GB2111316A

GB2111316A - An unjointed amorphous metal core for an electrical induction apparatus

Info

Publication number: GB2111316A
Application number: GB08234811A
Authority: GB
Inventors: Chi Lin Kou; Paul Philip Corbett; Charles Edward Burkhardt
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1981-12-11
Filing date: 1982-12-07
Publication date: 1983-06-29
Also published as: KR840003130A; BE895330A; NO824096L; FR2518305A1; JPS58112310A; GB2111316B

Abstract

A magnetic core for electrical induction apparatus is formed of amorphous magnetic strip material wound upon itself to form radially adjacent laminations (12), and it includes an inner reinforcement (12a) of non-amorphous metallic material inwardly adjacent and preferably bonded to the innermost lamination of amorphous material. Furthermore, it is rendered impervious to liquid dielectric, such as transformer oil, by a sealant (70) applied at least to the core edges, and may have a reinforcing insulating wrap (71) on the core section or section which is/are to an electric coil (72). <IMAGE>

Description

SPECIFICATION An unjointed amorphous metal core for an electrical induction apparatus The present invention relates generally to magnetic cores for use in transformers and like electrical induction apparatus and, more particularly, to construction of a transformer core made from amorphous strip material and nonamorphous material.

Electrical induction apparatus, such as transformers, are constructed with cores of magnetic material to provide a path for magnetic flux. One common way to make such cores is to use magnetic strip material having a preferred direction of orientation parallel to the longitudinal direction of the material, for example, nonamorphous materials such as grain-oriented silicon steel. This material is relatively rigid yet flexible and easy to form into the ultimate shape of the core, either before or after the core has been annealed. After such a core is formed, it can be readily provided with an unconnected joint, for example by cutting entirely through one section of the core, and because of the flexibility of nonamorphous material, an associated electrical coil can be easily assembled around a section of the core by merely opening the joint and inserting the coil therethrough.This technique, however, is not entirely satisfactory where the core is made from an amorphous metal strip material.

Amorphous metal strip material has lower core losses than non-amorphous material. However, amorphous strip material is very thin, very brittle, and very hard. Annealing amorphous material further reduces its ductility and flexibility. All of this presents problems in fabricating amorphous cores.

One problem associated with the fabrication of amorphous cores is related to the manner in which an electrical coil or coils is assembled about the core. As indicated heretofore, the technique of assembling a coil about a non-amorphous core by inserting the coil through an open joint in the core is not entirely satisfactory for amorphous cores.

This is because an amorphous core is less ductile and flexible than a non-amorphous core, and thus, it is more difficult to flex open a joint in an amorphous core for assembling the coil without chipping or otherwise breaking core laminations.

This is undesirable because stresses imposed upon the core can greatly increase core losses.

Handling of the core for purposes other than coil assembly may also impose stresses on the core.

In view of the foregoing, one object of the present invention is to reduce the assembly and handling problems caused by the brittleness of an amorphous magnetic core.

A more specific object of the present invention is to provide an unjointed amorphous core which is less likely to be damaged during core handling and assembling of an associated electrical coil or coils about the core.

As will be seen hereinafter, the magnetic core disclosed herein is one which is constructed of amorphous strip material wound upon itself to form adjacent laminations. The core has an inner reinforcement of non-amorphous metallic material disposed radially inwardly adjacent the innermost lamination of the amorphous strip material. A coating is provided on the core to hermetically seal the core and to make the core impervious to air and/or oil. An insulating paper may be placed about a section of the core. The insulating paper reinforces the core, and an electrical coil can be placed about the insulating paper.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Fig. 1 schematically illustrates a magnetic core embodying the invention; and Figs. 2a-2c diagrammatically illustrate steps for making such core.

Referring now to the drawings and to Fig 1 in particular, the wound magnetic core, generally designated with reference numeral 10, is especially suitable for use in a transformer or similar electrical induction apparatus. The core 10 is formed of a continuous strip of amorphous metal wound about itself to form adjacent laminations 12 in the shape of a closed loop. One example of amorphous strip material making up the core is the METGLAS amorphous strip material manufactured by Allied Chemical Company. (METGLAS is a registered trademark for Allied Chemical's amorphous metal alloys.) Magnetic cores may be round, somewhat rectangular, rectangular as illustrated in Fig. 1, or have any other suitable shape. In the rectangular shape shown, the core 10 includes opposite legs 14 and 16, an upper yoke 18, and a lower yoke 20.The core does not inciude a joint for placing an associated coil or coils upon the core, coil 72 being assembled about core 10 by winding the coil about a section of the core, as well known in the art.

Referring now to Fig. 2a, a method of fabricating core 10 from a continuous strip of amorphous metal and a non-amorphous metal strip material is shown. As illustrated in Fig. 2a, a continuous strip or amorphous metal 22 is initially stored on its own reel 35 for winding about a cylindrical mandrel 90. A non-amorphous metal strip material 24, such as Hipersil, which is a grain-orientated silicon steel such as manufactured by Armco of Butler, Pennsylvania, is stored on reel 45 for winding about mandrel 90.

The method of manufacturing core 10 calls for winding amorphous strip 22 and non-amorphous strip 24 about mandrel 90 to form an initially round core generally indicated at 100. Reels 35 and 45 are positioned relative to mandrel 90 so that when strips 22 and 24 are wound onto the mandrel, strip 24 forms the innermost wrap of the core. Strip 24 is thus located adjacent to the innermost lamination formed by the amorphous strip material to face in the direction of core window 6 (Fig. 1) of core 10. The inner non laminated surface 80 of core 10 is thus formed by strip 24. The length of strip 24 will be substantially less than that of amorphous strip 22 since strip 24 just forms the innermost wrap or innermost lamination 1 2a of core 1 0.

