US2730589A

US2730589A - Circuit breaker with hydraulic motor controlled by main and pilot valves

Info

Publication number: US2730589A
Application number: US331043A
Authority: US
Inventors: Elijah R Perry; Nicholas W Morelli
Original assignee: Allis Chalmers Corp
Current assignee: Allis Chalmers Corp
Priority date: 1953-01-13
Filing date: 1953-01-13
Publication date: 1956-01-10
Anticipated expiration: 1973-01-10
Also published as: GB738150A

Description

E. R. PERRY ET AL CIRCUIT BREAKER WITH HYDRAULIC MOTOR CONTROLLED BY MAIN AND PILOT VALVES Filed Jan 13 1953 Jan. 10, 1956 QNWMM: (Mg/$1M @X. amp @Mvim Q50. @Kmd/U.

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United States Patent CIRCUIT BREAKER WITH HYDRAULIC MQTQR CONTROLLED BY MAlN AND PKLGT VALVES Elijah R. Perry, Stoughton, and Nicholas W. lllorelii,

Westwood, Mass., as'signors to Allis Chalmers facturing Company, Milwaukee, Wis.

Application January 13, 1953, Serial. No. SSLMS ll) Claims. (Cl. Mill-452) This invention relates to circuit breaker operating sys terns and more particularly to high speed circuit breaker operating devices which use energy stored in pneumohydraulic accumulators for closing pairs of arcing contacts.

The operation of a high capacity circuit breaker requires an energy storage device which will substantially instantaneously release a tremendous quantity of energy. The closing operation of a typical high capacity circuit breaker may demand as much as 130,960 inch pounds of ellort delivered during one-tenth of a second. This is approximately two hundred horsepower. it is not economical to provide a continuous source of power of such a value. Hence, energy storage at the location in the form of storage batteries, compressed air, or springs, has been the conventional solution. These systems have all been handicapped by the means required to translate the stored energy into final mechanical motion, or by the complex methods of the original translation of energy to the bulky storage means.

As circuit breakers are frequently required to operate in isolated locations, an operating mechanism which requires a minimum of maintenance is imperative.

The hydraulic operating mechanism described herein is proved to meet all of the requirements or" a circuit breaker prime mover. This particular arrangement of the hydraulic operating mechanism couples a pneumohydraulic system with a mechanical trip free operator. It should be understood, however, that other arrangements can be made similarly adaptable to the non trip free and electrically trip free types of operator without departing from the spirit of this invention.

Hydraulic systems have certain characteristics which make them desirable as an operating medium. The in compressibility of liquids permits the instantaneous transmission of power between two points as with a mechanical linkage. Unlike the mechanical linkage however, liquids can be transmitted through tubes in all directions without loss of function and without the use of hell cranks or other bulky or complicated apparatus. Bearings and guides are unnecessary. Transformation and translation of power can be easily and simply accomplished. Compactness is an inherent characteristic of modern high pressure hydraulic systems.

The new and improved hydraulic system disclosed herein was arranged to meet six major requirements, namely:

1. Simple and rugged design.

2. Greater dependability than with the prior art structures.

3. Greater ease of maintenance than with the prior art structures.

4. Higher speed of operation than with the prior art structures.

5. Manual operation under load.

6. At least five operations stored in the hydraulic system.

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This new and improved hydraulic mechanism solved three major problems of the prior art by:

1. Providing means of energy storage which meets the requirements of releasing a tremendous amount of power for a short period of time and is reliable and unaffected by temperature variations.

2. Providing a reliable hydraulic valve of simple and rugged design which is capable of high speed operation.

3. Providing a compact hydraulic system which reduces the volume of fluid flow and utilizes reasonable fluid velocities while maintaining maximum efficiency.

