Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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HIGH OLEIC ACID ELECTRTCAL INSULATION FLUIDS AND METHOD OF MAKING THE SAME
FIE?~D OF THE INVENTION
The invention relates to a high oleic oil
composition useful as an electrical insulation fluid, to
electrical insulation fluid compositions and electrical
apparatuses which comprise the same. The high oleic oil
compositions of the invention have electrical properties
which make them well suited as insulation fluids in
electrical components.
BACRGROUND OF THE INVENTION.
The electrical industry uses a variety of
insulating fluids which are easily available and cost
effective. Examples are mineral oil, silicone fluid, and
synthetic hydrocarbon oils used in transformers, power
cables and capacitors. Examples of such fluids include
those described in U.S. Patent Number 4,082,866 issued April
4, 1978 to Link, U.S.. Patent Number 4.,206,066 issued June 3,
1980 to Rinehart, U.S. Patent Number,4,621,302 issued
November 4, 1986 to Sato et al., U.S. Patent Number
5,017,733 issued May 21, 1991 to Sato et al. U.S. Patent
Number 5,250,750 issued October 5, 1993 to Shubkin et al.,
and U.S. Patent Number 5,336,847 issued August 9, 1994 to
Nakagami.
Many of these fluids are not considered to be
biodegradable in a reasonable time frame. Some have
electrical properties which render them less than optimal.
In recent years regulatory agencies have become increasingly
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concerned about oil spills which can contaminate the ground
soil and other areas. A biodegradable oil would be
desirable for electrical apparatus such as transformers used
in populated areas and shopping centers.
Vegetable oils are fully biodegradable, but the
oils presently available in the market are not electrical
grade. A few vegetable oils such as rapeseed oil and castor
oil have been used in limited quantities, mostly in
capacitors, but these are not oleic esters.
There is a need for a fully biodegradable
electrical fluid. There is a need for electrical
apparatuses which comprise such an oil. There is a need for
a method of processing vegetable oil to electrical grade.
SIJNIMARY OF THE INVENTION
The present invention relates to high oleic acid
triglyceride compositions that comprise fatty acid
components of at least 750 oleic acid, less than l00
diunsaturated fatty acid component; less than 3%
triunsaturated fatty acid component; and less than 8%
saturated fatty acid component; and wherein said composition
is further characterized by the properties of a dielectric
strength of at least 35 KV/100 mil (2.5 mm) gap, a
dissipation factor of less than 0.05% at 25°C, acidity of
less than 0.03 mg KOH/g, electrical conductivity of less
than 1 pS/m at 25°C, a flash point of at least 250°C and a
pour point of at least -l5oC.
The present invention relates to an electrical
insulation fluid comprising at least 75% of a high oleic
acid triglyceride composition that comprise fatty acid
components of at least 75% oleic acid, less than 10%
diunsaturated fatty acid component; less than 3%
triunsaturated fatty acid component; and less than 8%
saturated fatty acid component; and wherein said composition
is further characterized by the properties of a dielectric
strength of at least 35 KV/100 mil gap, a dissipation factor
of less than 0.05% at 25°C, acidity of less than 0.03 mg
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KOH/g, electrical conductivity of less than 1 pS/m at 25°C,
a flash point of at least 250oC and a pour point of at least
-lSoC, and one or more additive selected from the group of
an antioxidant additive, a pour point depressant additive
and a copper deactivator.
The present invention relates to electrical
apparatuses comprising the electrical insulation fluid.
The present invention relates to the use of
electrical insulation fluid to provide insulation in
electrical apparatuses.
The present invention relates to a process for
preparing the high oleic acid triglyceride composition
comprising the steps of combining refined, bleached and
deodorized high oleic acid triglyceride with clay to form a
mixture and filtering the mixture to remove the clay.
DETAILED DESCRIPTION OF THE INVENTION
This present invention provides a novel
application for high oleic vegetable oils as electrical
insulation fluids. Vegetable oils usually have a high
percent of triglyceride esters of saturated and unsaturated
organic acids. When the acid is saturated, the triglyceride
is either a semi-solid or a liquid with high freezing point.
