US3189681A - Angular channel-shaped coil insulation - Google Patents

Description

June v15, 1965 L. 1-; FEATHER 3,189,681 ANGULAR CHANNEL-SHAPED COIL INSULATION Fj led March 11, 1960 Fig. I

40 42 m l/4V] F lg. 5

INVENTOR Londis E. Feather ATTORNEY United States Patent 3,189,631 ANGULAR CHANNEL-SIMPED CGIL INSULATIQN Landis E. Feather, Hickory Township, Mercer County, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Penusyivania Filed Mar. 11, 1960, Ser. No. 14,397 3 Claims. (Cl. 174-421} This invention relates to insulation for electrical apparatus, and particularly to insulating barriers associated with multiple coil transformer windings which utilize nested barriers of insulating material.

In electrical apparatus, such as transformers, a large quantity of built-up pressboard spacing and insulating structures of a great variety of dimensions and shapes is required. Such built-up structures are particularly useful for insulating the live portions of transformers from the casing and for separating the electrical elements from one another.

Included among these insulating members for transformers and like electrical apparatus are angled channel members that are used to insulate the inside corners and the outside corners of substantially rectangular coils, and particularly the rectangular coils in pancake form used in shell-type transformers.

Heretofore, in preparing insulating structures for rectangular coils, and particularly the angled channel members, a special grade of pressboard or fuller board was first soaked in water and worked by hand into a condition such that a cold-pressed preform could be prepared therefrom. After the preform was dried, it was then moistened and inserted into a suitably formed mold and hot pressed to form the desired structure.

This invention is directed to electrically insulating channel members adapted for use as insulating barriers for the windings of transformer coils, particularly the rectangular coils in pancake form. The insulating channel members of this invention comprise a pair of side walls depending from an end wall, the side walls and end walls forming substantially continuous U-shaped channels. The U-shaped channel will be disposed at certain angles depending upon the configuration of the coil to which the insulating channel member is applied. The channeled insulating members of this invention are laminated members formed from a plurality of plies of a specific stretchable paper sheet material and a specific thermoplastic bonding resin.

For a complete understanding of the nature of this invention, reference is made to the following detailed description taken in conjunction with the drawing, in which:

FIG. 1 is a front elevational view of a stack of resintreated sheet material prior to molding;

FIG. 2 is a view in perspective of a channel member of this invention;

FIG. 3 is a View in perspective of another channel member of this invention;

FIG. 4 is a plan view of a transformer coil of the pan cake type showing an inside angled channel member applied thereto; and

FIG. 5 is a cross-sectional view taken on the line V-V of FIG. 3.

In accordance with this invention, it has been determined that highly satisfactory channel members adapted for barrier insulation for coils such, for example, as rectangular pancake coils used in the shell-type power transformers, can be prepared by molding in a suitable mold with the application of heat and pressure a plurality of plies of a specific creped paper treated with a specific thermoplastic resin adhesive.

The specific crepe paper employed in preparing the accompanying laminated channel members of this invention is a crepe paper prepared by creping a high density sulfate kraft paper. The sulfate kraft paper, prior to creping, has a basis weight of from about 70 pounds to 85 pounds, and a thickness of about 5 mils. The high density sulfate kraft paper is creped in the machine direction by known methods to provide a sheet of creped paper having a thickness of from about 40 mils to 50 mils and a stretch of at least about 200% in the machine direction. The paper has from about 30 to 40 crimps per inch.

The thermoplastic resinous adhesive or bonding material employed to bond together a plurality of plies of the above-described crepe paper is a polyvinyl acetate resin.

The degree of polymerization of vinyl acetate can be controlled by methods known in the art to produce polyvinyl acetates of various degrees of polymerization. Polyvinyl acetates that have given very satisfactory results in this invention are the polyvinyl acetates, a solids solution of which in acetone at C. will have a viscosity of from about 15 to seconds as measured by a No. 4 Ford cup whose use is described in Protective and Decorative Coatings, by Mattiello, volume 5, page 187,

1946 edition.

The polyvinyl acetate is applied to the creped paper in solution form, usually of about 50% solids content. Suitable solvents for polyvinyl acetates are known in the art and include toluene, methanol, ethanol, methyl ethyl ketone, acetone, and mixtures of two or more.

