FORM 2
THE PATENTS ACT, 1970 COMPLETE SPECIFICATION
(See Section 10)
SWITCHING DEVICE WITH ENHANCED SHORT-TIME WITHSTAND PERFORMANCE
Numbered as dated
INVENTORS:
a) VISHNU ANDHARE
b) YOGESH.N. PATIL
c) HARI KUMAR THANGUDU
APPLICANT:
M/s. LARSEN & TOUBRO LIMITED
L&T House, Ballard Estate, P.O. Box No 278, Mumbai, 400 001, Maharashtra,
INDIA
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THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE
NATURE OF THE INVENTION

SWITCHING DEVICE WITH ENHANCED SHORT-TIME WITHSTAND PERFORMANCE
A) Technical field
[0001] The embodiments herein generally relate an enhanced switching device adapted for opening and closing electrical circuits and more specifically to a switch capable of withstanding short time high current.
B) Background
[0002] A switching device is normally designed to withstand currents having values in the order of 12 times of the rated current of switch. If the closed contact of the switching device is subjected to a high current impulse, electrodynamic force may open the contact, and resulting arc may damage the device.
[0003] U.S. Patent No. 5,815,058 discloses contact enhancement apparatus for an electric switch. The compensation in the switch is obtained by means of the combination of an electromagnetic bar and a U shaped electromagnetic bar. When an undesired high current passes by the contacts, the counter repulsive force generated by the electro-magnetic bars keeps the contacts together. The force of attraction between the electromagnetic bars varies inversely as the air gap between them. Because of constructional limitations, the prior art can achieve a minimum air gap, sin the order of 1 millimeter.
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[0004] While the conventional solutions are advantageous for their intended purposes, the existing state of the art generally does not provide adequate solutions for a switching device that can withstand much higher values of short circuit forces as compared with prior arts.
[0005] Hence, there is a need to develop a switching device that is capable of withstanding short time high current which would prevent connecting surfaces and conductors from deformation, welding and other phenomenon that might damage apparatus due to repulsion or heat.
C) Object of the invention
[0006] An object of the invention is to provide a switching device capable of withstanding short time high current.
[0007] Another object of the invention is to provide means for compensating the effect of electro-dynamic repulsion forces that arise between fixed and moving contacts during passage of short circuit current, so as to prevent the contacts from malapropos separating.
[0008] Yet another object of the invention is to provide a solution that would prevent connecting surfaces and conductors from deformation, welding and other phenomenon that might damage apparatus due to repulsion or heat when
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short time high current flows through switch.
D) Summary
[0009] The embodiments herein provide a switching device capable of withstanding short time high current; to prevent connecting surfaces and conductors from deformation, welding and other phenomenon damaging apparatus due to repulsion or heat.
[0010] According to one embodiment switching device comprises: front housing which is a thermoset plastic housing which covers inside components of switch like moving contact, bridge etc; rear housing which is a thermoset plastic housing and supports fixed contacts; top terminals that are fix contact of switch made up of copper and are mounted on top side of rear housing; bottom terminals that are fix contact of switch made up of copper and are mounted on bottom side of rear housing ; a shaft which is a rotating member that is supported between front housing and rear housing; phase barriers that are insulating walls inside switch and act as partition between two switches; moving contacts that are copper contacts mounted on plastic bridge; magnetic latches that are 'C shaped steel pieces placed above and below moving contact; contact springs that are leaf spring made up of sheet spring steel, wherein two ends of leaf springs are placed on moving contact as central part is supported against bridge and facilitate contact pressure between moving contact and respective terminal in contact; a bridge which is a plastic housing that moves
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and translates on the rail form between front housing and rear housing, wherein said bridge houses moving contact, magnetic latch and contact spring in it.
[0011] Overall bridge assembly is an assembly of 16 moving contact, 16 contact springs and a bridge. Bridge assembly is guided and allowed to reciprocate in guiding path of front housing and rear housing.
[0012] A set of electromagnetic bars is fixed surrounding moving contacts, in such a way that any high current passing through the moving contacts develops a force of attraction between the said electromagnetic bars, which in turn hold the moving contacts pressed with the fixed contacts. This ensures the contact between the fixed and the moving contacts, even at short circuit currents for a given duration.
[0013] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
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E) Brief description of the drawings
[0014] The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
[0015] FIG. 1 illustrates isometric view of a switching device.
[0016] FIG. 2 illustrates isometric view of a switching device without front housing and shaft.