In accordance with this invention a new and improved device is provided which employs a pneumo-hydraulic accumulator controlled by an electrically actuated con trol valve means for producing an oil flow for controlling the movement of a pair of arcing contacts. This compact circuit breaker operating device may have a control valve and an electrically actuated pilot valve therefor mounted in the cylinder structure of the hydraulic motor of the high speed trip free operating mechanism. By combining the control valve and the electrically operated pilot valve in the cylinder structure of the fluid actuated motor for closing the circuit breaker contacts, the shortest possible fluid paths from the accumulator to the fluid motor are provided, thus eliminating losses due to friction of the fluid flowing through the pipe lines.

in this invention the normal time constant for the closing operation of a high speed reclosing circuit breaker system, which imposes the demand for a transient rather than a steady state condition of fluid flow in a hydraulic operator, is recognized. This new and improved operating system can be made to utilize effectively the extraordinary high rates of fluid flow that are obtainable within the limits of the hydraulic transient period of the operator. Hence, because of the transient type of fluid flow required in this operator, the rate of flow may be made very high for the size of the component parts without undue friction losses. Test results show that excessive flows over very short periods of time, as encountered in this device, do not result in excessive pressure drops or friction losses.

it is, therefore, one object of the present invention to provide a new and improved control arrangement for controlling the opening and closing velocities of the movable contacts of a circuit breaker structure.

Another object of this invention is to provide a new and improved circuit breaker operating system in which the fluid frictional losses and their consequent pressure drops are reduced to a minimum to provide high speed circuit breaker operation.

Yet another object of this invention is to provide a new and improved circuit breaker operating system in which the time constant of operation of the valve means for controlling flow of fluid to the contact actuating fluid motor is reduced to a minimum to enhance high speed circuit breaker operation.

A further object of this invention is to provide a new and improved hydraulic operator in which the shortest fluid paths possible are provided all external feed lines between a pilot valve, a control valve and the cylinder of a contact actuating fluid motor are eliminated.

A still further object of this invention is to provide a circuit breaker operating system in which the opening and reclosing speeds thereof are not aiiected by the ambient temperature, corrosive atmosphere in the immediate vicinity of the operator or long periods of inactivity of the operator.

Other objects and advantages of this invention will be apparent from the description when read in connection with the accompanying drawing, which represents, partly in section, a circuit breaker operating system in contact closed position embodying the present invention.

Referring more particularly to the drawing by characters of reference, the figure illustrates a hydraulically operating trip free mechanism 11 for a circuit breaker 12. The hydraulically operating trip free mechanism 11 comprises a hydraulic motor 13 of the cylinder and piston type and a trip free type linkage 14. Motor and circuit breaker 12 are operatively connected linkage 14.

As diagrammatically shown, the circuit breaker 12 comprises a pair of stationary contact members 15 and a movable contact member 16. The circuit breaker 12 is biased to open circuit position by means of accelerating spring 17. The movable contact member 16 is supported by a breaker rod 18 which, in turn, is supported by lever 19 pivoted at 2%. Lever 19 is connected to the trip free operating linkage 14 by means of operating rod 21.

The operating linkage 14 comprises a lever 22 pivoted at 23 and a lever 24 pivoted at 25. Levers 22 and 24 are interconnected by a toggle comprising two toggle elements 26 and 27. Toggle element 26 is pivotally connected to lever 24 by a pin carrying a roller 28, and toggle element 27 is pivotally connected at 29 to lever 22. Toggle elements 26 and 27 are pivotally joined together by a pin 39. Pin 30 supports a roller 31 which is acted upon by an operating ram 32.

In the contact closed position of the operating linkage 14, the upper position of pin 38 and roller 31 is controlled by an abutment 36. This abutment is made of any suitable resilient material and is adapted to minimize vibrations of the frame of the trip free mechanism 11 due to the impact of linkage 14- upon abutment 36. In the closed position of the circuit breaker 12, pin 3-1 forming the joint or connection between toggle elements 26 and 27 is supported by a spring biased prop 33. Spring 34 resets linkage 14 upon a trip free operation. Spring 34 is secured at one end on the frame of the trip free operating mechanism 11 and at the other end to a lug 35 of toggle element 27.

The circuit breaker 12 is tripped by spring 17 upon a predetermined movement of a tripping mechanism 4%. Tripping mechanism 49 comprises a first lever 41 pivoted at '42, a second lever 43 pivoted at 44 and a trip solenoid 45 comprising a plunger 4-6 adapted to act on lever 43. Plunger 46 can be operated either electromagnetically by energizing solenoid 45 or mechanically by manual means, i. e., by operation of a lever 47 pivoted at 43. Upon rotation of lever 43 about point 44 in the counterclockwise direction, lever 41 is free to pivot about pin 42 in the counterclockwise direction under the action of a force component transmitted to it by roller 28. The counterclockwise rotation of lever 41 causes counterclockwise movement of lever 24 followed by collapse of the toggle formed by toggle elements 26 and 27 and return of lever 24 to the position shown to cause the separation of the

circuit breaker contacts

15, 16.

