US3171093A - Magnetizable laminated cores for transformers and reactors - Google Patents

Description

E. RQLF Feb. 23, 1965 MAGNETIZABLE LAMINATED CORES FOR TRANSFORMERS AND REACTORS Original Filed April 11, 1952 United States Patent This application is a division of my copending application Serial No. 281,831, filed April 11, 1952, now Patent My invention relates to laminated magnetizable core structures for transformers, reactors and other, electrically inductive devices. 7

In the design of magnetizable high-quality cores for transformers and reactors increasing attention is being given to the use of ferromagnetic materials of a preferred magnetic orientation. For any given field strength and hence any given magnetizing current, such cores admit a larger magnetic induction than is otherwise obtainable and thus permit corresponding savings in weight. The superior magnetic properties of sheet material having a preferred magnetic orientation can best be realized in wound strip cores of annular shape. Therefore such cores are now being given preference for certain exacting applications, such as in the commutating reactors of contact converters. However, the mounting of the windings on wound cores is more time-consuming and expensive, and the utilization of the available winding space obtainable thereby is more limited than with rectangular cores. It is therefore often desirable to stack the cores from punched or cut sheets rather than winding them from strip material.

On the other hand, in the conventional design of stacked F lamination cores, the necessary junction gaps greatly impair the magnetization characteristic and thus tend to diminish the advantages of a preferred magnetic orientation. Also to be considered is the fact that with silicon iron, in contrast to nickel iron, punched sheets cannot be used to advantage if thefmagnetic flux lines extend, though only partially, transversely to the rolling direction. This is sobecause silicon iron has only one preferred magnetic orientation, and this orientation is coincident with the rolling direction. In this respect, the material differs from nickel iron which. has two preferred orientations in the plane of the sheet, one being coincident with the rolling direction and the other perependicular thereto. In the transverse direction the magnetic properties of silicon iron laminations are so markedly inferior that cores of silicon iron must be so designed that the rolling direction of the sheet material is everywhere identical with the direction of the magnetic lines of flux.

In a known laminated core of rectangular frame shape, the individual laminations consists of rectangular strips and the junction gaps'at two parallel frame sides lie perpendicular to the strip direction and are alternately displaced relative to each other. This permits placing all strips with their rolling direction in line with the flux direction. However, at each junction gap nearly the entire flux from the lamination layer interrupted by that gap passes temporarily through the adjacent layers, which are continuous beside the gap. Consequently, the magnetic induction in the adjacent layers is about twice as high locally beside the gap as in the other portions. Hence, at these localities the iron is already saturated when the induction in the other portions is only about half as large as the saturation induction B In other 3,171,093 Patented Feb. 23, 1965 words, when in the major portions of the core the induction value B /Z is exceeded, the saturated iron next to the gaps starts acting like an air gap. Hence, above the value B 2 a move or less pronounced break or shearing occurs in the magnetization characteristic depending upon the length of the junction gaps. For that reason the iron can be utilized with only about one half of the saturation induction if the magnetizingcurrent is to remain at the same small magnitude.

It is known, for improving the magnetic conditions, to place the butt gaps not into the geometrical extensions of the frame-opening sides but in a diagonal direction at an angle of about 45. The alternate gap displacement is effected by displacing each alternate strip of the longitudinal frame portions (limbs) parallel to itself in its longitudinal direction and to reverse the pertaining transverse frame portions (yokes). The required strip shapes result in an enlarged cross section of the yoke portion. This design reduces the induction beside the gaps does not sufficiently eliminate the impairment of the magnetic characteristic which remainssheared at inductions above about 0.718,. The gap displacement in such cores does not affect their angular relation. That is, all junction gaps at any one corner of the frame structure have the same direction, the gaps in adjacent layers being parallel to one another.

It is an object of my invention to devise a magnetizable core structure which, though composed of individual laminations, affords a greatly improved magnetization characteristic by reducing the detrimental effect of the butt gaps down to its virtual elimination.

To this end, according to my invention, the sheet laminations of a frame-shaped core structure are so shaped and assembled that at each corner of the frame structure the gap edges to be traversed by the flux have respectively different angular directions in the manner explained in the following with reference to the drawing in which:

FIG. 1 shows a front view of a portion of a rectangular core structure according to the invention, and FIG. 2 shows schematically a cross section of the structure along the plane indicated in FIG. 1 at IIII.

In the core shown in FIGS. 1 and 2 each individual corner portion of the frame-shaped structure is composed of differently designed lamination layers. In the layers of one of said designs, a limb strip 8 with a diagonal edge 8a abuts at the corner against a diagonal edge in of a yoke strip 7. In the layers of the other design, in the same corner, a limb strip extends rectangularly up to the full height of the yoke strip; that layer of the corner is therefore formed only by the limb strip.

