US2318095A - Core structure - Google Patents

Description

H. V. PUTMAN CORE STRUCTURE May 4, 1943.

Filed Aug. 17, 1940 INVENTOR WlTN ESSES:

Patented May 4, 1943 CORE STRUCTURE Henry V. Putman, S-liaron, Pa., assigner to Westinghouse Electric &`Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August I7, 1940, Serial No. 353,024

The invention relates, generally, to core structures and, more particularly, to core structures having butt joints suitable for use in dielectrics.

In the operation of transformers and other lnductive apparatus utilizing magnetic cores immersed in dielectrics, considerable difiiculty has been experienced with joints having worked faces. This results from the oil or other dielectric becoming acid in the course of time with the result that the acid dielectric attacks the iron.

The object of the invention is to provide in cores to be used in dielectrics a butt joint having a worked face which is protected from the dielectric and acids that may be developed.

It is also an object of the invention to provide a core structure in which the eddy current losses are small.

Other objects of the invention will, in obvious and, in part, appear hereinafter.

'Ihe invention, accordingly, is disclosed in the accompanying drawing and comprises the feapart, be

tures of construction, combination of elements,

and arrangement of parts which will be exemplified in the structure hereinafter set forth and the scope of the application of which Awill be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference may be had to the following detailed description taken in connection with the accompanying drawing, in which:

Figure l is a view in perspective of a plurality of bonded core sections having worked faces assembled in accordance with the present invention; and

Fig. 2 is'a view in perspective showing how the worked vfaces may be drawn together to give a predetermined thickness of the oil and acid resisting material.

A butt joint in a magnetic core may cause such high eddy current losses that the application of the core is limited and it has no place in electrical apparatus which is required to be eflicient. The eddy currentswhich result from contacts in the butt joint can be reduced to the point where the eddy current losses are small and the core may be utilized without noticeably lowering the efliclency of the electrical apparatus.

ln the making of butt joints it has been found to be desirable to work the meeting faces of the core sections in order to get a smooth surface. In working the faces the usual practice is to grind the surfaces to the desired contour. In the grinding operation burrs ,are produced which in some instances may extend between the lamina- 7 Claims. (Cl. F75- 356) -tions of the core sections. These burrs are objectionable since they establish electrical connection between adjacent laminations.

'Ihe burrs may be removed by etching or any method known to the art. In order to etch the burrs away it may be necessary to impregnate the laminations constituting a core with some acidresisting material to prevent the acid from penetrating between the laminations. An etching method set forth in the copending application Serial No. 295,750 filed September 20, 1939, now Patent No. 2,293,951, August 25, 1942', in the name of Seastone et al. and assigned to the Westinghouse Electric & Manufacturing Company may be employed.

When the core section has been prepared in this manner, the surface oxide or silicate films which ordinarily protect the laminated magnetic material from acids and the like are completely removed from the core faces. Therefore, when such material is immersed in a dielectric which upon continued use may become acid, there is a possibility that the acid dielectric will attack the worked faces.

In the present invention, an acid and cilresisting thermoplastic resin i0 is applied to the worked faces of the core shown generally at H. Many different oil and acid-resisting thermoplastic resins are available. Good results have been obtained by using certain resins sold to the trade as Bakelite. Experience indicates that the worked faces may be properly protected by the use of one or more of phenol aldehyde, alkyd, vinyl, or other suitable resins of this type.

It is found to be good practice to paint the worked faces with the thermoplastic resin selected. In the preparation of the thermoplastic resin, it will be prepared of the proper consistency io facilitate painting and of a softness which will permit the reducing of it to-a predetermined thickness.

Any suitable method may be employed to bring the core faces together to reduce the thermoplastic material to the predetermined thickness suitable for the structure being built. In the perspective showing of Fig. 2 a signode strap or band I 2 is provided for drawing the worked faces toward one another to reduce the thickness of the thermoplastic material I0.

signode straps i2 may be applied to the assembled sections of the core structure Il to take the place of clamping members. tween the faces of the butt joint resulting from the use of the signode strap increases when the transformer is placed in an oven for the purpose The pressure beof drying it. Stresses of the-order of 25,000.

pounds per square inch are developed in the slgnode straps i2. It has been found that when stresses of -this order are developed that the resin in the butt joint is reduced to e. satisfactoryV core sections may then be assembled on the coil Il, subjecting them to pressure by means of signode straps. After the assembling operation, the transformer is heat-treated to effect the well known drying operation. The heating will result in the thermoplastic material bonding the core sections together giving a core which is not subject to attack from an acid dielectric.

