FORM 2

THE PATENTS ACT, 1970 (39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]
A MOVABLE CONTACT ASSEMBLY FOR SWITCHING DEVICES;
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 THE INVENTION
The present invention relates to switching devices, and more particularly to current limiting circuit breakers and assembly of movable contacts thereof.
DESCRIPTION OF THE BACKGROUND ART
Switching devices such as current limiting circuit breakers are well known in the related field of art. Generally, a circuit breaker is installed at an electric power distributing board among several electric power systems. The circuit breaker serves as a switch for supplying or cutting off power to a load side under no load state, and cuts off power supplied to a load side from a power side in order to protect a circuit and components of the load side when a great abnormal current due to a short-circuit or a ground fault flows on a circuit under a load state. The circuit breaker comprises of various components and contact system forms one part of the same. When a very high current flows through the system the contacts are so shaped that they repel because of current repulsion effect. Also known in the art is the different mechanism by which the contact arms of the circuit breakers are linked to the housing (1) in which the contact arms are operatively arranged. Normally, upon flow of high current in the electric circuit the movable contacts open thereby breaking the circuit and stopping the current flow further. Most of the circuit breakers having movable contact arms that are linked via a spring and lever arrangement that helps in efficient mobility of the contact arms in case of flow of high value current.
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Currently, these circuit breakers are available according to various industrial
needs, the most common of which entrusts the opening of the contacts to
complicated kinematic mechanisms actuated by the mechanical energy stored
beforehand in special opening springs.
In certain operating conditions, particularly when the presumed short-circuit
current can assume significantly high values, the use of devices that utilize in a
traditional manner the energy that can be accumulated in the opening springs
can be scarcely efficient and uneconomical for opening the contacts, in such
cases, it is common to resort to special types of automatic circuit breaker that
have technical solutions aimed at increasing their breaking capacity.
The flow of current is interrupted in each pole of the circuit breaker in two
separate regions that are arranged electrically in series to each other, so that
each region is subjected to a lower mechanical and thermal stress
A particularly critical aspect of known types of circuit breaker is the fact that the
presence of electrodynamic repulsion forces, despite contributing positively to the
generation of the thrust useful for contact separation, helps the moving contact
structure to reach the end of its stroke at high speed and therefore with great
energy; this aspect tends to cause violent impacts against the case of the circuit
breaker, to the point of requiring the possible use of additional cushioning
elements, and may cause bouncing of the moving contacts toward the fixed
contacts and undesirable restrikes of the electric arc.
To contrast this possibility, some known solutions use additional systems for
latching the moving contacts in the open position, in other known solutions, the
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structure of the moving contacts and of the functional elements associated
therewith is instead configured appropriately so that during the separation stroke
of the contacts the moving contacts are slowed. An example in this regard is
given in EP 0560697.
It is quite evident after going through the aforementioned patent that however the
functional elements are so configured that upon separation movement of the
contacts gets slowed but still possibility of bouncing back of the moving contacts
is there which may erode the contact arms.
According to patent number US6259048 B1, there is a provision of a link
connection between a contact housing assembly and a movable contact arm to
improve the performance of a circuit breaker during contact separation as well as
contact closure. The arrangement of atleast one expansion spring between the
link and the associated contact housing provides the optimum contact force by
compensating for component tolerance and contact erosion and wear while
maintaining a reliable means for locking the contact arm open in the event of an
over current condition.
However, the aforementioned patent addresses to the problem of locking the
contact arms upon separation, still the components of the operating mechanism
as arranged In the circuit breaker tends to be very complex, which may lead to
maintenance problems later on.
Hence there is a need of such an assembly of a circuit breaker that is relatively
simpler in construction and still efficiently solves the above-discussed problems.
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SUMMARY
An object of the present invention is to lock the movable contacts in open
position.
Another object of the present invention is to provide a simpler assembly of
moving contacts for switching devices.
According to an embodiment of the present invention, a movable contact
assembly for switching devices employs a housing having atleast two holes that
runs throughout the width of the housing. An arrangement for is provided for
adapting an operating mechanism in the housing. Atleast one movable contact
having a first contact end and a second contact end is arranged in the housing,
said movable contact having atleast two elongated slots at the central portion
provided side by side and arranged inside the housing. Atleast two springs each one of which engages said two elongated slots respectively and at diagonally opposite ends of the slots within the housing. The operating mechanism consists of movable contacts and springs operatively connected to each other in such a way that as the circuit breaks, one of the ends of the springs traverses in their respective slots to the other end in order to regain normal length thereby locking the movable contact in open position.
