US 3208021 A
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Description (OCR text may contain errors)
Sept. 21, 1965 T. ELLIOTT 3,208,021
' SHORTING SWITCH MECHANISM Filed Sept. 12, 1962 2 Sheets-Sheet 1 Sept. 21, 1965 T. ELLlOTT SHORTING SWITCH MECHANISM 2 Sheets-Sheet 2 Filed Sept. 12, 1962 Pies United States Patent 3,208,021 SHORTING SWITCH MECHA-NiSM Theodore Elliott, Brooklinc, Mass, assignor to Astra Corporation, Boston, Mass, a corporation of Massachusetts Filed Sept. 12, 1962, Ser. No. 223,077 2 Claims. (Cl. 336-107) This invention rel-ates to instrument transformers and more particularly to shorting switch mechanisms part-icularly useful with current transformers.
Current transformers are utilized to measure or monifor relatively heavy electrical currents flowing in a conductor. Typically the conductor is made a primary winding and a secondary Winding having a multiplicity of turns is inductively coupled to the primary winding. The voltage induced in the secondary winding is an accurate measure of the current flow in the primary. When the secondary winding of such a current transformer is open and energized there is a high potential between its terminals even where no current is flowing in the secondary winding. In order to work on such devices safety precaution-s demand that the secondary winding be closed (shorted). A variety of devices are employed in the art such as throw over links or clips, which often are awkward to use, frequently require insulated tools of some kind to manipulate the shorting element, and in some cases the shorting element is a loose part which may be misplaced or lost.
Accordingly, it is an object of this invention to provide a new and improved current transformer shorting mechanism.
Another object of the invention is to provide a novel and improved current transformer shorting switch mechanism which is safe and easy to operate and does not require tools.
A further object of the invention is to provide an improved instrument transformer terminal shorting mechanism which may be operated without exposing the terminals.
Still another object of the invention is to provide a compact instrument transformer shorting mechanism which may be easily secured in position and sealed to deter tampering.
A further object of the invention is to provide a new and improved instrument transformer shorting mechanism which provides positive indication of the position of the shorting mechanism and is arranged to minimize the possibility that the mechanism be inadvertently left in shorted condition.
In accordance with the invention there is provided in combination with a current transformer having secondary terminals brought out to a surface thereof, an electrically insulating actuator cap arranged to enclose the terminals and to operate the shorting switch mechanism. The
shorting switch mechanism is secured to the transformer case and is movable by the cap between a shorting position and an open circuit position. The cap is also arranged for positioning in a seated or locked position and a released position in which the switch can be operated by manipulation of the cap. This structure is a safe and easy to operate structure which does not require any tools for a technician to operate. It completely encloses the transformer terminals so that they are not accessible through accident or inadvertence. Further, the mechanism is tamper proof as the cap may be sealed in position by conventional means either with the terminals connected to external metering circuitry for example or locked in short circuited position with the indication of the switch position clearly evident. Thus there is provided a novel and improved instrument transformer shorting mechanism.
In the preferred embodiment of the invention the instrument transformer secondary winding is in the form of a toroid which has two secondary terminals brought out through a rectangular top surface of the transformer casing. A rotatable shorting switch mechanismis positioned between the two terminals and has two opposed legs which cooperate in wiping engagement with flat conductive surfaces of the terminals. The switch mechanism is rotatable between a shorting position and an open circuit position. Detent means are provided in the top surface of the casing to aid in positioning the shorting switch member in the shorting position or in the open circuit position. A resilient coupling cooperates with the switch mechanism and engages a boss on an actuator cap that is formed in rectangular configuration similar to the configuration of the top surface of the transformer. This boss may be moved axially relative to the shorting switch mechanism between a first position which the cap is directly seated on the top surface and a raised position. Also provided on the top surface are a series of tabs which cooperate with the skirt wall of the cap to prevent its rotation when it is seated, thus positively positioning the cap and shorting switch mechanism. When the cap is moved to the raised position the boss is still in engagement with the shorting switch mechanism but is clear of the tabs on the transformer surface so that it is free to be rotated. The cap skirt wall has two out out portions through which wires connected to the terminals can pass. The cap and boss are arranged so that these out out portions are aligned with the tabs when the shorting switch mechanism is in the shorting position so that the cap cannot be seated on the top surface properly if there are external connections to the terminals. This provides a positive indication of the position of the shorting switch cap controlmember. In addition, there is provided securing means in the cap which acts to pull the cap down into seating relation with the top surface of the transformer in which position a sea-ling wire may be employed to seal the cap and switch mechanism in the desired position (positively enclosed either in circuit or out of circuit) so that unauthorized accessibility to the terminals and to the shorting switch mechanism is prevented. Thus the invention provides a simple, safe, attractive and easy to operate shorting switch mechanism.
