FORM 2
The Patents Act 1970
(39 of 1970) &
The Patent Rules 2003 PROVISIONAL SPECIFICATION
(See Section 10 and rule 13)


TITLE OF THE INVENTION: ELECTRICAL CONTACT ASSEMBLY FOR SWITCHES
APPLICANT:
LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No. 278,
Mumbai- 400 001, Maharashtra. INDIA.

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


A) TECHNICAL FIELD
[0001] The present invention generally relates to the electrical switching device like switch fuse units, switch disconnector, switch disconnector fuse, etc., and particularly relates to electrical contact system in the switches. The present invention more particularly relates to flexible moving contacts in the electrical contact system of an electrical switching device like circuit breakers.
B) BACKGROUND OF THE INVENTION
[0002] The Electrical switches have plurality of contact systems which can turn the current ON, OFF or carry normal and overload currents. The switch comprises of various components including a contact system. The contact system includes a moving contact and at least a stationary contact. The moving contact is mounted on a moving bridge. In a Switch unit, a moving contact slides between a set of contacts comprising fixed contact and fuse contact, whenever the unit is switched ON. The contact system in a switch unit is capable of making (turning ON), breaking (turning OFF) & carrying normal and overload currents. The contact system can also be used in switch Fuse unit that besides doing all function of switch (ON, OFF) also protect the electrically connected equipment from short circuit current (by blowing of fuse). Depending upon the quantum of electrical power to control, the no. of the contacts used in a set is varied.
[0003] The moving contact is made to engage with the stationary contact to close the circuit in the contact system. The moving contact may further slide between
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the stationary contact and fuse contact to complete the circuit in the electrical switching device. In a switching device with fuse units, the coupled equipments are protected from short circuit current by blowing off the fuse.
[0004] At present the moving contacts are rigid or flexible. The rigid contacts which are made from a single metal establish a firm contact pressure between the stationary and moving contacts. The flexible contacts can be made from plurality of metallic foils or braided metallic wires.
[0005] The moving contact may be formed using a single or plurality of conducting materials like copper, aluminum or other metals. The shape, size and profile of the moving contacts may be designed according to the contact surface of the stationary and moving contacts.
[0006] The currently available contact systems are provided with moving contact made out of single contact strip of required thickness. Such construction caused limitation in the shape, size and profile of the moving contacts. None of the currently available switching system is provided with electrical contact systems having switchable contacts provided with flexibility and rigidity in the same contact.
[0007] Hence there is a need to develop switchable contacts having a combination of flexibility and rigidity in the same contact element to improve contact efficiency, to lower the contact joint resistance and to reduce the heat generated in the switch.
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C) OBJECT OF THE INVENTION
[0008] The primary object of the present invention is to provide an improved electrical contact assembly provided with moving contact having flexible and rigid portions for switching devices.
[0009] Another object of the present invention is to provide an improved electrical contact assembly provided with moving contact having flexible and rigid portions to maintain adequate contact pressure on the fixed contacts and terminals.
[0010] Yet another object of the present invention is to provide an improved electrical contact assembly provided with moving contacts having flexible and rigid portions to decrease the contact joint resistance and to reduce the heat generated in the electrical switching device thereby preventing the increase in temperature.
[0011] Yet another object of the present invention is to provide an improved electrical contact assembly for switching devices having a cost effective contact system.
[0012] Yet another object of the present invention is to provide an improved electrical contact assembly with reduction in the number of components used in the assembly.
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[0013] Yet another object of the present invention is to provide an improved electrical contact assembly in which the moving contact may be designed according to the power requirements.
[0014] Yet another object of the present invention is to provide an improved electrical contact assembly for switching devices to provide flexibility in the contact system while maintaining the rigidity in the contact surface.
[0015] Yet another object of the present invention is to provide an improved electrical contact assembly provided with moving contacts made up of metal foils of single metal.
[0016] Yet another object of the present invention is to provide an improved electrical contact assembly that may be used in switches with or without fuse.
[0017] 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.
C) SUMMARY OF THE INVENTION
[0018] The various embodiments of the present invention provide an improved electrical contact assembly provided with moving contacts having both flexible and rigid portions to provide sufficient contact pressure on fixed contacts, to reduce contact resistance, to improve heat dissipation and to reduce the increase in temperature in the switch.
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[0019] According to one embodiment the moving contacts are formed with a preset number of metallic foils made up of single metal like copper. The moving contacts are made in U-shape. The set of foils are brought together and solidified at both the ends under temperature and pressure to provide rigid contacts at the ends to maintain adequate contact pressure on the fixed contacts and terminals so as to maintain continuity. The ends of the movable contact are solidified to provide rigid contacts while the rest of the portions in the movable contact are maintained in the foil form to maintain the flexibility. Thus the moving contacts are provided with both flexible and rigid portions. A compression spring is inserted between the two limbs of the moving contact. Two peeps/projections are provided in the inner side of the moving contact to hold the spring in its place. The springs are compressed to provide and maintain adequate contact pressure on the terminals and fixed contacts, when the springs are subjected to force during the switching ON period. The moving contacts are inserted between the fixed contacts and the terminals in the contact assembly to close the circuit to establish a current supply path.