The polyvinyl acetate is applied to the crepe paper in any convenient manner as, for example, by passing the paper through a varnish dip pan containing a solution of the polyvinyl acetate in toluene and subsequently evaporating from the treated crepe paper the toluene solvent by the application of external heat.

The sheet of creped paper is treated to a resin ratio of from about 1.10 to 1.20. Resin ratio is defined as the weight of the sheet plus the weight of the resin to the weight of the untreated sheet. Therefore, the treated sheet of creped paper comprises polyvinyl acetate resin applied thereto in an amount of from about 10% to 20% of the weight of the sheet alone.

Referring to FIG. 1 of the drawing, there is shown a stack 10 of polyvinyl acetate-treated creped paper. For the purposes of this invention, the stack 10 preferably comprises a top sheet 12 and a bottom sheet 14 of substantially the same length and width, while sandwiched therebetween is a plurality of sheets 16 arranged in a pyramidal form as shown. The sheets 16 are of substantially the same width as sheets 12 and 14 but are of varying lengths as shown. The sheets can be all of the same size if desired. The preferred arrangement as shown in FIG. 1 provides for relatively thin and flexible end portions on the channeled members prepared therefrom. The flexible and thin end portions provide for ease in nesting together the channel members when a plurality of channel members are applied to a coil member.

The stack 10 is placed in a suitable mold where it is formed by folding and stretching the stack, and subjected to pressure of from about 250 to 500 pounds per square inch and at a temperature of from about C. to C. for a period of time of from about 4 minutes to 6 minutes to produce an angled channel member 20 as shown in FIG. 2 of the drawing.

The channeled angle member 20 of FIG. 2 is adapted for use on the inside corners of pancake coils and comprises side walls 22 and 24 depending from a bottom wall 26. The side walls 22 and 24 and bottom wall 26 form a continuous substantially U-shaped channel in the member and the bottom 26 of the channel formed thereby is curved substantially at a right angle. End portions 21 and 23 of the member 2% are tapered and relatively thin owing to the arrangement of the sheets of stack ill as above described. The thin flexible end portions 21 and 23 provide for ease of nesting adjacent channel members. The laminated angled channeled member 29 is fitted over one of the inside corners of a wound coil body to insulate the inside corners of the wound coil body from other electrical conducting members that comprise the electrical apparatus.

FIG. 3 of the drawing shows an angled channel member 3d of this invention adapted to be fitted over the outside corners of a wound coil body. Channel member 3t) comprises side walls 32 and34 and bottom wall 36.

As illustrated in FIG. 4 of the drawing, there is shown an angled channel insulating member of this invention fitted over a Wound coil body 42 of pancake form. The coil body 42 is formed of flat wound copper strap with some form of flat insulation (not shown) disposed between the layers of copper strap. The coil body 42 is substantially rectangular in shape with a central opening therethrough for accommodating a magnetic core (not shown). As shown in FIG. 4, there is just one channeled angled member 4% applied thereto; however, each of the inside corner angles thereof will be provided with an angled channeled insulating member to provide for insulating the wound coil body 42 from a magnetic core which will be subsequently placed Within the central opening therethrough. The outside corner angles of coil body 42 can be insulated with channel members formed as shown in FIG. 3 of the drawing. V

The laminated molded channeled angled members of this invention are easily and readily prepared, and the stretch of at least 200% provided by the creped paper employedin preparing these members permits of molding of members of complex shapes, as for example, the angled channel members 2t and fill of FIGS. 2 and 3 of the drawing. Owing to the great amount of stretch of the creped paper employed in carrying out this invention, members and can be formed by folding and stretching the plurality of plies of resin treated creped kraft paper so that the U-shaped channel provided therein is at an angle of about 90. However, members can also be prepared in which the U-shaped channel therein is bent at an angle of from about to 130. Heat and pressure are subsequently applied to form a unitary structure. in practice the plurality of plies of resin treated creped paper are placed in a heated mold where the'forming and stretching are accomplished in one operation. Pressure is applied during this operation to bond the plies together into a unitary member of desired shape.

The laminated insulating angled channel members of this invention have outstanding electrical insulating properties and good mechanical properties. Furthermore, by preparing the members as above described, the members have excellent flexibility properties so that they can be easily and readily applied to the Wound coil body.

