FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10; rule 13)
1. Title of the invention. - AN ENHANCED ELECTRICAL SWITCHING DEVICE
HAVING ROLLER- TYPE CONTACTS
2. Applicant
(a) NAME : LARSEN & TOUBRO LIMITED
(b) NATIONALITY : 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:

Field Of Invention
The present invention relates to an enhanced switching device adapted for opening and closing electrical circuits. More particularly, it relates to an enhanced switching device comprising knife type contact system which au fond uses a set of fixed contacts, a set of moving contacts that slide over the fixed contacts during make/break operation.
Background And Prior Art
When an electrical switch opens to break the circuit, an arc appears between the fixed and moving contacts. The performance of the switch can be ameliorated if the contact surface is not fixed but changing and also, the time for which the arc persists and/or the intensity of the arc is reduced.
The state-of-the-art knife type switches use a set of moving contacts of either of the following type :
1. Contacts with translational motion only.
2. Contacts having roller/cylindrical profile, which undergo rotational along with translational motion. However, a major facet of disparity between the contemporary designs utilizing cylindrical/roller moving contacts and the said invention is that the moving contacts, in the former case, are spring loaded (Reference US3411037, US3648003, US1740640), unlike the invention under consideration.
This spring force inhibits the rotational motion of the moving contacts, though not completely, but allowing it for a restricted span only viz. Just before the breaking or just after making operation of the switch, when the moving contacts are in touch with the fixed contacts.
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In such type of applications, the moving contacts, during arcing undergo translational motion. It has been found in a comported functioning of the switch, the arcing, ineluctable during breaking operation of the switch, is borne by a predetermined surface of the moving contacts. As a consequence, the electrical life of the moving contacts and hence the switch gets curtailed to a limited value. As compared to the contemporary designs, wherein roller contacts have been used, the potency of the rollers as moving contacts is tapped to the fullest extent in the present invention. A further elaboration as regards the above-mentioned disparity with the stated patents has been made below.
US3411037 describes an electrical switch utilizing movable roller contacts co-acting with fixed elongated bar contacts. It has a roller contact movable along a bar contact, the electrical connection being broken when the roller moves off the end of the bar. The rollers, however, are urged together to make pressure contacts with the bar, restricting their rotational motion after break operation of the switch.
US3648003 discloses an electrical switch having contacts provided with rollers. It incorporates a blade contact and a pair of roller contacts between which the blade contact moves when the switch closes. However, the design makes use of spring means to constantly urge the rollers toward each other. Hence their rotational motion during make/break operation, particularly after the break operation of the switch, gets restricted despite the fact that the rollers are rotatable about axes perpendicular to the direction of the blade movement between them.
US 1740640 describes an electrical switch in which the rollers are stationary and switch blade readily moves into and out of closed position. The blade is given a wedge shape so that as it enters between the rollers, the rollers are forced outwardly against the force of the springs. Whereas in the proposed
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invention, the springs are not directly under the spring force, hence can freely rotate after breaking.
Thus there is a need to provide an enhanced switching device comprising knife type contact system adapted for reducing arcing time and its severity in the moving contacts thereby increasing the electrical performance of the switch and enhancing the electrical life of the moving contacts.
Objects Of Invention
The basic object of the present invention is to reduce arcing time and its severity as experienced by the moving contacts and thus improve the electrical performance of the switch thereby enhancing the electrical life of the moving contacts, and hence the switch.
Another object is to provide specific arrangement and the profile of the moving contacts reducing the overall size and weight of the switch as compared to the contemporary electrical switches.
The object of the present invention is to provide easy handling and panel mounting or installation of the switch.
Summary Of Invention
Thus according to the basic aspect of the present invention, there is provided an enhanced switching device adapted to reduce arcing time and its severity in the electrical contacts thereby increasing the electrical performance of the switch and enhancing the electrical life of the contacts, the said device comprising :
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(i) housing assembly comprising top and base housings wherein said top housing being economically designed to encompass the whole switch when placed on the base housing with constituent members therein forming the contact system of the switch; said base housing being configured in a predetermined manner to provide guided motion to moving entity placed in operative connection with terminal means on the base housing;
(ii) contact means operatively connected to the said moving entity;
(iii) said terminal means rigidly placed on the base housing in a manner to provide smooth entry of the said contact means; and
(iv) means mounted on the top housing being positioned just above the terminal means rigidly placed in the housing in a manner that it is free to perform defined movement by virtue of spring means.
