Document gD7mzMnGXBY288nG2vJp1Bg3V

cr> $ 'f ENVIRONMENTALLY ACCEPTABLE INSULATING FLUIDS MAY REPLACE ASKAREL 1u- BY: D. A, DUCKETT CHIEF PRODUCT ENGINEER RTE Corporation PRESENTED AT: The General Meeting of the Edison Electric Institute Transmission and Distribution Committee Minneapolis, Minnesota May 8, 1975 MQNS 045123 Environmentally Acceptable Insulating Fluids May Replace Askarel The transformation of electrical energy poses a fire hazard in highrise buildings, large industrial plants, and other locations. Utilities and contractors have four choices in supplying power to these locations, none of which have been economically practical but have met the fire codes and non-flammable conditions set forth by insurance underwriters and other regulatory bodies. These four choices include: 1. Remote transformers with long secondary runs at utilization voltage (occasionally at intermediate voltages which employ additional dry type transformers at key locations) 2. Dry type or gas cooled transformers 3. Fire-p roo f vaults A. Askarel cooled transformers The disadvantages of remote transformers are Immediately apparent. High cost and system complexity are difficult to justify. Voltage reg ulation problems exist. Gas cooled and dry type transformers have limitations in physical size and voltage. High cost, low overload capacity, and poor reliability make these a difficult choice. Fire-proof vaults with mineral oil transformers also have high installation costs. Space limitations tend to make this choice unaccept able for many instaIIations. This leaves the latter choice of askarel cooled transformers. Askarel cooled transformers have the advantages of lower initial unit cost than the previously mentioned choices, higher kV and kVA ratings, and better reliabil ity, physical size, and weight. The disadvantages of askarel come from Its fire-proof characteristics. Askarel, a polychlorinated biphenyl, is extremely stable in the environment. It does not bio-degrade and builds in the food chain affecting fish and certain types of birds. This has led to criticism by environmentalists. Costly precautions must be taken to either reclaim or dispose of askarels when their useful life is expended. Askarel is a powerful solvent and requires special sealing and insulation systems which add to its cost. Under arcing conditions, askarel produces hydrogen chloride, which is corrosive and toxic, and carbon, which prevents the use of submerged fuses and switching devices. MOWS 04514 Environmentally Acceptable Insulating Fluids May Replace Askarel The purpose of this paper is to acquaint you with the problems associated with askarel, and to share with you our attempts to develop a substitute insul ating fluid that is environmentally acceptable and will still do all the things necessary to provide successful transformer performance. The concern over askarel began in the mid-1960's with the search for the presence of 001 in the oceans. Refinements led to improved test equipment and monitoring techniques. Biphenyls, closely related to DOT, were also found to be prevalent in the environment. This led to restrictions and limitations on the amounts of biphenyls that could be allowed to enter the waterways. Open and semi-open systems utilizing askarels were abandoned and their use outlawed. In Japan, during the early 1970's, a food processing company was using askarel as a heat transfer fluid. A leak occurred, and many people were poisoned with excessive amounts of biphenyls. Because of this, and several other political issues of the time, Japan outlawed the use of askarels. They have since approved silicones for use In electrical devices on the National Rail System, where a replacement was necessary. These events led Dow Corning into research toward developing a silicone fluid for use as an alternate transformer coolant. Dow Corning reviewed their alternative fluid with Commonwealth Edison who suggested a joint venture with RTE, who could produce additional tests and sample transformers. During