CA1086487A - Insulating oil, method of use and electrical equipment utilizing said oil - Google Patents

Abstract

INSULATING OIL, METHOD OF USE
AND ELECTRICAL EQUIPMENT UTILIZING SAID OIL

Abstract of the Disclosure The unique, relatively nonflammable, environment-ally safe, insulating oil comprises a saturated hydrocarbon oil having a molecular weight of about 500 to about 700, and a fire point above 200°C. The electrical equipment comprises an oil-sealed tank, a unique insulating oil filling said tank, and an electrical component such as a conductive coil immersed in said insulating oil. A method of filling the oil-sealed tank of an electrical apparatus with the unique insulating oil also is disclosed.

Description

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Rel~ated Cases ; This application corresponds with our United States Patent No. 4,082,866 whieh issued April 4, 1978.
- Background of the Invention An insulating oil for use in transformers and - other electrical equipment has two important functions. First, -it aets as an electrical insulating medium and second, it .~ transports heat generated in the windings and eore of the transformer or in connected circuits to cooling surfaces. In addition to possessing dielectric strength and ~.~

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cooling capacity, the ideal insulatiny oil. should be environmentally safe and relatively nonflarnmable.
Hydrocarbon or mineral oils derived from crude petroleum oil were used extensively for many years as . insulating oils in elec-trical equipment. ~lowever, such oils have been replaced -to a great extent by less flam-mable oils. Since -the 1930's the polychlorinated ., biphenyls (PCB) which are generally considered -to be non-flammable have been widely utilized as r~placements for mineral oils insulating oils in electrical equipment. Non-flammability is a required property for insulating oils to ~ , .
;:: be used in equipment which is placed within and around . ~ . . .
:. building structures where it is necessary to minimize the hazard of fire and explosion damage in the event of ; electrical faults within the equipment.
~ In recent years, it has become yenerally recognized ; that polychlorinated byphenyls (PCB) are environmentally .
hazardous liquids. As a result, strict requirements have . been established concerning the construction and the .~ 20 installation of equipment intended.for use wi-th such oils . . . - .
to prevent any fluid leakaye in event of a catastrophic failure. In addition, the disposial of liqui.ds or fluids containing PCB mus-t now be made in compliance with the "
very exacting procedures outlined in the new environmental protection laws. Furthermore, the polychlorinated biphenyls because they lack the ability to extinguish internal arcing . i cannot be used in safety and operational devices such as . submerged high voltage fuses, breakers and switches. l~' .: Because of the disadvantages and shortcomings of the ,` 30 polychlorlnated biphenyls, there have been numerous efforts : 2 ;

' -":-6~7 made to develop relatively inexpensive, env:ironmentally safe, nonflammable insulating oils. To date these efforts have not been completely successful.
Representative of the prior art insulating oils are those disclosed : in United States Patent Nos. 3,000~807; 3,095,366; 3,406,111; 3,5~7,168 and 3,753,1880 Summary of the Invention It is the general object of the present invention to provide electrical equipment utilizing an insulating oil which is relatively nonflammable, biodegradable, environmentally safe, and comparatively ~ 10 inexpensiveO More particularly, it is an object to provide an insulating .: oil which minimizes th~ hazards that can result from catastrophic explosions during high fault conditions and to disclose the use of that oil in electrical equipment. Other objects and advantages will appear from the description to follow.
. Thus this invention relates to the method of minimizing the .~ detrimental effects that can result in oil filled electrical apparatus . .
during high fault conditions which comprises employing as an insulating oil in such electrical apparatus a relatively nonfl~mmable and biodegradable ; oil consisting essentially of a saturated hydrocarbon oil having an average .` 20 molecular weight of about 500 to about 700 and a fire point above 200C., :- which oil is liquid throughout the temperature range of 0 to ~0CO
It is also concerned with an improved electrical apparatus wherein in an electrical apparatus comprised of an oil tank, an electrical component in the tank and an insulating oil filling said tank, the improved `` insulating oil which minimizes the detri.mental effects that can result during high fault conditions and consists essentially of a saturated hydrocarbon oil having an average molecular weight of about 500 to about 700 and a fire point above 200C., which oil is liquid throughout the temperature range of 0 to 40C.

