OIL-IMPREGNATED PAPER Effect of Anhydrous Oxidation Products on Power Factor and Conductivity JOHN D. PIPER, D. E. F. THOMAS, A N D C. C. SMITH
Power factor and conductivity measurements were made on oil-impregnated papers contaminated with each of ten compounds selected to represent common types of oxidation products formed by oxidation of hydrocarbons. The oilsoluble compounds of medium and high molecular weight caused very little increase in either the power factor or the conductivity of the impregnated paper. The acids of low molecular weight, however, caused large increases in the power factor but only small increases in the conductivity of the impregnated insulation.
The Detroit Edison Company, Detroit, Mich.
ECENTLY the authors (2) described one phase of an investigation designed to determine which of the types of products that may be formed by service degradation of insulating oils cause serious dielectric losses in insulating oils a t 60 cycles, and which do not, The class of degradation products with which that phase of the investigation was primarily concerned was the oil-soluble oxidation products. It was found that moderately large quantities of many chemical types of oxidation products caused only small increases in the 60-cycle power factor and the d. e. conductivity of liquid paraffi as long as the oxidation products remained in solution in the oil. The present paper constitutes part of a similar but separate investigation concerning the effect of degradation products on oil-impregnated paper. As before, the primary interest is centered on oil-soluble oxidation products. During the course of the study several oil-insoluble oxidation products were also used. Data for these compounds are included for comparison with the data for the oil-soluble compounds.
The impregnating liquids were of three kinds: liquid paraffin alone, solutions of the several oil-soluble compounds in liquid paraffin, and emulsions of the oil-insoluble compounds in liquid paraffin. Relevant information concerning both the liquid paraffin and most of the compounds used in the preparation of the impregnating liquids was given previously (2). Similar information concerning four compounds used in this work, but not in the previous work, is given in Table I. The volume of the liquid used for impregnating each paper sample was approximately the same as that used in the investigation concerning liquids alone-that is, about 30 ml. The weight of dry paper in each sample was 14 grams. Thus the ratio between the weight of the impregnants (which had specific gravities slightly less than 0.9) and the weight of paper was nearly 2. Since in the insulation of high-voltage underground cables the "oil-paper ratio" is around 0.6, the results of the tests must be interpreted in the light of the purpose for which the work was intended-namely, to find which types of oxidation products cause appreciable increases in power factor and conductivity, rather than to estimate the quantitative effect produced by a given concentration of any definite compound.
Materials and Procedure The paper used in the tests was a highly calendered kraft paper of American manufacture, representative of the papers used in the manufacture of high-voltage underground cables. The paper was cut in strips of a uniform size. Each strip was wound tightly over the high-voltage electrode of the electrical-measurements cell which, with the details of the test procedure common to both studies, was described in the previous paper (2). The roll so formed was of sufficient length to cover the high-voltage electrode and of sufficient thickness (nine layers) to fit snugly between the high-voltage electrode and the cylinder constituting the measuring electrode with its guard rings. After the apparatus was assembled, the paper was dried for one hour a t 100" C . and a pressure of less than 1 mm. of mercury, which treatment was sufficient to dry the paper to constant power factor. These power factor measurements were made at atmospheric pressure attained by introducing dry nitrogen into the cell. The usual procedure for impregnating the paper was to invert the complete apparatus, prepare the impregnating liquid in the mixing bulb, evacuate the system, place the apparatus in an upright position in the bath which was controlled to 80" C., and, by slowly admitting dry nitrogen, sllow the impregnating liquid to enter the cell proper and impregnate the paper. When the test sample came to equilibrium, as indicated by constancy of the electrical measurements, the power factor and d. e. conductivity values were determined.
Effect of Acids of Different Molecular Weights The relative effect of each of five organic acid son the power factor of impregnated paper is shown in Figure 1. From the same figure a comparison can be made between the power factor of the impregnated paper and that of the impregnating liquid alone. For this comparison some of the data which were previously reported (2) have been replotted. In both Figures 1 and 3 some of the power factor data obtained a t 843
INDUSTRIAL AND ENGINEERIKG CHEMISTRY
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OF FOUR COMPOUNDS USEDWITH LIQUIDPARAFFIN TO FORM IMPREGNATING LIQUIDS TABLEI. DESCRIPTION
Name of Compound Acetic acid
Class of Oxidation Product Represented Acid of low molecular weight
Eastman Kodak Co., “Eastman” grade
Formic acid
Carboxylic acid of lowest molecular weight
Eastman Kodak Co., “Eastman” grade
tert-Amyl alcohol
Alcohol of medium molecular weight
Eastman Kodak Co., “Eastman” grade
Ethyl alcohol
Alcohol of low molecular weight
U. S. I. absolute, 99.8 to 100% (scientific)
Origin
60°, 40”,and 30” C . were not plotted. I n all these cases the values were below the respective values determined a t 80” C. Stearic acid, the compound chosen to represent the class of oil-soluble organic acids of fairly high molecular weight, was found to cause little increase in the power factor of impregnated paper (Figure 1 B). Similar observations had previously been made concerning the effect of stearic acid in the oil without paper (Figure 1 A ) .
