FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
&
THE PATENS RULES, 2003
COMPLETE SPECIFICATION [See section 10, Rule 13]
A CONTACT HOLDING ARRANGEMENT FOR A CIRCUIT BREAKER;
LARSEN & TOUBRO LIMITED, A COMPANY INCORPORATED UNDER THE COMPANIES ACT, 1956, WHOSE ADDRESS IS L&T HOUSE, BALLARD ESTATE, MUMBAI - 400 001, MAHARASHTRA, INDIA.
THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.
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FIELD OF INVENTION
The present invention relates to a current limiting circuit breaker and particularly to an arrangement to hold the contacts during electromagnetic repulsion.
BACKGROUND OF THE INVENTION
The current limiting circuit breakers work on the principal of electromagnetic repulsion of contact elements. The current limiting circuit breakers facilitate low let through energy by reacting faster to high value currents.
A current limiting circuit breaker usually comprises of two contact elements mounted on separate contact arms. On occurrence of high current, the two contacts carrying current in opposite direction develops the repulsive force, this repulsion force moves contacts away from each other. A major concern in circuit breakers is of re-closing of contact arms, as the repulsive forces tend to decrease as distance between the contact arms increases.
Circuit breakers attempting to provide simple arrangements have been suggested in prior arts. Specifically in US 5363076 is enclosed a blade suspension assembly for a circuit breaker including a first electrical contact, an elongated contact arm having a second electrical contact adjacent a first end of the contact arm, a compression spring, and an elongated lever. The second electrical contact is movable about a first pivot axis between a contacts-closed position and at least one contacts-open position with respect to the second electrical contact. The lever has a first end adjacent a second pivot axis, a second end supported by the
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compression spring, and a contoured support surface between the first and second ends which supports a second end of the contact arm. The compression spring exerts a force against the second end of the lever so that the contoured support surface biases the second end of the contact arm about the first pivot axis in the contacts-closed position during normal operation and in the contacts-open position in response to the contact arm moving to the contacts-open position.
It is seen that the invention disclosed in US 5636076 involves designing complex surfaces and intricate positioning of the elements. Moreover, the profiled surfaces involved, lead to a non-continuous force variations as the circuit breaker moves from contact closed to the blown open position.
There is therefore a need of a simple yet efficient contact arrangement to enable smooth transition of contact arm from contact closed position to blown open position and still maintaining ease of manufacturability and assembling.
OBJECT OF THE PRESENT INVENTION
It is an object of the present invention to provide faster and reliable current limiting circuit breaker with contact locking and holding arrangement thereby overcoming the problems of re-closing of circuit breaker.
It is further an object of the present invention to provide.a simple in construction and working contact locking arrangement for circuit breaker to further improve the time response to the fault currents.
SUMMARY
The present invention provides a contact holding arrangement for a circuit breaker comprising, a first electrical contact, an operating shaft that
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rotates about first axis of rotation to bring the circuit breaker into and out of on position wherein the said electrical contacts are in engagement. A contact arm having two ends is provided wherein one end has second electrical contact attached while on other side is profiled surface which has a rounded corner and a substantially plain surface on either side of the said rounded corner. The contact arm is pivotally held in said operating shaft for rotation about a second axis of rotation with respect to the said operating shaft.
A spring is provided on the said operating shaft .A cylindrical surface being mounted along spring axis allowing the said profiled surface of the moving contact to rest on, transfers a spring force to the said profiled surface in a line of direction through the spring axis and the said cylindrical surface.
As per the present invention a pedal is pivotally adapted on the operating shaft and a cylindrical surface mounted on the free end of the pedal.
As per the second embodiment of the present invention a single-phase circuit breaker comprising the contact holding arrangement is described as in first embodiment.
As per the third embodiment of the present invention a multi phase circuit breaker is provided comprising at least one of the contact holding arrangement as in first embodiment of the present invention.
Other objects, features and advantages of the invention will be apparent from the drawings, and from the detailed description that follows below.
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DETAILED DESCRIPTION OF THE DRAWINGS
Fig. 1 shows elevation view of the arrangement embodied in single-phase circuit breaker in OFF position
Fig. 2 shows elevation view of the arrangement embodied in single-phase circuit breaker in ON position.
Fig. 3 shows elevation view of the arrangement embodied in single-phase circuit breaker in Blown open position.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As per the present invention the contact holding arrangement is embodied in a single-phase circuit breaker (10) as shown in fig. 1- fig.3 The first electrical contact (22) is mounted on the fixed arm (20) as shown in fig. 1.The fixed arm (20) can alternatively be moving. The contact arm (10) on which the second electrical contact (12) is mounted, is pivoted about pivot point (14) on the operating shaft (42) and is free to rotate with respect to operating shaft about second axis (46) and along with the operating shaft (42).
An operating mechanism (40) is provided which enables manually or automatically by a mechanical actuator, the operating shaft (42) to rotate about first axis(44) of rotation as shown in fig. 1 causing the contact arm (10) to engage leading to position as shown in fig.2 or disengage as shown in fig. 1.
The contact arm (10) having second electrical contact (12) on one end has a profiled surface (16) on the other end. A spring (30) is provided on operating shaft (42) the one end of which is fixed onto operating shaft (42). The said spring is a compression spring and thus allows various
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forms of compression springs to be used for the purpose. Also, a tension or torsion spring can alternatively be used by slight modification. The other end of the spring (30) lets the free end of a pedal (34) to rest over while the other end of the said pedal (34) is pivoted about pivot pin (36) on the operating shaft (42) free to rotate with respect to the operating shaft (42).
