CA1259461A - Method for replacing pcb-containing coolants in electrical induction apparatus with substantially pcb-free dielectric coolants - Google Patents

Abstract

IMPROVED METHOD FOR REPLACING PCB-CONTAINING COOLANTS IN
ELECTRICAL INDUCTION APPARATUS WITH SUBSTANTIALLY
PCB-FREE DIELECTRIC COOLANTS

ABSTRACT OF THE DISCLOSURE
Method of replacing a PCB-containing coolant in electrical induction apparatus having a vessel containing said PCB-containing coolant, an electrical winding and porous solid cellulosic electrical insulation immersed in, and impregnated with, said PCB-containing coolant with a substantially PCB-free high boiling dielectric permanent coolant into which any residual PCBs elute at no greater than a selected target rate. The method comprises steps of (a) removing a major portion Or the PCB-containing coolant from the vessel, (b) filling the vessel with an interim dielectric coolant substantially free of PCB which is (i) miscible with said PCB-containing coolant, (ii) sufficiently low in viscosity to circulate within the vessel and penetrate the interstices of the porous electrical insulation and (iii) capable of being readily separated from PCB, (c) electrically operating the apparatus to elute PCB contained in the coolant impregnated in the pores of the insulation therefrom into the interim coolant, (d) thereafter removing interim coolant containing eluted PCB, (e) repeating the cycle of steps (b), (c) and (d) if the PCB elution rate into the interim coolant after step (c) exceeds 5 times the selected target rate, a sufficient number of times until the PCB elution rate does not exceed 5 times said selected target rate, (f) filling the vessel with PCB-free high boiling dielectric silicone oil as coolant, (g) electrically operating the apparatus to elute interim coolant and additional PCB impregnated in the porous insulation therefrom into the silicone oil coolant, (h) thereafter removing the silicone oil coolant containing the eluted PCB from the vessel, (1) repeating the cycle of steps (r), (g) and (h), if the elution rate of PCB into the silicone oil exceeds the selected target rate, a sufficient number of times until the PCB elution rate into the silicone oil is less than the selected target rate, and refilling the vessel with a substantially PCB-free dielectric cooling liquid.

S P E C I F I C A T I O N

Description

~ACKGROUND OF THE INVENTION

Field of the Invention This invention relates to electrical induction apparatus, e.g. electric power trans~ormers, specifically to the dielectric liquid coolants consisting of or containing as a constituent, poly-chlorinated biphenyl, PCB. More particularly, the present invention relates to methods for converting PCB-containing electrical induction apparatus, e.g.
transformers, into substantailly PCB free transformers in order to qualify said transformers as "non-PCB" transformers under U.S. government regulations.

Prior Art Because of their fire resistance, chemical and thermal stability, and good dielectric properties, PCB's have been found to be excellent transformer coolants. USP 2,582,000, discloses the use of PCB's alone or in admix~ure with compatible viscosity modifiers, e.g., trichlorobenzene, and such ~richlorobenzene-PCB mixtures have been termed generically "askarels". These askarels may also contain minor ~uantities of additives such as ~ ~ ~ 5 ~

ethyl slllcate, epoxy compounds an~ other mate.lals used as scavenge.s ror halogen decomposltlon products whlch may .esult f~om potentlal electrlc arclng. ASTM
D-2283-75 descrlbes seve-al types Or askarels and ellneates thelr physlcal and chemlcal speclflcations.
However, PCB's have been clted ln the Unlted States Toxlc Substances Control Act Or 1976 as an envl~onmental and physlologlcal hazard, and because o~ thelr high chemical stablllty, they a-e non-blodegradable. Hence, they will perslst in the envlronment and are even sub~ect to blologlcal magnl~lcatlon (accumulatlon ln hlghe- orders of llfe through the rood chaln).
Accordlngly, ln the U. S., trans~ormers are no longe~
made wlth PCB or askarel flulds. Whlle older unlts contalnlng PCB may ~tlll be used under some clrcumstances, lt ls necessary to provlde speclal precautlons such as contalnment dlkes and malntain regular lnspectlons. Trans~ormers contalnlng PCB's are at a further dlsadvantage slnce malntenance ~equlrlng the core to be detanked 1~ prohlblted, and the tran~former owner remalns responslble for all env~ronmental contamlnatlon, lncludlng clean-up costs, due to leakage, t~nk rupture, or other ~plllage Or PC~'s, or due to toxlc by-product eml~slons resultlng rrom tires. To replace a PC~-contalnlng tran~rorme-, lt ~25~

ls necessa-y to (l) remove the t-ansrormer ~rom servlce,

(2) d~aln the PCB and rlush ~he unlt in a prescrlbed ~ manne~, (3) remove the unlt and replace with a new transfo-mer, and (4) transport the old transrorme- to an approved land~lll ror burlal (or to a solid waste lnclnerator). Even then, the owner who contracts to have lt bu-led stlll owns the t-ansforme- and ls stlll responslble (llable) rOr any futu-e pollutlon problems caused by lt. Llquld wastes generated durlng -eplacement must be lnclne-ated at cpeclal approved sites. Thus replacement o~ a PCB transrormer can be expensive, but more lmportantly, slnce most pure PCB o-askarel t-an~formers are indoors, ln buildlng basements o- ln speclal enclosed vaults wlth llmlted access, lt may not be physlcally feaslble to remove or ~nstall a trans~ormer, nor would lt be deslrable rrom an asset management perspectlve.
A de~lred approach to the problem would be to replace the PCB oll wlth an lnnocuous, compatible rluld.
A number o~ ~luld types have been used ln new transrormers as reported ln Robert A. Westln, "Assessment Or the Vse Or Selected Replscement Flulds for PCB's ln Electrical Equlpment", EPA, NTIS, ~B-296377, March 1, 1979; J. Reason and W. Bloomqulst, "PCB Replacements: Where the Transrormer Industry Stands Now~, Power, October, 1979, p. 64-65; Harry R.
Sheppa-d, "PCB Replacement in Transrormer~", Proc. Or the Am. Power Conr., 1977, pp. 1062-68; Chem. Week, 130,

3, 24 (1/20/82); A. Kaurman, Chem. Week, 130, 9, 5 ~3/3/82); CMR Chem. Bus., October 20, 1980, p. 26; Chem.
Eng., July 18, 1977, p. 57; Belglan Patent 893,389;
Eu-op. Plastic News, June, 1978, p. 56. Among these a~e slllcone olls, e.g., polydlmethylsiloxane olls, modlfied hydroca-bons (ro- hlgh rlash polnts, e.g. RTFmp, a p~op-ieta-y fluid Or RTE Co.p.), synthetlc hydrocarbons (poly-alpha-oleflns), hlgh vlscoslty este-s, (e.g.
dloctyl phthalate and PAO-13-C, a proprletary ~luld Or Unl~oyal Co~p. )J and phosphate esters. A numbe- of halogenated alkyl and aryl compounds have been used.
Among them a-e the llquid trlchloro- and tetrachlorobenzenes and toluenes and proprletary mlxtureQ thereof (e.g., llquld mlxtu~es Or tet-achlorodlarylmethane wlth trlchlorotoluene lsome~s).
Llquid mlxtures o~ the trlchloro- and tetrachlo~obenzene lsome-s are particularly sultable because Or thelr low ~lammabllltles (e.g., hlgh r~re polnts) and slmllar physical and chemlcal propertles to askarel~ being removed. Other proposed rlulds a-e tetrachloroethylene (e.g. Dlamond Shamrock's Perclene TG) and polyols and other esters.

~259~

Of all the non-PCB rlulds~ slllcone 0118 have been the most wldely accepted. Thel. chemlcal, phy~lcal, and elect-lcal properties are excellent. They have hlgh fl-e points (>300~C)) and no known toxlc or environmenkal problems. These olls are trlmethylsllyl end-blocked poly(dlmethylslloxanes) o~ the formula:

(CH3)3Sl~t(CH3)2SlO]nSi(CH3)3 whereln n ls of a value sufrlclent to provlde the deslred viscoslty (e.g., a vlscoslty at 25C of about 50 centistokes). Commerclal slllcone olls sultable fo- use a-e avallable from Unlon Carbide (L-305), and others.
In addltlon, U. S. Patent 4,146,491, Brltlsh Patent 1,540,138 and Brltlsh Patent 1,589,433 dlsclose mixtures Or sllicone olls wlth a variety of addltlves to improve electrlcal perfo-mance ln capacltors, transformers and simllar electrlcal equipment, and dlsclose polyslloxanes with alkyl and aryl groups other than methyl.
Replacement o~ PCB-contalning aska-els in olde~
trans~ormers wlth ~lllcone olls or one Or the other substitute ~lulds would seem to be a slmple matter, but lt ls not. A typlcal trans~ormer contalns a g-eat deal Or celluloslc lnsulating materlal to prevent electrlcal colls, etc~, ~rom lmproper contact and electrlcal 5~fl~i~

arclng. Thls materlal is naturally soaked wlth askarel, and may contain rrom 3 to 12% of the total rluld volume of the transforme-. Thls absorbed askarel wlll not drain out, nor can lt be flushed out by any known means, howeve- efflcient. Once the orlglnal bulk askarel ls replaced wlth a rresh non-PCB ~luld, the slow process o~
- difruslon permlts the old abso-bed askarel to g-adually leach out, and the PCB content Or the new rluld will ~lse. Thus, the new eoolant becomes contamlnated.
For pu-poses of classl~lcetlon of transfo-mers, the U. S. government regulatlon has deslgnated those ~lulds wlth grea~er than 500 ppm PCB as "PCB
transfo-mers", those wlth 50-500 ppm PCB as "PCB
contamlnated trans~ormers", and those wlth less than 50 ppm PCB as "non-PCB transfo-mers". Whlle ma~o- expenses may be entalled wlth the ~lrst two classl~lcatlons ln the event o~ a splll or the necessity Or dlsposal, the last catego-y is rree Or U. S. government regulatlon.
To achleve the last classlrlcatlon, the PCB
concentratlon must remaln below 50 ppm for at least 90 days, wlth the transro~mer ln ~ervice and surrlclently energlzed that temperatures Or 50C or hlghe~ are reallzed. This requlres a 90-day ave~aged rate Or elutlon Or 0.56 ppm/day. It 1~ antlclpated that most, lr not all, ~tate~ Or the U. S. wlll adopt regulatlons ~z~
.