Other objects, features and advantages of the invention will be seen as the following description of a preferred embodiment of the invention progresses, in conjunction with the drawings, in which:
FIG. 1 is a perspective view of a current transformer and shorting switch mechanism constructed in accordance with principles of the invention;
FIG. 2 is a top view of the current transformer shorting switch mechanism in open circuit position with the operating cap removed;
FIG. 3 is a sectional view along the line 3--3 of FIG. 1 with the cap in place in seated relation on the top surface of the current transformer housing;
FIG. 4 is an exploded view of components of the rotatable shorting switch structure;
FIG. 5 is a perspective view of the cap in inverted position with a portion thereof broken away; and
FIG. 6 is a sectional view of a portion of the cap.
With reference to FIG. 1 there is shown a current transformer having a casing 10* of conventional electrical insulation material such as molded epoxy resin mounted on a base 12 for securing to a suitable support. Within the case 10 is a secondary winding wound in toroidal shape so that an aperture 14 is provided in the case through which a primary conductor may pass. Terminals of the secondary winding are connected to studs 16, 18 which are brought out of the top surface 20 of the current transformer casing. The configuration of the top surface is square in the preferred embodiment as best indicated in FIG. 2. Molded in the top surface 20 on either side of each terminal stud and in slightly from the edge of the surface are two aligned tabs 22. Also molded into the top surface at each corner are receptacles 24 to receive studs for mounting a conduit box adjacent the terminals if desired.
7 Each terminal 16, 18 is in the form of a stud and has a flat washer-like member 26 seated on the transformer top surface which includes a flat surface 28 that extends inwardly towards the other terminal stud. This member is secured on the stud by means of a first nut 30. Immediately above this nut are two washers 32, 34 which are secured in place by a second nut 36. Conventionally a conductor is attached to each terminal stud between the washers and then the upper nut 36 is tightened down on the washers to secure the electrical conductor in positive electrical relation to the terminal.
Positioned centrally between the terminals 16, 18 is a shorting switch mechanism which includes a stud 40 secured to the casing in suitable means as by molding the lower portion 42 (FIG. 4) directly into the epoxy material. An intermediate portion 44 of the stud is formed as a seating and bearing element and the upper portion 46 is threaded. Mounted on the intermediate portion 44 is an electrically insulating washer 48 which has a lower flange 50 and an upstanding collar portion 52. Positioned immediately above and seated on the flange 50 of the washer 48 with the hollow portion protruding through a central aperture 54 is a oouplingmember 56 which has two upstanding side walls 58, 60. Each side wall has a detent portion 62 in the form of a V. A bridging member 64 of suitable conductive material, phosphor bronze for example, has a central aperture 66 which also is spaced from stud 40 by the collar portion 52 of the insulating washer 48 when its intermediate portion with straight side walls 68 is fitted inside the side walls 56, 58 so that positive alignment is maintained between the coupling member 56 and the bridging member 64. The bridging member has opposed legs 70, 72 which extend outwardly and slightly downwardly from the plane of the intermediate portion to provide resilient'wiping surfaces 74 which may be disposed in engagement with the terminal elements 28 in a shorting position. The edges of the wiping surface portions are in the form of turned up flanges 76 which enable the legs to easily ride up over the arcuate guide ridges 80 that are molded in the top of the transformer casing. A second electrically insulating washer 86 fits over the collar portion 52 of the washer 48 and a nut 88 engages the threaded portion 46 of the stud to secure the several components of the switching mechanism together on the stud 40.
