F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)

1. Title of the invention:
IMPROVED OPERATING MECHANISM FOR HIGH TORQUE APPLICATION IN CIRCUIT BREAKERS

2. Applicant(s):

(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : An Indian Company
(c) ADDRESS : L & T House, Ballard Estate, Mumbai 400 001, State
of Maharashtra, India

3. PREAMBLE TO THE DESCRIPTION

The following specification particularly describes the invention and the manner in which it is to be performed:

TECHNICAL FIELD OF THE INVENTION

The present invention relates generally to operating mechanism and more particularly to an improved operating mechanism for high torque application in circuit breakers.

BACKGROUND AND THE PRIOR ART

Circuit breakers are mechanical switching devices capable of making, carrying and breaking currents under normal circuit conditions and also making, carrying for a specified time and breaking currents under specified abnormal conditions. A circuit breaker basically consists of a pair of separable contacts and an interrupting medium. The function of the contacts is to conduct the electrical current when the breaker is closed and to withstand the arcs while interrupting. Generally the electrical contacts have a stationary part and a moving part. By bringing the moving contact to touch the stationary contact, an electric current flows and the breaker is closed. By driving the moving contact away from the stationary contact, an electric arc is developed and by quenching the electrical arc, the flow of electrical current is stopped and the breaker is opened.

Some of the prior arts related to present field of invention are as follows:

US4528531 provides a molded case circuit breaker includes a highly integrated operating mechanism having an over-center toggle mechanism for opening and closing a pair of electrical contacts and a trip mechanism for responding to overload and short circuit or fault current conditions to separate the pair of electrical contacts. A generally flat, intermediate latch plate includes an upper latch surface for latching with a movable cradle of the over-center toggle mechanism and a lower latch surface for latching with a trip bar of the trip mechanism and a pair of outwardly projecting pivot arms disposed between the upper and lower latch surfaces. The over-center toggle mechanism includes a pair of upper toggle links and a pair of lower toggle links interconnected by a toggle spring pin. To increase the speed of separation of the first and second electrical contacts during a trip operation, the cradle is physically configured to engage and upwardly propel the toggle spring pin and, also, the upper toggle links have projections for physically contacting a rigid stop.

US6479774B1 provides a circuit breaker operating mechanism comprises a movable handle yoke, a mechanism spring extending in tension from the handle yoke to a pin, and a lower link extending from the pin to a crank operably connected to a contact arm bearing a movable contact. The crank is positionable in open and closed positions, being in an open position when the movable contact is separated from an associated fixed contact and being in a closed position when the movable contact is mated to said associated fixed contact. The circuit breaker further comprises an interface formed on said crank and a blocking prop having a first surface that engages said interface, the first surface preventing the crank from rotating towards the closed position.

US6590172B1 provides a circuit breaker is provided wherein the circuit breaker comprises a contact arm movable between a closed position, an open position and a blown open position wherein the contact arm is disposed in the circuit breaker. A bumper disposed to contact the contact arm when the contact arm is in the blown open position. In addition, a stop member disposed to be in contact with a linkage assembly so as to create a gap between the bumper and the contact arm when the contact arm is disposed in the open position.

US5369384 provides the breaker mechanism for power circuit breakers is the energy storage link between the handle and the contact systems. Known breaker mechanisms are generally too expensive to manufacture. When contact welding occurs, there is also the risk that, in spite of the tripping of the breaker mechanism, the contact system will not open. The new breaker mechanism reliably opens the contact system and consists of fewer and technologically simpler individual parts. It is inserted between two symmetrical breaker plates held in a die cast housing, and in which a connecting piece is mounted. Two toggle levers are connected at a distance from one another by means of a connecting shaft engaged in crossbar cam slots. A toggle lever spring is engaged between the connecting piece and the connecting shaft. A bracing lever which can be driven by the connecting piece is friction locked in the breaker plates, and the toggle levers in the bracing lever. A latch lever and a latch holding the latter in the locked position are friction locked by means of a latch spring in recesses of the breaker plates.