Treatment Refluxed under reduced pressure over anhydrous CuSOa: distilled in same apparatus: melted, as used, a t 16.4’ C. (after crystallizing three times, melted a t 16.6’ C.) Crystallized from its own mother liquor 3 times in closed system into which it was distilled after drying as above: melted a t 8.4’ C . Dried over anhydrous CaS04, distilled under reduced pressure in all-glass apparatus Same as acetic acid
Solubility in Liquid Paraffin Entirely soluble a t all temperatures and concentrations used
Only slightly soluble at temperatures as high as 80’ C. Entirely soluble at all temperatures and concentrations used Sparingly soluble a t .the lower temperatures used
As an example of acids of medium molecular weight, mixed naphthenic acids were chosen. These acids were chosen instead of a pure chemical compound because among some cable research workers an opinion, apparently unpublished, was held that the presence of these acids in cable insulation was a major cause of high power factor. Like the stearic acid, however, the naphthenic acids used caused little increases in the power factor of either the oil or of the oilimpregnated paper (Figures 1 C and D). Propionic acid, the compound used to represent the class of acids of low molecular weight in the previous work ( X ) , was the first acid of low molecular weight investigated in the present study. It was found that propionic acid caused a marked increase in the power factor of the impregnated paper (Figure 1F ) , although it had previously been found that propionic acid had little effect on the power factor of the liquid paraffin alone (Figure 1 E ) . For this reason acetic acid was also studied. As shown in Figure 1 H , given concentrations of acetic acid caused the power factor of the impregnated paper to be even higher than for similar concentrations of propionic acid. Like the propionic acid and the other oil-soluble compounds, the acetic acid had only a small influence upon the power factor of the liquid paraffin when no paper was present (Figure 1 G). Since the effect of a given amount of acid seemed to increase with decreasing molecular weight of the acids, the carboxylic next acid of lowest molecular weight-formic acid-was selected for test. Although when carefully dried all the other acids used were readily soluble in liquid paraffin, formic acid was very sparingly soluble. Especially at the lower temperatures and higher concentrations the mixtures of formic acid and liquid paraffin formed visibly heterogeneous emulsions which had very high power factors as shown in Figure 1I. The power factors of paper impregnated with the emulsions of formic acid in liquid paraffin were very high a t first but decreased rapidly until equilibrium was reached, under which conditions the cloudiness of the excess oil above the paper had practically disappeared. The resulting values, though still high, were not nearly so high as those of the emulsions, and differed further from those of the emulsions in that the higher values were a t the higher temperatures. When the impregnation was carried out in the cell in the usual manner, there was a tendency for some of the formic acid droplets to be caught by a small part of the roll of paper near the inlet opening of the cell. For this reason the samples represented FIGURE 1. EFFECT OF ANHYDROUS ORGANICACIDS ON POWER in Figure 1 J were impregnated in a special apparatus which FACTOR OF LIQUID PARAFFIN AND LIQUIDPARAFFIN AND PAPER permitted the entire paper sample to come in contact with the emulsions a t practically the same time. After being * Previously reported ( 8 )
JULY, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
FIQURE 2. POWER FACTOR AT 80’ C. OF OIL-PAPER IN5ULATION CONTAINING EQUIMOLECULAR QUANTITIES OF FIVEORQANIC ACIDS A . Formic acid; power factor, 0.10 at 0.06 millimoles per gram B. Acetic acid D. Stearic acid C . Propionic acid E. Mixed naphthenic acids
thoroughly impregnated, the samples were quickly transferred to the measuring cell. The data for the experiments concerning formic acid, as well as those for the experiments involving acetic and propionic acids, indicate that the power factor of impregnatedpaper insulation may be markedly increased by the presence in the insulation of low-molecular-weight acids such as these. As previously stated, the effects of the high-molecular-weight acid tested were very small. The concentration values shown in the various figures are based on percentage by weight. The molar concentration for a given percentage concentration is much higher in the case of the acids of lower molecular weight than of those of higher molecular weight. That the difference in the number of functional carboxyl groups for a given percentage composition is not primarily responsible for the differences in the power factors of the impregnated paper containing the several acids is shown in Figure 2 , where part of the power factor data from Figure 1 are replotted against the molar concentrations of the acids in the oil. Even on this basis the magnitude of the effect of the acids in increasing the power factor appears to be in the order of the decreasing molecular weight of the acids. The similarity between the power factors of the paper impregnated with the emulsions consisting of the oil-insoluble formic acid suspended in liquid paraffin and those of the paper impregnated with the solutions of the oil-soluble acetic or propionic acids in liquid paraffin seem to indicate that the power factor increases caused by both classes of acids may be due to similar mechanisms. The power factors of the paper impregnated with formic acid emulsions were only about as much higher than the respective values for the paper impregnated with the acetic acid solutions as might be expected from the corresponding increase for acetic acid over propionic acid, provided the difference in solubility behavior between formic and acetic acids were ignored. As has been stated previously, after paper had been thoroughly impregnated with the oil emulsions of formic acid, the excess oil appeared clear or only slightly hazy, thus indicating that the formic acid droplets had been sorbed almost entirely by the paper. I n view of the similarity of effect on power factor it seems probable that the acetic and propionic acids were also strongly sorbed by the paper. Support for this hypothesis may be given by the fact that the power factor values for the paper impregnated with the oil solutions of acetic and propionic acids rose rapidly at first and then progressively more slowly untiI the equilibrium values shown were attained. An investigation of the relative sorption of organic acids of different molecular weights from oil by paper is now in progress.