whlch may be the 3ame a~, or st-lcter, kh~n U. S.
government -egulatlons. More lenlent regulatlons may be possible elsewhere.
The~e a.e a numbe. Or commercial ,etrorill procedu-es on the ma~ket lncludlng those desc-lbed ln `'The Ret-oSll PCB Removal System", Promotlonal llte~ature Or Dow Co~nlng Corp., #10-205-82 (19a2), and t-ade llte-ature of Posltive Technologles, Inc. on the Ze-o/PC/Forty p-ocess. These utlllze inltlal clean-out procedu-es of as hl~h errlclency as possible durlng whlch ~he electrlcal apparatus ls not ln operation.
Most lnclude a serles Or flushes wlth llqulds such as fuel oll, ethylene glycol, o~ a number of chlorlnated allphatic or a-omatlc compounds. Trlchlo-oethylene ~s a ravorlte rlush fluld. Some processes, such as the Posltlve Technologles, Inc. Zero/PC/Forty process use a fluorocarbon vapor scrub alternating wlth the llquld ~lushes. When the lnltlal clean-out procedure ls complete, the transfo~mer ls ~llled wlth slllcone rluld.
As erfectlve as these elaborate flu~hlng p~ocedures m~ght have been expected to be, they cannot remove PCB
adqorbed lnto the interstlces Or the celluloslc material. Consequently, the PCB content Or the slllcone c~olant gradually rl~es as the resldual PCB leaches out ~hlle the transrormer ~8 ln use. Thererore, ir one ~:5~34~i~

1476~-1 wlshes ~o reach a PCB-free state ("non-PCB" as deflned by ~. S. government regulatlons), it 18 necessary to elthe- pe-lodlcally change-out, or contlnually clean up, the sillcone fluld untll a leach rate o~ less than 50 ppm for 90 days ls reached.
Perlodlc change~out ls very expenslve, and because both the sillcone and PCB are essentlally non-volatlle, dlstlllatlon to separate them ls not p-actlcable and other methods o~ separatlon a-e expenslve or lnerfectlve. Dow Cornlng ln lts Ret-oSll process uses a contlnual carbon rlltratlon to clean up the rluld ("The RetroSil PCB Removal System", Promotlonal llteratu-e of Dow Co.nlng Corp., ~10-205-82 (1982); Jacquellne Cox, "Slllcone T-ansrormer Fluld from Dow Reduces PCB Levels to EPA Standards", Paper Trade Journal, Sept. 30, 1982;
T. O'Neil and J. J. Kelly, "Slllcone Retroflll of Askarel Tr nsrormers", Proc. Elec./Electron. Insul.
Con~., 13, 167-170 (1977); W. C. Page and T. Mlchaud, .
"Development Or Methods to Retroflll Transforme~~ wlth Slllcone T-ansrormer Llquid", Proc. Elec./Elect~on.
Insul. Conf., 13, 159-166 (1977)). Westlnghouse ln U. S.
Patent 4,124,834 has patented a transrormer wlth a rlltratlon procesq ror removlng PCB rrom the coolant, ~hlle RTE ln European Patent 0023111 has descrlbed the use o~ chlorlnated polymers as an ad~orblng medl~.

1 4?60-1 Howeve-, the rllters used in these processes are ve-y expenslve and the removal Or PCB ls very lner~ectlve, ~ due both to lack Or selectlvlty and the very low concent-ations Or PCB belng rlltered. In lieu Or filt-atlon, p-ocedu~es have been proposed lnvolvlng decantatlon (U. S. Patent 4,299,704) whlch ls lmp-actical due to solubllity llmltationsJ and only good at hlgh concentratlons; extractlon wlth polyglycols (F.
J. Iaconlannl, A. J. Sagglomo and S. W. Osbo-n, "PCB
Removal from T-ansformer Oll", EPRI PCB Semlnar, Dallas, Texas, December 3, 1981) or wlth ~upercritical CO2 (Rlchard P. deFlllppl, "CO2 as a Solvent: Application to Fats, Olls and Othe- Mate-lals", Chem. and Ind., June l9, 1982, pp. 390-94), and chemlcal destructlon Or the PCB's with sodlum (Brlti~h Patent 2,063,908). None of these schemes have been round to be economlcally or comme-clally practlcal for a~karel transformers.
However, the fllt~atlon scheme could be a reasonably erfectlve, though expensive, procedure 1~ it were not ~ for the ract that the leach rate 18 80 810w that it could take many years to reduce the resldual PCB to a polnt where the rlnal leach 18 reduced to an scceptable value (Gllbe~t Addls and Bentsu Ro, "Equlllbr1um Study o~ PCB's Between Tran~rormer Oll and Transrormer Solld ~5 Materlals", EPRI PCB Semlnar, December 3, 1981).

The problem and its cause are discussed ln L. A~
Mo-gan and R. C. Ostor~, ~'Problems A~soclated wlth the Retro~llllng of Askarel T-ansforMer~", IEEE Power Eng.
Soc., Wlnter Meetlng, N.Y., N.Y., Jan. 30 - Feb. 4, 1977, pap. A77~ p. 120-9. The solubility Or a typlcal sillcone oll in PCB ls p~actically nll (<0.5%) at tempe atures up to and over 100C, whlle the solubillty o~ PCB ln the silicone ranges from only 10% at 25C to 12% at 100C. Whlle thls llmited solublllty does not rest-lct the bulk slllcone from dlssolving the avallable f-ee PCB, lt does restnlct the ablllty Or the PCB to diffuse ~rom the pores or lnte-stlces Or the celluloslc matter.
Wlthln any glven pore f111ed wlth PCB-contalnlng coolant, dl~fuslon o~ PCB ouk must be accompanled by dlf~uslon Or sllicone ln. At some polnt wlthln the pore the-e must exlst an lnterface between the PCB-contalnlng coolant and the sillcone, across which nelther materlal can very rapidly dlfruse. Because the PCB ls more soluble ln the sllicone than the reve-se, the PCB wlll 910wly dl~use lnto the slllcone whlle the lnter~ace advance gradually lnto the pore. The llmlted ~olublllty restrlct~ the rate Or dlrruslon and whlle thls mech~nl~m mlght eventually clean the pore Or PCB, lt 18 orders o~ magnltude slower than lr the slllcone and PCB were mlsclble. The high viscosity Or the sillcone (and many other coolants) ls also an lnhibitlng ~actor. The result ls a long d-awn-out leach perlod Or perhaps several yea-s, durlng whlch the slllcone must be contlnually f~ltered or perlodlcally replaced to remove PCB's f~om lt. Thus, the slow leachlng of PCB's out of the solld lnsulatlon by the sillcone ls wo~se than no leaching at all since the dange-s o~ a splll Or PCB-containlng mate-lals wlll persls~ ove- a pe-lod of yea-s. Experlmental studles by Morgan and Ostho~f showed, rO- example, that e~fective PCB dlrruslvitles lnto a typlcal slllcone oll were only 1/10 Or those lnto a 10 centlstoke hydrocarbon oll. Although one mlght pre~e., then, to retrorlll wlth such a hyd~ocarbon oll, lf lt were not for the flre hazard of hydrocarbons, the-e stlll also ls the problem Or separatlng the PCB
f~om the contamlnated hydrocarbon oll whlch ls hlgh bolllng llke the PCB and llke the slllcone oll.
More lmportantly, undlluted PCBs are hlghly vlscous and thus relatlvely lmmoblle. Aska-els contaln PCB
dls~olved in "TCB" (trlchlorobenzene) or mlxtures Or TCB
and "TTCB" (tetrachlorobenzene) which thlns out o-reduces the vlsco~lty Or the PCB. TCB is much mo-e soluble ln slllcone than ls PCB ~n~, there~ore, TCB 1~
. 25 removed from the a~ka-el resldlng wlthln the lnterstlces .~S~4~i~