the 1960's, RTE was studying dielectric fluids for use in a new high temperature transformer. This design, the Power Seed, is a small kVA, porcelain enclosed, Class H, direct buried transformer. It was produced In the early 70's as a pilot project for development of a total underground system and is presently undergoing field testing at various utility sites. When approached by Commonwealth Edison and Dow Corning, RTE chose to also include the fluid used inthe Power Seed, RTEMP, and leave the door open for additional choices to provide an atmosphere for development. Fault Tests The main question was, "How do the fluids react when subjected to a high energy arc?" A fluid which continues to burn after a catastrophic fault has occurred could expand the explosion into a building fire. A fluid which does not continue to burn would limit the explosion to the immediate vicinity of the device. Would these new fluids, mainly because of their high flash points, put themselves out after an explosion, or would they continue to burn? A series of high current fault tests were performed. These tests compared transformer oil. Silicone DC-200, RTEMP, and askarel under high current submerged arcing conditions. Approximately four gallons of each fluid were placed In separate cylindrical containers and pre-heated to !50C. Each container had fused internal electrodes MONS 045125 Page Three Environmentally Acceptable Insulating Fluids May Replace Askarel Fault Tests (cont'd): mounted on the end of SBT Bushings. The electrodes were shaped upward with an expanding gup; this produced an effect which forced the arc upward and into the gas space, where it was present in the gasses and vaporized fluids as they were blown out of the test container (Figure I). The container was sealed before the test to contain the hot gasses in the air space prior to the explosion. A cable was attached to the cover to prevent it from leaving the test site. Barriers (Figure 2) were placed around the test container to simulate types of wall surfaces which might collect the flaming liquids and promote burning. r~r i i i- CONCRETE BLOCK 4' x 4' STEEL PLATE 4' x 4' To protect the surrounding environment from contam?nation, a nylon reinforced plastic sheet v/as laid down approximately 30 feet in the direction of the wind (less than 5 mph at test time). This was covered with a coating of sand to collect any unburnt fluids. After the tests were completed, the entire package was buried in a dry land fill area. MQNS Page Four Environmentally Acceptable Insulating Fluids May Replace Askarel Test Circuit The test circuit utilized is shown in Figure 3. SOURCE FIGURE 3 TEST C I RCU I T HONS 045127 Environmentally Acceptable Insulating Fluids May Replace Askarel Comments on each test follow with the visual and electrical data summarized: Test Number One - Transformer QiI This test was expected to be violent in nature and was placed in the series as a control sample. Results met expectations. The test current applied was A820 amperes at A800 volts. The back-up fuse cleared the fault after 10 cycles. The explosion was very violent with an initial fireball, orange and yellow in color, approximately 20 feet high by 15 feet in diameter. This mushroomed into a cloud of flame and smoke approximately 55 feet high by **0 feet in diameter. The resulting smoke cloud produced was voluminous and black to dark grey in color. The test container and surrounding area were covered with burning liquid which was manually extinguished quickly to avoid damage to the test cable and connectors. Test Number Two - Silicone Fluid DC-200 (50 CS) The test current applied was **760 amperes at **800 volts. The back-up fuse did not blow. The fault self-cleared after *'i cycles; this will be discussed later. Compared to Test One, the explosion and the noise produced were mild. A fireball, orange and yellow in color, approximately 30 feet high by 15 feet in diameter was noted. The flash appeared to be very bright In comparison to the other