Title of Invention

CURRENT LIMITING RESISTOR FOR CAPACITOR SWITCHING DUTY CONTACTOR

Abstract

A current limiting resistor unit to avoid resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards comprises former having insulation coating of defined thickness. The former (8) have top, bottom and lateral surfaces (19, 20 and 21) wherein the lateral surface (21) is wound around by wire means (9). The resistor unit comprises protruded conducting portions (15) in predetermined angular relationship with said lateral surface (21) of the former (8) and is operatively disposed in insulating channel means (13). Screw terminal means (14) is located in co-operation with said insulating channel means (13) and has ergonomically designed fixation means (12) adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. A current limiting resistor block comprises said resistor unit and cover (22) having plurality of walls comprising lateral walls (23) in perpendicular relation with top surface (24) of the cover (22), wherein said lateral walls (23) being provided with semi-circular space (25) ergonomically designed in a manner to provide co-operative engagement of said resistor unit into the cover (22). Figure 1

Full Text

FORM2 THE PATENTS ACT, 1970 (39 of 1970) & The Patents Rules, 2003 COMPLETE SPECIFICATION (See section 10; rule 13) 1. Title of the invention. - CURRENT LIMITING RESISTOR FOR CAPACITOR SWITCHING DUTY CONTACTOR 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 a current limiting resistor for a capacitor switching duty contactor. More particularly, the invention relates to a current limiting resistor for a capacitor switching duty contactor adapted to dampen the high inrush current in the capacitor switching contactor and avoids unnecessary resistor loop overlapping thus minimizing probabilities of short circuit, flashover and fire hazards. Background and Prior Art Over the period of time capacitor bank switching contactor have been provided with resistor or inductor in series with the line to limit the inrush current during closing of the circuit. These intended resistors normally used to be insulated sleeved heater wire either in coiled form or stretched free form. In both the cases the overall panel volume of the contactor increases due to additional space required by the resistor wire. Over the years, the capacitor switching contactor has been explored in various ways. The Basic capacitor switching duty contactor consists of a Main circuit CI and a limiting circuit LI in parallel to it. Figure 3 shows such circuit. The capacitive load Cc is connected to the distribution load via the capacitor switching contactor. As the contactor switches ON, the limiting circuit is closed first through the arcing contact system Al, which leads the Main contact system Ma. The higher inrush current is limited to the desired rating through the resistor R connected in series between the main contact and arcing contact. While opening the Capacitive load Cc, the arcing contact breaks before the main contact. Commonly known conventional current limiting resistor consists of a heater wire with insulation sleeve wrapped over it. The resistor wire depending upon the KVAR rating of the contactor, are available in stretched or coiled form. The extreme end of the wires is connected with suitable lug for fitment with the standard contactor Cs and Aux. contact block Ca. Especially for the higher KVAR rating there has been frequent field complaint of resistor burning and insulation failure at the extreme end of the resistor. Thus the scope of the conventional current limiting resistor is limited to Low KVAR rated contactor. Also to 2 maintain the resistance per pole with adequate thermal mass, the length of the sleeved heater wire becomes so high that it results in increase in the overall height of the contactor. This further increases the panel volume. To a larger extent, the contactor height is reduced by means of looping the sleeved resistor in coiled form. But due to increase in the overall diameter of the loop, the clearance in the resistors between the phases reduces. Since the sleeved heater wire is flexible, they overlap with respect to each other under actual field condition; a slight pinhole in the insulation could result to a dead short circuit and flashover across the phases. For every instant of closing operation, the resister is under severe electro dynamic stress, resulting into change in the pitch of the resistor between alternate phases. The solution for this lies in providing means for securing the resistor per phase through phase barrier guards, which always maintain the desired clearance and creepage between the phases. US6285271 and FR2735279 disclose capacitor switching duty contactor, which claims about the innovative ideas for arrangement of resistor with respect to the standard contactor and aux. contact block. In both the patents, it is claimed that part of resistors are secured inside an insulating attachment housing, and remaining part is connected via input and output contact block in between the main contact and arcing contact system. US 4595812 discloses a circuit interrupter comprising a housing including a