US2874242A - Fluid-pressure controlled operating mechanism for a circuit breaker - Google Patents

Description

Feb. 17, 1959 D. R. KURTZ SUR FLUID-PRES E CONTROLLED OPERATING MECHANISM FOR A CIRCUIT BREAKER Filed Hay 23. 1957 Inventor: Donald R. Kurtz His ttorneg.

United States Patent Otiice 2,874,242 Patented Feb. 17, 1959 FLUID-PRESSURE CONTROLLED OPERATING MECHANISM FOR A CIRCUIT BREAKER Donald R.. Kurtz, Drexel Hill, Pa., assignor to General Electric Company, a corporation of New York Application May 23, 1957, Serial No. 661,126

8 Claims. (Cl. 200-82) This invention relates to a duid-pressure controlled operating mechanism for an electric circuit breaker, and more particularly, to improvements in the general type of operating mechanism shown and claimed in U. S. Patent No. 2,783,338, issued to I. W. Beatty and assigned to the assignee of the present invention.

In an operating mechanism of the type shown in the Beatty patent, the circuit breaker contacts are held in the1r fully-open position by fluid pressure forces derived from pressurized gas trapped in a cylinder space at one side of a contact-controlling piston. A contact-closing operation is produced by venting gas from this cylinder space through a suitable bleed passage so as to reduce the liuid pressure forces tending to hold the contacts open, thus allowing suitable biasing means to force the contacts closed.

If the aforementioned bleed passage is relatively restricted, there are a number of problems which tend to arise. First, there is the problem that insufticient closing force will be available to overcome the high opposing forces which are abruptly established near the end of the closing stroke if and when the breaker is closed on a fault. Second, there is the problem that the gas ahead of the contact-controlling piston will still be pressurized, to some extent, when the contacts reach their fully-closed position. If the breaker is required to immediately reopen (say, due to a fault on the power line), then contactopening pressure will be built up from an initial pressure appreciably above atmospheric. In contrast, if the opening operation takes place after the breaker has been closed for an extended interval, as would be the ordinary case, then opening pressure will be built up from an initial pressure equal to atmospheric. Since the opening-speed characteristics depend upon the initial pressure which is present, consistent characteristics would not be present for all opening operations. Undesirable variations depending upon how long the breaker had been closed would be present.

One way of overcoming these two problems is to form the aforementioned bleed passage of a relatively large size so that it is capable of dumping air from the cylinder space at a very high rate. This approach is disadvantageous, however, in that it tends to result in unduly high contact-closing speeds which could cause damage to the contacts.

An object of my invention is to provide, in a circuitbreaker of the above type, a novel control arrangement which enables the contacts to be closed at moderate speeds but yet enables the mechanism to overcome the opposing forces which are abruptly established near the end of the closing stroke.

Another object is to provide an improved duid-pressure controlled operating mechanism of the above type which has consistent opening-speed characteristics irrespective of the length of time the breaker has been closed when opening is initiated.

In carrying out my invention in one form, there is provided a circuit breaker vwhich has a movable contact operatively connected to a contact-controlling piston. A supply of pressurized gas is maintained at one side of the piston in order to hold the contact in open position. Contact-closing is produced by venting this pressurized gas to atmosphere through a suitable bleed passage, thus allowing suitable biasing means to force the contact into closed position. An additional passage which extends from said one side of the piston to the other is sealed olf during initial contact-closing but is suddenly opened near the end of the closing stroke. This abruptly reduces the pressure of the gas -ahead of the piston and also tends to momentarily build up pressure behind the piston. Such action makes available added force for final contact-closing and also helps to insure that the pressure in the contact-opening chamber ahead of the piston will have been reduced to atmospheric by thel time a subsequent opening operation is initiated.

For a better understanding of my invention reference may be had to the accompanying drawings, wherein:

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

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

Referring now to Fig. l, there is shown a circuit breaker of the sustained-pressure gas-blast type comprising an interrupting unit generally indicated at 10. This interrupting unit comprises an enclosed interrupting chamber 11 deiined, in part, by a spherical metallic casing 12 which is iilled with pressurized arc-extinguishing gas.

A pair of elongated conductive studs 15 and 20 project into the casing 12 from diametrically-opposed points and each of these studs carries a suitable stationary contact assembly 16 at its radially-inner end. Cooperating with each stationary contact assembly is a movable contact 28 pivotally mounted upon a stationary pivot 29. These pivots 29 are supported on stationary brackets 31 which are integral with one end of a stationary cylinder 32. Suitable means (not shown) are provided for transferring current between the movable contacts and the brackets 31, so that the brackets 31 together with the cylinder 32 form a conductive path electrically interconnecting the two movable contacts 28.

