US2783338A

US2783338A - Operating mechanism for a fluid-blast circuit breaker

Info

Publication number: US2783338A
Application number: US535619A
Authority: US
Inventors: John W Beatty
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1955-09-21
Filing date: 1955-09-21
Publication date: 1957-02-26
Anticipated expiration: 1974-02-26
Also published as: DE1035728B; GB842986A; CH346272A

Description

Feb. 26, 1957 J. W. BEATTY Filed Sept. 21, 1955 3 Sheets-Sheet l 3/ m0 7: is

iii: W v r V -/4 l Fl 1 VF/ 4 1 ,p

I I I i 4 24 g a 1 a Inventor:

John W. Beattg,

J. W. BEATTY Feb. 26, 1957 OPERATING MECHANISM FOR A FLUID-BLAST CIRCUIT BREAKER Filed Sept. 21, 1955 3 Shets-Sheet 2 1n ventor: John W. Beatby, 5 m Hi Attorneg.

Feb. 26, 1957 I J. w. BEATTY 2,783,338

OPERATING MECHANISM FOR A FLUID-BLAST CIRCUIT BREAKER Filed Sept. 21. 1955 3 Sheets-Sheet 3 Inventor: 77 John W.- Bettg,

United States Patent M OPERATING MECHANISM FOR A FLUID-BLAST CIRCUIT BREAKER John W. Beatty, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application September 21, 1955, Serial No. 535,619 16 Claims. (Cl. 200-148) This invention relates to an operating mechanism for a fiuid-blast type of circuit breaker. More particularly, it relates to a fluid-actuated operating mechanism for the type of breaker which comprises a blast valve which can be opened to produce an arc-extinguishing blast of compressed fluid adjacent the contacts of the breaker.

It is important in breakers of this type, first, that the blast valve be capable of opening quickly so as to provide for quick arc-extinction and, second, that the blast valve remain open only so long as is necessary for the arc to be extinguished, so as to prevent wastage ofcompressed fluid. Prior valve-control arrangements of which I am aware have either been complex in structure and operation or have not effectively fulfilled the above two performance requirements.

Accordingly, it is an object of my invention to provide, for the blast valve of a circuit breaker, operating mechanism which is simple in structure and operation and which effectively fulfills the above two performance requirements.

Another object is to provide an operating mechanism which is capable of quickly returning the blast valve to closed position after arc-extinction without the need for the usual heavy valve-return springs and without the necessity for dumping the operating mechanism in order to permit rapid reversal of its parts. Such heavy return springs are undesirable in that they detract from the opening speed of the blast valve, Whereas such dumping means is undesirable because of its complexity both from the 2,783,338 Patented Feb. 26, 1957 tween said pistons. From the instant that pressurized fluid is first admitted into the inter-piston space, the second piston acts, during a contact-opening operation, to seal this space against leakage of the pressurized fluid therefrom. Accordingly, the pressurized fluid acts, after said predetermined valve-opening movement, to return the first piston and valve member to their respective closed positions and to hold the contact in its open position.

In accordance with another feature of a preferred form of my invention, the valve-controlling piston has a larger elfective working area exposed to pressurized fluid admitted to the inter-piston space than its effective working area which is exposed to pressurized fluid admitted to said one end of the cylinder. Moreover, the blast valve member is so located that it closes in the same general direction as the blast flows through the valve so that the blast does not materially interfere with closing of the valve member. As a result, fluid admitted to the interpiston space is etfective to overcome fluid, of equal pressure supplied to said one end and, accordingly, to return said first piston and valve member to closed position.

For a better understanding of my invention reference may be had to 'the following specification taken in connection with the accompanying drawings, wherein: Fig. l is a partially schematiccross-sectional view through a circuit interrupter embodying the operating mechanism of my invention, the interrupter being shown in closed-circuit position; Fig. 2 is'jan enlarged sectional view showing a portion of the operating mechanism at an intermediate point during a circuit opening operation; Fig. 3

is an enlarged sectional view showing the operating standpoint of its own structure and that of the required control equipment.

Another object of the invention is to positively drive the blast valve and the movable contact structure toward their respective fully-open positions substantially in unison and thereafter to positively return the blast valve to closed position while maintaining the movable contact structure in an open position.

Still another object is to provide a compact, reliable, and structurally-simple operating mechanism which is capable of controlling the blast valve and the movable contact structure in the manner set forth in the preceding paragraph.

In accordance with one feature of a preferred form of my invention, the circuit breaker is provided with a normally-closed valve member movable to an open position to produce an arc-extinguishing blast adjacent the breaker contacts, an operating cylinder, and a first piston movably mounted in said cylinder and coupled to said valve member. A second piston, which is coupled to one of said contacts, is also movably mounted in said cylinder and is biased toward engagement with said first piston. Means for admitting pressurized fluid into one end of the cylinder is provided for driving the first piston in a valve-opening direction and for causing said first piston to drive said second piston in a direction to produce contact-opening. Means responsive to a predetermined valve opening movement of said first piston is provided for admitting pressurized fluid into a space bemechanism in its fully-open position; and Fig. 4 is a diagrammatic illustration of a control arrangement for the interrupter of Figs. l-3. Fig. 5 shows a modified form of circuit-interrupter embodying my invention.