Unsaturated acids produce oils with low freezing points.
However, monounsaturated acids are preferred over
diunsaturated and triunsaturated acids because the latter
tend to dry fast in air due to cross-linking with oxygen.
Increasing the amount of diunsaturates and triunsaturates
makes the oil more vulnerable to oxidation; increasing the
saturates raises the pour point. Ideally, the higher the
monosaturate content, the better the oil as an electrical
fluid.
Oleic acid is a monounsaturated acid found as
triglyceride ester in many natural oils such as sunflower,
olive oil and safflower in relatively high proportions
(above 60%). High oleic acid content is usually above 75%
of the total acid content. Oleic acid content above 80% is
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achieved by genetic manipulation and breeding. Two oils
that are currently available in the United States with high
oleic acid content and low saturates are sunflower oil and
canola oil. These oils are of value in producing high
quality lubricating oils but have not been used in the
production of electrical insulation fluids.
High oleic oils may be derived from plant seeds
such as sunflower and canola which have been genetically
modified to yield high oleic content. The pure oils are
triglycerides of certain fatty acids with a carbon chain
ranging from 16 to 22 carbon atoms. If the carbon chain has
no double bonds, it is a saturated oil, and is designated
Cn:O where n is the number of carbon atoms. Chains with one
double bond are monounsaturated and are designated Cn:l;
with two double bonds, it will be Cn:2 and with three double
bonds Cn:3. Oleic acid is a C18:1 acid while erucic acid is
a C22:1 acid. The acids are in the combined state as
triglycerides, and when the oils are hydrolyzed they are
separated into the acid and glycerol components. High oleic
oils contain more than 750 oleic acid (in combined state
with glycerol), the remaining being composed mainly of
CI8:0, C18:2 and C18:3 acids (also in combined state with
glycerol). These acids are known as stearic, linoleic and
linolenic. Oils with a high percentage of double and triple
unsaturated molecules are unsuitable for electrical
application because they react with air and produce
oxidation products. Monounsaturated oils such as oleic acid
esters may also react with air, but much slower, and can be
stabilized with oxidation inhibitors.
A typical 85% high oleic oil has the following
approximate composition:
Saturates: 3-5%
monounsaturates: 84-850
diunsaturates: 3-7%
triunsaturates: 1-3%
While the present invention provides for the use
of vegetable oils, the invention may use synthetic oil
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having the same compositional characteristics of those oils
isolated from plants. While plant derived material is
suitable for almost all applications, synthetic material may
provide a desirable alternative in some applications.
According to the present invention, high oleic
acid content oils are used as starting materials for the
production of an oil composition which has physical
properties useful for electrical insulation fluids. The
present invention provides the processed compositions having
specific structural and physical characteristics and
properties, methods of making such composition, electrical
insulation fluids which comprise the composition, electrical
apparatuses which comprise the electrical insulation fluids
and methods of insulating electrical apparatuses using such
fluids.
The.present invention provides a high oleic acid
triglyceride composition useful as an electrical insulation
fluid and more particularly as a component material of an
electrical insulation fluid. A triglyceride composition is
a glycerol backbone linked to three fatty acid molecules.
The triglyceride compositions~of the invention comprise
fatty acid components of at least 75% oleic acid. The
remaining fatty acid components include less than l00
diunsaturated fatty acid component, less than 30
triunsaturated fatty acid component; and less than 80
saturated fatty acid component.
The triglyceride compositions of the invention
preferably comprise fatty acid components of at least 80%
oleic acid. The triglyceride compositions of the invention
more preferably comprise fatty acid components of at least
85% oleic acid. In some embodiments, the triglyceride
compositions of the invention comprise fatty acid components
' of 90% oleic acid. In some embodiments, the triglyceride
compositions of the invention comprise fatty acid components
3S of greater than 90% oleic acid.