The Worked faces of the core sections lmay be brought together to reduce thethickness of the applied varnish to the predetermined amount suitable for the particular apparatus by energizing the coil I3 on the core with direct current. This latter method lends itself to shop practice wherever direct current is available and gives excellent results. Other methods of appylingl,

There- The cost of the making `which permitsthe tensionin the bands to bring the faces still closer together there was a further reduction in the apparent watts loss to 251. The reduction in the eddy currents in the faces due to the insulating eect of the acid resistant material is shown in thereduction of the true watts loss from 68.8 to 64.6.v

' illustrated example constitutes a practical emthe following speciiicationhave shown satisfacl.

example.y

assembly. l Signode bands-Applied to iron circuits separately.

Approxi- Apparent Truewatts matetem wattsloss loss Demme Acid resistant material on A' C'.

bodiment ofmy invention, I do not limit myself to the exactdetails described since the materials may be considerably varied without departing from the spirit ofthe invention as defined in the appended claims'. y

I claiml as my invention:

'1. In a transformer, in combination, a plurality of core sections, worked and etched faces for making a butt joint on the core sections, and an acid-resistant material applied to the faces, the faces being brought together in the making of a butt joint to reduce the acid-resistant material to a predetermined thickness.

2. In a transformer, in combination, a plu'- rality of core sections built up from laminations of magnetic material, bending material for bendsponsiveto temperature to effect the bonding of `the core sections to one another during-the v i drying of the transformer by subjecting itl to a heat-treatment. v

3. Ina transformer, in combination, a `plu.

rality of core sections comprising a plurality of laminations of magnetic material bonded to-one another, faces on the core sections Worked and etched for the purpose of making a butt Joint and a resin selected from the group consisting of a phenol aldehyde, alkyd, or vinyl type of resin applied to the Worked faces of the core sections.

the resin being ofsuch character that it may be reduced to a predetermined thickness under pressure applied to the core sections and dried, bonding the core sections to one another by the subjecting of the transformer to a heat-treatment to dry it.

'4. A butt joint for velectrical apparatus com-,

prising a yplurality of core sections built up of laminations` of magnetic material bonded together,l faces provided on the core sections, the faces being `Worked and etched to give the proper contour andremove buns, and anacid and oilresisting resin applied to the worked and etched It will be noted in the foregoing report on per-V l formance that applying the acid resistant material to the worked faces of the core resulted in A an increased air gap which caused the apparent watts loss to increase from 264 to 2,90. Applying the bands under tension brought apparent watts loss down to 282, and after the heating in the oven faces, .the resin being of a character to lend itselfto the bonding of the worked faces when subjected to heat.y

5.In a'f transformer core' structure, in combination, aplurality of'core sections'built up from` laminations-of magnetic material, acid'resistantv bonding material for bonding the laminations to one vanother in themaking of the core sections, facesworked on the core sections for the making of a'butt joint, and an acid resistant. l

another to compress the thermoplastic material to give van insulating nlm, the .thermoplastic material being responsive to temperature to effect the bonding of the worked faces of the core sections to one another.

6. In a transformer core structure, in combination, a plurality of core sections comprising groups of laminations of magnetic material, resinous material for bonding the laminations to one another in the making of the core sections, faces worked on the core sections for the making of a butt joint, an acid resistant thermoplastic material disposed between the worked faces of the core sections and a binding member applied to the core sections for drawing the worked faces toward one another to compress the thermoplastic material to provide a nlm, the thermoplastic material being responsive to temperature and capable of bonding the worked faces of the core sections to one another.

7. In a transformer core structure, in comblnation, a plurality of core sections comprising groups of laminations of magnetic material, a resinous material for bonding the laminations to one another in the making of the core sections, faces worked on the core sections for the making of a butt joint, an acid resistant thermoplastic material disposed between the worked faces and a binding member applied to the core sections for drawing the worked faces toward one another to compress the thermoplastic material to provide a lm between the worked faces of the order of .00025 inch in thickness, the thermoplastic material being responsive to temperature and capable of bonding the worked faces of the core sections to one another.

HENRY V. PUTMAN.

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