[0017] FIG. 3 illustrates isometric view of contact system that includes all terminals and bridge assembly when switch is in OFF condition.
[0018] FIG. 4 illustrates isometric view of contact system that includes all terminals and bridge assembly when switch is in ON condition.
[0019] FIG. 5 illustrates enlarged isometric view of contact system when switch is ON condition.
[0020] FIG. 6 illustrates front view of switch in ON condition.
[0021] FIG. 7 illustrates front view of switch in OFF condition.
[0022] FIG. 8 illustrates sectional view of contact system when switch is in OFF condition.
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[0023] FIG. 9 illustrates sectional view of contact system when switch is in ON condition.
F) Detailed description of the Invention
[0024] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.
[0025] A preferred embodiment provides a switching device comprises a set of fixed contacts and a set of resilientiy held moving contacts, which ride over the former. A set of electromagnetic bars is fixed surrounding the moving contacts, in such a way that any high current passing through the moving contacts develops a force of attraction between the said electromagnetic bars, which in turn hold the moving contacts pressed with the fixed contacts. This ensures the contact between the fixed and the moving contacts, even at short circuit
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currents for a given duration.
[0026] FIG. 1 illustrates isometric view of a switching device. Front housing 102 is a thermoset plastic housing which covers inside components of switch like moving contacts (120a, 120b), bridge 116 etc. Rear housing 104 is a thermoset plastic housing which supports fixed contacts (106, 108). It also acts as a guide for translating motion of Bridge 116 and rotary movement of shaft 110. Top terminals 106 are fix contact of switch made up of copper and are mounted on top side of rear housing 104. Bottom terminals 108 are fix contact of switch made up of copper and are mounted on bottom side of rear housing 104. Shaft 110 is a rotating member of which is supported between front Housing 102 and rear housing 104.
[0027] FIG. 2 illustrates isometric view of a switching device without front housing and shaft. Phase barriers 112 are insulating walls inside switch which acts a partition between two switches.
FIG. 3 illustrates isometric view of contact system that includes all terminals and bridge assembly when switch is in OFF condition. Bridge assembly 114 is an assembly of 16 moving contact (120a, 120b), 16 contact springs (122a, 122b) and a. bridge 116. Bridge assembly 114 is guided and allowed to reciprocate in guiding path of front housing 102 and rear housing 104.
[0028] FIG. 4 illustrates isometric view of contact system that includes all terminals and bridge assembly when switch is in ON condition.
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[0029] FIG. 5 illustrates enlarged isometric view of contact system when switch is ON condition. Bridge 116 is a plastic housing which is a moving member which translates on the rail form between front housing 102 and rear housing 104. Bridge 116 houses moving contact (120a, 120b), magnetic latch (118a, 118b) and contact spring (122a, 122b) in it Magnetic latch (118a, 118b) are 'C shaped steel pieces place above and below moving contact (120a, 120b) respectively. Moving contacts (120a, 120b) are copper contacts mounted in plastic bridge 116. Contact springs (122a, 122b) are leaf spring made up of sheet spring steel. Two ends of leaf springs are placed on moving contact (120a, 120b) as central part is supported against bridgell6. Contact spring (122a, 122b) facilitates contact pressure between moving contacts (120a, 120b) and respective fixed contacts (106, 108).
[0030] FIG. 6 illustrates front view of switch in ON condition. Figure illustrates terminals (106, 108) and bridge 116 configuration during the ON condition.
[0031] FIG. 7 illustrates front view of switch in OFF condition. It only illustrates terminals (106, 108) and bridge 116 configuration during the OFF condition.
[0032] FIG. 8 illustrates front view of switching device when switch is in OFF condition. Bridge 116 houses moving contact (120a, 120b), magnetic latching (118a, 118b) and contact spring (122a, 122b) in it. Moving contacts (120a, 120b) are assembled in bridge 116 in such a way that both are parallel and
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facing to each other. The 'C shaped magnetic latching (118a, 118b) are kept on each moving contact as shown in FIG. 8 and FIG. 10. Contact springs (122a, 122b) are placed between moving contact and bridge slot. These contact springs give required contact pressure on moving contacts (120a, 120b) during normal condition. During OFF condition the gap between two moving contacts (120a, 120b) is zero and the gap between two magnetic latching parts is also equal to zero.