Di-unsaturated, triunsaturated and saturated fatty
acid components present in the triglyceride are preferably
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C16-C22. It is preferred that 80% or more of the remaining
fatty acid components are C18 diunsaturated, triunsaturated
and saturated fatty acids, i.e. linoleic, linolenic and
stearic acids, respectively. In some embodiments, the
diunsaturated, triunsaturated and saturated fatty acid
components of the triglyceride comprise at least 75% oleic
acid, less than 3% linoleic acid, less than 4% stearic acid
and less than 4% palmitic acid (saturated C15).
The triglyceride compositions of the invention are
of an electric grade. That is, they have specific physical
properties which make them particularly suited for use as an
electrical insulation fluid. The dielectric strength of.a
triglyceride composition of the invention is at least 35
KV/100 mil (2.5 mm) gap, the dissipation factor is less than
0.05% at 25°C, the acidity is less than 0.03 mg KOH/g, the
electrical conductivity is less than 1 pS/m at 25°C, the
flash point is at least 250°C and the pour point is at least
-l5oC.
The dielectric strength, dissipation factor,
acidity, electrical conductivity, flash point and pour point
are each measured using the published standards set forth in
the Annual Book of ASTM Standards (in Volumes 5 and 10)
published by the American Society for Testing Materials
(ASTM), 100 Barr Harbor Drive West Conshohocken PA 19428,
which is incorporated herein by reference. The dielectric
strength is determined using ASTM test method D 877. The
dissipation factor is determined using ASTM test method D
924. The acidity is determined using ASTM test method D
974. The electrical conductivity is determined using ASTM
test method D 2624. The flash point is determined using
ASTM test method D 92. The pour point is determined using
ASTM test method D 97.
The dielectric strength is measured by taking 100-
150 ml oil sample in a test cell and applying a voltage
between test electrodes separated by a specified gap. The
breakdown voltage is noted. The test is preferably run five
times and the average value is calculated. The dielectric
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strength of a triglyceride composition of the invention is
at least 35 KV/100 mil (2.5 mm) gap. In some preferred
embodiments, it is 40 KV/100 mil (2.5 mm) gap.
The dissipation factor is a measure of the
electrical loss due to conducting species and is tested by
_ measuring the capacitance of fluids in a test cell using a
capacitance bridge. The dissipation factor of a
triglyceride composition of the invention is less than 0.05%
at 25C. In some preferred embodiments, it is less than
0.020. In some preferred embodiments, it is less than
0.01%.
The acidity is measured by titrating a known
volume of oil with a solution of alcoholic KOH to
neutralization point. The weight of the oil in grams per mg
KOH is referred to interchangeably as the acidity number or
the neutralization number. The acidity of a triglyceride
composition of the invention is less than 0.03 mg KOH/g.
In some preferred embodiments, it is less than 0.02 mg
KOH/g.
The electrical conductivity is measured using a
conductivity meter such as an Emcee meter. The electrical
conductivity of a triglyceride composition of the invention
is less than 1 pS/m at 25°C. In some preferred embodiments,
it is less than 0.25 pS/m.
The flash point is determined by placing an oil
sample in a flashpoint tester and determining the
temperature at which it ignites. The flash point of a
triglyceride composition of the invention is at least 250dC.
In some preferred embodiments, it is at least 300°C.
The pour point is determined by cooling an oil
sample with dry ice/acetone and determining the temperature
at which the liquid becomes a semi-solid. The pour point of
a triglyceride composition of the invention is not greater
than -lSoC. In some preferred embodiments, it is not
greater than -20oC. In some preferred embodiments, it is
not greater than -40oC.
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_ g _
In some preferred embodiments, the triglyceride
composition of the invention is characterized by the
properties of a dielectric strength of at least 40 KV/100
mil (2.5 mm) gap, a dissipation factor of less than 0.02% at
25oC, acidity of less than 0.02 mg KOH/g, electrical
conductivity of less than .25 pS/m at 25°C, a flash point of
at least 300°C and a pour point of not greater than -20o.C.
In some preferred embodiments, the pour point is not greater
than -40oC.
