US2400994A

US2400994A - Transformer core

Info

Publication number: US2400994A
Application number: US580862A
Authority: US
Inventors: Clifford C Horstman; John H Bramble
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1945-03-03
Filing date: 1945-03-03
Publication date: 1946-05-28
Anticipated expiration: 1963-05-28

Description

Patented May 28, 1946 TRANSFORMER CORE Clifford C; Horstman and John H. Bramble,

' Sharpsville, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 3, 1945, Serial No. 580,862

6 Claims.

Our invention relates to magnetic core structures for electrical apparatus such as transformers, and, particularly, to core structures having three winding legs for accommodating the several phase windings of a three-phase electrical apparatus.

Our invention relates, particularly, to core structures for electrical transformers formed of layers of magnetic sheet steel having preferred magnetic characteristics in the direction of the sheet in which the core parts are formed, the layers of steel sheets or laminations being bonded together into solid brick-like sections having butt joints at their adjoining faces.

It has been found that if a core is formed of layers of sheet steel having the most favorable magnetic characteristics in the direction in which the magnetic flux passes through the strip or sheet of steel, a core having high permeability and low watts loss will result.

The magnetic material comprising the core may be formed into magnetic circuit loops by winding a continuous strip of material flatwise to give the desired dimensions, the loop being cut to provide butt joints at suitable places to form separable core sections that fit over the copper circuit conductors comprising the windings of the transformer. These butt joints may be located in the winding leg portions of the core or adjacent the ends of the Winding leg portions.

It has been found desirable to Work the meeting faces between the separable core sections in order to provide smooth fiat surfaces at the butt joint between them and to provide a minimum air gap. It has also been found desirable to insulate the magnetic material between the separable sections of the core meeting at the butt joints. Material suitable for this purpose may be one of the combination of long-chain molecules of the alvar or vinylite type or other oil and acid-resisting resins, such as described in U. S. Patent 2,318,095, issued May 4, 1943, to H. V. Putman for Core structures, and assigned-to the same assignee as this application. These materials are somewhat thermoplastic and have the property of tenaciously adhering to the metal surfaces. It is necessary to bring'the core faces together under pressure to reduce the thermoplastic material tothe desired predetermined thinness.

It has been found that transformer cores formed of wound loops of magnetic material cut to provide butt joints as above described are sensitive to changes in pressure, and if the pressure is not applied perpendicularly to the face of.

(Cl. F15- 356) the joint, the watts loss of the core increases somewhat with increase in pressure. For example, if the core sections are clamped together in such manner that the surfaces of the butt joints are not parallel, localized strains will be set up in the core structure which will increase the loss. It has been found that the best results are obtained by providing pressure at the joint perpendicularly to the worked faces of the laminations such as is supplied by metal bands applied as herein disclosed. When the separable sections of such cores are held together by means of metal bands, the bands provide for drawing the worked faces toward each other to reduce the thickness of the thermoplastic material between them. These bands are elastic and are applied under sufficient tension and elongation to maintain the desired pressure after the worked faces are drawn together, and in spite of the slight contraction of the band that may be caused by any flowing of the insulating material in the butt joint due to its plastic nature.

The Putman patent referred to above shows loops of magnetic material employed for singlephase transformers in which there are only two core legs having butt joints to be held under pressure.

It is an object of this invention to provide a three-phase core structure of the above-indicated character having three parallel winding leg portions involving butt joints associated with each leg portion in which the core parts are held together by means of metal bands that are suiciently elastic and are sufficiently elongated as to provide a continuous force on the parts of the core in spite of shrinkage of the overal1 dimensions thereof.`

It is another object of the invention to provide means particularly adapted to secure a continuous pressure on the middle one of the three core legs of a three-phase core structure in which the three legs are in alignment in order to insure substantially the same pressure on the butt joints in each ofthe three leg portions of the core structure.

kOther objects and advantages of the invention will be apparent from the following description of preferred embodiments thereof, reference being had to the accompanying drawing, in which:

Figure 1 is a side elevational View of a single core loop in which a metal band is applied in accordance with prior art practice;

Fig. 2 is a side elevational view of a threephase core having three winding legs in which a metal band is applied following the manner illustrated in Fig. 1;

, Fig. 3 is a side elevational view of a three-phase core in which means is provided in accordance with one embodiment of the` invention for maintaining substantially constant pressure on the faces of thebutt joints associated with each of the three winding legs of the core structure;

Fig; 4 is a side elevational view of a portion of a core structure illustrating another embodiment of the invention;`

Fig. 5 is a top plan view of a core corresponding to Fig. 4 and in which portions thereof are broken away; l"

Fig. 6 isa side elevational view of a three-phase core structure organized in accordance with an other embodiment of the invention;

Fig. 'I is a ide elevational view of a portion of the core s ructure `illustrating another embodiment of the invention;

Fig. 'la is a. detail; and

Pig. 8 is a side elevational view of a core structure illustrating a further embodiment of the invention. l

Referring to Fig. 1, a single core loop magnetic structure I is illustrated consisting of a-plurality of layers ofiturns of a strip 2 of magnetic material wound` continuously to provide a plurality of )animations or sheets of steel outlining a substantially, rectangular window 3. After the loop has beenlwound tolprovide the necessary number of turns and d several turns bonded together as hereinafter pointe out, the core loop is cut along the line 4 to provde upper and lower loop sections ll and 3. each forming a U-shaped member with the laminations bent'i'latwise at the bends of the U, thecut ends presenting s. plurality of faces at the butt joint surfaces 4. Either during tine winding operation or thereafter, prior to cutting along the lines 4, the layers of magnetic material are bonded together by an insulating and bonding material adhering to the opposite sides of each of the several turns or laminations comprising the core and heat-treated so that the group of laminations are yieldably but rigidly at tached so that when cut along the line 4, solid U-shaped pieces result which maybe reassembled about preformed coil structures comprising the copper conductors of the transformer windings. The particular treatment may correspond to that described in Patent No. 2,293,951, filed by J. B. Seastone and C. C. Horstman, for Induction apparatus and method of core construction therefor, issued August 25, 1942, and assigned to the same assignee as this application. The core loop shown in Fig. 1 when reassembled about the copper conductors of the transformer winding is held with the faces of the two U-shaped core sections under pressure at the surfaces 4 by applying a steel band I about the coe loop, and attaching a clip 3 locking the ends of the steel band l together while the band is retained under a predetermined tension so as to maintain the band sumciently elongated as to maintain the desired pressure on the butt joint surfaces 4.

Fig. 2 illustrates a core structure comprising three core loops II, I2, and I3 formed in the manner above described with respect to Fig. 1, with the two smaller loops I I and I2 surrounded by the larger loop I3. The two smallerloops II and vI2 are formed of an equal number of turns of the strip of magnetic material and then surrounded by the turns of the loop I3, also having a number of turns equal to those in the loops II and I2. The three core loops in a unit are annealed and impregnated in a manner described for Fig. 1 and are then cut at three places indicated by the numeral I4 along the same plane to provide upper and lower core sections. The several surfaces formed by cutting along the lines I4 are worked in the same manner as described for the structure shown in Fig. 1 to provide cooperating accurately smooth surfaces engaging correspondingly accurately smooth surfaces to form the butt joints in the three core legs. When the core structure is cut along the line I4, the loop II is separated into upper and lower sections I5 and IB, respectively, the loop I2 into upper and lower sections I1 and I3, respectively, and the loop I3 into upper and lower sections I9 and 20, respectively. When the core structure is reassembled about the transformer windings, a steel band 2l similar to the band 1 in Fig. 1 passes about the outer one I3 of the three magnetic loop structures and is held together by a clip 22, the band being applied under tension as described with respect to Fig. l. When reassembled, the structure provides three

winding legs

23, 24, and 25 for accommodating thewindings of the three phases, respectively, of the apparatus, the winding leg 23 including the left vertical portions of the loops I3 and II, the winding leg 24 including the two adjacent vertical portions of the loops I I and I2, and the winding leg 25 including the two right portions of the loops I2 and I3. The winding leg portions of the core structure are connected by yoke portions comprising the arched-shaped end members of the three loops, the three upper arches being shown at 26, 21, and 28, and the three lower archedshaped yoke members being shown at 29, 30, and 3I.