housing wall, an interrupting mechanism including a pair of separable contacts and an operating mechanism, and an optional accessory unit used in connection with an opening operation of the interrupting mechanism. The optional accessory unit may be a unit which includes a movable member operable in connection with the opening operation of the interrupting mechanism, such as an alarm switch, an auxiliary switch, a voltage trip device or an under voltage trip device. The optional accessory unit may be a connecting terminal block connectable between an external circuit and the circuit interrupter. The housing has formed in the outer surface thereof a receptacle cavity for receiving therein the optional accessory unit. When the unit is received in the cavity, no substantial portion of the unit projects from the housing. A fastening means comprises a slider, a guide rail engaging the slider for allowing a sliding 3 movement of the optional accessory unit only in the direction of extension of the guide rail, and a screw for securing the optional accessory unit to the housing wall. US 5483213 discloses an auxiliary terminal block for an electrical switching device includes a molded block and at least one terminal for terminating the internal wiring and external wiring of the switching device. The molded block has a first wiring channel for the external wiring, a second wiring channel for the internal wiring, and a partial partition between the two wiring channels. The partition has a slot for engaging and locking the terminal after the internal wiring has been terminated. The partition may include two walls having a generally constant width therebetween. Shoulders or tabs may be disposed on each of the walls for engaging and locking the terminal to the block. Alternatively, the partition may include two walls which are at least partially resilient and which form a generally V-shaped opening between the two wiring channels. A shoulder may be disposed on each of the walls for engaging and locking the terminal to the block whenever the terminal is fully inserted within the partition. The terminal may have an L-shape, a first arm which terminates the external wiring, and a second arm having a crimp terminal or solder terminal for terminating the internal wiring. The first arm may have on opposite sides thereof two notches mating with the two walls. The two notches of the first arm form a neck which is generally freely insertable within the V-shaped opening and which is generally resisted by further insertion within the V-shaped opening until the neck is fully inserted and confined within an opening adjacent the shoulders. Hence there is a need for current limiting resistor for dampening high inrush current in the capacitor switching contactor and to avoid unnecessary resistor loop overlapping thus minimizing probabilities of short circuit, flashover and fire hazards. The present inventor have found that the insulation co-ordination and secureness of the current limiting resistors per phase at the incoming and the outgoing terminals of the capacitor switching contactor can be ameliorated providing a definite ergonomical design and construction in the current limiting resistor. Such current limiting resistor is not only compact and sturdy but also being mechanically coupled with the contactor in a way maintains constant pitch through out the life cycle of the product. 4 Objects of Invention Thus the basic object of the present invention is to provide a current limiting resistor for a capacitor switching duty contactor wherein the resistor is capable of dampening high inrush current in the capacitor switching contactor. Another object is to avoid unnecessary resistor loop overlapping thus minimizing probabilities of short circuit, flashover and fire hazards. The other object is to provide current limiting resistor, which is simple in design with reduced number of variants making it cost effective. Summary of Invention Thus according to the basic aspect of the present invention there is provided a current limiting resistor unit adapted to avoid resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards, the said resistor comprising: (i) former having insulation coating of defined thickness, said former comprising top, bottom and lateral surfaces wherein the lateral surface being wound around by a wire means; (ii) protruded conducting portions in predetermined angular relationship with said lateral surface of the former, said protruded portion being operatively disposed in an insulating channel means located in juxtaposition with said former; and (iii) screw terminal means located in co-operation with said insulating channel means and having economically designed fixation means adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. According to another aspect of the present invention there is provided a current limiting resistor block for a capacitor switching duty contactor adapted to dampen high inrush current 5 in the capacitor switching contactor avoiding resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards, said resistor block comprising: (i) cover having plurality of walls comprising lateral walls in perpendicular