact passage 52 to chamber 50 except when piston 37 is driven against seat 56 as in the open position of interrupter unit 10 (Figure 3) where it is latched open by latch means 100. Slots 53 may be cut in the face or mating surface of movable contact 38 and/or the face of stationary contact 17 to assure equalpressures on both sides of piston assembly 36 when interrupter unit 10 is closed even though the opening or blast valve 60 may leak.

With the interrupter unit 10 in the closed position of Figure 1, high pressure gas is present on both the front 58 and back 59 faces of piston assembly as so that closing springs 45 are free to urge the piston assemblies 36in diverging directions into high pressure contact with stationary contact 17. To open interrupter unit 10 blast valve 60 is opened by applying power to coil 61 which attracts plunger 62. to the left with respect to Figure 4 pressure reservoir 65.

and thereby moves valve disc 64 off seat 63, against the force of spring 66. Chamber 50 now communicates with low pressure reservoir 35 through gas line 67, connected between fitting 35 and 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 3). 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 to low pressure reservoir 65, which cools and deionizes the are bringing about its rapid extinction. The arcing products are rapidly removed 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. If movable contacts 38 have pressure equalizing slots 53 cut therein the gas blast will be initiated at the moment blast valve 60 is opened. However, if movable contacts 38 do not have pressure equalizing slots 53 the gas blast will begin at the moment the contacts 38, 17 part. Because of inertia and friction effects, the movement of movable contact 38 will necessarily be delayed after opening blast valve 60.

As piston assemblies 36 travel from the closed position of Figure l to the open position of Figure 3, pistons 37 engage cam surfaces 101 to move latch member 102 thereby moving latch tips 104 away from the longitudinal axis of cylinder 30. When the pistons 37 have moved past latch tips 104 the tips 104 once again are caused to project into cylinder 30 by springs 105 and thereby be in latching position. Should the pressure in tank 11 drop materially, or completely vanish, latch tips 104 are positioned to block movement of the piston assemblies 36 to their diverging position of Figure 1.

Latch means 100 further includes a latch cylinder 106 positioned at the shell end of insulator standoff 28 and a latch piston 107 slidably disposed in latch cylinder 106 for movement transverse to the longitudinal axis of cylinder 30. Connecting rod 108 is disposed in passage 112 through insulator 28 and operatively connects latch piston 107 to pin 103, on which, latch member 102 is mounted. A valve seat 110 is secured to the inside surface of latch cylinder end closure 109 having orifice 111 centrally located therein which is connected through line 39 to closing valve 72.

In its deenergized state, closing valve 72 provides a connection, indicated as A, between line 39 and line 69 which is connected to high pressure reservoir 71 thereby supplying high pressure gas to the back 120 of latch piston 107 when the interrupter unit is open to aid springs 105 in maintaining latching means 100 in the latching position.

By the time piston assembly 36 rests against seat 56 the arc is extinguished. The gas blast is essentially shut off by seat 56 which seals oif chamber 50 from contact passage 54. Piston ring 42 in peripheral groove 42' serves as a bearing and provides a seal between piston 37 and the inside wall 39 of piston 30 sufficient for this application. gap between cooperating contacts 38, 17 since tank 11 isconnected 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 the pressure in chamber 50 will build up as high pressure gas slowly leaks past piston ring 42. However, closing springs 45 will not as yet be effective to close interrupter 10 since movement of pistons 37 is blocked by latch tips 104. Closing valve 72 must be energized to interrupt connection A and complete connection B thereby connecting line 39, through line 95, to low Now low pressure is present on the back 120 of latching piston 107 and high pressure on the front 121 which drives the latching piston 107 High pressure gas is present in the radially outward to its unlatched position shown in dashed lines Figure 3. Both sides 58, 59 of piston assembly 36 are at the same pressure level so that closing springs 45 may expand to bring cooperating contacts 38, 17 into engagement.

Filter unit 83 is interposed between the input of compressor 84 and low pressure reservoir 65 to remove arcing products from the gas after it has interrupted a first arc and before it will be played on a second arc. The output of compressor 84 is connected to both high pressure storage reservoir 71 and high pressure gas line 69 to assure a continuous supply of high pressure gas within tank 11. Safety valves 82 are strategically placed throughout the system to bleed excess pressures back to low pressure reservoir 65 and prevent damage because of excessive gas pressures.

High pressure gas line 69 also has located therein check valves 85, a shut off valve 89, reducing valve 88, and pressure switch 86. Reducing valve 88 controls the pressure level within tank 11 while pressure switch 86 controls the operation of compressor 84 responsive to the pressure in high pressure reservoir 71. Check valves prevent a loss of pressure in tanks 11 even though the pressure in high pressure reservoir 71 or compressor 84 should drop below that of tank 11.