In the structure shown in Fig. 2, the force applied by the steel band 2| is so applied that the vertical components that are available for maintaining pressure on the surfaces on the opposite sides of the butt joints I4 do not maintain sufficient pressure on the middle leg 24.

We have provided means for increasing the pressure on the butt joint of the middle leg above that existing in the structure shown in Fig. 2. In the embodiment of the invention shown in Fig. 3, blocks 35 and 36,` which may be of wood or other suitable material, are positioned between the central part of the upper and lower yoke portions of the core and the steel band 2I surrounding the core, so as to hold the band 2I arched above and below the upper and lower yoke portions of the core to provide a vertical component of force which is communicated through the blocks 35 and 36, respectively, and through the yoke portions of the core structure to the surfaces on thc opposite sides of the butt joint I4 in the middle winding leg 24. By providing blocks of the proper shape giving the necessary spacing of the band 2| from the yoke of the core, it is possible to apply an equal force to all three butt joints in the three core legs. The arrows on the outside of the band 1 in Fig. 1 and on the outside of the band 2i shown in Fig. 3, indicate the general direction of the force applied to the yoke portions of the core.

Fig. 4 illustrates a portion of a core structure similar to that shown in Fig. 2 in which the central winding leg 24 is formed by the adjacent parts of two magnetic loops II and I2 in the same manner as in Fig. 2, and the core structure is cut along the line I4. For the purpose of applying the desired force to the opposite surfaces of the butt joint I4 in the embodiment of the invention shown in Figs. 4 and 5, a wedgeshaped block 4I is provided having a trapezoidal cross-sectional area adapted to engage the outer

curved portions

42 and 43, respectively, of the winding loops II and I2. The block 4I may have a length corresponding substantially to the width of themagnetic sheet steel employed to form the core loop structures and is provided with a depression therein along the outer surface providing a seat to accommodate the steel band 44 which is similar in general character to the steel band 2I applied about the three core loops. It will be understood that a similar block 4I is provided at the lower end of the middle winding leg 24, and that the band 44 is positioned in the two blocks so that when drawn together under a predetermined force and attached by a clip 45, as shown in Fig. 5, a predetermined force will be applied from the steel band 44 through the blocks 4I to the adjacent parts of the core loops I I and I2 to maintain a predetermined desired pressure on the opposite faces of the butt joint I4.

Fig. 6 illustrates another embodiment of the invention generally similar to that shown in Figs. 4 and 5 in which the seats provided for receiving pressure from the steel band 44 are shown as the surfaces of strips of steel 5I and 52. The strip 5I is welded securely to the U-shaped portions I5 and I1 of the loops II and I2, respectively, and the strip 52 is welded to the U-shaped sections I6 and I3. The steel band 44 passes between the steel strip 5I, and the upper U-shaped section I9 ofthe core loop I3 and between the lower strip 52 and the U-shaped section 20.

Fig. 7 is a side elevational View of a portion of the core structure generally similar to Fig. 4, illustrating a method of applying the band 44 about the entire core structure. A trapezoidal steel pressure element 5I is shown welded to a strip of steel 52 to `apply pressure to the curved portions of the U-shaped sections I5 and II, respectively, of the core loops II and I2. In this embodiment of the invention, a block 53 is mounted above the U-shaped section I9 of the outer core loop for accommodating the band 44, and may be rounded at the ends, as shown in Fig. 7a, to more readily accommodate the band 44. It will be appreciated that the structure shown at the upper end of the winding leg 24 in Fig. 7 is duplicated at the lower end, and that the band 44 applies pressure to two blocks 53 at the upper and lower central portions of the outer core loop I3 which pressure is communicated through the outer loop to two pressure members 5I at the upper and lower ends of the two loops I I and I2, respectively, to directly apply pressure thereto on opposite sides of the butt joint I4.

