US3835275A

US3835275A - Electric power circuit breaker equipped with a latching mechanism wherein restoring forces are provided as a function of switching shaft position

Info

Publication number: US3835275A
Application number: US00352202A
Authority: US
Inventors: B Preuss
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1972-04-19
Filing date: 1973-04-18
Publication date: 1974-09-10
Anticipated expiration: 1991-09-10
Also published as: GB1426642A; JPS559774B2; JPS4916864A; DE2219892C3; IT982037B; FR2202359A1; DE2219892A1; DE2219892B2; FR2202359B1

Abstract

An electric power circuit breaker is disclosed wherein the latching mechanism as well as other parts which affect the motion of the contacts are returned by restoring forces to their initial position after the breaker is opened. The restoring forces are made ready in dependence on the position of the switching shaft of the breaker and are smaller in the closed position of the switching shaft than in the open position thereof. The invention is suited particularly for low-voltage power circuit breakers for high rated currents wherein the economic configuration of the required springs is of importance.

Description

United States Patent 1191 Preuss 1 Sept. 10, 1974 [5 1 ELECTRIC POWER CIRCUIT BREAKER 3,098,134 7/1963 Nijland 200/153 H EQUIPPED WITH A LATCHING 3,600,541 8/1971 Goodwin, Jr. 200/153 G MECHANISM WHEREIN RESTORING FORCES ARE PROVIDED AS A FUNCTION OF SWITCHING SHAFT POSITION Inventor: Bernhard Preuss, Berlin, Germany Siemens Aktiengesellschaft, Munich, Germany Filed: Apr. 18, 1973 App]. No.: 352,202

Assignee:

Foreign Application Priority Data Apr. 19, 1972 Germany 2219892 Primary Examiner-Robert K. Schaffer Assistant Examiner-Gerald P. Tolin Attorney, Agent, or Firm-Kenyon & Kenyon Rielly Carr & Chapin An electric power circuit breaker is disclosed wherein the latching mechanism as well as other parts which affect the motion of the contacts are returned by restoring forces to their initial position after the breaker is opened. The restoring forces are made ready in dependence on the position of the switching shaft of the breaker and are smaller in the closed position of the switching shaft than in the open position thereof. The invention is suited particularly for low-voltage power circuit breakers for high rated currents wherein the economic configuration of the required springs is of importance.

ABSTRACT 8 Claims,- 3 Drawing Figures ELECTRIC POWER CIRCUIT BREAKER EQUIPPED WITH A LATCHING MECHANISM WHEREIN RESTORING FORCES ARE PROVIDED AS A FUNCTION OF SWITCHING SHAFT POSITION BACKGROUND OF THE INVENTION Electric power circuit breakers can be equipped with a latching mechanism which serves in particular for mechanical latching and tripping as well as trip-free releasing the contact members and effecting force transformation when switching the breaker to the closed position. These functions are realized by lever arrangements, clutches, linkages, cams or similar members. These members can occupy two main positions, namely, for the closed position and the open position of the contact members of the circuit breaker.

If a power circuit breaker is to be reclosed after opening, certain parts of the latching mechanism must first be returned to their initial position in preparation for the breaker closing operation. A latching lever, for instance, must be returned from the released position to the latched position. In conventional arrangements, this is achieved by means of auxiliary forces which are supplied, for example, by means of suitable springsor by means of a reversible motor drive. In this connection, reference may be had to the German publication: Starkstromtechnik, Vol. II, 8th ed., 1960, Verlag Wilh. Ernst & Sohn, pp. 188 to 190.

SUMMARY OF THE INVENTION The invention is based on an electric power circuit.

breaker provided particularly for low voltage. The circuit breaker includes a drive mechanism and a latching mechanism containing a switching shaft as well as a latching lever which can be released by a tripping device. Also provided are additional members which can be returned to their initial position by restoring forces after the breaker opens.

It is an object of the invention to provide an electric power circuit breaker which achieves an improved balance of forces of the latching mechanism which makes possible, in particular, energy storage devices of more economical construction for closing and opening the power circuit breaker.