[0020] According to another embodiment of the present invention, a switch fuse unit is provided with a front housing and a rear housing. A bridge assembly provided with a moving contact is arranged inside the rear housing provided with terminals. The moving contact is inserted between the terminals and the fixed contacts that are arranged above the rear housing. The moving contacts are formed by a set of metallic foils made up of single metal like copper. Both the ends of the coils are bent to form the limbs. The ends of the contacts are solidified to form a rigid portion while the rest of the contacts are maintained in the foil
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form to provide a flexible portion. A compression spring is inserted between the limbs of the moving contact. Two peeps are provided at the inner side of the moving contacts to hold the compression spring in its place.
[0021] The moving contact assembly has a bridge portion provided with grooves/slots to receive the moving contacts made up of copper foils. After inserting the compression spring, the moving contacts are inserted into the slots/grooves of the bridge assembly. The moving contacts are secured to the bridge assembly by inserting the two circular clips from the two ends of the contact bridge assembly thereby restricting the movement of the moving contacts. Two fuse contacts are provided above the rear housing to hold a fuse link.
[0022] When the switch is turned ON, the current from one terminal provided at one end is passed to another terminal provided at another end through one moving contact, one fixed contact, the fuse link, another fixed contact and another moving contact respectively.
[0023] Thus the various embodiments provide a contact system with a moving contact formed with a set of copper foils having rigid and fixed portions to provide adequate contact pressure, to reduce the contact resistance, to improve heat dissipation and to prevent the increase in temperature.
E) BRIEF DESCRIPTION OF THE DRAWINGS
[0024] 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:
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[0025] FIGURE. 1 illustrates the perspective view of the bridge assembly with moving contacts in a switch according to one embodiment of the present invention.
[0026] FIGURE. 2 illustrates the exploded perspective view of the bridge assembly with moving contacts in a switch according to one embodiment of the present invention.
[0027] FIGURE. 3 illustrate the side sectional views of the moving contacts (before and after solidification) used in a switch according to one embodiment.
[0028] FIGURE. 4 illustrates the partial perspective view of the contact system when the electrical switch is in OFF condition according to one embodiment of the present invention.
[0029] FIGURE.5 illustrates the partial perspective view of the contact system when the electrical switch is in ON condition according to one embodiment of the present invention.
[0030] 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 combined with any or all of the other features in accordance with the present invention.
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F) DETAILED DESCRIPTION OF THE INVENTION
[0031] 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.
[0032] The various embodiments of the present invention provide an improved electrical contact assembly provided with moving contacts having both flexible and rigid portions to provide sufficient contact pressure on fixed contacts, to reduce contact resistance, to improve heat dissipation and to reduce the increase in temperature in the switch.
[0033] According to one embodiment the moving contacts are formed with a preset number of metallic foils made up of single metal like copper. The moving contacts are made in U-shape. The set of foils are brought together and solidified at both the ends under temperature and pressure to provide rigid contacts at the ends to maintain adequate contact pressure on the fixed contacts and terminals. The ends of the movable contact are solidified to provide rigid contacts while the rest of the portions in the movable contact are maintained in the foil form to maintain the flexibility. Thus the moving contacts are provided with both flexible and rigid portions. The thickness and the flexibility of the foils may be set to any
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desired level based on the application. The copper sheets are brought together and solidified at areas where flexibility is not required. The copper sheets are solidified under the application off temperature and pressure.
[0034] A compression spring is inserted between the two limbs of the moving contact. Two peeps are provided in the inner side of the moving contact to hold the spring in its place. The springs are compressed to provide and maintain adequate contact pressure on the terminals and fixed contacts, when the springs are subjected to force during the switching ON period.
[0035] The moving contacts are inserted between the fixed contacts and the terminals in the contact assembly to close the circuit to establish a current supply path.
[0036] According to another embodiment of the present invention, a switch fuse unit is provided with a front housing and a rear housing. A bridge assembly provided with a moving contact is arranged inside the rear housing provided with terminals. The moving contact is inserted between the terminals and the fixed contacts that are arranged above the rear housing. The moving contacts are formed by a set of metallic foils made up of single metal like copper. Both the ends of the coils are bent to form the limbs. The ends of the contacts are solidified to form a rigid portion while the rest of the contacts are maintained in the foil form to provide a flexible portion. A compression spring is inserted between the limbs of the moving contact. Two peeps are provided at the inner side of the moving contacts to hold the compression spring in its place.
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[0037] The moving contact assembly has a bridge portion provided with grooves/slots to receive the moving contacts made up of copper foils. After inserting the compression spring, the moving contacts are inserted into the slots/grooves of the bridge assembly. The moving contacts are secured to the bridge assembly by inserting the two circular clips from the two ends of the contact bridge assembly thereby restricting the movement of the moving contacts. Two fuse contacts are provided above the rear housing to hold a fuse link.
