US3492922A

US3492922A - Hydraulically operated circuit breaker with tandem piston construction

Info

Publication number: US3492922A
Application number: US683676A
Authority: US
Inventors: Roswell C Van Sickle
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1967-11-16
Filing date: 1967-11-16
Publication date: 1970-02-03
Anticipated expiration: 1987-02-03
Also published as: JPS5011077B1; BE723504A

Description

Feb. 3, 1970 R. c. VAN SlCKLE 3,492,922

HYDRAULICALLY OPERATED CIRCUIT BREAKER WITH I I TANDEM PISTON CONSTRUCTION Filed Nov. 16, 1967 2 Sheets-Sheet 1 FIG.|. 1

,Feb. 3, 1970 R c. m 5mm 3,492,922

HYDRAULIQALLY OPERATED CIRCUIT BREAKER WITH TANDEM PISTON CONSTRUCTION Filed Nov. 16, 1967 2 Sheets-Sheet 2 H CLOSING OPERATION WITH LOW CLOSING FORCE END OF CLOSING OPERATION INVENTOR Roswell C. Van Sickle WITNESSES United States Patent 3 492 922 HYDRAULICALLY OPERATED CIRCUIT BREAKER WITH TANDEM PISTON CONSTRUCTION Roswell C. Van Sickle, Wilkinsburg, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 16, 1967, Ser. No. 683,676 Int. Cl. F01b 7/20; F15b 11/08, 13/04 U.S. Cl. 91173 11 Claims ABSTRACT OF THE DISCLOSURE A hydraulically operated circuit breaker has a pair of separable contacts which are biased by accelerating springs to the open-circuit position. A hydraulic operating mechanism is provided having a tandem piston construction, in which the operating cylinder for one of the pistons is fixedly secured to the other piston of the hydraulic device, so as to provide a higher force toward the end of the closing stroke of the circuit breaker than during the middle portion of the circuit-breaker closing operation. Another embodiment of the invention includes an additional piston, movable for a predetermined distance on closing, to obtain initially, during the closing operation, a high closing force to bring the operating parts up to a high closing speed. When this occurs, the additional piston halts and the rest of the closing stroke is similar in force characteristics to the first embodiment in which an extremely high closing force is obtained at the end of the circuit-breaker closing operation to charge one or more accelerating springs.

CROSS REFERENCE TO RELATED APPLICATIONS Applicant is not aware of any related applications pertinent to the present invention.

BACKGROUND OF THE INVENTION Power circuit breakers may be hydraulically operated during the closing operation with a part of the energy supplied during the closing stroke being stored in biasing springs, which, when released by an electrical control circuit of low energy, will Open the breaker at high speed. To get fast opening operation, the initial opening acceleration must be high and a large amount of energy must be supplied quickly to bring the parts up to a high opening speed. This is, of course, necessary to rapidly establish arcing and to quickly lengthen the established arc to bring about are extinction in the order of two cycles, for example. It is, therefore, highly desirable to provide one or more biasing springs with say, for example, one of the biasing springs operable over the entire opening travel of the circuit breaker, whereas the other accelerating spring or springs may function as kick off springs, which are operable only through a short distance but which in this distance bring the moving parts, many of which may be of considerable mass, up to a high speed of opening travel, which results in obtaining quickly a length of are which can be extinguished by the interrupter.

It is, therefore, desirable to provide a hydraulic operating mechanism, which will provide a varying force through the closing stroke of the circuit breaker in which toward the end of the closing stroke an extremely high force is available to provide the final charging of the biasing springs including any so-called kick oif accelerating springs, which are charged only as the extreme end of the closing stroke of the circuit breaker is approached.

Consequently, it is a general object of the present invention to provide an improved simplified low-cost hydraulic operating mechanism, which functions so as to ice provide a variable closing force. Generally, the structure is such as to provide a rather low, or medium-value closing force during the major part of the closing stroke of the interrupter, whereas at the end of the closing stroke a considerably higher force is available to effect a final charging of all accelerating springs, including the so-called kick 01f springs. Reference may be had to U.S. Patent 3,291,947, which illustrates a high-voltage circuit interrupter in which a torsion bar provides an initial kick off acceleration to bring the moving parts rapidly up to speed. However, this torsion bar kick oil spring is only operable for a short period of the opening travel, and other biasing springs take over to supply the necessary energy to complete the opening operation of the breaker.

