US2930997A - Magnetic core construction - Google Patents

Description

March 29, 1960 F, J, FISHER ETAL- 2,930,997

MAGNETIC CORE CONSTRUCTION Filed Aug. 11. 1954 Unitted States Patent MAGNETIC CORE CONSTRUCTION Frank llames Fisher, Sutton Coldiield, and Kenneth John Park, Birmingham, England, assignors to General Electric Company, New York, N.Y.

This invention relates to magnetic core constructions for inductive devices and more particularly to a core for a combined reactor and transformer for operating arc discharge devices such as fluorescent lamps.

It is well known that an arc discharge device, such as a fluorescent lamp, has a negative current characteristic, i.e., its resistance decreases as the current flow through the device increases, once the device has discharged. In order to prevent the current flow through the arc discharge device from reaching dangerously high values which may destroy the device, ballasting devices have been provided connected in series with the lamp in order to limit the current ilow to safe values. Although such ballasting devices may be either a resistance, an inductance, or a capacitor, inductive devices have most commonly been used.

It is also well known that arc `discharge devices, such as fluorescent lamps, start more readily and at lower applied voltages when the cathodes are preheated. In prior fluorescent lamp designs, the cathodes would not vstand prolonged `heating and therefore various arrangements were provided for initially heating the cathodes in order to facilitate discharge or starting and subsequently reducingthe cathode heating after discharge had oc curred. A comparatively recent development in fluorescent lamp iield is the so called rapid start lamp which includes cathodes which can be continuously heated. It is thus merely necessary to provide a small transformer, similar to a radioY filament transformer to reduce or step down the available supply voltage to the proper value for energizing the lamp cathodes. In addition, when the available supply voltage is suciently high to start the lamp, thus eliminating the necessity for a step-up transformer or autotransformer arrangement, a reactor or choke is conventionally connected in series with the lamp to provide the ballasting action. It is thus seen that at the present to provide for the operation of rapid start lamps where no voltage step-up is necessary to effect starting, both a small transformer for continuously heating the lamp cathodes and a separate reactor or choke have been necessary. It is desirable therefore in the design of such arrangement-s that the cathode heating transformer and choke or reactor be arranged on a single magnetic structure thereby effecting economies in material and space. Such a combined transformer and reactor must of course efliciently provide the necessary voltage step-down for the lamp cathodes and also provide sufficient reactance for the ballasting functions. It is also, of course, essential that such a unit Ibe simple, and inexpensive to manufacture.

It is therefore an object of this invention to provide a magnetic core for a reactor and transformer which ncorporates the desirable features set forth above.

Further objects and advantages of this invention will become apparent by reference to the following description and the accompanying drawing, and the features of novelty which characterize this invention will be pointed 2,930,997 Patented Mar. 29, 1960r out with particularly in the claims annexed to and forming a part of this specification.

According to the present invention, a single laminated magnetic core is provided for carrying both the choke andy transformer windings. This core is divided at one or more places in one or more planes perpendicular to the general plane of the core and after the windings have been placed on the core, the parts are suitably held together, as by welding, to complete the unit.

In the drawing:

Fig. 1 is a schematic view of one form of the improved core of this invention and also showing the connection to a rapid start fluorescent lamp; 1

Fig. 2 schematically shows another form of this invention;

Fig. 3 schematically shows yet another modification of this invention;

Fig. 4 schematically shows still another form ofthis invention; and

Fig. 5 schematically shows a still further modification of this invention.

Referring now to Fig, 1, one construction of a com- Y bined choke and transformer incorporating a core in accordance with the present invention will be described. Here, the core of the composite choke and cathode heating transformer consists of two stacks of laminations of magnetic material 1 and 2, each stack comprising lamination of E-form however the stack 2 has shunt parts 3 and 4 projecting from the side legs 13 and 14 respectively toward its center leg 15. Shunt parts 3 and 4 are very close or may even touch the center leg 15 however they are nevertheless separated from center leg 15 by slits 16 for a purpose to be hereinafter described. The ends of the side legs 10 and 11 of lamination stack 1 are respectively abutted against the ends of side legs 13 and 14 of lamination stack 2 leaving an air gap 5 between the end of center leg 15 of lamination stack 2 and the end of center leg 12 of lamination stack 1. A choke or reactor winding 8 is mounted on the center legs 12 and 15 in the window defined by shunts 3 and 4 and end leg 17 of lamination stack 1. Transformer windings 9 are arranged on center leg 15 of lamination stack 2 in the window defined 4by shunt parts 3 and 4 and end leg 18. Transformer windings A9 may conventionally include a pri-mary winding 19 adapted to be energized from an external source of alternating current by lines 20 and step-down secondary windings 21 and 22 connected re' spectively to energize cathodes 23 and 24 of fluorescent lamp y25. It will be seen that the choke or reactor Winding 8 has one side connected to one of the lines 20 by means of line 26 and its other side connected to cathode 23 of lamp 25 by a line 27. It will also be seen that the other cathode 24 is connected to the other supply line 20 by means of a line 28. It is now readily seen that the reactor winding 8 and the lamp 25 are serially connected across Ilines 20 and in parallel with primary winding l19 of transformer 9.

