US2911492A - Operating mechanism for a fluid blast circuit breaker - Google Patents

Description

OPERATINC MECHANISM FOR A FLUID BLAST CIRCUIT BREAKER Filed Feb. 25, 1957 2 Sheets-Sheet 1 Figj.

Inventor: John W. Beattg,

by M

Hi Attorneg.

Nov. 3, 1959 J. w. BEATTY 2,911,492

OPERATING MECHANISM FOR A FLUID BLAST CIRCUIT BREAKER Filed Feb. 25. 1957 2 Sheets-Sheet 2 Inventor: John W. Beattg,

by A

United States Patent MECHANISM FOR A FLUID BLAST CIRCUIT BREAKER John W. Beatty, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application February 25, 1951, Serial No. 642,100

1 Claims. 01. 200-32 OPERATING This application is a continuation-impart of my application S.N. 535,619, now Patent No. 2,783,338, filed September 21, 1955, and issued February 26, 1957, as Patent No. 2,783,338.

The present invention relates to an operating mechanism for a fluid blast type circuit breaker, and, more particularly, to an operating mechanism for a circuit breaker of the type which has its contacts located within an interrupter containing pressurized arc-extinguishing The arc-extinguishing ability of such fluid varies directly with its pressure. Thus, if there is an abnormal loss of fluid pressure, it is desirable that no are be estab' lished within the arc-extinguishing fluid so long as the pressure remains below a predetermined safe level.

For preventing the establishment of an arc while such conditions prevail, some circuit breaker users desire that the contacts be permitted to change position only when the pressure is appreciably above the predetermined safe level. To this end, if the contacts are in fullyopen position when an abnormal pressure loss occurs, they should remain fully-open until a safe pressure can be restored. Similarly, if they are fully-closed during this interval, they should remain fully-closed until a safe pressure can be restored.

In a circuit breaker of the type shown and claimed in my aforesaid application S.N. 535,619, fluid pressure :forces are utilized to aid in holding t e contacts open. These fluid pressure forces are dependent upon the pres sure of the arc-extinguishing fluid since the contact-operating mechanism freely communicates with the arcextinguishing fluid in the interrupter. Thus, it will be apparent that an abnormal pressure loss in the arc-extinguishing fluid would lessen the net forces holding the contacts open, thus tending to increase the possibility of contact-closing as the pressure decreased.

.An object of my invention is to insure that, for a cir- \Cllit breaker of this general type, no contact-closing results from abnormal pressure losses in the arc-extinguishdng fluid communicating with the operating mechanism.

Another object is to provide a simple contact-control- Eling arrangement which allows the contacts to change position only when the pressure of the arc-extinguishing fluid is above a predetermined minimum safe level.

If thecontacts are closed when an abnormal pressure iloss occurs, it is an object of my invention that they reunain closed even against short-circuit currents.

In carrying out my invention in one form, I provide :a circuit interrupter which has its contacts immersed in :a pressurized arc-extinguishing fluid. The contacts are :moved from closed to open position by a fluid-actuated operating mechanism and are held in open position by pressurized arc-extinguishing fluid supplied from the interrupter. An abnormal loss of pressure in the arc-extinguishing fluid tends to decrease the net force holding the contacts open, but the contacts are prevented from .closing under these conditions by overcenter springs which resist movement of the contacts out of their fully-open position. Normal contact-closing is produced by addi- I interrupter remain in fluid communication, this additional fluid-pressure means is ineiiective to overcome the overcenter springs.

For a better understanding of the invention, reference may be had to the ;following specification taken in connection with the accompanying drawings, wherein:

Fig. 1 is a partially schematic sectional view of an interrupter embodying my invention. The interrupter is shown in the contact-closed position.

Fig. la is a plan view of a portion of the interrupter in the region of its contacts.

Fig. 2 is a view similar to that of Fig. 1 but with the interrupter in the contact-open position.