The inner wrap, which is formed by the Hipersil material, of the core reinforces the core and makes the core more rigid. Strip 24 prevents the brittle amorphous strip material of the core from being damaged during coil assembly or other handling of the core.

The method of winding the non-amorphous strip material onto a mandrel is described for illustrative purposes only. A number of other methods could be used to form the core of the present invention. For example, non-amorphous strip 24 could be manually positioned about mandrel 90, and amorphous strip 22 could then be wound from reel 35 onto mandrel 90. Also, non-amorphous strip 24 could comprise a number of discrete segments rather than a continuous strip of material as shown.

After the wound core 1 00 has been formed, the ultimate shape of core 10 may be provided by the clamping arrangement shown in Fig. 2b. Fig. 2b shows a number of inner and outer clamping plates 50 which form part of a suitable clamping apparatus generally designated with numeral 52 and including means (not shown) for adjusting the spacing between the various confronting plates and the location of the plates relative to one another to provide the desired shape of the core.

In Fig. 2b, the round core 100 of Fig. 2a is shown converted to the rectangular shape of the core 10 seen in Fig. 1. As shown in Fig. 2b, the rectangular core has on one section thereof a current coil 54 which is connected to a source 56 of either direct or alternating current to be passed through the coil for the purpose of subjecting it to a magnetic field.

While the core is being subjected to such magnetic field, it may be annealed, preferably in a protective atmosphere, for example, a vacuum, an inert gas such as argon or nitrogen, or a reducing gas such as a mixture of nitrogen and hydrogen, The core may be annealed from between 2 and 5 hours, most preferably for about 2 hours, at a temperature of between about 3400C and 3700C for Allied Chemical's METGLAS material 2605-SC, and between 3900C and 41 00C for Allied Chemical's METGLAS 2605S-2 material.

The core is cooled down gradually, and specifically at a rate of 20C per minute, until the core reaches a temperature of 1 500 C. By annealing the core while subjecting it to a magnetic field, as described, its core losses are reduced. After the core has been annealed and sufficiently cooled, the coil 54 can be removed.

After removal of the coil 54, the core 10 is provided with a protective coating 70 (Fig. 1) in order to render the core impervious to oil such as used as a coolant in electrical induction apparatus.

Without such protective coating, oil would penetrate between the core lamination and thereby cause uneven stresses in the laminations which could increase the required core exciting power. The coating may be applied to the entire core or joust to the laminated surfaces of the core.

As iron base amorphous metal strip material rusts easily in air, coating 70 could also be used to hermetically seal the core to prevent the core from rusting.

Coating 70 may be applied to the core in a number of different ways. For example, core 10 may be dipped in a vat 40 containing a plastic sealant 42, such as Seal-Peel from Peel, Inc..

Troy, Michigan. Or the core may be dipped in various types of protective varnishes, such as B142-1 and B225 varnishes manufactured by the Westinghouse Electric Corporation, Benolite Department, Manor, Pennsylvania. A commercially available product known as Bond Master, manufactured by Pittsburgh Plate Glass Company, Adhesive Products Division, Bloomfield, New Jersey, may also be applied to core 1 0.

Additionally, coating 70 may be formed on core 10 by electrostatically coating the core with a powder from the 3M Company of Minneapolis, Minnesota. A fluorosilicone sealant, of the type known as 730 RTV manufactured by Dow Corning, Midland, Michigan, may also be used to coat the core.

As shown in Fig. 1, core 10 may also include an insulating paper 71 wrapped around that section of the core onto which coil 72 is wound. In addition to serving as an insulating medium, insulating paper 71 will reinforce the core. Various types of insulating papers may be used, such as, INSULDUR paper manufactured by Mosinee Paper Corporation, Pulp and Paper Division, Department 2R63, Mosinee, Wisconsin, or NOMEX paper manufactured by Dupont Company, Wilmington, Delaware, or KAPTON SHEET manufactured by the 3M Company, St. Paul, Minnesota. The paper can be bonded to the core using the same bonding material which is used to bond the grainorientated silicon steel strips to the amorphous strip material.

Claims

1. A magnetic core for an electrical induction apparatus, comprising amorphous magnetic strip material wound upon itself to form laminations radially adjacent each other, and an inner reinforcement of non-amorphous metallic material disposed radially inwardly adjacent the innermost lamination formed by the amorphous magnetic strip material.

2. A magnetic core according to claim 1, wherein said non-amorphous metallic material is grain-oriented silicon steel.

3. A magnetic core according to claim 1 or 2, wherein said non-amorphous metallic material is in strip form.

4. A magnetic core according to claim 1, 2 or 3, wherein said non-amorphous metallic material is bonded to said innermost lamination.

5. A magnetic core according to any of the preceding claims, including a coating of a sealant applied at least upon the outer edges of the core to render the core impervious to liquid dielectric employed in said induction apparatus.

6. A magnetic core according to claim 5, wherein said sealant is an insulating varnish.

7, A magnetic core according to claim 5, wherein said sealant is fluorosilicone.

8. A magnetic core according to claim 5, wherein said coating is formed of an electrostatically applied powder.

9. A magnetic core according to any of the preceding claims, wherein at least one section of the core has thereabout a reinforcing insulating wrap for placement thereon of an electric coil.