US3870982A

US3870982A - Impregnated electromagnetic coil having a layer voltage applied thereto

Info

Publication number: US3870982A
Application number: US347041A
Authority: US
Inventors: Takashi Shibano; Koichi Hirakawa; Toshimitsu Yonehara
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1972-03-31
Filing date: 1973-04-02
Publication date: 1975-03-11
Anticipated expiration: 1992-03-11
Also published as: CA1013824A; JPS4899647A; GB1415225A

Abstract

A novel electromagnetic coil is provided which is manufactured by placing and fixing an impregnable insulating material in such a manner that the insulating material contacts the whole surface of each side of an elementary electromagnetic coil consisting of a wire or self-bonding wire, to each side of which is applied a layer voltage, and then impregnating an impregnant into the elementary coil. The electromagnetic coil according to this invention ensures an improved working property in the manufacture of coils, reduction in manufacturing cost and an improved space factor.

Description

United States Patent Shibano et al.

IMPREGNATED ELECTROMAGNETIC COIL HAVING A LAYER VOLTAGE APPLIED THERETO Inventors: Takashi Shibano, Suita; Koichi Hirakawa, Kawanishi; Toshimitsu Yonehara, Takarazuka, all of Japan Assignee: Matsushita Electric Industrial Co.,

Ltd., Kadoma-shi, Osaka, Japan Filed: Apr. 2, 1973 Appl. No.: 347,041

Foreign Application Priority Data Mar, 31, 1972 Japan 47-32781 U.S. Cl. 335/297, 336/205 Int. Cl. HOlf 3/00 Field of Search 335/299, 282; 336/205,

References Cited 7 UNITED STATES PATENTS DOrio 336/205 X Mar. 11, 1975 2,814,581 11/1957 Flynn 336/205 X Primary E.\'aminerG. Harris Attorney, Agent, or Firm-Stevens, Davis, Miller & Mosher [57] ABSTRACT A novel electromagnetic coil is provided which is manufactured by placing and fixing an impregnable insulating material in such a manner that the insulating material contacts the whole surface of each side of an elementary electromagnetic coil consisting of a wire or self-bonding wire, to each side of which is applied a layer voltage, and then impregnating an impregnant into the elementary coil. The electromagnetic coil according to this invention ensures an improved working property in the manufacture of coils, reduction in manufacturing cost and an improved space factor.

4 Claims, 4 Drawing Figures PATENTEB 1 1975 3870.982

sum 2 0f 2 IMPREGNATED ELECTROMAGNETIC COIL HAVING A LAYER VOLTAGE APPLIED THERETO The present invention relates to an electromagnetic coil having an improved insulating property and a method for manufacturing the same.

Generally, heretofore known electromagnetic coils having an interlayer insulating material disposed between all the layers have been manufactured employing various processes of applying insulating materials, e.g., the varnishing process, the process of molding by pouring or impregnation or the use of a casing filled with an insulating oil. These processes have been selectively employed depending on the applications to which the coils are intended.

A drawback of these conventional electromagnetic coils is that the use of the interlayer insulating material causes a deteriorated working property in the manufacture and moreover a low space factor of the electromagnetic coil has prevented the realization of smaller and more compact apparatus.

It is therefore an object of the present invention to minimize the use of interlayer insulating material in the manufacture of electromagnetic coils, thereby ensuring an improved working property in the production of coils and a higher space factor.

According to the manufacturing method of this invention, it is possible to provide an electromagnetic coil which has a good working property and which is compact and lighter, thereby making a great contribution toward improving the productivity.

Other objects and advantages of this invention will be readily apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a perspective view of an elementary electromagnetic coil employed with the present invention;

FIG. 2 is a partial perspective view of the elementary coil which has been provided with an insulating material but not yet subjected to the process of impregnation;

FIG. 3 is a perspective view of another embodiment of the elementary electromagnetic coil of this invention which is composed of a self-bonding wire; and

FIG. 4 is a schematic diagram showing in crosssection the coils of FIG. 2.