In the core shown in FIGS. 1 and 2, the butt gaps of part of the punched lamination strips extend diagonally. The strips of the yoke 7 have twice the width of the strips of the limb 8. Each alternate layer of the core is a complete frame the opposite sides of which are comprised by diagonally abutting strips 7' and 8'. The intermediate layers have only pairs of limb strips 8" of rectangular shape that extend over the whole width of the yoke portion and are separated from each other by a space 9. Consequently, the limb portions 8', 8" of the core are completely filled with iron, while the middle parts of the yoke portions are filled only 50%. The induction in the middle parts of the yokes therefore has the same magnitude as the induction in the limb portions. However, at the junction gaps where the total flux from two strips passes through only one, here continuous strip, the magnitude of induction is 2/ /5B or approximately 0.9B, assuming that the density of the flux lines is uniform along the entire length of the gap. Actually the induction is somewhat higher because the lines of force do not penetrate to the outermost point of the corner. However,

the induction does not appreciably exceed the value B. Hence, the invention satisfies the aim to keep the induction beside the junction gaps at a value not higher than that obtaining in the other core parts while requiring an only slight increase in weight as compared with the known core design.

For a laminated core according to FIGS. 1 and 2, without yoke enlargement, three different shapes of punchings are needed, namely one for the yoke strips, another one for the bevelled limb strips, and the third for the rectangular limb strips.

Minor departures from the illustrated shapes are permissible without essentially impairing the advantageous effects. Particularly, a relatively smaller width of the yoke laminations may be sufficient.

Core structures according to the invention are mainly applicable for sheet material with a single preferred mag netic orientation, such as sheets of silicon iron, whose use necessitates composing the magnet core of individual strips so that the flux direction does not extend locally transverse to the flux direction. However, cores according to the invention are also advantageous for sheet material with two preferred magnetic orientations, for instance sheets of nickel iron, especially when the core size is so large that the individual layers of laminations, for reasons of manufacture, must be composed of individual strips.

Cores according to the invention are preferably used for transformers and reactors, particularly in the end stage of a magnetic amplifier or in a direct-current premagnetized saturable reactor such as used for controlling the operation of barrier-layer rectifiers. Especially desirable is the use of such cores in the switching or commutating reactors for pulse-controlled switches and contact rectifiers for which so far wound strip cores have almost exclusively been used.

I claim:

1. A jointed magnetizable core designed to minimize increase in magnetic induction at the joints, comprising a cornered frame forming a closed magnetic flux path, the frame being formed of a plurality of layers of assembled laminations formed from sheet-metal strip material having a favorable magnetic direction lengthwise of the strip, a number of said layers each comprising two trapezoidal limb strips and two trapezoidal yoke strips, the said limb strips of said number of layers each having a straight diagonally extending end edge and the yoke strips each having two opposite straight diagonally extending end edges, the diagonal edges of the yoke strip adjoining the diagonal edges of respective limb strips at the corners of the frame, the yoke strip being at least twice the width of the limb strips, the diagonal end edges of the yoke strip providing, in conjunction with the diagonal edges of the limb strips, straight diagonal butt joints which extend from each innermost point of the corner to each outermost point of the corner, there being disposed, intermediate said number of layers, second limb sheet-metal strip layers which are rectangular in outline and are codirectional with the first-recited limb strips and which are provided, at the frame corners, with edges which are at right angles to the yoke strips and thus are angularly disposed with respect to the diagonal end edges of said first-recited limb strips, to provide overlap at the joints, each of the second limb sheet-metal strips extending at their ends to the two outer upper and lower edges of the core, the corner joints of each layer being overlapped by magnetic material of an adjacent layer.

2. A jointed magnetizable core for transformers, reactors and other electrical inductance devices designed to avoid or minimize increase in magnetic induction at the joints, comprising limbs formed of limb laminations and yokes formed of yoke laminations, being sheets having a preferred magnetic orientation in the flux direction and forming together a stacked rectangular frame structure having a plurality of lamination layers all of the same sheet thickness, each corner of said structure comprising alternately different portions of said layers, the corner portion of each second one of the said layers at-said corner being composed of the respective portion of one of said limb laminations and of the respective portion of one of said yoke laminations, both portions having at said corner respective straight-line edges extending diagonally in a straight line from each innermost point of said corner to each outermost point of said corner and being coextensive with and opposing each other, and the corresponding corner portion of each intermediate layer comprising at said corner another limb lamination extending at right angle to said yoke laminations and extending to the corresponding end edge of the core, the corner joint of each second layer being overlapped by magnetic material of an adjacent layer, said yoke laminations having a width at least about 1.5 times the width of said limb laminations.

