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:
ENCAPSULATED RESISTOR DEVICE FOR CONTACTORS


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 switching devices and particularly to the contactors such as capacitor switching duty contactors used for electric motors, capacitor bank, resistance furnace, etc. The present invention more particularly relates to encapsulated and pre inserted resistor units for the auxiliary add-on block in a capacitor switching duty contactor.
B) BACKGROUND OF THE INVENTION
[0002] A contactor is an electrically controlled switch that is used generally to control or remotely switch the power to any electric power driven circuit like electric motor, capacitor bank, resistance furnace etc. The contactor is used to make and break the flow of current in the electric power driven circuit and carries the rated current under the closed condition. The current under switching conditions viz. making or breaking is higher than the rated current. The magnitude of this switching current depends upon the type of device being switched e.g. induction motors it is 12 times rated current in making and 10 times rated current while breaking. For Capacitor switching duty, the capacitor during switching draws very high current, of the magnitude of 180 - 200 times the rated current, which is pretty high. Hence during switching of capacitors the making current is of the order of 180-200 times the rated current of capacitor.
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[0003] The contactor is basically composed of three different systems namely a contact system that carries current, an electromagnet system that generates the driving force to close the contact system for carrying current and an enclosure system comprising of housings molded from engineering plastics. The contact system of contactor includes moving contacts, situated in a contact carrier, called as Contact Bridge, which are movable under the action of electromagnetic force. The fixed contacts are secured in a plastic moulded housing. The contact bridge also carries contact springs, which generates contact pressure when the moving contacts close against the fixed contacts. This generates low resistance path for an electric current to flow.
[0004] Apart from the main contact, the contactor has auxiliary contact system, which is enclosed separately in a auxiliary contact block that is engaged to main contact bridge of a contactor. As in the case of main contact system, the auxiliary contacts also comprise of moving contacts which are housed in the auxiliary bridge and fixed contacts that are secured in the housing of an auxiliary contact block. The auxiliary contact bridge is directly engaged with the main contact bridge. As a result the moving contacts of auxiliary contacts also move, when the main contact bridge moves. The distance between the moving contact tip and fixed contact tip is known as "contact gap". The contact gap in the auxiliary contacts is kept lower than that of main contact gap. Hence the auxiliary contacts close first to establish the current path before the closure of the main contacts at a later instant.
[0005] In applications where the initial current drawn is very high like in a capacitor switching contactor, the auxiliary contacts are connected in series with the pre insertion
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resistors. Thus when the contactor is being switched on (being closed) the auxiliary contacts close first. As the pre insertion resistors are connected in series with auxiliary contacts the initial current in the circuit is limited to a lower value. Then the main contacts close at a later instant. As the main contact are in parallel to the auxiliary contacts, the current is diverted to the main contacts as the resistance of the path containing main contacts is less than that of the path containing auxiliary contacts. Thus the value of current is also reduced to nearly rated current.
[0006] When the contactor is switched off (being opened) , the main contacts of the contactor open first causing the entire current to flow through the auxiliary contacts. The auxiliary contacts now have to break the current. However, the auxiliary contacts are not designed to break the said high current. Further, the auxiliary contacts are burnt due to the current conduction and heating generated during the arcing thereby generating the premature failure of the auxiliary contacts.
[0007] Generally, all the currently available capacitor duty contactors have resistor wires hang outside the auxiliary contact block. The resistor wires externally connected between the main and the auxiliary blocks. Hence each capacitor duty contactor has, traditionally, 6 wires which are external. In practice, this leads to many faults like interphase faults, resistor wires becoming loose hence opening the auxiliary path. As the resistor wires are arranged externally, this leads to the manhandling by the service personnel
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[0012] Another object of the present invention is to design a pre insertion resistor assembly so that the resistor unit is encapsulated in the add on block thereby preventing any access from the outside to avoid the manhandling from the service person/customer's end.
[0013] Yet another object of the present invention is to build a resistor cassette base to house all the three resistor wire units which is physically separated from each other by a fixed distance.
