FORM 2
The Patents Act 1970
(39 of 1970)
&
The Patent Rules 2003
COMPLETE SPECIFICATION
(See Section 10 and rule 13)
TITLE OF THE INVENTION:
JAW ASSEMBLY FOR WITHDRAWABLE TYPE CIRCUIT BREAKERS


APPLICANT:

LARSEN & TOUBRO LIMITED
Mysore Works, having office at KIADB Industrial Area,
Hebbal, Hootagahalli, Mysore- 570 018, Karnataka INDIA.

PREAMBLE OF THE DESCRIPTION:
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED

29 AUG 2008

A) TECHNICAL FIELD
[0001] The present invention generally relates to circuit breakers and particularly to withdrawal type circuit breakers. The present relation more particularly relates to jaw assembly for holding the withdrawal part of the circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] A Circuit breaker is a switching device used to interrupt the fault currents which occur in a circuit. It is mainly required to prevent the electrical system from the faults occurring in the system like over voltage, over current, short circuit etc. Circuit breakers are mainly of two types namely Fixed and Withdrawable type.
[0003] The circuit breaker mainly consists of a make/break contacts and the interrupting medium. The function of the make/break contacts is to conduct the electrical current when the breaker is closed and withstand the arcs while interrupting. Generally, the make/break contacts have a stationary part and a moving part. By bringing the moving contact to touch the stationary contact, electric current flows and the breaker is closed. By driving the moving contact away from the stationary contact the electric arc develops and by quenching it the current stops flowing and the breaker is open.
[0004] The design of the electrical contacts for the circuit breaker plays an important role in order to establish an efficient electrical connection between the fixed and withdrawable part of the circuit breaker. The moving part and the stationary part
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contact each other on closing and slide into each other to a certain distance before stopping at closed position. On opening, they slide out until their separation. The sliding action helps to make better contact on closing.
[0005] For an efficient electrical connection between the fixed and withdrawable part of the circuit breaker, a suitable contact connections are needed so that one can clamp unclamp the current carrying conductors of the withdrawable part effectively once breaker is in service and isolated positions respectively.
[0006] The prior art discloses a jaw assembly for connecting the fixed and movable part of the draw-out circuit beaker. The Jaw assembly completes the electrical circuit of the circuit breaker once the withdrawable type circuit breaker is in service position The jaw assembly used earlier utilizes a leaf spring slightly bent towards the centre. But this design is sufficient when the contact surfaces are on the inner sides of the jaw assembly. But when the contact surfaces are required to be at the outer surface of the jaw assembly this design cannot be used. Hence there is a need to develop a contact structure to maintain a uniform and adequate contact pressure at the contact point between the fixed and withdrawable part of the circuit breaker.
[0007] Thus there is a need to develop a jaw assembly to enhance the electrical contact between the fixed and the withdrawable parts of the circuit breakers. Also there is a need to maintain an effective contact pressure between the sliding surfaces of the circuit breaker thereby reducing the contact resistance and the power loss in the form of heat generated at the junction of the sliding surfaces.
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C) OBJECTS OF THE INVENTION
[0008] The primary, object of the present invention is to develop a jaw assembly to improve the electrical connection between the fixed and withdrawable parts of a circuit breaker reliably.
[0009] Another object of the present invention is to develop a jaw assembly to maintain the effective contact pressure between the sliding surfaces thereby reducing the contact pressure and the power loss due to heat at the junction of the sliding surfaces.
[0010] Yet another object of the present invention is to develop a jaw assembly to maintain a uniform and adequate contact pressure at the contact point.
[0011] Yet another object of the present invention is to develop a jaw assembly provided with a U shaped leaf spring so that the spring forces are reduced towards the end thereby reducing the racking force required initially to slide the current carrying conductors into the jaws.
[0012] Yet another object of the present invention is to develop a jaw assembly with a leaf spring to with stand the high amount of forces resulted from the faults like short circuit.
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[0013] Yet another object of the present invention is to develop a jaw assembly to prevent the two set of contacts from coming close to each other due to the high amount of electrodynamic forces generated due to high currents.
[0014] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
D) SUMMARY OF THE INVENTION