relation with top surface of the cover, wherein said lateral walls being provided with semicircular space ergonomically designed in a manner to provide co-operative engagement of said resistor unit into the cover; (ii) said resistor unit comprising former having insulation coating of defined thickness, said former comprising top, bottom and lateral surfaces wherein the lateral surface being wound around by a wire means; (iii) protruded conducting portions in predetermined angular relationship with said lateral surface of the former, said protruded portion being operatively disposed in an insulating channel means located in juxtaposition with said former; and (iv) screw terminal means located in co-operation with said insulating channel means and having ergonomically designed fixation means adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. Detailed Description Of Invention In the present invention the resistor comprises aluminium former having Kapton polyamide coating of thickness 1 mm on which the wire means comprising nichrome wire coiled round over through out the length of the former having adequate pitch -in between windings of the wire. The former comprises means to grip-holding the windings in predetermined position on the former. The said means comprises plurality of copper terminal clamps at the top and the bottom ends of the former such that the extreme ends of the wire windings being spot-welded with the clamp remain in position. Tinned copper conductor of desired length and diameter is spot welded to the clamp at one end and the other end is crimped with fixation means which comprises insulated ring type lug. The ring type lug when terminated in contact block of any standard contactor give fixation to the protruding conducting portions of the resistor unit. The said ring type lug and the copper conductor are partially disposed in screw terminal means operatively connected to the former via the protruding conducting portion of the resistor unit. 6 The said protruding conducting portion comprises prongs, which are guided through guided insulating channel means. The insulating channel means comprises silicon fibre based glass sleeve ergonomically designed and placed in juxtaposition with the former providing desired secureness and insulation co-ordination to the prongs. The prongs are ergonomically designed in a manner that required pitch between the resistors per phase remains unaltered providing desired secureness and insulation co-ordination between phases. This also minimizes the chances of short circuit and flashover to a greater extent since the resistors between phases are arrested in all degrees of freedom. The said prongs are routed on lateral surface of the former in a manner that the intentional tool for termination is easily accessible to all the terminal of the standard contactor. The resistor unit comprises special encapsulation of vitreous enamel coating having predetermined thickness providing desired heat dissipation, insulation and makes the unit to a single moulded part. Unlike to the convention resistors, the chances of sleeve burning and corrosion of the wire coils (due to melting material of sleeve depositing on the wire) is avoided. In the present invention the current limiting circuit comprising current limiting resistor block is integrated with a capacitor switching contactor comprising a standard contactor and an auxiliary contact block, which carries a set of early make and break arcing contacts and auxiliary contact system. These are in parallel to the main contact system. The standard contactor and auxiliary contact block is electrically and mechanically coupled by the current limiting circuit which comprises two resistors per phase connected in series between the main contact and the arcing contact. The set of resistors per phase comprises protruding conducting portions comprising prongs located at the incoming and the outgoing terminals of the capacitor switching contactor. The former comprises supporting guard means having predetermined holes wherein the protruding prongs are disposed. Preferably, the insulated prongs are routed on the set of the resistors with adequate angles having predetermined angular relationship with the former so that the intentional tool is easily accessible to the power terminal and wire overlapping between the phases is avoided The complete factory built assembly 'A' of auxiliary contact block alongwith the resistor unit block of the present invention is connected at the incoming and the outgoing terminals to the standard contactor via the insulated prongs protruding out of the resistor unit. 7 Brief Description Of Accompanying Figures Figure 1 illustrates capacitor switching contactor with the current limiting resistor of the present invention. Figure 2 illustrates the isometric view of capacitor switching contactor with the current limiting resistor of the present invention. Figure 3 illustrates limiting circuit for capacitor switching duty contactor. Figure 4 illustrates an enlarged isometric view of factory inbuilt resistor unit assembly 'A'. Figure 5 illustrates the top view of the assembly 'A'. Figure 6 illustrates isometric view of the