DE1300825B - Stabilizing agent for electrical insulating material - Google Patents

Description

Cellulosic materials, e.g. B. paper, cotton fabric, cotton ribbon, Press plates and wood have long been used for insulation in the electrical industry used in various parts of electrical apparatus. Such materials are particularly due to their economic advantages compared to others available materials a cheap starting material for electrical insulation. Furthermore, the cellulose insulation has adequate physical properties and initially a satisfactory dielectric strength.

Cellulosic materials, however, quickly degrade at temperatures above 100 ° C when they are in contact with air, and this is deterioration even more pronounced in the presence of a liquid dielectric. Both the physical as well as the electrical properties are influenced. The result is that the insulation quickly loses its electrical insulating strength and its mechanical Strength is deteriorated.

The electrical and thermal properties of cellulosic materials, such as B. Paper, cotton fabric, cotton tape, and wood deteriorate quickly at temperatures above 100 ° C when in contact with air or a liquid Are dielectric. For example, paper retains after only a few weeks was immersed in highly purified transformer oil at 120 to 150 ° C, only one few percent of its original dielectric strength and practically nothing of its original tensile strength. In general, a layer of fresh electric kraft paper must be bent several hundred times before it breaks. However it already breaks after just a few days in transformer oil at 150 ° C was submerged in the places where it was double folded. In these cases, im individual has been stated that in electrical apparatus which has a cellulose insulation the prevailing working temperatures should not exceed 105 ° C.

It has been found that certain nitrogen-containing organic compounds with one or more nitrile groups, which have a stabilizing effect on cellulose paper act, not only improve the thermal stability of a cellulose insulation, but, surprisingly, the insulation also has excellent electrical properties to lend. The favorable properties do not only occur in the presence of a liquid Dielectric on, but are also preserved if the insulation is in air or another gas is used.

It is known that the hydroxyl groups of cellulose are known as pulp of wood fibers, cotton fibers or the like. Is used, etherified by acrylonitrile can be. That formed by cyanoethylation, a chemical reaction Cellulose derivative is said to have increased dielectric strength.

The invention now relates to the use of 0.02 to 10 percent by weight, based on the cellulose material used, a nitrogen-containing organic one Compound of the general formula X-R-CN in which R is an alkyl, alkoxy, alkoxyalkane radical or an aromatic or substituted aromatic radical and X = H or CN means, which are preferably in aqueous solution, in a carrier made of a cellulosic material is incorporated in a manner known per se during manufacture, as a stabilizing agent for electrical insulation material based on cellulose. The stabilizing ones Compounds are finely distributed in the fiber interstices and from the cellulosic material adsorbed. The cellulose-based electrical materials stabilized according to the invention are characterized by improved thermal resistance and excellent electrical Properties.

The invention is explained in more detail with reference to the drawing.

F i g. 1 is a graphical drawing plotting Mullen's burst strength versus aging, measured in days, of stabilized and unstabilized Kraft paper in transformer oil at 150 ° C. The curve "A" applies to Kraft paper to which no stabilizing compounds have been added. The curve “B” shows the aging resistance of Kraft paper to which succinonitrile has been added according to the invention.

F i g. 2 is a graph of dielectric strength; which stabilized and non-stabilized kraft paper aged in transformer oil retained at 150 ° C. The curve "A" applies to untreated Kraft paper that Curve “B” for Kraft paper to which succinonitrile was added according to the invention, and the curve "C" for Kraft paper, the dicyandiamide according to the invention and succinonitrile were added.

F i g. 3 is a perspective view, partly in section, of one Transformer core which insulates with the cellulose insulation according to the invention is.

According to the present invention it is possible to adjust the time of residence greatly increase, with the dielectric strength and mechanical strength the cellulose insulation at elevated temperature both in gases and in one liquid dielectric is retained. The cellulose-based electrical insulation material contains the stabilizing agent according to the invention evenly and everywhere in the Distributed intermediate layers. Little of the compounds are used. Through her However, cellulose insulation is now very much improved in terms of physical and physical properties given electrical properties.

Suitable nitriles correspond to the general formula X-R-CN wherein R is an alkyl, alkoxy, alkoxyalkane radical, an aromatic or substituted aromatic Radical and X = H or -CN. Nitriles and their substituents are particularly suitable are hydrophilic so that they are soluble in water and relatively insoluble in oil. Dinitrile proved to be particularly beneficial. Particularly suitable nitrogen-containing compounds are also cyano compounds, such as. B. butyl nitrile, octyl nitrile, isooctyl nitrile, Adiponitrile, malononitrile, isophthalonitrile, succinonitrile, p-aminobenzonitrile, ß-ethoxypropionitrile and benzyl nitrile as well as the simple substitution products of these compounds containing, for example, alkyl groups on the benzene ring of the aromatic compounds.