In order to close the circuit breaker 12, a suitable liquid under pressure such as oil is admitted to hydraulic motor 13 which comprises a cylinder 7, a piston 8, and ram 32, from a reservoir of stored energy. In this hydraulic system energy is stored in a pneumohydraulic accumulator 50 which comprises a homogeneous, seamless, high pressure shell 51, cylindrical in shape and spun semispherical at either end. One end has an opening for a gas valve 52 which is molded to a pear shaped synthetic rubber bladder 53. The other end of accumulator 50 has an opening provided with a plug assembly 55. Incorporated in the plug assembly 55 is a poppet valve 56 which seals off opening 54 when the oil is completely expelled from shell 51. This action prevents the bladder 53 from extruding through theopening 54. I

The accumulator bladder 53 is precharged with dry nitrogen to approximately two-thirds of the desired system operating pressure. With no oil in the accumulator,

the bladder fills the entire interior of the accumulator shell 51. As oil is forced into the accumulator 50 from a reservoir 60 by means of a hand pump 61 or a motor driven pump 62, it compresses the bladder 53 and the pressure rises in accordance with Boyles Law. The only permanent stress which the bladder encounters is compression of its wall which is equal to the systems or precharge pressure. To insure proper operation throughout the temperature range encountered in circuit breaker applications, a commercial oil having a nearly fiat viscosity curve is chosen as the operating medium.

Accumulator 50 is connected to motor 13 through a high speed solenoid actuated pilot valve 63 and a control valve 64. Pilot valve 63 comprising a valve stem 65 and

valve elements

66 and 67 of minimum size and weight is actuated by a low power solenoid 68 having a very small time constant and controls the system pressure in such a manner as to control the actuation of the main control valve 64 without excessive delay. Main valve 64 comprises a valve stem 69 and valve elements 70, 71 and 72.

In order to increase the speed of operation of this pneumo-hydraulic operating system, the pilot valve 63 and the control valve 64 are arranged in cylinder 7 of motor 13. The speed of operation of the pneumo hydraulic operating system is determined by the velocity flow of liquid through the system. The velocity flow of liquid through the system is determined by the horsepower requirements of the circuit breaker, the pressure of the operating system and the pipe size of the system. The higher the system pressure, the greater the horsepower per cubic inch of liquid. It is desirable to use as high a pressure as practicable to keep the volume of liquid to be moved to a minimum. The choice of pressures to be used is one of economy and reliability. A pressure of three thousand pounds per square inch was found to be acceptable. The pipe size of the system was determined by the liquid volume and velocity relationship required. All pipe lines are kept as short as possible and with smooth bends where needed.

The circuit breaker system in the drawing is shown with the

contacts

15 and 16 in the closed circuit position and the tripping mechanism in a corresponding position. Upon the energization of trip solenoid 45, plunger 46 actuates lever 43 counterclockwise about point 44. After a predetermined movement of lever 43, lever 41 is released to rotate counterclockwise about point 42 under the action of a force component transmitted to it from roller 28. The counterclockwise rotation of lever 41 releases or unlocks the tripping mechanism 14. Upon counterclockwise movement of lever 41, roller 28 moves upward under the action of spring 17 causing the collapse of the toggle formed by elements 26 and 27 and the separation of

contacts

15, 16. During the collapse of elements 26, 27, pin 30 slides on prop 33.

Upon the complete collapse of the toggle formed by elements 26, 27, roller 28 settles back on its support 37. and lever 41 rotates clockwise under its biasing means to its original position where it holds roller 28 against its support 37. Trip latch 43 rotates back to its'origiual position by the action of a spring biasing means (not shown) to hold lever 41 in its original position.