BRIEF DESCRIPTION OF DRAWINGS
Reference will be made to embodiments of the invention, examples of which may be illustrated in the accompanying figures. These figures are intended to be illustrative, not limiting. Although the invention is generally described in the
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context of these embodiments, it should be understood that it is not intended to
limit the scope of the invention to these particular embodiments.
Fig.1 illustrates the complete assembly of the movable contact system in two
different views. The side view and the top view
Fig.2 shows the isometric view of the whole assembly as it appears.
Fig.3 is the exploded view of the contact system, springs & connecting pin
arrangement
Fig 4. Illustrates the cut section view of the assembly and shows positions of
various components when the contact is in closed position.
Fig 5. Illustrates the contacts in locked position.
Details of operation of the instant invention and further objects thereof will
become evident as the description proceeds and from an examination of the
accompanying drawings which illustrates embodiments of the invention in which
similar numerals refer to similar parts throughout the several views.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
In the following detailed description of the embodiments of the present invention reference is made to the accompanying figures, which in conjugation with this detailed description, illustrates and describes working principle of assembly of moving contacts for circuit breakers, more particularly to the contact locking being achieved through a spring crossing the dead centre. According to an embodiment of the present invention a movable contact assembly for switching devices, comprises a housing (1) having atleast two holes
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(6) running throughout the width thereof and an arrangement for adapting an operating mechanism in said housing (1), atleast one movable contact (2) having a first contact end and a second contact end, said movable contact (2) having atleast two elongated slots (7) at the central portion provided side by side and arranged inside the housing (1), and atleast two springs each one of which engaging said two elongated slots (7) respectively and at diagonally opposite ends of the slots within the housing (1), said operating mechanism consists of movable contacts (2) and springs (5) operatively connected, wherein as the circuit breaks, one of the ends of the springs (5) traverses in their respective slots to the other end in order to regain normal length thereby locking the movable contact (2) in open position.
Reference herewith is made to figure 1, which illustrates the contact assembly in two views, the first one is the top view and the second one is the side view of the current limiting circuit breaker. The circuit breaker has a housing (1) with an arrangement to adapt the two movable contact (2) arms made separately as they can be manufactured easily in case of high current capacity breakers. For lower capacity the contacts can be made as one single piece. The housing (1) have atleast two holes (6) provided diametrically opposite to each other and extending through out the width of the housing (1). An arrangement is also provided for adapting an operating mechanism thereof. The housing (1) can rotate with respect to the movable contact (2) arms adapted therein. Figure 2 shows the isometric view of the contact assembly of the circuit breaker. The movable contact (2) is especially designed by keeping in mind the design
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consideration and which consists of atleast one movable contact (2), however more than one movable contact (2) could also be employed in the housing (1) in order to meet the requirement of load. There are two ends of the movable contact (2) referred to as first contact end and the second contact end, said movable contact (2) has got atleast two elongated slots (7) provided at the central portion thereof. The elongated slots (7) are provided side by side on the movable contact (2) as illustrated in figure 3. For providing more than one
movable contact (2) the elongated slots (7) on both the contacts should be coaxially placed. The movable contact (2) is placed in the arrangement provided in the housing (1) for adapting thereof. Actually, the arrangement provided in the housing (1) for containing the movable slots has a thick cavity that runs through the periphery of the housing (1).
In the whole assembly of the circuit breaker there is provided a pair of fixed pins (3), a pair of movable pins (4) and atleast a pair of expansion springs (5) attached operatively in the housing (1) with the movable contact (2). Exploded view of which is shown in figure 3. A pair of fixed pins (3) extends through the two holes (6) provided on the housing (1) and running through the width thereof. Figure 4 shows a cut section view of the contact housing (1) when the contacts are in closed position. In each of the two elongated slots (7) provided on the movable contact (2) said movable pin (4) is extended that engages one of the end of the expansion spring (5). Other end of the spring (5) is engaged with the fixed pin (3) extending through the holes (6) provided on the housing (1). Similarly, arrangement of the spring (5) is made for the second elongated slot.
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According to another feature of the invention a pair of springs (5), one above the movable contact (2) and another below the movable contact (2) for both the elongated slots (7) is provided and engaged in the same manner as explained for a single spring (5).