While this invention has been directed specifically to laminated angled channel members for insulating inside corner angles of coil bodies such, for example, as coil bodies of pancake form, it will be understood that other insulating bodies of complex structures and shapes can be easily and readily prepared therefrom.

It is'to be understood that the above description and drawing are illustrative of the invention, and not in limitation thereof,

I claim as my invention:

1. An insulated electrical coil comprising, in combination, an electrical conductor having curved surfaces and a flexible insulating channel member applied to at least one of the curved surfaces thereof, said channel member comprising a plurality of plies of high density creped kraft paper sheeting having about 36 to 40 crimps per inch, each of said plies having an original thickness of from about 40 mils to 50 mils and a stretch of at least about 200% and-a polyvinyl acetate resin bonding the plurality of plies of creped kraft paper into a unitary member, said member having side walls and a bottom wall forming a channel conforming to the configuration of the curved surface of the electrical conductor and fitting snugly over the surfaces thereof, and said crimps in each ply disposed essentially laterally with respect to said bottom wall.

2. insulated electrical coil comprising, in combination, an electrical conductor having curved surfaces and a flexible insulating channel member applied to at least one ofthe curved surfaces thereof, said channel member comprising a plurality of plies of high density creped kraft paper sheeting having about 30 to 40 crimps per inch, each of said plies having an original thickness of from about 41) mils to 50 mils and a stretch of at least 200% and a resin bonding the plurality of plies of creped paper into a unitary member, said resin consisting of a polyvinyl acetate resin, said polyvinyl acetate resin being present in an amount of from about 16% to 28% by weight of the'sheet material alone, said flexible insulating channel member having side walls and a bottom wall forming a channel conforming to the configuration of a curved surface of the electrical conductor and fitting snugly over the surface thereof, and said crimps in each ply'disposed essentially laterally with respect to said bottom'wall.

3. An angular channebshaped electrically insulating memberconsisting essentially of a plurality of plies of high density creped kraft paper sheeting having about 30 to '40 crimps per inch, each of said plies having an original thickness of from about 40 mils to about 50 mils and a stretch of at least 200%, a polyvinyl acetate resin bonding the plies of creped paper into a unitary member, said member having side walls depending from a bottom Wall thereby defining a U-shaped channel, said bottom wall curved. to define an angle of about 40 to about and said crimps in each ply disposed essentially laterally with respect to said bottom wall.

Reierences Cited by the Examiner UNITED STATES PATENTS 1,488,504 4/24 Keyes l56222 X 1,735,684 11/29 lurgensen 156-222 2,025,540 12/35 Langley l56190 2,135,315 11/38 Walters et al. 336-209 2,576,864 ll/5l Valente 156-222 X 2,749,525 6/56 Henderson 336-209 2,754,355 7/56 Bartlett 336-206 X FOREIGN PATENTS 577,676 5/46 Great Britain. 466,975 a 8/50 Canada.

JOHN F. BURNS, Primary Examiner;

MILTON 0. l-llRSl-iFlELD, C. F. .(RAFET,

LARAMEE E. ASE-ZEN, E. IAMES SA), examiners,

Claims (1)

1. 3. AN ANGULAR CHANNEL-SHAPED ELECTRICALLY INSULATING MEMBER CONSISTING ESSENTIALLY OF A PLURALITY OF PLIES OF HIGH DENSITY CREPED KRAFT PAPER SHEETING HAVING ABOUT 30 TO 40 CRIMPS PER INCH, EACH OF SAID PILES HAVING AN ORIGINAL THICKNESS OF FROM ABOUT 40 MILS TO ABOUT 50 MILS AND A STRETCH OF AT LEAST 200%, A POLYVINYL ACETATE RESIN BONDING THE PLIES OF CREPED PAPER INTO A UNITARY MEMBER, SAID MEMBER HAVING SIDE WALLS DEPENDING FROM A BOTTOM WALL THEREBY DEFINING A U-SHAPED CHANNEL, SAID BOTTOM WALL CURVED TO DEFINE AN ANGLE OF ABOUT 40* TO ABOUT 130*, AND SAID CRIMPS IN EACH PLY DISPOSED ESSENTIALLY LATERALLY WITH RESPECT TO SAID BOTTOM WALL.

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