Document YDvvQEY7eEzwy5gawQw457B18

Atkaral coolant, being (ire-resistant, per mits Indoor Installation ot liquid-tilled transformers and capacitors. Future of this polychlorinated biphenyl (PCB) is being questioned. The probable allernallves are outlined here by author W.C. Bloomqulsl, consultant with a rich background In industrlal-power-system design and equip ment application UI W' Plan! electric systems What is the future for askarel? After serving for years as a successful fire-resistant transformer and capacitor coolant and insulator, askarel has been labeled toxic. The designation goes back some years, but is getting a fresh appraisal by government, equipment manufacturers, fluid suppliers, and engineers responsible for transformer and capacitor selection. Here's where we stand today--along with meager data on possible alternative liquids and dry-type designs By W C Bloomqultt, PE, President, Industrial Power Systems Engineering Co The Icnn askarel describes a class or fire-resistant synthetic insulating liquids which industry and the lay press more accurately call PCBs- polychlorinated biphenyls. The prime reason for its use over the years is high fire resistance: The auto-ignition point of askaicl is 1240F, while that of mineral oil is 680F. The sole manufacturer of PC Hr in the US is Monsanto Chemical Co. which markets its product under (he trade name Aroclor. When mixed with chlorobenzenes, the PCB fluid is la beled h'tunal by General Electric and hu'rtcvtt by Wtfsiinghousc. I*ruvcn values. Askarel is among the best liquid man-made insulations. It is ftrc-rcxlstanl and chemically stable, and has high dielectric strength. Because of these plus characteristics, askarel has found many industrial and consumer- product applications since i( was intro duced over 45 years ago. Askarel use in the US today totals about 40-million lb annually, with about V> of this being used in capacitors. '/* in transformers. Power capacitors use about 14% of the capacitor-usc total, with most of the re mainder sptcad among fluorescentlighting ballasts, singlc-phnsc-motor ca pacitors, und TV and other electronic devices, Fire resistance is the principal reason insurance companies and the National r.lcctrica! Code permit use of asknrclfillcd equipment indoors without fur ther enclosure. Askarcl-fillcd inter rupter switches were used for years throughout industry; however, most have now been superseded by the airtype. Ecology and health. Although askarel has been in use for close to a half-cen tury. it is only in recent years that EPA has placed PCBs on its Toxic Pollutant List. Since askarels are chemically stable, they are not biodegradeable-a major environmental concern. PCBs are found widely dispersed on land and in our waterways. They were first clearly identified as a food contaminant in the mid-1960s, when they were found in fresh-water fish. Here the source ranged from polychlorinated biphenyls used in carbonless paper to food-packaging ma terials. where PCBs had migrated into the food product. It is unfortunate that suitable detection equipment was un available until recent years. It was a Dr Jensen of Sweden who. in 1966, referred to PCB as a "new pollutant." Ecologists use a thrcc-prongcd ap proach in classifying PCB applications: open, nominally closed, and closed. The open classification spans the manufac turing of paints, plastics, and some ad hesives; nominally closed refers to sys tems thal include hydraulic, healtransfer, and lubricating fluids. Both of these classifications arc generally free of PC'Hs today, through voluntary ban ning. Closed applications-sealed trans formers and capacitor'-- now account for our total domestic askarel consump tion. About five years ago. poultry and eggs in Minnesota and North Carolina were found to have large concentrations of PCB. and were destroyed. The PCB source was traced to a nominally dosed system- a leaking heat exchanger in a fish-meal processor's plant. The fish meal, in turn, found its way into a com mercial poultry-food product. A federal lavk force was established in 1971 to coordinate governmental ef forts aimed at understanding the family of PCB chemical compounds. Its report, now somewhat dated1, reflects the pos ture of various governmental agencies at thiit time. On (he basis of available information, the task force issued a nine-point report: lour of the points arc summarized here: PCBs should he restricted to essen tial or nonrcplitceahlc uses that involve minimal direct human cxposoic. since they can have adverse health cllcciv Currently |I97I) there are no toxic ological or ecological data available to indicate thal (he levels of PCBs known to be in the environment commute a threat to health: Additional tests are un der way to evaluate the impact of long term, tow-level exposure to PCBs Housekeeping is particularly im portant in the manufacture, use. and disposal of PCBs. MONS 032454 Power PeO'uery 19/ft mi* wzij-- Xu-;y vxMwmzws.m EiiV/wi.'wwr*!eV l*GB use should nol be banned en tire!)'