US3082389A - Current transformer - Google Patents

Description

March 1963 J. L. SETTLES ETAL 3,082,389

CURRENT TRANSFORMER Filed Jan. 25, 1960 INVENTORS James L. Settles 8 Edmond E. Conn BY; 'ATTORNEY 94 {M}. Mi-

United States Patent 3,082,389 CURRENT TRANSFORMER James L. Settles, Sharon, Pa., and Edmond E. Conner,

Brookfield, Ghio, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa, a corporation of Pennsylvania Filed Jan. 25, 1969, Ser. No. 4,288 4 Claims. (Cl. 336-174) This invention relates to electrical induction apparatus and, more particularly, to current transformers.

In conventional current transformers of the types which are known as the through-type and the bar-type, the

effective primary win ing comprises a current-carrying electrical conductor, which may take the form of a bartype electrical conductor which is provided as part of the current transformer assembly, and a secondary winding which is toroidal in configuration and which is disposed in inductive relationship with said primary winding. Sufficent electrical insulation must be provided between the effective primary winding and the secondary winding of a current transformer of the type described, the amount and the type of electrical insulation depending upon the voltage of the electrical circuit with which the current transformer is to be employed. It is, therefore, desirable to provide and improved current transformer of the type described which more readily lends itself to convenient assembly for application at wherever circuit voltage is involved in a predetermined operating range of operating voltages.

It is an object of this invention to provide a new and improved current transformer.

Another object of this invention is to provide a new and improved current transformer which more readily lends itself to assembly for application at a predetermined voltage within a predetermined range of voltages.

A further object of this invention is to provide a new and improved current transformer in which the major insulation is formed from resilient, elastomeric material.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompaning drawing in which:

FIGURE l'is a top plan view of a current transformer embodying the teachings of the invention;

FIG. 2 is a side elevational view of the current transformer shown in FIG. 1; and

FIG. 3 is an end elevational view, partly in section, of the current transformer shown in FIG. 1.

Referring now to the drawing and FIGS. 2 and 3 in particular, this invention is illustrated by reference to a current transformer shown generally at 10. As illustrated in this embodiment, the current transformer comprises winding 72 from a resilient, elastomeric, electrically insulating, thermosettable composition or material 82, such as a polyester resin of the type disclosed in US. Patent 2,871 ,420 by H. F. Minter et al. which issued January 27, 1959, and which is assigned to the same assignee as the present application, and in the copending applications Serial No. 647,748, filed March 22, 1957, and Serial No. 745,847, filed July 1, 1958, by H. F. Minter and also assigned to the same assignee as the present'application. The casing 30 includes an axial opening or aperture/therethrough, as indicated at 46, which is adapted to receive the associated insulating bushing 20, as will be explained hereinafter.

In order to support the core 74 and the toroidal secondary winding 72 during the forming or molding of the casing 30, and for other purposes whichwill be described hereinafter, a generally ring-shaped bracket member 116 the magnetic core 74 which may be of the ring or v toroidal type, the secondary winding 72 which is also toroidal in shape and which is inductively disposed on the magnetic core 74, the insulating casing 30 which is formed or molded around said core and secondary winding, and the insulating bushing 20 which passes through an opening in said casing and through which an associated primary winding (not shown), such as a current carrying conductor, passes. The current transformer 10 is illustrated as being of the type known in the art as the through-type.

