US3324222A - Treated cellulosic material and electrical apparatus embodying the same - Google Patents

Description

A. J.,IPA|.uMBo "E TAL TREATED CELLULOSIC' MATERIAL AND ELECTRICH Fig. l.

Filed 10m. '28; 1965 Fig.2.

Fig.3.

WITNESSES:

United States Patent 3,324,222 TREATED CELLULOSIC MATERIAL AND ELECTRICAL APPARATUS EMBODYING THE SAME Anthony J. Palumbo, Sharon, and James G. Ford, Sharpsviiie, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Oct. 28, 1963, Ser. No. 319,174 4 Claims. (Cl. 17417) paratus. Such material-s represent a desirable source of electrical insulation from the standpoint of their economic advantages over other available types of insulation. Moreover, cellulosic insulation possesses good physical properties, generally speaking and satisfactory initial dielectric strength.

However, cellulosic materials deteriorate rapidly at temperatures appreciably above 100 C. when in contact with air or when in contact with liquid dielectrics such as are used in electrical transformers, for example oil, where oxidation products include acids which attack cellulosic materials. Both the physical and electrical properties are aifected by this deterioration with the result that the insulation gradually loses its electrical insulating strength and its mechanical strength is rapidly dissipated.

The electrical and physical properties of cellulosic material such as paper, cotton cloth, cotton tape, pressboard and wood deteriorate at an increasing rate when the temperature is increased above 100 C. whether exposed to air or in contact with fluid dielectric compositions. Thus, for example, after being immersed for only a few weeks in refined petroleum transformer oil at 120 to 150 C. paper will retain practically none of its original tensile strength. Generally a length of fresh electrical grade kraft paper may be bent or flexed several hundred times before it will break. However, after only a weeks immersion in transformer oil at 120 C. to 150 C. it will break upon being double folded one time.

- This deterioration in physical properties is accompanied by a corresponding decrease in electrical insulat- I ing properties. For these reasons it has been specified in the industry that, in electrical apparatus employing cellulosic insulation, for continuous operation the temperatures not exceed about 105 C.

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Other objects of the invention will be obvious and will appear hereinafter.

For a better understanding of the nature and objects of the invention reference should be made to the following detailed description which will be given with particular reference to the accompanying drawings, in which:

FIG. 1 is a View in perspective, partly in cross section, of a transformer core insulated with the novel cellulosic insulation of the invention; 7

FIG. 2 is a view in elevation partly in cross section, of a transformer; and

FIG. 3 is a view in elevation, partly in cross section, illustrating an insulated cable.

In accordance with the present invention it is now possible to greatly increase the retention of both dielectric strength and mechanical strength of cellulosic insulation at elevated temperatures by substantially uniformly distributing throughout the insulation effective amounts of certain chemical stabilizing compounds. The amounts of the compounds to be employed may be small, but these small proportions thereof impart a highly beneficial stabilizing effect to the electrical insulation. The chemical compounds which have been found to impart these improvements are l,5-dihydroxyanthraquinone, and the nitrogen bearing compounds p-phenylazoaniline, ammelide, 1,3-dimorpholino-Z-propanol, triallylcyanurate, Z-aminothiazole, and polyvinylpyrrolidone. Two or more of these compounds may be employed simultaneously in stabilizing cellulose.

It is to be noted that, generally speaking, these compounds exhibit substantial solubility in water or water and alcohol solutions which considerably enhances their incorporation into cellulosic insulation especially from an economic standpoint. An exception applies-in the case of ammelide whose solubility is somewhat less than that of the other stabilizing compounds of the invention. It is to be also noted that these compounds exhibit substantial insolubility in oil which facilitates their use in an electrical apparatus employing an oil type liquid dielectric. Obviously if the compounds were soluble in such dielectrics they would tend to be depleted from the insulation by dissolution into the dielectric.

Several factors are involved in obtaining the benefits of the invention. First, the chemical stabilization compounds must be present in the cellulosic insulation in amounts within the range of about 0.02% to about 10% by weight based on the weight of the cellulosic material.

It has now been discovered that there are certain com- -i properties are not only apparent in the presence of liquid dielectrics but are obtained as well when the insulation is employed in an atmosphere of air or other gas.