. Continued use in transformers and capacitors, at least in (he near fu ture. is necessary because of the inctcascd risk of fire and explosion-and the resulting disruption of electrical ser vice- that might possibly icmiIi from an outright ban. Also, continued use of 1*01)% in transformers arid cnpucilors presents n minimal environmental risk. Mine information is needed. The total exposure of a human to a given substance from all sources- uir. water, and food- must be considered, and in teractions of I'CHs and other sub stances. within and outside the body, must be evaluated. Ihe report went on to slate that the then-current body of knowledge gained fiom animal experiments was inade quate to allow reliable extrapolation to possible effects on man. Also, it said, the basis for interpreting such tests had to be improved. Net results of this 1971 report was an uneasiness throughout industry about many of FDA's proposed rules. Some fell they were nol practical or fell short on ecological fact. Example: Maximum recommended concentration of PCBs in fresh water is a meaningful number, yet tire proposal was nol supported by sound ecological data. An Rt'A meeting held last fall brought together the latest data and ex perience to help clarify problems associ ated with I'Clls. In one sense, the threeday conference served to update the 1971 task-force report. During Ihe three-day gathering, (here were reviews of laboratory and field studies, and re ports on monitoring programs, human cx|>osurc and health effects, and impnet on ecology. Also, there was an assess ment of steps being token to reduce problems associated with PCBs. Of di rect interest were those reports on sub stitutes for askarcl2. which arc high lighted here. When Questions about Ihe ell'cct of PCBs on Inc environment first surfaced, Monsanto Co.-the sole US manufac- hirer of PCBs-rcviewcd its product line and PCB applications. It stopped sale of PCBs for applications in Ilie first two catcgories-o/wi and nominally dosed', this step cut PCB output by 50%. Today. PCBs manufactured by Monsanto and sold only to the electrical industry for use in dosed systems as a dielectric and coolant in transformers and capacitors. While recognising that there is some loss of ihe askaret fluid in service, re member that there is no fully acceptable substitute to dale. In recent years, evidence of PCBs have been found in fish in the upper Mississippi River, the Hudson River, the Great Lakes, and along the southern California coast. According to Russell ii, Train, head of EPA, 300-million lb of I'CBs arc currently in use, and another 300-million in the air, soil, and water. The picture today differs drastically from that of four years ago. Through elimination of the open and nominally closed applications, use of the PCBs has been hnlved. The impact on our water ways can be materially reduced through an educational program directed to users of PCBs, stressing proper handling and disposal. Housekeeping is of key importance in the manufacture, use, and disposal of PCBs. For current guidelines to handling and disposal, study references, 3,4, and S listed at the end of (his article. What are Ihe alternatives? Many arc working on the problem of finding flu ids having the attractive characteristics of nskarcl yet without its environmental and health drawbacks. Much work has already been done. lQ.J971,_Mpnsanu> injroduced Aroclor 1016 for capacitors, and it has found growing use, TlmTIiiul retains the high dielectric properties of traditional askaret. is fire-resistant and partially dcgradeable. Time may prove it to be sufficiently degradeable to re main in.cpnirollcd.usc. Others have announced potentially acceptable replacements for askaret in capacitors, even though they are not fully fire-resistant. Three arc in the mar- ket development Mage: General F.lec- tric's liquid for small capacitors is la beled Econo!', Dow Chemical has an alkylated chiorodiphcnyl oxide fluidXFS-4I69L: Moosauio has a fluid iden- MiCliuMaiJW ' Another liquid, potentially useful in transformers, is dimethyl siloxanc, a silicone oil. This is made lodas by at least four US manufacturers, with Dow Corning and General Llcctric the two major suppliers. Bear in mind, however, that the silicone fluid has an uuto-igmtion point of 7501'. only about 80 de grees above that of mineral oil. Silicone liquids have many of the de sirable electrical characteristics of ask- arcl and arc not toxic. 1 he fine electrical properties of silicone fluids stern from their unique chemical structure*1-'. As with all likely fluids, the electrical char acteristics will be reduced by gross con tamination or water. Silicones arc available with a range of viscosities and for many applications Fluid suppliers have set 50 ccntistokcs as n suitable viscosity for transformers. Transformer askaret has no flash point, while a 50-cs silicone fluid tests out nl 300C. The silicone fluids have low tox icity and arc classified as "physi ologically inert." They have been cleared by the FDA. and arc currently being used in a variety of medical and chemical applications Ihe fluids are not biodcgradcnblc. but arc nontoxic. With the exception of silicone rubber, sometimes used for gasketing, the sili cone liquids are compatible with mate rials found today in askarcl-cooicd transformers. Since the silicone lluids will ignile at 7501'. they arc nol classed as (ire-resistant*. above that tempciiiturc they will burn. If the heat source is re moved or fluid temperature drops be low 750F. burning will cease. Thus, the fluid is self-extinguishing Underwriters Lab (Ul.) docs not ap prove or reject liquids intended for elec trical test equipment, nor will they test or list any liquid-filled electrical equip ment. They do. however, provide a Pow*, Fl>lu*ry (9(6 MONS 032455 PLAN! ELECTRIC SYSUMS 99 classification mm vice or flammability rulings, Hollowing is n typical compari son: Fluid Flammsbillljr Rating Elhar..................................................... 100 Mineral oil (ifanaformer)................... 10-20 Silicone oil (50 cs lortransformers).... 