[0014] Yet another object of the present invention is to pot the cassette base to enhance the heat dissipation.
[0015] Yet another object of the present invention is to spot weld the resistor wires onto a copper wire which is connected to a fast on lug to the riser connected to the main terminals to prevent loosening of the resistor during the handling operation by the customer or maintenance personnel.
[0016] Yet another object of the present invention is to develop an encapsulated resistor base to prevent any external damage or injury to the customer.
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[0017] Yet another object of the present invention is to provide a cassette base mechanism to house the pre-insertion/current limiting resistors inside the auxiliary contactor block.
[0018] Yet another object of the present invention is to provide safety to the user by encapsulating the resistor wires such that there are minimum chances of the product failing due to inter phase shorting.
[0019] Yet another object of the present invention is to provide a cassette base housing partition to physically separate the resistor units and to prevent inter-phase shorting even if the resistors are damaged.
[0020] Yet another object of the present invention is to provide a fast-on lug for connecting the copper conductor to the main terminals.
[0021] Yet another object of the present invention is to provide a fast-on lug safety sleeve to prevent the customer from touching the fast-on lug which is clamped on to the riser.
[0022] Yet another object of the present invention is to provide a Riser flange for fixing the fast-on lug.
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[0023] Yet another object of the present invention is to provide a riser arrangement to keep the continuity of the resistors even when the screws are loosened by the customers to connect the cable.
[0024] Yet another object of the present invention is to provide Safety during customer man-hand ling.
[0025] Yet another object of the present invention is to prevent the interface between the resistor wires when the screw driver is inserted in to the resistor assembly for tightening the screws during maintenance.
[0026] 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
[0027] The above mentioned shortcomings, disadvantages and problems are addressed herein and which will be understood by reading and studying the following specification.
[0028] The various embodiments of the present invention provide a contactor system with an encapsulated resistors housing arranged inside the contactor auxiliary block. According to one embodiment of the present invention, a cassette base is arranged inside an auxiliary contact block. The cassette base houses three resistor wires which are
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separated from each other and potted in a resin case. The three resistor wires are connected to the copper conductor wires which are coupled to the riser connected to the main terminals through a fast on lug. A safety sleeve is provided around the copper conductor to prevent the customer from touching the fast on lug which is clamped to the riser. The risers are held tightly by the screws.
[0029] Thus the present invention provides a cassette base housing with partition inside to physically separate the resistor units. The encapsulated resistors housed in the contactor auxiliary block to prevent interface faults. The cassette base mechanism with the riser and fast-on lug assembly also prevents the interface between the resistor wires when the screw driver is inserted in to the resistor assembly for tightening the screws during maintenance.
[0030] 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 IF THE DRAWINGS
[0031] 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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[0032] FIG.l illustrates a front perspective view of the capacitor switching duty contactor provided with encapsulated resistor wires according to an embodiment of the present invention.
[0033] 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.
F) DETAILED DESCRIPTION OF THE INVENTION
[0034] 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.
[0035] The various embodiments of the present invention provide a contactor system with an encapsulated resistors housing arranged inside the contactor auxiliary block. According to one embodiment of the present invention, a cassette base is arranged inside an auxiliary contact block. The cassette base houses three resistor wires which are separated from each other and potted in a resin case. The three resistor wires are spot welded to the copper conductor wires which are coupled to the riser connected to the
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main terminals through a fast on lug. A safety sleeve is provided around the copper conductor to prevent the customer from touching the fast on lug which is clamped to the riser. The risers are held tightly by the screws.
[0036] Thus the present invention provides a cassette base housing with partition walls inside to physically separate the resistor units. The encapsulated resistors housed in the contactor auxiliary block to prevent interface faults. The cassette base mechanism with the riser and fast-on lug assembly also prevents the interface between the resistor wires when the screw driver is inserted in to the resistor assembly for tightening the screws during maintenance.