Referring now to Fig, 1, there is shown a circuit breaker of thefgas-blast type comprising an interrupting unit generally indicated at 10. This interrupting unit comprises an enclosed interrupting chamber 11 defined, in part, by a spherical metallic casing 12. This casing 12 is mounted on a tubular insulating column 13, preferaably of porcelain, by means of a cylindrical adapter 14 welded within an opening in the lower side of the casing 12. Extending through this porcelain column 13 from a suitable lower terminal (not shown) is an elongated conductive stud 15. At its upper extremity, this stud 15 carries a suitable stationary contact assembly 16 which will soon be described in greater detail.

If desired, the lower portion of stud 15 can be utilized as the primary turn of an instrument current transformer and the supporting column 13 as an insulating housing for the transformer.

Diametrically opposed to the adapter 14 and at the upper side of casing 12, a second cylindrical adapter 18 is welded to the casing 12. This adapter 18 supports a porcelain column 19, which at its upper end carries the upper terminal (not shown) of the breaker. Extending downwardly from the upper terminal through the porcelain column 19 is an elongated conductive stud 20. At its lower extremity, this stud 20 carries an upper stationary contact assembly 22 which corresponds in structure to the lower contact assembly 16.

The upper stud 20 is surrounded by a tubular insulating member 23 suitably sealed at its upper end, (not shown) whereas the lower stud 15 is surrounded by a similar tubular insulating member 24 which serves as a conduit communicating freely with a source (not shown) of high pressure gas. Thus, it will be apparent that the interrupter casing 12 is normally filled with gas at a pressure equal to that of the source, thereby constituting a sustained pressure type gas-blast circuit breaker.

Each of the

stationary contact assemblies

16 and 22 comprises a pair of current-carrying contact fingers 25, biased together by suitable compression springs 27, and an arcing electrode 26 locatedadjacent the fingers 25. Cooperating withthe respective stationary contact assemblies 16 and .22 are a pair of movable contacts 28, each of which is pivotally mounted ona stationary pivot 29. In their respective closed-circuit positions shown in 'Fig. l, the movable contacts 28 are received between the contact fingers 25, which are urged by the springs 27 into high-pressure, currentcarrying engagement therewith.

The movable contacts 28 are supported by means of their current-carrying pivots 29 on a centrally-disposed stationary bracket 31, which, thus, electrically interconnects the two movable contacts 28; The bracket 31 is mounted on one end of a cylinder 32 which, at its other end, is suitably supported from a generally cylindrical casting 33. The casting. 33, at its left hand end, has an annular flange 34 which is-suitably bolted (by means not shown) against a mating flange 35 rigidly carried by the metallic casing 12.

For producing a gas-blast action for extinguishing the arcs which are established by separation of the contacts (as will soon be described), the casting 33 is provided with a normally-closed annular exhaust passage 36 which leads from the interrupting chamber 11 to the surrounding atmosphere. The casting 33 at its right hand end is formed with a pair of generally diametrically-opposed nozzle-type electrodes 38 defining inlets to the exhaust passage 36. For controlling the flow ofarc-extinguishing gas through the nozzle electrode 38 and through the exhaust passage 36, there is provided at the outer end of the exhaust passage 36 a cylindrically-shaped reciprocable blast valvemember 40 which slides smoothly in a surrounding tubular valve housing 41 integrally formed in the casting33. In Fig. l, the valve member 40 is shown in its closed position wherein an annular flange 42 formed at its left hand end sealingly abuts against the stationary flange 34, which serves as a valve seat. The valve member 40 normally maintained in this closed position of Fig. 1 by the action of a contact biasing spring 64 '(soon to be described) and by the action of the pressurized gas within the passageway 36. This gas produces upon the flange 42 an unbalanced force urging the valve member 40 to the left into its closed position.

Since the chamber 11 is normally filled with pressurized gas, it will be apparent that when the valve member 40 is opened by movement to the right (by means soon to be described), gas in the chamber 11 will flow at high speed through the nozzles 38 and out the passage 36 past valve member 40 to atmosphere, as is indicated by the arrows shown in Fig. 1. This rapid flow of gas through the nozzles 38 creates an axial arc-enveloping blast which, in a known-manner, acts rapidly to ex tinguish the arcs which are drawn adjacent the nozzles by movement of the movable contacts 28 away from their fixed fingers 25.

For operating the blast valve 40 and the movable contacts 28, I provide a combined operating mechanism 50 constructed in accordance with the present invention. This mechanism 50 comprises two cooperating

pistons

51 and 52 mounted for reciprocation in the cylinder 32. The piston 51 is connected to the blast valve member 40 by means of a piston rod 54 which is shown extending through a central opening in the valve member 40. This piston rod 54 has suitable threads formed at its outer end for receiving a retaining nut 55 which clamps the valve member 40 against a shoulder 56 formed on the piston rod 54. The piston rod 54 also extends, in slidable relationship, through a central opening in a stationary end wall 57 provided fo rthe cylinder 32. A suitable seal 57 mounted in this end wall 57 encircles the piston rod 54 and prevents gas from leaking around the piston rod.