After the torodial winding 72 is assembled ,on the associated magnetic core 74 as best shown in FIG. 3, the insulating casing or housing 30 which is generally cylindrical in shape is preferably formed by a suitable method, such as molding, about the core 74 and the secondary is provided which extends nearly around the outer periphery of the toroidal winding 72. and which extends axially along the longitudinal dimension of said core and secondary winding. To assist the bracket member 116 in supporting the core 74- and the secondary winding 72, the supporting members or feet 112 are disposed at each side of the casing 30 and welded or otherwise secured to the underside of the bracket member 116, as best shown in FIG. 3. The casing 30 is also provided with a plurality of smaller openings or apertures 53 which extend axially through said casing to receive the bolt means 52 for reasons which will be discused hereinafter. Each of the openings 53 may be provided with a suitable liner or tube member 114 which is preferably formed from a suitable corrosion-resistant material, such as brass, and which may be welded or otherwise secured to the bracket member 116 prior to the molding or forming of the casing 30. Each of the supporting members or feet 112 may be provided with suitable means, such as the projection weld nuts 118, which are adapted to receive suitable fastening means such as bolts (not shown) for securing the associated mounting bracket or base member 42, which may be of any conventional type, to the bottom of the casing 30, as best shown in FIGS. 2 and 3. The casing 30 may also include a terminal portion formed integrally therewith or a separate terminalcover 64 into which the terminals of the secondary winding 72 are brought and which is secured or fastened to the casing 30 by suitable means, such as the stud or bolt means 62.

In order to make up the necessary electrical insulation required to apply the current transformer 10 at a particular voltage, the insulating bushing 20 is provided to add to or supplement the electrical insulation of the casing 30. The bushing 20, which is generally cylindrical in shape, is illustratedjas being of the hollow cylindrical or tubular type having an axial opening or aperture therethrough, as indicated at 75. The bushing 20 is preferably formed by a suitable method, such as molding, from a resilient, elastomeric, electrically insulating composition of material having anti-tracking properties, such as butyl rubber with an aluminum trihydrate filler.

in particular, the bushing 21) comprises a center or rent transformer may be applied, said end portions each including a plurality of ridge portions or petticoats 43 which extend around the outer periphery of said bushing and which, in this instance, are uniformly spaced apart along the axis of the bushing 20. The ridges 43 of the bushing 29 are spaced apart by a distance equal to the spaces between said ridges, as indicated at 45 in FIG. 1. The outer diameter or peripheral dimension of the intermediate portion 20C of the bushing 20 is arranged to be less than the diameter or peripheral dimension of the opening or aperture 46 in the casing 30 so that the bushing 20 may readily pass through said opening when said bush ing is assembled with the casing 30. It is to be noted that the casing 30 may be readily assembled with a variety of bushings similar to the bushing 20 and having an outer diameter or peripheral dimension less than the diameter or peripheral dimension of the opening 46 in the casing 30 and having any suitable axial dimension required to provide the insulation supplemental to that of the casing 30 for application of the current transformer at a particular voltage. The bushing is preferably molded or formed about a suitable'supporting member, such as the 'hollow cylindrical or tubular member 98, which is prefe ably formed from a non-magnetic material, such as brass, having the necessary mechanical strength to support the end portions 20A and 20B of the bushing 2t) when said bushing is assembled with the casing 30.

As mentioned previously, the bushing 20 is adapted to receive the effective primary winding of the current transformer 10, which may be any conventional type of current-carrying conductor of a size suitable to pass through the tubular member 98 of the bushing 20. It is to be understood, however, that the current transformer 10 may be provided with a bushing similar to the bushing 20 having a generally cylindrical shape in which the resilient, elastomeric, electrically insulating material is molded or formed about a suitable current carrying conductor such as that of the bar-type to form a current transformer similar to the current transformer 10, but of the bar-type rather than of the through-type as illustrated. The current-carrying conductor in the latter construction would normally be adapted for coupling or connection to the current-carrying conductors of an associated electrical circuit.