According to the invention, the restoring forces are made available in dependence on the position of the switching shaft and are smaller in the closed position of the switching shaft than in the open position. This makes it unnecessary for the restoring forces for the latching lever and other members of the latching mechanism to act continuously; instead, these forces are provided only when they are needed. As a consequence, the breaker opening spring required for opening the contacts of the power circuit breaker, for instance, can be made weaker than would be possible if the return spring of the latching lever in the latching mechanism were fully effective continuously. A delay in switching open is thereby avoided at the same time.

The electric power circuit breaker of the invention includes as a feature contact means switchable between open and closed positions; a latching mechanism for actuating the contact means; and a drive mechanism operatively connected to the latching mechanism for initiating the closing of the contact means by the latching mechanism. The latching mechanism includes a switching shaft operatively connected to the contact means and rotatable between first and second positions corresponding to the open and closed positions of the contacts respectively. Lever means is provided as part of the latching mechanism and is responsive to the drive mechanism for rotating the switching shaft from the first position to the second position. The lever means has a plurality of interacting lever parts movable between an initial position and an end position corresponding respectively to the first and second positions of the switching shaft. A latching lever coacts with the lever means to hold the switching shaft in the second position and tripping means releasably engages the latching lever for releasing the latching lever to withdraw the hold on the lever means. Breaker opening means is operatively connected to the shaft for moving the shaft from the second position to the first position when the latching lever is realeased by the tripping means. The latching mechanism further includes a first resilient means connected to the lever means for directing at least a portion of the interacting parts to the initial position by the action of a restoring force developed in the first resilient means in response to the movement of the switching shaft from the second position to the first position, and a second resilient means engages the latching lever and develops a restoring force for returning the latching lever to the tripping means in response to the movement of the shaft from the second position to the first position whereby the magnitude of the restoring force developed by the second resilient means is less when the shaft is in the second position than when the shaft is in the first position.

The invention can, for instance, be realized in a form that in a power circuit breaker which includes a switching lever rigidly connected with the switching shaft, the switching lever serves as an anchor for a return spring. The return spring is tensioned only when the switching shaft with the switching lever arrives in the open position. If, for instance, a latching lever is provided which is pivoted at one end and cooperates at its other end-with a tripping shaft, the switching lever may be connected articulately with a bending spring which is braced against a fixed anchor point and a stop of the latching lever and which develops a bending stress that increases as the switching lever moves into the open position. This bending spring may consist of spring wire for example.

Thus, according to another feature of the invention, one of the interacting parts of the lever means is a switching lever rigidly mounted on the switching shaft. The first resilient means can be a first spring having one end anchored to the switching lever, and the second resilient means can be a second spring also anchored to the switching lever.

Still another feature of the invention provides that the latching lever be pivotally mounted'at one end thereof and have a bracing stop disposed thereon for bracing the second spring. The tripping means can be a tripping shaft releasably engaging the other end of the latching lever. The latching mechanism can include stationary anchor means for bracing the second spring and the second spring is a bending spring articulately joined to the switching lever and drawn about the bracing stop to increase the bending stress in the bending spring as .the switching lever moves with the switching shaft from the second position to the first position. According to a subsidiary feature, the bending spring consists of spring wire.

The invention can also be used for returning members of the latching mechanism which serve to transmit the closing force. It is, for example, suited for power circuit breakers wherein the force is transmitted to the switching shaft via an idler lever pivotally mounted on the switching shaft and a coupling member arranged between the idler lever and the switching lever. In a further embodiment of the invention, the one lever of an elbow lever system can be articulately connected to the idler lever, and a tension spring can be arranged between the other lever of the elbow lever system and the switching lever. The points of connection of the spring is chosen so that the spacing therebetween is essentially maintained during the breaker closing operation. No restoring force of the elbow lever system must therefore be overcome .when the breaker is closed. The tension spring is tensioned only when the breaker opens whereby the restoring force is made available.

According to another feature of the invention, the first resilient means is a tension spring and one of the lever parts of the lever means is a switching lever rigidly mounted on the switching shaft. An other one of the lever parts is an idler lever pivotally mounted on the switching shaft and a further one of the lever parts is a coupling lever arranged between the switching lever and the idler lever. A still further one of the lever parts is an elbow lever made up of two lever arms pivotally connected to each other. One of the lever arms of the elbow lever is articulately joined to the idler lever. The switching lever and the other one of the lever arms of the elbow lever have respective spring mounts disposed thereon so as to maintain an approximately constant spacing therebetween as the switching shaft is rotated from the first position to the second position, the tension spring being arranged between the spring mounts.