The other piston 52 serves to control the movable con tacts 28 and is coupled to these contacts 28 by means of a piston rod 58, a crosshead 59, and a pair of connecting links 60. The crosshead 59 is rigidly secured to the piston rod 58 by suitable clamping means, Whereas the connecting links 60 are pivotally connected at 61 and 62 to the crosshead and the movable contacts, respectively. A heavy compression spring 64 bearing at one end against the crosshead 59 provides a force biasing the movable contacts 28 toward closed position. The other end of the compression spring 64 bears against a suitable annular stop 65 which is mounted on a series of axially extending bolts adjustably threaded into the bracket 31.

The contact-controlling piston 52 is formed with a skirt portion 66, which in Fig. l, is shown abutting the valve-controlling piston 51 and forming a space or chamber 67 between the two pistons. The skirt 66 is provided with a series of notches, or recesses, forming radial ports 68 extending through the skirt and into communication with the chamber 67. A circumferential bevelled groove 69 formed in the external wall of the skirt 66 assures communication between these radial ports external of the skirt 66. The purpose of this chamber 67 and the radial ports 68 will soon appear more clearly.

Operation of the

pistons

51 and 52 is initiated by supplying pressurized gas to a small clearance space 70 located at the left hand end of cylinder 32. Normally, this clearance space 70 is vented to atmosphere by means of a two-position control valve 71 which is mounted adjacent a duct 72 which leads into the clearance space 70. The control valve 71 comprises a casing 73 having. two

radial ports

74 and 75, the first of which 74 communicates with the surrounding atmosphere through a suitable exhaust duct 76 and the other of which 75 directly communic'ates with the pressurized gas in the chamber 11. Flow through these

ports

74 and 75 is controlled by means of a reciprocable valve element 77, which is releasably held in the elevated position shown in Fig. 1. In this elevated position, a passageway 78 extending through the valve element 77 afiiords communication between the lead-in duct 72 and the exhaust duce 76 whereas the port 75 is sealed off by the valve element 77. As a result, when the control valve element 77 occupies the position of Fig. l, the clearance space 70 is vented to atmosphere and is sealed off from the chamber 11.

In order to supply pressurized gas to the clearance space 70, it is necessary to move the valve element 77 downwardly to seal off the vent port 74 and to establish communication between the inlet port 75 and the lead-in duct 72. To this end, I provide a compression spring 79 biasing the valve element toward its lower position and a releasable electroresponsive latch 80 which, in its latched position shown in Fig. l, is eifective to hold the valve element in its elevated position against the bias of the spring 79. Release of the latch 80 can be effected either manually or in response to predetermined electrical conditions by energizing the coil 81 of the latch. For manual release, a push button switch 82 would be closed to complete an energizing circuit for the coii 81 of the latch. For release in response to predetermined electrical conditions, e. g., a fault on the power circuit controlled by the breaker, the contacts 83 of a suitable conventional fault responsive relay (not shown) would be a operated to closed position to complete an energizing circuit for the coil 81. In either case, the latch 80 would be released to permit the spring 79 to drive the control valve element 77 into its lower position.

For simplicity, this control system has been schematically shown closely adjacent the valve which, of course, is at high potential. Actually, this low voltage control circuit, preferably D.C., would be at the ground level, and the valve stem would be a long insulating rod which, for weather protection, preferably would run down inside of the supporting

columns

13 and 24.

When the control valve element 77 reaches the abovedescribed lower position, which is shown in Fig. 2, compressed gas flows from the chamber 11 through the port 75 and the lead-in passage 72 into the clearance space 70. Pressure in the clearance space quickly builds up and drives the piston 51 rapidly to the right. Since the contact-controlling piston 52 is then abutting the piston 51, it too is driven rapidly to the right. This movement to the right takes place against the bias of closing spring 64 and also against the operation of fluid contained within a restricted chamber 89 at the right of contact piston 52 as will be explained in greater detail hereinafter. This movement of the piston 51 to the right immediately opens the blast valve member 40, whereas this movement of piston 52 to the right immediately initiates opening movement of the contacts 28. Preferably, the contacts 28 are provided with an opening wipe of sutlicient length to permit the blast to be well established at'the instant of arc initiation.

To prevent wastage of compressed gas, it is important that the blast valve member 40 be open only so long as is necessary for the arc to be extinguished by the gasblast. As soon as extinction of the arc is assured, the blast valve member should be quickly returned to its closed position shown in Figs. 1 and 3 to prevent further consumption of the compressed gas. To this end, I provide a by-pass passage 85 which extends from the lefthand end-of the cylinder 32 to apreselec'ted intermediate point in the bore of the cylinder. When the

pistons

51 and 52 occupy the position of Fig. 1, .the outer periphery of the skirt portion 66 of piston 52. covers and closes off the bypass passage 85. The inter-piston chamber 65 is then at atmospheric pressure dueto communication through a one way valve 92 to atmosphere via duct 72;