resistor unit of the present invention. Figure 7 illustrates the isometric view of the cover securing the screw terminal in default position. Figure 8 illustrates the exploded isometric view of capacitor switching contactor alongwith the resistor unit of the present invention. Detailed Description Of Accompanying Figures In figure 1 capacitor switching contactor with the current limiting resistor of the present invention is illustrated. In the figure the main fixed magnet assembly (1) is rested on the bottom frame (2) of the contactor and is in operative magnetic relation with moving magnet (3). Mobile bridge (4) carrying the main moving contact assembly (5) is operatively connected to the moving magnet (3). Auxiliary contact block (6) comprising moving contact 8 assembly (26), fixed magnet assembly (1) is mechanically coupled with mobile bridge (4) and is connected in parallel to the main contact system (7). The auxiliary contact block (6) is mechanically and electrically coupled with the resistor unit. From figure 1 it is realizable that the resistor unit comprises kapton polyamide coated aluminium former (8) having nichrome wire (9) coiled round over through out its length with adequate pitch in between. The former (8) comprises plurality of copper terminal clamps (10) at the top and the bottom ends of the former (8). Tinned copper conductor (11) (shown in figure 6) of desired length and diameter is spot welded to the clamp (10) at one end and the other end is crimped with insulated ring type lug (12) (also shown in figure 6). Silicon fibre based glass sleeve (13) is economically designed and intermediately located in juxtaposition with the screw terminal means (14). The tinned copper conductor (11) (shown in figure 6) and former (8) having adequate shape for accessibility of the tool for power termination (intentional tool), provides the desired sturdy gripping and constant pitch. The resistor unit comprises special encapsulation of vitreous enamel coating (16) (shown in figure 6) having predetermined thickness providing desired heat dissipation, insulation and makes the unit to a single moulded part. In figure 2 the isometric view of capacitor switching contactor with the current limiting resistor of the present invention is illustrated. The prongs (15) protruding from the resistor unit is provided with adequate angle positioned as (17) and is operatively disposed within the glass sleeve (13) (also shown in figure 6). In figure 4 an enlarged isometric view of factory inbuilt resistor unit assembly 'A' is illustrated. Assembly (A) is mechanically coupled with the standard contactor via insulated prongs (15) protruding out of the resistor unit through supporting guards (18). In figure 5 the top view of the assembly 'A' is illustrated. In the figure the prongs (15) of lines (LI, L2 and L3) provided with predetermined adequate angles are disposed within the silicon fibre based glass sleeves (13) so that the intentional tool is easily accessible to the power terminal and wire overlapping between the phases is avoided. 9 In figure 6 isometric view of the resistor unit of the present invention is illustrated. The rectangular former (8) having predetermined dimensions comprises clamps (10) at the top and the bottom faces (19 and 20) of the former (8). The prong (15) protruding out from the lateral surface (21) of the former (8) is routed with adequate angles. The prongs (15) are guided through the insulated silicon fibre based glass sleeves (13) having desired secureness and insulation co-ordination. The tinned copper conductor (11) is crimped with ring type lug (12). Nichrome wire (9) is wound round the lateral surface (21) of the former (8). In figure 7 the isometric view of the cover securing the screw terminal in default position is illustrated. The cover (22) comprises two lateral walls (23) which are in perpendicular relation with the top surface (24) of the cover (22). The lateral walls (23) comprise semicircular space (25) (shown in figure 8), which on engagement with the auxiliary contact block (6) forms a circular hole for disposition of the screw terminal means (14). 10 We Claim 1. A current limiting resistor unit adapted to avoid resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards, the said resistor comprising: (i) former having insulation coating of defined thickness, said former comprising top, bottom and lateral surfaces wherein the lateral surface being wound around by a wire means; (ii) protruded conducting portions in predetermined angular relationship with said lateral surface of the former, said protruded portion being operatively disposed in an insulating channel means located in juxtaposition with said former; and (iii) screw terminal means located in co-operation with said insulating channel means and having ergonomically designed fixation means adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. 2. A current limiting resistor unit as claimed in claim 1, wherein the former comprises polyamide insulation coating of adequate thickness. 