The closing force is supplied in this case by a pneumatic operating mechanism in which the slightly decreasing force of a piston driven by air pressure moving through its stroke is modified by a mechanical linkage so that the output approximates the requirements of the breaker pole-unit. It is highly desirable to provide a simple operating mechanism, particularly of the hydraulic type, which, without a complicated mechanical linkage, can function to provide the variable force requirements of a power circuit breaker.

For economical use of energy, the present conventional closing device usually operates through a varying mechanical advantage so that a relatively constant force input can be converted to an output with an increasing force. The present invention is concerned with a multistep hydraulic closing device, which can exert a force which is variable with the position of the operating rod to match its output to the requirements of the circuit breaker. For simplicity, most of the description of the invention covers a two-step variation in force with a high force following a lower force. This is the most diflicult problem. A minor modification is shown to add a third step to provide a large force at the beginning of the closing stroke, as well as at the end of the closing stroke, without the necessity of dissipating alot of unecessary energy during the mid-portion of the closing stroke.

The invention is primarily concerned with a hydraulic means of producing a force, which varies approximately in accordance with the requirements of a power circuit breaker, for example. It can be designed to provide high acceleration during the first part of a closing stroke to bring the contacts up to speed, a lower force through the central part of the closing stroke before the energy for opening is being stored, high forces for storing this energy in the latter part of the closing stroke, and a control of the final closing speed by limiting the rate of fiuid flow into the hydraulic operating cylinder. Each of the stages is controllable independently, and with a much greater freedom than is possible with a comparable mechanical linkage.

Accordingly, it is a general object of the present invention to provide an improved hydraulic operating mechanism, including a hydraulic linkage including first and second pistons, and respectively first and second operating cylinders, with the second operating cylinder being fixedly secured to the first piston and movable therewith. Preferably, the arrangement is such that the pistons move in sequence to provide the varying force, which is desired during the closing operation.

SUMMARY OF THE INVENTION A hydraulic operating mechanism is provided for a power circuit breaker in which a pair of hydraulic pistons are provided movable within separate operating cylinders. The arrangement is such that the operating cylinder for one of the pistons is fixedly secured to, and movable with, the other piston so that initially the one piston is moved carrying with it the operating cylinder for the other piston. The piston has a hydraulic supply line through a piston rod extension thereof, which has hydraulic fluid supplied to it only after a predetermined delay. As a result, the first piston moves, carrying with it the operating cylinder for the second piston, and as it approaches the end of its stroke it opens the supply line to the second operating cylinder so that a final, relatively high-value closing force is obtained at the end of the closing operation.

A variation of the arrangement, to provide a high initial closing force, is provided by a separate piston member which is stopped after a predetermined closing travel, and the arrangement then operates in accordance with the first embodiment described above.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a vertical sectional view taken through a hydraulic operating mechanism embodying the principles of the present invention, with the circuit breaker structure and electrical control thereof diagrammatically illustrated, and the breaker shown in the fully open-circuit position;

FIG. 2 illustrates the circuit breaker of FIG. 1 during the initial portion of the closing o eration;

FIG. 3 illustrates the breaker in the closed position;

FIG. 4 illustrates a modified form of the invention in which an auxiliary piston is added to provide a high initial closing force during the initial portion of the closing stroke of the circuit breaker to bring the parts quickly up to a high closing speed; and

FIG. 5 fragmentarily shows a means of throttling the fluid flow at the end of the closing stroke to avoid excessive impact.