Positioned over the terminals and the shorting switch structure is a switch actuator in the form of a cap 90 of suitable material, which in this embodiment is of a square configuration corresponding to the configuration of the top surface 20 of the transformer casing. This cap has a depending skirt 92 which extends around the entire periphery of the cap and has a lower edge surface 94 that is seated on surface 20 outside of tabs 22. Also in one wall of the skirt near the seating surface are two out :out aperture portions 96 which in one position of the cap are aligned with the two of the tabs 22. Centrally located within the cap is a boss 98 which has two parallel side walls 100 which are adapted to receive the side walls 58 of the coupling member 56. Each wall 100 has a groove 102 that receives a detent 62 when the cap is in a raised position. A central aperture 104 is provided within the boss and secured in this aperture 104 is a securing member 106 which has a knurled knob 108 and a hollow shank 110, the lower portion of which forms a guide for stud 40 and the intermediate portion of which has threads to engage the threaded portion 46 of stud 40. This securing member 106 is secured in the cap by means of a resilient locking disc 114. A washer 116 is provided underneath the knurled knob. Immediately below the knob 108 there is a section which has a plurality of radially extending through passageways 118 which may be aligned with apertures 120 in the cylindrical wall 122 on which the washer 116 seats. A sealing wire may be passed through the apertures 120' and one of the passageways 118 to positively lock the securing member 106 relative to the cap 90.
When the cap is in seated position the tabs 22 are immediately inside the skirt wall 92 so that rotation of the cap is prevented. In order to operate the shorting switch mechanism the threaded securing 106 must be freed to permit the cap to be raised on the switch coupling member side walls 58, 60 until detent portion 62 engages the grooves 102 in the boss. In this position the lower edge 94 of the skirt clears the upper surface of the tabs and the cap may be rotated. The arcuate ridges molded into the upper surface of the transformer housing provide a guide to aid in insuring rotation of the switch mechanism. In addition, the skirt wall is again lined up with the periphery of the top surface of the transformer when 90 rotation has been accomplished, thus providing a positive indication of switch position.
In FIGS. 1-3 the transformer shorting switch is shown in the open circuit position with the leg portions 70, 72 out of contact with the terminal surfaces 28.. With rotation of the bridge member through 90 the two opposed legs 70, 72 contact the surfaces 28 and provide a direct short thereacross to remove any potential difference that may exist between the two terminals. The cap then can be removed by snapping the spring detents 62 out of the grooves 102 in a simple manner and the wiring on the terminals adjusted orchecked as desired. After inspection and/or adjustment, the cap can be placed back on the shorting switch mechanism only in the same position, due to the cooperating configuration of the coupling member 56 and boss 98. The cap then is screwed down by means of the threaded securing 106. However, if the switch element is left in the shorted position the apertures 96 in the skirt are aligned with the tabs 22 (as the cap is rotated 90 from the position shown in FIG. 1) and if there are any wires connected to the terminals the cap cannot be seated on the transformer top surface. This provides positive indication of the position of the shorting switch. Further, if the transformer is out of service and no connections are to be made the cap may be left in the shorted switch position so that the tabs are aligned with the cut outs and the terminals are totally enclosed and are not accessible to tampering or other unauthorized access.
Thus it will be seen that the invention provides a compact shorting switch mechanism, reliable and simple in operation which provides positive control over accessibility to the terminals of the instrument transformer. While a preferred embodiment of the invention has been shown and described, various modifications thereof will be obvious to those skilled in the art and therefore it is not intended that the invention be limited to the disclosed embodiment or to details thereof and departures may be made therefrom within the spirit and scope of the invention as defined in the claims.