In order to hold the bushing 20 in assembled relationship with the casing 30 of the current transformer 10, the current transformer 10 also includes the clamping means 22 and 24 which are disposed at the opposite ends of the casing 30 adjacent to the opening 46 in said casing and which are of the split ring type. The clamping means 24 includes the two generally C-shaped clamping members 24A and 248 which are arranged to substantially surround the outer periphery of the bushing 20 adjacent to the opening 46 of the casing 30 and which are secured to the casing 30 by the bolt means 52. Similarly, the clamping means 22 at the opposite end of the casing 30 includes the two generally C- shaped clamping members 22A and 22B which are arranged to substantially surround the outer periphery of the bushing 20 adjacent to the opening 46 of said casing and which are similarly secured to the casing 30 by the bolt means 52 which extend through the openings or apertures 53 in said casing, as best shown in FIGS. 1 and 2. The clamping means 22 and 24 are arranged or adapted to apply axial clamping forces to the intermediate portion 20C of the bushing 20 in opposite directions to hold said bushing in assembled relationship with the casing 30 as just mentioned. In order to prevent rotation of the bushing 20 with respect to the casing 30 after said bushing is assembled with said casing, the intermediate portion 200 of the bushing 20' is provided with one or more projecting portions or lugs 96 at each end thereof which are engageable by the ends of the associated clamping members 22A and 22B and 24A and 2413, respectively, at the opposite ends of the casing 30, as best shown in FIG. 3, if the bushing 20 should tend to rotate in place after assembly with the casing 30, It is to be noted that the inner diameter or peripheral dimension of the closed loop defined or formed by the clamping means 22 and 24, respectively, at the opposite ends of the casing 36 is conveniently arranged to be greater than the outer diameter or peripheral dimension of the bushing 20, as indicated in the spaces 45, but less than the outer diameter or peripheral dimension of the bushing 20 as taken at the top of the ridges 43.

It is important to note that the insulating casing 30 provides an insulation level which permits the application of the current transformer 10 at a first predetermined voltage even without the additional insulation provided by the insulating bushing 20. The insulating bushing 20 when assembled with the casing 30 in the manner previously described, then provides additional insulation which cooperates with the insulation of the casing 30 to permit the application of the current transformer 10 at voltages higher than the first predetermined voltage just mentioned and which varies with the axial dimension of the insulating bushing 29. The manufacture or assembly of the current transformer 10 may therefore be conveniently accomplished in two steps. In the first step, the secondary winding 72 is assembled on the associated magnetic core 74 and then an insulating casing 30 is formed or molded about said core and winding as previously described. The second main step in the assembly of the current transformer 10 is to select a suitable insulating bushing similar to the bushing 20 in order to provide the additional insulation required for application of the transformer 10 at a particular voltage in an overall range of voltages. The insulating bushing 20 of a suitable axial dimension is then assembled with the casing 30 in the manner just described. It is important to note that if the current transformer 10 is to be applied at a different voltage, only the insulating bushing similar to the bushing 20 need be changed by removing the clamping means 22 and 24 and then assembling the casing 30 with a new insulating bushing as required for application at a particular voltage.

Although the clamping means 22 and 24 have been described in detail, it is to be understood that other suitable means may be employed to hold or secure the bushing 20 and the casing 30 in proper assembled relationship.

The apparatus embodying the teachings of this invention has several advantages. For example, a current transformer as disclosed more readily lends itself to convenient assembly for application at different voltages in a predetermined range of voltages. In addition, a cur rent transformer as disclosed readily lends itself to application at a different voltage by the relatively simple operation of changing the insulating bushing which forms part of the overall assembled current transformer as described. Finally, a current transformer as disclosed permits a reduction in the number of subassemblies or components which must be available to provide a Wide variety of current transformer ratings.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter con tained in the foregoing description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A current transformer comprising a closed loop magnetic core, a secondary winding inductively disposed on said core, a casing having an aperture therethrough molded around said core and winding from a resilient, elastomeric, electrically insulating, thermosetting material, a cylindrical bushing having an intermediate portion disposed to pass through said aperture and first and second end portions extending longitudinally in each direction outwardly from said aperture, said bushing being molded from a resilient, elastomeric electrically insulating material, and clamping means secured to said casing at each end thereof for applying longitudinal clamping forces to said bushing to hold said casing and said bushing in assembled relationship, said clamping means comprising split clamping rings disposed to substantially surround said bushing at each end of said casing adjacent to said opening and to bear longitudinally against the intermediate portion of said bushing.