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It may be of interest to investigators who work with highvoltage underground cables to note that a peculiar acrid odor was usually perceived whenever the paper impregnated with the formic acid-oil emulsions was removed from the power factor cell. This odor seemed to be identical with that often found in cables which have a high power factor and in which intensive oxidation has taken place. The odor was not that of formic acid itself. No investigation concerning the origin of the odor has yet been undertaken. The d. c. conductivities of the impregnated samples described and those whose descriptions follow did not exceed 1.5 X mho per cc. except in some of the cases involving formic acid in which the droplets of the acid were not entirely sorbed by the paper. The d. c. conductivities were determined after one minute of voltage application (1).
Effect of Alcohol, Aldehyde, and Ketone Since the magnitude of the power factor of the impregnated paper increased with decreasing molecular weight of the acids used &s contaminants, an attempt was made to determine whether a similar order would result from the use of other chemical classes of oxidation products such as the alcohols. As an example of an alcohol of high molecular weight, cetyl alcohol was selected. The results of the power factor measurements made upon paper impregnated with solutions of cetyl alcohol in liquid paraffin are shown in Figure 3 B . I n the impregnated paper as well as in the liquid paraffin alone (data for the latter are reproduced for comparison in Figure 3 A ) , the presence of the cetyl alcohol caused very little increase in the power factor of the insulation as long as the alcohol did not separate from the oil. Upon separation of the cetyl alcohol as a gel, however, the power factor of the impregnated insulation was very high, though not so high as for corresponding concentrations of the cetyl alcohol in the oil alone. As an example of an alcohol of medium molecular weight, tert-amyl alcohol was used. This alcohol, which was completely soluble in the oil a t all temperatures and concentrations used, had little influence upon the power factor of either the oil or the impregnated paper, as shown in Figure 3 C and D.
FIGURE3. EFFECTOF ANHYDROUS OXIDATIONPRODUCTS ON POWER FACTOR OF LIQUID PARAFFIN AND OF LIQUID PARAFFIN AND PAPER * Previously reported (a)
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INDUSTRIAL AND ENGINEERING CHEMISTRY
For purposes of this investigation desirable properties of an alcohol to be used to represent the class of alcohols of low molecular weight would be low volatility and complete solubility in liquid paraffin. Because of the volatility requirements imposed by the vacuum technic employed, no attempt was made to use methyl alcohol. Ethyl alcohol, the compound selected, was not entirely satisfactory in that it was only sparingly soluble in the liquid paraffin but, since the property of complete solubility could be attained only by using compounds of higher molecular weight than desired, the ethyl alcohol was used. I n concentrations beyond 1.5 per cent the mixtures of ethyl alcohol and liquid paraffin were visibly heterogeneous at the lower temperatures and under those conditions had high power factors as shown in Figure 3 E. Difficulty was experienced in obtaining the power factor values shown since t h e solutions had a tendency t o supersaturate before separating. The power factors of the paper impregnated with .the alcohol-oil mixtures were higher than those of the paper impregnated with the oil alone, but the effect of the alcohol waa not marked, as is shown in Figure 3 F. Because the acid and alcohol of medium molecular weight had about the same small effect upon the power factors of the impregnated paper as had the acid and alcohol of high molecular weight, only one aldehyde and one ketone were used to represent both medium- and high-molecular-weight oxidation products of these chemical types. The compounds selected were valeraldehyde and methyl n-amyl ketone. As shown in Figures 3 H and J, neither compound caused any appreciable increase in the power factor of the impregnated paper in which it was used as the contaminant. The behavior of each in this respect was similar to its corresponding behavior (Figures 3 G and I ) when each was used with liquid paraffin alone. Because of the high volatility of both aldehydes and ketones of low molecular weights, no examples of these types of oxidation products were investigated.