To close'the

circuit breaker contacts

15 and 16 and to return the trip free linkage 14 to the position shown in the drawing, solenoid operated pilot valve 63 is energized. Because of the small time constant of the solenoid. the current therein rapidly reaches its full intensity to actuate

valve elements

66 and 67 upward to permit liquid under pressure to flow from accumulator 50 through a pipe 75, pipe 76, pilot valve 63, pipe 77 to the right end of control valve 64. Liquid under pressure in pipe '77 moves valve stem 69 and valve elements 70, 71 and 72 to their extreme left position. With valve elements 76, 71 and 72 in their extreme left position liquid under pressure in pipe 75 flows through pipe 78, control valve 64, pipe 79 and into cylinder 7 of motor 13. At the same instant pipe 80 connected to the upper end of cylinder 7 of motor 13 provides an escape path for the liquid contained in the upper part of cylinder 7 through control valve 64, pipe 81 to reservoir 60.

The flow of liquid under pressure into cylinder 7 of motor 13 through pipe 79 causes piston 8 and ram 32 to move upward. The closing force of motor 13 is applied to linkage 14 by engagement of ram 32 with roller 31. Toggle elements 26 and 27 in moving upward during a closing stroke of piston 8, rotate lever 22 about its pivot point 23 in the counterclockwise direction. That rotary motion of lever 22 causes operating rod 21 to move downward. The downward movement of rod 21 causes lever 19 to rotate counterclockwise about its pin 29, thereby closing the breaker 12 against the action of accelerating spring 17.

When the toggle elements 26 and 27 reach prop 33 in their upward movement under the action of piston 8 and ram 32, pin 39 biases prop 33 clockwise and slides on it until roller 31 reaches abutment 36. After pin 3i) slides on prop 33, prop 33 rotates counterclockwise under the action of its biasing means until it is in a position to support pin 39. Lever 41 and trip latch 43 retain roller 28 in position adjacent stop 37. The toggle formed by elements 26 and 27 is retained in contact closed position by the combined action of prop 33, lever 41 and latch 43.

A closing operation is completed when prop 33, lever 41, and latch 43 have closed the contacts and locked the toggle elements in contact closed position. Then the supply of liquid under pressure may be automatically shut off. This may be achieved for instance, by a limit switch (not shown) controlled by pin which deenergizes solenoid es of pilot valve 63. Pilot valve 63 then moves to its lower position under the action of gravity and the action of an internally mounted solenoid spring (not shown).

Liquid under pressure from accumulator 54) then flows through pipes 75, 76, pilot valve 63, pipe 82 to the lefthand end of control valve 64 exerting pressure on valve element 70 to move valve stem 69 and valve elements '70, '71 and 72 to their extreme right position.

Liquid present in the right-hand end of control valve 64 is exhausted through pipe 77, pilot valve 63, pipe 83, pipe 84-, pipe 81 to reservoir 60. Liquid from accumulator 50 then flows through pipe 75, pipe '78, pipe 84 to the upper end of cylinder 7 of motor 13, causing ram 32 and piston 8 to return to their bottom or lower position. As the ram 3-2 and piston 8 return to their lower position, liquid under piston 3 flows through pipe 79, control valve 64, pipe and pipe 81 to reservoir 6d. Control valve 64 remains in the extreme right-hand position and pilot valve 63 remains in its lower position when solenoid 68 is deenergized. Reservoir 60 may be open to atmospheric pressure or closed and having an air cushion above the liquid level, thus preventing a pressure buildup in pipes 81, S5 and 79 which otherwise might cause creeping of the piston 8 of motor 13 toward its upper position.

Energy expended during operation is replenished in the accumulator by the power driven pump 62 or the hand pump 61. The maximum and minimum system pressures are controlled by a pressure actuated motor switch (not shown).

The hand pump 61 used for emergency closing can also be used as a maintenance closing device. To close the breaker by hand a small manual operating lever (not shown) is attached to the pilot valve 63 to latch the valve in its closed position. The hydraulic mechanism then acts as a simple hydraulic jack and the breaker can be jacked closed or to any intermediate position. Check valves within the hand pump lock the circuit breaker positively in any position, affording the maximum safety to inspection or maintenance personnel.