DESCRIPTION OF THE EMBODIMENT, FIGS. 13

Referring now to the drawings, there is shown in FIG. 1 a circuit breaker 1 comprising a set of separable contacts 2 and 3 for controlling a power circuit 4. The contacts 2 are stationary contacts and the contact 3 is a movable contact that is biased by means of suitable opening springs 5, 6 in a direction away from the stationary contacts 2. The movable contact 3 is arranged to be driven from its open position shown in FIG. 1 through its intermediate position of FIG. 2 into its closed position of FIG. 3 against the bias of springs 5, 6 to close the power circuit 4. Reverse movement of the contact 3 from the closed position of FIG. 3 toward the open position of FIG. 1 under the influence of operating springs 5, 6 interrupts the flow of current through the circuit 4.

Power for driving the contact 3 into its closed position of FIG. 3 is derived from a liquid motor 8 having a piston 9 that is coupled to the movable contact 3 through a linkage generally indicated at 10. This linkake 10, which has been shown in simplified form to facilitate an understanding of the present invention, comprises a piston rod 11, a pivoted lever 12, and a reciprocable operating rod 13. The lever 12 is pivotally mounted at one end on a stationary pivot 14 and is pivotally connected at its outer end, as at 15, to the operating rod 13. The piston rod 11 is pivotally connected to the lever 12 at a point 12a spaced from the pivot 14 and is capable of transmitting counter-clockwise closing motion to the lever 12 when the piston 9 of the hydraulic motor 8 is driven upwardly during a circuit-breaker closing operation. Such counterclockwise motion of lever 12 drives the operating rod 13 upwardly, and such upward motion forces the movable contact 3 into closing engagement with the stationary contacts 2 while compressing the opening accelerating springs 5, 6.

When the closed position of FIG. 3 is reached, a compression spring 17 forces a conventional latch 18 into place behind a roller 19 carried by the lever 12. The latch 18, which is mounted on a pivot 20', serves to hold the contact 3 closed against the bias of opening springs. 5, 6 after the closing stroke has been completed. Breaker opening is effected simply by driving the latch in a clockwise direction off the bottom of roller 19 to remove the restraint of the latch 18, and allow the contact 3 to be driven out of engagement with the contacts 2 by means of the opening springs 5, 6. The spring 5 may be a kickoff torsion spring, as set out in US. Patent 3,291,947 issued to Roswell Van Sickle, and the spring 6 may act throughout the entire opening stroke.

For producing upward circuit-breaker-closing motion of the piston 9 of the hydraulic motor 8, pressurized liquid is supplied to the lower side of the piston. 9 from a pneumo-hydraulic accumulator 22 via

supply lines

23 and 24. This accumulator 22 may be of any suitable conventional design, and in the disclosed embodiment contains a pocket 25 of highly pressurized gas trapped above a supply of liquid 26- contained within the accumulator. The accumulator is maintained in a charged, or pressurized condition by means of a suitable pump 28 which forces liquid from a sump 29 into the accumulator whenever pressure in the accumulator falls below a predetermined level, preferably about 2800 p.s.i., for example. A suitable pressure-sensitive cut-off switch terminates operation of the pump 28 when the accumulator pressure reaches a value of about 3,000 p.s.i., for example.

The flow of pressurized liquid 26 from the accumulator 22 to the motor 8 is controlled by valve means 31 disposed between the accumulator 22 and the motor 8 in the

supply lines

23, 24. Since the details of this valve means 31 are not my invention, and are disclosed and claimed in Patent No. 2,972,337, they will be described only in sufficient detail to provide an understanding of the present invention. This valve means 31 comprises an inlet port 32 interconnecting the accumulator and the motor 8, and a dump port 33, interconnecting the motor 8 and the low-pressure sump 29, which is at atmospheric pressure. The flow of liquid 26 through these ports is controlled by poppet valve member 34 that is movable between the closed position of FIG. 1 and a dotted fully-open position 35. In the closed full-line position of FIG. 1, the valve member 34 abuts against a valve seat 36 surrounding the inlet port 32, thus closing the inlet port 32 and thereby blocking communication between the accumulator 22 and the motor 8, while permitting free communication between the motor 8 and the sump 29 through the dump port 33.

The discharge through dump port 33 reduces the pressure in chamber 30 and hence the pressure holding exhaust valve closed. Valve 70 then opens and the fluid in chamber 71 can be discharged freely through port 91. The fluid in cylinder 74 can discharge through passage at first into chamber 24 and later directly to sump 67 as more fully described hereinafter.

