US2579308A

US2579308A - Transformer

Info

Publication number: US2579308A
Application number: US58297A
Authority: US
Inventors: Marshall H Dole
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1948-11-04
Filing date: 1948-11-04
Publication date: 1951-12-18
Anticipated expiration: 1968-12-18

Description

Dec. 18, 1951 DOLE 2,579,308

TRANSFORMER Filed Nov. 4. 1948 Inv'efitorw' Mar-"s hall H. Dole,

His Attorney.

Patented Dec. 18, 1951 TRANSFORMER Marshall H. Dole, Hudson, Ind., asslgnor to General Electric Company, a corporation of New York Application November 4, 1948, Serial No. 58,297

3 Claims. 1

This invention relates to an electric induction apparatus and more particularly to the construction of a magnetic core for an electric transformer device.

By utilizing a new and novel magnetic core construction which employs contiguous wedgeshaped segments of magnetic material bound together so as to form a cylindrical core numerous advantages result. In order to better explain what these advantages are and why they are the natural consequence of the invention disclosed in this application it will be advantageous. to explain, in concise terms, the nature of the invention. A cylindrical central winding leg of a magnetic core for stationary induction apparatus is constructed from a plurality of wedge-shaped segments which are maintained in intimate contact to one another. Mounted on this winding leg are the coils associated with the induction device. A magnetic yoke which surrounds the coils and serves to magnetically link the coils together is also constructed of wedge-shaped segments and is contiguous, in part with the central winding leg. Thus the yoke may be visualized as a hollow cylinder which accommodates within it the central winding leg and its associated windings.

The advantages this construction offers are manifold. Noise due to the leakage of flux into nearby magnetic materials is reduced since flux' leakage is reduced to a minimum by having the coils completely surrounded by the yoke member. A substantial saving results in the winding of coils which are mounted on a cylindrical core. This is due to the fact that the coils may be circular thus eliminating sharp corners. Since there are no sharp corners there is very little danger of fracturing insulation which may be incorporated on the surface of the wire. Thus the necessity of insulating each layer of wire by the use of an insulating material, such as paper, in addition to the insulation on the wire itself, is eliminated. Also since the winding leg is round and the coils are round less copper need be used in the circular coils than in the conventional type of coils where there are spaces between the coil and the winding leg due to the necessity of winding the copper around sharp corners. Since the yoke member surrounds the central winding leg and no coils areexposed, additional encasing means is not necessary and all that need be provided are caps which enclose each end of the core and provide means for mounting the induction apparatus. Insulating compound, which is very often used to fill the space between the enclosed electric device and its encasin means is eliminated. Another advantage of the construction disclosed by this invention results from the fact that air gaps separating the winding leg from the yoke member have much greater width, since they cover 360 degrees, than in a similar device using conventional fiat laminations. Also an important consequence of this invention is that noise due to the vibration of the wedges making up the core, this vibration resulting from the magnetic stresses set up between these wedges as a consequenceof the cyclic variation of current in the coils, is reduced. This is accomplished by the core clamping operation which forces all the wedges of the core more tightly together reducing audible vibrations.

It is an object of this invention to provide a core construction for electric induction apparatus which substantially eliminates the presence of noise in such devices.

Another object of this invention is to provide a core construction for electric induction apparatus which allows a minimum of leakage flux.

Still another object of this invention is to provide an electric induction apparatus which needs no additional encasing means, and the use of insulating compound is eliminated.

A further object of this invention is to allow the use of round coils allowing a saving in the total amount of copper to be used.-

Another object of this invention is to provide a core for electric induction apparatus which is constructed of wedge-shaped segments of magnetic material.

This invention has particular application to the construction of a fluorescent lamp ballast, though it is in no way limited thereto, and in the following description taken in connection with the accompanying drawing it will be described as applied to the construction of such a device.

In the drawing, the single figure shown is a perspective view of a two-lamp fluorescent ballast constructed in accordance with this invention.

Referring now to the drawing there is shown therein a two-lamp fluorescent ballast I having a central winding leg 2 which is constructed of wedge-shaped segments of magnetic material. The wedge-shaped segments are forced into intimate contact with one another so as to form the hollow cylindrical central winding leg 2. Mounted on the winding leg 2, in the illustrated case, is a primary coil 3 and the two secondary windings 4 and 5. To complete the magnetic path so as to allow for the coupling of the primary and secondary coils 3, 4 and 5 a magnetic yoke 8 is constructed of wedge-shaped segments I, mounted in contiguity, so as to completely surround the transtormer coils 3, 4 and 5.

Since the fluorescent ballast l is used in a circuit with an electric discharge device, which possesses negative resistance characteristics, it must provide means for limiting the flow of circuit current once conduction through the fluorescent lamp has been initiated. Circuit reactance is provided by having a high internal leakage reactance which is achieved by employing the shunts 8 and 9 located between the primary coil 3 and the secondary coil 4 and the primary coil 3 and the secondary coil 5, respectively. The shunts 8 and 9 are formed as integral parts of the yoke segments 1. In order to prevent the leakage fiux paths from having too low a reluctance it is usually necessary to provide them with a high reluctance section, such as an air gap, and it has also been found that desirable results are obtained when a portion of the core is provided with a bridged gap. In the figure, the air gap i separates the shunt leg 8 from the central winding leg 2, and the air gap II separates the,

shunt leg 9 from the central winding leg 2. A bridged gap 12 is provided at one end of the core as shown in the illustration. It can be seen that in cross-section the ballast construction provided by this invention appears to be' very similar to that shown in the patent application Serial No. 776,082, filed September 25, 1947 in the name of Wesley W. Brooks, and assigned to the same assignee as the present invention.