Although the invention is illustrated and described herein as an electric power circuit breaker equipped with a latching mechanism, it is nevertheless not intended to be limited to the details shown, since various modifications may be made therein within the scope and the range of the claims. The invention, however, together with additional objects and advantages will be best understood from the following description and in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of a power circuit breaker for low voltage according to the invention. The diagram shows essentialelements of the latching mechanism and the drive mechanism of the power circuit breaker.

FIG. 2 is a detailed schematic diagram of the latching mechanism shown separately in an enlarged scale. The latching mechanism is in its open position with the latching lever locked.

FIG. 3 shows a schematic diagram similar to FIG. 2 and shows the latching mechanism in two different positions, namely. at the start and at the end of the breaker opening operation.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION Referring to FIG. 1, a power circuit breaker 1 is shown which is equipped with a drive mechanism 2.

The current path of the power circuit breaker 1 includes an upper terminal block 3 and a stationary contact 4 rigidly connected therewith. A movable contact 5 is disposed opposite contact 4. A bendable conductor section 7 is arranged between the contact 5 and a lower terminal block 6. Between the fixed contact 4 and the movable contact 5 are situated parallel conductor sections 10 andv 11, which for high currents cause an increase of the contact pressure between the contacts 4 and 5.

The latching mechanism of .the power circuit breaker 1 which is shown in FIG. 1 includes a switching shaft 12 with a two-arm lever 13 having a lever arm 14 connected with an elbow lever system which in its entirety is designated by reference numeral 15 and having another lever arm 16 engaging the movable contact 5 by means of a lever 17. A link 20 serves to guide the movable contact 5. The movable contact 5 and the conductor section 11 connected therewith is further engaged by a spring 21 which generates the contact pressure in the closed breaker position and also opens the movable contact when the breaker is switched open. The elbow lever system 15 is braced with the one elbow lever 22 against an interlock device 23. The interlock device 23 comprises a latching lever 24, a latching pawl 25 and a return spring 26 for the latching pawl 25.

The drive mechanism 2 connected with the power circuit breaker 1 includes a torsion rod spring 30 which is clamped at one end in a support 31. The torsion rod spring 30 carries a cam 32 at its front end. A projection 33 of the cam 32 can be engaged by a dog 34 which is fastened on a shaft 35 upon which a hand lever 36 acts. The torsion rod spring 30 may be a solid member, but preferably, it is made up of a stack of individual leaf springs.

In FIG. 1, the hand lever 36 is shown in a position just before reaching the closed position indicated by the broken line 37. If the hand lever 36 is moved still further, the dog 34 slides off the projection 33 and releases the cam 32. The cam 32 rotates counterclockwise and presses against a roller 18 arranged at the joint of the elbow lever system 15 until the elbow lever system 15 goes past its dead center position and the elbow lever 22 comes to rest against a stop 28. The described motion of the elbow lever system 15 causes a clockwise rotation of the switching shaft 12 and therefore the closing of the power circuit breaker 1.

If the power circuit breaker l is to be switched open, the latching pawl 25 is pulled off the latching lever 24 in the direction of the arrow 29. The support of the elbow lever system 15 is thereby withdrawn, and the spring 21 pulls the movable contact 5 into the position shown in FIG. 1.

