US2246167A - Transformer - Google Patents

Description

June 17, 1941. FQR. DENTREMONT TRANSFORMER Filed March 16, 1940 2 Sheets-Sheet l 11 Illllllllllll Fig.2.

Inventor;

is ttorney Fran k I i n R DEntrernomt June 17, 1941.

F. R. D'ENTREMONT I TRANSFORMER Filed March 16, 1940 2 Sheets-Sheet 2 Irwverwtor:

D Entremont,

. JMAM, Attomey.

" along the line 2-2 of the Patented June 17, 1941 2,246,167 TRANSFORMER. Franklin E. DEntremont, Lynn, Mass, assignor to General New York Company, a corporation of Application March 16, 1940, Serial No. 324,396 4 Claims. (Cl. 175358) The present invention relates to transformers and more particularly to current transformers of the wound primary type.

Current transformers are generally connected permanently in series circuit with the power lines and accordingly will be subjected occasionally to heavy overloads, which may cause damage by mechanical stresses or by overheating the winding. Heavy current surges occurring on the power line may give rise to mechanical stresses not only through the bus connections but also within the transformer itself. Sustained heavy overloads may cause severe heating of the transformer windings to the point that the insulation thereof is damaged and with lesser overloads, even though the transformer may not appear to be damaged, its windings may have become short-circuited due to overheating thus producing an incorrect ratio of transformation. Fuse protection cannot be applied practicably to a current transformer because of its series connection in the line and accordingly, it must be designed so that it will carry all currents incident to the line.

It is, therefore, an object of this invention to provide a current transformer of the wound primary type having a new and improved primary and terminal structure whereby the tansformer is given great mechanical strength and heavy current carrying capacity.

For a consideration of what I believe to be novel and my invention, attention is directed to the following description and the claims appended thereto taken in connection with the accompanying drawings.

In the drawings Fig. 1 is a side view of a current transformer, partly in section, con structed in accordance with one form of the invention; Fig. 2 is a view, partly in section, taken transformer shown in Fig. 1 but showing the upper primary coil structure in full; Fig. 3 is a view in perspective of the component parts of the primary winding structure before assembly; Fig. 4 is a view of the completed primary assembly; and Fig. 5 is a view of the primary assembly with insulation wrapping applied.

Referring now to Figs. 1 and 2 of the drawings, the transformer includes a rectangular laminated magnetic core II). For obtaining greater accuracy in the electrical characteristics ofthe transformer, the primary and secondary windings are divided into two coils each, which are arranged upon opposite legs of the core structure. The two secondary winding coils i2 and i3 are relatively wide and are suitably wrapped with insulation such as varnished cambric, while the surrounding primary coils I4 and I5, respectively, are covered first with filler pieces l6 and I1 and then with wrapping l8 of suitable insulating material. An insulating spacer I9 is arranged between the adjacent inner turns of the primary coils, having been inserted in position before the wrapping l8 was applied. The two primary coils are connected in parallel between two terminal members 20 and 2| extending outwardly from the opposite sides of the transformer substantially along the axis thereof. The terminal members are preferably relatively wide so that they may be securely fastened to bus bars 22 and 23 in a good heat and current conducting relation by any suitable means such as bolts 24 and 25.

Referring now to Figs. 3 and 4, the structure of the primary winding coils will now be described in greater detail. The coils l4 and I5 are of similar configuration and are preformed of relatively wide copper strap wound flatwise in a single layer as regards the outer surface of the cooperating secondary coils. Each coil in this instance comprises two turns, that is, two portions 3|, 32, and 33, 34 adapted to extend through the window of the core structure and which portions are connected together by side and cross over portions 35 and 36, respectively. The coil ends, that is, the ends 31, 38, and 39, 40 are bent at right angles to the portions of each coil extending through the core window and lie parallel with and adjacent to the corresponding strap is preferably of maximum width, or, of such a width so that the overall width of the coils is substantially equal to the width of the secondary coils. A maximum heat radiating surface for the primary coils is thus provided.

The terminals 20 and 2| are each formed from relatively heavy flatstrips of copper having a width substantially equal to the overall width of the coils I4 and 55. One end of the terminals is first slotted as indicated at 4| and 42, respectively, the width of these slots being substantially equal to the spacing between the adjacent turns of the primary coils. The bifurcated end portions of each terminal are bent at right angles with respect to the main terminal portion providing oppositely extending lugs 43, 44, and 45, 46. The lugs 43, 44 are suitably secured, as by brazing, fiatwise to the ends 31 and 39 of the coils. l4 and I5, while lugs 45, 46 are similarly secured to the. other coil ends 38 and 40,

respectively, as shown more clearly in Fig. 4. The ends of the terminals may be provided with holes 41 and 48 for cooperatively receiving the fastening bolts 24 and 25.