Fig. 3 shows a modified form of control circuit which can be utilized for the interrupter.

Referring now to Fig. 1, there is shown a circuit breaker of the gas-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, preferably 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 whichwill soon be described in greater detail.

Diametrically opposed to the adapter 14 and at the up per 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 struc-' ture to the lower contact assembly 1 6.

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 two side-by-side pairs of conventional currentcarrying contact fingers 25. The fingers of each pair are biased together by suitable compression springs 27, and an arcing electrode 26 is located adjacent the fingers 25. Cooperating with the respective stationary contact assemblies 16 and 22 are a pair of movable contact blades 28. Each of these blades 28 is disposed transversely to its stationary contact assembly and is pivotally mounted on a stationary pivot 29. As shown in Fig. 1a, each of these blades 28 comprises a pair of spaced-apart interconnected segments 28a. tions shown in Fig. 1, each segment of blade 28 is re: ceived between a pair of contact fingers 25, and the contact'fingers 25 are urged by the springs 27 into highpressure, current-carrying engagement with the segments. As shown in Figs. 1 and 1a, the movable contact blades 28 are supported by means of their pivots 29 on stationary brackets 31, which are integral with one end of a stationary cylinder 32 Suitable resilient washers 29a urge In the closed-circuit posithe contact segments into current-carrying engagement with the brackets 31. Accordingly, the brackets 31 together with the cylinder 32 form a conductive path electrically interconnecting the two movable contacts 28. The shape of this, conductive path in relationship to the conductive path through the contacts serves an important purpose which will appear more clearly hereinafter.

The cylinder 32, at its left hand end, is suitably supported from a generally cylindrical housing 33.

which is suitably bolted (by means not shown) against a mating flange 35 rigidly carried by the metallic casing 12.

For'p'roducing a gas-blast action for extinguishing the arcs which are established by separation of the contacts (as will soon be described), the housing 33 is provided with a normally-closed annular exhaust passage 36 which leads from the interrupting chamber 11 to the surrounding atmosphere. The housing 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 of arc-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 valve member 40 which slides smoothly in a surrounding tubular valve housing 41 integrally formed in the housing 33. In Fig. 1,'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 is normally maintained in this closed position of Fig. 1 by the action of a suitable compression spring 44 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 acts rapidly to extinguish the arcs which are drawn adacent the nozzles by movement of the movable contacts 28 away from their fixed fingers 25.

A factor which contributes to rapid extinction of the arcs is that, for each contact assembly, the electrical circuit extending through the contacts forms a loop having a magnetic effect which aids the gas blast in driving the arc mto the nozzle electrode 38, where it is most vulnerable toextinction. For example, referring to the upper contact assembly 22, this loop, which is indicated by the dotted line 43, comprises a pair of arms extending away from the mouth of the nozzle and away from a jLlHCtlOIl interconnecting the two arms. As will be apparent from Fig. 1, this junction is disposed approximately in axial alignment with the nozzle 38. It will be apparent that the magnetic elfect of the loop is to increas ngly bow the arc and force it into the nozzle 38. In this zone, the gas blast is more effective in producing rapid arc-extinction.

For operating the blast valve 40 and the movable contacts 28, a combined operating mechanism is prov ded. 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 suitablethreads formed at its outer end for receiving a retaining nut 55 which The housing 33, at its left hand end, has an annular flange 34 4 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 for the cylinder 32. A suitable seal 57' mounted in this end wall 57 encircles the piston rod 54 and prevents gas from leaking aroun the piston rod.