[0015] The abovementioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[0016] The various embodiments of the present invention provide a jaw assembly comprising of a leaf spring bent in U shape and arranged between two set of copper conductors to maintain a uniform and adequate contact pressure at the contact point. According to one embodiment of the present invention, the jaw assembly comprises the plurality copper conductors stacked together. A leaf spring is arranged between the two sets of copper conductor stacks assembled opposite to each other in a fixture. The leaf spring is arranged between the two sets of stacked copper conductors. Each leaf spring has a U shaped profile and flanges provided at the two ends to maintain uniform contact pressure on all the individual copper conductors thereby providing a firm and reliable electrical contact between the conductors and the fixed and withdrawal parts of the electrical contacts in a circuit breaker.
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[0017] Each copper conductor has a curved profile to come into contact with the end terminals of both the withdrawable and fixed part of a circuit breaker to complete an electrical circuit. Each copper conductor has a groove that rests along the fixture. Each copper conductor has supporting ends at one side to support and maintain the position of the leaf springs in the respective positions intact.
[0018] The fixture has a slot to hold the stack of copper conductors. The holes are provided to rivet the two leaf springs with the fixture to hold the leaf springs firmly thereby holding the leaf springs between the copper conductors and the fixture.
[0019] These and other objects and advantages of the present invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The other objects, features and advantages will occur to those skilled in the art from the following description of the preferred embodiment and the accompanying drawings in which:
[0021] FIGURE.l shows a perspective view of the U-shaped leaf spring used in a jaw assembly according to one embodiment of the present invention.
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[0022] FIGURK.2 shows a front view of the U-shaped leaf spring used in a jaw assembly according to one embodiment of the present invention.
[0023] FIGURE.3 shows a perspective view of the fixture used to hold the copper conductors and the leaf spring in a jaw assembly according to one embodiment of the present invention.
[0024] FIGURE.4 shows a perspective view of a copper conductor used in a jaw assembly according to one embodiment of the present invention.
[0025] FIGURE.5 shows a top side perspective view of a jaw assembly according to one embodiment of the present invention.
[0026] FIGURE.6 shows a front side perspective view of a jaw assembly according to one embodiment of the present invention.
[0027] FIGURE.7 shows a front side view of the jaw assembly according to one embodiment of the present invention.
[0028] FIGURE.8 shows a cross sectional view of the jaw assembly arranged between the end terminals of the fixed and withdrawal parts of the circuit breaker, according to one embodiment of the present invention.
[0029] Although specific features of the present invention are shown in some drawings and not in others. This is done for convenience only as each feature may be
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combined with any or all of the other features in accordance with the present invention.
F) DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0030] In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which the specific embodiments that may be practiced is shown by way of illustration. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments and it is to be understood that the logical, mechanical and other changes may be made without departing from the scope of the embodiments. The following detailed description is therefore not to be taken in a limiting sense.
[0031] The various embodiments of the present invention provide a jaw assembly comprising of a leaf spring bent in U shape and arranged between two set of copper conductors to maintain a uniform and adequate contact pressure at the contact point. According to one embodiment of the present invention, the jaw assembly comprises the plurality copper conductors stacked together. A leaf spring is arranged between the two sets of copper conductor stacks assembled opposite to each other in a fixture. The leaf spring is arranged between the two sets of stacked copper conductors. Each leaf spring has a U shaped profile and flanges provided at the two ends to maintain uniform contact pressure on all the individual copper conductors thereby providing a firm and reliable electrical contact between the conductors and the fixed and withdrawal parts of the electrical contacts in a circuit breaker.
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[0032] Each copper conductor has a curved profile to come into contact with the end terminals of both the withdrawal and fixed part of a circuit breaker to complete an electrical circuit. Each copper conductor has a groove that rests along the fixture. Each copper conductor has supporting ends at one side to support and maintain the position of the leaf springs in the respective positions intact.
[0033] The fixture has a slot to hold the stack of copper conductors. The holes are provided to rivet the two leaf springs with the fixture to hold the leaf springs firmly thereby holding the leaf springs between the copper conductors and the fixture.