3. A current limiting resistor unit as claimed in claims 1 and 2, wherein the wire means wound round the former comprises nichrome wire having vitreous enamel coating, said nichrome wire being wound around the former in a manner to provide adequate pitch in between windings of the wire. 4. A current limiting resistor unit as claimed in claim 1, wherein the protruded conducting portions comprises prongs being routed on the lateral surface of the former in a manner that adequate angle is provided between the former and the prongs, angles being such that intentional tool is easily accessible to the power terminal and wire overlapping between phases is avoided maintaining unaltered pitch between resistors per phase. 11 A current limiting resistor unit as claimed in claims 1 to 4, wherein the insulated channels comprising silicon fibre based glass sleeves ergonomically designed and intermediately located in juxtaposition with the screw terminal means and former such that the prongs disposed within the sleeves have desired secureness, insulation co-ordination and accessibility of the tool for power termination providing sturdy gripping and constant pitch. A current limiting resistor unit as claimed in claims 1 to 5, wherein screw terminal means comprises ring type lug and operatively connected to the former by the prongs. A current limiting resistor block for a capacitor switching duty contactor adapted to dampen high inrush current in the capacitor switching contactor avoiding resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards, said resistor block comprising: (i) cover having plurality of walls comprising lateral walls in perpendicular relation with top surface of the cover, wherein said lateral walls being provided with semicircular space ergonomically designed in a manner to provide co-operative engagement of said resistor unit into the cover; (ii) said resistor unit comprising former having insulation coating of defined thickness, said former comprising top, bottom and lateral surfaces wherein the lateral surface being wound around by a wire means; (iii) protruded conducting portions in predetermined angular relationship with said lateral surface of the former, said protruded portion being operatively disposed in an insulating channel means located in juxtaposition with said former; and (iv) screw terminal means located in co-operation with said insulating channel means and having ergonomically designed fixation means adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. 12 8. A current limiting resistor block as claimed in claim 7, wherein the economically designed semi-circular space on the lateral surface of the cover being provided in a manner that on co-operative engagement of the cover with auxiliary contact block circular hole is provided such that the screw terminal means being disposed inside it the fixation of the resistor unit is assured. 9. A current limiting resistor block as claimed in claim 8, wherein the cover comprises protrusion such that locking of the cover with the screw terminal prevents tampering of mechanically coupled assembly (A) with conventional contactor at actual field condition. 10. A current limiting resistor and block as herein substantially described and illustrated with reference to the accompanying figures. Dated this 3 rd day of August, 2005 13 ABSTRACT Title : Current Limiting Resistor For Capacitor Switching Duty Contactor A current limiting resistor unit to avoid resistor loop overlapping minimizing probabilities of short circuit, flashover and fire hazards comprises former having insulation coating of defined thickness. The former (8) have top, bottom and lateral surfaces (19, 20 and 21) wherein the lateral surface (21) is wound around by wire means (9). The resistor unit comprises protruded conducting portions (15) in predetermined angular relationship with said lateral surface (21) of the former (8) and is operatively disposed in insulating channel means (13). Screw terminal means (14) is located in co-operation with said insulating channel means (13) and has ergonomically designed fixation means (12) adapted to maintain standard pitch between phases of conductor when fixed to any conventional contactor. A current limiting resistor block comprises said resistor unit and cover (22) having plurality of walls comprising lateral walls (23) in perpendicular relation with top surface (24) of the cover (22), wherein said lateral walls (23) being provided with semi-circular space (25) ergonomically designed in a manner to provide co-operative engagement of said resistor unit into the cover (22). Figure 1

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917-MUM-2005-ABSTRACT(8-8-2005).pdf

917-MUM-2005-ABSTRACT(GRANTED)-(19-3-2012).pdf

917-mum-2005-abstract.doc

917-mum-2005-abstract.pdf

917-MUM-2005-CANCELLED PAGES(26-9-2011).pdf

917-MUM-2005-CLAIMS(AMENDED)-(26-9-2011).pdf

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917-MUM-2005-CORRESPONDENCE(26-7-2010).pdf

917-MUM-2005-CORRESPONDENCE(29-9-2008).pdf

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917-MUM-2005-CORRESPONDENCE(IPO)-(21-3-2012).pdf

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917-mum-2005-description (complete).pdf

917-MUM-2005-DESCRIPTION(GRANTED)-(19-3-2012).pdf

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