Detailed Description Of Invention
The switching device of the present invention comprises electric switch comprising moving contact means and plurality of means for carrying current. The said moving contact means comprises plurality of rollers being operatively connected to carriage means for holding the rollers. The said carriage means for holding the rollers comprises bridge being able to move translationally with the rolling motion of the rollers. The plurality of means for carrying current comprises two linear current carrying members of which one being elongated and spring loaded adapted to exhibit resilient action and the other member has width span designedly kept greater than the first one. The roller contacts are pressure engaged/sandwiched between the two linear members, and come out with sliding, rolling and rotational motion in the respective order, during break operation.
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The said embodiment of the invention will be here forth particularly described with reference to a four-pole switch disconnector with quad break feature.
The switching device of the present invention comprises housing assemblies comprising rectangular base housing/casing and top housing/casing, wherein the said base housing/casing is ergonomically designed and provided with pre determined grooves and channels, the major purpose being to house the various current carrying parts and give required support to them, apart from lending a guided path for the moving entity viz. Moving bridge assembly. The said moving assembly capable of moving in the guideway comprises of insulating carriage provided with limbs extending outwards in a perpendicular direction to the direction of its travel, which are adapted to carry contact means. The said contact means in operative connection to the moving assembly/insulating carriage comprises of roller moving contact means and are mounted, on the said limbs with the help of circlips. The said carriage/ moving bridge slided in the guideway is adapted to bridge the gaps in the current carrying path between chamfered conducting means mounted on the inside surface of the top housing and terminal means fixed on the base housing. The said guideway is located at the center of the base housing and extends all along the width of the base housing in a manner that the moving bridge, when placed in the said guideway, can be subjected to translatory movement in the lateral direction, parallel to the walls of the base housing.
The base of the housing comprises pair of current carrying terminals rigidly fixed on the base with the help of screws and mounted in front of each other, perpendicular to the guideway in the base housing and being chamfered on one side in a manner for allowing the smooth entry of the moving roller contacts onto them. The moving roller contacts being housed on the limbs of the moving bridge with the help of circlips in a manner that
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they are free to rotate about their own axes, the axes being same as that of the bridge limbs. The said rollers being located at predetermined distance such that sliding on the fixed terminals and making themselves contact-free, they are in rotational motion at the instant when arc strikes during breaking operation. Hence from the inception of the arcing to its extinction, it is faced by different surfaces on the roller i.e. there is a rapid displacement of the arc over the moving contacts. This motion prohibits the arc to get concentrated on a particular surface and thus reduces the pitting, erosion and overall wear and tear of the roller moving contacts, thus increasing the electrical life of the switch. The rotation of the rollers while making/breaking keeps the spot of its initial striking or root of the arc changing, offering a different surface every time, which is at comparatively lower temperature, the arc extinction becomes quicker i.e. the arcing time is reduced.
There are four rollers per pole, one pair corresponding to each of the two terminals in the pole and the emplacement of these two rollers per contact is in a side by side fashion. The said moving bridge in conjunction with the roller contacts is adapted for converting the translational motion into rolling motion
The rectangular top housing/casing is adapted to encompass the whole switch and when placed on the base housing with constituent members therein, forms the contact system of the switch. The top housing/casing comprises of means chamfered on one side adapted for smooth entry of the roller contact. The said means comprises elongated rectangular conducting element i.e. the shorting link being mounted in the top housing with its position just above the fixed terminals, and face parallel to them in a manner that it is free to perform lateral movement by virtue of the spring means, which are located in the top housing. The width span of the shorting link is designedly kept shorter than that of the terminals.
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The said spring means comprises of contact springs, one end of which is hooked in the top housing, the other resting on the shorting link surface, thus directly exerting force on it and adapted to keep the rollers firmly held in between the fixed terminals and the shorting link, when the switch is in ON condition.
The electrical switch has two positions viz. ON and OFF. There is a quick make, quick break mechanism for moving the bridge horizontally between the positions where the rollers are sandwiched tightly between the fixed terminals and shorting link, and wherein rollers are clear off or isolated from the fixed terminals and shorting link.