[0034] The FIGURE.l shows a perspective view of the U-shaped leaf spring used in a jaw assembly according to one embodiment of the present invention, while the FIGURE.2 shows a front view of the U-shaped leaf spring. With respect to F1G.1 and FIG.2, a U shaped leaf spring has a U shaped base I provided with flanges 2 at the ends.
[0035] The leaf spring is arranged in U-shape leaf spring so that the spring forces are decreased towards the end thereby reducing the racking force which is initially required to slide the current carrying conductors into the jaws. But once the jaw assembly is completely engaged with the contacts of the circuit breaker, the leaf spring provides good contact pressure. Thus the variation in the spring action can be utilized. Also due to high stress bearing capacity of the leaf spring, the design is efficient in withstanding the high amount of forces resulting from high current faults like short circuit etc.
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[0036] FIGURE.3 shows a perspective view of the fixture used to hold the copper conductors and the leaf spring in a jaw assembly according to one embodiment of the present invention. With respect to FIG.3, the fixture has a frame provided with two slots 4 to receive two sets of stacked copper conductor assembly respectively. The fixture has holes to receive a fastener to secure the U shaped leaf spring provided between the two sets of stacked copper conductor assembly. The U shaped leaf springs provided between the stacks of copper conductor assembly is riveted to the fixture to hold the leaf springs firmly between the copper conductors and the fixture.
[0037] FIGURE.4 shows a perspective view of a copper conductor used in a jaw assembly according to one embodiment of the present invention. With respect to the FIG.4, each copper conductor has a curved profile 5 to come into contact with the fixed and the withdrawal parts of the electrical contacts in a circuit breaker to complete an electrical circuit. Each copper conductor has a groove 6 that rests along the fixture to hold the conductor assembly firmly and intact inside the fixture. Each copper conductor has supporting ends 7 like mini projections, at one side to support and maintain the position of the leaf springs in the respective positions intact.
[0038] FIGURE.5 shows a top side perspective view of a jaw assembly according to one embodiment of the present invention, while the FIGURE.6 shows a front side perspective view of a jaw assembly according to one embodiment of the present invention and the FIGURE.7 shows a front side view of the jaw assembly according to one embodiment of the present invention. With respect to FIGURE 5, 6 & 7, each jaw assembly has two sets of stacked copper conductor assembly inserted inside the slots of a fixture. The grooves in the copper conductors are made to receive the side
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frames of the fixture to hold the copper conductor assembly tightly. A U shaped leaf spring is arranged between the sets of copper conductor assembly and riveted to the fixture to hold the copper conductor assembly firmly.
[0039] FIGURE.8 shows a cross sectional view of the jaw assembly arranged between the end terminals of the fixed and withdrawal parts of the circuit breaker, according to one embodiment of the present invention. With respect to FIG.8, a jaw assembly 10 is inserted in a circuit breaker so that the curved profiles of the copper conductor are made to contact the end terminals 8, 9 connected to the withdrawal and the fixed parts of the electrical contacts in a circuit breaker.
[0040] Thus the various embodiments of the present invention provide a jaw assembly with a U shaped leaf spring to maintain effective contact pressure between the sliding surfaces in a circuit breaker thereby reducing the contact resistance and the power loss in the form of heat generated at the junction. The jaw assembly helps maintaining a uniform and adequate contact pressure at the contact point. The leaf spring provided between the copper conductors in the jaw assembly is formed in U-shape so that the spring force is decreased towards the end thereby reducing the racking force which is initially required to slide the current carrying conductors into the jaws. But once the jaw assembly is completely engaged, the spring provides good contact pressure. Thus the variation in the spring action is utilized to well to maintain a uniform and adequate contact pressure at the contact point. Also, due to the high stress bearing capacity of the leaf spring, the design is efficient in withstanding the high amount of forces resulting from high current faults like short circuit etc. Thus the U shaped leaf spring also prevents the two sets of electrical conductors from coming close to each other