The cylinder 32, at its left hand end, is suitably supported from a generally cylindrical housing 33. The housing 33, at its left hand end, has an annular `iiange 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 housing 33 is prov1ded 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 fiow 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. l, the valve member 40 1s shown in its closed position wherein an annular flange 42 formed at its left hand end sealingly abuts against the stationary ange 34, which serves as a valve seat. The valve member 40 is normally maintained in this closed position of Fig. l 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 tothe right (by means soon to be described), gas in the chamber 11 will ow at high speed through the nozzles 38 andout the passage 36' past valve member 40 to atmosphere, as is indicated by the arrows shown in Fig. 1. This rapid ow of gas through the nozzles 38 creates lan axial arce'nv'eloping blast which acts rapidly to extinguish the arcs which are drawn adjacent the nozzles by movement of the movable contacts 28 away from their xed fingers 25.

For operating the blast valve 40 and the movable contacts 28, a combined operatingrnechanism 56 is provided. 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 4t) 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 4Gy 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. Al suitable seal 57 mounted in this end wall 57 lencircles the piston rod 54 and pre- Y vents gas from leaking around 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 S, 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 b y 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. 1, the movable contacts 28 are biased into closed position by means of overcenter compression springs 64. Each kof 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 pivotallysupported 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 contact-opening direction.

lThe contact-controlling piston 52 is formed Vwith a skirt portion 66, which in Fig. 1, 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 Askirt 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 morerclearly.

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 throughY a suitable exhaust duct '76 and the other of which 75 directly communicates with the pressurized gas inthe chamber 11. Flow through these ports 74 v 4 and 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 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. l, the clearance space 70 is vented to atmosphere and is sealed olf 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. This downward movement of valve element 77 can be initiated either manually 0r in response to predetermined electrical conditions, e. g., a fault on the power circuit controlled by the breaker. Any suitablemeans can be used for this purpose, and an example of such means is shown in the aforementioned Beatty patent. v

u When the control valve element 77 reaches the lower position, which is shown in Fig. 2, compressed gas ows 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 5I 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 iluid contained within a-dash pot cylinder 112V at the right of contact piston 52, as will be explained in greater detail hereinafter. The spiace 89 yimmediately to the right of piston 52 is always freelyvvented to atmosphere through the duct 108, so relatively little opposition is encountered fromsluid in this space. This movement of the piston 51 to the right immediately opens the blast valve member 40, whereas thismmovement of piston 52 to the right immediately initiates opening movement of the contacts 28. The position of the pistons 51 and 52 after this movement to the right is shown in Fig. 2, with the valve-controlling piston shown in dotted lines. y

As soon as extinction of the arc is assured, the blast valve member 40 is quickly returned to its closed position shown in Fig. l to prevent further consumption of the compressed gas. To this end, a by-pass passage is provided 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. l, the skirt portion 66 of pistoiiSZ covers and closes off the by-,pass passage 85.` The interpiston chamber 67 is then at atmospheric pressure due to communication through a one-way valve 92 to atmosphere via duct 72, and also due to the presence of a passage 200 (soon to be described). Whenthe two pistons 51 and 52 are moved simultaneously to the rightV 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 by the dotted lines of 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 Vbuilds up to substantially the same value as the pressure at the left hand side of piston 51. Because that working surface of piston51 which is `exposed to pressurized Huid within the chamber 67 is substantially larger than that working surface which is exposed to pressure tending to open the valve, thepiston 51 is subjected to an unbalanced 'force which quickly drives the piston 51, together with valve member 41), back into the closed position shown by solid lines in Fig. 2, asis desired. During this return movement, the fluid at the left hand side of the piston 51 is expelled either throughl asma-12 the by-pass passage 85 or through the port 75 leading to the main chamber 11. The mouth of the by-pass 85 isso 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 suiciently to assure that the arc drawn by separation of the contacts will have been extinguished.