. Accordingly, a primary object of the invention is to provide a stabilized cellulosic electrical insulation characterized by both improved thermal stability and im-.

proved dielectric integrity.

-A further object of the invention is the provision of improved cellulosic electrical insulation containing effect ve amounts of certain chemical stabilizing compounds.

Less than .02% stabilization compounds do not impart to the insulation any appreciable improvement in either electrical insulation or mechanical strength at elevated temperatures. The presence of more than about 10% of r the compounds is uneconomical and does not appreciably increase the degree of improvement beyond that obtained with 10%. Within this broader critical range it is preferred to employ about .5 to about 5% of the stabilization compounds, these amounts having been found to impart the optimum desired improvements in the electrical insulating and thermal stability properties of the cellulosic insulation.

Second, the stabilizing compound or compounds, it more than one is used, must be present in substantially uniform distribution, intimately present throughout the interstices of the fibers comprising the cellulosic insulation, to obtain optimum benefits. This requirement is readily satisfied because of the fact that (1) all of the members of the group of stabilizing compounds of the invention excepting to some degree ammelide, are substantially soluble in water or water alcohol solutions thus facilitating uniform and thorough incorporation into the cellulose insulation from 'such solutions, and (2) these v, compounds are substantially oil insoluble thus preventing depletion of the uniform distribution of the stabilization compound in the cellulosic insulation in the presence of oil type dielectrics. To maintain the high dielectric properties and mechanical strength it is requisite that the stabilizing compounds be closely associated at all times with the cellulosic fibers to obtain the hereinbefore discussed benefits particularly where the insulation is to be immersed in a liquid dielectric such as oil during use. Where, for example, the stabilizing materials are merely suspended in the dielectric, an extended period of time elapses before the stabilizers permeate the cellulosic insulation and function at maximum effectiveness.

As mentioned hereinbefore since. substantially all th members of the group of stabilizing compounds in the invention possess a suitable degree of solubility in water or water-alcohol mixtures, they may be desirably incorporated in the insulation during its manufacture or fabrication. In the case of paper insulation, particularly, incorpassed between calendar rolls to impart a particular surface finish or density and finally it is rolled for storage and shipment. Also, generally, the drier is split so that the paper web is partially dried in the first portion thereof and is finish dried in the second portion. Between these two drying sections of heated rolls a tank is positioned for application of sizing materials to the paper.

In practicing the present invention with respect to paper insulation the stabilizing compounds, in substantially aqueous solution, are present in the conventional sizing tank. The partially dried paper is passed through the aqueous solution and, by means of appropriate adjustments in the concentration of the solution, the paper absorbs a predetermined amount of stabilizing compounds. In this respect it is to be noted that it may be necessary to adjust the temperature of the solution in order to obtain desired concentration. Usually solution temperatures of about 60 to 90 C. are adequate to produce a suitably concentrated solution. After this treatment the paper passes through the second portion of the drier. The temperature of the rolls is determined by trial so as to obtain suflicient paper drying and avoid sticking to the calendar rolls. The process is applicable to either the Fourdrinier or cylinder type paper-making machine. The dried paper contains the stabilizing compounds uniformly distributed throughout its interstices.

-In order to more fully describe some of the benefits obtained by practicing the invention reference should be had to Table I which lists mechanical strength retention of treated paper for the stabilization compounds of the invention together with the mechanical strength retention for untreated kraft paper for comparison purposes. In each case, 3% by weight of the particular stabilizing compound was added to kraft paper during its manufacture. In most instances the paper was about 5 mils thick and had a density of approximately one. Each of the samples of paper was wound with enameled wire into a coil and sealed in a tank filled with transformer oil. Strips of transformer core iron were also placed in the tank. Suflicient current was circulated through the coil to generate temperatures of 140 C. The coil unit was removed after seven days and a Mullens bursting strength test run on the aged paper. Table I lists the percent strength retention of the aged sample as compared to the pro-aging Mullens bursting strength. It is to be noted that there is some direct relation between mechanical strength retention and dielectric integrity retention for the cellulosic materials of the invention in that where the treated cellulosic material exhibits a high retention of mechanical strength, such 4 as the treated paper indicated in Table I, it also exhibits corresponding high retention of dielectric integrity.