After the primary windings have been assembled, the insulating spacer member I9 is inserted into the space between the adjacent turns 3|, 32, and 33, 34 of the two primary coils engaging tightly therewith. The filler pieces [6 and ll, of insulating material such as pressed paper, are then fitted over the cores and the assembly is wrapped with a suitable insulation, such as crepe paper, the wrapper assembly being shown in Fig. 5. The secondary coils are then nested concentrically into the primary coils after which the laminations of the core are stacked through coils and fastened together by bolts The transformer may then be thoroughly dried and dipped in an asphaltum insulating compound for filling any spaces which may exist within the assembly.

The primary coils will possess relatively ical strength so as to constructed in this manner great rigidity and mechaneii'ectively resist any deformation from their original shape due to any mechanical stresses which may be imposed thereupon through the bus bars or other connections to the terminals. The lugs 43, M, and 45, 46 extending in opposite directions from the ends of the terminals and being securely fastened to the ends of the winding coils will provide suflicient rigidity for the terminals as regards any laterally imposed stresses. Any force acting longitudinally of the terminals will be transmitted to the portions of the primary windings extending through the core windows, but because of the fact that the primary coils fit tightly around the secondary coils there will be no play which may be taken up by a relative separation of the two terminals.

The thermal limit of transformers having a primary coil construction as described is very high due to various design features. The greatest heating will normally take place within the core window due to the fact that no space exists therein for the circulation of air currents. By the construction shown, the heat will be readily conducted from the core window portions of the primary turns since the terminals are directly connected thereto immediately adjacent the window. The broad flat terminals fastened in a good heat conducting relationship to the bus bars will in turn carry the heat away from the transformer at a high rate. The cross over portions of the primary winding being near the surface of the assembly will dissipate heat by radiation to the ambient atmosphere.

The symmetrical arrangement of the coils on the core and the primary coils closely surrounding the secondary coils reduces the leakage re- I, actance of the transformer to a minimum and tends to improve materially the accuracy of the device.

Having described the invention in what I now consider to represent the best embodiment thereof, I desire to have it understood that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a transformer having a rectangular magnetic core structure, two secondary winding coils one being arranged around each of a pair of opposite core legs, two primary winding coils one surrounding each of said secondary coils, said primary coils each comprising a strap conductor wound fiatwise around the corresponding secondary coil in a single layer, the ends of said conductor extending through the core window andshort distances along opposite sides of said core, a pair of terminals each having at one end lugs substantially the width of said conductor extending at right angles on opposite sides thereof, said lugs being secured to said ends of said primary coil and an insulating member arranged in the window of said core and separating said two primary coils.

2. A transformer comprising a magnetic core structure, two secondary winding coils one surrounding each of a pair of opposite legs ofsaid core, two primary winding coils one surrounding each of said secondary coils, said primary coils each comprising a relatively wide strap conductor extending fiatwise around the corresponding secondary coil in a single layer to a Width substantially equal to the width of said secondary coils, the ends of said conductor extending through the core window and terminating along the opposite sides of said core, and a pair of terminals each having at one end a pair of lugs extending at right angles on opposite sides of said terminals, said lugs being rigidly secured flatwise to corresponding ends of each of said primary coils.

3. In a transformer having a magnetic core structure and a secondary winding having portions arranged around opposite portions of said core structure, a primary winding comprising a strap conductor wound flatwise in a single layer around said secondary winding providing a plurality of turns through the window of said core structure, the ends of said turns extending along opposite sidesof said core, and a pair of terminals having portions extending across the window of said core on opposite sides thereof, said portions being secured with respect to spaced portions of said primary winding, said ends of said turns being connected to corresponding terminal portions.

4. In a current transformer having a rectangular magnetic core and a pair of secondary windings arranged around opposite legs of said core, a pair of symmetrical and parallel connected primary windings arranged around said secondary windings, said primary windings each comprising a plurality of turns of a relatively wide conductor wound flatwise in a single layer, the corresponding ends of the two windings extending in opposite directions on opposite sides of the window of said core, relatively wide terminal members having a pair of lugs at one end extending substantially across the core window, the lugs of each terminal member being rigidly connected to corresponding winding ends.

FRANKLIN R. D'ENTREMONT.

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