When the two

pistons

51 and 52 are moved simultaneously to the right from the position of Fig. l, as above-described, the by-pass 85 remains covered until the peripheral groove 69 is moved into registry with the mouth, or port, of the by-pass. At this instant, which is illustrated in Fig. 2, compressed gas flows from the by-pass 85 through the groove 69 and the radial ports 68 into the chamber 67, which is then sealed against leakage therefrom at least partially by the piston'52. As a result, the fluid pressure within the chamber 67 quickly builds up to substantially the same value as the pressure at the left hand side of piston 51. Because that working 'surface of piston 51 which is exposed to pressurized fluid within the chamber 67 is substantially larger than that working surface which is exposed to pressure tending to open the valve, the piston 51 is subjected to an unbalanced force which quickly drives the piston 51, together with valve member 40, back into the closed position shown in Fig. 3, as is desired. The fact that the valve member 40 closes in the same general direction as the blast flows through the valve allows the valve to close without material opposition from the blast. During this return movement of the valve member and its piston 51, the fluid at the left hand side of the piston 51 is expelled either through the by-pass passage 85 or through the port 75 leading to the main chamber 11. The mouth of the by-pass 85 is so located along the length of the cylinder wall that the blast valve member 40 is returned to closed position only after the

pistons

51 and 52 have moved sufliciently to assure that the arc drawn by separation of the contacts will have been extinguished.

The above-described difference in the opening and closing working surface areas of the valve piston 51 is due primarily to the presence of the large-diameter piston rod 54. Since this piston rod 54 projects from the opening working surface through a sealed opening to atmosphere, it will be apparent that the efiective area of this opening working surface is substantially smaller than that of the closing working surface, which is disposed at the opposite side of the pistonSl.

As will be apparent from Fig. l, the valve piston 51 has projecting from its left hand face a shoulder portion which is received in a suitable groove in the end wall 57 to provide a dashpot effect for softening the closing impact of the blast valve.

It should be apparent from the description hereinabove set forth that no heavy return springs are necessary in order. to restore the blast valve 40 to closed position after circuit interruption. The differential relationship between the opening and closing working areas of piston 51 is sufiicient to provide for quick and positive restoration of the valve member. Although not required, in some cases it might be desirable to provide the blast valve with a light return spring (not shown) which would act to insure that the blast valve remained closed even when there was no pressurized fluid in the chamber 11. Such a spring-would facilitate initial filling of the chamber 11 after it had been evacuated.

The admission of fluid into the inter-piston chamber 67, in addition to closing the valve member 40 as abovedescribed, also maintains the movable contacts 28 in open position. More particularly, so long as the control valve element 77 remains in its lower position shown in Figs. 2 and 3, the pressure in the space between the two pistons corresponds to that of the chamber 11 and is sufficient to overcome the action of the closing spring 64, and, thus, to maintain the contacts 28 in open position. During this breaker-open interval, the high internal pressure within the. chamber 11 provides adequate high dielectric insulation for the relatively short isolating gap which now is maintained between the spaced contacts or electrodes.

Another feature of my invention which can be observed from Figs. 2 and 3 is that the opening stroke of piston 52 is positively terminated when the peripheral groove 69 is moved into alignment with the mouth of by-pass 85. Further opening travel beyond this point is positively prevented by the right hand end wall of the cylinder 32. So limiting the opening stroke of piston 52 insures that the groove 69 will not be moved past the mouth of bypass before sufficient pressure can be bulit up in chamber 67 to elfect valve-closing movement of the other piston 51.

It will be apparent from the above description that substantially all fluid-pressure forces acting to drive the contact-controlling piston from the closed position of Fig. 1 into the open position of Fig. 2 are supplied through the valve controlling piston 51, and, as a result, there is no material independence of motion between these two pistons until the bypass 85 is opened. This .absence of such independance further assures that the by-pass 85 will be opened only after the blast valve has completed its required opening stroke.

The speed at which the two

pistons

51 and 52 move to the right during the above-described opening operation is controlled by dashpot means forming a part of the operating mechanism. More particularly, the cylinder space 89 to the right of the contact-controlling piston 52 is sealed otf from the chamber 11 and communicates with atmosphere through a small metering passage 90. Initial opening movement of the

pistons

51 and 52 is permitted to take place at relatively high speed due to the ease with which the gas within the dashpot space 89 is initially compressed and due to the relatively unrestricted access to the metering passageway 90. However, toward the end of the stroke of piston 52, the compression has been sutficiently increased and access to the metering passageway has been sufiiciently restricted to provide a retarding action which smoothly decelerates the piston 52. This restricted access at the end of the stroke results primarily from the relatively close fit between the projecting piston hub 91 and the mating cylindrical wall of the recessed portion located at the right hand end of the main cylinder. Although, in the embodiment of Figs. 1-3, I have utilized the space at the right hand side of the piston 52 for a gas-filled dashpot, it will be apparent that, if a suitable overflow reservoir is provided, thisspace can equally well be used for a liquidfilled dashpot having appropriate decelerating characteristics.

Assume now that the circuit breaker is in its fully open position, i. e., with the

pistons

51 and 52 occupying the position of Fig. 3, and that it is desired to close (or reclose) the breaker. This can be accomplished simply by lifting the control valve element 77 from its lower position of Fig. 3 into its elevated position, thereby establishing communication between the exhaust port 74- and the lead-in passage 72 so as to vent the lead-in passage 72 to atmosphere. As a result, pressurized fluid flows quickly and freely to atmosphere from the interpiston space 67, through the by-pass 85, the clearance space 70, and the lead-in passage 72. The sudden venting of the space 67 in this manner permits the then-compressed closing spring 64 quickly to expand and thereby drive the contact piston 52 to the left, thus moving the contacts 28 rapidly toward closed position. After the contact piston 52 has moved past the point wherein its skirt 66 covers the mouth of the by-pass 85, continued venting of the space 67 takes place through the check valve 92 provided in the valve piston 51. At the end of the closing stroke, the contact piston 52 occupies the position shown in Fig. 1 wherein it abuts the valve piston 51.