4-5 Aekerel..................................................2-3 Meld experience with the silicones ns transformer coolants is limited. Dow Corning Inis had several load-center transformers retrofitted with 50-os sili cone oil for several years. And silicone oil is slated for all of Dow's future plant transformers. If you want to consider changing transformers from askarel to silicone oil, first check with the trans former manufacturer. I;ew physical changes should he necessary. Trans former rating may be reduced 10% be cause of difference in fluid viscosity and heal conductivity. At present, rnsurancc carriers have no formal policy covering lire use of silicone oils. They have ap proved use in a limited number of cases. The Japanese National Railway has used silicone fluid as the transformer coolant on its electric coaches for the past five years with good results. Here several design modifications were nec essary. ( ode-making bodies .should consider a tentative approval or interim amend ment of silicone-fluid applications in specified environmental and plant loca tions to obtain operating experience. Net result would be lo determine if such transformers can replace askarel, under what conditions, ami in which locations. Hear in mind that it generally fakes two to four years for Code approval for such a basic change: The changing from a proven fire-resistant product to a noniirc-resisiant fluid, for indoor use. Cost can be a problem: Silicone flu ids cos! about twice us much as askarel. Thus, for a typical 1000-kVA load-cen ter transformer, total transformer cost may increase 8-10%. The actual increase in cost is a function of (he specific de sign. Dry-type designs may be used in place of askarel if the user recognizes the inherent limits of dry-type tiansformers (Table 2). Failure testing. In recent years, a series of explosion tests were conducted in the US pod Japan using mineral oil. ask arcl, and silicone oil. The fluids were tested itt small tanks with a loose cover, and 'shot' wit)) 4000-5000 amp at 4.8 kV. In each ease, and with each fluid, the covers blew olT. This was to be ex pected. since a high-current arc in any liquid-filled transformer will generate gas, followed by a pressure buildup. Such tests are not representative of nc* UkiI operation. True, explosions do oc casionally occur with pole-type trans formers on outdoor utility systems. But they arc rare indeed for industrial trans formers located indoors and protected from lightning. Transformer failures arc generally turn-to-iuri). and therefore carry limited fault current. This is a far cry from the magnitude of the tests outlined above. Manufacturers of industrial trans formers oiler sensors u> deled incipient arcing faults and severe faults. I know of but one catastrophic occurrence lightning struck an askarel transformer on the roof of a building Hut there w.is no fire damage. Spot-checking with an insurance eauicr confirms the rarity of such accidents. Still other answers? It is possible that a new nonliquid transformer will emerge Several Furopenn manufac turers. and at least one in the US. now offer an epoxy cast-coil design in the 100-500-kVA range. With more devel opmental work. fcVA ratings may reach llu* currently popular transformer sizes. Another alternative lies in modification of present dry-type transformers. The present senled-drv gas is pc is too large, too heavy, and too expensive for gen eral use. Unity;j;.|.\A_jvqhibih use of askarel. {his fluid will continue io he used inln- door transformers and capacitors untTT an approved substitute is available. tPA may wisely restrict import or ask- itrcls to use only in closed sc stems, as is practiced by Monsanto domestically. A new policy of indemnification by the buyer to ihc seller is one faelor Ibal may affect use of askarel-lillcd trans formers. Wording of the indemnifica tion contract may vary. 1 lie key lies in its application to any and till liabilities and expenses, including actions, suits, proceedings, investigations, instituted or issued by any government agency or body. The liability would include han dling. possession, use. or disposition of askarels Dial may contaminate the envi ronment. JOC TO PIAN1 ri fCTniC 6YS1EMS HONS Reference! t "Polychlorinated B'phenyti endlhe EmOonmeni." Report No ITF-PCB-7?-l, Inlerdepa'tmenlet TK Fore*on PCB Com r?-104 Ip, df(nOuled toy in* Neuonenechmeei Intormeiion Service. US Dept otCommeiee. Springfield. Va??l$t 16 pe' copy 2 Oevid Wood, "Chlorinated Biphenyl D<lecluct-1oaif UtiMy and Potential Substitutes" Pep*' < ihe Nenona' Conference on Polychlorinated Biphenyls. November 1974 Available Irom author; Monsanto. St Louis. Mo 3 'Translo>me>. Aikarel. Impaction 4 Maintenance Outdo." Bulletin No IC'FF-36R, Monsanto indusinal Chemicals Co. 600 N Lindberg Blvd St Lours Mo 63166 Free 4 1 Guidelines lor Handling and Disposal ot Capacitor and Tramiomor Grade Askareii Containing Polyehtorinaiad Biphenyls' Publication 0)07 1-1974, Amancan National Standard* Institute. 1430 Broadway. Nana York. NY 10016 66 per copy 5 "IEEE Guide lor Acceptance end Maintenance Ot Tremtormer Askarel in Equipment.'' IEEE Standard 76-1974 Pubiifhed ttyIEEE. 34} East 47ihSl, New York, NY 10017 |4 pel copy 6 R F Buron end 7 Otbeck. Performance Capabilities ot Silicone Fluids at Insulating liqnidi lor High Voltage Trsnstormen '' Pieienied at 1974 Oobte Engineering Conference Available liomauthori. Dow Corning Corp. Midland. Mich 4B640 7 j S Hurley end A TprkeNon Silicone Dielectric Fluid! lor lmudf tiled Yraneloimei! " Conterence neper C-74 ?64 |, Power Engineering Socrely Available bom author!, General Electric Co. Weteilord. NY 032456 Power rsbmtir '*76