In the following, the construction and operation of the latching mechanism will be described in detail. In FIGS. 2 and 3, the switching shaft 40 corresponds to the switching shaft 12 shown in FIG. 1. The

levers

42 and 43 form the elbow lever system designated by reference numeral 15 in FIG. 1. The lever 43 is pivotally mounted on a stationary bearing post 44 and has an extension 45 which projects out beyond the pivot post 44 and which in the, open position of the breaker according to FIG. 2 rests against a stop 48. The other lever 42 is linked with an idler lever 47 by means of a further pivot pin 49. The idler lever 47 is mounted on the switching shaft 40'and has a working surface 50 which coacts with a roller 52 of a roller lever 51. The roller lever 51 is supported by means of a pivot pin 53 on a switching lever 54 which is rigidly connected with the control shaft 40. On the roller lever 51, a further roller 55 is provided and is guided on a circular track 57 of a latching lever 56. The latching lever 56 is of approximately sickle-shaped configuration and is pivotally mounted at its one end about a pin 60. At its other end, the latching lever 56 has a nose 62 which, in the closed position, rests against a tripping shaft 63. A fixed stop 68 limits the travel of the latching lever 56 when the breaker switches to the open position.

At the end of the switching lever 54 there is an opening 61 wherein a long bendable spring 65 is engaged. The spring 65 is guided between the stationary stops 66 and 67 and coacts with a stop 70 of the latching lever 56, the stop 70 being in the region of the circular track 57.

The switching lever 54 further has a rear extension 71 at which a pin 73 is arranged as the anchor for a tension spring 72. With its other end, the tension spring 72 engages the anchor point 74 of the extension 45 of the elbow lever 43.

If a force acts on the elbow lever joint 41 of the elbow levers 42 and 43 as already explained in connection with FIG. 1, the idler lever 47 is swung counterclockwise as the elbow levers 42 and 43 stretch out to a greater extent and the roller lever 51 with its roller 55 is thereby led along the circular track 57 of the latching lever 56. The switching lever 54 and the switching shaft 40 are likewise taken along in a counterclockwise direction. With this movement the breaker enters its closed position (depicted by solid lines in FIG. 3) where the lever 43 rests against a stop 46 and is in a position beyond the dead center positionv In this breaker closing operation, the rear extension 71 of the switching lever 54 and the extension 45 of the lever 43 are moving in the same direction, so that the spacing of the anchor points 73 and 74 of the tension spring 72 remains practically unchanged. The tension spring 72 is therefore not tensioned.

To switch the breaker to the open position, the nose 62 of the latching lever 56 is released by rotating the tripping shaft 63. The latching lever 56 thereby assumes the position shown by solid lines in FIG. 3. In this movement, the roller 52 of the roller lever 51 slides off the working surface 50 of the idler lever 47 and the switching lever 54 with the switching shaft 40 rotate to arrive in the open position under the influence of the stored breaker opening force as shown by the brokenline contour in FIG. 3.

The point of application of the bending spring 65 on the switching lever 54 moves along a circular line during the opening operation which has the consequence that the bending spring 65 lies against the stop 70 of the latching lever 56 and is bent in such a manner that a re storing force is exerted on the latching lever 56. A comparison of FIGS. 2 and 3 shows that the bending stress in the open position is greater than in the closed positlon.

FIG. 3 shows furthermore that the movement of the switching lever 54 from the closed position to the open position is accompanied by a tensioning of the tension spring 72 thereby making available the restoring force which is necessary to bring the elbow levers 42 and 43 into the position corresponding to FIG. 1.

Because of the fact that the tension spring 72 is not tensioned in the breaker closing operation, the drive mechanism of the power circuit breaker need not overcome additional forces in closing. Similarly, the breaker opening spring need not overcome any additional forces during the opening operation because the bending spring 65 is largely relaxed. This results not only in a favorable balance of forces, but also in particularly rapid tripping. I

What is claimed is:

1. An electric power circuit breaker comprising contact means switchable between open and closed positions; a latching mechanism for actuating said contact means; and a drive mechanism operatively connected to said latching mechanism for initiating the closing of said contact means by said latching mechanism; said latching mechanism including: a switching shaft operatively connected to said contact means and rotatable between first and second positions corresponding to said open and closed positions of said contact means respectively, lever means responsive to said drive mechanism for rotating said switching shaft from said first position to said second position, said lever means having a plurality of interacting lever parts movable between an initial position and an end position corresponding respectively to said first and second positions of said shaft, a latching lever coacting with said lever means to hold said switching shaft in said second position, tripping means releasably engaging said latching lever for releasing said latching lever to withdraw said hold on said lever means, breaker opening means operatively connected to said shaft for moving said shaft from said second position to said first position when said latching lever is released by said tripping means, first resilient means connected to said lever means for directing at least a portion of said interacting parts to said initial position by the action of a resilient restoring force developed in said first resilient means only in response to the movement of said shaft from said second position to said first position whereby the force developed by said drive mechanism acting upon said lever means is unopposed by the resilient force of said first resilient means when said switching shaft is rotated from said first position to said second position, and second resilient means engaging said latching lever so as to be largely relaxed when said shaft is in said second position and to develop a restoring force for returning said latching lever to said tripping means in response to the movement of said shaft from said second position to said first position whereby the magnitude of said restoring force developed by said second resilient means is less when said shaft is in said second position than when said shaft is in said first position.