[0038] When the switch is turned ON, the current from one terminal provided at one end is passed to another terminal provided at another end through one moving contact, one fixed contact, the fuse link, another fixed contact and another moving contact respectively.
[0039] Thus the various embodiments provide a contact system with a moving contact formed with a set of copper foils having rigid and fixed portions to provide adequate contact pressure, to reduce the contact resistance, to improve heat dissipation and to prevent the increase in temperature.
[0040] The flexibility of the moving contact can be increased by increasing the number of copper foils. The preset portions in the copper foils, where the flexibility of the foils are not required, are bent and embossed to form a rigid zone.
[0041] FIG. 1 illustrates the perspective view of bridge assembly with moving contacts according to one embodiment of the present invention, while FIG. 2
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illustrates the exploded view of bridge assembly with moving contacts according to one embodiment of the present invention.
[0042] With respect to the FIG 1 and 2, the moving contact assembly has a bridge portion 1 provided with grooves/slots 5 to receive the moving contacts 2 made up of copper foils. The moving contacts 2 are formed by a set of metallic foils made up of single metal like copper. Both the ends of the coils are bent to form the limbs. The ends of the contacts 2 are solidified to form a rigid portion 10 while the rest of the contacts 2 are maintained in the foil form to provide a flexible portion 11. A compression spring 3 is inserted between the limbs of the moving contact 2. Two peeps/ protrusions 12 are provided at the inner side of the moving contacts 2 to hold the compression spring 3 in its place.
[0043] After inserting the compression spring 3 between the limbs of the moving contact 2, the moving contacts 2 are inserted into the slots/grooves 5 of the bridge assembly 1. The moving contacts 2 are secured to the bridge assembly 1 by inserting the two circular clips 4 from the two ends of the contact bridge assembly 1 thereby restricting the movement of the moving contacts 2.
[0044] FIGURE.3 illustrates the side sectional view of copper foils used as the moving contacts, before and after a solidification process. With respect to FIG.3, the moving contacts 2 are formed with a preset number of metallic foils made up of single metal like copper. The moving contacts 2 are made in U-shape. Both the ends of the coils are bent to form the limbs. The ends of the contacts 2 are solidified to form a rigid portion 10 while the rest of the contacts 2 are maintained in the foil form to provide a flexible portion 11.Two projections/peeps 12 are
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provided at the inner side to hold a compression spring between the two limbs at the two ends of the moving contact 2
[0045] The set of foils are brought together and solidified at both the ends under temperature and pressure to provide rigid contacts 10 at the ends to maintain adequate contact pressure on the fixed contacts and terminals. The ends of the movable contact 2 are solidified to provide rigid contacts 10 while the rest of the portions in the movable contact are maintained in the foil form to maintain the flexibility. Thus the moving contacts are provided with both flexible and rigid portions 11,10. The thickness and the flexibility of the foils may be set to any desired level based on the application. The copper sheets are brought together and solidified at areas where flexibility is not required. The copper sheets are solidified under the application off temperature and pressure.
[0046] FIGURE. 4 illustrates the partial perspective view of the contact system when the electrical switch is in OFF condition according to one embodiment of the present invention. With respect to FIG.4, the contact system has fixed contacts 13 mounted with fuse holder 8 to hold a link 7 coupled to a fuse spring 9. During the switch off condition, the moving contact 2 is not inserted between the terminal 6 and the fixed contact 13. A Link or Fuse or both may be used depending upon the Type of Switch, such as Switch Disconnector or Switch Disconnector Fuse.
[0047] FIGURE. 5 illustrates the partial perspective view of the contact system when the electrical switch is in ON condition according to one embodiment of the present invention. With respect to FIG.5, the contact system has fixed contacts 13
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mounted with fuse holder 8 to hold a link 7 coupled to a fuse spring 9. During the switch off condition, the moving contact 2 is not inserted between the terminal 6 and the fixed contact 13.
G) ADVANTAGES OF THE INVENTION
[0048] Thus the various embodiments of the present invention provide an improved and cost effective moving contact in a contact system for switching devices. The moving contacts are provided with rigid portions to maintain adequate contact pressure between the terminals and the fixed contacts. The moving contact has flexible portion to permit the thermal expansion of the metal to provide enhanced heat dissipation and vibration isolation. The flexible foils are solidified selectively to provide rigidity. The rigidity of the braided contact increases the contact surface between the moving contact and fixed contacts. Further, the increased contact surface offers lesser contact joint resistance which in turn reduces the heat generation in the electrical switching device. Moreover the number of components used in the switching device may be reduced by designing the moving contact according to the power requirements and by varying the number of copper foils in the contact. The flexible zone of the copper foil which is not solidified offers flexibility to the moving contact. The braided copper foils provide a simple contact system with reduced number of components. The system provides a cost effective improved contact system.
[0049] 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
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modifications. However, all such modifications are deemed to be within the scope of the claims.
[0050] 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.
The detailed scope of the monopoly claimed for the invention shall be ascertained and provided at the time of filing of the Complete Specification.

Rakesh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA
To,
The Controller of Patents,
The Patent office,
Mumbai
Dated this 28th of November, 2008
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