The present invention will be explained in greater detail with reference to FIGS. 1 and 2.

FIG. 1 shows an elementary electromagnetic coil comprising a wire of the type which is commonly used. In FIG. 1, numeral 1 designates a wire which is suitably selected depending on the actual operating temperature of an apparatus and the environment in which 'it is used. Among Class E insulating materials in terms of heat resisting properties, polyvinyl formal wire has been used widely. Those which have slightly higher heat resisting properties include epoxy wire, polyester wire, etc. Polyesterimide wire, heat resistant polyester wire, polyimide wire, etc., have still higher heat resist ing properties. Numeral 2 designates lead wires which are normally used by connecting intermedially with an insulated wire having reinforced mechanical and electric insulating properties. Numeral 3 designates an adhesive insulating tape. After the completion of the winding of the coil, the insulating tape 3 is provided on the coil at predetermined places to prevent the loosening of the coil. It is essential that the properties of the insulating tape 3 are such that it possesses an excellent adaptability with the wire and other component materials with which it contacts in the actual working surroundings. More particularly, Nomex (trademark for a heat-resistant nylon manufactured by E. I. du Pont de Nemours and Company) including silicone resin as an adhesive may be used advantageously, if the wire cornprises polyimide wire, polyesterimide wire or polyamideimide wire and if the varnish used to impregnate the electromagnetic coil comprises epoxy resin, polyester resin or silicone resin. While the heat resisting properties are slightly less favorable, glass cloth having an adhesive, e.g., epoxy resin applied thereon or Nomex using the similar resin as an adhesive may lend itself to be an excellent insulating tape, if the wire comprises epoxy wire or polyester wire and if the varnish comprises similarly polyester resin, epoxy resin or phenol resin. However, it is necessary to conduct tests on these materials in the presence of the associated materials to confirm their reliability before putting them to the actual use.

When the elementary coil has been prepared in the manner as above described, a readily impregnable insulating material is placed in contact with each of the sides of the elementary coil and a varnish or the like is impregnated into the insulating material to reinforce the electrical insulator strength of the coil sides.

In other words in FIG. 2 numeral 4 designates an insulating material which is preferably such a porous material that a maximum contact area is ensured between the coil side and the insulating material. The reason is that the wire at the coil side receives the voltage for two layers and the voltage increases as the distance between the coil side and the insulating material increases, thus tending to cause corona discharge, surface tracking or arc discharge. These undesirable phenomena are avoided by closely fitting the insulating material to the coil sides thereby preventing the formation of voids between the coil side and the insulating sheet 4 and assuring that the effectiveness of an impregnant subsequently applied to make the coil sides more dense is not impaired. Referring to the crosssectional diagram of FIG. 4, the wire segments comprising the coil 1 are designated by the numerals l to 24 and the layers of the wound coil are indicated by the letters a to d. If a voltage V is applied across the coil, then the voltages impressed between the wires I and 2, 2 and 3 22 and 23, and 23 and 24 respectively v/24. The layer voltage appliedbetween the wires 1 and I2, 7 and 18 and 13 and 24 is equal to l2/24V. That is, the layer voltage, which is higher than the voltages between the wires, is applied between the coil sides.

To obtain better results from this effect, those materials which meet the previously mentioned requirements should preferably be used. Materials which may produce an excellent effect include kao wool (ceramic fiber) which is made of kaolin, glass fiber mat, polyethylene terephthalate nonwoven fabric, etc. When these materials are used singly, the insulating material does not fit tightly on the coil sides and it is therefore necessary to use a highly resilient material 5 as a supporting material. Numeral 6 designates an insulating tape for tightly fitting the

materials

4 and 5 on the coil sides. Numeral 7 designates an insulating material which is effective when a high electric field is applied to the coil and its exterior and it is also essential that the insulating material 7 is such that it fits tightly on the coil and is readily impregnable so as to leave voids-free between the coil and the insulating material 7. For this reason, a material having the similar property as the insulating sheet 4 may be preferred. If a layer of air is allowed between the insulating material 7 and the elementary coil, the corona discharge in the voids causes the breakdown of the insulating layer and shortens the life of the coil. A material having a good electrical insulating property and porosity may be suited for the highly resilient material 5, since the porosity ensures an improved impregnation of the impregnant into the coil. More specifically, asbestos, porous sheet material and the like meet these essential requirements. However, the resilient material needs not always be of porous nature. More specifically, it may be a molded plate of epoxy resin, polyester resin or phenol resin, or a laminated plate of glass fibers employing any of these resins.