The above-described lifting of the control valve ele ment 77 to effect closing of the breaker can be accomplished in any suitable manner, as by means of a solenoid such as shown at 94 in Fig. 4. Referring now to Fig. 4

when this solenoid 94 is energized, as by closing of' a' control switch 95, an energizing circuit for the solenoid is completed and the solenoid responds by driving the operating rod for the valve element 77 upwardly. The solenoid armature is provided with contacts 96 which are arranged to close at the end of the upward stroke, thereby energizing an auxiliary relay 97 which responds by opening its contacts 98 to interrupt the energizing circuit for the solenoid. Under normal conditions, the valve element 77 is then held in its elevated position by means of the latch 80. However, should the breaker be closed on a fault, the fault responsive relay which has the contacts 83 would close its contacts 83 to trip the latch 80. This would cause the spring 79 immediately to drive the valve element 77 downwardly. The solenoid would offer no significant resistance to this downward motion since it had been deenergized at the end of its upward stroke, in the manner previously described.

If the circuit breaker automatically reopens in response to a fault, it should not reclose until the operator has released the control switch 95 and subsequently returned it to the closed position. In other words, the circuit breaker should close only once in response to a single closing of the control switch 95, and no pumping or repeated reclosures should take place in response to such single closing of control switch 95. Such pumping is effectively prevented in my control arrangement by a seal-in circuit 99 for the auxiliary relay 97. This seal-in circuit 99, which extends through seal-in contacts 99a, maintains the relay 97 energized even when the solenoid contacts 96 are opened in response to downward, or breaker-opening, movement of the valve element 77. Thus, the contacts 98 of the auxiliary relay 97 remain open so long as the control switch 95 is held in closed position, thereby preventing further energization of the solenoid 94 during this interval. This prevents additional reclosures of the breaker, as is desired. Whenthe control switch 95 is released and thus returned to open position, it interrupts the seal-in circuit 99 permitting the auxiliary relay 97 to reset to its normal position, thereby restoring the solenoid energizing circuit to an operative condition. As a result, subsequent closing of the control switch 97 after such release will energize the solenoid 94 and initiate another breaker-closing operation, as may be desired.

For enabling the entire'blast valve and operating-mechanism assembly'to be removed from the casing 12 so as to permit repair or maintenance; I provide an access opening 100 which is normally sealed by a pivotally mounted cover 101. If it is desired to=remove this entire assembly from the casing 12, all that' is necessary is that the cover be opened, the mounting bolts (not shown) at

flanges

34, 35 unfastened, and the valve .71 disconnected. If the movable contacts 28 are then suitably held in open position, as by an appropriate jack-screw (notshown) compressing the closing spring 64, the entire assembly can be withdrawn through the access opening 100;

In Fig. 5, I have shown a modified form of circuit interrupter which corresponds generally to the interrupter of Figs. 14 except for the dashpot means and the contact-controlling spring means. Accordingly, correspondingparts of these two interrupters have been assigned corresponding reference numerals. Referring now to the modification of Fig. 5, it will be apparent that the main piston 52 no longer serves as a dashpot piston since the cylinder space at its right hand side is vented comparatively freely to atmosphere through a duct 108 which remains accessible throughout the entire opening stroke. Dashpot action for the opening stroke is provided by means of an auxiliary piston 110 which is slidably mounted within an auxiliary cylinder 112 rigidly supported from the right hand end of the main cylinder 32. A piston rod 58 integral with the main piston 52 extends, in sealed relationship, through an end wall 114 common to the two cylinders. The auxiliary piston 110 is rigidly clamped to the pistonrod 58 intermediate its ends by means of a suitable retaining nut 116. At its outerend, the piston rod '58 carries a crosshead 59 which is pivotally-connected to the-movablecontacts 28 in thesarne manner as described in connection with Fig. 1.

The auxiliary cylinder 112 is-provided with an outer end wall 118 containing a central opening through which the piston rod 58 extends inslidable relationship. For reasons which will soon be. apparent, the end wall 118 also contains a metering passage 119 and. a check. valve 120 permitting fluid to flow therethrough only in a direction out of the cylinder. The piston rod 58 contains a keyway port 122 which permits fluid to flow through the central opening in the end wall 118 when the piston rod 58 is in or adjacent the closed-circuit position of Fig. 5.

In the position of Fig. 5, the movable contacts 28 are biased into closed position by means of overcenter compression springs 125. These springs 125 at their inner ends are supported on telescoping couplings 126 which, in turn, are pivotally-connected to the movable contacts 28 by pins 127. At their outer ends, the springs 125 are supported on suitable pivotally-mounted guide rod couplings 128. When the contacts 28 are driven in an opening direction about their respective pivots 29, each of the springs 125 is compressed until its pin 127 moves past the line connecting pivot 29 and the pivot for guide rod 128. At this point the springs 125 are free to expand and aid the opening motion of contacts 23.