The said spring helps maintain the required contact pressure by providing force through the cylindrical surface (32) mounted on the free end of said pedal (34) keeping the circuit breaker in closed position.
During said contacts closed position as shown in fig. 2 of the circuit breaker the cylindrical surface (32) makes a contact with the straight portion (16 a) of the profiled surface (16); since the contact arm (10) is pivoted about pivot point (14) the force provided by the said spring (30) acts so as to keep the two contacts in firm engagement. The force vectors in closed position act along the spring (30) axis to the said straight portion (16 a) of the profiled surface (16). When the operating mechanism (40) is used to bring the circuit breaker into open position, the contact arm (10) rotates along with the operating shaft (42) about the first axis(44). This position of the circuit breaker is usually referred to as the normal open position as shown in fig.2.
While the circuit breaker works under normal current condition as shown in fig.2 the electrical contacts remain engaged supplying the required current to downstream equipments. In case of occurrence of a fault current the said electrical contacts tend to repel each other governed by the principle of electromagnetic repulsion. The said contact arm (10) repels from the fixed arm (20) to "break" the circuit. Simultaneously the
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said straight portion (16 a) of the profiled surface (16) moves against the cylindrical surface (32) overcoming the biasing force offered to it by the spring (30). As the cylindrical surface (32) moves over rounded corner (16 b) of the profiled surface (16) a force reversal about the pivot point (14) takes place. The contact arm (10) is quickly brought into open position as shown in fig 3 by the force transition as a combinatorial result of the profiled surface (16), cylindrical surface (32) and the spring (30) force being supplied. The force characteristics as described are further facilitated by the pedal (34) which rotates about pivot pin (36) axis allowing movement of the profiled surface (16) over the cylindrical surface (32) during transition as required.
It is seen that the cylindrical surface (32) aims to provide the quick and smooth force reversal as described, during blown open position. Though the cylindrical surface (32) is considered best for the arrangement a hemispherical or equivalent surface can be alternately used.
Further to movement of the cylindrical surface (32) over the rounded corner of the profiled surface (16), the spring (30) and the pedal (34) arrangement restricts movement of the profiled surface (16) back over the cylindrical surface (32) thereby locking the said contact arm (10) in blown open position as seen in fig.3. Locking of contact arm (10) in blown open position ensures low arc time resulting out of re-closing of contacts.
Thus the arrangement provides for a simple yet efficient arrangement in terms of manufacturability, assembling and replacement of parts in case of damage. Additionally the arrangement results in low arc time thereby improving reliability and response time of the circuit breaker.
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The invention as inhere described is liable to modifications by substitutions or variations by a person skilled in the art and thus are part of the disclosure given herein.
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WE CLAIM
1. A contact holding arrangement for a circuit breaker comprising:
a first electrical contact;
an operating shaft rotatable about first axis of rotation to bring the circuit breaker into and out of on position in which the said electrical contacts are in engagement;
a contact arm having two ends wherein one end has a profiled surface and on the other end is the second electrical contact attached, said contact arm pivotally held in said operating shaft for rotation about a second axis of rotation with respect to the said operating shaft;
a pedal pivotally adapted on the operating shaft;
a spring adapted below free end of the pedal, in the operating shaft;
a cylindrical surface being mounted on the free end of the pedal allowing the said profiled surface of the moving contact to rest on .transfers a spring force to the said profiled surface in a line of direction through the spring axis and the said cylindrical surface.
2. A contact holding arrangement for a circuit breaker as described in claim 1, wherein the said profiled surface has a rounded corner and a substantially plain portion on either side of the said rounded corner.
3. A contact holding arrangement for a circuit breaker as claimed in claim 1 wherein the profiled surface of the contact arm slides over the
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cylindrical surface causing the direction of force to reverse after crossing the said rounded corner in the blown open position.
4. A single-phase circuit breaker comprising the contact holding arrangement as claimed in claims 1-3.
5. A multi phase circuit breaker comprising at least one of the contact holding arrangement as claimed in claims 1-3.
Dated this 30th day of September, 2005.

ABSTRACT
A contact holding arrangement for a circuit breaker comprising, a first electrical contact, an operating shaft that rotates about first axis of rotation to bring the circuit breaker into and out of on position is provided in which the said electrical contacts are in engagement. A contact arm having two ends is provided wherein one end has second electrical contact attached while on other side is profiled surface which has a rounded corner and a substantially plain surface on either side of the said rounded corner. The contact arm is pivotally held in said operating shaft for rotation about a second axis of rotation with respect to the said operating shaft. A spring having is provided on the said operating shaft .A cylindrical surface being mounted along spring axis allowing the said profiled surface of the moving contact to rest on, transfers a spring force to the said profiled surface in a line of direction through the spring axis and the said cylindrical surface. As per the present invention a pedal pivotally adapted on the operating shaft and a cylindrical surface mounted on the free end of the pedal. As per the second embodiment of the present invention a single-phase circuit breaker comprising the contact holding arrangement is described as in first embodiment. As per the third embodiment of the present invention a multi phase circuit breaker is provided comprising at least one of the contact holding arrangement as in first embodiment of the present invention.
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