3. The core defined in claim 2, the yoke strips being about twice as Wide as the limb strips.

4. A jointed magnetizable core for transformers, reactors and other electrical inductance devices, designed to avoid or minimize increase in magnetic induction at the joints, comprising limbs formed of limb laminations and yokes formed of yoke laminations, being sheets having a preferred magnetic orientation in the flux direction and forming together a stacked rectangular frame structure having alternately different lamination layers all of the same sheet thickness, each second one of said layers at each corner of said structure being composed of one said limb laminations and one of said yoke laminations, both being trapezoidal in outline and having at each corner respective straight-line edges extending diagonally in a straight line from each inner corner to each outer corner and being coextensive with and opposing each other, and each intermediate layer comprising at each corner another limb lamination which is rectangular in outline and extends at right angles to said yoke laminations and extends to the corresponding end edge of the core, the corner joints of each layer being overlapped by magnetic material of an adjacent layer, said yoke laminations having a width at least about 1.5 times the width of said limb laminations.

5. The core defined in claim 4, the yoke strips being at least about twice as wide as the limb strips.

References Cited by the Examiner UNITED STATES PATENTS 1,805,534 5/31 Troy 336-218 2,393,038 1/46 Forbes 3362l7 2,579,578 12/51 Horstman et al 336-217 X 2,896,181 7/59 Zwelling 336-217 FOREIGN PATENTS 699,549 8/52 Great Britain.

LARAMIE E. ASKlN, Primary Examiner.

JOHN F, BURNS, Examiner.

Claims (1)

1. A JOINTED MAGNETIZABLE CORE DESIGNED TO MINIMIZE INCREASE IN MAGNETIC INDUCTION AT THE JOINTS, COMPRISING A CORNERED FRAME FORMING A CLOSED MAGNETIC FLUX PATH, THE FRAME BEING FORMED OF A PLURALITY OF LAYERS OF ASSEMBLED LAMINATIONS FORMED FROM SHEET-METAL STRIP MATERIAL HAVING A FAVORABLE MAGNETIC DIRECTION LENGTHWISE OF THE STRIP, A NUMBER OF SAID LAYERS EACH COMPRISING TWO TRAPEZOIDAL LIMB STRIPS AND TWO TRAPEZOIDAL YOKE STRIPS, THE SAID LIMB STRIPS OF SAID NUMBER OF LAYERS EACH HAVING A STRAIGHT DIAGONALLY EXTENDING END EDGE AND THE YOKE STRIPS EACH HAVING TWO OPPOSITE STRAIGHT DIAGONALLY EXTENDING END EDGES, THE DIAGONAL EDGES OF THE YOKE STRIP ADJOINING THE DIAGONAL EDGES OF RESPECTIVE LIMB STRIPS AT THE CORNERS OF THE FRAME, THE YOKE STRIP BEING AT LEAST TWICE THE WIDTH OF THE LIMB STRIPS, THE DIAGONAL END EDGES OF THE YOKE STRIP PROVIDING, IN CONJUNCTION WITH THE DIAGONAL EDGES OF THE LIMB STRIPS, THE DIAGONAL END EDGES JOINTS WHICH EXTEND FROM EACH INNERMOST POINT OF THE CORNER TO EACH OUTERMOST POINT OF THE CORNER, THERE BEING DISPOSED, INTERMEDIATE SAID NUMBER OF LAYERS, SECOND LIMB SHEET-METAL STRIP LAYERS WHICH ARE RECTANGULAR IN OUTLINE AND ARE CODIRECTIONAL WITH THE FIRST-RECITED LIMB STRIPS AND WHICH ARE PROVIDED, AT THE FRAME CORNERS, WITH EDGES WHICH ARE AT RIGHT ANGLES TO THE YOKE STRIPS AND THUS ARE ANGULARLY DISPOSED WITH RESPECT TO THE DIAGONAL END EDGES OF SAID FIRST-RECITED LIMB STRIPS, TO PROVIDE OVERLAP AT THE JOINTS, EACH OF THE SECOND LIMB SHEET-METAL STRIPS EXTENDING AT THEIR ENDS TO THE TWO OUTER UPPER AND LOWER EDGES OF THE CORE, THE CORNER JOINTS OF EACH LAYER BEING OVERLAPPED BY MAGNETIC MATERIAL OF AN ADJACENT LAYER.

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