The operating mechanism as adapted into the housing (1) of the circuit beaker assembly comprises of movable contact (2), expansion springs (5), fixed pins (3) and movable pins (4) and the manner in which they are operatively connected. When the contacts are closed, as shown figure 4 the movable pin (4) is at one end of the slot of the movable contact (2). At this point the springs (5) pull the
movable contact (2) down and hence provide the required contact pressure. As the two spring (5) pull in the same direction of rotation, the movable contact (2) (2) remains stable. The spring (5) is of normal length at two points, one when the contacts (2) are close and second when the contacts (2) are open. When the movable contact (2) is closed the rod (4) to which the spring (5) is connected is in one end of the slot and keeps the movable contact (2) in the required position. There are two pairs of springs (5) pulling the contact in opposite direction keeping it in position. When the movable contact (2) is repulsed due to a high value of short circuit current the ends of the movable contact (2) try to move away from the fixed contacts (not shown) and in doing so the spring (5) is elongated and tries to return back to original length. As the movable contacts (2) move apart the slope of the slot changes from sloping downwards to sloping upwards as can be seen in fig 4 and fig 5. Normally what happens the movable contact (2) when they are repelled, travel and because the repulsion force is
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same on both sides of the contact the contact rotates. When the contact moves, the spring (5) expands and exerts a pulling force on the pin. As the pin (4) has only one direction to move in, the pin slides and in doing so reduces the spring (5) length to normal and the direction of the force acting on the spring (5) changes so earlier when the springs (5) were keeping the contact closed now they keep it open. As one end of the spring (5) is fixed (attached to (3) which is fixed in housing (1)) the other end has to move in order to get back the normal length of the spring (5). During this transition the elongated slot comes across a position in which it is parallel to the fixed contact i.e. gets horizontal. It is after this position that the movable pin (4) starts to force its way to the back of the slot as the spring (5) tries to regain the natural length. When the rod reaches the center of the contact (2) the line of force of the spring (5) changes as it has crossed the dead center and because of the natural tendency of the spring (5) to maintain its natural length it keeps the contact (2) open even when the repulsion force ceases to act. This position of the contacts can be seen in fig 5. So in this way, the movable contact (2) gets locked in the open position and the possibility of bouncing back and rebuilding the circuit gets removed substantially. The foregoing description of the invention has been set for merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
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WE CLAIM
1. A movable contact assembly for switching devices, comprising:
a housing having atleast two holes running throughout the width thereof and an
arrangement for adapting an operating mechanism in said housing;
atleast one movable contact having a first contact end and a second contact end,
said movable contact having atleast two elongated slots at the central portion
provided side by side and arranged inside the housing; and
atleast two springs each one of which engaging said two elongated slots
respectively and at diagonally opposite ends of the slots within the housing, said
operating mechanism consists of movable contacts and springs operatively
connected, wherein as the circuit breaks, one of the ends of the springs traverses
in their respective slots to the other end in order to regain normal length thereby
locking the movable contact in open position.
2. The assembly as claimed in claim 1, wherein the two holes on the housing are provided diametrically opposite to each other and extends throughout the width of the housing.
3. The assembly as claimed in claim 1, wherein two fixed pins extends through the two holes respectively.
4. The assembly as claimed in claim 1, wherein more than one movable contact arms having elongated slots and arranged coaxially is placed inside the housing having an arrangement thereof.
5. The assembly as claimed in claim 1 wherein, the spring is an expansion spring.
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6. The assembly as claimed in claim 1, wherein a pair springs whose first end engages with the fixed pin and second end engages at one of the ends of the first elongated slots via a movable pin.
7. The assembly as claimed in claim 1, wherein another pair of springs is provided whose first end engages with another fixed pin and second end engages at one of the ends of the second elongated slots via another movable pin.
8. The assembly as claimed in claim 1, wherein both the movable pins extends through the two elongated slots.
9. The assembly as claimed in claim 1, wherein in both the close and open positions, the springs are in their normal lengths.
10. The assembly as claimed in claim 1, wherein the two pairs of springs pull the
contacts in opposite direction thereby keeping said contacts locked in close and
open position.
11. The assembly as described in the preceding claims, description and
drawings.
Dated this 28th day of February, 2007
FOR LARSEN & TOUBRO LIMITED By their Agent

(GIRISH VIJAYANAND SHETH) KRISHNA & SAURASTRI
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