2. The electric power circuit breaker of claim 1, one of said interacting parts of said lever means being a switching lever rigidly mounted on said switching shaft, said first resilient means being a first spring having one end anchored to said switching lever, and said second resilient means being a second spring also anchored to said switching lever.

3. The electric power circuit breaker of claim 2, said latching lever being pivotally mounted at one end thereof and having a bracing stop disposed thereon for bracing said second spring, said tripping means being a tripping shaft releasably engaging the other end of said latching lever, said latching mechanism including stationary anchor means for bracing said second spring. said second spring being a bending spring articulately joined to said switching lever and drawn about said bracing stop to increase the bending stress in said bending spring as said switching lever moves with said switching shaft from said second position to said first position.

4. The electric power circuit breaker of claim 3, said bending spring consisting of spring wire.

5. The electric power circuit breaker of claim I, said first resilient means being a tension spring, one of said lever parts of said lever means being a switching lever rigidly mounted on said switching shaft, an other one of said lever parts being an idler lever pivotally mounted on said switching shaft, a further one of said lever parts being a coupling lever arranged between said switching lever and said idler lever, a still further one of said lever parts being an elbow lever comprising two lever arms pivotally connected to each other, one of said lever arms of said elbow lever being articulately joined to said idler lever, said switching lever and said other one of said lever arms of said elbow lever having respective spring mounts disposed thereon so as to maintain an approximately constant spacing therebetween as said switching shaft is rotated from said first position to said second position, said tension spring being arranged between said spring mounts.

6. The electric power circuit breaker of claim 5, said drive mechanism including force generating means arranged with respect to said elbow lever of said latching mechanism for imparting a force thereto whereby said elbow lever coacts with said idler lever, said coupling lever and said switching lever to transmit said force to said switching shaft.

7. The electric power circuit breaker of claim 6, said second resilient means being a bending spring, said latching lever being pivotally mounted at one end thereof and having a bracing stop disposed thereon for bracing said bending spring, said tripping means being a tripping shaft releasably engaging the other end of said latching lever, said latching mechanism including stationary anchor means for bracing said bending spring, said bending spring being articulately joined to said switching lever and drawn about said bracing stop to increase the bending stress in said bending spring as said switching lever moves with said switching shaft from said second position to said first position.

8. The electric power circuit breaker of claim 7, said bending spring consisting of spring wire.

Claims

3. The electric power circuit breaker of claim 2, said latching lever being pivotally mounted at one end thereof and having a bracing stop disposed thereon for bracing said second spring, said tripping means being a tripping shaft releasably engaging the other end of said latching lever, said latching mechanism including stationary anchor means for bracing said second spring, said second spring being a bending spring articulately joined to said switching lever and drawn about said bracing stop to increase the bending stress in said bending spring as said switching lever moves with said switching shaft from said second position to said first position.

5. The electric power circuit breaker of claim 1, said first resilient means being a tension spring, one of said lever parts of said lever means being a switching lever rigidly mounted on said switching shaft, an other one of said lever parts being an idler lever pivotally mounted on said switching shaft, a further one of said lever parts being a coupling lever arranged between said switching lever and said idler lever, a still further one of said lever parts being an elbow lever comprising two lever arms pivotally connected to each other, one of said lever arms of said elbow lever being articulately joined to said idler lever, said switching lever and said other one of said lever arms of said elbow lever having respective spring mounts disposed thereon so as to maintain an approximately constant spacing therebetween as said switching shaft is rotated from said first position to said second position, said tension spring being arranged between said spring mounts.