In the embodiment of the invention shown in Fig. 8, pressure is applied to the central winding leg 24 in a manner generally similar to that illustrated in Fig. 3 by spacing the band 2| along the central part of the yoke portion of the core so as to apply a vertical component of force opposite the ends of the middle winding leg that does not exist where the band 2| is flat or straight as in Fig. 2. This is accomplished in the structure shown in Fig. 8 by providing a series of steel strips 6| between the successive turns of the sheet steel forming the outer loop I3 of the core structure. These sheets of steel 6I are of different lengths, the longer sheets being closer to the smaller core loops I I and I2, and the larger ones further away so as to space the steel band 2I a greater amount directly opposite the ends of the middle winding leg 24 to provide a greater vertical component of force from the steel band 2I to the core structure that is communicated to the opposite faces of the butt joint I4 of the middle leg 24.

It will be noted that in the embodiments of the invention illustrated in Figs. 3 and 8, the force applied to the opposite surfaces of the buttr joint I4 in the middle winding leg 24 is applied directly from the band 2| through the yoke portions of the outer loop of the magnetic circuit I3. In the embodiments of the invention illustrated in Figs. 4, 5, 6, and 7, an additional steel band 44 is employed. In Fig. '7, this band also applies pressure to the outer surfaces of the yoke portions 28 and 29 of the outer core loop I3 which is applied therefrom to the inner core loops I I and I2 and to the butt joint in the middle winding leg 24. In the embodiment of the invention shown in Figs. 4 and 5 and also in Fig. 7, the force is applied directly from the steel band 44 to the opposite ends of the inner core loop members II and I2 directly adjacent the portions of these two loops forming the middle winding leg'24.

rIt will be apparent to those skilled in the art that modifications of the subject matter described and illustrated within the spirit of our invention may be made without departing from the invention, and we do not wish to be otherwise limited than by the scope of the appended claims.

We claim as our invention:

1. In a three-phase core structure for electrical apparatus, in combination, core parts comprising three leg portions positioned in a row in parallel relation and connecting yoke portions connecting the leg portions, the core structure comprising separable core parts formed of laminations of magnetic sheet material united by bonding material applied to the laminations, the separable core parts having meeting faces worked thereon for providing butt joints in the several leg portions of the core, the yoke structure at each end of the leg portions of the core comprising three arch-shaped portions adjacent the opposite ends of the leg portions, two of the three arch-shaped portions being of lesser span than the third, the two arch-shaped portions of lesser span connecting the middle leg portion with the two outer leg portions, respectively, and the archshaped portion of greater span connecting the two outer leg portions of the core, a resilient band of metal under tension about the core structure for maintaining the core parts in position and for maintaining a substantially constant pressure on the butt joints, and additional means for applying pressure on the butt joint in the middle one of the three winding leg core portions.

2. In a three-phase core structure for electrical apparatus having three winding legs arranged in a row with their axes lying in the same plane and parallel to each other, the core structure comprising a plurality of core loops each formed of magnetic sheet material wound ilatwise, the spaces between the successive layers of magnetic sheet material being filled with a substantially non-flowable, non-volatile, molded, solid material for solidly supporting the several layers of material against relative movement, each loop being cut to form closely fitting butt joints on opposite sides thereof and to provide separable core sections, the core structure including three core loops, two of the core loops 'having side portions adjacent each other together forming the central one of the three winding legs and having side portions remote from each other forming parts of the two outer winding legs, respectively, the third core loop extending about and enclosing the other two and including parts of the two outer winding legs, a resilient band of metal under tension about the outer loop of the core structure for maintaining a substantially constant pressure on the butt joints, and additional means for applying pressure on the butt joint in the middle one of the three winding legs.