Or the lnsulatlon leavlng hlghly vlscous PCB (wlth o~
wlthout ~mall amounts of dlluentY, TCB or mixtures) withln the lnterstlcesO Consequently, treatments wlth sllicone (e.g. as in the Dow RetroSll system), wlthout prior treatment accordlng to thls lnvention, a~e counter-productlve and rende- the PCB remalning ln the lnterstlces even mo~e dl~ricult to remove. Thls can explaln the lack Or comme~clal success Or prlor systems in reclasslfylng t~ansfo.mers to a "non-PCB" status.
SVMMARY OF THE INVENTION
-. The p~esent inventlon ls based upon the unexpected findlng that dlelectric slllcone 0118 can and do elute PCB from the lnternal ln~ulatlon o~ electrlcal apparatus at an unexpectedly high rate, provlded that the coolant in the t-ansformer ls rlrst replaced wlth a relatively low viscoslty lnterlm coolant that is mlscible with PCB, for example, TCB o- mlxtures thereof wlth TTCB. The subsequent rate of elutlon of PCB lnto ~lllcone oll coolant, when practlclng the present lnventlon, was round to be surprl lngly hlgh and approxlmates o~ comes close to approxlmat~ng the rates Or elutlon Or PCB lnto relatlvely low vlscosit~ lnterlm coolants such as TCB o-~lxtures thereor with PCB.
No prlor art has been round to dlsclose the concept Or the p-esent lnvention whlch lnvolves rlrst uslng a ~9 -elatlvely low viscoslty interlm coolant substantlallY
free of PCBs as a comblned coolant and eluant durlng elect~lcal operatlon Or a t-ansformer o~ other electrlcal appa-atus ~ollowed by the use Or a dlelect~lc slllcone oll as a comblned PCB-eluant-coolant durlng subsequent electrical operatlon Or the transforme~
befo~e changlng ove- to the pe~manent slllcone oll coolant. Much less ls there any prior a~t ~uggesting that a sllicone oll coolant becomes, arter the lnte-lm coolant treatment, a relatlvely errlclent eluant fo~
PCB's.
The present lnventlon, more partlcularlyJ lnvolves a sultable temporary o~ lnterlm leachlng-coollng llquld (readlly mlsclble wlth PCB and havlng a -elatlvely low vlscoslty) as a substltute fo- PCB-contalnlng coolants ln electrlcal lnductlon apparatus, e.g. transforme~s, hsvlng a vessel contalnlng the coolant and an electrlcal wlndlng wlth porous ~olld celluloslc electrlc~l lnsulatlon lmme~sed ln and lmpregnated wlth PCB whlle electrlcally operatlng the tran~rormer for a su~flclent perlod Or tlme to elute PCB rrom the solld elect-lcal lnsulatlon contalned ln the transrormer. Durlng the perlod Or lnterlm operatlon, the interlm dlelectrlc Goollng llquld can be ch~nged to ~peed up the elutlon proce3s; the lnterlm goal belng to schleve a rate Or elutlon Or PCB into sald lnterlm coolant whlch is not more than 5 tlmes the selected target rate J pre~erably not more than 3 tlmes the selecked tarBet rate, and more preferably not mo-e than 2 tlmes the ~elected target -ate. In te-ms of U. S. gove~nment regulatlons for obtalnlng a "non-PCB" transformer, the interlm goal ls to achleve a rate of elution of PCB lnto sald lnterlm coolant not greater than 3 ppm PCB per day and preferably in the range of o.6 to 3 ppm PCB pe- day based on sllicone oll dlelectrlc to be used as permanent coolant [e.g., 0.4 to 5 ppm PCB per day based on the welght of lnterim coolant when sald lnte-lm coolant is "TCB mix" (a mlxture o~ 65-70 wto S of trlchlorobenzene and 35-30 wto % of tetrachlorobenzene)~. The dlrfe-ence in denslty (gram~ pe- cublc centlmeter at 25C.) o~ TCB
mix (1.492) and sillcone oll (0.975 for L-305) accounts for the difrerences ln the PCB elution rate flgu-es depending upon the eluant basls, e.g. TCB mlx basls o~
slllcone oll basls, because the elutlon rates are expressed ln ppm which 13 on a welght basls, the volume o~ eluants or coolants ln the transformer belng constant. Slnce the denslty Or TCB mlx 1 1.51 tlmes the denslty Or slllcone oil the rate of elutlon based on ~llcone oll ls 1.51 tlmes the rate o~ elutlon based on TCB mlx. In o-der to meet the U. S. government -equirement ror non PCB transrormers, the ultlmate selected target .ate Or elutlon woùld have to average below 0055 ppm PCB pe. day, based on the welght Or the slllcone oll dlelectrlc, ln order ror the PCB content of the slllcone oll coolant ln the transforme- to remaln below 50 ppm over a 90 day period. The ultlmate selected target rate Or elutlon can be lowe. or hlgher dependlng upon the regulatlons o~ the partlcular ~u~lsdlctlon ln whlch the trans~o-mer belng treated ls located. The-e may be some Jurlsdlctlons out~lde the Unlted States whlch have no regulatlons concernlng PCB
content, ln whlch case the transrormer owner may select a target -ate to reduce potentlal llabillty ln the event of a transformer ~plll. After the amount o~ leachable PCB ln the transrormer has been reduced to the deslred deg-ee, the lnte~lm dlelectrlc coollng liquld 18 removed ~rom the ve~sel and the vescel ls then ~llled wlth a PCB-rree dlelectric ~lllcone oll coollng llquld compatible wlth the transformer. The tran3rormer ls then operated untll the rate of elutlon of PCB into the ~lllcone oil coolant 18 less than the selected target rate Or elutlon. The dlelectrlc slllcone oil coolant can be changed over to rresh dlelectrlc ~llicone oll coolant as many tlmes as 18 necessary or deslrable ln order to achleve lesY than the ~elected target rate Or elutlon. A~ter a rate less than the selected ta-get rate is reached, the t.ansrormer ls recla~sl~ied as a non-PCB transro-me-. As an lmpo-tant pa~t Or the present invention, the resultlng transrormer contains slllcone oll coolant whlch ls not only ~ubstantl~lly f-ee o~ PCB bu~ which ls also substantially f-ee of TCB
or TTCB.
The following desc-lbes a procedure acco-dlng to this invention by whlch a PCB fluld ln a t-ansforme- ls replaced wlth a permanent PCB-free llquld coolant:
- (1) The transforme- ls deene-gized and the PCB-containlng fluld dralned and dlsposed Or ln acco-dance wlth environmentally acceptable procedu-es.
The ~ransrormer may be flushed wlth a flu~hlng rlu~d, e.g., t~lchIorobenzene or t-lchloroethylene, liquld o~
vapor, to remove "free" PCB rluld.
~2) The trans~ormer 18 rllled wlth a temporary or lnterim cooling rluld, such a~, trlchlorobenzene, TCB, or a mlxture thereof wlth tetrachlorobenzene, whlch ls ~ ml~clble wlth or dlssolves PCB and i8 capable o~.
penetratlng lnto the po~es Or the electrlcal lnsulatlon and whlch i~ al~o capable Or belng readlly ~eparated rrom the PCB, and elect-lcal operatlon ls resto-ed.
(3) The riuld temperature 18 monltored, and lf the electrlcal loadlng Or the transforme- does not provlde ~2~94 sufficlent fluid temperatune to provlde the deslred rate Or PCB elutlon, the.mal lagglng or even external heatlng can be provlded. Clrculatlon of the fluld through an exte-nal loop and pump for the purpose of heatlng same~
or fo- augmentlng the inte-nal clrculation, may also be provided.

(4) The rate of PCB elut~on lnto the lnterlm cooling fluld can be dete-mlned by perlodlc sampllng and analysls. The accumulated PCB ls perlodlcally -emoved D by removing the lnterlm coollng rluld containlng the PCB
and distillatlon Or the lnterlm coollng rluld, e.g., trichlorobenzene (TCB) rrom the PCB. Thls may be done by deenergizln~ the t-ansro~mer, dralnlng the old fluld ~or distlllatlon, and replaclng wlth r-esh lnte-lm coollng fluld, e.g., TCB. Alternatlvely, the tr~nsformer may be left operatlonal whlle r-esh lnterlm coollng ~luld, e.g., TCB, 18 added and old TCB removed vla a sllp st-eam or clrculatlon loop.

(5) The PCB-contamlnated TCB fluld ls dlstllled to provlde an essentlally PCB-~ree TCB dlstlllate, and a bottom product of PCB contaminated wlth TCB. The PC~
may be d~sposed of according to app~oved U. S.
government procedures, e .e., by lnclneratlon.

(6) When the elutlon rste Or PCB lnto the lnterlm coolant reaches the desired level, e.g. a rate ln the range o~ .4 to 2.0 ppm Or PCB per day based on the weight of sald lnterlm coolant when lt ls TCB mlx, the trans~orme- ls deenerglzed, dralned, and rllled with the dlelect-lc sllicone oll compatlble wlth the transrormer.
It ls then .etu~ned to service.

(7) The transformer ls then placed back in elect-lcal operatlon which ls contlnued untll the elutlon -ate drops below the selected target elution rate. If i~ does not, the PCB contamlnated sillcone oil ls removed and replaced wlth fresh sillcone oll and the electrlcal operatlon ls contlnued. The slllcone oll temperature ls monltored and, 1~ the electrlcal loadlng Or the trans~or~er does not provlde su~flclently hlgh ~luld tempe-ature (e.g., above 50C.) to provlde a desired hlgh rate Or PCB elutlon, thermal lagglng o-even external heatln~ can be provlded. Clrculatlon Or the Ylllcone oil through an external loop and pump ~or the purpose of heatlng same and 2ugmentlng lnternal clrculatlon may al~o be provlded.

(8) The transformer 1~ electrlcally operated, wlth or without slllcone oll changeovers, untll the elutlon rate drops below the selected target elutlon rate.