tests. The smoke produced was white in color and of less volume than Test One. Black flakes were seen in the cloud. White particles, identified as silica, were noted floating in the air after the explosion. Films show a flame, low in magnitude and quiet in nature, to burn for a few seconds in the test container after the explosion then self-extinguish. Test Number Three - RTE High Temperature Liquid (RTEMP) The test current applied was **700 amperes at **800 volts. The fault self-cleared after i| cycles. The explosion was mild in comparison to Test One and resulted in a fireball approximately 15 feet high by 10 feet in diameter. A quantity of non-burning fluid was noted preceding the fireball upward; this can be seen failing back to earth in the films. The smoke was grey-white in color and similar in volume to the smoke cloud of Test Number Two. Noise was mild compared to Test One. HONS 04512a Environmentally Acceptable Insulating Fluids May Replace Askarel Test Number Three (cont'd) A re-strike occurred approximately M5 cycles after the initial fault. The loss of fluid in the test container was due to the placement of the arc and the physical dimensions of the container. The fluid self-cleared and the electrodes were energized as the remaining fluid began to settle. The current tracked across the contaminated surface and was cleared by the back-up fuse. This effect was noted in the rehearsal tests for both Silicone and RTEMP and should not be considered a negative point toward the fluids, but a criticism of the physical parameters selected for the containers and electrodes. Comments were made that possibly the secondary flashover extinguished the flame; however, films show RTEMP burning in the test container after the re-strike and self-extingulsh. Included with this report is a series of sequential photographs for each test. The machine driven camera speed was 12 frames/ll seconds, or approximately 0.92 seconds (55 cycles) between frames. By this timing, the re-strike would occur between frame two and three of the sequence. From the remaining frames, It can be seen that the flame was present for a few seconds after the re-strike. High speed movies also verify this. Test Number Four - Askarel The askarel used in the test was Inerteen* 70-30. The test current was *660 amperes at ^800 volts. The back-up fuse cleared the circuit after ll-J cycles. A fireball of bright orange flame, approximately 25 feet high by 15 feet in diameter, rose in a pitch black smoke cloud for l~i seconds after the explosion; black stringers were noted falling from the cloud. There was no fire in or around the test sample. The smoke cloud was voluminous, approximately 25 feet high by *40 feet in diameter, and remained n the air about 20 feet above the ground for approxi mately five to ten minutes before dissipating. The test site and equipment were covered with black fluid and the area had a very noxious odor. Dielectric tests show the fluid to retain little dielectric strength after the fault. Before the test, the fluid was good for kV; after the test, it was reduced to only 7 kV. It would be an understatement to say that the observers were shocked at the poor performance of this approved "safe" fluid. Although the fluid itself did not burn, flame was present in the smoke cloud (experts from Monsanto have Identified this as possibly "free carbon" igniting). The dense smoke was considered a dangerous by-product. *Trademark of Westinghouse Electric Corporation HONS 045129 Environmentally Acceptable Insulating Fluids May Replace Askarel Test Cone(unions Both RTEMP and Silicone DC-200 (50 CS) passed the test requirements and deserve further investigation toward approval as an alternate for the environ mentally hazardous askarels. In Test One, transformer oil, all liquid thrown out of the container would have been consumed by fire if it had not been extinguished. This could have led to a disastrous building fire. As the temperature of the liquids were below the fire point in the