Control cabinet 90 houses pressure gauge 91 and operation counter 94 which is operated by means of auxiliary switch 93 and air valve 92 connected to gas line 39.

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.

The recirculating gas system also contributes to a compact construction by supplying non-contaminated gas to the-interrupter. Because of this, the safety factor used in calculating creepage distances within the tank 11 of the interrupter unit 10, tank 11 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 apparent 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 50 and in the open position of the circuit interrupter, the newly designed piston assemblies will be positioned back to back to act as a closed valve between passage 34 of insulator 26 and central passage 54 of movable contact 38.

Thus a gas blast circuit interrupter 10 of especially compact and simplified construction has been provided which includes a latch means to prevent accidental or unscheduled closing of the interrupter 10. That is, even though the cooperating contacts 38, 17 are always biased toward engagement by closing springs 45, and moved to the disengaged position by the action of high pressure gas in tank 11 and low pressure gas in chamber 50, the loss of gas pressure in tank 11 will not result in the closing of contacts 38, 17. High pressure gas must be available to unlatch. latch means 100 before movable contacts 38 are free to engage stationary contacts 17. Furthermore, a loss of control circuit power cannot result in closing of the interrupter 10 since a positive energization of closing valve 72 is required to supply high pressure to chamber 50 in order to close the interrupter 10.

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

I claim:

1. in combination a low pressure source of dielectric gas, a high pressure source of dielectric gas, a gas blast type interrupter unit, and means interconnecting said sources of dielectric gas and said interrupter unit to form a closed recirculating gas system; said gas blast type 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 axially aligned in spaced relationship with respect to each other; said movable Contact structure being positioned between said first and second stationary contacts in axial alignment therewith; said tank being operatively connected to said high pressure source of dielectric gas; said movable contact structure being selectively connectibly to said low pressure source of dielectric gas; said movable contact structure comprising a cylinder, two piston assemblies and a closing spring; said piston assemblies being slidably disposed within said cylinder; said closing spring being positioned between said piston assemblies and operatively arranged to urge piston assemblies along the axis of said cylinder in diverging paths into engagement with said stationary contacts to bring said interrupter unit to a closed position; said piston assemblies being moved by means of gas pressure derived from said sources of dielectric gas along converging paths to the open position of said circuit interrupter when said movable contact structure is connected to said low pressure source; a latch means comprising a iatch member, a latch piston, and a latch cylinder; said latch cylinder axis being arranged transverse to said cylinder axis; a first end of said latch cylinder communicating with said cylinder to thereby be at vthe same pressure as said movable contact structure; a second end of said latch cylinder being selectively connectible to said high and said low pressure sources; said latch member being secured to said latch piston; said latch piston being slidably disposed within said latch cylinder; said latch member engaging said piston assemblies when said interrupter unit is in said open position to thereby latch said interrupter unit open; said latch member being unlatched when said movable contact structure is not connected to said low pressure source and said second end of said latch cylinder is connected to said low pressure source.

2. In combination a low pressure source of dielectric gas, a high pressure source of dielectric gas, a gas blast type interrupter unit, and means interconnecting said sources of dielectric gas and said interrupter unit to form a closed recirculating gas system; said gas blast type 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 axially aligned in spaced relationship with respect to each other; said movable contact structure being positioned between said first and second stationary contacts in axial alignment therewith; said tank being operatively connected to said high pressure source of dielectric gas; said movable contact structure being selectively connectible to said low pressure source of dielectric gas; said in vable contact structure comprising a cylinder, two piston assemblies and a closing spring; said piston assemblies being slidably disposed within said cylinder; said closing spring being positioned between said piston assemblies and operatively arranged to urge said piston assemblies along the axis of said cylinder in diverging paths into engagement with said stationary contacts to bring said interrupter unit to a closed position; said piston assemblies being moved by means of gas pressure derived from said sources of dielectric gas along converging paths to the open position of said circuit interrupter when said movable contact structure is connected to said low pressure source; a latch means comprising a latch member, a latch piston, and a latch cylinder; said latch cylinder axis being arranged transverse to said cylinder axis; a

rst end of said latch cylinder communicating with said cylinder to thereby be at the same pressure as said movable contact structure; a second end of said latch cylinder being selectively connectibly to said high and said low pressure sources; said latch member being secured to said latch piston; said latch piston being slidably disposed within said latch cylinder; said latch member being entered into said cylinder when said latch means is in a latching position; said latch member being withdrawn from said cylinder when said latch means is in an un- .ched position; said latch member engaging said piston assemblies when said interrupter unit is in said open position to thereby latch said interrupter unit open.