[0037] According to one embodiment, a cassette base is arranged in an auxiliary housing attached to the main contactor block. The cassette base houses three resistors which are encapsulated in a resin case. The three resistor wires are separated from each other by the partition walls. The resistance wires are screwed to the auxiliary block at one end. A copper conductor provided with a PVC coating is spot welded to the resistors and connected to the fast on lugs attached to the risers to connect the resin wires to the main terminals provided in the main contactor block. The risers are held tightly by the main termination screws provided in the main block of the contactor. Even when the screws are loosened to connect the cable by the customer, the risers still maintain the continuity of the resistors. The copper conductors are surrounded by a safety sleeve to prevent the customer from touching the fast on lug.
[0038] The resistance wires are wound on a plate and encapsulated in the cassette. The cassette is potted with resin to prevent the burning of the resistors to avoid injury to the
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customer. A copper conductor with a poly vinyl chloride coating is connected to the risers through the fast on lugs to connect the resistance wires to the main block. The cassette is arranged inside the auxiliary block connected to the main block. The external copper conductor ^nd the fast on lug are arranged leaving space for the screw driver to enter through the tliree circular holes on the top cover of the main block.
[0039] Thus the present invention has an encapsulated, pre-insertion resistor units housed in the auxiliary add-on block in a capacitor switching duty contactor, to prevent any inter¬phase shorting. The encapsulated resistor wire prevents the interface faults and any chances of customer man handling. The pre insertion resistor assembly is encapsulated in the cassette base and potted in the auxiliary housing. The Resistor cassette houses three resistors units and is physically separated from each other by a fixed distance through cassette base housing partition. The resistors are placed inside the cassette base housing with slots for resistor snap-fitting. The cassette base housing includes partition walls to physically separate the three resistors units to prevent the inter-phase shorting. The cassette is potted with resin so that it will not cause any injury even if the resistors burn.
[0040] FIG.l illustrates a perspective view of the capacitor switching duty contactor. It includes an auxiliary block housing 1 with an auxiliary block bridge 2. An auxiliary block bridge indicator 2 is a popup which pops out to indicate the auxiliary bridge. A Cassette base housing 5 is potted on either side of the auxiliary block bridge 2. The cassette base housing 5 encapsulates the pre insertion resistor wires 7 and potted inside the auxiliary add-on block. The encapsulated resistor wire 7 in the present invention prevents the interface faults and any chances of customer man handling. The resistor
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cassette base 5 houses all the three resistor units and is physically separated from each other by a fixed distance through cassette base housing partition 6. The cassette casing 5 includes slots 4 for resistor snap-fitting. The Resistor cassette 5 houses the three resistors. The cassette base housing includes partition walls 6 to physically separate the three resistors units to prevent the inter-phase shorting. The cassette is potted with resin so that it will not cause any injury even if the resistors burn.
[0041] Accordingly, the Resistors 7 are screwed to the auxiliary block 1 at one end and the other end is screwed to the main termination 14 where customer cables have to be terminated. The Customer frequently loosens the main termination screws to connect the cables and ends up loosening the resistance or completely disconnecting it from the circuit which may be disastrous. Hence in order to over come this problem a Riser 12 is used which is tightly held by the main termination screws so that even when screws are loosened by the customers to connect the cable the riser will still keep the continuity of resistors.
[0042] Three resistors 7 are totally enclosed in the auxiliary block 1 and potted, a copper conductor wire 9 coated with PVC (Polyvinyl chloride) is drawn out from the resistor housing 1 to connect the resistances to the main block. The cassette base 5 is potted to enhance its heat dissipation. Further, the resistor wires are spot welded onto a copper wire which is connected externally by a fast on lug 11 and with the riser connected to the main terminals. As this connection is not along with the main termination, the user handling will not lead to the wires getting loosened. The fast-on lug 11 is used for connecting the
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copper conductor 9 to the main terminals. A safety sleeves 10 provided around the copper conductor 9 prevents the customer from touching the fast-on lug which is clamped on to the riser flange 12. The Riser flange 12 is used for fixing the lug. The external copper conductor and fast-on lug are arranged leaving space for the screw-driver to enter through the three circular holes on the main block top cover.