(9) In order to meet U. S. gove-nment regulatlons ~or "non-PCB" tran3rormers, an analy~ls at the end Or 90 days should show a PCB concentratlon Or les~ than 50 ppm 2~9 ~

_760-1 arter whlch the kransrormer ls reclasslried as nnon-PCB" .
Flg. 1 contalns plots of concentratlons, ppm, of PCB ln an lnte-lm dlelectrlc rluid (TCB mlx) durlng the ~ourth leach cycle, ln the slllcone oll durlng cycles 5, 6 and 7 in an actual t-ansformer with concentrations plotted on khe vertlcal ~cale vs. days elapsed (or soak tlme) on the horlzontal scale. (TCB mlx was used ln the rlrst th-ee cycles). The rlgure graphlcally lllust-ates the su-p-islng ~esults ob~alned by thls lnventlon. The rate o~ elutlon of PCB by the slllcone oll resultlng rrom the appllcatlon Or the present lnventlon ls unexpectedly hlgh.
Flg. 2 contalns plots Or concentratlons, ppm, of PCB ln the sllicone oll during cycles 2 and 3 ln an actual transro-mer wlth concentratlons plotted on the vertlcal scale ve~sus days elapsed on the horlzontal scale.
Fig. 3 contaln~ plots Or concentrations, ppm, Or PCB in the slllcone oll during cycle 2 ln an actual transrormer wlth concentratlons plotted on the vertlcal ~cale versus days elapsed on the horl~ontal 3cal~.
The selected ta-get rate Or elutlon Or PCB lnto sillcone oll coolant i~ .~6 ppm Or PCB per day b~sed on the weight o~ slllcone oll coolant when lt 1~ de~lred to proYlde less than 50 ppm PCB elutlon ror a 90 day perlod. In order to take advantage Or the rapldne~s Or elutlon of PCB by the slllcone oll as lllust~ated by Cycle 5 in the flgure wlthout sustalning the relatlvely slower elutlon .ate by the slllcone oll as shown ln the latter stages of Cycle 6, lt ls pre~erred that the changeove- from inte.lm coolant to the slllcone oll coolant be made after the elution rate lnto the lnte-lm coolant drops below three tlmes the selected target -ate Or elutlon. More prererably, the changeover ls made when the .ate Or elutlon of PCB lnto the lnterim coolant drops below 2.5 tlmes the selected target rate of elutlon, Stlll more preferably, the chflngeover ls made when the elutlon rate lnto the lnterlm coolant drops below about 2 tlmes the selected target rate Or elutlon.
Wlth respect to the flushlng step, whlle ef~lclent dralnlng and ~lushlng technlques should be used, these do not in them~elves constltute the lnventlon, but a-e a part o~ all heretofo-e known retro~lll procedu.es. They are a prelude to the most errlclent embodlment Or the lnventlon lt elr, but thelr value heretofore has been overrated, ln that lt i8 the 810w leach rate, not the errlclency Or flush which haq been round to llmlt the rate o~ PCB removal. A wlde varlety Or ~olvents may be u~ed in the ~lu~hlng step, lncludlng hydrocarbons such ~X59~

1~760-1 as gasollne, ke~osene, mlne.al oll or mlneral spirlts~
toiuene, turpentlne, or xyleneJ a wlde range of chlorlnated allphatic o. aromatlc hydroca~bons, alcohols, esters~ ketones, ~nd ~o rorth. However, from a mate-ials handling standpolnt and PCB separatlon logistlcs, lt is practical to avoid uslng any mo-e chemlcaI types than necessary, so that the use of the lntended temporary leach fluld, e.g., TCB or mlxtures thereor wlth tetrachlorobenzene, as the lnltlal flush ls most practical.
Inte.l~ dlelectrlc coollng flulds other than normally llquid t-lchlorobenzene, TCB, or a mlxture thereof wlth te~rachlorobenzene, can be used. The p-eferred inte~im fluid has the ~ollowing characterlstlcs: (a) it 13 compatible wlth PCB (i.e.
preferably dissolving at least 50% Or lts weight Or PCB, more prefe~ably, at least 90% of lts weight Or PCB and, most prererably, belng ml~clble ln all proportlons wlth PCB), and 18 compatlble wlth the slllcone oll; (b) it ls o~ low enough molecular weight to have good molecular moblllty to be able to enter the pores or lnterstlces of the solld ln~ulatlng materlal and lt promotes r~pld mutual dlr~uslon, pre~erably~ havlng a vlscosity at 25C
o~ 10 centlstokes or less and, more prererably, 3 centlstokes, or less,; (c) lt can be easlly sepflrated ~ai'3 14760-l ~e.g., by dlstlllatlon) rrom PCB and it preferably, has a bolllng polnt of 275C or less and, more prererably, 260C o- less from PCB; (d) lt 18 presently consldened envlnonmentally lnnocuous; and (e) it 15 compatlble wlth i typical t-ansrormen internals. Whlle TCB, or mlxtures wlth tet-achlorobenzene, ls prefe~red, a number Or alte-natlves, as above-mentioned can be used. These would include modlfied and synthetlc hydrocarbons, and va-lety of halogenated aromatlc and allphatlc co~pounds.
There are also a va-lety of llquld trlchlorobenzene lsomer mlxtures. The pre~erred TCB ~luld would be a mlxture Or these lsomers wlth or wlthout tet~achlo.obenzene lsomers. The advantage lles in the ~act that such a mlxture has a lowe- rreezlng polnt than do the indivldual lsomers, thus reduclng the chance of it solldl~ylng wlthln the trans~ormers ln very cold climates. Further, the mlxtures are o~ten the no-mal result Or manufacture and hence can C08t less than the separated and purlfled lndlvldual lsomers.
However, ~ny ~olvent ln whlch PCB is oluble can be used ~or ~lushlng and as an lnterlm dlelectrlc coollng llqu1d ror the leachlng Or PCB contalned ln a trans~ormer. Chlorlnated ~olvent~ such as trichloroethylene, trlchloroethane, tetrachloroethylene, tetrachloroethane, chlorlnated toluenes, chlorlnated ~9 xylenes, llquld t-lchlorobenzene and lts lsome.s ~nd ~lxtures, and llquld tetrachlorobenzene and its isomers Rnd mlxtu.es a.e suitable. Hydroca-bon solvents such as gasollne, kerosene, mlneral oll, mlneral splrlts, toluene, turpentlne and xylene can also be used but may be consldered to be too ~lammable ~or sare use.
Pa-tlcularly sultable solvents are the trlchlorobenzenes and tetrachlo-obenzenes because Or thelr low flammabllity cha-acte-lstlcs, thelr hlgh PCB
compatlblllty and thel. ablllty to clrculate throughout the transformer vessel and lnto the po-es or lnterstices Or the solld lnsulatlng materlal.
Because the prefer-ed obJective here ls to leach out the PCB at the rastest practlcal -ate, the preferred embodlment lnvolves operatlng the transformer to obtaln the fastest posslble dlfruslon r~tes Or PCB lnto the interlm coolant pu-suant to step (3) above and lnto the dlelectrlc silicone oll pursuan~ to step (7) above.

When used at its rull rated loadlng, a transrorme-~hould automatlcally provlde enough heat for thls purpose. However, slnce many transrormers are operated below thelr rated loading and below thei~ rated sare temper~ture (usually 70C to 110C), surrlclently elevated temperatures (e.g., at lea~t 50C) mlght not be ~chleved wlthout thermal lagglng or external heatlng.

Whlle thls thermal control represents a prererred embodlment Or thls lnventlon, lt 15 optlonal and not an essentlal ~equi-ement, there belng many transrorme~s rOr whlch such lagglng or heatlng may be lmpractlcal.
Leaching at lower tempe-atu-es, even amblent, ls workable but wlll take longe-.
Fluld ci~culatlon as speclfied ln steps (3) and (7) ls optlonal but ls an advantageous embodlment ln that such cl-culatlon wlll prevent the bulld-up Or concentratlon gradlents whlch can act to reta-d diffusion. Slnce elution ls a slow process, the clrculatlon rate need not be very rapld. Vlolent clrculatlon, Or cou-se, ls to be avolded ln order to avold damage to the lnternal st-ucture Or the transrormer. It ls recognlzed that many t-ansrormers may not, by thelr constructlon or placement, be -eadlly modlfled to utllize a clrculatlon loop, and such clrculation ls not consldered a necessa~y aspect, but only one embodlment Or thls lnventlon to lncrease elution rates. In most transrormers~ natural thermal gradlents alone wlll lnduce surrlclent clrculation e~peclally in tho~e cases where a relatlvely low vl~coslty, moblle coolant, such as TCB, ls uaed.
As the PCB content ln the TCB or other lnterlm coolant or ln the sillcone oll dleleotrlc ooolant ln the l4760-transfo-mer builds up, lt can eventually reach a polnt ~here dlrrusion no longer ~e.ves to leach PCB rrom the celluloslc pores o~ lnterstlces Or the lnsulatlon withln the transrorme- tankO A reductlon ln elutlon rate as dete~mined by sample analysls, ls a clue that thls may be occur-ing. If it ls determlned that thls ls occu--lng~ it may become necessary as specifled ln steps (4) and (7) to replace the PCB-laden lnterlm dlelectrlc coollng ~luld o- the dlelect-lc slllcone oil wlth fresh PCB-free fluld or oll. Thl~ ls most easlly accompllshed by deenerglzlng the transro~mer, dralnlng out the contamlnated leach rluid (lnterlm dlelectrlc coolant or slllcone oil), and replaclng lt wlth rresh rluld or oil.
As a practlcal matter, lnstead Or monltorlng the elutlon rate to determlne when dlfruslon no longer serves to efrectlvely leach PCB rron, the pores or lnter~tices of the elect-lcal lnsulatlon, it ls more practlcal to schedule the tran3former ror regular coolant changes.
Ir a non-PC~ tran~rorme~ is de31red, coolant changes are made arter selected perlods Or electrlcal operatlon untll the coolant elutes les~ than 50 ppm Or PCB (on slllcone oll coolant basls) arter 90 days operation.
Perlods Or electrlcal operatlon between coolant changes c~n be Aelected to be 20 day~ to 1 year tor more, lr the transrormer owner's needs prevent ~huttlng down the ~5 147~0-1 t-ansformer except at rare 3peclrled klmes, e.g., speclal hollday perlods 3 such that there may be more than one year between ~hutdowns, and po~sibly shutdowns can take place only every other year), pre~erably 30 to 120 days and most prererably 45 to 90 days.
The contamlnated leach fluid may then be dlstilled off and condensed ~or re-use to leave a PCB bottom product whlch is lnclnerated or otherwise dlsposed Or pursuant to ~. S. government regulatlons. Whlle a complete change o~ lnterlm coolant iæ prererred, lt ls posslble that the lnconvenlence Or addltlonal shutdGwns p-edlcates a dl~ferent p-ocedure, l.e., that Or ~lmultaneously lntroducing new fresh rluld and removlng the old contamlnated fluld whlle the transformer remalns ln operatlon. Simllarly, PCB-laden slllcone oll can be removed contlnuously rrom the transformer whlle ~lmultaneously contlnuously lntroduclng rresh PCB-free ~lllcone oil. It 1~ less efflclent because the fresh rluld or oll ~lxes with the old ln the transrormer, and fluld or oll of reduced PCB concentratlon ls actually removed. Thu~ to ellmlnQte all the PC~, more leach rluld or oll wlll ~have ko be removed than ror the prererred procedure. Thls penalty can be reduced 1~ one takes palns to avold excesslve mlxlng. For example, fre~h chllled TCB or other lnterlm dlelectrlc coollng .. . . . .. .. . . . . . . .