In some preferred embodiments, the triglyceride
composition of the invention comprises fatty acid components
of at least 75% oleic acid, linoleic acid at a proportion of
less than 10%, linoleic acid at a proportion of less than
3%, stearic acid in a proportion of less than 4%, and
palmitic acid in a proportion of less than 4%, and is
characterized by the properties of a dielectric strength of
at least 40 KV/100 mil (2.5 mm) gap, a dissipation factor of
less than 0.02% at 25°C, acidity of less than 0.02 mg KOH/g,
electrical conductivity of less than .25 pS/m at 25°C, a
flash point of at least 300°C and a pour point of not
greater than -20oC. In some preferred embodiments, the pour
point is not greater than -40oC.
Triglycerides with high oleic acid oil content are
described in U.S. Patent Number 4,627,192 issued December 4,
2986 to Fick and U.S. Patent Number 4,743,402 issued Mav 10,
1988 to Fick.
These oils or those with similar fatty acid component
content according to the present invention may be processed
to yield an oil with the desired physical properties. High
oleic vegetable oils may be obtained from commercial
suppliers as RBD oils (refined, bleached and deodorized)
which are further processed according to the present
invention to yield high oleic ails useful in electrical
insulation fluid compositions. There are several suppliers
of high oleic RBD oils in the USA and overseas. RBD oil
useful as a starting material for further processing may be
obtained from SVO Specialty Products, Eastlake OH, and
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Cargill Corp., Minneapolis MN. The oil manufacturer goes
through an elaborate process to obtain RHD oil during which
all nonoily components (gums, phospholipids, pigments etc.)
are removed. Further steps may involve winterization
(chilling) to remove saturates, and stabilization using
nontoxic additives. The processes for converting oil to RBD
oil are described in Bailev's Industrial Oil and Fat
Products, Vols. 1, 2 & 3, Fourth Edition 1979 John Wiley &
Sons. and in Bleachinct and Purifyincr Fats and Oils by H.B.W.
Patterson, AOCC Press, 1992.
RBD oils are further processed according to the
present invention in order to yield an oil with the physical
properties as defined herein. The purification of the as
received oil designated RBD oil is necessary because trace
polar compounds and acidic materials still remain in the
oil, making it unfit as an electrical fluid. The
purification process of the present invention uses clay
treatment which involves essentially a bleaching process
using neutral clay. RBD oil is combined with 10% by weight
clay and mixed for at least about 20 minutes. It is
preferred if the oil is heated to about 60-80oC. It is
preferred if the mixture is agitated. The clay particles
are removed subsequently by a filter press. Vacuum
conditions or a neutral atmosphere (by nitrogen) during this
process prevent oxidation. Slightly stabilized oil is
preferable. More stabilizer is added at the end of the
process. The purity is monitored by electrical
conductivity, acidity and dissipation factor measurement.
Further treatment by deodorization techniques is possible
but not essential. The polar compounds that interfere most
with electrical properties are organometallic compounds such
as metallic soaps, chlorophyll pigments and so on. The
level of purification needed is determined by the measured
properties and the limits used. An alternative embodiment
provides passing RBD oil through a clay column. However,
stirring with clay removes trace polar impurities better
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than passing through a clay column. In preferred
embodiments, neutral Attapulgite clay, typically 30/60 mesh
size, is used in.a ratio of 1-10% clay by weight. In some
embodiments, clay particles are removed using filters,
preferably paper filters with a pore size of 1-5 ~Cm. The
clay is preferably mixed with hot oil and agitated for
several minutes, after which the clay is filtered off using
filters. Paper or synthetic filter sheets may be used if a
filter separator is used. The filter sheets are
periodically replaced.
Electrical insulation fluids of the invention
comprise the triglyceride composition of the invention and
may further comprise one or more additives. Additives
include oxidation inhibitors, copper deactivators and pour
point depressors.
Oxidation inhibitors may be added to the oils.
Oxidation stability is desirable but in sealed units where
there is no oxygen, it should not be critical. Commonly
used oxidation inhibitors include butylated hydroxy toluene
(BHT), butylated hydroxy anisole (BHA) and mono-tertiary
butyl hydro quinone (TBHQ). In some embodiments, oxidation
inhibitors are used in combinations such as BHA and BHT.
Oxidation inhibitors may be present at levels of 0.1-3.0%.