remaining tests, Silicone, RTEMP, and askarel,the fluids self-extinguished. This would limit the after effects of an explosion and, with reasonable precautions, would allow electrical equipment with these fluids to be mounted inside building structures. The gasses produced by the askarel are considered extremely dangerous to the well-being of anyone In the area. Askarels are non-biodegradable in the environment and dangerous as they build in the food chain. They were established at a time when little or no concern was felt for these objections, and it's doubtful that any testing was done to research these areas. A simple non-flam mability test would meet the requirements for indoor applications; historical usage has gained universal approval. Silicone fluid, although also non-biodegradable, is not known to be dangerous in the environment. The only questionable by-product of an explosion is silica particles, of which only minimal exposure is possible. The RTE High Temperature Fluid, like transformer oil, is biodegradable. The gasses produced during an explosion are essentially hydrocarbons. Both Silicone and RTEMP limited the duration of the fault and self-cleared; this is a property which adds to the value of these liquids and is a desirable feature for designs requiring submerged high voltage fuses, breakers, and switchii devices. Table l shows the fluid properties before and after the arcing tests. This data reflects the remaining dielectric integrity of the fluids after high current arcing and shows RTEMP to surpass all tested fluids. The electrodes in all cases showed signs of arcing along the entire length and burning at the top. This indicates that the arcs followed theory and were present in the gasses and vaporized fluids as they were thrown upward. Approximately one gallon of fluid was left in each of the test containers after each test. HONS 045130 Environmentally Acceptable Insulating Fluids May Replace Askarel Test Conclusions ( cont'd.) The level of fault currents applied during the tests, *1,000 to 5,000 amperes, and the voltage, 4.8 kV, could be considered low under today's conditions of higher available fault energy and increasing voltage levels. These values were selected to extend the possible fault time to 8-12 cycles with available back-up fusing. Higher values of energy, l^t, could be released into the test containers if the current were increased. Higher voltages might promote arc expansion to the walls of the container and other ground points. The physical placement of the arc and the mass of the fluid in the container would also effect the results. It has been discussed that this should suggest further testing to study the explosive potential of the various liquids under these varied conditions; however, the purpose of these tests was to determine the flammability of the liquids after an explosion. Both Silicone and RTEMP self-extinguished and passed the test. 2 Higher values of I t might create a greater explosion in any of the fluids but would not effect the self-extinguishing feature unless the mass of the fluid was so small as to have its surface temperature raised to values in excess of the fire point of the liquid. Although the temperature at the point of arcing Is several thousand degrees, this can last only for a few cycles and cannot significantly effect the temperature of a container the size of even a small distribution transformer. Greater values of l^t would create a more spectacular test, but the flammability results would remain the same. HONS 045131 DIELECTRIC FLUIDS - EXPLOSION TESTS NOV. 9.197* r. TEST No. 3 RTE HIGH TEMP (RTEMP) TEST No. 4 PCB (ASKAREL) RTE CORPORATION Waukesha. Wisconsin HONS 045132 MONS 0 4 5 1 3 3 HONS 0 4 5 1 3 4 HONS 045X35 MONS 045136 TRANSFORMER OIL SILICONE FLUID DC-200 RTE HIGH TEMPERATURE FLUID (RTEMP) ASKAREL BEFORE TEST AFTER TEST BEFORE TEST AFTER TEST BEFORE TEST AFTER TEST BEFORE TEST AFTER TEST DIELECTRIC STRENGTH (kV) ASTM 087 32.0 20. 