TABLE I Stabilizing agent: Percent retention *1,S-dihydroxyanthraquinone 87 *p-Phenylazoaniline 86 Ammelide 85 *1,3-dimorpholino-2-pr-opan0l 94 *Triallylcyanurate 96 2-aminothiazole 85 *Polyvinylpyrrolidone 88 The asterisks in Table I indicate preferred stabilizing compounds since the paper treated therewith retains over 85% of its original Mullens bursting strength. Good stabilization of paper insulation will be obtained when the paper contains as little as 0.02% to as much as 10% of these stabilizers.

As an illustrative example of an embodiment of the stabilizing compounds of the invention in an electrical apparatus, a transformer is wound in a manner as illustrated in FIG. 1 using paper treated in accordance with the invention containing 3% by weight of one or more of the stabilizing compounds disclosed in the invention.

Referring now to FIGURE 1, the numeral 10 represents the treated kraft paper which is wound around the individual coils and which is wound between the high and low voltage coils of the transformer. Thus, the transformer coil comprises low voltage coils 14 and 16, as well as high voltage coils 18, 20 and 22,v insulated by layer-tolayer application of the treated paper. In addition, the low voltage coil 14 is insulated from the treated windingtO-Winding by insulation 24. The electrical conductors employed may comprise enameled wire which resists softening at temperatures of up to 250 C. Suitable enamels are epoxy resin enamels, polyester resin enamels such as isophthalateglycol-maleate resins, silicone modified enamels and polyvinyl formal-phenolic resin enamels.

These enamels may be applied directly on top of wire or may be employed with asbestos or glass fiber wrapping or other fibrous materials. In the finished transformer, a liquid dielectric such as oil or a chlorinated aromatic dielectric, will fill the channel 26 and will, as well, completely permeate the paper insulation. Subsequent to being wound and assembled the entire assembly is vacuum treated to remove air and moisture from the paper and the coil is thereafter baked to eliminate fully any moisture.

Referring to FIGURE 2, a transformer is prepared in accordance with the present invention. The transformer comprises a tank 28 carrying a support 30 internally on which magnetic core 32 and a coil 34 are disposed. Coil 34 comprises a high voltage winding 36 and a low voltage winding 38, each insulated with a wire enamel composition which resists softening at temperatures up to 250 C. The turns of the windings 36 and 38 are insulated by Wrappings comprising the stabilized cellulosic insulation of the invention. The windings are also insulated from one another by stabilized cellulosic insulation 40, prepared according to the present invention, which comprises paper, cotton or other cellulosic insulation. An exterior cellulosic wrapping 42 of cloth or paper may be applied to the coil 34. In some cases, pressboard, wood or cardboard spacers or various other cellulosic products may be applied to the electrical windings. A liquid dielectric 44 is disposed within the tank 28 to cover the core 32 and coil 34 in order to insulate them and to dissipate the heat produced in operating the transformer. The treated cellulosic materials of this invention retain their dielectric properties and mechanical strength when in contact with a liquid dielectric containing a small amount of an oxidation inhibitor, such as p-tert-butyl phenol.

FIGURE 3 illustrates an electrical conducting cable comprising an electrical conductor 50 having cellulosic sheath covering 54; The cellulosic insulation 52 is stabilized material which has been treated according to the present invention.

It is to be noted with regard to the application of the invention to transformers that transformer construction may be more solid and tighter because the treated cellulosic spacers and other components will lose less than half the thickness loss on thermal aging exhibited by untreated pressboard, kraft paper or other cellulosic materials.

It has also been found that where certain properties are desired, such as higher initial tensile strength of cellulosic insulation and waterproofness, that certain resins can be incorporated in the paper in the process of beating the pulp. These resins can be introduced in finely divided or emulsified form in the beating of the pulp or they can be introduced later from organic solution. Small amounts of up to several percent of resins such as phenolic, epoxy, acrylic, diallylphthalate, etc., have been found to be compatible with the stabilizing compounds of the invention and further enhance mechanical, electrical and thermal stability in the finished product.

It is to be noted that the cellulosic insulation stabilizing compounds of the invention may be used singly or in combination with one another, or further, in combination with these or the stabilizing compounds disclosed in co pending patent applications Ser. No. 164,113, filed Jan. 3, 1962 and Ser. No. 839,166, filed Sept. 10, 1959 and its continuation-impart Patent 3,102,159 issued Aug. 27, 1963, or application Ser. No. 319,387 (Westinghouse Case 34,984), filed concurrently herewith.

