US3074039A

US3074039A - Magnetic stabilization-wound cores

Info

Publication number: US3074039A
Application number: US769258A
Authority: US
Inventors: James G Ford
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1958-10-23
Filing date: 1958-10-23
Publication date: 1963-01-15
Anticipated expiration: 1980-01-15

Description

Filed 001;. 23, 1958 Fig.|.

Fig.2.

INvENToR James G. Ford United States Patent 3,074,039 MAGNETIC STABILIZATION-WOUND CORES James G. Ford, Sharon, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporaton of Pennsylvania Filed Oct. 23, 1958, Ser. No. 769,258 2 Claims. (Cl. 335-213) The invention relates generally to cores for inductive apparatus and more particularly to wound cores. This application is a continuation-in-part of application Serial No. 574,170, filed March 27, 1956.

Heretofore, in the manufacture of cores of all kinds, and particularly wound cores, the laminations are subjected to some distortion by the application 'of external forces. If the `distortion is great enough it introduces stresses into the magnetic material which, if they cannot be relieved by further annealing, greatly increase the core losses in service.

In the manufacture of transformer cores, and wound transformer cores in particular, many methods have been tried to support the laminations, such for example, as the making of the core in a solid mass so that the laminations are not subject to distortion and the building up of stresses in the core iron.v

In order to provide a core which is a solid mass, it has lbeen common practice toimpregnate wound cores with' The organic materials and the iron have different coefficients of expansion and with changes in temperature, the expansion and contraction cause stresses to be locked in the core iron.

In order to prevent the setting up of stresses in the core v iron and assure low exciting current and substantially no change from climatc and other conditions that may be found where such transformers are employed, it is desirable to find means for so supporting the laminations relative to one another that there can be substantially no distortion of the laminations and no building up of stresses in the core iron.

The object of the invention is to provide for supporting the laminations of magnetic material of a core against distortion when subjected to external forces and the setting np of stresses in the magnetic material which increase I core losses. It is also an object of the invention to provide for the supporting of the laminations of a core of magnetic material whereby the setting up of permanent stresses in the magnetic material and the increasing of Operating losses is avoided.

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FIG. 2 is va section of the core taken along the line II-II of FIG. 1.

Referring now to the drawing, and FIG. 1 in particular, the embodiment of the invention illustrated is a wound core. The wound core comprises a number of turns of a cold rolled oriented Silicon iron strip. The number of turns will depend on the specification to be met in the design of the transforrner. The turns of the core are, in effect, laminations superimposed on one another.

In this embodiment the invention is applied to a wound core. However, it will be appreciated that it can be applied to any type of core built up from individual laminations. The main function of the invention is to so support the laminations that there is no distortion of the metal in handling the core which sets up stresses in the core iron and causes an increase in core losses.

The core shown generally at 10 comprises -a plurality of turns or laminations 11 which are in close contact with one another. Therefore, when pressures are applied to the external surface of the core they are transmitted from one lamination to another and set up stresses in a number of the laminations, depending on the distorting force ap- I plied.

vnations, with changes in temperature is applied to the edges of the laminations 11. The amount of cementitious material 12 applied may be varied somewhat to meet design requirements. It has been found that in the manufacture of most wound cores good results may be obtained by 'applying the cementitious material 12 to a thickness of the order of 3%4 inch to 1/16 inch. However, it is to be understood that these are not positive limitations. The thicknesses prescribed have been arrived at by experimentation and careful checking and will give good results.

It has been found that nearly any inorganic cementitious material which will air dry and on baking take on the characteristic of a ceramic may be used. In tests made to determine the utility `of the invention, cementitious material such as sodium silicate and silica or some other similar filler was found to be satsfactory. Magnesium oxychloride cement, a cement sold under the trade name Portland cement and litharge glycerine were also found to give good results.

The applying of the cementitious material may be effected in any well known manner. In the cores made a cement was prepared which was of such consistency that it could be applied by lmeans of a trowel or other similar tool. A layer of the required thickness was then applied to the edges of the laminations. When the cement was of the right consistency it adhered and soon air dried. After the cement dried and became hard it was subjected to a baking step to remove any unnecessary moisture. The core with the applied cementitious material may be baked in any suitable oven at temperatures Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the features of construction, combination of elements and arrangement w of parts which will be exemplified in the construction hereconstructed in accordance with the features of this invention; `and of 105 C. to 150 C.

When the cementitious material has been applied it will penetrate only slightly between the edges of the laminations. However, this penetration together with its 'adherence to the edges of the metal is suflicient to enable the hardened cementitious material to support one lamination in a predetermined position relative to the adjacent lamination. j

In the manufacture of cores of this type it has been found that when the inorganic cementitious material has been properly hardened that the laminations of the core are so supported that there is substantially no stresses introduced into the core iron by the ordinary handling operations which follow the application of the cementitious material.

The inorganic cementitious materials remain hard and sprgosa a U firm over the complete range of treating and operating temperatures. Therefore the laminations are supported in proper relationship to one another and stresses are not introduced into the iron during treatment or operation.