In order to build up the composite unit shown in Fig. l, the transformer windings 9, preferably prewound on a spool, would first be placed on the lamination stack 2 by threading the individual laminations of the stack through the coil, deilecting the center leg 15 of each lamination for this purpose. When the desired number of laminations are thus in place, the choke winding 8, also preferably prewound on a spool, would be placed on center leg 12 of lamination stack 1 and the two stacks 1 and 2 are then butted together as shown and are preferably held in assembled relation by welds 6 and 7 made along the edges of the core. It will be readily seen that the split in the core which permits assembly of the transformer reactor windings thereon is in a plane perpendicut 3 lar to the general plane of the core and it will be further readily understood that in order to minimize the magnetic coupling between the transformer windings 9 and the reactor winding v8, the shunt parts 3 and 4 of lamination stack 2 should approach the center leg 15 as closely as possible.

Referring now to Fig. 2, like elementsbeing indicated by like reference numerals, it will be seen that the shunt parts may be formed of separate stacks or bunches of laminations 29 and 30 inserted between side legs 13 and 14 of lamination stack 2 and center leg 15 after transformer windings 9 are in place. It will be readily apparent that with the embodiment of Fig. 2, laminated shunt parts 29 and 39 may be arranged so that they closely abut side legs 13 and 14 and center leg 15 respectively.

. Referring now to Fig. 3, in which like parts are again indicated by like reference numerals, it will be seen that the shunt parts may be made integral with the center leg. Here, the E-shaped stack of laminations 1 has its side legs and 11 abutting side legs 31 and 32 of U-shaped stack of laminations 33. A separate center leg 34 is provided abutting the end leg 35 of U-shaped part 33 as at 36. Shunt parts 37 and 38 are formed on center leg portion 34 and extend outwardly toward side leg members 31 and 32 of U-shaped lamination stack 33, preferably abutting the same. Here, it will be readily apparent that the transformer windings 9 will be positioned on the center leg 34 and that the resultant assembly will then be pushed into U-shaped lamination stack 33, after which the balance of the assembly will take place in a manner identical to the assembly of the embodiment of Fig. l.

Referring now to Fig. 4 in which like elements again are indicated by like reference numerals, it will be seen that the shunt parts 39 and 40 may be formed of blocks of pressed magnetic powder, the blocks being forced between side legs 13 and 14 of lamination stack 2 and center leg respectively after transformer windings 9 have been positioned on the center leg 15 in the manner of the assembly of Fig. 2.

Referring now to Fig. 5, with like parts again being indicated by like reference numerals, lamination stack 41 has its center leg 42 shorter than its side legs 43 and 44. It will be seen that side legs 10 and 11 of lamination stack 1 again abut side legs 43 and `44 of lamination stack 41. Here again, a separate center part 45 is utilized having one end abutting center leg 42 of lamination stack 41 and its other end defining the air gap 5 with center leg 12 of lamination stack 1. Shunt parts 37 and 38 extend outwardly from part 45 toward and preferably abut side legs 43 and 44 of lamination stack 41.

It will now be readily apparent that this invention provides a simple and readily fabricated core construction for a combined transformer and reactor.

CTI

improvements will occur to those skilled in the art. We desire that it be understood therefore that this invention is not limited to the form shown and we intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

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

1. Ballast apparatus for uorescent lamps having cathodes adapted to be continuously heated comprising, a two part laminated magnetic core, each part having an Eshape, the outer legs of one E-shaped part abutting the outer legs of the other E-shaped part with the center legs of both parts confronting and spaced from one another to form an air gap located in the general plane of separation between said parts, a pair of shunt members extending between the center and outer legs of one of said parts remote from said plane of separation, a transformer portion of said apparatus having a primary winding and at least two cathode heating windings located on the center leg of said one part in the windows partially defined by said shunt members, and a reactor portion of said apparatus having a choke winding connected between one end of said primary winding and one end of one of said cathode heating windings, said choke winding being located on the center leg of said other part and extending over said air gap.

2. The ballast apparatus of claim 1 wherein the shunt members are formed integral with said one core part and are slit in a direction perpendicular to said plane of separation to permit the threading of said transformer windings into said windows by deflection of the laminations of said one part.

3. The ballast apparatus of claim 2 wherein said shunt members Vare independent laminated blocks each inserted While we have shown and described a particular em- 55 bodiment of this invention, further modifications and as a press lit between the center leg and a respective outer leg, the laminations of said blocks being in planes perpendicular to the laminations of said magnetic core. 4. The ballast apparatus of claim 3 wherein said shunt members are independent blocks of pressed magnetic powder each inserted as a press fit between the center leg and a respective outer leg of said one part.

References Cited in the le of this patent UNITED STATES PATENTS-v 1,777,256 Daley Sept. 30, 1930v 1,803,868 Porter May 5, 1931 2,170,446 Edwards Aug. 22,v 1939 2,493,683 Meyerhans Jan. 3, 1950 2,611,885 Bridges Sept. 23, 1952 2,630,478 Howlett Mar. 3, 1953 2,824,263 Strecker et al. Feb. 18, 1958 FOREIGN PATENTS 517,020 Belgium Feb. 14, 1953

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