~2 ~3~1 rluld can be lntroduced lnto the bottom o~ the transrorme-, whlle warm, PCB-laden interlrn dlelectrlc - coollng ~luld ls removed rrom the top. The denslty dlffe-ence will retard mlxlng. Slmllarly, f.esh chllled sillcone oll (relatlvely hlgher denslty) can be lntroduced ln step (7) lnto the bottom Or the transforme- whlle warm, PCB-laden sllicone oll (relatlvely lowe- density) ls removed ~rom the top.
Regardless of the method used, the process wlll -equlre repetitlon untll the deslred PCB level ln sillcone oll can be malntained.
Whlle dlstlllatlon is the preferred method ror separatlng TCB or other lnterlm dielectrlc coolant and PCB, other methods may be feaslble, especially lf ~luld other than TCB ls cho~en as the tempora~y ~luld. The PCB can be removed ~rom the PCB-laden slllcone oll that may result from step (7) by contactlng lt (e~g. on-slte whlle step (7) i~ belng carried out or or~-slte a~ter PCB-laden slllcone oll ~as been removed) with act9vated charcoal, zeolltes or o~her adsorbant~ capable Or adsorblng the PCB rrom the slllcone oll. Any other method ror removlng PCB rrom the spent sllicone oll can be employed.
There 18 30me concern ~hat TCB ltselr, or other chlorlnated inte~lm dlelectrlc coolant, such as TTCB and ... .. .

~X~ 6~

othe~ h~logenaked solvents~ may eventually become 3uspect as a health hazard, and ~ha~ the transrormer should not be contamlnated wlth TCB or othe~
ob~ectlonable lnte-lm fluld. The rurther advantage of the p~ocedu-e of ~his lnvention ls that the transforme-at the concluslon of the method of thls lnventlon not only does not conta1n any ob~ectlonable amounts of PCB
but also ls substantlally free of TCB or any othe~
potentlally obJectlonable lnte~lm fluld. Accordlngly, the lnterlm coolant csn be replaced and the old batch sent to a stlll for purlrlcatlon, and the flrst cha-ge Or silicone oll can be replaced and khe old batch sent to an adso~ptlon system for purlflcatlon.
It ls preferred to make the rlnal flll of the t-ans~orme- wlth the same Rlllcone oll as was used ln the p~evlous leachlng-wlth-slllcone oll step, e.g. step (7). Alterna~lvely, other slllcone 0118 can be employed ~n 8teps (r) through (J) Or the broad scope Or thls lnventlon and ln steps (6) and (8) Or the more speclflc embodlments descrlbed he-elnabove. Sultable sillcone olls have the general rormula:

(CH3)3SlO[(CH3)2SiO]nSl(CH3)3 (Formula A) ~hereln n 18 Or a value surrlclent to provlde the 4~

desired vlscoslty (prererably a viscoslty at 25~C. of 20 to 200 centistokes, more prererably a ~lsc031ty at 25C.
o~ 30 to 100 centlstokes and most preferably a vlscoslty at 25~C. of 45 to 75 centlstokes).
It ls permlsslble to use other pe-manent coolants rather than slllcone oll in the ~lnal flll Or the transfo~me-. Other prefe-red coolants Or a pe~~anent nature- that can be used ln place pr the rlnal slllcone oll rlll lnclude dloctylphthalate, modlfled hydrocarbon oils, e.g. RTEmp Or RTE Corp., polyalphaoleflns, e.g.
PA~-13-C Or Unlroyal, synthetic ester ~lulds, and any othe- compatlble permanent rluld. It ls prererred that the pe~manent dlelectrlc fluld be characterlzed by a relatlvely hlgh boillng polnt compared to sald lnterlm dielectrlc solvent B0 that the lnterlm dlelectrlc solvent can be separated rrom the permanent fluld 1~ the need a-lses and also to avold releaslng permanent ~luld due to volatlllzatlon ln the event the transrorme-vessel (e.g., tank) ls ruptured.
Whlle the rollowlng have been suggested, and ~n some cases u~ed, as the rlnal rlll permanent dlelectrlc rlulds, they are less prererred than the relatlvely hlgh visco~lty, hlgh bolling permanent dlelectrlc rlulds:
tetrachlorodla-yl methane wlth or wlthout trlchlorotoluene l~omers, rreon, halogenated hyd~oca~bons, tetAachlo~oethylene, the trlchlorobenzene lsomers and the tetrachlorobenzene isomers. The trlchlorobenzene lsomers, the tetrachlorobenzene lsome-s, and mlxtures thereor have hlgh flammablllty ratlngs and other physlcal propertles slmllar to aska~el and the~efo-e are pre~erred amongs~ the les~ preferred pe-manent rlulds.
The rollowing lllustratlve examples are presented.
Each of the examples represents the actual t-eatment of actual t-ansformers and the data pre~ented ln Table l con~titutes or ls based upon data actually obtalned durlng the treatment of these t-ansrormers. In the examples, the rollowlng abb-evlatlons have been used.
TCB trichlorobenzene TTCB tetrachlorobenzene TCB mlx 30-35 wt~ S tetrachlorobenzene, TTCB, and 70-65 wt. S ln trichlorobenzene, TCB
(contalnlng an erfective amount Or a chlorlne scavenglng epoxlde-ba~ed lnhlbitor) PCB polychlorlnated blphenyls pDm parts Or PCB or TCB mlx per mllllon of coolan~ based on weight Aska-el A~a~el type A which 1~ 60 wt. S A~oclor 1260 and 40 wt. % TCB

s9~

Aroclor 1260 polychlorlnated blphenyl (60 wt. %
chlorlde) L-305 A slllcone oll wlthln the scope Or ~ormula (A) above havlng a vlscoslty Or 50 centistokes at 25C.
A "cycle" ls the period o~ time between changes ln the coolant. A "park" Or a cycle ls a portlon of a cycle where the leach rate lnto the coolant ls markedly dlrferent from the rate ln the earller or later portion o~ the cycle.

~S~63L

Examples 1, 2, 3, 4~ 5 and A
Table 1 glves summary data ror 8iX tran8rormers-The t~ans~o-mers fo- Examples 2, 3 and 4, deslgnated as ~460, #461 and #45g respectlvely, are a bank Or three ldentical Up~egrarf t-ansrormers Or 333 KVA capacity and electrlcally connected such that the load ls equally distrlbuted. Each Or these transfo~me~s contalned about 159 gallons Or mlne-al oil (Exxon Univolt lnhlblted oll, t-ansfo-mer g.ade). They had at one tlme been aska~el filled, and subsequently ~wltched to mlneral oll; hence contalned the resldual PCB levels shown in the Table.
The t-ansrormers ~or Examples 1, A and 5, deslgnated as #667, #668 and #669 -espectlvely, a~e a clmlla- bank Or three ldentlcal transrorme-s Or 333 KVA capaclty) and simlla-ly connected, but ln this case are Westlnghouse transrorme~s, and contalned about 190 gallons each of Type A a karel (60% Aroclo- 1260 and 40% TCB ) . These trans~ormers were expected to be about the most dlfflcult to le~ch. They are splral wound transforme-s ln whlch the paper lnsulatlon, and hence dl~fuslonal path length can be several lnche~ in depth. In contrast~ many tran~rormer~ sre Or the pancake design ln ~hlch path lengths wlll be less ~han sn lnch. All slx trans~orme-s were deenerglzed, dralned, then rln~ed and re~llled wlth the coolant ~s ~hown ln the Table ror .. ..