US4864263 provides an industrial rated molded case circuit breaker having an electronic trip circuit contained within the circuit breaker enclosure includes a reset spring in cooperation with the circuit breaker latch spring to insure manual reset of circuit breaker after an automatic trip function. The reset spring allows the circuit breaker latch assembly to be manually reset upon minimum travel of the circuit breaker operating handle due to internal circuit breaker component space restrictions. The circuit breaker latch assembly is robotically loaded to the operating mechanism which is then attached to the circuit breaker case by an automated fastening process.

The inventions mentioned have the Upper Link construction such that the point where the spring is attached to the Upper Link and the point where the Upper Link is attached to the Lower Link are the same. In the cases that the afore-mentioned is not true, the distance of the Upper Link pivot from the Spring Pivot point is less than or the same as its distance from the point where it is connected to the Lower Link.

Therefore there is a need to provide an Upper Link whose construction is in such a way that the distance of the Upper Link pivot from the spring pivot (via the Bell Crank) point is greater than its distance from the point where it is connected to the Lower Link. This ensures a mechanical advantage of the force exerted by the Upper Link on the Lower Link with respect to the force with which the spring pulls the Upper Link towards the Spring Pin.

The present invention therefore provides a compact Operating Mechanism of Molded Case Circuit Breaker which enables it to make, carry and break current under normal circuit condition and also break during abnormal conditions. This invention describes a compact Operating Mechanism which is used for Molded Case Circuit Breakers, whose Contact Systems require very high Making Torque. The Operating Mechanism consists of various linkages and use extension springs as energy means.

OBJECTS OF THE INVENTION

A basic object of the present invention is to overcome the disadvantages/drawbacks of the known art.

Another object of the present invention is to provide an improved operating mechanism for high torque application in circuit breakers.

Yet another object of the present invention is to reduce stress at extension springs.

These and other advantages of the present invention will become readily apparent from the following detailed description read in conjunction with the accompanying drawings.

SUMMARY OF THE INVENTION

The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the present invention. It is not intended to identify the key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concept of the invention in a simplified form as a prelude to a more detailed description of the invention presented later.

There is provided an improved operating mechanism for high torque application in circuit breakers.

According to one embodiment of the present invention, there is provided an improved operating mechanism for high torque application in circuit breakers comprising atleast one side plate (3a) having four bar linkage pivoted thereon; atleast one upper link (3c) provided on side of latch; atleast one lower link (3b) connecting said upper link with a rotor and a moving contact (4) attached thereto; atleast one latch link (3d), said latch link having upper link pivoted thereto; atleast a fork (3e) carrying one end of an extension spring and other end of said extension spring connected to a bell crank (3h); atleast one spring pin (3f) placed on a groove on said fork having said extension spring mounted thereon; atleast a knob (3g)acting as a user interface for said circuit breaker; atleast one spring means (3i) having one end connected to a spring pin and other end connected to a floating pin; atleast one upper link retainer connecting said upper links thereby restricting independent movement; wherein said operating mechanism adapted to provide substantially high torque to the contacts.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The following drawings are illustrative of particular examples for enabling methods of the present invention, are descriptive of some of the methods, and are not intended to limit the scope of the invention. The drawings are not to scale (unless so stated) and are intended for use in conjunction with the explanations in the following detailed description.

Fig. 1 illustrates Isometric view of the 3 pole Circuit Breaker cassette with Breaker in ON condition.
Fig. 2 illustrates Isometric view of the single pole Circuit Breaker cassette with Breaker in ON condition.
Fig.3 illustrates Isometric view of Mechanism in ON condition with Breaker Cassette hidden.
Fig. 4 illustrates sectional view of Mechanism in ON position.
Fig. 5 illustrates sectional view of Mechanism in OFF position.
Fig. 6 illustrates sectional view of Mechanism in TRIP condition.
Fig. 7 illustrates Mechanism in ON condition.
Fig. 8 illustrates Isometric view of the Linkages in OFF position.
Fig.9 illustrates Mechanism in TRIP position.
Fig.10 illustrates exploded view of the Linkages in OFF position.
Fig.11 illustrates exploded view of the mechanism in ON position.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly in the present invention an improved operating mechanism for high torque application in circuit breakers is provided.