In some preferred embodiments, 0.2o TBHQ is used. Oxidation
stability of the oil is determined by AOM or OSI methods
well known to those skilled in the art. In the AOM method,
the oil is oxidized by air at 100°C and the formation of
peroxide is monitored. The time to reach 100
milliequivalents (meq) or any other limit is determined.
The higher the value, the more stable the oil is. In the
OSI method, the time to reach an induction period is .
determined by the measurement of conductivity.
Pour points depressants may also be added if low
pour points are needed. Commercially available products can
be used which are compatible with vegetable-based oils.
Only low percentages, such as 20 or below, are needed
normally to bring down the pour point by 10 to lSoC. In
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some embodiments, the pour point depressant is
polymethacrylate (PMA).
Since copper is always present in the electrical
environment, another type of additive is copper
deactivators. Copper deactivators such as benzotriazole
derivatives are commercially available. The use of these in
small, such as below 1%, may be beneficial in reducing the
catalytic activity of copper in electrical apparatus. In
some embodiments, the electrical insulation fluid contains
less than 1% of a copper deactivator. In some embodiments,
the copper deactivator is a benzotriazole derivative.
In some embodiments, the pour point may be further
reduced by winterizing processed oil. Essentially, the oils
are winterized by lowering the 'temperature to near or below
OoC and removing solidified components. The winterization
process may be performed as a series of temperature
reductions followed by removal of solids at the various
temperature. In some embodiments, winterization is
performed by reducing the temperature serially to 50, 0o
and -l2oC for several hours, and filtering the solids with
diatomaceous earth.
In some embodiments, the electrical insulation
fluid of the invention that comprises at least 75 percent
triglyceride composition of the invention as described above
further comprises about 0.1-5% additives and then up to
about 25% other insulating fluids such as mineral oil,
synthetic esters, and synthetic hydrocarbons. In some
embodiments, the electrical insultion fluid comprises 1-24%
of insulating fluids selected from the group consisiting of
mineral oil, synthetic esters, synthetic hydrocarbons and
combinantion of two or more of such materials. In some
embodiments, the electrical insultion fluid comprises 5-15%
of insulating fluids selected from the group consisiting of
mineral oil, synthetic esters, synthetic hydrocarbons and
combinantion of two or more of such materials. Examples of
mineral oils include poly alpha olefins. An example of a
mineral oil which may be used as part of the present
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invention is RTEemp, Cooper Power Fluid Systems. Examples
of synthetic esters include polyol esters. Commercially
available synthetic esters which can be used as part of the
invention include those sold under the trade names MYDEL,
REODEC and ENVIROTEMP 200, Cooper Power Fluid Systems. In
some preferred embodiments, the electrical insulation fluid
comprises at 1-east 850 of the triglyceride composition of
the invention. In some preferred embodiments, the
electrical insulation fluid comprises at least 95°s of the
triglyceride composition of the invention.
The present invention relates to an electrical
apparatus which comprises the electrical insulation fluid of
the invention. The electrical apparatus may be an
electrical transformer, an electrical capacitor or an
electrical power cable. U.5. Patent Number 4,082,866, U.S.
Patent Number 4,206,066, U.S. Patent Number 4,621,302, U.S.
Patent Number 5,017,733, U.S. Patent Number 5,250,750, and
U.S. Patent Number 5,336,847, which are referred to above
describe various
applications of electrical insulation fluids for which the
electrical insulation fluid of the invention~may~.be used. In
addition, U.S. Patent Number 4,993,141 issued February 19,
1991 to Grimes et al., U.S. Patent Number 4,890,086 issued
December 26, 1989 to Hill, U.S. Patent Number 5,025,949
issued June 25, 1991 to Adkins et al., U.S. Patent Number
4,972,168 issued November 20, 1990 to Grimes et al., U.S.
Patent Number 4,126,844, and U.S. Patent. Number 4,307,364
issued December 22, 19'81 -to Lanoue et al.,
contain descriptions
of various electrical apparatuses in which the electrical
insulation fluid of the invention may be used. In some
preferred embodiments, the eletrical apparatus fo the
invention is a transformer, in particular,a power
transformer or a distribution transformer.