The other piston 52 serves to control the movable contacts 28 and is coupled to these contacts 28 by means of a piston rod 58, a crosshead 59 of suitable insulating material, and two sets 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.

in the position of Fig. l, the movable contacts 28 are biased into closed position by means of overcenter compression springs 64. Each of these springs 64 has one end pivotally supported at 65 on a projecting portion of one of the brackets 31. At their inner ends, the springs 64 are pivotally supported on the crosshead 59. These overcenter springs 64 tend to urge the contacts closed while the crosshead 59 is to the left of a reference line connecting the pivots 65. But, when the crosshead is moved to the right beyond this reference line (as occurs during a contact-opening operation), the overcenter springs thereupon tend to urge the contacts in a contactopening direction.

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 52is initiated by suppyling 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 directly communicates with the pressurized gas in the chamber 11. Flow through these ports 74 and 75 is controlled'by means of a reciprooable 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 affords communication between the lead-in duct 72 and the exhaust duct 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. 1, the clearance space 70 is vented to atmosphere and is sealed off from the chamber 11. V

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. 1, is effective 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 conditionsby energizing the coil 81 of the latch. F rmanual release, a push button switch-82 I would be closed to complete an energizing circuit for the coil 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) Wouldbe 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.

When the control valve element 77 reaches the lower position, which is shown in Fig. 2, compressed gas flows from the chamber 11 through the port 75 and the leadin 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 springs 64 and also against the opposition of fluid contained within a dashpot cylinder 112 at the right of contact piston52, as will be explained in greater detail hereinafter. The space 89 immediately to the right of piston 52 is always freely vented to atmosphere through the duct 108, so relatively little opposition is encountered from fluid in this space. 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 suflicient length to permit the blast to be well established at the instant of arc initiation.

To prevent wastage of compressed gas, the blast valve should be open only so long as is necessary for the arc to be extinguished by the gas-blast. As soon as extinction of the arciis assured, the blast valve member 40 should be quickly returned to its closed position shown in Fig. 1 to prevent further consumption of the compressed gas. To this end, I provide a by-pass passage 85 which extends from the left-hand end of the cylinder 32 to a preselected intermediate point in the bore of the cylinder. When the pistons 51 and 52 occupy the position of Fig. 1, the skirt portion 66 of piston 52 covers and closes off the by-pass passage 85. The inter-piston chamber 67 is then at atmospheric pressure due to 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. 1, 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 bypass. At this i11- stant, 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. 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 by dotted lines in Fig. 2, as is desired. During this return movement, 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 bypass 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 sufiiciently to assure that the are drawn by separation of the contacts will have been extinguished.

The above-described dilierence 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 effective 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 piston 51.

The admission of fluid into the inter-piston chamber 67, in addition to closing the valve member 40 as above described, also tends to hold the movable contacts 28 in open position. More particularly, so long as the control valve element 77 remains in its lower position shown in Fig. 2, the pressure in the space between the two pistons corresponds to that of the chamber 11 and provides a force tending to hold the piston 52 in its open circuit position of Fig. 2. This force together with the action of the overcenter springs 64 is effective to maintain the contacts 28 in open position, as will soon appear more clearly. During this breaker-open interval, the high internal pressure within the chamber 11 provides adequate high di-electric insulation for the relatively short isolating gap which now is maintained between the spaced contacts or electrodes.

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 operthrough which the piston rod 58 extends in slidable relationship. The piston rod 58 contains a keyway port 122 which permits fluid to flow through the central opening in the end wall 48 when the piston rod 58 is in or adjacent the closed circuit position of Fig. 1.

The dashpot means allows initial opening movement of the pistons 51 and 52 to take place at relatively high speed since the keyway port 122 is then open and air ahead of the piston 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 the piston 110. Thereafter, air can flow only through the restricted passage 119, and as a result, there is established at the end of the opening stroke a retarding action which smoothly decelerates the pistons and contacts.