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Brief Description of the Drawing Figure 1 is an elevational view partially in section of a power , transformer employing the present inventionO
: Description of Preferred Embodiment ' In the drawing, a transformer 1 is shown as comprising an : oil-sealed tank 2, a ferrous metal core 3, a primary coil 4, a secondary coil 5 and an insulating oil 6 which surrounds and covers the core and coilsO The oil-sealed tank 2, the core 3 and the coils 4 and 5 are of - conventional construction. However, the insulating oil 6 is unique and will be described in detail hereafterO
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I have made the surprising discover~ tlla-t contrary to -the teachings of the prior art there are certain highly refined petroleum oils or mineral oils which are ; sufficiently nonflammable to serve as insula-ting oil substitutes for the polychlorinated biphenyls in elec-trical equipment which is operated at moderate ambien-t temperatures of 0C to about 40C. This is truly surprising as conventional transformer oils or known insulating oils derived from petroleum oils cannot be used as they are highly flammable and explosive under high fault conditions.
The oils I have found to be useful as insulating oils are comprised of straight and branched chain ali-phatic paraffinic hydrocarbons, which have a molecular weight of about 500 to about 700, preferably about 600, and a fire point above 200C, naphthenic hydrocarbon oils having similar characteristics and mixtures of the - forementioned paraffinic and naphthenic hydrocarbons.
A suitable paraffinic oil is that available ~rom the Sinclair Oil Company under the formula number L-1811.
This oil is dual treat base oil which is solvent treated, deeply hydrogenated bright stock and is predominàtely paraffinic oil with a molecular weight in excess of 600. ?
; It has a distillatiori range by ASTM test -- D1160 as '; follows. The initial boiling point at atmospheric pressure is 760F; the 5% point is 891F; and 10go point is 920F; the 50% point is 1,050F. ~bove 50% it is 1,051F to 1,250F. It has an aniline point of 256F (an l''' indication of a high degree of paraffinic structure).
This oil has characteristics as follows:

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Formula ~ravity, ~PI 28.9 Flash Point C 296 Fir~ Point C 321 K Vis. at 100F, cs 414.1 K Vis. at 210F, cs 27.33 Vis. at 100F, SSU 1919 Vis. at 210F, SSU 130.5 Extrapolated Vis. at 0F, SSU-; 10 17.78C 450,000 Pour Point F -5 Color 30 Sulfur, % I,ess than 0.001 Corrosive Sulvur (D-1275) Pass Vapor pressure at 200C, mm Mercury 0-01 ; rrhe above oil may be prepared from a base oil having the following characteristlcs:
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Cravity, API 28.8 Specific Gravity 60/60F 0.88?6 Flash, F 565 Pour, F 25 Color, Saybolt D-156 ~25 Sulfur, % 0.001 Aniline Point, F 276 Acid Number o~oo Refractive Index at 20C i,4835 Distillation, F, D-1160 5% 89 10% 920 50~ 1050+
90~ -UV Absorp-tivity at 250 mu 0.028 Ti02 Discoloration, 48 hrs. None Specific Dispersion 100.3 A suitable naphthenic oil is that available from Sinclair Oil Company under the formula Number N-1810.
This oil is a dual treat base oil which is solvent treated, ~ . , .
` 40 deeply hydrogenated bright stock and is predominately ;- ~ naphthenic oil with a molecular weight of about 600.
This oil has characteristics as follows:
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Naphthenic Gravity, ~PI 14.8 Flash Point, C 204 ',' . ~ ' .
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86~87 Fire Poin-t, C 237 K Vis. a-t 100F, cs 40.13 K Vis. at 210F, cs 4.88 Vis. at 100F, SSU 187 Vis. at 210F, SSU 42.3 Extrapolated Vis. at 0F, SSU 45,000 Pour Point F -10 Color Dark Sulfur, % 0.94 Corrosive Sulfur (D-1275) Pass ; Vapor Pressure a-t 200C, mm Mercury 2 Blends of the previously described and similar paraffinic and naphthenic oils can be also utilized,as can mixtures pr-epared from Mid-Con-tinental or mixed crudes. The per-centage of each type of molecule in the oil is not critical provlded the resulting mixture possesses the desirable high Eire point and good dielectric proper-ties.
Additional suitable oils may be prepared from a highly paraffinic crude oil such as a Pennsylvania or .... .
Eastern crude or a highly naphthenic crude oil or mixed crudes by the methods disclosed in U.S. Patents Nos.
3,494,854; 3,011,972; 3,431,198 and 3,642,610.l - To demonstrate the desirable properties of the novel insulating oil of the present invention a series of hlgh current fault tests were conducted. These tçsts compared a control comprising an ordinary transformer oil of a ; hydrocarbon base, a silicone oil available from Dow , ,~
~0 Corning as silicone DC-200, the insulating oil of the present invention (L-1811~, and a widely used polychlorinated biphenyl. The experiment was conducted as follows:
r' I Approximately four gallons of each fluid were placed in separa-te cylindrical containers and pre-heated at 150C. Each container had fused internal ; - electrodes mounted on the end of SBT Bushings. The-. . .