Brief Description Of Accompanying Figures
Figure 1 illustrates the front view of the roller contact switching device when the switch is in ON condition.
Figure 2 illustrates the front view of the roller contact switching device depicting the intermediate position (transition from On to OFF) of the switch i.e. the in between state during the transition of the switch from ON to OFF.
Figure 3 illustrates the front view of the switching device in OFF condition.
Figure 4 illustrates the top view of the switching device in OFF condition.
Figure 5 illustrates the side view of the switching device.
Detailed Description Of Accompanying Figures
In figure 1 the front view of the roller contact switching device when the switch is in ON condition is illustrated. The enlarge view of detail A in figure 1 illustrates the bridge. 5 is at position B and the roller contacts (6a and 6b)
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are 'sandwiched' between the fixed terminals (2) and shorting link (4), thus bridging the gap between them. The contact springs (7) are fully compressed and exert contact pressure on the shorting link (4). The top housing (3) is adapted to encompass the whole switch when placed on the base housing (1).
In figure 2 the front view of the roller contact switching device depicts the intermediate position (transition from ON to OFF) of the switch i.e. the in between state during the transition of the switch from ON to OFF is illustrated. From the enlarged view of Detail B in figure 2 it is realizable the opposite sides of the roller contacts (6a and 6b) being engaged with the fixed terminal contacts (2), initially the motion of the contacts is purely sliding (translational), with constant pressure. As the width span of the shorting link (4) is kept shorter than the fixed terminals (2), initially the roller contact (6a) looses its contact with the shorting link (4), still touching the fixed terminals (2). The mechanism is charging and well nigh the dead center position. The moving bridge (5) moved out further is adapted for rolling the roller contact (6a) about its own axis, on the surface of the fixed terminals (2), converting the translational motion of the roller contact (6a) into rolling motion. The mechanism reaches the dead center and is in a state just about to flip or toggle.
The mechanism flips and the roller contact (6b) adapted to break the electrical circuit, undergoes the same sequence of events i.e. with a time lag with respect to the roller contact (6a), except with a difference that an arc is formed, between the roller contact (6b) and shorting link (4). Eventually, as both the roller contacts are taken out briskly to loose the contact with the fixed terminals (2) (shown in figure 3), the rolling action gets converted into the rotational motion i.e. they keep on rotating after leaving the fixed terminals (2) and eventually come to stop in the final position A of the bridge (5).
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In figure 3 the front view of the switching device in OFF condition is illustrated.
Detail C of figure 3 illustrates the electrical isolation of the fixed terminal (2) and the shorting link (4) in OFF condition by maintaining a sufficient distance between terminals (2) and shorting link (4). As there is no continuity, there is no current flow in the circuit. The moving bridge (5), which carries the roller/moving contacts (6a and 6b), is at position A. The contact springs (7) are in released state, adapted for offering no force to compress the shorting link (4).
In figure 4 the top view of the switching device in OFF condition is illustrated. The base housing (1) comprises guideway (8) adapted for lending a guided path for bridge (5).
In figure 5 the side view of the switching device in ON condition is illustrated. The continuity is established in the electric circuit and the current flows from first fixed terminal (2a) to first set of rollers (6a) to shorting link (4) to second set of rollers (6b) and finally to second fixed terminal (2b).
The invention has been shown and described in a preferred form only, and by way of example, and many variations may be made in the invention, which will still be comprised within its spirit. It is understood, therefore, that the invention is not limited to the details cited above. There may be a set of fuses, or any other overload safety devices integrated in the said design, which will then act as a switch-disconnector-fuse. Though four-pole design is mentioned, two or three pole design, if required, may easily be designed on the similar lines. While the present embodiment of the invention refers to a quad break switch, it may conveniently be retracted or extended
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to any number of breaks. Means may also be provided for adjusting the contact pressure.