It is to be understood that the above description and drawings are illustrative and not in limitation of the invention or its application.

What is claimed is:

1. An improved sheet cellulosic product having increased stability and resistance to thermal deterioration and particularly adapted for use in electrical apparatus in combination with a fluid dielectric impregnant in contact with the cellulosic product, the cellulosic product comprising cellulosic fibers in sheet form, the sheet having uniformly distributed therethrough from about 0.02% to about by weight based on the weight of the cellulosic fibers, of at least one stabilizing compound selected from the group consisting of 1,5-dihydroxyanthraquinone, p-phenylazoaniline, ammelide, 1,3-dirnorpholino-Z-propanol, triallylcyanurate, 2-arnino-thiazole, polyvinylpyrrolidone.

2. The improved sheet cellulosic product of claim 1 having increased stability and resistance to thermal de terioration and particularly adapted for use in electrical apparatus in combination with a fluid dielectric impregnant in contact with the cellulosic product wherein the sheet has uniformly distributed therethrough from about .5 to about 5% by weight based on the weight of the cellulosic fibers, of at least one stabilizing compound selected from the group consisting of 1,5-dihydroxyanthraquinone, p-phenylazoaniline, ammelide, 1,3-dimorpholino- 2-propanol, triallylcyanurate, 2-aminothiazole, polyvinylpyrrolidone.

3. 'In an electrical apparatus comprising in combina tion a container and disposed therein an electrical conductor winding provided With a hard, tough flexible enamel coating which resists softening at temperatures up to about 250 C. and cellulosic electrical insulation substantially disposed around the winding, the improvement which comprises providing from about 0.02% to 10% by weight, based on the weight of the cellulosic electrical insulation, of a stabilizing compound, the stabilizing compound being uniformly distributed throughout the cellulosic electrical insulation, and a liquid dielectric consisting essentially of a petroleum hydrocarbon oil in the said container surrounding at least part of said electrical conductor winding and substantially completely permeating said cellulosic electrical insulation,

the said stabilizing compound serving to improve the resistance of the cellulosic insulation to thermal deterioration when heated in the presence of the said liquid dielectric, the said stabilizing compound comprising at least one compound selected from the group consisting of 1,5- dihydroxyanthraquinone, p-phenylazoaniline, ammelide, 1,3-dimorpholino-Z-propanol, triallylcyanurate, 2-aminothiazole, polyvinylpyrrolidone.

4. The improvement for electrical apparatus of claim 3 wherein the said liquid dielectric contained in said electrical apparatus contains an oxidation inhibitor.

References Cited OTHER REFERENCES The Condensed Chemical DictionaryfiSixth edition, Reinhold Publ. Co., N.Y., 1962, QDSCS, page 900.

LEWIS H. MYERS, Primary Examiner.

D. A. KETTLESTRINGS, H. HUBERFELD,

Assistant Examiners.

Claims (1)

1. AN IMPROVED SHEET CELLULOSIC PRODUCT HAVING INCREASED STABILITY AND RESISTANCE TO THERMAL DETERIORATION AND PARTICULARLY ADAPTED FOR USE IN ELECTRICAL APPARATUS IN COMBINATION WITH A FLUID DIELECTRIC IMPREGNANT IN CONTACT WITH THE CELLULOSIC PRODUCT, THE CELLULOSIC PRODUCT COMPRISING CELLULOSIC FIBERS IN SHEET FORM, THE SHEET HAVING UNIFORMLY DISTRIBUTED THERETHROUGH FROMABOUT 0.02% TO ABOUT 10% BY WEIGHT BASED ON THE WEIGHT OF THE CELLULOSIC FIBERS, OF AT LEAST ONE STABILIZING COMPOUND SELECTED FROM THE GROUP CONSISTING OF 1,5-DIHYDROXYANTHRAQUINONE, P-PHENYLAZOANILINE, AMMELIDE, 1,3-DIMORPHOLINO-2-PROPANOL, TRIALYLCYANURATE, 2-AMINO-THIAZOLE, POLYVINYLPYRROLIDONE.

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