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INSULATING OILS C. E. Trautmar~ Oulf Research & Development Company Pittsburgh, PennsyIvanla Principal contributions to the literature on insulating oils that appeared in 1946 are reviewed brieny in the following text . ~ iL~ A very significant series of pep era on transformer 0118 was presented at a meeting of the Institute of Petroleum, London, England, April 9, 1946. ~ All of the papers and the valuable general disoussior~s which followed at the meeting have been pririted in the bourns of ~ Institute of Petroleum (July, 1946~. Tt is impossible in this review to discuss in detail the large mount of information and data presented. lye following slmrnaries give some idea of the scope covered by the papers and discussions. ~ I. 30881iDg and Michi~ contribution of the Internationa:t ELectrotechnical Commission to research on transformer oila. Efforts have been directed toward obtaining a better underetanding of the mechanism of the deterioration of transformer oils in use, and also toward the development of suitable specification tests. During the course of early work the majority of opinion was that Sludge formation was considered to be the moat dangerous resu:~t of transformer oil aging. However, the British Committee in 1937 found it advisable, as a result of experience with corrosion dur- ing deterioration, to Occupy acidity fcrrmation, partioularly with respect to the highly refined class "A' oils. As expected, the acidity development of the class nB" oils was in genera:L lower than that of the class aAN oil. ClaseaB" oils were found to vary con- siderably as to acidity development, and for this reason the Committee proposed amendment of B. S. No. 148/1933 to income teats to enable selection of Class IBM Otis of low acid forming type. A critical review of accepted laboratory oxidation teat procedures was presented by Pollitt.:b The British tes~G (B. S. 148/1933) was Judged to be run under conditions closer to actual operation than others. The provision of a renux condenser to Return most of the volatile products of oxidation was considered to be important. The A. S. T. M. D_670-42T methods were criticized as fol lows: Method A ~ Sludge accumulation teat ~ was Judged to be too long (two weeke) for use as an acceptance test. The lose of volatile oxidation products and evaporation of the oil was regarded as ob] ectionabl e. The sp-eGification of the copper and method cf cleaning was said to be too :008e~y directed. - 106 -

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Method B (High pressure oxidation test) was thought to be short enough for an acceptance test, but the use of high pressure oxygen and the determination of sludge onl y vrere regarded as ob] ec~cionabI e features . Detain ~ of the British test hi. P. 56/45 included in B. S. 148/1933) were conel.~ered by Gossling and Romney.\C In an effort to improve the reproducibility arid repeatability of the method, data were obtained to show the influence of the condenser water temperature on ache final so urge value`, These data show the t modern' e increase in the temperature of `~he Condenser water temperetllre increases both sludge and acidity oorlsiderablyO In a Caper Presented by Barton)5, an historical review of British experience with the sludge test (B. S. 148/1933) was given. Barton concluded that the lack of repeatabi~ ity and re- producibilit~r is sufficient ~Go disqualif~r the test as a basis for specifications' apart from the Question of whether or not the use of a sludge value is sound. Barton recommended that the British sludge test should either be abandoned or completely revised. R~. Woodcock reviewed past and present methods of production of transformer oils. Data were presented to support the general premise that increasing the amount of sulfuric acid- refining riot only improves the sludge forming tendency of an oil, but when refining is increased beyond a certain point, eventually the acid forming tendencies of an oil increase. The genera: idea of adding selected aromatic extracts or known compounds to control the properties of the finished oil was regard deaf as a development which presents considerable opportunities for the production of better oils. Oblation and Antioxid~Q~. The s'~o &~ ec ~ of oil oxidant tion from was thoroughly disous.~ed by the authors of three papers. George and Robertson if revi - ~d theories concerning the mechanism of oxidation of liouid hydrocar- bone. The course of the oxidation is assumed to start with hydro- peroxide formation proceeding to ketones, then to acids, and finally to further oxidation products. The hydroperoxides also form alcohols as final products. The authors elaborated on the nature of the reactions by which hydroperoxides are formed e The Genetics o' thermal and catalyzed oxidation reactions were dis- cu s s ed in detail . Evanalg gave a paper in which he outlined and gave examples of a number of classes of antiox'dants suggested for use in transformer oils. References to most of the compounds were found in the patent literature. In a second paper, George and Robertsonlh examined a number of factors relating to oxidation of oils 9 including. intermediate and fine] reactions produc'ce, stability of odious types of aompounde to oxidation, catalysts, and inhibition. - 107