The admission of fluid into the inter-piston chamber 67, in addition to closing the valve member 40 as abovedescribed, 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 dielectric 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 operating mechanism. This dashpot means comprises an auxiliary piston structure 110 which is slidably mounted within a tubular `extension 112 of the main cylinder 32 located at the right hand end of the main cylinder 32. The tubular extension 112 is provided with an outer end wall 118 containing metering passage 119 and a central opening through which the piston rod 58 extends in slidable relationship. The piston rod 5S contains keyway p orts 122 which permit fluid to ow 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 ports 122 are then open and air ahead of the piston can i'low freely therethrough. After a predetermined portion of the opening stroke has been completed, the piston rod 58 has moved suiciently to the-right to render the keyway ports 122 no longer effective to vent air ahead of the piston 110. Thereafter, air can iiow 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 iluid 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. This piston structure 110 is always acted upon iby a pneumatic force from the right which tends to close the contacts and which varies directly in accordance with the uid 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 vposition of Fig. 2 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 iiuid is vented to atmosphere from the inter-piston space 67, through the check valve 92, the clearance space 70, and the lead-in passage 72. In response to such venting, the iiuid pressure forces exerted on the auxiliary piston structure 110 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 uid pressure within the interrupter is above a predetermined safe level, the pressure forces on the auxiliary piston predominate and overcome the resistance of the overcenter springs. Once the contacts 28 are moved beyond dead center, the springs 64 would, of course, aid this contact-closing action and apply a desirable added closing force as the contacts approached engagement. The keyway ports 122 also contribute to increased closing force near the end of the stroke by permitting a comparatively free iniiux of air into the tubular extension 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 arrangement shown inthe aforementioned Beatty patent.

In connection with the above-described closing action, I prefer to make the valve 92 and the passageways 76 and 78 of relatively small size so that air from the interpiston space 67 is vented at a relatively moderate speed, which allows the air within the chamber 67 to exert an appreciable retarding action on the piston 52 during initial contact-closing.

If these vent passages were of a relatively large size and therefore vented the interpiston space 67 at an appreciably greater speed, then objectionably high contactclosing speeds would be obtained. In this regard, excessively high closing speeds can damage the breaker contacts due to high velocity impacts.

If the above-described closing action took place when there was a fault, or short-circuit, present on the power circuit in question, then as soon as current began t0 ow between the contacts, very high opposing forces of a well-known character would be abruptly established.

For overcoming these opposing forces, I provide a passageway 200 which extends through the contact-controlling piston 52 between its opposite sides. In the closed-circuit position shown in Fig. l this passageway 200 alords free communication between the inter-piston space 67 and the cylinder space 89 behind the piston 52.

As will be apparent from the drawings, the mouth 201 of the passageway 200 is located in the axially-projecting rod portion 202 of the piston 52. When the breaker is in the fully-open position of Fig. 2, the rod portion 202 is disposed within the tubular extension 112 of the cylinder 32. Because this tubular extension closely surrounds the rod portion 202 in the position of Fig. 2, it covers the mouth 201 and therefore acts to seal ofr the passageway 200. When the piston 52 is driven to the left toward the closed-circuit position, as described hereinabove, the passageway 200 remains sealed off by the tubular extension 112 during the initial portion of the closing stroke. However, just before the piston 52 reaches a point at which current iiows between the thenclosing contacts, the mouth 201 moves out of the tubular extension 112 thereby allowing free communication to be established between the inter-piston space 67 and the cylinder space 89 at the rear of the piston 52. This abruptly reduces the pressure in the inter-piston space 67 and also momentarily increases the pressure in the space 89 behind the piston 52. As a result of the abrupt drop in pressure on the front side of the piston 52, the uid pressure forces opposing closing-motion of the piston 52 areabruptly reduced; and as a result of the momentary increase in pressure on the rear side of the piston 52, additional huid-pressure forces are temporarily available to aid in closing the contacts. Each of these factors, especially the rst, materially aids the mechanism to overcome any short-circuit-produced opposing forces which might be encountered at the end of the closing stroke.

Another important function of the passageway 200 is that it insures consistent opening-operation characteristics irrespective of whether the breaker vis opened immediately after closing or a considerable length of time after closing, as would be the ordinary case. In this regard, assume rst that the passageway 200 was not present and that air was bled through the exhaust passages 76, 78, during closing, at the comparatively moderate rate described above. Under such circumstances, due to the restricted venting, there is a delinite tendency for the pressure within the chamber 7() to be above atmospheric immediately after the breaker is fully-closed. If a subsequent opening operation immediately followed, then pressure in the contact-opening chamber 70 would build up from an initial pressure higher than atmospheric. This is in contrast to any ordinary opening operation, in. which such pressure builds up from an initial pressure equal to atmospheric. Thus, without the passageway 200, diiierent opening-speed characteristics would be obtained, depending upon the length of time the breaker remained closed.