Opening of the contacts 28 is initiated by driving the

pistons

51 and 52 to the right in the same manner as described in connection with Figl. The

dashpot

110, 112 permits this opening action to be initiated at a relatively high speed since the keyway port 122 is then open and air ahead of piston 110 can flow freely therethrough. After a predetermined portion of the opening stroke has been completed, the piston rod 58 has moved sufliciently to the right to render the keyway port 122 no longer effective to vent air ahead of piston 110. Thereafter, air can flow only through the restricted passa es 119 and 120, and, as a result, there is established at the end of opening stroke a retarding action which smoothly decelerates the pistons and contacts.

The movable contacts 28 are held in their respective 75open-circuit positions by fluid pressure maintained between the

pistons

51 and 52 in the same manner as described in connection with Fig. 1. The overcenter springs 125 also provide a force which tends to hold the contacts in open-circuit position. These two forces which tend to hold the contacts open are opposed by the fluid pressure forces exerted on the auxiliary piston structure 110, 116. This will be apparent from Fig. 5, where it can be seen that the auxiliary piston structure 110, 116 has a pair of opposed working

surfaces

130 and 131 which are exposed to pressurized insulating fluid from the casing of the surrounding interrupter, the surface 130 receiving fluid through an opening 133 and the surface 131 through metering passage 119. Since the portion of piston rod 58 extending through the left-hand end wall 114 has a substantially larger cross-section than that portion extending through the right hand end wall 118, it will be apparent that the effective working area of the piston structure which is exposed to pressurized fluid tending to drive the piston toward the left is substantially larger than that exposed to pressurized fluid tending to drive the piston toward the right. The result is that the piston structure 110, 116 is always acted upon by a pneumatic force from the right which tends to close the contacts and which varies directly in accordance with the fluid pressure of the insulating gas in the surrounding interrupter.

Assume now that the interrupter is in fully-open position, i. e., with the contacts 28 fully separated from their respective stationary contacts and the

pistons

52 and 110 held in their extreme right hand positions by pressurized fluid in the inter-piston space 67, and that it is desired to close the interrupter. To accomplish this, the inter-piston space 67 is vented to atmosphere in the same manner as described in connection with Fig. 1. In response to such venting, the fluid pressure forces exerted on the auxiliary piston structure 110, 116 become operative to drive the pistons 52 and-110 to the left and to carry these pistons, together with the contacts 28, into their respective closed-circuit position. The overcenter springs 125 resist initial displacement of these parts from their respective closed-circuit positions, but if the fluid pressure within the interrupter is above a predetermined safe level, the pressure forces on the auxiliary piston 110,

116 predominate and overcome the resistance of the overcenter springs. Once the contacts 28 are moved beyond dead center, the springs 125 would, of course, aid this contact-closing action and apply a desirable added closing force as the contacts approached engagement. The keyway port 122 also contributes to increased closing force near the end of the stroke by permitting a comparatively free influx of air into the cylinder 112 near the end of the stroke.

The fact that the closing force exerted on the auxiliary piston 110, 116 varies directly in accordance with the fluid-pressure in the surrounding circuit interrupter is effectively utilized to prevent closing of the interrupter when the pressure therein is below a safe level. For example, if for some reason, the pressure within the interrupter chamber should fall below a predetermined safe level when the contacts were in fully-open position, then evacuation of the inter-piston space 67 would not produce closing of the contacts. This is the case because, under such conditions, the differential closing force on the piston structure 110, 116 is insufiicient to overcome the opposition of the overcenter springs 125. Thus, un der such conditions, the overcenter springs would safely maintain the contacts 28 in fully-open position even though the inter-piston space 67 was vented to atmosphere.

No mention has been made in the above discussion of the force due to pressure acting on the projecting end of the piston rod 58. Since this projecting end is immersed in the pressurized fluid of the interrupter chamber, it too is always subjected to a force acting toward the left with a magnitude varying in accordance with the pressure of the fluid in the interrupter. Thus, even considering this added force, the closing force exerted on the dashpot piston structure varies directly in accordance with the fluid pressure in the surrounding interrupter.

The modification of Fig. 5, like that of Fig. 1, can, if desired, be provided with alight-weight spring which tends to bias the blast valve closed to facilitate initial filling of the arc-extinguishing chamber of the interrupter.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects and I, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a fluid-blast type of circuit breaker having separable contacts, a normally-closed valve member movable to an open position to produce an arc-extinguishing blast adjacent said contacts, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston movably mounted in said cylinder and coupled to one of said contacts, means biasing said one contact into closed position and said second piston toward engagement with said first piston, means for admitting pressurized fluid into one end of said cylinder for driving said first piston in a di rection to open said valve member and in a direction to produce contact-opening movement of said second piston, a normally-closed passageway adapted when open to supply pressurized fluid to a space between said pistons whereby to urge said second piston in a contactopening direction and said first piston in a valve-closing direction, and means responsive to a predetermined valveopening movement of said first piston for opening said passageway and admitting fluid to said inter-piston space whereby then to close said valve member and to hold said one contact in open position, said second piston acting from the instant that said passageway is first opened to seal said inter-piston space against leakage therefrom during a contact-opening operation.