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because of the high amount of electro dynamic forces generated due to high currents, the U shaped leaf spring mainly acts as an obstacle/isolator between the two sets of conductors. The flanges provided at the ends of the leaf spring helps in maintaining uniform contact pressure on all the individual copper conductors. Thus each individual conductor has a firm contact with the end terminals of both the fixed and withdrawal parts of the circuit breaker. The main benefit of using the U-shaped bent leaf spring is that in such a construction of a leaf spring, the amount of deflection per unit force applied increases towards the end of the profile thereby reducing the initial force required to insert the jaw assembly into the end terminal when the end terminals are racked into the jaw assembly. When the jaw assembly is completely inserted, then the deflection of the leaf spring towards the centre is decreased thereby maintaining a high contact pressure between the conductors and the end terminals.
G) ADVANTAGES OF THE INVENTION
[0041] Thus the various embodiments of the present invention provide a jaw assembly with a U shaped leaf spring to maintain effective contact pressure between the sliding surfaces in a circuit breaker thereby reducing the contact resistance and the power loss in the form of heat generated at the junction. The jaw assembly helps maintaining a uniform and adequate contact pressure at the contact point. The leaf spring provided between the copper conductors in the jaw assembly is formed in U-shape so that the spring force is decreased towards the end thereby reducing the racking force which is initially required to slide the current carrying conductors into the jaws. But once the jaw assembly is completely engaged, the spring provides good contact pressure. Thus the variation in the spring action is utilized to well to maintain a uniform and adequate
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contact pressure at the contact point. Also, due to the high stress bearing capacity of the leaf spring, the design is efficient in withstanding the high amount of forces resulting from high current faults like short circuit etc. Thus the U shaped leaf spring also prevents the two sets of electrical conductors from coming close to each other because of the high amount of electro dynamic forces generated due to high currents, the U shaped leaf spring mainly acts as an obstacle/isolator between the two sets of conductors. The flanges provided at the ends of the leaf spring helps in maintaining uniform contact pressure on all the individual copper conductors. Thus each individual conductor has a firm contact with the end terminals of both the fixed and withdrawal parts of the circuit breaker. The main benefit of using the U-shaped bent leaf spring is that in such a construction of a leaf spring, the amount of deflection per unit force applied increases towards the end of the profile thereby reducing the initial force required to insert the jaw assembly into the end terminal when the end terminals are racked into the jaw assembly. When the jaw assembly is completely inserted, then the deflection of the leaf spring towards the centre is decreased thereby maintaining a high contact pressure between the conductors and the end terminals.
[0042] Although the invention is described with various specific embodiments, it will be obvious for a person skilled in the art to practice the invention with modifications. However, all such modifications are deemed to be within the scope of the claims.
[0043] It is also to be understood that the following claims are intended to cover all of the generic and specific features of the present invention described herein and all the statements of the scope of the invention which as a matter of language might be said to fall there between.
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CLAIMS
What is claimed is:
1. A jaw assembly for circuit breaker having fixed and withdrawal parts, the
assembly comprising:
pluralities of conductors stacked together to form a stacked electrical
conductor assembly;
a U shaped leaf spring arranged between the two sets of stacked electrical
conductor assembly; and
a fixture to hold the stacked electrical conductor assembly together with the U
shaped leaf spring.
2. The assembly according to claim 1, wherein the electrical conductor is a copper conductor.
3. The assembly according to claim 1, wherein the U shaped leaf spring has U shaped base part.
4. The assembly according to claim 1, wherein the U shaped leaf spring has flanges at both the ends of the base.
5. The assembly according to claim 1, wherein the copper conductor has curved profiles to contact the terminals connected to the fixed and the withdrawal parts of the circuit breaker.
6. The assembly according to claim 1, wherein the copper conductor has projections at both the ends of one side surface to hold the U shaped leaf spring.
7. The assembly according to claim 1, wherein the copper conductor has groove to hold the fixture.
8. The assembly according to claim 6. wherein the groove is provided between the curved profiles of the copper conductor.
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9. The assembly according to claim 1, wherein the fixture has slots to receive the stacks of the copper conductor assembly.
10. The assembly according to claim 1, wherein the fixture has holes to secure the U shaped leaf spring.
11. The assembly wherein the U shaped leaf spring is riveted to the fixture through the holes.

Rakesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA

To,
The Controller of Patents,
The Patent office,
At Chennai

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