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I: At the fall meeting of A. 30 T. M. Committee D_9, October l6, 1946, at Atia=~ic ~ity9 N. ~ , the fires in a series of Symposia on insulating oils was held.t The subjects included: the application and significance of the interracial 'Gension test, the steam emulsion number test, and atatio~cical analysis of data applied to 3lelectric strength measurements. It was announced that arre.ngement.s would be made to publish these papers in the A. S. T M. Bulletin _ _ _e _ ~ _ Gee. Method of Test and Correlation with Service. The A. S. T. M. D~9 Suboommi~Gtee IV has continued its work on methods of test for insulating ollsO Progress has beer mere toward re organization of method D_117 to eventually make tt a reference method giving only definitions and statements of significance. Tentative methods approved vrere: Dielectric Strength, Inorganic Salts, ~d Samplir~g, Methods of lest for Power Factor and Sulfur Corrosion are tr. Ire process of preparation. A test procedure for determination of moleture in oil is being investigated. The Inter facial Tens' on Test is e, so being studied. Cooperative tests have been continued to determine the correlation of data obtained ty D67~42T sludge tests arid other methods of Relic with performance in commercial transtormere. 4 Horsch3 reported in a series of three publications the results of an extended investigation of the oxidation properties of transformer oils. A simulated field test in which small commercial transformers are used was developed and a considerable amount of data ~rB,6 collected during a period of over 10 years. The transformers were ~ .5 K ~ VO A. , 2, 500/230 vol ts, of about 5 gallon ail capacity. The transformere were loaded by a feed-back circuit which supplied the heat losses and resulted in an 85C top oil temperetureO The simulated field service life was arbi- trarily chosen as the time for the oil to reach a neutralization of I.0. Horech was able to obtain data on oils tested by a number of accelerated laboratory tests in an attempted correlation with his simulated field service test. Very little correlation with the laboratory tests was found. A. S. T. M. D 670-2 methods A and B. the Sligh Oxidation test' act the German Ter test did not predict accurately the simulated field life. A sludge accu- mulatic~n test as run by an eerily method, similar to the A. S. T. M. D 670_42T ~ A, but without the copper catalyst, appeared to show some correlation. Be~rera:L interesting points were shown by tests departing from the adopted starboard s et of operating conditions of the ~Gransformers. The presence of about l/2 inch depth of water in the bottom of the transformer case caused more sludge to form at 17 months than in dry transformers in eight years. Cycling scents to simulate fluctuations in temperature in the field caused the deterioration to ~ ncrease about twofold. Restrictions of breathing and s'~bstitlltior of nitrogen for`air above the oil _ 108

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permit~ced the neutre-li"e Bias number of the oil to rise I only orle~half of At of 'the same oil in ~ transformer USA t0 breathe ~ ~i ca~- as~s ana the practical application of measurements of tile s:3re~din~; tendencies of Qi1 samples on water were dinged 'cry Ragethc/~n and Sty elt:es<, Tin ~ method is based :n the m=~=ement of -2~ `~a of surface oco^~4 ed by the partly ty=rophilllo or ?~ =~ules. The method eras suggested as an aid in following Ache ^~" of oxidation of cil ~ and to determine the state ct pi ty 0[ icing oils. cap ~e~ant6 Is ruble shed further data - obtained from conductome Brie investigations of electrolytic solutions in hydrooart<:r:~ Oonsidex,~e data are preser~ted =~d analyzed [~r ~ possi.~e e~:~or~ of high conductivitles o~ served ire deteriorated Oils. 3~nt proposed that the mech&ntem of cor~uctivity in oil in,701;res con~pow,5 Connation between come ?oner.~Gs a~d ~ subsecue?;~t ionic dissociation. He reasoned that the ultimate carriers of en ectricity, even in the presence of colloidal particles~ are in a] ~ probability molecularly dispex$~d ions `, 7~ bang' suppled data to show the relationship between aie)6CtriG 09S ~] Viscosity of ~ oil. The data support pre- vious conclusions that provided there is no dipole loss, the dielectric loss of ~ deteriorated oil varies inversely as 11s viscosityO This was shown deco be true over a limited temperature range. Increastr~g the temperature causes an increase in ion con centratior~ by further ionic dissoolation. ~ Among the United States Patents dis- closing oxidation inhibitors for petroleum oils in general, one issued to Amott~ covers the use of the esters of tartaric acid to impart oxidation resistance A transformer oil. Examples are: dicyclohexgl ~Gartrate, diisopropyl ~Gartrate9 arid dibenzyl tartra1;e. Laing9 disclosed that the use of about 15~ by weight of ~ catalyst composed of ~ to lO parts of activated a~ u;,mina to one part of fullers ~ earth improves the steam emus sion numbers of oils over that of usual greasing mixtures. A patent is sued to Alexar~eriO olaims the use off metal hydrides to dry transformer oils. Alkali or Alkaline earth metal hydrides ~ such as oaletum hydride are contacted with the Gil in one of various ways. The water reacts with the hydride to form ~ soild compound which may be separated by filtration or pistil ration. _ 1~:)9 -

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BIBLIOGRAPHY 10 General Discussion on Transformer oils, meeting of the Institute of Petroleum London,, April 9, 1946. d. Inst. Pet., 32, 356-464 (July 19465. a. Gossling, P. W. 1.., and Michie, A. C., pp. 356-364. b. Pollitt, A. A., pp. 414~423. c. Gossling, P. W. L., and Romney, J., pp. 424~433. -it. Barton, O. H., pp. 408_413. e. Wood_l!~al~ ock, d. C., pp. 365~3~31. f. George, P., and Robertson, A., pp. 382~391. g . Evan s, E: . A . , Up . 39 2~ 39 9 . h. George, P., and Robertson, A., pp. 4()0 i. Discussions, pp. 434-464 2. A. S. T. M., Committee D_9 meeting, Atlantic City, N. i., October 16, 1946, Symposium on Insulating Oils. Horsch, W. G., Elec. World, 126,(3 parts) #5, 54-7, 67, 72~74, #9, 56_59. (1946). A. S. T. M. Proc., 46, p. 393~94. (1946). Hagethorn N. E. M., and Stielt3es, F. H., J. Inst. Pet., jig, 587-597. t1946) . Gemant, A., J. Chem. Phys., 14, 42~434. (1946) 7. Rang, Bun Pa, Elec. Engr., 65, 403~407. (1946) . 8. Amott, E. ~ Assignor to Union nt! Company of California, U. S. Patent 2, 397, 33~, March 26, 1946. 9. I.aing, K. M., Assignor to Aluminum Company of America, U. 8. Patent 2,403,08S, July 2, Ig46. 10. Alexander, P. P., Assignor to Metal Hydrides Incorporated, U. S. Patent 2,399,122, April 30, 1946. - 110 _