The presence of the passageway 2Gb, however, overcomes this problem because it provides a parallel venting path Vwith respect to that path extending through the valves 92 and 77. As a result, much less air is required to ow through the latter venting path, thus minimizing the likelihood that the pressure in the chamber 70 will be above atmospheric at the time the breaker reaches its fully-closed position.

f. The air which flows into chamber 89 from the interplston space 67 brieliy provides added closing force on the piston 52, as described hereinabove, but quickly falls to atmospheric (due to the bleed passage 108) in time to avoid interference with a subsequent opening operation.

Because of its particular location, the passageway 200 1n no way interferes with a normal opening operation. In this regard, during initial opening movement, the bypass 85 is sealed oil" by the skirt portion 66 of the piston 52, thus preventing pressurized air from owing through the passsageway 200 to the chamber 89 at the rear of the piston. Before the bypass 85 is uncovered near the end of the opening stroke, the mouth 201 of passageway 200 is covered by the internal wall of tubular extension 112. This closes off the passageway 200 and, thus, when the bypass 85 is opened lnear the end of the opening stroke, pressurized air `still is unable to ow through the passageway 200 to the chamber '89 at the rear of the piston. Thus, since pressurized air is blocked from flowing through the passageway 200 during the entire opening operation, its presence in no way interferes with the opening operation. l

.Another important advantage of locating the passageway 200 in the particular position shown is that a very effective seal can be readily provided to preventl leakage through the passageway 200 to atmosphere during the time the breaker remains in the fully-open position. In this regard, when the breaker is in the fully open position of Fig. 2, leakage of pressurized gas through the passageway 200, about the rod portion 202 to the atmospheric chamber 89 is positively prevented by a resilient seal 210 provided between the piston 52 and the end wall 212 of the cylinder 32. This resilient seal 210, which is preferably carried in an annular groove in the piston 52, is compressed between the piston 52 and the end wall 212 when the breaker is in the fully-open position of Fig. 2 by those forces tending to normally hold the contacts in open position. y

The internal wall of the tubular extension 112 is capable of sealing the passageway 200 suiciently to prevent the ow of any appreciable amount of air through the passageway on a short time basis (say, during a breaker-operation). But this sealing action is not adequate to prevent appreciable air leakage on along time basis (say, for the extended 'periods duringv which the breaker might remain in open position). During such intervals, the resilient seal 210 is effective to prevent leakage to atmosphere.

When the breaker is in the closed position of Fig. l, an O-ring 214 prevents any air from leaking about the rod portion 202 to the atmospheric chamber l89.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that various changes and modications 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 modiiications 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: l

l. In an electric circuit breaker comprising a contact movable between spaced-apart open and closed position, biasing means urging said contact toward closed position, a movable piston operatively connected to said contact and also urged toward a closed position by said biasing means, means for maintaining a supplyof pressurized gas on one side of said piston for holding said contact in open position in opposition to said biasing means, means for bleeding pressurized gas from said one side of the piston to allow said biasing means to drive said contact and said piston toward closed position, a passageway leading from said one side of the piston to the other side thereof, and means for sealing oli said passageway during initial contact-closing movement and for opening said passageway during nal contact-closing movement, said passageway opening occurring prior to the point at which said contact reaches closed position and acting to abruptly reduce the forces opposing final contact-closing movement.

2. vIn an electric circuit breaker comprising a contact movable between spaced-apartV open and closed positions, biasing means urging said contact toward closed position, a movable piston operatively connected to said contact and also urged toward a closed-contact position by said biasing means, contact-opening means for driving said piston from said closed-contact to an open-contact position to produce opening of said contact, means for maintaininga supply of pressurized gas on one side of said piston for holding said contact in open position in opposition to said biasing means, means for bleeding pressurized gas from said one side of the piston to allow said biasing means to drive said Contact and said piston toward closed position, a passageway leading from said one side of the piston to the other side thereof, and means for sealing ott said passageway during initial contact-closing movement and for opening said passageway during final contact-closing movement, said passageway opening occurring prior to the point at which said contact reaches closed position and acting to abruptly reduce the Vforces opposing nal contact-closing movement. i 3. In an electric circuit breaker comprising a contact movable between spaced-apart open and closed positions, a movable piston operatively connected to said contact and movable from a contact-open to a contactclosed position during a contact-closing stroke, biasing means urging said contact and said piston toward their respective closed positions, said piston having a rod portion projecting axially from one side thereof, cylinder means slidably receiving said piston and having a tubular portion projecting from an end wall thereof for slidably receiving said rod portion, means for maintaining a supply of pressurized gas on the other side of said piston for holding lsaid contact in open position in opposition to said biasing means, means for bleeding pressurized gas from said other side of the piston to allow said biasing, means to drive said contact toward closed position, a passageway `extending through said piston and terminating in a mouth which is located in said rod portion, .said mouth being so located that it is sealed off by said tubular portion when said piston is in the region of contact-open position and communicates freely with the cylinder space at said one side of the piston when the piston nears its closed-contact position, said free communication being established during a closing operation prior to the point at which said contact reaches closed position.