~94~i~

cycle 1. They we.e reene-glzed, and during the leaching cycles they we-e operated normally. Samples Or the ~ ~luid we-e taken pe-lodlcally rO- analysis, and Table 1 shows the results Or these analyses at the ends of parts of the leach cycles. The Table also Qhows temperatu~es of the fluld durlng the leach cycles. The normal load regulred of these transro~mers was rar below thelr rated capacity, and thus the normal temperatures Or operatlon were low (50C. o- less). Hlgher tempe-atu-es we-e achleved by lnsulatlng the cooling Tlns and ln some cases wrapplng them wlth heatlng tapes. Table 2 shows addltlonal detalled data ror the later cycles of these transrormers, especlally those cycles ln whlch L-305 ~lllcone oll was the solvent. In cases where the sillcone solvent leached bask out TCB or TCB mlx, these data also are glven ln Table 2.
Example 1~ #667, lllustrates this lnventlon. The transforme- was dralned of lts a~karel, rlnsed wlth TCB
mlx and re~llled wlth TCB mlx. The lnltlal leach rate was hlgh, due p.lmarlly to re~ldual unrlnsed llquor and due to the most eaqy to leach PCB (l.e., that in cou~se or shallow lnsulation), whlle the rate arter about rirty day~ wa~ much lower. Thus, cycle 1 ln Table 1 1~
dlvlded lnto two parts. The a~erage rate data ~or cycles 2~ 3 and 4 are glven ln Table 1. Whlle cycle 1 ... . .

was car-led out under amblent condltlon3, the transrormer was heated to 55qC. ~or cycle 2, and ~5C.
~or cycles 3 and 4. The average leach rate rO- cycle 4 was 4.78 ppm/day (on an L-305 basls), but because of the curvatu-e of the leach curve, the rate at the end of the cycle was about 2.5 ppm/day, a little less than flve tlmes the ta-get leach rate Or 0.55 ppm/day rO~
reclassl~lcatlon to non-PCB status. Thls ls lllust.ated ln Flgu~e 1, which shows the accumulatlon of PCB ln the solvent ror cycles 4, 5, 6 and 7. In the case of cycle 4, the solld llne rep-esents the analytlcal results ln ppm PCB by welght ln the TCB mlx, whlle the dashed llne represents the ~ame quantity Or PCB converted to an L-305 solvent basis. (For the other cycles with L-305 as the solvent the analytlcal data are automatlcally on an L-305_basls.) On the recognltlon that slllcone oll no-mally leaches askarel at a much slowe- rate than TCB
mix, and conslderatlon Or the fact th~t the transrorme-had he.etorore been artlrlcally heatedJ lt was expected that replacement Or the coolant wlth L-305 ~llicone oll would glve a leach rate whlch would be low enou6h ror reclasslrlcation. It wa8 surprl31ngly round, however, that such was not the case. Even though the heatlng had been reduced, the L-305 leached lnitlally ra3ter (6.06 ppm/day) than the TCB mlx had done at the end o~ cycle 4 . . .

147~0-1 (2.5 ppm/day~, and subqequently to a steady rate (2.38 ppm/day) approxlmately equal to that at the end Or cycle 4. This, too, ls shuwn in Flg. 1. It was recognized that this unexpectedly h1gh rate meant addltlonal PCB
S could be leached out, whlch would result ln a cleaner t~ansforme~, and ~o hasten thls leachlng, the trans~o-me- was reheated to 85C. (Thls reheating coincldes wlth the rapid rlse Or PCB in coolant around day 370 of cycle 5.) The ove-all average leach rate ln cycle 5 was 3.33 ppm/day. The t-ansro~mer was redralned and rllled wlth ~resh L-305 on day 390. ~he average rate durlng cycle 6 was 0.86 ppm/day, and on day 524 the flnal coolant of ~-esh L-305 was lntroduced. The artiflclal heatlng was removed, and the transformer was reclasslrled 91 days later as non-PCB. Whlle three cycles o~ L-305 were ~ctually used, it would have been posslble to comblne cycle~ 5 and 6, 80 that only one batch o~ L-305 would have been needed ror the "preparatory" leach and hence contamlnated wlth PCB.
Whlle lt was recognlzed that the une~pectedly hlgh leach rate lnto L-305 would requlre one or more preparator~ L-305 leach cycles, and hence the necesslty ~or a means Or separatlng L-305 and PCB (posslbly by adsorptlon, extr~ctlon, or chemical me~ns, e.g., 8S
2~ dlsclosed ln Fe~sler, U.S. 4,477,3549 October 16, 1984), 3 4~

it was also reallzed that thls would allow the removal Or most o~ the TCB mlx lnterim solvent f-om the transforme-. Table 2 glves addltlonal detall on the L-305 cycles, includlng the TCB mlx leached back out.
~able 2 shows that the rlnal ~111 Or pe-manent coolant contalns only 0.038% TCB or TTCB, whereas the ~lfth eycle would have contalned 4.5% chlorlnated compounds.
Table 1 shows also that the PCB level ln the TCB mlx at the end of cycle rour was only 351 ppm (calculated rrom 530 on an L-305 basls), whlle at the beglnnlng Or cycle 5 tbe ratlo o~ PCB to TCB mlx eluting (Table 2) ls 6.06/3375, or the equlvalent Or 1~00 ppm PCB ln TCB mlx.
Thus the hlgh rate could not be explalned completely on the basls of resldual llquo- left rrom cycle 4. TCB mlx wlth a hlghe~ concentration of PCB than the cycle 4 llquor was obviously leachlng. It 1~ clea- then that havlng treated the PCB wlth TCB mlx leads to faste-leachlng by L-305 than would have been expected on the basls Or the normal dlrrerences ln the leachants.
Example A ls a contrastlng example ln whlch the askarel was not treated with TCB mlx prlor to leaching wlth L-305. Trans~ormer ~668 was dralned Or askarel, spray rln3ed wlth L-305 and rllled wlth fresh L-305. At tbe end o~ the 392nd day the transrormer was again dralned, apray rlnsed wlth L-305, sub~equently rllled with fresh L-305, and operated ~o day 539 ln cycle 2.
At the end Or cycle 2 lt was stlll leachlng ak about 11~6 ppm/day. The lmportant lllustratlon Or thls example ls that leachlng with L-305 alone dld not lead to a reduced leach r~te in a reasonable pe-lod of tlme.
Although the leach rate ln the f~rs~ 28 days Or cycle 1 was compa~able to khe early leach rates ~or #667 and #669, lllust.atlng the removal Or the easily leached po~tlons of the contalned PCB, the rate dropped off rapldly ror #658, and contlnued ln the 6 to 11 ppm/day range for over 500 days (cycles 1 and 2). Transrormers #667 and #669, filled wlth TCB mlx, leached substantlally more ln the ~lr~t 96 days than trans~o-mer #668, rllled with L-305, dld ln 392 days. The elutlon rates ln each Or transrorme-s #667 and #669 ~ell because Or the gradual depletion Or the contalned PCB.
Example 2, #460, was dralnedJ rlnsed, and refllled wlth TCB (not the TCB mlx). At the end Or cycle 1 the PCB leach rate was reduced to 1.02 ppm/day, and lt was accordlngly dralned~ rln~ed wlth L-305, and rerllled wlth L-305. As ln the case o~ ~667, the PCB leach rate lncreased dramatically, extractlng much more PCB ln the rlr~t 10 days than would have been expected by L-305.

Thls is lllustrated ln Flg. 2. The concentration Or TCB

al80 rO8e dramatlcally, Table 2, more 80 than could have ~9 been explalned by resldual und-alned llquor alone, By day 283, howeve-, the rate Or PCB elutlon was reduced to only 0.12 ppm/day, and the coolant was d.alned and replaced by ~resh L-305. Nlnety-two days ~nto cycle 3 the t-ansfo-me- was reclasslfled as non-PCB at a PCB
level of only 5.5 ppm. The TCB level ln the flnal coolant was only 0.378%~
Example 3, #461, ln contra~t ~o Example 2, was leached wlth two cycles of TCB mlx, and was leaching at only 0.24 ppm/day when changed out to L-305. Thus only one cycle Or L-305 was requlred to recla~siry to non-PCB
status. However, the chlorinated compounds left ln the coolant amounted to 4.72~, and i~ lt ls deslred to -emove these, then anothe- L-305 cycle will be requi-ed.
In this event, it would have been ~ore er~lcient to have used L 305 ror the second cycle and taken advantage of the ~ood leachlng quality Or L-305 ror TCB treated PCB.
Example 4, ~459, represent~ another clrcumstance where the leach rate was reduced to a very low level before the L-305 wa~ lntroduced. Consequently lt wa~
possible to reclasslry with one cycle Or L-305, the ~inal coolant, but at the rather hlgh PCB level Or 37 ppm. Whlle the preparatory L-305 leach was not requlred ln thls speclrlc case, the transrormer dld exhlblt the abnormal rapld leachlng by L-305 Or PCB whlch hss been pretreated with an lnterlm ~olvent, the basis Or ~his inventlon. Thl~ i8 lllustrated ln Flg. 3. Example 4 represents the clrcumstance in whlch mlne-al oll was u~ed as the interlm solvent, a posslbllity ror those ~-ansro.mers whlch a-e not ~ubJect to strlct rl.e hazard regulations. Such a transformer would not normally be changed to L-305, unless a change ln locatlon or the rules applicable to that locatlon were anticlpated. The flnal flll o~ L-305 would be expected to contaln several percent Or mineral oll rrom the prevlous leach cycle, and very llkely thls would be su~flclent to reduce the ~ire polnt of the coolant below that required rO- the specirlc situatlon. Hence, an addltlonal refill Or L-305 would then llkely be required. Thus, mlne~al oll is a sultable lnterlm solvent for tho~e transforme-s whlch are 80 located that rlre is not a critlcal hazard.
It cannot be as easlly separated rrom PCB as is TCB o-TCB mlx, bu~ chemlcal methods are available, and ~olvent extrRctlon, e.g., Fessler, U. S. 4~477~354) October 16, 1984, ls also posslble.
Example 53 ~669, was treated slmlla-ly to #667 with the exceptlon that dur1ng the second and third cycles lt waq operated at lower temperatures than ~667, and hence lags behind. For thls reason, and becau~e Or a desire to be closer to the target value o~ 0.55 ppm/day before ~S9~

changlng to the rlrst cycle Or L-305 o- anothe~ rlnal coolant, lt ls stlll belng leached wlth TCB mlx.
Accordlngly, at present, lt pa~tlally lllu3trates the practlce of thls lnventlon.