5 1(2.0 15.5 35.0 25.5 35-0 7.0 1 FT (dyne/cm) ASTM D971 VISCOSITY (SSU) ASTM 088 59.0 58 0 25: 55.5 20.8 22.2 25.5 50.0 50.0 55.5 11.U p 25c 50 e 25C 66 p 25C 8000 9 25C 1900 0 25C 5L p 25C 66 @ 25C TABLE I FLU I D PROPERTI ES BEFORE ANO AFTER FAULT TESTS MUNS 045137 MONS 0 4 5 1 3 8 TEST No. 2 SILICONE FLUID DC-- 200 TEST No. 4 RTE CORPORATION WaAortu, Wmanm CHEMICAL BONOS AND GASES PRODUCED DURING ARCING Askare1s Askarels arc mixtures of polychlorinated biphenyls. Depending on the manufac lurur, they may be such a mixture as Pyranol* 1 ^*70 which is chlorinated diphenyl, trichlorobenzine and tetrach1orobenzine, with 0.125?; by weight, amount of tin-tetraphenyl added as a "getter" to react with the hydrochloric acid produced during aging. The material used in the tests was 70? pentachlorobiphenol and 30? trichlorobenzine. Ihese have the following chemical bonds: PENTACHLOROBIPHENOL CL \ C CL / /\/ \ \/ c CL \/ c / \ #\ CL '``Trnilpmnrk of Onoral Electric Company MONS 045139 TRICML0R0BEN2INE H I CL C CL \/\ / cc II I cc /\/ \ HC H CL During breakdown, the products of decomposition are: ABSENCE OF OXYGEN Hydrochloric Acid (HCL) Free Carbon (C) PRESENCE OF OXYGEN Hydrochloric Acid (HCL) Carbon (C) Water (HO) Carbon Monoxide (CO) Carbon Dioxide (C0^) Further, with arcing in the presence of paper, phosgene gas (C CL2 0) is also possible. HONS 045140 S i 1icone DC-200 The silicone fluid used in the test was DC-200, 50 CS. This i a dimethyl silicone fluid which has the chemical bonds shown below: DIMETHYL SILICONE FLUIDS Some of the gasses produced during arcing are: ABSENCE OF OXYGEN Silicon Dioxide (Si 0 ) Hydrogen (H ) Hydrocarbons (CHn) PRESENCE OK OXYGEN S i 1icon Dioxide {Si Hydrogen (H ) Water (H^O) Carbon Monoxide (CO) Carbon Dioxide (CO^) Hydrocarbons (CHn) 0*) ' MQNS 045141 RTEMP RTCMP is substantially o mineral oil. It is refined from a paraffinic type base oil. A special two-stage hydro-treating process Is used in its manufacture which results in a highly refined stable oil of food grade. It has been used in food products and associated equipment, and would be considered safe in the environment. The chemical bonds of this type of oil would be similar to the paraffinic group shown below: TYPICAL PARAFFINIC TYPE OILS H H- C -H K-C-H I H H-C-H I H As can be seen, the paraffins are characterized by long straight chain segments with relatively few off-shoots or attachments. Under arcing conditions these chains would be broken and the products of decomposition would be those released during the breakdown of any hydro-carbon of similar structure. Shown below are some of the typical products of decomposition which would be found during this process: ABSENCE OF OXYGEN Hydrogen (H ) Carbon (C) Hydrocarbons (CHn) PRESENCE OF OXYGEN Water (H2O) Carbon Monoxide (CO) Carbon Dioxide (CO2) Hydrocarbons (CM n) mons FLU 1D PROPERT1ES : TRANSFORMER OIL RTEMP SILICONE DC-200 ASKAREL ELECTRIC Dielectric Strength (ASTM D-877) kV (25C-flulds as received from vendor) 31 37 36 40 Dielectric Constant Power Factor 50C I00C 150C Dissipation Factor (ASTM D-150) Volume Resistivity (ASTM D~1169) Ohm-cm 2-2.5 <.01 1.0 2.5 2.2 0.6 2.2 10.5 2.76 0.6 0.9 1.5 6.5 _ -- -- .00011 1.0 x 10 i 2 <05 1.1 x I013 .0002 5.6 X 10,<t .03 5.0 x 1012 THERMAL Flash Point C Fire Point C Pour Point C Thermal Conductivity 25C cal/(sec-cm -C)/cm Specific Heat (cal/gm/C) 25C Coefficient of Expansion(cc/cc-C) PHYSICAL Specific Gravity (ASTM D-IST0) 25C Interfacial Tension (dyne/cm) Neutralization Number (mgKOH/gram) Viscosity (cent 1 stokes) 25C 50c I00C 150 C 150 162 <-57 .000318 296 321 -21 .000297 393 .00063 .650 .0008 .883 69. 