In the fully-open dotted position 35 of FIG. 1, the valve member 34 closes the dump port 33 and allows free communication between the accumulator 22 and the motor 8 through the inlet port 32.

On the accumulator side of the valve member 34 there is a chamber 37 that freely communicates with the accumulator 22 and is normally filled with pressurized liquid 26 from the accumulator 22. This pressurized liquid exerts a force directly on the valve member 34 tending to drive the valve member 34 upwardly out of its closed position of FIG. 1. But this opening force is overbalanced by the force that the pressurized liquid in chamber 37 exerts on a balancing piston 38 fixed to the valve member 34 through a piston rod 39 integral with the valve member34 and the piston 38. As is evidenced by the slightly enlarged bore 40 of the chamber 37 that receives piston 38, the piston 38 has an effective working face slightly larger than the area of the valve member 34 bounded by the seat 36 of inlet port 32, and thus the pressurized liquid in chamber 37 exerts a net force on the valve member 34 tending to hold it in the closed position of FIG. 1. In the disclosed valve, the difierence in these total areas is rather small so that the net force holding the valve member 34 closed is correspondingly small. The region of the valve immediately beneath the piston 38 is always freely vented to the sump 29 through port 42, and thus the liquid in this region plays no significant part in the force relationships described immediately above.

Valve-opening operation is controlled by means of an actuating piston 43 disposed immediately beneath the piston rod 39 of the valve member 34. This actuating piston 43 is separate from the valve member 34 but bears against the lowermost face of the piston rod 39 and is capable of transmitting upward motion to the valve member 34 through the piston rod 39. Such upward motion of the actuating piston 43 is produced by supplying pressurized liquid 26 to the space 44 beneath the piston 43 from the accumulator 22. This pressurized liquid quickly overcomes the above-described net force holding the valve member 34 closed, and thus forces the piston 43 together with the valve member 34 upwardly. Since the net force holding the valve member 34 closed is relatively small, as was explained hereinabove, a relatively small actuating piston 43 can be used for overcoming the net closing force. This means that only a relatively small volume of pressurized liquid need be supplied to the actuating piston 43 to enable it to overcome the net closing force and thereby effect valve-opening.

For controlling the flow of liquid to and from the space 44 beneath the actuating piston 43, a three-way pilot valve 45 is provided in a line 46 leading from the accumulator 22 to the space 44. This pilot valve 45 comprises an inlet port 47 interconnecting the accumulator 22 and the space 44 beneath the actuating piston 43 and a dump port 48 interconnecting the space 44 and the low pressure sump 2'9, and a movable pilot valve member 49 for controlling flow through these

pilot valve ports

47 and 48. When the pilot valve member 49 is in its lower position of FIG. 1, it blocks the flow of liquid through the inlet port 47, but permits free communication between the chamber 44 and the sump 29 through the dump port 48. When the pilot valve member 49 is in its upper dotted position 50 of FIG. 1, it closes the dump port 48 to seal off the sump 29 from the chamber 44 but allows free communication between the accumulator 22 and the chamber 44 through the inlet port 47.

For providing a force to bias the pilot valve closed under normal conditions a small piston 51 is fixed to the valve member 49 through an integral piston rod 52. This piston 51 is disposed at the lower end of a chamber 53 communicating with the accumulator 22 so that full pressure from the accumulator normally acts on its upper surface. As will be apparent from the slight enlargement at the lower end of chamber 53, this piston 51 has an effective working face slightly larger than the area of the valve member 49 bounded by the inlet port 47, and thus the pressurized fluid in the chamber 53 provides a net force biasing the pilot valve member 49 closed.

For overcoming this net closing force on the pilot valve member 49 so as to effect opening of the pilot valve, a solenoid schematically indicated at 54 is provided. This solenoid 54 is controlled by means of

control circuits

55 and 56 generally corresponding to those shown and claimed in US. Patent 2,381,336, Coggeshall, and reference may be had to such patent for a more detailed description of such circuits.