It has surprisingly been found that the dielectric Strength of paper or other cellulosic material, e.g. vulcanized Hard fiber, which according to the invention with one or more of the above-mentioned compounds is treated and in a dielectric liquid, for example in a hydrocarbon oil or in chlorinated diphenyl, is not only better than that same untreated paper, but also the temperature resistance increases. the dielectric strength also increases and peaks at one Temperature from 125 to 150 ° C and also higher. With untreated paper, the dielectric strength to decrease rapidly, already at a temperature of 25 to 50 ° C below the temperature at which the peak of dielectric strength of the treated paper.

The power factor of treated cellulose insulation, immersed in a liquid dielectric, is inferior to that of a similar paper, which has not been treated that way. This applies to a wide area. Further come Reducing agent before if the liquid dielectric is an oil, which antioxidants contains, such as B. alkylated phenols, e.g. B. p-tert-butylphenol and dibutylp-cresol in amounts of 0.01 to 4% or more. The treated paper shines through its presence such inhibitors to be favorably influenced. A synergistic working together Improvement takes place when the nitrile treated paper is in contact with it.

Such was the power factor of a purified, uninhibited hydrocarbon oil with Kraft paper dipped in it originally 0.008% and the color "1" according to the Lovibond scale. After one year at 95 ° C, the power factor was 0.29% and the color »5-f-«. If the oil was inhibited and the Kraft paper untreated, so After one year at 95 ° C the power factor was 0.36% and the color "5-".

In the case of Kraft paper treated with nitriles according to the invention, After a year at 95 ° C the color was about "31/2" and the power factor 0.1 to 0.05.

Particular advantages are achieved when the chemically stabilizing Compounds in the cellulose insulation in a total amount of about 0.02 to 10 percent by weight are present based on the weight of the cellulosic material. Less than 0.02% of one or more of the compounds imparted cellulose insulation no notable improvement in electrical insulation or mechanical strength with aging at elevated temperatures or with exposure elevated temperatures. The presence of more than about 101% of the compound is uneconomical and does not increase the degree of improvement obtained with 10% will. Within the range mentioned, it was found to be particularly favorable, 1 to 5 percent by weight of the nitrogenous compound to be used. It was found, that these amounts in the cellulose insulation the thermal stability of the electrical Significantly improve cellulose insulation.

Furthermore, the stabilizing compound or compounds must be in essentially the same distribution and uniformly present everywhere around a cellulose insulation with optimal effect. This requirement is easy to meet as everyone eligible stabilizing compounds used according to the invention easily are water soluble and essentially oil insoluble. To the good dielectric To obtain properties and high strength, it is necessary that the stabilizing Connections are firmly and stably connected to the cellulose fibers. Just be like that the advantages described here first achieved, especially when the isolation into a liquid dielectric, e.g. B. oil, is immersed during use. For example, if the stabilizing materials are only suspended in the dielectric a large period of time elapses before the stabilizers stabilize the cellulose penetrate and develop the maximum effectiveness. This was the case with urea or similar materials disclosed in U.S. Patent 2,722,561 are. Here the stabilizing compounds are used as a dry powder of insulation, for example a transformer coil added during winding. The advantages of the present invention are thus not achieved.

Since the compounds with a stabilizing effect used according to the invention (Nitriles) a suitable degree of solubility in water or water-alcohol mixtures they can be used with advantage in such solutions to improve cellulose insulation to penetrate completely during manufacture. In the case of a paper or Press plate insulation can easily incorporate the connection or connections take place in the paper machine. Paper is generally fed either on the Fourdrinier machine or produced on the cylinder board machine. After each procedure, the the endless web formed by the entangled cellulose fibers from the wire onto a belt headed to dry. The endless web is passed through a dryer, which includes a number of steam heated rollers. Then she can, if desired, between Calender rolls are directed to give it a special surface finish or Finally, it is rolled up for storage and shipping. in the In general, the dryer is divided so that the paper web in the first part is partially and in the second it is completely dried. Between the two heated rollers is usually a tank arranged with finishing material for the paper.