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EXAMPLES
Example 1
Several high oleic oils were further purified and
stabilized according to the present invention to make them
electrically suitable. Electrical tests showed that such
- purified oils had properties similar to currently used high
temperature fluids in distribution transformers. Table 1
compares the properties of the purified oils of the present
invention with currently used fluids.
Table 1
Comparison of Purified Vegetable Oils with High Temperature
Fluids Used in Transformers
High Oleic High Temp. Synthetic
Veg. Oil Mineral Oila Ester Fluidb
Dielectric 42.4 40-45 50
Strength,
KV/100 mil gap
Dissipation 0.02 0.01 p.!
Factor, o at
25oC
Neutr. No. mg 0.05 - 0.03
KOH/g
Electrical 0.25-1.0 (0.1 0 10)* (5.0)*
Conductivity
pS/m, 25C
Flash Point 328oC 275-300oC 257oC
Pour Point -28oC -24oC -480
a r,rn,-,_~ ~
..~L~."r,, ..-wv~ci. rvwcl r.LUlC1 ~y5Cem5
b Polyol Esters
* deduced from resistivity
The properties listed for the high oleic oil are for
purified oils with no additives.
SUBSTITUTE SHEET (RULE 2~
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Example 2
The purification of the as received oil designated
RBD oil (refined, bleached and deodorized) is necessary
because trace polar compounds and acidic materials still
remain in the oil, making it unfit as an electrical fluid.
The purification we attempted involved clay treatment as
follows: approximately l gal. of the RBD oil was treated
with 10% Attapulgite clay. Oil was produced with electrical
conductivity of ;less than.l.pS/m. The attapulgite treated
oil showed conductivities as low as 0.25 pS/m. Commercial
grade oils had conductivities in the range of 1.5 to 125
pS/m. Conductivity below 1 pS/m (or resistivity above 1014
ohm. cm) is desired for electrical grade oil. Other
indicators of purity are dissipation factor and
neutralization number (acid number). Dissipation factor is
a measure of electrical losses due to conduction caused by
conducting species, usually organometallic trace components,
and should be below 0.050 at room temperature. The clay
treated oils had dissipation factor of 0.020. Untreated RBD
oils had DF ranging from 0.06% to 2.0%.
Example 3 .,;
Oxidation stability tests were conducted on
treated and untreated oil samples using ASTM and AOCS
methods. The untreated and treated RBD oils failed the
tests. Oxidation inhibitors were added to the oils and the
tests were repeated. Several oxidation inhibitors were
tested: BHT (Butylated Hydroxy Toluene, BHA (Butylated
Hydroxy Anisole) and TBHQ (mono-Tertiary Butyl Hydro .
Quinone) in 0.2% by weight in oil. In the AOCS method used
(Cd 12.57) 100 ml samples are bubbled with air at 100C, and
the peroxide formation was measured at several time
intervals. Hours to reach 100 meq of peroxide were noted.
Since copper is always present in the electrical
environment, all oil samples had copper wire placed in them.
With no additive, the time to reach the limit was 18 hours;
with additive (0.2%), the times were 100 hours for BHT +
BHA. With TBHQ, even after 400 hours, the peroxide value
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reached only 8.4 meq. TBHQ proved to be the best
antioxidant of the three. Without an oxidation inhibitor
the oils upon oxidation would produce hydroperoxide which is
then converted to acids, alcohols, esters, aldehydes,
ketones and polymer structures. Most electrical apparatus
that use a fluid insulation operate in low oxygen or oxygen-
free environment, so the concern over oxidation is not
great.
Example 4
The pour point of the treated oil was typically -
25oC. To lower the pour point further, the treated oils
were winterized at 50, Oo and --l2oC for several hours, and
the solids that separated were filtered with diatomaceous
earth. The lowest pour point reached so far was -38oC,
close to the specified value of -40oC for transformer oil.
Further lowering is possible by extended winterization.
Another approach is by the use of pour point depressants
such as PMA (polymethacrylate) which has been used for
mineral oil.