Such circuits

55 and 56 are shown in simplified, schematic form in the present application to facilitate an understanding of the present invention. Referring now to the solenoid 54, it will be noted that the solenoid has an armature 58 mechanically connected to the pilot valve member 49 through a pilot valve operating rod 59, and also has a coil 60 connected in the control circuit 55. This control circuit 55 extends from a positive to negative terminals of a suitable control power source and contains a manually-operable closing-control switch 61 connected in series with the solenoid coil 60 and a suitable anti-pump device 62 of conventional design, such as shown in the Coggeshall patent for preventing inadvertent repetitive closing operations. When the switch 61 is closed, the coil 60 is energized through the circuit 55 and responds by lifting its armature 58 and the pilot valve member 49 to open the pilot valve against the opposition of the previously-described net force holding the pilot valve closed. The anti-pump device 62 opens the energizing circuit 55 immediately after the solenoid has opened the pilot valve and maintains this circuit open so long as the closing control switch 61 is held closed. By opening the circuit 55 before the motor 8 has completed a breaker closing operation, no significant flux from the coil 60 is available to interfere with return motion of the armature 58 at the end of the breaker-closing operation.

The armature 58 is held in its upper position until the circuit-breaker-closing operation can be completed by means of a permanent magnet 63 provided above the armature 58. This permanent magnet 63 has insufficient strength to lift the armature 58 from its lower position, but is sufficiently strong to hold the armature in its elevated position once moved into such position. At the end of the circuit-breaker-closing stroke the normally open switch 64 is closed by suitable means sensitive to the position of the breaker. Closing of this normally-open switch 64 completes a pilot valve closing circuit 56. This circuit 56 contains a flux-neutralizing winding 65 capable when energized of quickly neutralizing the holding flux of the permanent magnet 63. Thus, when the breaker 1 reaches closed position, the switch 64 is closed to complete the circuit 56 to cause the winding 65 to effect release of the armature 58 from the permanent magnet 63, thereby allowing a small spring 66 to return the pilot valve to its closed position.

When the pilot valve member 49 returns to its closed position, it blocks the inlet port 47 and opens the dump port 48 thereby relieving the pressure in the space 44 beneath the actuating piston 43. This allows the pressurized liquid acting against the upper surface of the piston 38 of the main controlling valve to return the valve member 34 from the dotted open position 35 position of FIG. 1 to its full line of FIG. 1. As soon as the main valve member 34 begins leaving the dump port 33, it begins relieving the pressure in the cylinder of the fluid motor 8. When the valve member 34 reaches its full line position of FIG. 1, it blocks the inlet port 32and thus blocks the further flow of pressurized liquid through this port 32. Pressure within the hydraulic operator 8 is thus relieved.

A circuit breaker closing operation would be initiated by closing the control switch 61 to cause the solenoid 60 to lift the pilot valve member 49 from its position of FIG. 1. Such upward movement of the pilot valve member 49 would permit liquid to flow at high speed from the accumulator 22 through the line 46 and the pilot valve inlet port 47 into the chamber 44 beneath the actuating piston 43 of the main control valve. This pressurized liquid in the chamber 44 would force the piston 43 upwardly, and the piston 43, in so moving, would drive the main valve member 34 from the position of FIG. 1 to the dotted open position 35 of FIG. 1. Pressurized liquid would then flow from the accumulator 22 into the cylinder of the fluid motor through the inlet port 32. This liquid would quickly force the motor piston 9 upwardly, thereby effectively driving the contacts into the closed position as more fully described hereinafter.

If a breaker is closed on a faulted power line, it must be capable of reopening within a very short time, e.g. sec. after its contacts first touch. If it be assumed that a fault were present on the power line 4 at the time the breaker contacts touched at the end of the abovedescribed closing operation, heavy current would immediately flow through the circuit 4, energizing a conventional overcurrent relay through a current transformer 84. The relay would respond to such energization by closing its normally-open contacts 85, thereby completing a tripping circuit for a conventional tripping solenoid 86. This tripping solenoid 86 would respond by forcing the latch 18 clockwise about its pivot 20 thereby allowing the breaker 1 to be opened by the opening springs 5, 6 without further restraint from the latch 18.