The stabilizing compound or compounds are according to the invention present in aqueous solution. They are added in the conventional size press. The partially dried paper is rendered more suitable by the aqueous nitrile solution Concentration directed. It adsorbs a specific amount of the stabilizing agent Link. After this treatment, the paper passes through the second part of the dryer. The temperature of the drying rollers is regulated so that there is a sufficient degree of drying achieved and a later gluing of the treated paper on the calender rolls ruled out. The process can be used in both Fourdrinier and cylinder board machines be performed.

The resulting dried paper contains the stabilizing compound evenly and intimately distributed in all spaces between the fibers. Because, as in the case of Succinonitrile, the water solubility of the stabilizing compound increases with the temperature of the water, it may be desirable that solution to heat and saturate so that the concentration of succinonitrile is high, whereby it is achieved that the paper passes a certain amount of the compound. In general, temperatures of 60 to 90 ° C are appropriate.

In order to show more clearly the advantages achieved with the invention, the following examples are given.

In each example, 3 percent by weight of the stabilizing compound was added to the kraft paper during its manufacture. In all examples the paper was 0.75 mm thick and had a density of approximately 1. Each of the paper swatches was wound into a spool with lacquered wire and placed in a tank filled with transformer oil. Enough current was passed through the coil to generate temperatures of 140 ° C. The spool was removed after 7 days and a Mullens burst strength test was performed on each sample of the aged paper. The following table shows the Mullens burst strength values before and after the test. Retained Stabilizing Mullens Burst Strength mean in percent before I after (retention) None (100o / o power paper) ......... 73 18 24.6 Succinonitrile ....... 52 50 96-f- p-aminobenzonitrile 65 59 91 ß-ethoxypropionitrile 61 54 90 ß, ßi-iminodipropio- nitrile ........... 58 58 100 Diethylaminoaceto- nitrile ........... 64 55 86 a-hydroxyisobutyro- nitrile ........... 59 50 85 From the preceding physical data it can be seen that the Kraft paper, which contains no stabilizing agent, only retains 24.6% of its original strength. The nitriles impart such resistance to aging to the treated kraft paper that the treated paper has 85% or more of its original burst strength. From Fig. 1, which lists the results of other similar tests, it can be seen that even after 28 days of aging, by immersion in oil, the succinonitrile treated paper retained approximately 80% of its original burst strength, while the untreated Kraft paper only retained about 3%. retained.

Tests were made of the dielectric strength of the nitrile treated Made of paper. From Fig. 2 it can be seen that the nitrile treated Kraft papers have greatly increased dielectric strength with increasing temperatures in comparison to an untreated Kraft paper.

Using the same treated paper containing approximately 3% succinonitrile, a transformer coil was wound as shown in FIG. 3 shows. Figure 10 shows the treated Kraft paper wrapped around the individual coils and between the high and low voltage coils of the transformer. The transformer coil thus consists of low voltage coils 14 to 16 and high voltage coils 18, 20 and 22. They are isolated by placing one layer on top of the other of the treated paper. The low-voltage coil 14 is insulated with the treated paper by wrapping the insulation 24 in layers. The electrical conductors used can consist of coated wire, which does not soften up to temperatures of 250.degree. Suitable paints are epoxy resins, polyester resin paints, for example those made from isophthalate glycol maleate resins, silicones and polyvinyl formalphenol resins. The lacquers can be applied directly to copper wire or to copper wire wrapped with asbestos or fiberglass or other fibrous material. In the completed transformer, a liquid dielectric will fill the channels 26 and also completely penetrate the paper insulation. The whole is vacuum treated to remove air and moisture from the paper, and the coil is then baked to completely remove any moisture.

The nitrile treated insulation of the invention makes the transformer stronger and denser because the treated cellulose liners and other components lose less than half the thickness on thermal aging than untreated ones Press plates, kraft paper and other cellulosic materials.

The paper or other cellulose products can contain up to small amounts 5% of one or more heat-stabilizing ones and the dielectric ones Strength-increasing materials such as B. melamine and dicyandiamide contain. The cellulosic materials can also be resins or binders, such as. B. polyacrylamide and melamine aldehyde resins.

Claims (2)

Claims: 1. Use from 0.02 to 10 percent by weight, based on on the cellulose material used, a nitrogen-containing organic compound of the general formula X-R-CN wherein R is an alkyl, alkoxy, alkoxyalkane radical or denotes an aromatic or substituted aromatic radical and X = H or CN, which, preferably in aqueous solution, in a carrier made of a cellulosic material is incorporated in a manner known per se during manufacture, as a stabilizing agent for electrical insulation material based on cellulose. 2. Use according to claim 1, characterized in that a carrier made of cellulose material is used, up to 5% of a material that is already heat stabilizing and the increases dielectric strength, contains.