As explained hereinabove, the movable contacts 28 are held in their open-circuit position by fluid pressure maintained between the two pistons 51 and 52 and also by the action of the overcenter springs 64. 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. 1, where it can be seen that the auxiliary piston structure 110, 116 has a pair of opposed working surfaces and 131 which are exposed to pressurized insulating fluid from the casing of the surrounding interrupter, the surface 131 receiving fluid through an opening 113 and the surface 130 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 circuit breaker is in its fully open position, i.e., with the pistons 51 and 52 occupying their position of Fig. 2, 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. 2 into its elevated position, thereby establishing. communication between the exhaust port 7d 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 bypass 85, the clearance space'70, and the lead-in passage 72. 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 positions. The overcenter springs 64 resist initial displacement of these parts from their respective open-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 spring 64 would, of course, aid this contactclosing 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 above-described lifting of the control valve element 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. l. The control circuit for this solenoid is described in my floresaid application S.N. 535,619, and reference may be had thereto for a more complete description of the circuit. For the purposes of the present application, it is believed sufficient merely to understand that the control circuit comprises a control switch 95 connected in series with the solenoid 94 and a conventional anti-pump device 96 suitably connected in. oircuit with the solenoid to prevent inadvertent repetitive operations.

The fact that the closing force exerted on the auxiliary piston110, 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 interpiston 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 insufficient to overcome the opposition of the overcenter springs 64. Thus, under 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 immered 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.

An alternative manner of preventinga closing operation while the pressure within the interrupter is below a predetermined safe level is to block operation of the control valve 77 from its lower to its upper position during such interval. For example, referring to the modified control circuit of Fig. 3, this can be accomplished by asuitable pressure-sensitive interlock switch 97 connected in the energizing circuit of the valve-actuating solenoid 94. This switch is of a conventional type and preferably comprises a spring biasing its contacts towardopen position against the opposition of a pressuresensitive bellows which is in fluid communication with the interrupter. The switch acts to open the solenoid energizing circuit in response to an abnormal loss of pressure in the interrupter, thereby precluding operation ofthe solenoid 94 and the control valve 77. By so disabling the control valve 77, the pressure sensitive switch acts to prevent venting of the interpiston space, thus precluding a normal closing operation when the interrupter pressure is below a predetermined safe level.

Assuming that a pressure-sensitive switch such as 97 is relied upon, then the overcenter springs 64 are required to provide considerably less hold-open force than would be otherwise required. For example, assume that an abnormal loss of pressure occurred and the control valve 77 was blocked in its lower position by opening of the pressure-sensitive switch 97. The interpiston space would remain at essentially the same pressure as the surrounding fluid in the interrupter due to the free communication alforded by the passage 75. As a result, there would still be a net fluid pressure force tending. to hold the contacts open (inasmuch as the left hand face of the piston 52 has an area considerably greater than the net area subject to fluid-pressure closing forces). This net force tending to hold the contacts open would decrease as the pressure in the interrupter decreased, but so long as the passageway remained open, there would be no net fluid-pressure force tending to close the contacts.

In this latter arrangement, the overcenter springs 64 would assure that vibrations or similar forces would not initiate a contact-closing operation when the net fluid-pressure forces tending to hold thev contacts open were low due to an abnormal pressure loss in the interrupter. Resisting the action of vibrations and similar forces would require relatively little hold-open force from the overcenter springs 64. Thus, where a pressure-sensitive interlock switch such as 97 is used, the overcenter springs need provide considerably less hold-open force than would otherwise be required. 1

If the contacts of the breaker happen to be in fullyclosed position when an abnormal pressure loss occurs, then it is desirable that they remain fully-closed until a safe pressure can be restored. In this regard, it is most desirable that the contacts not be forced open by shortcircuit produced magnetic forces.

When my disclosed interrupter is in the position of Fig. 1, its contacts are held closed by the overcenter springs 64 and by the net fluid-pressure force present on the auxiliary piston 110. If an abnormal pressure loss should occur, then the net fluid-pressure force'on the auxiliary piston would correspondingly decrease, and less force would. be available to hold the contacts closed.

