US2337920A - Insulated conductor - Google Patents

Description

Dec. 28, 1943. J. R. PATTERSON ET AL 2,337,920

INSULATED CONDUCTOR Filed Nov. 28, 1939 FABRIC I/ARN/SHED WITH RES/N01,? REACT/0N PRODUCT OF PENTAER l/R/TOL FATTY OIL. ACID AND POLYSAS/C ACID PROTECTIVE COVERING OF COTTON BRA/D Inventors. James Q. Patterson, James Q. Qeid, Harry A. Lethe on,

heir Attqrney.

Patented Dec. as, 1943 INSULATED CONDUCTOR James R. Patterson, Scotia. and James B. Reid and Henry A. Letteron, Schenectady, N. Y., asslgnors to General Electric Company, a corporation of New York Application November 28, 1030, Serial No. 300,520

1 Claim. (01. 174-121) This invention relates to insulated electrical cables and more particularly is concerned with an improved electrical insulation of the varnished cambric type.

Insulated electrical cables or conductors have previously been prepared in which all or part of the insulation is made up of varnished fabrics, as for example, a fabric coated with a composition containing the usual alkyd resins composed of g-lycerine, phthalic anhydride and fatty oils or acids. However, these insulated cables have not been wholly satisfactory-primarily because of the high power factor of these varnished fabrics at elevated temperatures.

We have now discovered that insulated cables of improved electrical properties maybe obtained if the insulation thereon comprises a fabric varnished with a composition comprising the resinous reaction product of pentaerythritol, a monobasic organic acid, specifically the acids of drying, semi-drying or non-drying oils, and, in addition, a polybasic organic acid or anhydride such as maleic, phthalic, etc. The low loss insulation of this invention is characterized by a high dielectric strength of above 1000 volts per mil, and a low power factor not only at ordinary temperatures but also at such a high temperature as 100 C. The varnished fabric is smooth-surfaced and has excellent resistance to oil, moisture, abrasion and aging. The resin film contained therein is hard, flexible and tough.

In the accompanying drawing, we have illustrated one form of our invention in which a conductor l is provided with one or more layers of our low power factor insulation 2 and an outer protective covering of cotton braid 3, preferably varnish treated. It is to be understood, however, that our invention is not limited to this particular cable structure. The outer covering may suitably consist of a layer of metal such as a lead sheath or strands of wrapped or woven steel wire or the like. Again, other insulating materials than those mentioned above may be used. For certain applications, it may be desirable to cover or coat the conductor with a layer of asbestos, cotton thread, rubber, or an enamel before applying the varnished fabric. Or the conductor may be provided with altemating coverings of the varnished fabric and any of these insulating materials.

In order that those skilled in the art better may understand how the present invention may be carried into effect, the following specific examples are given for the purp se of illustrating the preparation of the varnish and the varnished fabric:

1 hour. The temperature is raised to about 235 to 250 C. and the resin cooked to an acid number of about 5. The resulting resin is dissolved in a suitable solvent, for example petroleum spirits, in ratios such as to yield a varnish of the desired viscosity. Usually the varnish contains from about 50 to per cent by weight of solids. Driers are added and the resulting varnish is applied to cloth or other flexible material in accordance with conventional practice. The coated cloth is usually baked to harden the coating, but it can be air dried. The electrically insulating tapes or sheets are made by cutting the dried cloth to the desired width and are applied as conductor insulation in the usual manner.

All the ingredients except the maleic anhydride are placed in a kettle and heated for about 1 hour at approximately to 200 C. The maleic anhydride is added and the batch is held at 190 to 200 C. until a clear pill is produced. The temperature is now raised to about 235 to 250 C. and cooking continued until a resin having an acid number of about 5 is obtained. The maleic anhydride is not added until the other ingredients have partially reacted, whereby a clear homogeneousresin will be produced. The varnish and the coated fabric insulation are made from this resin in substantially the same manner as described under Example 1.

Maleic anhydri 4 Essentially the same procedure is followed as described under Example 2.

Example 4 Parts by weight Pentaerythrltol 13.9 Soya bean oil fatty acids 81.2 Maleic anhydrlde 4.9

The procedure is essentially the same as described under Example 2.

Example 5 Same as Example 4 with the exception that linseed oil fatty acids are used instead of soya bean oil fatty acids.