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l4760-1 Slnce slllcone oll ls vlrtually lnsoluble in chlorobenzenes whlch, ln turn, are only sllghtly soluble ln the sllicone oll, (e.g. TCB mix ls soluble up to about 28 wt. % ln L-305 at 25C.), the pe~meatlon Or the sillcone oll into the inte~stlces or pores contalnlng the chlorobenzenes ln order to leach the chlorobenzenes o~ PCB wlthin the pores, must lnvolve an lnterrace.
Without being bound by theory, lt ls hypothesized that two types of mechanisms prevall, l.e. caplllary displacement or dralnage ln those ca~es where the pore ls open at bo~h ends and a dlrfuslonal mechanlsm ln those cases, fo- example, whe~e the pore ls open only at one end whereln the chlorobenzene, e.B. PCB and/or TCB
and/o- TTCB dl~uses lnto the sllicone oll and the lnterrace moves lnto the pore. The purpose Or thls example ls to lllu~trate the rate Or movement Or the lnterface lnto a slmulated pore.
Thls example utlllzed an ~pparatus comp~lslng a gla~s caplll~ry tube havlng a 2 mm. lnslde dlameter extendlng downwardly rrom ~he bottom o~ a stoppered glas~ vessel. The lower end o~ the caplllary was closed Orr and the upper end opened lnto the lnterlor Or the glas~ ve~sel. The caplllary tube when two-thlrds ~ull held 0.125 cc. and the glass ve3sel held about 15 cc.

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The capillary tube was marked wlth a mllllmete~ scale.
In each Or experlments ~1-12, a lower phase as identlrled ln Table 3 was introduced lnto the caplllary tube to flll lt about two-thlrds full. An uppe- phase S ~as ldentlfled ln Table 3 was then placed ln the upper thi-d of the capill~ry tube in the glass vessel. The lnltlal position o~ the lnterrace between the upper and lowe- phases was measured and the posltlon Or the inte-face was measu-ed on a dally basls to determlne the ~ate o~ downward movement of the lnte-face. The rates glven ln Table 3 for experlments #1-6 were dete-mlned over a 35 to 40 day perlod and the rates glven ln Table 3 for experlments #7-12 were measured over a 20 day perlod.

14760~

Table 3 Rates of Sllicone Penet~ation for Dlrfuslon_Alone Expt. Temp. Upper Lowe- Rate, No. ~C Phase Phase mm/day _ 1 60 L-305 1,2,4-TCB 0.307 2 60 L-305 TCB mix 0.225 3 60 L-305 Aska-el(l) 0.113 4 60 10% TCB/ 1,2,4-TCB 0.222 L-305(3) 5% TCB/ Askarel 0.059 L-305(4) 6 60 10% TCB/ Aska-el 0.020 L-305~3) 7 40 L-305 TCB mlx 0.152 8 40 L-305 Askarel 0.072 9 100 L-305 TCB mlx 0.229 100 L-305 Aska~el 0.111 11 40-100(2) L-305 TCB mlx 0.219 12 40-100 L-305 Askarel 0.079 (1) 60 wt. % PCB ~nd 40 wt. % TCB
(2) 40-100 means the temperature was alternated at 40C. on one day snd at 100C. on the next day (3) 10 wt. S TCB ln 90 wt. % L-305 (4) 5 wt. S TCB ln 95 wt. Z L 305 . . .

1~760-It is noted that the ratio Or the rate rOr TCB mlx to the rate for Askarel was about Z ~egardless Or tempe-atu-e (compare experiment #2 and #3 wlth #l and ~8 with #9 and #10). The da~a given ln Table 3 also lllust-ates that the rate at 600C. was about 1.5 tlmes the rate at 40C. and there appears to be no additlonal commensu-ate increase at 100C. Table 3 also shows the rate of penetratlon of TCB into the slllcone oll was g-eater than the rate Or penetration of TCB mlx which, ln tu-n, was g-eater than the rate Or penet~atlon of aska.el. The ~esults Or experlment ~6 suggest that back dl~ruslon Or TCB rrom the upper phase back lnto the lower phase may be re~ponslble ror the very low rate Or the dlfrusion found ~or experlment #6. Back dlfruslon ln expe.lment ~4 would not signlrlcantly erfect the rate because the lower pha~e was about 100% TCB whereas ln experlment #6 the lower phase contalned only 40% TCB.
The rlrst conclu~lon above, l.e., the fact that TCB mlx was eluted twlce as rast as Aska-el by L-305 is ~o the key rlndlng behlnd the use o~ the L 305 p~eparatory leach (e.g., Cycle 2 Or Example 2 and Cycle 5 Or Example 1). While L-305 may elute Aska~el ltselr slowly, once the latter ls dlluted wlth TCB mlx, the TCB mlx wlth lts contalned PCB can be eluted much raster. Thls permits the rinal L-305 leach to remove substantlally all the 9~

TCB mix, and much of the PCB whlch the TCB mlx has ltself falled to leach, p-lor ~o the flnal slllcone oll flll and reclasslrlcatlon to a non-PCB transformer.
The present lnventlon ls not llmlted to use ln transformers but can be used ln the case Or any electrical lnductlon apparatus uslng a dlelectrlc coolant llquld includlng electromagneks, llquld cooled electrlc motors, and capacltors, e.g., ballasts employed in fluorescent lights.

Claims (36)

WHAT IS CLAIMED IS:

1. A method for replacing a coolant containing PCB
in an electrical induction apparatus having a vessel containing said coolant, an electrical winding and porous solid cellulosic electrical insulation immersed in said PCB-containing coolant with a substantially PCB-free high boiling dielectric permanent coolant into which any residual PCBs elute in the apparatus at no greater than a selected target rate, said solid porous electrical insulation initially being impregnated with said PCB-containing coolant, said method comprising the steps of:
(a) removing the major portion of said coolant contained in the vessel;
(b) filling said vessel with an interim dielectric cooling liquid substantially free of PCB, said cooling liquid being (i) miscible with said PCB-containing coolant, (ii) sufficiently low in viscosity to circulate within said vessel and penetrate the interstices of said porous solid electrical insulation, and (iii) capable of being readily separated from PCB;
(c) electrically operating said electrical induction apparatus to elute PCB contained in said coolant impregnated in said porous solid insulation therefrom into said interim dielectric cooling liquid;

(d) thereafter removing said interim dielectric cooling liquid containing said eluted PCB from said vessel;
(e) repeating the cycle of steps (b), (c) and (d), if the rate of elution of PCB into said interim dielectric cooling liquid after electrical operation pursuant to step (c) exceeds 5 times said selected target rate, a sufficient number of times until the rate of elution of PCB into said interim dielectric cooling liquid does not exceed 5 times said selected target rate;
(f) filling said vessel with a substantially PCB-free dielectric silicone oil as cooling liquid;
(g) electrically operating said electrical induction apparatus containing said PCB-free dielectric silicone oil cooling liquid to elute interim dielectric cooling liquid and additional PCB impregnated in said porous solid insulation therefrom into said dielectric silicone oil;
(h) thereafter removing said dielectric silicone oil containing said eluted PCB from said vessel;
(i) repeating the cycle of steps (f), (g) and (h), if the rate of elution of PCB into said dielectric silicone oil exceeds said selected target rate of elution, a sufficient number of times until the rate of elution of PCB into said dielectric silicone oil is less than said selected target rate of elution; and (j) refilling said vessel with a substantially PCB-free permanent dielectric cooling liquid.

2. Method as claimed in claim 1 wherein step (c) is carried out for a period of 20 days to 2 years, the cycle defined in Step (e) is repeated if the rate of elution of PCB into the said interim dielectric cooling liquid after electrical operation pursuant to step (c) is in the range of 0.6 to 3 ppm of PCB per day based on the weight of said permanent coolant, and step (g) is carried out for a period of 20 days to 2 years.

3. Method as claimed in claim 1 wherein the cycle of steps (b), (c) and (d) is repeated as step (e) until the rate of elution of PCB into said interim dielectric cooling liquid is in the range of 1 to 3 times the selected target rate of elution into the coolant of an electrical apparatus rate as non-PCB.

4. Method as claimed in claim 1 wherein the cycle of steps (b), (c), and (d) is repeated as step (e) until the rate of elution of PCB into said interim dielectric cooling liquid is in the range of one to two times the selected target rate of elution into the coolant of an electrical apparatus rated as non-PCB.

5. Method as claimed in claim 4 wherein each step is continued for 30 to 120 days.

6. Method as claimed in claim 4 wherein, when carrying out step (d) of the previous cycle and step (b) of the next succeeding cycle, said interim cooling liquid is removed from the top of said vessel while fresh chilled interim dielectric cooling liquid is fed into the bottom of said vessel and while electrical operation of the apparatus is continued.

7. Method as claimed in claim 4 wherein, when carrying out step (h) of the previous cycle and step (f) of the next succeeding cycle, said dielectric silicone oil cooling liquid of the previous cycle is removed from the top of said vessel while fresh chilled dielectric silicone oil cooling liquid is fed into the bottom of said vessel and while electrical operation of the apparatus is continued.

8. Method as claimed in claim 4 wherein said vessel is provided with heat insulation in order to raise the temperature of the interim dielectric cooling liquid contained by it during each step (c) or to raise the temperature of the dielectric silicone oil cooling liquid contained by it during each step (g) while electrically operating said electrical induction apparatus.

9. Method as claimed in claim 4 wherein said interim dielectric cooling liquid in said vessel is heated during step (c) or said dlelectric silicone oil cooling liquid in said vessel is heated during step (g) while electrically operating said electric induction apparatus.

10. Method as claimed in claim 4 wherein during step (c) said interim dielectric cooling liquid or during step (g) said dielectric silicone oil cooling liquid is removed from said vessel, heated and returned to said vessel while maintaining sufficient dielectric fluid in said vessel and electrically operating said electrical induction apparatus.

11. Method as claimed in claim 4 wherein said interim dielectric liquid is more volatile than said PCB
and is separated from said PCB contained by distilling off said interim dielectric cooling liquid.