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elec-trodes were shaped upward wi-th an expanding gap;
this produced an effec-t which forced the arc upward and into -the gas space, where it was present in the gases and vaporized fluids as they were blown out of the test container.
The tes-t results may be summarlzed AS follows:

Test Number One -Transformer Oil This tes-t was expected to be violent in nature and was placed in the series as a control sample;
results me-t expectations.
The test current applied was 4820 amperes at 4800 volts. The back-up fuse cleared the fault after 10-l/2 cycles.
The explosion was very violent wlth an initial fireball, orange and yellow in color, approximately 20 feet high by 15 feet in diameter. Thi-s mushroomed into a cloud of flame and smoke approximately 55 feet high by 40 feet in diameter. The resultin~ smoke cloud produced was voluminous and black to dark grey in color.
The test container and surrounding area were , cove~ed 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) . ~ (Dow Corning).
This fl~lid has been approved for use as a PCB l, substitute in Japan.
The test current applied was 4760 amperes at 4800 volts. The back-up fuse did not blow. The fault ~c'r~

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4~37 self-cleared after 4-1/2 cycles.
Compared to test one, the explosion and the noise produced were mild. A fireball, oranye and yellow in color, approximately 30 feet high by 15 Eeet 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.
The flame was of low magnitude and very quiet in nature, and it burned for a few seconds in the tes-t ` container after the explosion -then self-extinguished.

Test Nu~ber Three - Insulating Oil of Present Invention (L-1811) The test current applied was 4700 amperes at 4800 volts. The fault self-cleared after 4 cycles.
The explosion was mild in comparison to test one and resulted in a fireball approximately 15 feet hi~h by .:, . . .
10 feet in diameter. A quanti-ty of nonburning fluid was noted preceding the fireball upward, The smoke .
; was grey-white in color and similar in volume to the;
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- smoke cloud of test number two. Noise was mild ` compared to tes~ one.
` A restri-ke occurred approximately 115 cycles after the initial fault. This was cleared by the back- -~, ~ up fuse.
It could be theorized that possibly the secondary flashover extinguished the flame; ho~ever, a review ~; ; of films taken show that oil burning in the test con-'''' " , j:

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~86~37 tainer aEter -the restxike did self-extiJIguis}l.

Test Number Four - PCB
The PCB used ln the test was Interteen 70-30 B~ which is available Erom Monsanto Chemical Company.
The test curxent was 4660 amperes at ~00 volts.
The back-up fuse cleaxed the cixcuit af-ter 11-1/2 cycles.
A fireball of bright orange flame, approxima-tely : , 25 feet high by 15 feet in diameter, rose in a pitch black smoke cloud for 1-1/2 seconds after the explosion;

; black stringers were noted falling from the cloud.

There was no fixe in ox around the -test sample.
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The smo]ce cloud was voluminous, approximately 25 feet high by ~0 feet in diameter, and remained in the air about 20 feet above the ground for approxi-., .
mately 5-10 minutes before dissipating. The test site and equipment were covered with black fluid-and the area had a very noxious odor.

From the results oE the test it is obvious that the PCB fluids although they do not burn themselves produce gases that do and in addition produce a dense smoke which constituted a dangérous by-product of considerable magnitude. , The results also indi~cated that bo-th the silicone fluid and the novel insulating oil of the present invention surpass the PCB's in limiting the u~safe conditions resulting from an internal fault within the fluid and provide suit-able alternates for the environmentally hazardous poly-chlorinated biphenyls.
Further it is no-teworthy that the test, which was , .
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designed to determine the flammability of the liquids after an explosion, demonstrates that both -the silicone oil and the insulating oil (1811) are self-extinguishing.
This would, of course, limit the after effects of an explosion and al]ows electrical equipment filled with these fluids -to be mounted inside building s-tructures provided reasonable precautions are taken. Both the silicone oil and the insulating oil of the present invention limit the duration of the fault and selE-clear.
This is a property which is a desirable fea-ture for designs requiring submerged high voltage fuses, breakers and .. . . . ..
switching devices. In the insulating oil of the present invention there was a res-trike, however, this can be explained by the loss of fluid in the tes-t container - due to the placemen-t of the arc and physical dimensions ; of the container. The fluid self-cleared and the elec-' trodes were still energized as the remaining fluid began to settle in the container.
The fluid properties of the insulating oils before ~ 20 and after the arcing test are shown in Table I.