2. The circuit breaker of claiml in combination with means for evacuating said inter-piston space after a contact-opening operation to permit said biasing means to return said one contact toward closed position.

3. In a fluid-blast type of circuit breaker having separable contacts, a normally-closed valve member movable to an open position to produce an arc extinguishing blast adjacent said contacts, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston movably mounted in said cylinder and coupled to one of said contacts, said first piston having a valve-closed position adjacent one end of said cylinder, said second piston having a contactopen position located at the other end of said cylinder and a contact-closed position located adjacent the valveclosed position of said first piston and on a side of said first piston opposite to said one end of the cylinder, means for admitting pressurized fluid into said one end of the cylinder for driving said first piston in a direction to open said valve and for causing said first piston to drive said second piston in a direction to produce contact opening, and means responsive to a predetermined valve-opening movement of said first piston for admitting pressurized fluid into a space between said pistons whereby then to return said first piston to valve-closed position and to hold said second piston in a contact open position, said inter-piston space and said other end of the cylinder being sealed against communication during a contact-opening operation at least from the instant that pressurized fluid is first admitted into said inter-piston space.

4. The combination of claim 3 in which said lastmentioned means comprises a by-pass passage arranged to interconnect said one end of the cylinder and said inter-piston space, said by-pass passage being closed oti 11 by the outer periphery of said second piston until completion of said predetermined valve-opening movement whereupon said passage is opened to supply pressurized fluid to said inter-piston space.

5. The combination of claim 3 in which the other end of said cylinder forms a fluid-confining dash-pot chamber containing fluidwhich opposes the contact-opening movement of said second piston.

6. In a fluid-blast type of circuit breaker having separable contacts, a normally-close valve member movable to an open position to produce an arc-extinguishing blast adjacent said contacts and past said valve member, said valve member being so located that opening movement thereof is in a direction generally opposite to the direction of the blast in the region of the valve member and closing movement is in the same general direction as that of the blast, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston movably mounted in said cylinder and coupled to one of saidcontacts, said first piston having a valve-closed position adjacent one end of said cylinder, said second piston having a contactclosed position located adjacent the valve-closed position of said first piston and on a side of said first piston opposite to said one end of the cylinder, means for admitting pressurized fluid into said one end of the cylinder for driving said first piston in a direction to open said valve member and for causing said first piston to drive said second piston in a direction to produce contactopening movement, piston control means responsive to a predetermined valve-opening movement of said first piston for returning said first piston to valve-closed position and for holding said second piston in a contactopen position, said piston control means comprising a normally-closed passageway which in response to said predetermined valve-opening movement is opened to admit pressurized fluid to a space between said pistons, said second piston acting from the instant that said passageway is first opened to seal said inter-piston space against leakage therefrom during a contact-opening operation, the effective working area of said first piston exposed to pressurized fluid admitted to said inter-piston space being substantially larger than the effective working area of said first piston exposed to pressurized fluid at said one end of the cylinder.

7. In a fluid-blast type of circuit breaker having separable contacts, a normally-closed valve member movable to an open position to produce an arc-extinguishing blast adjacent said contacts, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston movably mounted in said cylinder and coupled to one of said contacts, said first piston having a valve-closed position adjacent one end of said cylinder, said second piston having a contactclosed position located adjacent the valve-closed position of said first piston and on a side of said first piston opposite to said one end of the cylinder, means for admitting pressurized fluid into said one end of the cylinder for driving said first piston in a direction to open said valve member and for causing said first piston to drive said second piston in a direction to produce contactopening movement, and a passageway communicating with said cylinder and terminating in a month which is normally covered by the outer periphery of said second piston and which when uncovered directs pressurized fluid from said passageway into a space between said pistons whereby to urge said first piston in a valve-closing direction and 'said second piston in a contact-opening direction, one of said pistons having a recessed portion in its outer periphery which after a predetermined valveopening movement of said first piston is moved into registry with said mouth whereby to uncover said mouth and cause pressurized fluid to flow into said inter-piston space.

8. The circuit breaker of claim 7 in combination with 12 motion-limiting means for preventing said second piston from moving in a contactope'n'ing direction past the position wherein said recessed portion registers with said mouth.

9. In a fluid-blast type of circuit breaker having separable contacts, a normally-closed valve member movable to an open position to produce an arc e'xtinguishing blast adjacent said contacts, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston movably mounted in said cylinder and coupled to one of said contacts, said first piston having a valve-closed position adjacent one end of said cylinder, said second piston having a contact-closed position located adjacent the valve-closed position of said first piston and on a side of said first piston opposite to said one end of the cylinder, means for admitting pressurized fluid into said one endof the cylinder for driving said first piston in a direction to open said valve member and for causing said first piston to drive said second piston in a direction to produce contact-opening movement, piston control means responsive to a predetermined valve-opening movement of said first piston for returning said first piston to valve closed position and for holding said second piston in a contactopen position, said piston control means comprising a passageway which when open supplies pressurized fluid to a space between said pistons, said passageway normally being closed off by the-outer periphery of said second' piston and being openedby said second piston at the end of said predetermined valve ope'ning' movement.