A trip button 88 for manual opening operation may be used in electrical parallel with the overload relay contacts 85, as well known by those skilled in the art.

With particular reference being directed to the opencircuit position of the hydraulic operating mechanism 8 illustrated in FIG. 1, it will be noted that the breaker 1 can be moved to the closed position and held in the closed position by the above-described control arrangement. With reference to FIG. 1, it will be noted that the pump 28 draws hydraulic fluid from a reservoir 67 through a pipe 68 and discharges it to the accumulator 22 to store the energy. Energy applied to the motor 8 is converted to energy and compressed gas 25 in the accumulator 22 and can be used at a much higher rate than it is stored.

The three-way control valve 31 controls the flow of the high-pressure fluid from the accumulator and for a closing operation admits it to chamber passages in the base 69. The pressure of the fluid holds discharge valve 70 in the closed position to seal the chamber 71. Fluid flowing through check valve 72 raises the pressure in flowing through check valve 72 raises the pressure in chamber 71 and drives the cylinder 73 upwardly within a first operating cylinder portion 69a of base 69. The force exerted is equal to the area of the cylinder 73 multiplied by the pressure in chamber 71 and (neglecting weights and friction) is the force exerted through the initial part of the closing stroke of the circuit breaker 1. The force is transmitted through cylinder 73 to second operating cylinder 74, which is mechanically attached to it. Piston 9, carried on piston rod 11, operates in second operating cylinder 74, but at this time is resting on stops 76 which transmit the force from cylinder 73 to the piston 9 and piston rod 11. When valve 31 transmits high-pressure fluid 26 from accumulator 22 to chamber 71, cylinder 73 acting as a piston exerts an upward force which is transmitted by piston rod 11 to operate the circuit breaker 1 by moving it through the first part of the closing stroke.

FIGURE 2 fragmentarily shows the position at the end of movement under the action of the pressure on the cylinder 73 moving within first operating cylinder 69a. The upward motion of piston rod 11 has permitted the highpressure fluid from the valve 31 to flow upwardly through the piston rod extension 11a to the chamber 77 in second operating cylinder 74 below piston 9. Pressurizing this chamber 77 exerts a force equal to the product of the piston area 9 and the fluid pressure on the piston rod 11 and on the end of the second operating cylinder 74. This force on the cylinder 74 acts downwardly but cylinder 73 cannot be moved downwardly because the check valve 72 prevents reverse flow of the fluid, and the discharge valve 70 is held closed by the pressure of the fluid still flowing from the accumulator. Pressure in the cham ber 71 becomes higher than the accumulator pressure and prevents cylinder 73 from being pushed downwardly. The upward force on operating rod 11 is increased by the accumulator pressure now acting on the large area of piston 9 instead of the area of the end of cylinder 73. Piston 9 now moves away from the stops 76 to push the piston rod 11 through the second stage and to complete the stroke of the operating mechanism.

FIGURE 3 shows the mechanism at the end of the closing operation. It can be held here either by the holding prop latch 18 or alternatively (not shown) by keeping the valve 31 in the p n p ti n By moving the valve 31 to the off full-line position shown, the passage 23 from the accumulator 22 is closed, and the pressure in the actuator 8 is discharged. The removal of pressure from beneath the valve 70 lets the fluid in chamber 71 discharge to the sump 67 through port 91 as the piston 73 moves downwardly under the opening or retrieving forces of springs 5, 6. The fluid in the second operating cylinder 74 can start to discharge to the sump through the valve 31 but most of it will be discharged directly from the passage 75 after the lower end of passage 75 moves downwardly and opens into the sump 67.

The weight of the valve 70 is balanced by a spring 78 in the closed position. A pressure beneath it seals it and holds it closed against a much higher pressure during the second stage of the closing operation. A balanced valve will open quickly on a small cylinder pressure when the pressure beneath it is reduced to zero by opening valve 34. However, after the piston rod 11 has reached the open position and the pressure in chamber 71 has been dissipated, the valve 70 will close or nearly close, and be ready for the next closing operation.