4. In combination with the circuit breaker of claim 3, resilient sealing means located between said one side of the piston and said cylinder end wall for preventing leakage of pressurized gas through said passageway and about said rod portion when said piston is in the contactopen position.

5. In an electric circuit breaker comprising a contact movable between spaced-apart open and closed positions, biasing means urging said contact toward closed position, a movable piston operatively connected to said contact and also urged toward closed position by said biasing means, said piston having one side thereof vented to a region of relatively low pressure, means for maintaining a supply of pressurized gas on the other side of said piston for holding said contact in open position in opposition to said biasing means, means including a bleed passage for venting pressurized gas from said other side of the piston to allow said biasing means to drive said contact toward closed position, a second passageway extending through said piston to aiord communication between opposite sides thereof, and means for sealing ott' said second passageway during initial contact-closing movement and for opening said passageway during nal contact-closing movement said passageway opening occurring prior to the point at which said contact reaches closed position and acting to abruptly reduce the forces opposing nal contact closing movement.

6. In an electric circuit breaker comprising a contact movable between spaced-apart open and closed positions, biasing means urging said contact toward closed position, a movable piston operatively connected to said contact and also urged toward a closed-contact position by said biasing means, cylinder means slidably receiving said piston and deiining a contact-opening chamber at one side of said piston, means responsive to the admission of pressurized gas to said contact-opening chamber for driving said piston from said closed-contact to an opencontact position to produce opening of said contact, means for maintaining a supply of pressurized gas on one side of said piston for holding said contact in open position in opposition to said biasing means, means including a bleed passage extending from said one side 10 movable between spaced-apart open and closed positions, biasing means urging said contact toward closed position, a movable piston operatively connected to said contact and also urged toward a closed-contact position by said biasing means, cylinder means slidably receiving said piston and dening a contact-opening chamber at one side of said piston for receiving pressurized gas which acts to drive said piston from said closed-contact to a contact-open position to produce opening of said contact, means for maintaining a supply of pressurized gas on one side of said piston for holding said contact in open position in opposition to said biasing means, closing-control means including a bleed passage which upon opening acts to vent said contact-opening chamber.

and to allow said biasing means to drive said Contact toward closed position, a second passageway leading from said one side of the piston to the other side thereof, and means for sealing off said second passageway during initial contact-closing movement and for opening said second passageway during final contact-closing movement, said passageway-opening occurring prior to the point at which said contact reaches closed position and acting to abruptly reduce the forces opposing final-closing movement.

8. In an electric circuit breaker comprising a contact movable between open and closed positions, a movable piston operatively connected to said contact and movable between a contact closed position and a contact open position during contact opening, contact-opening means for driving said piston from said contact-closed position to said contact-open position to produce opening of said movable contact, a first passageway adapted when open to supply pressurized gas to a space at one side of said piston whereby to hold said contact in open position, means acting to close olf said first passageway during initial contact-opening and to open said passageway during tnal contact-opening, a second passageway affording communication between opposite sides of said piston when the piston is in the region of its closed position, means for sealing oi said second passageway at an intermediate point in the opening stroke prior to the point at which said first passageway is opened, and means for initiating contact-closing in response to venting of said space at said one side of the piston, said sealing means acting to seal ott said second passageway during initial contact-closing but allowing gas to How therethrough during nal contact-closing from a time just prior to the point at which said contact reaches closed position.

References Cited in the tile of this patent UNITED STATES PATENTS 2,578,349 Goodwin Dec. l1, 1951 2,730,588 Kelle Jan. 10, 1956 2,736,295 Peek Feb. 28, 1956 2,783,338 Beatty Feb. 26, 1957 FOREIGN PATENTS 122,860 Austria May 26, 1931

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