To insure that, under such conditions, adequate force is available to hold the contacts closed, even against short-circuits, I have designed the contact structure in such a manner that the magnetic forces tending to open the movable blades 28 are largely balanced out. For example, referring to the upper contact assembly of Fig.

1, the magnetic forces produced by current traversingthe loop circuit 43. would tend to force the blade 28 open (due to the mutual repulsion between the arms of. the loop), but those forces produced by the currentflowing through a second loop formed by the blade 28'and the bracket structure 31 would tend. todrive the contacts closed. Thus the magnetic forces produced by the two adjacent loop circuits on the blade28 tend, to cancel out 4 each other. It will be noted that the arms of the second loop circuit 135 are generally parallel to each other and are therefore disposed at ana'ngle relative to each other of considerably less than 90 degrees. Preferably, the configuration of the bracket structure 31 is such that there is a slight resultant magnetic force tending to bias the contact 28 open. This force is so slight, evenduring short-circuits, that the overcenter springs are easily capable of maintaining the contacts closed.

Thus, my contact arrangement not only provides magnetic forces which aid in quickly extinguishing the are but also provides magnetic forces which aid in maintaining the contacts closed even during short circuit conditions which might occur after an abnormal loss of pressure.

While I have shown and described a particular em bodiment 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 circuit interrupter containing pressurized arcextinguishing fluid, a circuit-controlling contact immersed therein and movable between spaced-apart open and closed-circuit positions, overcenter spring means coupled to said contact and operable to resist movement of said contact out of its open-circuit position and also out of its closed-circuit position, an operating cylinder, first piston structure movably mounted in said cylinder and coupled to said movable contact, second piston structure also coupled to said movable contact, fluid-pressure means acting on said second piston structure and urging said contact toward closed position with a force varying directly in accordance with the pressure of the arc-extinguishing fluid in said interrupter, means for driving said contact and said first piston structure into opencircuit position, means operable when said first piston structure is in open-circuit position for affording communication between said interrupter and the cylinder space at one side of said piston so as to hold said first piston structure and said first contact in said open-circuit position with a force varying directly in accordance with the fluid pressure in said interrupter, closing-control means for isolating said cylinder space from fluid communication with said interrupter and for thereafter evacuating said cylinder space whereby to allow said fluidpressure means to drive said contact into closed-circuit position, said overcenter spring means acting to block movement of said contact out of its open-circuit position so long as said cylinder space communicates with said interrupter, whereby so long as said communication is maintained, said contact remains open despite an abnormal loss of fluid pressure in said interrupter.

2. In a circuit interrupter containing pressurized arcextinguishing fluid, a circuit-controlling contact immersed therein and movable between spaced-apart open and closed-circuit positions, overcenter spring means coupled to said contact and operable to resist movement of said contact out of its open-circuit position and also out of its closed-circuit position, an operating cylinder, first piston structure movably mounted in said cylinder and coupled to said movable contact, fluid-pressure means urging said contact toward closed position with a force varying directly in accordance with the pressure of the arc-extinguishing fluid in said interrupter, means for driving said contact and said first piston structure into open-circuit position, means operable when said first piston structure is in open-circuit position for affording communication between said interrupter and the cylinder space at one side of said piston so as to hold said first piston structure and said first contact in said opencircuit position with a force varying directly in accord ance with the fluid pressure in said interrupter, closingcontrol means for isolating said cylinder space from fluid communication with said interrupter and for thereafter block. movement of said contact but of its open-circuit position so .long as said cylinder space communicates with said interrupter, whereby so long as said corn-r munication is maintained, said contact remains open despite an abnormal loss of fluid pressure in said inter-f rupter, a I

3. The interrupter of claim 2 in combination with pressure-sensitive means for disabling said closing-control means whenever the pressure-in said interrupter falls below a predetermined level, whereby to prevent a normal closing operation when the interrupter pressure is abnormally low. p v