3. In a three-phase core structure for electrical apparatus having three winding legs arranged in a row with their axes lying in the same plane and parallel to each other, the core structure comprising a plurality of core loops each formed of magnetic sheet material wound flatwise with intervening bonding layers of an adherent insulating bond between adjacent laminations solidly holding the laminations together, each loop being cut to form closely fitting butt joints on opposite sides thereof and to provide separable core sections, the core structure including three separate core loops including, respectively, the first and second winding leg, the second and third winding leg, and the first and third winding',` legthe third-named loop extending about and enclosing the other two loops, a resilient band of .metal under tension about the outer loop of the core structure for maintaining a substantiallyl constant pressure on the butt joints, and additional means for applying pressure on the butt joint in the middle one of the three `winding legs.

4. In a. three-phase core structure for electrical apparatus. in combination, core parts comprising three leg portions positioned in a row in parallel relation and connecting yoke portion-s connecting the leg portions, the core structure comprising separable core parts formed or laminationg of magnetic sheet material united by bonding material applied to the laminations, the separable core parts having meeting faces worked thereon for providing butt joints in the several leg portions of the core, the yoke structure at each end of the leg portions of the core comprising three arch-shaped portions adjacent the opposite ends of the leg portions, two of the three arch-shaped portions being of lesser span than the third, the two arch-shaped portions of lesser span connecting the middle leg portion with the two outer leg portions, respectively, and the arch-shaped portion of greater span connecting the two outer leg portions of the core, a resilient band of metal under tension about the core structure for maintaining the core parts in position and for maintaining 'a substantially constant pressure on the butt joints, and additional means for applying pressure on the butt joint in the middle one of the three winding leg core por tions, said means comprising a seat at each end of the middle winding leg portions adjacent the two arch-shaped portions of lesser span and within the arch-shaped portion of greater span and a resilient metal band positioned in said seats at the opposite ends of themiddle winding leg under tension about the middle winding leg for maintaining constant pressure on the butt joint in thatleg.

5, In a three-phase core structure for electrical apparatus having three winding legs arranged in a row with their axes lying in the same plane and parallel to each other, the core structure comprising a plurality of core loops each formed of magnetic sheet material wound flatwise, the spaces between the successive layers of magnetic sheet material being lled with a substantially non-flowable, non-volatile, molded. solid material for solidly supporting the several layers oi' material against relative movement, each loop being cut to form closely fitting butt joints on opposite sides thereof and to provide separable core sections, the core structure including three core loops, two of the core loops having side portions adjacent eacli other together forming the central one of the three winding legs and having side portions remote from each other forming parts of the two outer winding legs, respectively, the third core loop extending about and enclosing the other two and including parts of the two outer winding legs, a resilient band of metal under tension about the outer loop of the core structure for maintaining a substantially con stant pressure on the butt joints, and additional means for applying pressure on the butt joint in the middle one of the three winding legs, said additional means comprising a seat at each end of the middle winding leg and a resilient metal band under tension positioned in said seats and extending about the leg along the opposite sides thereof.

6. In a three-phase core structure for electrical apparatus having three winding legs arranged in a row with their axes lying in the same plane and parallel to each other, the core structure comprising a plurality oi core loops each formed of magnetic sheet material wound flatwise with intervening bonding layers of an adherent insulating bond between adjacent laminations solidly holding the laminations together, each loop being'cut to form closely fitting butt joints on opposite sides thereof and to provide separable core sections, the core structure including three separate core loops including,' respectively, thx: rst and second winding leg, the second and third winding leg, and the first and third winding les. the third-named loop extending about and enclosing the other two loops, a resilient band of metal under tension about the outer loop of the core structure for maintaining a substantially constant pressure on the butt joint-s, and addi tional means for applying pressure on the butt. joint in the middle one of the three winding legs. said additional means comprising a seat at cach end of the middle winding leg and a resilient metal band under tension positioned in said seats and extending about the leg along the opposite sides thereof.

CLIFFORD C. HORSTMAN. JOHN H. BRAMBLE.