Since the transformer coils 3, 4, and 5 are entirely surrounded by the magnetic yoke 6 means must be provided for allowing the electrical leads from the coils to be connected to their co-operating circuit. ,This is accomplished by employing one magnetic wedge 13 in the yoke 6 which is hollowed out so as to provide room to accommodate the lead wires l4. Encasing means completely enclosing the core is not necessary and all that need be provided are end caps I5 and I6 which clamp the wedges 6 together as a unit. The end caps l5 and I6 may have mounting feet I! associated with them so as to provide means for securing the fluorescent lamp ballast i to its associated equipment.

The transformer may be assembled as follows: First, a suflicient number of the wedge-shaped laminations or segments for forming the winding leg 2 are placed against each other until the cylindrical winding leg 2 is formed. Then the windings 3, 4 and 5 are pressed on to the Winding leg assembly so as to hold it together and the coils or windings are properly spaced so as to receive the magnetic shunt members 8 and 9. Then leads are attached to the coils or else previously attached leads for the coils are aligned by turning the coils the proper amount and then these leads are encased in the hollow wedge-shaped segment [3. Additional wedge-shaped segments 1 are then successively placed against each other and against the segment l3 until the cylindrical yoke member is built up with the magnetic shunt portions 8 between the coils 3 and 4 and the magnetic shunt portions 9 between the coils 3 and 5. Then the clamping caps 5 and 6 are pressed on the ends of the completed assembly so as to hold the unit to ether.

While there has been shown and described a particular embodiment of this invention it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

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

1. A magnetic core for stationary induction apparatus comprising, a substantially cylindrical central winding leg member, said winding leg member constructed of a plurality of wedgeshaped winding leg sections, said wedge-shaped winding leg sections maintained in contiguous relationship to one another, a yoke member similarly constructed of a plurality of contiguous wedge-shaped yoke sections, each of said wedgeshaped yoke sections having a plurality of sidewise extending legs including end legs and at least one intermediate leg, said yoke members having a substantially hollow cylindrical shape, the opening therein having a minimum diameter approximately equal to the outer diameter of said central winding leg member, portions'of said end legs of said wedge-shaped yoke sections being contiguous with said winding leg member, said yoke member substantially surrounding said winding leg member, and clamping means surrounding the ends of said yoke member for holding said sections in assembled relation.

2. A magnetic core for stationary induction apparatus comprising, a substantially cylindrical central winding leg member, said winding leg member constructed of a plurality of wedgeshaped winding leg sections, said wedge-shaped winding leg sections maintained in contiguous relationship to'one another, a yoke member similarly constructed of a plurality of contiguous wedge-shaped yoke sections, each of said wedgeshaped yoke sections having a plurality of sidewise extending legs including end legs and intermediate legs, said end legs being longer than said intermediate legs, said yoke member having a substantially hollow cylindrical shape, the opening therein having a minimum diameter approximately equal to the outer diameter of said central winding leg member, portions of said end legs of said wedge-shaped yoke sections being contiguous with said winding leg member, air gaps separating said intermediate legs of said wedge-shaped yoke sections from said winding leg member, one of said end legs forming a bridged-gap joining said winding leg member and said yoke member, said yoke member substantially surrounding said winding leg member, and cup-shaped clamping means surrounding the ends of said yoke member for holding said sections in assembled relation.

3. A two-lamp fluorescent ballast comprising, a substantially cylindrical central winding leg member, said winding 18g member constructed of a plurality of wedge-shaped winding leg sections, each of said wedge-shaped winding leg sections formed as a portion of a hollow cylinder, said wedge-shaped winding leg sections maintained in contiguous relationship to one another, said central winding leg member having a plurality of induction coils mounted thereon, a yoke member similarly constructed of a plurality of contiguous wedge-shaped yoke sections, each of said wed e-shaped yoke sections having a plurality of sidewise extending legs including end legs and intermediate legs, said end legs being longer than said intermediate legs, said yoke member having a substantially hollow cylminimum diameter approximately equal to the outer diameter of said central winding leg member, said end legs of said wedge-shaped yoke sections bein contiguous with said winding leg member, said induction coils occupying the spaces between said legs 01 said wedge-shaped yoke sections, air gaps separating said intermediate legs of said wedge-shaped yoke sections from said winding leg member, one of said end legs forming a bridged-gap joining said winding leg member and said yoke member, said yoke member substantially surroundin said winding leg member, at least one of said wedge-shaped yoke sections having ahollow portion, the conductive leads fastened to said induction coils being housed within said hollow portion of said last mentioned wedge-shaped yoke section, and cup-shaped clamps encompassing the ends of 6 said fluorescent lamp ballast so as to hold the The following references are of record in the tile 01 this patent:

UNITED STATES PATENTS 10 Number Name Date 342,553 Westinghouse May 25, 1886 432,050 Kammeyer July 15, 1890 1,804,852 Zaimboni May 12, 1931 2,053,176 Bouwers Sept. 1, 1936 2,150,382 Leischner Mar. 14, 1939 2,370,633 Coucher et al Mar. 6, 1945 2,433,898 Gilman Jan. 6, 1948 2,531,697 Meyerhans Nov. 28. 1950