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TABLE I

Fluid Properties - Before and After Tests :
- . Dielectric IFT Viscosity Strength (kV) (dyne/cm) . (SSU) _ __ASTM D87ASTM D971 ASTM D88 Before Test 32 49.0 58 sec : . Transformer at 25C
Oil After ~: .- Test 20.4 45.5 77.4 sec : a~ 25C
.. Before Test 42 20.8 ' 50 sec : Silicone at 25C
Fluid After DC-200~ Test 15.5 22.2 at 25C

Before Test 34 25.5 1568 sec : L-1811 at 100F
After ~est 24.5 50.0 834 sec at 100F
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. Before . Test ,35 50 54 sec , PCB at 25C
: After ~- Test 7 54.5 66.0 sec - 30 at 25C
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dielectric integrlty of the fluids after high current arcing and demonstrates that the insulating oil of the present invention is superior to hoth the control trans-former oil and the PCB liquid.
., Tests to establish compatability and thermo ~tudies ''- also were conducted and these studies indlcate that the ::
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; . liquid for use in transformers and other high voltage equipment at moderate ambient temperatures of 0C to 40C.
, !l ' ~ ~ Compositions falling within the scope of the present . , , ~ invention, if desired, may contaln relatively small .
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86~7 amounts of conventional chemical additives. For example, pour depressants may be used to lower the pour point of the oil. A par-ticularly suitable class of pour point depressants are -those sold under the trademark PARAFLOW.
These additives are complex condensation produc-ts of paraffin wax and naphthalene which are prepared by chlorinating the wax and condensing the same with naphthalene by the Friedel-Crafts reaction. Although the composi-tions of this invention possess extremely good oxidation stabillty, it may be desirable in some instances to increase the stability in which event con-ventional oxidation inhibitors such as dibutyl para-creosol may be employed.
The insulating oil is introduced into the trans-former under vacuum impregnating conditions. The coil and cores are heated to 120C,'placed in an impregnating 'tank and a vacuum drawn on the tank until an absolute pressure of 6mmHg is attained. Then sufficient oil is ' introduced to cover the core and coil. ~t this time ~ ' , .
the vacuum is removed and the pressure in the tank re-` stored to atmospheric pressure to force the oil into the .
~ apparatus.
, ' 'It will be readily apparent to those skilled in the ' art that although the pre'ferred use of our unique insu-' lating oil has been described in connection with the .j .
transformer, the use of the oil is not so limited.

Obviously, the oil can be used in any electrical apparatus utilizing an insul'ating oil, including capacitors and ` safety and operational devices, including submerged high voltage fuses, breakers and switches. From the fore-.. . .

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' ~86~87 going it will be obvious that I have made a truely sur-prising discovery tha-t hydrocarbon oils of -the defined composition and properties are remarkably safe insu-lating oils.
It will be obvious to those skilled in the art that various modiflcations may be made to the compo-sitions of this invention without departing from the spirit and scope of the invention.
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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The method of minimizing the detrimental effects that can result in oil filled electrical apparatus during high fault conditions which comprises employing as an insulating oil in such electrical apparatus a relatively nonflammable and biodegradable oil consisting essentially of a saturated hydrocarbon oil having an average molecular weight of about 500 to about 700 and a fire point above 200°C., which oil is liquid throughout the temperature range of 0° to 40°C.

2. The method of claim 1 in which the saturated hydrocarbon oil is selected from oils consisting essentially of (a) straight and branch chain aliphatic hydrocarbons, (b) naphthenic hydrocarbons, and (c) mixtures of (a) and (b).

3. The method of claim 1 in which the oil consists essentially of straight and branch chain aliphatic hydrocarbons.

4. The method of claim 1 in which the oil consists essentially of naphthenic hydrocarbons.

5. In an electrical apparatus comprised of an oil tank, an electrical component in the tank and an insulating oil filling said tank, the improved insulating oil which minimizes the detrimental effects that can result during high fault conditions and consists essentially of a saturated hydrocarbon oil having an average molecular weight of about 500 to about 700 and a fire point above 200°C., which oil is liquid throughout the temperature range of 0° to 40 C.

6. The electrical apparatus of claim 5 in which the oil is selected from oils consisting essentially of (a) straight and branch chain aliphatic hydrocarbons, (b) naphthenic hydrocarbons, and (c) mixtures of (a) and (b).

7. The electrical apparatus of claim 5 in which the insulating oil consists essentially of straight and branched chain aliphatic hydrocarbons.

8. The electrical apparatus of claim 5 in which the insulating oil consists essentially of naphthenic hydrocarbons.

9. In the method of impregnating an electrical apparatus with an insulating oil under vacuum, the improvement which comprises utilizing as the impregnating insulating oil a relatively nonflammable, environmentally safe biodegradable oil having a fire point above 200°C., said oil being a liquid consisting essentially of saturated hydrocarbons having an average molecular weight of about 500 to about 700.