The impregnating varnish may consist of epoxy resin, unsaturated polyester resin, silicone resin or the like, while mineral oil, silicone oil or the like may provide a suitable liquid impregnant that may be employed to impregnate the coil after it has been assembled in an apparatus and housed in a casing.

Further, the elementary wire shown in FIG. 1 may comprise a self-bonding wire 1' as shown in FIG. 3.

It is to be noted that an electromagnetic coil prepared by subjecting an elementary coil having the interlayer insulating material between some of the wire layers to the processes similar to those of the illustrated embodiment, also comes under the scope of this invention.

The electrical properties of the electromagnetic coil obtained in the manner so far described compare quite favorably with those of conventional electromagnetic coils having the interlayer insulating material disposed between the wire layers. On the contrary, the electromagnetic coil according to the present invention ensures an improved reliability and makes the process of product design easier owing to its simplified structure and the resultant decrease in the variations of the electrical properties with different electromagnetic coils.

Further, the elimination of the use of interlayer insulating material considerably improves the working property in the manufacture of coils and it is also a great advantage from the standpoint of material cost.

Furthermore, a remarkable improvement in the space factor makes it possible to achieve the ultimate object of the invention, i.e., the realization of more compact and lighter apparatus.

What is claimed is:

1. An electromagnetic coil comprising an elementary electromagnetic coil composed of a self-bonding electric wire wound in the form of a plurality of layers and having no interlayer insulating paper; impregnable ring-shaped insulating sheets closely fitted to and secured on each side of said elementary coil, to which a layer voltage is applied, to allow said wire at each of said coil sides to be embedded in one of said insulating sheets; and a varnish impregnated and hardened in said. elementary coil to make the electromagnetic coil voidfree between said coil sides and said insulating sheets to prevent an arc discharge from being generated between coil layers along a surface of each of said coil sides.

2. An electromagnetic coil according to claim 1, further comprising another insulating sheet superimposed on said ring-shaped readily impregnable insulating sheet, said another insulating sheet having a mechanical strength greater than that of said first insulating sheet, whereby a first insulating sheet is tightly fitted and secured on each of said coil sides.

3. An electromagnetic coil according to claim 1, further including a long and narrow insulating sheet consisting of a readily impregnable nonwoven fabric, said long and narrow insulating sheet being wound around an outer surface of said coil, whereby the joints be-- tween said first insulating sheet and said long and narrow insulating sheet are tightly connected and secured together.

4. An electromagnetic coil according to claim 2, wherein said first insulating sheet fitted on the coil sides to which the layer voltage is applied and said another insulating sheet superimposed on said first insulating sheet are taped integrally with said coil, whereby said wire is embedded in said first insulating sheets.

Claims

1. An electromagnetic coil comprising an elementary electromagnetic coil composed of a self-bonding electric wire wound in the form of a plurality of layers and having no interlayer insulating paper; impregnable ring-shaped insulating sheets closely fitted to and secured on each side of said elementary coil, to which a layer voltage is applied, to allow said wire at each of said coil sides to be embedded in one of said insulating sheets; and a varnish impregnated and hardened in said elementary coil to make the electromagnetic coil void-free between said coil sides and said insulating sheets to prevent an arc discharge from being generated between coil layers along a surface of each of said coil sides.

3. An electromagnetic coil according to claim 1, further including a long and narrow insulating sheet consisting of a readily impregnable nonwoven fabric, said long and narrow insulating sheet being wound around an outer surface of said coil, whereby thE joints between said first insulating sheet and said long and narrow insulating sheet are tightly connected and secured together.