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Conclusions The data presented seem to indicate that in oil-impregnated paper, as well as in oil alone, the presence of the more common chemical types of oil-soluble oxidation products that have medium t o fairly high molecular weights, has little influence upon either the 60-cycle power factor or the d. c. conductivity of the insulation. Two oil-soluble acids of low molecular weight have been found, on the other hand, t o have a large influence upon the power factor of oil-impregnated paper even though they, like the other soluble oxidation products, had little influence upon the power factor of the oil alone. The d. c. conductivity of the impregnated paper in which these acids were used as contaminants was found t o be little changed. I n their effect upon the power factor of the impregnated insulation these two oil-soluble acids were found to be similar to a closely related but oil-insoluble acid. Judging from the single set of data available, the presence of anhydrous, low-molecular weight oxidation products other than acids contributes in a mild way to power factor increases in oil-impregnated insulation. These increases, however, are not considered sufficiently great to warrant their further investigation at this time. The work is being continued, the major emphasis being shifted to an examination of the effect of dispersions of oilinsoluble materials on the power factor and conductivity of both oil and oil-impregnated paper.
Literature Cited (1) Am. SOC. Testing Materials, Standard Methods, Designation D 257-33 (1933). (2) Piper, J. D., Thomas, D. E. F., and Smith, C. C., IND.ENQ. C H ~ M28, . , 309 (1936). RECEIVED April 29, 1936. This work forms part of an investigation on the deterioration of high-voltage underground cable being conducted by The Detroit Edison Company under the direction of C. F. Hirshfeld, chief of research.
Our Magnesia Resources Several articles have appeared recently in the technical press on the value of the magnesia content of the ocean with particular reference t o the production of basic magnesia salts from raw sea water. The latest article appeared on page 383 of the April number of INDUSTRIAL AND ENQINEERINQ CHEMISTRY.The author, H. H. Chesny, describes some of our ma nesia resources and claims that the production by the Marine 8hemicals Company shows the superiority of sea water as a source. Sea water is pumped to the works and chlorinated, and the magnesia is extracted while the bromine is lost. The Ethyl Dow Company pumps vastly more water daily from the Atlantic and also chlorinates it; here bromine is recovered and magnesia is neglected. Perhaps the companies should trade patents. In the manufacture of bulky and cheap chemicals the study of freight rates is frequently the most necessary problem. Austrian and Greek magnesites have been supplying the demand in the eastern states for refractories, plastics, cements, etc. The Austrian material is best for refractories, and the Greek for operations where freedom from iron is essential. Owing to cheap westward ocean freight rates, these magnesites can be brought here as ballast if the cost of loading and unloading is realized. Only a high tariff will prevent their use in the most populous sections. As mentioned, dolomites are plentiful all over the United States and are used (where freight rates allow) for making “85 per cent magnesia insulation,” and the bicarbonate is brought into solution under pressure by blowing in carbon dioxide. The use of tbis old method is indicated by the necessity of precipitating a basic carbonate of the physical condition t o give the highest insulating value for pipe and boiler coverings. The German fertilizers consisting of carnallite could be worked here to concentrate the potash contents and leave a concentrated magnesium chloride which could be converted into sulfate, if the demand justified the cost of manufacturing.
Mixed calcium and magnesium chlorides are made from the residues of salt manufacture from the Ohio River and Midland, Mich., bittern or brines; they have also been made at Tulsa, Okla., from brines of about the same composition ratio but differing in total solids content. The process of separating magnesia is about the same as that described by Chesny. The early Dow process at Midland for the by-product manufacture of magnesia is cited, but the costs of digging wells and of general operations are erroneously charged to magnesia production. These costs cannot be charged to this by-product since well digging and other general operations are already necessary in making the other chemicals. The amount of magnesia made is thus limited t o the possibility of selling it for more than its manufacturing cost, which includes only the special operations for precipitating the magnesium. Magnesia has also been manufactured on the Pacific Coast from the bitterns left after salt is manufactured by solar evaporation of sea water. This is a concentrated solution of magnesia as compared with ocean water. About 300 tons of salt are made daily at Charleston, W. Va., according t o E. T. Crawford [IND. ENG.CHEM.,27, 1274, 1411 (1935)], who gives the history of salt manufacture there. Now “calcium” is sold t o the coal mines for floating coal off the slate, and no separation of the calcium and magnesia is necessary. It will not be separated until there is no longer a market for the mixed product. Thus, we have man sources of magnesia suitable for manufacture in the United Jtates and better supplies of raw materials abroad which will be used unless a high tariff prevents. H. 0.CHUTD 50 E A S T 4 1 ~ T STREET
NEWYORL,N. Y. April 23, 1936