1. An instrument current transformer having a secondary winding in the form of a toroid to provide an axial opening adapted to receive a conductor which extends through the opening and functions as a primary conductor,
an outer casing of molded electrical insulation sur rounding said secondary winding,
a support base secured to said .outer casing,
the top of said casing being substantially flat and having two secondary winding terminals extending upwardly therefrom,
each terminal including means for fastening a conductor thereto and a conductive wiping surface disposed substantially in the plane of said top surface,
a shorting switch structure positioned between said secondary terminals,
said shorting switch structure including an upstanding stud secured in said outer casing,
an electrically conductive bridging element having opposed legs mounted for rotation on said stud,
said bridging element being rotatable between a first position where said legs are in Wiping engagement with said teminal wiping surfaces and a second position where said legs do not short said terminals,
means comprising spaced ridge portions disposed along the circular path of movement of said bridging element legs, the spaces between said ridge portions receiving said bridging element legs for positive posit-ioning in said first and second positions,
two aligned upstanding tabs positioned on said casing top surface outside of each terminal,
means to insulate said bridging element from said upstanding stud comprising a flanged electrically insulating washer and a second electrically insulating washer,
a resilient coupling element having two upstanding spaced parallel side walls secured to said bridging element for rotation therewith,
thread means in the upper end of said stud,
a rotatable cap having a centrally located boss adapted to be disposed between said coupling element side Walls for cooperative engagement therewith,
threaded securing means positioned in said boss for engagement with said stud thread means to secure said cap to said stud,
said cap having a depending skirt wall extending entirely therearound adapted to seat on said top surf-ace outside of said terminals,
said skirt wall having two spaced cut out portions in the seating surface of one portion of said skirt wall,
said cut out portions providing paths for electrical conductors connected to said terminals to extend externally of said cap when said cap is seated on said casing top surface and said bridging element is in said second position, and
said cut out portions being aligned with said tabs when said bridging element is in said first position so that conductors connected to said terminals prevent said cap from being seated on said casing top surface,
said tabs preventing rotation of said cap and said shorting switch structure when said cap skirt wall is seated on said top surface,
and said threaded cap securing structure permitting said cap to be raised without disengaging the cap from the shorting switch structure so that said cap may be rotated to move said shorting switch structure between said first and second positions,
and means cooperating with said threaded securing structure to receive sealing wire for locking said cap on said casing top surface to prevent unauthorized accessibility to said terminals and tampering with said shorting switch structure.
2. An instrument current transformer having a secondary Winding in the form of a toroid to provide an axial opening adapted to receive a conductor which extends through the opening and functions as a primary conductor,
an outer casing of molded electrical insulation surrounding said secondary winding,
a support base secured to said outer casing,
a surface of said casing being substantially fiat and having two secondary winding terminals extending upwardly therefrom,
each terminal including means for fastening a conductor thereto and a conductive switch surface,
a shorting switch structure positioned between said secondary terminals,
said shorting switch structure including means defining a switch pivot axis secured in said outer casing,
an electrically conductive bridging member mounted for rotation on said pivot axis defining means,
said bridging member being rotatable between a first position in which said bridging member electrically contacts said terminal switch surf-aces to provide a short circuit position therebetween and a second position to provide an open circuit between said terminal switch surfaces,
means for positively positioning said bridging member in said first and said second positions,
a resilient coupling element secured to said bridging member for rotation therewith,
a rotatable cap having a means for receiving said coupling element and a depending skirt wall extending entirely therearound adapted to seat on said surface of said casing outside of said terminals,
said skirt wall having two spaced out out portions for providing paths for electrical conductor-s connected to said terminals to extend externally of said cap when said cap is seated on said casing surface and said bridging member is in said second position,
two upstanding tabs fixed in position on said casing surface and aligned with said out out port-ions of said cap when said bridging member is in said first position to prevent said cap from being seated on said casing top surface when conductors are connected to said terminals,
said tabs preventing rotation of said cap and said shorting switch structure when said cap skirt wall is seated on said casing surface,
a cap securing structure having a first position for securing said cap in seated position on said casing surface,
a second position permitting said cap to be raised to allow said skirt wall to clear said tabs without disengaging the cap from said coupling element so that said cap may be rotated to move said shorting switch structure between said first and second positions,
and means cooperating with said securing structure for locking said cap securing structure in said first position to prevent unauthorized access to said terminals and tampering with said shorting switch structure.
References Cited by the Examiner UNITED STATES PATENTS 1,667,617 4/28 Zelt 200-168 X 1,786,746 12/30 Gibbs 200-168 X 2,589,084 3/52 Hoffman 200--155 2,672,532 3/54 Robinson 20051.08 X 3,098,133 7/63 J. Van Den Driest ZOO-51.07
JOHN F. BURNS, Primary Examiner,