6 <02 16 8 3 .883 25.5 .011 800 150 24 8 306 360 -55 .000360 .360 .00106 .961 20.8 <.01 50 30 16 12 _ -- -37 .000262 .266 .00067 1.565 50.0 <01 18 10 6 <3 f MONS 045143 l MATERIAL COMPATIBILI TV STUDY TrunsTorr.jer oil, RTEMP, Silicone DC-200, and Askarel have been compared in sealed bomb accelerated aging tests. Tins is a sramiard material compatibility test at 150C for 6 weeks, The sealed bombs contain paper, epoxies & varnishes, various coated wire samples, and the insulating fluid. Physical and electrical character i st i c ?; are compared at the end of the test period. RESULTS: TRANSFORMER OIL RTEMP SILICONE DC-200 ASKAREL INITIAL 6 WKS AGING (>>i50oc INITIAL 6 WKS AGING @I50C INITIAL 6 WKS AGING @150C INITIAL 6 WKS AGING (i 1 5 0 C FLUID PROPERTIES Dielectric Strength (kV) 1 FT (dyne/cm) NEUT NUMBER (mgKOH/gr) 37. l 48.0 .0015 21.5 40. 4 .078 39.8 55.7 .011 24.7 35.0 0-7 .099 30.8 .0025 (290 38.5 29. 0 24.2 . 103 35-9 .005 432.2 .095 PAPER Tensi1e Strength (kpsi) Dielectric Strength (v/ini 1) 14.9 1480 11.6 1540 14.9 1480 12.0 1610 14.9 1480 12.2 1530 14.9 148o 11.7 1460 WIRE Dielectric Strength (v/mi1) 3000 3400 3000 3500 3000 3330 3000 3600 ''Average of best three readings(discussed further in test conclusion? HONS 045144 Insulating Fluids (Alter Aging) Ti on s f onne r 0 i 1 The t i'<mr> f orne r oil was clear and without sediment. The color was a golden amber. RTCMP The RTEMP fluid was free of sediment and yellow to amber in color. DC-200 The color of the DC-200 in one bomb was a water white and clear. The other bombs' fluid was milky white. Askarel The askarel yellowed slightly during aging. The duplicate bomb of this set was full of sediment and the wire film insulation had blackened considerably Paper and Magnet Wire (After Aging) Examination of the paper and magnet wire revealed that one bomb containing askarel exhibited severe blackening of the film insulation on the magnet wire. The other bomb containing askarel exhibited a jelly-like material on the paper insulation. The remaining bombs containing transformer oil, RTEMP, and Silicone DC-200 did not show any visible signs of degradation. TesL Conclusions The RTEMP fluid compares favorably with askarel and slightly better than transformer oil. The dielectric strength of both the magnet wire and paper for transformer or I, RTEMP, and Silicone DC-200 showed some improvement during I he aging tests. This is because of the increased quality of impregnation of the materials. This would be reduced on longer test runs where breakdown of the insulation would begin to occur. The paper in the askarel shows both physical and dielectric deterioration. The dielectric strength of the Silicone DC-200 is difficult to measure on ASTM D-877- The materia) forms resistive bridges (approximate1y 13k ohms) across the gaps on each test shot which must be cleaned off before continuing the test. This phenomena is very questionable and should be investigated fur the However, it should be pointed out that initial dielectric strength is more important than rehealing ability after an arc. The insulating fluid should * prevent the arc and the silicone appears to be an excellent fluid from tins standpoint. The resistive bridges would be of interest in designs utilizing load tap changers and similar load switching devices. MOMS 045145 (HAT RUNS ON SAMPLE 167 kVA 7200 - 120/2^0 TRANSFORMERS Transformers of identical design have been constructed and filled with t rani, f or me r oil, RTEMP, and Silicone DC - 200 (50C S) . Hea t Run*j have been mode to determine the thermal effects of the higher viscosity fluids at opeia ting loads: TRAN5F0RMER 01 L RTEMP S 1 L 1 t0NE DC- 200 (50CS) TOP 01L R 1 SE C AVERAGE WINDING RISE C TOP 01L R 1 SE oc AVERAGE W1 NO 1NG RISE C TOP 0 1 L R 1 SE C AVERAGE WINDING RISE C 100? LOAD 53 1 25? LOAD 85 1 50? LOAD 111 65 90 120 73 95 125 83 110 Ul 69 96 1 76 80 113 157 TABLE I I STEADY STATE TEMPERATURE RISE MOWS 045146 This data agrees with the measured viscosity-tempera tore characteristics of tlir fluids and questions the ability to make direct fluid substitutions witbuul design modificot ioiis to maintain a 65C rise limitation in transformers designed for Mineral oil. Mineral oil, however, has been shown to be about 30?. better as a hnt transfc modi,i than askarel. This would suggest that direct replacement of either Si1icom DC-tOO ..a RTEMP for askarel in units designed for askarel is probably possible. Environmentally