[0033] FIG. 9 illustrates front view of the compensated switching device when the switch is in ON condition. The two terminals (106, 108) are sandwiched by the two moving contacts (120a, 120b). The continuity is established in the electric circuit and the current flows from first fixed terminal 106 to the moving contacts (120a, 120b) and finally to second fixed terminal 108. During the normal rated currents, the required contact pressure at contacts is obtained by contact springs (122a, 122b).
[0034] When short circuit current flows through the switch, there will be a high repulsive force produced at the actual contact position. The forces obtained by contact springs (122a, 122b) are not sufficient to compensate these repulsive forces. To counteract this repulsion forces, preferred embodiment uses two ways of generating attraction forces between the moving contacts (120a, 120b). The first one comprises of the special arrangement and profile of moving contacts (120a, 120b) connected in parallel, and as shown in Fig 9. The second way, which acts in conjunction with the first one, comprises of magnetic latching (118a, 118b).
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[0035] When current starts flowing in the circuit, the moving contacts (120a, 120b) experience parallel flow of current in same direction. So by laws of magnetism there will be an attraction force generated between these two moving contacts (120a, 120b). This force is direcdy proportional to the overlap length of two moving contacts (120a, 120b) and inversely proportional to distance between them. To generate more force the invention uses the contact system in such a way that two moving contacts (120a, 120b) have minimum gap between them. The embodiment reduces the gap between the moving contacts (120a, 120b) by changing the profile of moving contacts (120a, 120b) as shown in FIG. 8 and FIG. 9. Central non contact portion of moving contacts (120a, 120b) is bent as to achieve minimum gap. This results in zero gap between the two moving contacts (120a, 120b) when the switch is in OFF position. When the switch is in ON position, each one of the moving contacts (120a, 120b) gets displaced by an amount equal to the deflection required to maintain contact between moving contact (120a, 120b) and terminal (106, 108). Due to the redesigned profile of moving contacts (120a, 120b) the gap between both contacts (120a, 120b) is equal to twice the deflection of each instead of it being equal to the thickness of terminal (106, 108).
[0036] When high current flows through moving contacts (120a, 120b), a magnetic field is produced around them. The flux lines will pass through the magnetic latchings (118a, 118b) which are above the moving contacts (120a, 120b). During ON condition there is a small gap between two magnetic latchings (118a, 118a) which as shown in FIG. 10. A reluctance force is
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produced between these two parts, by which the magnetic latchings (118a, 118b) move inward in longitudinal direction. So the moving contacts (120a, 120b) which are present inside these ‘C’ type magnetic latchings (118a, 118b) experience mutually attractive force. This force increases as gap between two magnetic latchings (118a, 118b) is further reduced. In present embodiment with new construction this gap is reduced to zero.
[0037] A finite gap is intentionally maintained between moving contacts (120a, 120b) and magnetic latching (118a, 118b) on both sides. The magnetic latching (118a, 118b) is slightly above the moving contacts (120a, 120b). When the switch is in the transition phase from OFF to ON, the bridge 116 moves in horizontal fashion, whereas the moving contacts (120a, 120b) start moving outwards in a longitudinal direction, i.e. towards the magnetic latching (118a, 118b). In present embodiment, as the construction permits magnetic latchings(118a, 118b) are stationary even when the contacts gradually start moving outwards. When the switch is just to become ON i.e. the moving contacts (120a, 120b) moves outwards by most of the intended distance, the distance between the moving contacts (120a, 120b) and the magnetic latching (118a, 118b) becomes zero. For a very short while, the relative motion between them ceases to exist and both start moving outwards. This results in a near-zero air gap between the two magnetic latching parts (118a, 118b) in ON condition, and which further leads to maximization of the intended counter-attractive force. This force obtained can be increased by increasing the thickness and length of magnetic latching (118a, 118b).
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[0038] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.
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CLAIMS
What is claimed is:
1. A switching device capable of withstanding short time high current, comprising of:
a front housing, wherein said front housing is a thermoset plastic
housing which covers inside components of switch;
a rear housing, wherein said rear housing is a thermoset plastic housing
and supports fixed contacts;
a bridge which is a plastic housing, wherein said bridge moves and
translates on the rail form between said front housing and rear housing,
a set of fix contacts mounted on top side of rear housing;
a set of moving contacts mounted on said bridge;
a shaft which is a rotating member supported between front housing and
rear housing;
a phase barrier that is insulating wall inside switch and act as partition
between two switches;
a set of magnetic latches that are