While the various drawings depict two rollers per contact per pole of the switch, arranged side by side, it is seen that the general principle of the roller contacts may be accomplished in one of several ways, such as use of any suitable number of rollers, the arrangement being the same more particularly elaborated in the description of the invention (side by side) or different (concentric positioning of the rollers), use of a set of balls (spheres) operating in slots or cages, in place of rollers. Furthermore, while in the present illustration the rollers are the moving contacts, and the terminals and the resiliently held elongated shorting links as stationary contacts, obviously this arrangement can be reversed to achieve the same effect. The essence of the said invention, will also remain intact, if the rollers are arranged so that the rotational axis of the rollers is not perpendicular, but is inclined at an angle to the motion of the roller carrying member viz. bridge in this case.
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We claim
1. An enhanced switching device adapted to reduce arcing time and its
severity in the electrical contacts thereby increasing the electrical
performance of the switch and enhancing the electrical life of the
contacts, the said device comprising :
housing assembly comprising top and base housings wherein said top housing being ergonomically designed to encompass the whole switch when placed on the base housing with constituent members therein forming the contact system of the switch; said base housing being configured in a predetermined manner to provide guided motion to moving entity placed in operative connection with terminal means on the base housing;
contact means operatively connected to the said moving entity; said terminal means rigidly placed on the base housing in a manner to provide smooth entry of the said contact means; and means mounted on the top housing being positioned just above the terminal means rigidly placed in the housing in a manner that it is free to perform defined movement by virtue of spring means.
2. Switching device as claimed in claim 1, wherein the base housing comprises rectangular casing comprising guide way located at the center running all along the width of the said base housing and with pre determined grooves, slots and channels in a manner providing housing and support to the means rigidly placed in the said base housing.
3. Switching device as claimed in claim 1, wherein the moving entity comprising insulating carriage provided with limbs extending
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outwards in a perpendicular direction to the direction of its travel are adapted to carry the contact means.
4. Switching device as claimed in claims 1 to 3, wherein the contact means in operative connection to the insulating carriage comprises roller moving contacts being mounted on the limbs of the carriage in conjunction with the insulating carriage with the help of circlips in a manner converting the translational motion into rolling motion, flipping or toggling of the mechanism thereby resulting in rotational motion of the roller moving contacts.
5. Switching device as defined in claim 4, wherein the rollers being of cylindrical or spherical configuration and made of conducting material are housed on the limbs of the insulating carriage in such a manner that they, without any direct attachment of springs, are free to rotate about their own axes adapted for making and breaking operation of the switch reducing the arcing time prohibiting the arc to get concentrated on particular surface thus reducing pitting, erosion and overall wear and tear of the roller moving contacts enhancing the electrical performance of the switch.
6. Switching device as claimed in claim 1, wherein the means rigidly placed in the housing comprises current carrying terminals rigidly fixed on the base housing perpendicular to the guideway being chamfered on one side so as to allow the smooth entry of the moving roller contacts onto them.
7. Switching device as claimed in claim 1, wherein the means mounted in the said housing assembly comprises elongated rectangular conducting shorting link mounted in the top housing being positioned
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just above the rigidly fixed current carrying terminals such that it is free to perform defined movement by virtue of spring means.
8. Switching device as claimed in claims 1 to 7, wherein the spring means comprises of contact springs one end of which is hooked in the top housing with the other resting on the surface of the shorting link adapted to directly exert force on the shorting link and keeping the rollers firmly held in between the fixed terminals and the shorting link during ON condition of the switch.
9. Switching device as herein described and illustrated with reference to the accompanying figures.
Dated this 6th day of July, 2005.

Dr. Sanchita Ganguli
of S. Majumdar & Co.
Applicant's agent
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ABSTRACT
Title: An Enhanced Electrical Switching device Having Roller-Type Contacts
An enhanced switching device adapted to reduce arcing time and its severity in the electrical contacts thereby increasing the electrical performance of the switch and enhancing the electrical life of the contacts, the said device comprising housing assembly comprising top housing (3) and base housing (1) wherein said top housing (3) encompass the whole switch when placed on the base housing (3) with constituent members therein forming the contact system of the switch; said base housing (1) being configured in a predetermined manner to provide guided motion to moving entity (5) placed in operative connection with terminal means (2) on the base housing (1), contact means (6a, 6b) operatively connected to the said moving entity (5), and means (4) mounted on the top housing (3) being positioned just above the terminal means (2) rigidly placed in the housing in a manner that it is free to perform defined movement by virtue of spring means (7).
Figure 1