12. Method as claimed in claim 4 wherein said interim dielectric cooling liquid containing PCB eluted from said solid insulation is drawn off from said vessel as a slip stream during step (c) and fresh interim PCB-free dielectric cooling liquid substantially equivalent to the amount of PCB-containing interim dielectric fluid drawn off in said slip stream is added to said vessel.

13. Method as claimed in claim 4 wherein said dielectric silicone oil cooling liquid containing PCB
eluted from said electrical apparatus is drawn off from said vessel as a slip stream during step (g) and fresh dielectric silicone oil cooling liquid substantailly equivalent to the amount drawn off into said slip stream is added to said vessel.

14. Method as claimed in claim 4 wherein said vessel is flushed with a solvent for said PCB
following step (a) and before step (b).

15. Method as claimed in claim 14 wherein said flushing solvent is the same liquid as said interim dielectric cooling liquid used in step (b).

16. Method as claimed in claim 4 wherein said vessel is flushed with dielectric silicone oil cooling liquid following step (h) and before refilling said vessel.

17. Method as claimed in claim 1 wherein said interim dielectric cooling liquid is trichloro-benzene.

18. Method as claimed in claim 1 wherein said interim dielectric cooling liquid is mixture of trichlorobenezene and tetrachlorobenzene.

19. Method as claimed in claim 1 wherein said interim dielectric cooling liquid is trichloro-ethylene.

20. Method as claimed in claim 1 wherein said dielectric silicone oil cooling liquid is a poly(dimethylsiloxane) oil having a viscosity of about 50 centistokes at 25°C.

21. Method as claimed in claim 1 wherein said substantially PCB-free permanent dielectric cooling liquid used in step (j) is a dielectric silicone oil.

22. Method as claimed in claim 1 wherein the selected target rate of elution is 50 ppm after 90 days of electrical operation without change of coolant.

23. Method as claimed in claim 1 wherein said dielectric silicone oil cooling liquid is a poly-(dimethylsiloxane) oil having the formula:
(CH3)3SiO[(CH3)2SiO]nSi(CH3)3 wherein n is of value sufficient to provide a viscosity at 25°C of 20 to 200 centistokes.

24. A method for the replacement of PCB
containing coolant fluids from electrical induction apparatus which comprises:
A. removing PCB containing fluid from said apparatus and replacing said PCB containing fluid with a relatively low viscosity essentially non-PCB containing coolant fluid which is readily miscible with or capable of dissolving PCB;
B. electrically operating said apparatus to accelerate the elution of PCB contained in the insulation and other internal elements of said apparatus into said low viscosity fluid; and C. continuously or intermittently removing and replacing said low-viscosity fluid containing PCB
eluted from the internal elements of said apparatus with essentially non-PCB containing fluid until the amount of residual PCB
contamination within said apparatus is reduced to a desired level.

25. A method for the replacement of PCB
containing coolant fluids from electrical induction apparatus which comprises:
A. removing PCB containing fluid from said apparatus and replacing said PCB containing fluid with a low viscosity essentially non-PCB
containing fluid containing one or more halogenated aromatic or aliphatic solvents;
B. electrically operating said apparatus to accelerate the elution of PCB contained in the insulation and other internal elements of said apparatus into said low viscosity fluid; and C. continuously or intermittently removing and replacing said low-viscosity fluid containing PCB
eluted from the internal elements of said apparatus with essentially non-PCB containing fluid until the amount of residual PCB
contamination within said apparatus is reduced to a desired level.

26. A process for removing polychlorinated biphenyls from an electrical apparatus comprising:

A. filling the electrical apparatus with a dielectric fluid in liquid state in which polychlorinated biphenyls are soluble, thereby providing adequate insulation during the operation of the electrical apparatus;
B. dissolving polychlorinated biphenyls contained within the electrical apparatus into said dielectric fluid to form a solution;
C. conducting said solution from the electrical apparatus to a cleansing means;
D. cleansing said solution to thereby separate polychlorinated biphenyls from said dielectric fluid so that said dielectric fluid is re-usable; and E. recirculating said dielectric fluid back to the electrical apparatus for reuse, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

27. A process as recited in claim 26 wherein: said dielectric fluid has a boiling point lower than the boiling point of polychlorinated biphenyls so that said dielectric fluid is separated from the polychlorinated biphenyls by distillation.

28. A process as recited in claim 26 wherein: said cleansing is accomplished by distilling said solution and thus causing vaporization of said dielectric fluid while PCB's remain in liquid phase; and condensing the dielectric fluid vapor generated by said distilling step in preparation for the recirculating step.

29. A process for removing polychlorinated biphenyls and other contaminants from electrical apparatus, comprising the steps of:
A. substantially filling the electrical apparatus with a liquid dielectric fluid having a boiling point lower than that of polychlorinated biphenyls and in which the polychlorinated biphenyls are soluble so as to be dissolved within said liquid dielectric fluid, said liquid dielectric fluid providing adequate insulation during the operation of the electrical apparatus;
B. removing the liquid dielectric fluid from the electrical apparatus and cleansing the polychlorinated biphenyls from said fluid; and C. recirculating the cleansed liquid dielectric fluid back to the electrical apparatus for reuse therein, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

30. A process for removing polychlorinated biphenyls and other contaminants from electrical apparatus, and wherein the steps for so removing polychlorinated biphenyls from operating electrical apparatus are:
A. introducing to the apparatus a liquid solvent having a boiling point lower than that of polychlorinated biphenyls and in which the polychlorinated biphenyls are soluble so as to be dissolved within said solvent, said solvent having sufficient dielectric properties to insulate the electrical apparatus during the operation of the electrical apparatus;
B. removing said liquid solvent from the electrical apparatus and cleansing the polychlorinated biphenyls from said solvent; and C. recirculating said cleansed liquid solvent back to the electrical apparatus for reuse therein, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

31. A process for removing polychlorinated biphenyls from an electrical apparatus comprising:
A. introducing a dielectric fluid in liquid state in which polychlorinated biphenyls are soluble, to the electrical apparatus thereby filling the electrical apparatus with said dielectric fluid so that the polychlorinated biphenyls contained within the electrical apparatus form a solution with said dielectric fluid;

B. elevating the temperature of the dielectric fluid above ambient but below the boiling point of said dielectric fluid;
C. conducting said solution from the electrical apparatus to a cleansing means for separating said dielectric fluid from the polychlorinated biphenyls;
D. cleansing said solution to thereby separate polychlorinated biphenyls from said dielectric fluid so that said dielectric fluid is substantially free of polychlorinated biphenyls;
E. recirculating said dielectric fluid back to the electrical apparatus for substantially continuous removal of polychlorinated biphenyls from the electrical apparatus, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

32. A process for removing polychlorinated biphenyls and other contaminants from transformers and other electrical apparatus, and wherein the steps for so removing polychlorinated biphenyls from nonoperating electrical apparatus are:
A. continuously introducing to the electrical apparatus a liquid solvent having a boiling point lower than that of polychlorinated biphenyls and in which the polychlorinated biphenyls are soluble so as to be dissolved within said solvent;
B. continuously removing said liquid solvent from the electrical apparatus and cleansing the polychlorinated biphenyls from said liquid solvent;
C. continuously recirculating the cleansed liquid solvent back to the electrical apparatus for reuse therein; and D. maintaining the level of said liquid solvent in the electrical apparatus such that the electrical apparatus is substantially filled with said liquid solvent during said introducing, removing and recirculating steps, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

33. A process for removing polychlorinated biphenyls and other contaminants from transformers and other electrical apparatus, and wherein the steps for so removing polychlorinated biphenyls from operating electrical apparatus are:
A. de-energizing the electrical apparatus;

B. introducing to the apparatus a liquid solvent having a boiling point lower than that of polychlorinated biphenyls and in which the polychlorinated biphenyls are soluble so as to be dissolved within said solvent, said solvent having sufficient dielectric properties to serve as the dielectric fluid;
C. energizing the electrical apparatus thereby placing the electrical apparatus back in operation;
D. removing said liquid solvent from the electrical apparatus and cleansing the polychlorinated biphenyls therefrom;
E, recirculating said cleansed liquid solvent back to the electrical apparatus for reuse therein; and F. maintaining the level of said liquid solvent in the electrical apparatus such that the electrical apparatus is substantially filled with said liquid solvent during said introducing, removing and recirculating steps, said steps effectively and substantially removing the polychlorinated biphenyls from the electrical apparatus so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

34. A process for removing polychlorinated biphenyls in the dielectric fluid of an operating transformer comprising the steps of:
A. de-energizing the transformer;
B. draining the transformer of the dielectric fluid;
C. filling the transformer with a dielectric fluid in liquid phase in which polychlorinated biphenyls are soluble;
D. energizing the transformer;
E. conducting said dielectric fluid in liquid phase to a cleansing means and separating the polychlorinated biphenyls dissolved in said dielectric fluid from said dielectric fluid;
F. circulating said dielectric fluid from said cleansing means back to the transformer for repetition of the removal of dielectric fluid therefrom to the cleansing means, thus causing the polychlorinated biphenyls to concentrate in said cleansing means, said steps effectively and substantially removing the polychlorinated biphenyls from the transformer so that the leaching of residual polychlorinated biphenyls into the dielectric fluid will not exceed 50 ppm.

35. A process for removing polychlorinated biphenyls from an operating transformer as recited in claim 34 wherein:
said cleansing means is a distillation vessel.

36. A process for removing polychlorinated biphenyls from an operating transformer as recited in claim 34 further comprising:
maintaining the level of said dielectric fluid in liquid phase during said circulating and conducting steps such that the transformer remains substantially filled.