Acceptable Insulating Fluids Hay Replace Askarel Cone 1 usions: The availability of RTEMP, Silicone Fluid, and askarel depend upon demand. Presently, facilities are in existance for manufacturing large quantities of the oskarels. Monsanto is working to develop new fluids which are mure enviruumento11y acceptable and will utilize their facilities. Dow Corning is studying the equipmenl necessary to enter this market. The supplier of RTEMP is ready to go with limited quantities presently hut can, over a period of time, increase fits facili ties and lower the cost of RTEMP considerably. The possibility of new fluids other than those already studied is great. Dow Corning is working to modify their silicones and, as already mentioned, Monsanto is developing new fluids for use in their facilities. After having several discussions with various oil companies, it appears as though possible new candidates may be setting on laboratory shelves woiting for someone to find a use for them. These are being explored. For RTEMP to find total acceptability, a modification must be made in the material to obtain a lower pour point. Tests will have to be conducted to make sure these modifications do not affect the fluid's desirable properties. Presently, usage of this material should be limited to sub-surface (below the frost line) and indoor applications. Precautions for installation during extreme cold periods would be necessary. For any dielectric fluids to find acceptability, national approval and recog nition must be obtained. We arc currently working with insurance underwriters to set up a testing program and provide a proposal for modification of the national fire code. If approved, the earliest possible date any new fluid could be listed in the NEC would be in the 19/8 printing. In the meantime, several utilities are conducting testing programs and requesting sample transformers for evaluation. Economic studies covering the total installed, operating, insurance, and disposal costs are being planned. Manufacturers must explore the impact of storage, processing,and handling fac i lilies. Additional testing may be required. Thermal and dielertric properties might be further explored. Tests such as submerged switching of loads and perhaps addi tional explosion tests with higher kV, kA arcs may be necessary. Additional measurement of explosion violence and gasses produced may be desired. If you, as a user of these products, now feel a positive step is required, we ask for your patticipat ion. Please write RTE and express your interests. Feci freo to ask questions and make suggestions. We need all comments, positive and negative, to formulate future planning. 1. What further testing should be done to probe the flammability questions? 2. Who needs to be convinced to get acceptabi1ity of these new products? 3. How do we go about it? . What testing program must be submitted to the NEC to gain notional approv.il HONS 045147 SOURCES: INSULATING MATERIALS FOR DESIGN AND ENGINEERING PRACT John W i 1 ey and Sons., Inc., 1962 TRANSFORMER ENGINEERING, SECOND EDITION, Blume, Wi ley TRANSFORMER ASKAREL INSPECTION AND MAINTENANCE GUIDE, Monsanto Bulletin No. IC/FF-33 SILICONE FLUIDS VS. HYDROCARBON OILS: A COMPARISON OF THERMAL AND ELECTRICAL PERFORMANCE CAPABILITIES, R. F. Buran and G. A. Vincent, Dow Corning Corporation, IEEE Paper No. C7^ 258-0, 197^ PERFORMANCE CAPABILITIES OF SILICONE FLUIDS AS INSULATING LIQUIDS FOR FOR HIGH VOLTAGE TRANSFORMERS, R. F. Buran and T. Orbeck, Dow Corning Corporation, 197^ GUIDE FOR ACCEPTANCE AND MAINTENANCE OF TRANSFORMER ASKAREL IN EQUIPMENT, IEEE SILICONE FLUID FILLED TRANSFORMERS - AN ALTERNATIVE TO ASKAREL AND DRY-TYPE TRANSFORMERS?, R. F. Buran and T. Orbeck, Dow Corning Corporation, 19/3 ASIM STANDARDS, Book AO CATASTROPHIC EXPLOSION TESTS IN INSULATING FLUIDS, D. A. Duckett, RTC Corporation, November 197^ LONG TERM AGING OF INSULATING FLUIDS, D. J. Winter, RTE Corporation, April 1975 D. A. Duckett April !', 19/5 DAD/kb HONS O'*5148