10. In a valve mechanism for controlling the flow of pressurized fluid through a circuit interrupter, a valve member movable between. closed and open positions to produce in response to valve-opening a blast of fluid past said valve member, said valve member being so located that closing movement thereof'is in a direction generally the same asthe direction of the blast in the region of said valve member, an operating cylinder, a piston movably mounted in said cylinder andcoupled to said valve member, said piston having a pair of opposed working surfacesone of which constitutes an opening working surface for transmitting force in a direction to open said valve and the other of which constitutes a closing working surface for transmitting force in a direction to close said valve, means for supplying pressurized fluid to said opening working surface for opening said valve member, a normally-closed passage adapted when open to supply pressurized fluid to said closing working surface, means for opening said passage in response to predetermined valve opening movement of said piston thereby to supply pressurized fluid to said closing working surface, the effective area of said closing working surface being substantially larger than the effective area of said opening working surface whereby pressurized fluid supplied to said closing working surface is effective to overcome fluid of equal pressure supplied to said opening surface and to return said piston and valve member to closed position.

11. In a valve mechanism for controlling the flow of pressurized fluid through a circuit interrupter, a valve member movable between closed and open positions to produce in response to valve-opening a blast of fluid past said valve member, said' valve member being so located that closing movement thereof is in a direction generally the same as the direction of the blast in the region of said valve member, an operating cylinder, a piston movably mounted in said cylinder and coupled to said valve member, means for admitting pressurized fluid into the cylinder space at one side of said piston for driving said piston in a direction to open said valve memher, a normally-closed by-pass passage extending through a wall of said cylinder and arranged to communicate with opposite sides of said piston, means for opening said by-pass passage inresponse to'= predetermined move- -ment of saidpiston in a valve opening direction whereby to admit pressurized fluid from said one to the other side of said piston, the effective working area of said piston exposed to fluid admitted to said other side being substantially larger than the effective working area of said piston exposed to fluid at said one side whereby admission of fluid to said other side returns said piston and valve member to closed position.

12. In a valve mechanism for controlling the flow of pressurized fluid through a circuit interrupter, a valve member movable between closed and open positions to produce in response to valve-opening a blast of fluid past said valve member, said valve member being so located that closing movement thereof is in a direction generally the same as the direction of the blast in the region of said valve member, an operating cylinder, a piston movably mounted in said cylinder and coupled to said valve member, means for admitting pressurized fluid into one Bid of said cylinder for driving said piston in a direction to open said valve member, a normally-closed passage adapted when opened to supply pressurized fluid to the other end of said cylinder, means for opening said passage in response to predetermined valve opening movement of said piston whereby to supply pressurized fluid to said other end of the cylinder, the effective working area of said piston exposed to fluid admitted to said other end of the cylinder being substantially larger than the effective working area of said piston exposed to fluid at said one end whereby admission of fluid to said other end returns said piston and valve member to closed posinon.

13. In a valve mechanism for controlling the flow of pressurized fluid through a circuit interrupter, a valve member movable between closed and open positions to produce in response to valve-opening a blast of fluid past said valve member, said valve member being so located that closing movement thereof is in a direction generally the same as the direction of the blast in the region of said valve member, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston also movably mounted in said cylinder, means biasing said second piston toward a position adjacent one side of said first piston, means for supplying pressurized fluid to the opposite side of said first piston for driving said first piston into driving relationship with said second piston and for opening said valve member, a passageway communicating with said cylinder and terminating in a mouth which is normally covered by said second piston and which when uncovered directs pressurized fluid into a space between said pistons whereby to urge said first piston back 14 toward its valve-closed position, one of said pistons having a recessed portion which after a predetermined valveopening movement of said first piston is moved into registry with said mouth whereby to uncover said mouth and cause pressurized fluid to flow into said inter-piston space.

14. The valve mechanism of claim 13 in combination with motion-limiting means for preventing said second piston from moving past the position wherein said recessed portion registers with said mouth.

15. in a valve mechanism for controlling the flow of pressurized fluid through a circuit interrupter, a valve member movable between closed and open positions to produce in response to valve-opening a blast of fluid past said valve member, said valve member being so located that closing movement thereof is in a direction generally the same as the direction of the blast in the region of said valve member, an operating cylinder, a first piston movably mounted in said cylinder and coupled to said valve member, a second piston also movably mounted in said cylinder, means biasing said second piston toward a position adjacent one side of said first piston, means for supplying pressurized fluid to the other side of said first piston for driving said first piston into driving relationship with said second piston and for opening said valve member, piston control means responsive to a predetermined valve-opening movement of said first piston for returning said first piston to valve-closed position, said piston control means comprising a passage which when opened supplies pressurized fluid to a space between said pistons, said passageway normally being closed off by the outer periphery of said second piston and being opened by said second piston near the end of said predetermined valve-opening movement.

16. The circuit breaker of claim 3 in which substantially all fluid-pressure forces acting to drive said second piston from said contact-closed position to the region of said contact-open position are supplied through said first piston, thus tending to preclude independence of motion of said two pistons during movement of said sec: ond piston from said contact-closed position to the region of contact-open position.

References Cited in the file of this patent UNITED STATES PATENTS 2,153,400 Trencham Apr. 4, 1939 2,290,726 Bartlett July 21, 1942 2,665,351 Forwald Jan. 5, 1954