It is of course understood that our invention is not limited to the specific ingredients other than pentaerythritol named above in the illustrative examples. For example, as monobasic carboxylic acids, we may use in addition to those mentioned above the fatty acids of China-wood oil, perilla oil, fish oil, oiticica oil, etc., or mixtures of such acids. As polybasic carboxylic acids or anhydrides, we may use in addition to those mentioned above such acids or anhydrides as, for instance, malonic, succinic, glutaric, adipic,

pimelic, suberic, sebacic, fumaric, etc., or mixtures of such acids or anhydrides. Maleic acid or anhydride is particularly suitable for use because it provides a further improvement in the power factor of the finished product. Especially good results also are obtained by using mixtures of maleic acid or anhydride with other polybasic organic acids or anhydrides. The term acid" as used broadly in the appended claims is intended to include within its meaning the anhydride of the acid.

In making the varnish, the resinous composition may be thinned with any suitable solvent, for example turpentine, coal tar solvents, petroleum hydrocarbon solvents, etc. Any suitable drier and in any convenient form may be used, for example the naphthenates, linoleates or resinates of metals such as calcium, manganese, lead, cobalt, zinc and iron.' The percentage of drier required may be varied to suit manufacturing requirements for producing dry cloth or other material in a minimum of time. Or, in some cases, the drier may be omitted.

The method of combining the various ingredients maybe varied in many ways. For example, the temperature and time of heating required for obtaining a particular resinous composition may be varied in accordance with the differences in the properties of the starting materials.

To form the sheet electrical insulation, the liquid coating composition or varnish is applied to textile or other fibrous materials (e. g., cotton, linen, fiber-glass cloth or fabric, etc.) by brushing, sprinkling, spraying or, preferably, by immersion means and under temperature and other conditions well known to those skilled in the art. Upon heating the coated and impregnated material at a temperature of about 110 C. or thereabove, the solvent is evaporated and an insulating material of low power factor at normal and at elevated temperatures is produced. It is permanently flexible, is highly resistant to oil, moisture and aging, has a high dielectric strength and a high tear strength. It has good smoothness or slip and is highly resistant to heat. In testing for heat resistance a sample of the varnished cloth is, heated in a suitable oven at a temperature of about 125 C. and tested for cracking of the resin film at the end of varying periods of time. This is done by wrapping the cloth around a mandrel of suitable size, for example 0.125 inch in diameter, and noting whether or not the resin film has cracked. varnished materials of this invention will stand heating at this temperature for from 800 to 1000 hours without cracking of the resin film when tested in the described manner, whereas fabrics coated with the ordinary alkyd resin varnishes when similarly tested show cracking of the film in approximately 400 hours.

The surprising reduction in power factor obtained by using the pentaerythritol resins instead of glycerol resins is shown by the following comparison of power factors of cloths varnished with resins made with pentaerythritol and glycerol:

Power factor at- Type of polyhydric alcohol used in making the resin The series 1 resins were prepared from Parts by weight Parts by weight Glycerol 18 Pentaerythritol 20 Soya bean oil fatty acids 60 60 Phthalic anhydride 19 17 Maleic anhydride 3 3 The power factor of the materials of this invention generally does not exceed substantially 10 per cent at 100 C. and usually is considerably less, for instance from 5 to 8 per cent As previously described, this low power factor, in

combination with the other desirable properties,

especially adapt these products for the purposes of this invention, that is, for cable insulation, in insulating electrical coils, and the improved physical and electrical properties are imparted to these electrical structures. The products may replace ordinary varnished cambric in any of its applications to produce an insulation characterized by a high dielectric strength and outstanding resistance to oil, moisture, abrasion and aging.

What we claim as new and desire to secure by Letters Patent of the United States is:

An insulated conductor insulated with a flexible heatand age-resistance varnished sheet material consisting of a fibrous sheet varnished with the resinous heat-reaction product of a mixture of ingredients consisting by weight, of about 19 parts pentaerythritol, 60 parts cottonseed oil fatty acid, 18 parts phthalic anhydride, and 3 parts maleic anhydride, the said resinous product having an acid number of about 5 and the said varnished sheet material having at a temperature of 100 degrees C. a power factor not exceeding substantially 10 per cent.

JAMES R. PATTERSON. JAMES R. REID. HENRY A. LE'ITERON.

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