Elements and Construction:

1: Circuit Breaker Cassette: It is the base on which the Circuit Breaker Operating Mechanism module is mounted. It houses the Contact System.
2: Rotor: It is the part which houses the Moving Contact assembly.
3: Operating Mechanism module: It is used to provide the Contact Pressure necessary for making the circuit. It consists of a 4-bar linkage.
3a: Side Plate: It is where the 4-bar linkage of the Operating Mechanism is pivoted.
3b: Lower Link: It connects the Upper Link with the Rotor. There is one Lower Link for each Upper Link.
3c: Upper Link: It is the prime-mover for the Operating Mechanism. It decides the position of dead centre during ON-OFF and OFF-ON operation. Its pivot is fixed during ON-OFF and OFF-ON operation and moving during TRIP operation. There is two of them pivoted on either side of the latch.
3d: Latch Link – It is the link on which the Upper Link is pivoted. It moves during ON to TRIP condition.
3e: Fork: It is the link which is to be moved to operate the Operating Mechanism. It carries one end of the extension springs, the other end of which is connected to the Bell Crank.
3f: Spring Pin – It sits on a groove on the Fork. It is where the extension spring is mounted.
3g: Knob – It is a part of the Fork. It acts as the user interface for the Circuit Breaker.
3h: Bell Crank: It is a stiff rotary member that holds the other end of the extension spring. The Upper Link derives torque from the Extension Spring through this link.
3i: Springs: springs are energy storing elements. One end of which is connected to spring pin and another end is to floating pin.
3j: Upper Link Retainer: It connects the two Upper Links together to ensure that they don’t move independent of each other.
4: Moving Contact: It is the moving part of the current carrying circuit.
5: Fixed Contact: It is the fixed part of the current carrying circuit.

Dead centre- Dead centre is an equilibrium condition of the Operating Mechanism. In this condition, the extension springs are fully charged, and beyond this point- the Operating Mechanism flips and operates independently due to the energy discharged by the extension springs.

WORKING:

The present invention relates to a Circuit Breaker which is a mechanical switching device, capable of making (i.e. switching ON), carrying and breaking (i.e. switching OFF) current under normal circuit conditions and more specifically breaking current (Tripping) during abnormal circuit conditions such as short-circuit. Quite often, the short circuit current is sensed automatically and the signal is given to the mechanism as a TRIP command which leads to opening of the contacts by means of mechanism. However, during normal ON-OFF and OFF-ON operation, input to mechanism is given through the rotation of Knob (3g) by manual means. The rotation of Knob (3g) leads to storing potential energy (spring charging) in the extension spring member (3i) while restricting the contact movement during the charging operation. At a specified instance the potential energy of the springs is released in the form of kinetic energy through the Mechanical Linkages leading to the rotation of the contacts at high velocity. Circuit Breaker Operating Mechanisms use dead-centre based extension spring arrangements.

Circuit breaker Operating Mechanism module (3) consists of Upper Link (3c), Lower Link(3b), Latch link(3d), Fork link (3e). A Spring Pin (3f) is connected to the Fork link(3e) and Bell Crank(3h) is connected to the Upper Link(3c). Extension spring is connected between Spring Pin (3f) and Bell Crank(3h). Knob(3g), is a part of the Fork link(3e) through which user gives the input. Lower Link(3b) is connected to the Rotor(2) to which the Moving Contact (4) is attached. During OFF-ON and ON-OFF operation, the Latch link(3d) is locked by in position by some means.

Fig. (5) illustrates the sectional view of the Operating Mechanism which is in OFF position. When Knob(3g) is rotated by user-applied force, spring(3i) connected between Spring Pin (3f) and Bell Crank(3h) get deflected up to dead-centre condition and after the dead-centre, the stored energy in the spring is converted into kinetic energy- which is used to rotate the Rotor(4) from OFF to ON position through Upper Link(3c) and Lower Link(3b). Moving Contact(4) touches the Fixed Contact (5) and the Breaker gets ON.