The inorganic cementitious materials and the ferrous magnetic laminations disclosed and claimed herein each have a coefficient of thermal expansion per degree Fahrenheit of from to 10-6. On the other hand, organic resins have a coeflicient of thermal expansion per degree Fahrenheit of from 50 to 100 10-5 and even higher. Therefore, cores bonded with such organic resins are not completely satisfactory since both core losses and exciting current are appreciably increased by stresses 'caused by differential expansion and contraction of the bond and ferrous magnetic laminations as the cores are alternately heated and cooled. Since inorganic cementitious mate- 'rials have a coefficient of thermal expansion similar to that of the ferrous magnetic laminations, changes in temperature do not cause stresses to develop in cores bonded with such cementitious materials.

In order to illustrate how effective the application of inorganic cementitious material to the edges of the laminations is in keeping down the introduction of stresses into the iron by the Operations which follow in the manufacturing of transformers, a'table is given hereinafter of the tests made on twelve wound cores supported by layers of hardened cementitious materials applied to the edges of the laminations and two wound unbonded cores which were wound and very carefully handled so as not to subject them to any distortion which might result in the building up of stresses in the iron. The unbonded cores were, in effect, laminated cores which had been annealed to relieve all stresses and handled thereafter to prevent the setting up of any stresses.

Excting True. Watts Current in Loss Amperes Core Number of Cores having Iuorganc Cementitious Material Applied to the Edges of the Core:

1 .0365 .0077 .0350 .0072 .0350 .0070 .0375 0077 .0360 .0070 0385 .0074 .0375 0078 .0360 .0076 .0360 .0074 0340 0068 0380 0078 0360 .0075 Core Number of Cores Without Cementitious Material Applied to the Edges of the Laminations:

13 (Unbonded) .0360 .0075 14 (Unbonded) 0345 0073 It will be observed from the foregoing table that the exciting current and the true Watts loss in the first twelve cores which have inorganic cementitious material applied to the ends and hardened are substantially the same as the exciting current and true Watts loss in the cores which have not been subjected to any distortion and, therefore, does not have any stresses locked in the iron. In making 'the test, it was found that if the cores without the inorganic cementitious material applied to the edges of the laminations were subjected to pressures, such as the 'squeezng of them with the hand, that the exciting current increased to a marked extent. When the same pressure was applied to the cores carrying the hardened inorganic cementitious material there was no change in the exciting 'current 'This clearly-shows the great advantage gained by supporting the laminations relative to one another by the use of the applied cementitious material which when air dried and baked take on characteristics of a Ceramic.

This invention may be applied to cores for many types of transformers and other inductive apparatus. Considel' for instance current transformers used primarily for measuring purposes. It is highly important that the exciting current be low to cut down cost of operation and that the exciting current remain constant under all measuring conditions in the interests of accuracy. Then a core of this type in which the laminations are supported relative to one another so that stresses cannot be built up by distortion of lthe laminations is highly desirable.

It will also be evident to anyone that inorganic cementitious materials may be applied without distorting the laminations in any way and, therefore, there will be no build-up of stresses in the iron in the manufacturing operation. It is also well known that inorganic cementitious materials once properly hardened and dried are not subject to changes in weather conditions or to the atmospheres found in shops and other places where such transformers may be employed. i

Since certain changes may be made in the above construction and different embodiments of the invention could be made Vwithout departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In a wound bonded core, in combination, a plu. rality of turns of ferrous magnetic material in contact f with one another forming a substantially cylindrical core,

a hardened nonresilient inorganic cementitious material selected from at least one of the group consisting of sodium silicate and silica, magnesium oxychloride cement, Portland cement and litharge glycerine adhering to the edges and extending only slightly between the turns of the laminations, the hardened cementitious material cooperating with the ferrous magnetic material to resist distortion of the laminations upon-the application of outside forces and the setting up of stresses in the ferrous magnetic materials with changes in temperature and thereby core losses.

2. In a bonded core of ferrous magnetic material, in combination, a plurality of turns of magnetic material in contact with one another forming aV core,4 a hardened non-resilient inorganic cementitious material selected from at least one of the group consisting of sodium silicate and silica, magnesium oxychloride cement, Portland cement and litharge glycerine adhering to the edges and extending only slightly between the turns, the hardened inorganic cementitious material being of a thick'- ness of the orderof lfig of an inch to 1/16 of an inch in thickness and cooperating with the ferrous magnetic material to resist distortion when subjected to external forces and the hardened' cementitious material having a low coeflicient of thermal expansioncorresponding to that of the ferrous magnetic material whereby to minimize the setting up of stresses in the ferrous magnetic material with changes in temperature and thereby achieve low core losses.

References Cited in the file of this patent UNITED STATES PATENTS 1.586.889 Elmen June l, 19.126 2,579,560 Ford Dec. 25, 1951 FOREIGN PATENTS 573,780' Great Britain V Dec. 5,l 1945

Claims

1. IN A WOUND BONDED CORE, IN COMBINATION, A PLURALITY OF TURNS OF FERROUS MAGNETIC MATERIAL IN CONTACT WITH ONE ANOTHER FORMING A SUBSTATIALLY CYLINDRICAL CORE, A HARDENED NON-RESILIENT INORGANIC CEMENTITIOUS MATERIAL SELECTED FROM AT LEAST ONE OF THE GROUP CONSISTING OF SODIUM SILICATE AND SILICA, MAGNESIUM OXYCHLORIDE CE-