3. In combination a low pressure source of dielectric gas, a high pressure source of dielectric gas, a gas blast type interrupter unit, and means interconnecting said sources of dielectric gas and said interrupter unit to form a closed recirculating gas system; said gas blast type 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 axially aligned in spaced relationship with respect to each other; said movable contact structure being positioned between said first and second stationary contacts in axial alignment therewith; said tank being operatively connected to said high pressure source of dielectric gas; said movable contact structure being selectively connectible to said low pressure source of dielectric gas; said movable contact structure comprising a cylinder, two piston assemblies and a closing spring; said piston assemblies being slidably disposed within said cylinder; said closing spring being positioned between said piston assemblies and operatively arranged to urge said piston assemblies along the axis of said cylinder in diverging paths into engagement with said stationary contacts to bring said interrupter unit to a closed position; said piston assemblies being moved by means of gas pressure derived from said sources of dielectric gas along converging paths to the open position of said circuit interrupter when said movable contact structure is connected to said low pressure source; a latch means comprising a latch member, a latch piston, and a latch cylinder; said latch cylinder axis being arranged transverse to said cylinder axis, a first end of said latch cylinder communicating with said cylinder to thereby be at the same pressure as said movable contact structure; a second end of said latch cylinder being selectively connectible to said high and said low pressure sources; said latch member being secured to said latch piston; said latch piston being slidably disposed within said latch cylinder; said latch member being entered into said cylinder when said latch means is in a latching position; said latch member being withdrawn from said cylinder when said latch means is in an unlatched position; a biasing means urging said latch means to said latching position; said latch member including a latch tip and a cam surface at each end thereof; said cam surfaces being engaged by said piston assemblies during a portion of their movement from said closed to said open positions of said interrupter unit to thereby move said latching means to said unlatched position; said latch means being moved to said unlatched position by the differential gas pressures on each side of said latch piston when said movable contact structure is not connected to said low pressure source and said second end of said latch cylinder is connected to said low pressure source.

4. In combination a low pressure source of dielectric gas, a high pressure source of dielectric gas, a gas blast type interrupter unit, and means interconnecting said sources of dielectric gas and said interrupter unit to form a closed recirculating gas system; said interrupter unit comprising a pair of cooperating contacts having an engaged and a disengaged position; a closing spring urging said cooperating contacts into said engaged position; said cooperating contacts being operable to said disengaged 9 position by means of gas pressure derived from said sources of dielectric gas; a latch means comprising a latch member biased toward a latching position; said latch member being positioned to operatively engage at least one of said cooperating contacts when said cooperating contacts are in said disengaged position and thereby prevent engagement of said cooperating contacts upon a subsequent loss of gas pressure; said latch means also including a latch cylinder and a latch piston slidably disposed therein; said latch member being operatively connected to said latch piston through a first end of said latch cylinder; a second end of said latch cylinder and said first end each being operatively selectively connectible to said high and said low pressure source of dielectric gas; said latch member being moved to an unlatched position by movement of said piston when said first end is connected to said high pressure source and said second end is connected to said low pressure source; said latch member including a cam surface operatively engageable by one of said cooperating contacts during a 0 portion of its movement from said engaged to disengaged position to thereby move said latch member to said unlatched position.

5. In combination a low pressure source of dielectric gas, a high pressure source of dielectric gas, a gas blast type interrupter unit, and means interconnecting said sources of dielectric gas and said interrupter unit to form a closed recirculating gas system; said gas blast type interrupter unit comprising a tank, a stationary contact,

a movable contact, a cylinder, a piston, a latch cylinder,

a latch piston, a latch member; at least said cylinder and said contacts being disposed within said tank; said tank being connected to said high pressure source of dielectric gas; a first end of said latch cylinder being selectively connectible to said low pressure source of dielectric gas and said high pressure source; said cylinder being selectively connectible to said low pressure source; said piston being operably connected to said movable contact, said pistonrbeing slidably disposed within said cylinder and movable between a first position, wherein said movable contact is in engagement with said stationary contact, and a second position, wherein said movable contact is disengaged from said stationary contact; said latch piston being operatively connected to said latch member; said latch piston being slidably disposed within said latch cylinder and movable between a first position, wherein said latch member is clear of said piston, and a second position, wherein said latch member is engaged with said piston when said piston is in said second position to thereby latch said contacts in their disengaged position.

References Cited in the file of this patent UNITED STATES PATENTS 795,024 Case July 18, 1905 859,843 Rogers July 9, 1907 2,290,320 Duffing July 21, 1942 2,385,293 Logan Sept. 18, 1945 2,757,261 Lingal et a1 July 31, 1956 FOREIGN PATENTS 584,992 Germany Sept. 27, 1933 601,144 Germany Aug. 9, 1934 628,853 Germany Apr. 17, 1936 652,721 Germany Nov. 9, 1937 1,007,853 Germany May 9, 1957 593,230 Great Britain .L Oct. 10, 1947 252,627 Switzerland Oct. 1, 1948

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