It is sometimes desirable to provide a high initial closing force to produce a high initial acceleration of the contacts 3. This brings the contacts 3 up to a desired closing speed and a much smaller force is adequate to supply the losses and maintain the contact speed until the final heavy load is encountered. This invention can readily be modified to produce this high initial acceleration. FIGURE 4 shows such a modification. It consists of an additional cylindrical piston 80' fitting around the cylindrical piston 73. In the early part of a closing stroke it presses against cylinder 74. Its area is added to the area of piston 73 to increase the force in the early part of the closing stroke. Its contribution is governed by its area and the distance it moves before it is stopped by projections 80a which engage stops 81. The projections 80a shown in FIGURE 4 engage the main frame 69 but they may engage stops, which are adjustablefrom outside the housing 69. Such adjustments would control the energy contribution of this piston 80 and the closing speed of the mechanism. This would facilitate synchronizing the three poles of a breaker 1 which has each pole operated by one of these mechanisms.

Further speed controls can be obtained by control of the fluid passages. For example, as shown in FIG. 5, the final closing can be accomplished without excessive impact by shaping the entrance into passage 75 to throttle the flow of fluid as the closed position is approached. As shown in FIG. 5, several

small inlets

75a, 75b, 75c can be provided which are successively cut off at the extreme end of the closing stroke.

From the foregoing description, it will be apparent that there has been provided an improved hydraulic operating mechanism for a power circuit breaker in which the forces exerted by it can be matched to the needs of a circuit breaker. In particular, it can supply the high initial forces to start the contacts closing, it can supply the lower forces to maintain contact speed, and it can supply the very large forces during the time large amounts of energy are being stored to provide high initial acceleration on opening.

I claim as my invention:

1. A hydraulically-operated circuit breaker including a pair of separable contacts, at least one of which is moved to an open position and to a closed position; a hydraulic linkage including first and second pistons and respectively first and second operating cylinders, the second operating cylinder being fixedly secured to the first piston and movable therewith, the second piston having a piston-rod extension with a hydraulic supply line (75) disposed within said extension, and means for supplying hydraulic fluid into said supply line within said exterior extension only after a predetermined time delay during the closing stroke of the circuit breaker.

2. The combination according to claim 1, wherein an inlet chamber (71) is provided below the first piston (73) and an exhaust valve (70) controls the exhausting of fluid out of this chamber.

3. The combination according to claim 2, wherein a check valve (72) leads into the inlet chamber (71).

4. A hydraulic linkage for operating a mechanism which requires a higher force at the end of one direction of movement than during the middle portion of travel in said direction of movement comprising a first piston (73) movable within a first operating cylinder (69a) having an inlet chamber (71), a second operating cylinder (74) fixedly secured to said first position and having a second piston (9) movable therein, said second piston (9) having a piston-rod extension (11a) with a hydraulic passage (75) provided therein, and means for delaying the registration of the hydraulic passage (75 into the inlet chamber (71) [or a predetermined time during the movement in said one direction.

5. The combination according to claim 4, wherein a check valve (72) and an exhaust valve (70) controls said inlet chamber (71).

6. The combination according to claim 4, wherein cushioning is provided at the end of said one direction by throttling the passage of hydraulic fluid into said passageway (75).

7. The combination according to claim 1, wherein the cross-sectional area of the second piston is larger than that of the first piston.

8. The combination according to claim 1, wherein the hydraulic supply to said line occurs close to the time of halting of the closing movement of the first hydraulic piston.

9. The combination of claim 4, wherein the cross-sectional area of the second piston (9) is larger than that of the first piston (73).

10. The combination according to claim 1, wherein a check valve (72) leads into an inlet chamber (71) provided below the first piston (73).

11. The combination according to claim 1, wherein an additional piston moves with the first piston 73 only during the initial part of the closing stroke of the breaker.

References Cited UNITED STATES PATENTS 762,627 6/1904 Fink 9l189 1,612,007 12/1926 Furlong 91l73 1,997,965 4/1935 Daly 91-173 2,394,086 2/1946 Ludwig et a1. 91189 3,306,031 2/1967 Moiroux et al 91173 PAUL E. MASLOUSKY, Primary Examiner US. Cl. X.R.