[0043] The external copper conductor and fast-on lug are arranged in such a manner to leave space for the screw-driver to enter through the three circular holes on the main block top cover. The three holes are provided to enable the customer to insert the cables. The main contactor magnet 15 is placed between the auxiliary contact and the main contact to generate sufficient force to close and open the contact system.
[0044] The encapsulated resistors housed in the contactor auxiliary block according to the present invention is designed to not only encapsulate the three units but also to prevent inter- phase shorting between the resistor units, as it physically separates the resister units. Moreover the cassette base will be potted enhancing its heat dissipation. Furthermore, the resistor wires will be spot welded onto a copper wire which is connected externally by a fast on lug to the riser connected to the main terminals. As this connection is not along with the main termination, the user handling will not lead to the wires getting loosened.
[0045] Thus the various embodiments of the present invention provide a pre inserted resistor cassette. The device has an encapsulated, pre-insertion resistor units housed in the auxiliary add-on block in a capacitor switching duty contactor, to prevent any inter-phase
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shorting. The encapsulated resistor wire prevents the interface faults and any chances of customer man handling. The pre insertion resistor assembly is encapsulated in the cassette base and potted in the auxiliary housing. The Resistor cassette houses three resistors units and is physically separated from each other by a fixed distance through cassette base housing partition. The resistors are placed inside the cassette base housing with slots for resistor snap-fitting. The cassette base housing includes partition walls to physically separate the three resistors units to prevent the inter-phase shorting. The cassette is potted with resin so that it will not cause any injury even if the resistors burn.
G) ADVANTAGES OF THE INVENTION
[0046] Thus the various embodiments of the present invention provide a pre inserted resistor cassette. The device has an encapsulated, pre-insertion resistor units housed in the auxiliary add-on block in a capacitor switching duty contactor, to prevent any inter-phase shorting. The encapsulated resistor wire prevents the interface faults and any chances of customer man handling. The pre insertion resistor assembly is encapsulated in the cassette base and potted in the auxiliary housing. The Resistor cassette houses three resistors units and is physically separated from each other by a fixed distance through cassette base housing partition. The resistors are placed inside the cassette base housing with slots for resistor snap-fitting. The cassette base housing includes partition walls to physically separate the three resistors units to prevent the inter-phase shorting. The cassette is potted with resin so that it will not cause any injury even if the resistors burn.
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[0047] 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.

RAKESH PRABHU
Patent Attorney
[0048] 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.
Date: October 28, 2008. Place: Bangalore.
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CLAIMS
What is claimed is:
1. A resistor device for contactor including main contact block and auxiliary contact
block, the device comprising:
A cassette base mounted in the auxiliary block;
Three resistor wires arranged inside the cassette base;
Copper conductor connected to resistor wires;
Three termination screws provided in the main block;
A riser attached to the termination screws;
A fast on lug coupled to the riser;
Wherein the resistor wires are encapsulated in the cassette base and potted with
resin to prevent the burning of the resistors.
2. The device according to claim 1, wherein the three wires are separated by the partition walls.
3. The device according to claim 1, wherein the copper conductor is connected to the resistor wires and to the riser through fast on lugs to connect the resistor wires to the terminals of the main block.
4. The device according to claim 1, wherein the copper conductor is spot welded to the resistor wires.
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5. The device according to claim 1, wherein the copper conductor is provided with an insulated coating.
6. The device according to ciaim 1, wherein the copper conductor is coated with poly vinyl chloride coating.
7. The device according to ciaim 1, wherein the copper conductor is pro vided with sleeve to prevent the customer from touching on the fast on lug.
8. The device according to claim 1, further comprises circular holes provided in the main block for inserting screw drivers to tighten the copper conductors to the main terminals on the main contactor block.
9. The device according to claim 1, wherein the fast on lug and the copper conductors are arranged to provide space for inserting the screw drivers without interfering with the copper conductors and the
fast on lug. Dated this 28thof October, 2008
Rukcsh Prabhu,
Patent Agent, ALMT Legal,
No.2, Lavelle Road, Bangalore-560 001, INDIA
To,
The Controller of Patents, The Patent office, Mumbai
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