Fig. (4) illustrates the sectional view of the Operating Mechanism which is in ON position. When the Knob(3g) is rotated by user-applied force, spring(3i) connected between Spring Pin (3f) and Bell Crank(3h) get deflected till dead-centre condition and after the dead-centre, the stored energy in the spring is converted into kinetic energy- which is used to rotate the Moving Contact(4) from ON to OFF position through Upper Link(3c) and Lower Link(3b).

Fig. (6) illustrates the sectional view of the Operating Mechanism which is in TRIP position. The Latch link(3d), which was fixed during the OFF and ON conditions by some means, is now free to rotate- by the removal of the said means. At ON position, the spring has potential energy necessary to enable the Latch link(3d) rotation. Upper Link(3c) and Lower Link(3b) are connected to the Latch link(3d), and hence- the rotation of Latch link(3d) results in rotation of Rotor(2). Moving Contact(4) connected to the Rotor(2) also rotates and the Breaker gets disconnected and is in TRIP position.

Fig (8) illustrates the 4-bar Linkage in detail. The spring(3i), which is connected to the Upper Link(3c) via the Bell Crank(3h), gives a torque to the Upper Link(3c) in a direction towards the location of the Spring Pin(3f). Since the distance between the Bell Crank(3h) pivot and the Upper Link(3c) is larger than the distance between the Upper Link(3c)-Lower Link(3b) connection and the Upper Link(3c) pivot, the force exerted by the Upper Link(3c) on the Lower Link(3b) is much greater than the force with which the spring(3i) pulls the Upper Link(3c) via the Bell Crank(3h). The Upper Link Retainer(3j), which connects the two Upper Links(3c) pivoted on either sides of the Latch link(3d)- ensure that they do not move independently of each other.

Benefits of present invention:
1. The mechanical advantage provided by the improved Upper Link ensures that the Operating Mechanism can facilitate a very high contact pressure at the Contacts. This is because, the distance of the Upper Link pivot from the Bell Crank pivot is greater than its distance from the Upper Link-Lower Link connection point.
2. The Bell Crank ensures that the extension springs are not unduly stressed.
3. The features described above ensure that the Operating Mechanism is quite compact for a disproportionately high Making Torque requirement of the Contact System.
Although the embodiments herein are described with various specific embodiments, it will be obvious for a person skilled in the art to practice the embodiments herein with modifications. However, all such modifications are deemed to be within the scope of the claims.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the embodiments described herein and all the statements of the scope of the embodiments which as a matter of language might be said to fall there between.

WE CLAIM

1. An improved operating mechanism for high torque application in circuit breakers comprising:
atleast one side plate (3a) having four bar linkage pivoted thereon;
atleast one upper link (3c) provided on side of latch;
atleast one lower link (3b) connecting said upper link with a rotor and a moving contact (4) attached thereto;
atleast one latch link (3d), said latch link having upper link pivoted thereto;
atleast a fork (3e) carrying one end of an extension spring and other end of said extension spring connected to a bell crank (3h);
atleast one spring pin (3f) placed on a groove on said fork having said extension spring mounted thereon;
atleast a knob (3g)acting as a user interface for said circuit breaker;
atleast one spring means (3i) having one end connected to a spring pin and other end connected to a floating pin;
atleast one upper link retainer connecting said upper links thereby restricting independent movement;
wherein said operating mechanism adapted to provide substantially high torque to the contacts.

2. Mechanism as claimed in claim 1 wherein each said upper link having a lower link attached thereto.

3. Mechanism as claimed in claim 1 wherein said upper link adapted to derive torque from said extension spring through said bell crank.

4. Mechanism as claimed in claim 1 wherein said extension spring adapted to operate contacts by discharging extension springs.

5. Mechanism as claimed in claim 1 wherein said extension spring is substantially a dead centre based extension spring.

6. Mechanism as claimed in claim 1 wherein distance between said bell crank adapted to prevent stress of said extension springs.

7. An improved operating mechanism for high torque application in circuit breakers as herein described and illustrated with reference to accompanying drawings.