4. In a circuit interrupter containing pressurized arcextinguishing fluid, a circuit-controlling contact immersed therein and movable between spaced-apart open and closed-circuit positions, overcenter spring means operable to resist movement'of said contact out of its open-circuit position, an operating cylinder, first piston structure movably mounted therein and coupled to said movable contact, second piston structure also coupled to said movable contact, fluid pressure means acting on said second piston structure and urging said contact toward closed-circuit position with a force varying directly in accordance with the pressure of the arc-extinguishing fluid in said interrupter, means for admitting pressurized fluid into the cylinder space at one side of said first piston structure for holding said contact in open-circuit position against the force of said fluid pressure means, said fluid pressure means being operable to drive said contact into closed-circuit position in response to evacuation of said cylinder space while the fluid pressure in said interrupter is above a predetermined level, said overcenter spring means exerting suflicient force to hold said contact in open-circuit position if said cylinder space is evacuated while the fluid pressure in said interrupter is below said predetermined level.

5. The interrupter of claim 4 in which said second piston structure has a pair of opposed working surfaces exposed to said pressurized arc-extinguishing fluid, one of said surfaces being exposed to pressure urging said contact toward closed-circuit position and the other being exposed to pressure urging said contact toward opencircuit position, the eflective working area of said one surface being larger than that of said other surface whereby said second piston structure and said contact are urged toward closed-circuit position with a force varying directly in accordance with the pressure of said areextinguishing fluid.

6. In a fluid blast circuit interrupter; a first contact; a nozzle mounted in spaced relationship to said first contact; a pivotally-mounted second contact adapted to engage said first contact in circuit-closing relationship and separable therefrom to establish an are between said contacts; said second contact being disposed transversely to said first contact and defining with said first contact a first loop circuit in which the arms of the loop, in departing from a junction interconnecting said arms, extend away from the mouth of said nozzle and provide a magnetic elfect tending to drive said arc into said nozzle; said junction being located approximately in axial alignment with said nozzle; said magnetic effect also tending to separate said second contact from said first contact; conductive bracket structure supporting said second contact and defining a path for current flowing to and from said second contact; said bracket structure forming with said second contact a second loop circuit which has a magnetic eifect tending to hold said second contact in closed position whereby to oppose the magnetic efiect of 7. In a fluid blast circuit interrupter containing pres-' surized arc extinguishing fluid; a first contact; a nozzle mounted in spaced relationship to said first contact; a pivotally mounted second contact adapted to engage said first contact in circuit-closing relationship and separable therefrom to establish an are between said contacts; said contacts and said nozzle being disposed in said are extinguishing fluid; said second contact being disposed transversely to said first contact and defining with said first contact a first loop circuit in which the arms of the loop, in departing from a junction interconnecting said arms, extend away from the mouth of said nozzle and provide a magnetic effect tending to drive said are into said nozzle; said magnetic effect also tending to separate said v 12 to and from said second contact; said bracket structure forming" withsaid second Contact a second loop circuit whichhas a magnetic eif'ec't fendingto hold said second contact in closed position whereby to oppose the magnetic efiect of said first loop circuit, the arms of said second loopv circuit" being disposed at an angle relative to each other of less than ninety degress and the magnetic effect of said s'e'cond'loop circuit being sufli'cie'ritly strong to hold s'aid contact closed against short-circuit currents despite an abnormal loss of pressure in said'interrupter.

References Cited in the file of this patent UNITED STATES PATENTS 1 ,958,159

Bres son"; May 8, 1 934 2,153,400 Trencham Apr. 4, 1939 2,283,748 Mathieu May 19, 1 942 2,349,681 'Slepian Ma y 23, 1944 2,413,555 Flursheim Dec. 31; 1946 2,783,33 B'e'atty' Feb. 26, 195'7 2,821,594 Latour Jan. 28, 1958 FOREIGN PATENTS 409,963 Great Britain May 10, 1934 825,168 France Nov. 27, 1937

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