US2190018A - Impregnated paper insulation for electric cables - Google Patents

Description

A Feb. 13, A1940.

W. A. DEI. M AR 2,190,018

IMPREGNATED PAPER INSULATIONY FOR EI'JhC'l'vllICy CABLES Filed Aug. 22, 193s ATTORNEY Patented Feb. 13, 1940 UNITED STATES IMPREGNATED PAPER INSULATION FOR ELECTRIC CABLES Application August 22, 1939, Serial No. 291,313

4 Claims.

My invention relates to paper insulated cables, more particularly to impregnated paper insulation; and has for its object to produce a cable oil which is non-sludging and will not crystallize out, be light colored and possess valuable electrical characteristics not heretofore attained with rosin or other similar resins.

In preparing electrically insulated cables, it is customary to wrap the conducting metal wire with suitable paper or 'cellulosic material which has been impregnated with what is known as cable oil. This cable oil may be a solution of rosin in a petroleum oil. 'Bhs oil must not sludge out nor separate on standing and it must be stable under conditions of preparation, storage and impregnation of paper. Wood rosin, although soluble in paraiiin or naphthenic petroleum oils, often sludges out and/or crystallizes out on standing. This wood rosin is a commercial form of abietic acid and when used in cable oil itsfunctions are to assist the oil in "wetting the paper fibers, to increase its viscosity and to render the oil more stable under the influence of electrical discharges. Rosin, however, has the effect of in' creasing the power factor of the oil at high temperatures and consequently ofthe cable, at the higher operating temperatures. I have discovered that by substituting for rosin, a hydrogenated product of rosin, a low power factor of the oil is attained at all temperatures and that in addition, the stability of the oil under the influence of electrical discharges, isl greatly improved. This is particularly true with respect to power factor stability. For instance, one batch of bright stock paranin base oil was mixed with 15% rosin and another with 15% hydrogenated rosin. Both werev subjected to electrical bombardment in a Nederbragt cell, as described in Trans. A. I. E. E., 1937, vol. 56, pp. 1302-3, for 450 minutes and the power factor measured before and after. 'I'he results were as follows:

Power factor at 100 C.

Oil with addition of- Before bom- After bombardment bardment 100 C'., 60 C'. 100 C. 60 C. Wood rosin 6. 50 l. 50 10.00 0. 70 Hydrogenated rosin 0. 55 0.05 l. 55 0. 13

Stability tests in the Nederbragt cell also give a measure of the relative merits of oils with respect to evolution of These tests show that hydrogenated rosin 'materially retards the evolution of gas. For ingas under electric stress..

(Cl. 15b-2.6)

stance, the addition of 15% by weight of hydrogenated rosin to the oil described above reduces the gas evolution to 77% of the amount with pure oil. In this respect, however hydrogenated rosin is somewhat inferior to wood rosin, the corresponding figure for which is 69%.

In Figure l, I show a Nederbragt cell test curve recording the gassing characteristics in relation to the per cent of hydrogenated rosin. It will be noticed that the stability against gassing in- 1Q creases with the proportion of hydrogenated rosin. The curve shows the gassing in a 450 minute run under glow discharge. Temperature of test=30 C., initial carbon dioxide gas presr sure=l.0 millimeter of mercury, sixty cycle cur- 1 rent=1.0 milliampere.

The use of hydrogenated rosin, however is not merely a substitution of hydrogenated rosin for ordinary rosin. The latter material increasesl oil stability with increasing proportion of rosin up to at least 35%. Only the excessive viscosity of the compound limits the proportion to around 15%. Hydrogenated rosin, however, if used on this basis would lead one into trouble as we have found that its usefulness as a stabilizer is confined to a narrow range, as shown by Figure 2 which shows a curve giving'the relation between the power factor stability of oil compound in the Nederbragt cell test and the proportion of hydrogenated rosin used in the oil. The power factor stability is indicated by the rise of power factor, measured at C., produced by subjection to electrical discharge in the cell. The narrow dip in the curve corresponds with the stable range of proportions of hydrogenated rosin. I therefore make my cable with the proportions of hydrogenated rosin corresponding with the dip in the curve.

Taking into account all the properties of the materials, I prefer to use 10% hydrogenated rosin and of oil, but I obtain satisfactory results with proportions from 5 to 20% of hydrogenated rosin.

Cables made with 10% hydrogenated rosin compound have been subjected to accelerated aging tests in comparison with cables made with 15% wood rosin compound and as expected from the Nederbragt cell tests, the cable power factor readings show a greatly enhanced stability. While the rise of power factor in the rst ten load cycles does not differ very greatly from that with wood rosin, subsequent load cycles show a much less rise of power factor.

Furthermore the cable goes through many more load cycles before failure. In a vtypical load cycle accelerated laging test, cable made with oil and wood rosin passed 2% power factor after 27 load cycles and failed at about 30 load cycles. Cable with hydrogenated rosin in the oil, but otherwise identical has attained a power factor of only 1% after 80 load cycles, Without any sign of injury. A remarkable fact is that while the power factor of the cables with rosin kept on rising until failure, those with hydrogenated rosin have maintained a practically constant power factor from the 30th to the 80th load cycle, indicating not only greater relative stability but something approaching absolute stability, something quite unprecedented with cables outside of the oil-lled and pressure types.

I claim: '1. An impregnated paper used for electric insulation for cables, comprising a. paper impregnated with oil containing in solution from 5 to 20 per cent of hydrogenated wood rosin.

2. An impregnated paper used for electrical insulation for cables comprising a paper impregtion from 5 to 20% of hydrogenated Wood rosin., u

WILLIAM A. DEL MAR.

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