2. A through-type current transformer comprising a toroidal magnetic core having a secondary winding disposed thereon and an axial opening therethrough, a casing molded around said core and Winding from a resilient, elastomeric, electrically insulating, thermosettable resin, a hollow cylindrical bushing having an intermediate portion disposed substantially inside said opening and end portions extending outwardly in each direction from said opening, said bushing being formed from a resilient, elastomeric, electrically insulating material, and a pair of generally C-shaped clamping members secured to said casing adjacent to each end of said opening to substantially surround said bushing, said clamping members being arranged to apply axialclarnping forces to the intermediate portion of said bushing to maintain said casing and bushing in assembled relationship.

3. A through-type current transformer comprising a toroidal magnetic core having a secondary Winding disposed thereon and an axial opening therethrough, a casing molded around said core'and Winding from a resilient, elastomeric, electrically insulating, thermosettable resin, a hollow cylindrical bushing having an intermediate portion disposed substantially inside said opening and end portions extending in each direction outwardly from said opening, said bushing being formed from a resilient, elastomeric, electrically insulating material, and a pair of generally C-shaped clamping members secured to said casing adjacent to each end of said opening to substantially surround said bushing, said clamping members being arranged to apply axial clamping forces to the intermediate portion of said bushing to maintain said casing and bushing in assembled relationship, said intermediate portion including at least one axial projection at each end of said casing engageable by said clamping members to prevent rotation of said bushing with respect to said casing.

4. A transformer comprising a toroidal magnetic core having a Winding disposed thereon and an axial opening therethrough, a casing molded around said core and winding from an elastomeric, electrically insulating, thermosetting material, a cylindrical bushing having an intermediate portion disposed substantially inside said opening and end portions extending outwardly from said opening in each axial direction and each including a plurality of alternate ridge portions and spaces on the outer periphery thereof, said bushing being formed from an electrically insulating, elastorneric material, and a pair of generally C-shaped clamping members secured to each end of said casing to substantially surround said bushing, the inner peripheral dimension of the opening defined by each pair of said clamping members being greater than the outer peripheral dimension of said bushing in said spaces but less than the outer peripheral dimension .of said bushing at said ridge portions, said clamping References Cited in the tile of this patent UNITED STATES PATENTS 2,929,037 Breth et al. Mar. 15, 1960

Claims (1)

1. A CURRENT TRANSFORMER COMPRISING A CLOSED LOOP MAGNETIC CORE, A SECONDARY WINDING INDUCTIVELY DISPOSED ON SAID CORE, A CASING HAVING AN APERTURE THERETHROUGH MOLDED AROUND SAID CORE AND WINDING FROM A RESILIENT, ELASTOMERIC, ELECTRICALLY INSULATING, THERMOSETTING MATERIAL, A CYLINDRICAL BUSHING HAVING AN INTERMEDIATE PORTION DISPOSED TO PASS THROUGH SAID APERTURE AND FIRST AND SECOND END PORTIONS EXTENDING LONGITUDINALLY IN EACH DIRECTION OUTWARDLY FROM SAID APERTURE, SAID BUSHING BEING MOLDED FROM A RESILIENT, ELASTOMERIC ELECTRICALLY INSULATING MATERIAL, AND CLAMPING MEANS SECURED TO SAID CASING AT EACH END THEREOF FOR APPLYING LONGITUDINAL CLAMPING FORCES TO SAID BUSHING TO HOLD SAID CASING AND SAID BUSHING IN ASSEMBLED RELATIONSHIP, SAID CLAMPING MEANS COMPRISING SPLIT CLAMPING RINGS DISPOSED TO SUBSTANTIALLY SURROUND SAID BUSHING AT EACH END OF SAID CASING ADJACENT TO SAID OPENING AND TO BEAR LONGITUDINALLY AGAINST THE INTERMEDIATE PORTION OF SAID BUSHING.

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