The hydraulic operating system offers several important advantages to the user of power circuit breakers. Maintenance is reduced to a minimum by virtue of the few moving parts which are employed. All moving parts within the system are constantly immersed in a liquid having excellent lubricating properties, therefore Wear between sliding surfaces is minimized. The completely sealed system protects all internal surfaces from corrosive effects of moisture and dirt. The small physical size of the hydraulic operating mechanism and its light weight make it easy to handle.

The hydraulic operating mechanism provides high speeds of operation when needed. Reclosing speeds far in excess of those presently required by circuit breaker standards are easily attainable.

The high elficiency of the hydraulic system has resulted in the reduction of the size of the motor required in the liquid supply unit. Compared to a pneumatic system of the same capacity, the motor required by the hydraulic system is much smaller. The pump up time from zero pressure to full operating pressure is about twenty-five percent of the time required on an air pressure system.

Tests indicated the ability of the hydraulic operating mechanism to obtain very high reclosing speeds. When coupled with a toggle linkage as shown, it is necessary that the ram 32 be rapidly retrieved from its upper position during repetitive reclosures of the breaker contacts. This is necessary to allow the mechanical trip free mechanism to reset quickly and permit the next reclosure. The return of ram 3.2, to its lower position was found to be controlled by the time necessary to shift valve elements 70, 71 and 72 of control valve 64 from left to right. It was determined by experiment, that the valve speed is approximately proportional to the operating pressure of the hydraulic system. Oscillograms show that pressure is instantaneously applied to piston 8 of motor 13 to actuate ram 32 to its lower position immediately after valve stem 69 of valve 6 starts to move to the left. To fully utilize the high speed characteristics of the hydraulic system, it is necessary to secure hi h control valve speeds.

Although but one embodiment of the present invention has been illustrated and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A circuit interrupting device comprising a pair of relatively movable contacts, a motor comprising a cylinder and a piston for causing relative movement of said contacts, a pneumohydraulic accumulator for supplying liquid under pressure, a control valve and a pilot valve both arranged in one end of said cylinder for causing actuation of said piston upon the flow of liquid under pressure therethrough, and means for connecting said accumulator to said valves, said control valve arranged to admit liquid under pressure from said accumulator to said cylinder on one side of said piston to actuate said piston in one direction and substantially simultaneously drain liquid from said cylinder on the other side of said piston, said control valve further arranged to admit liquid under pressure from said accumulator to said cylinder on said other side of said piston to actuate said piston in another direction and substantially simultaneously drain liquid from said cylinder on said one side of said piston, said pilot valve controllin actuation of said control valve to cause said control valve to initiate actuation of said piston in first one direction and then another direction.

2. A circuit interrupting device comprising a pair of relatively movable contacts, a motor comprising a cylinder and a piston for causing relative movement or" said contacts, a pneumo-hydraulic accumulator for supplying liquid under pressure, a control valve and a pilot valve for causing actuation of said piston upon the flow of liquid under pressure therethrough, and means for connecting said accumulator to said valves, said control valve arranged to admit liquid under presure from said accumulator to said cylinder on one side of said piston to actuate said piston in one directionand substantially simultaneously drain liquid fromsaid cylinder on the other side of said piston, said control valve further arranged to admit liquid under pressure from said accumulator to said cylinder on said other side of said piston to actuate said piston in another direction and substantially simultaneously drain liquid from said cylinder on said one side of said piston, said pilot valve controlling the actuation of said control valve to cause said control valve to initiate actuation of said piston in first one direction and then another direction.

3. A circuit interrupting device comprising pair or relatively movable contacts, a motor operable by liquid under pressureand comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for operatively relating the breaker to said motor, tripping means for causing collapse of said linkage to cause opening of said contacts, a ram on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, a control valve and a pilot valve for controlling the supply of liquid under pressure to said cylinder to cause actuation of said piston to re close said contacts, said control valve arranged to admit liquid under pressure on one side of said piston and sub stantially simultaneously to drain liquid from said cylinder on the other side of said piston, and a pneumo-hydraulic accumulator for supplying liquid under pressure to said valves.

4. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for operatively relating the breaker to said motor, tripping means for causing collapse of said linkage to cause opening of said contacts, a ram on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, a pneumo-hydraulic accumulator for supplying liquid under pressure, a control valve and a pilot valve for causing actuation of said piston upon the flow of liquid under pressure therethrough, and means for connecting said accumulator to said valves, said control valve arranged to admit liquid under pressure from said accumulator to said cylinder on one side of said piston to actuate said piston in one direction and sub stantially simultaneously drain liquid from said cylinder on the other side of said piston, said control valve further arranged to admit liquid under pressure from said accumulator to said cylinder on said other side of said piston to actuate said piston in another direction and substantially simultaneously drain liquid from said cylinder on said oneiside of said piston, said pilot valve controlling the actuation of said control valve to cause said control valve to initiate actuation of said piston in first one direction and then another direction.

5. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for-operatively relating the breaker to said motor, tripping means for causing collapse of said linkage to cause opening of said contacts, a ram on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, valve means for admitting liquid under presure to said motor and arranged in one end of said cylinder, and a pneumo-hydraulic accumulator for supplying liquid under pressure to sai' valve means.

6. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston 'movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for. operatively relating the breaker to said motor, tripping 1 means for causing collapse of said-linkage to cause opening of, said contacts, a rarn on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, valve means arranged in said cylinder for admitting liquid under pressure to said cylinder on oneside of said piston and for drainingliquid from said cylinder on the other side of said piston, and a pneumo-hydraulic accumulator for supplying liquid under pressure to said valve means.

7. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for operatively relating the breaker to said motor, tripping means for causing collapse of said linkage to cause opening of said contacts, a ram on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, a control valve and a pilot valve both arranged in one end of said cylinder for controlling the supply of liquid under pressure to said cylinder to cause actuation of said piston to reclose said contacts, said control valve arranged to admit liquid under pressure on one side of said piston and substantially simultaneously to drain liquid from said cylinder on the other side of said piston, and a pneumohydraulic accumulator for supplying liquid under pressure to said valves.

3. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a collapsible linkage of the trip free type for operatively relating the breaker to said motor, tripping means for causing collapse of said linkage to cause opening of said contacts, a ram on said piston separate from said linkage and cooperating therewith upon collapse thereof for reclosing said contacts, a pneumo-hydraulic accumulator for supplying liquid under pressure, a control valve and a pilot valve both arranged in one end of said cylinder for causing actuation of said piston upon the flow of liquid under pressure therethrough, and means for connecting said accumulator to said valves, said control valve arranged to admit liquid under pressure from said accumulator to said cylinder on one side of said piston to actuate said piston in one direction and substantially simultaneously drain liquid from said cylinder on the other side of said piston, said control valve further arranged to admit liquid under pressure from aid accumulator to said cylinder on said other side of said piston to actuate said piston in another direction and substantially simultaneously drain liquid from said cylinder on said one side or" said piston, said pilot valve controlling the actuation of said control valve to cause said control valve to initiate actuation of said piston in first one direction and then another direction.

9. A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged therein for causing relative movement of said contacts, a linkage for operatively relating said contacts to said motor, tripping means for causing movement of said linkage to, cause opening of said contacts, said motor arranged for reclosing said contacts, a control valve and a pilot valve for controlling the supply of liquid under pressure to said cylinder to cause actuation of said piston to reclose said contacts, said control valve arranged to admit liquid under pressure on one side of said piston and said motor substantially simultaneously draining liquid from said cylinder on the other side of said piston, and a pneumo-hydraulic accumulator for supplying liquid under pressure to said valves.

it). A circuit interrupting device comprising a pair of relatively movable contacts, a motor operable by liquid under pressure and comprising a cylinder and a piston movably arranged thereinfor causing relative movement of said contacts, a linkage for operatively relating said hydraulic accumulator for supplying liquid under pressure contacts to said motor, tripping means for causing moveto said valve means.

ment of said linkage to cause opening of said contacts,

said motor arranged for reclosing said contacts, valve References Cited 111 the file of this P means for controlling the supply of liquid under pressure 5 UNITED STATES PATENTS to said cylinder to cause actuation of said piston to reclose said contacts, said valve means arranged to admit liquid i i i g 2? g under pressure on one side of said piston and said motor 471 FOX g 8 1946 substantially simultaneously draining liquid from said 2,578,204 Peek Dec. 11, 1951 cylinder on the other side of said piston, and a pneumo- 10