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BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to an electrical insulating oil and oil-filled
electrical appliances impregnated with the same.
More particularly, the invention relates to an improved electrical
insulating oil and oil-filled electrical appliances in which the
insulating oil comprises a mixture of monoolefin and/or diolefin having
two aromatic nuclei and an electrical insulating oil or oils other than
polyaromatic hydrocarbons. The electrical insulating oil of the invention
is quite suitable for use in oil-filled electrical appliances in which
insulating materials or dielectric materials made of plastics such as
polyolefins are employed.
(2) Description of the Prior Art
Electrical appliances such as oil-filled capacitors, oil-filled power
cables and transformers have recently been made to withstand high electric
voltages while being small in size. With this tendency, various kinds of
plastic films are used together with conventional insulating paper.
In the conventional art, refined mineral oils, polybutenes, alkylbenzenes,
polychlorinated biphenyls and the like are used as electrical insulating
oils; however, they have several drawbacks. For example, the use of
halogenated aromatics such as polychlorinated biphenyls (PCB) was
discontinued because it constitutes a public health hazard. Furthermore,
the conventional electrical insulating oils are not satisfactorily
compatible with the foregoing plastic materials such as polyolefin films
which are recently used in oil-filled electrical appliances.
With the requirements of high-voltage withstanding and size reduction, it
is necessary that the electrical insulating oil has a high dielectric
breakdown voltage, a low dielectric loss tangent, and good hydrogen gas
absorbing capacity.
The hydrogen gas absorbing capacity indicates the stability of the
insulating oil against corona discharge (partial discharge) under high
electric voltage conditions. The higher the gas-absorbing capacity, the
smaller the likelihood of corona discharge, which leads to the advantage
of the insulating oil having excellent stability or durability.
Meanwhile, in order to meet the requirement of high-voltage use, plastic
films such as polyolefin films, polystyrene films and polyester films are
used to replace either partially or completely the conventional insulating
paper as insulating materials or dielectric materials for electrical
appliances such as oil-filled electric cables and capacitors. In view of
their dielectric strength, dielectric loss tangent and dielectric
constant, polyolefin films, especially polypropylene and cross-linked
polyethylene films, are preferred as the plastic films.
When these polyolefin films are impregnated with insulating oils, some oils
cause the films to swell to some extent. If a film becomes swollen, the
thickness of the insulating layer increases. As a result, the resistance
to the flow of insulating oil increases in electrical cables, and
insufficient impregnation with insulating oil occurs in electric
capacitors, causing the formation of voids (unimpregnated portions) and
the undesirable lowering of the corona discharge voltage.
BRIEF SUMMARY OF THE INVENTION
In view of the above-described conventional state of the art, it is the
primary object of the present invention to provide an improved electrical
insulating oil and oil-filled electrical appliances which are impregnated
with the electrical insulating oil and are free from the above-described
disadvantages in the conventional art.
Another object of the present invention is to provide an electrical
insulating oil which has an excellent dielectric constant and other
electrical properties, which has a good hydrogen gas absorbing capacity,
and which is highly compatible with plastic film insulating materials.
It is a further object of the present invention to provide oil-filled
electrical appliances which have excellent corona discharge
characteristics, dielectric breakdown voltage and other advantageous
electrical characteristics, and have a long service life.
The present invention is, therefore, concerned with a novel and improved
electrical insulating oil and electrical appliances which are impregnated
with this oil.
The electrical insulating oil of this invention comprises:
(a) at least one electrical insulating oil other than polyaromatic
hydrocarbon, and
(b) at least one of monoolefins and/or diolefins having two condensed or
noncondensed aromatic nuclei.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in more detail.
The electrical insulating oils in item (a) are conventionally known ones
other than polyaromatic hydrocarbons. The polyaromatic hydrocarbons herein
referred to are those each of which has two or more condensed or
noncondensed aromatic nuclei but has no olefinic unsaturation. They are
exemplified by diarylalkanes such as phenylxylylethane,
diarylcycloalkanes, alkylbiphenyls such as monoisopropylbiphenyl,
cycloalkylbiphenyls, alkylnaphthalenes such as diisopropylnaphthalene,
cycloalkylnaphthalenes, triarylalkanes, terphenyl, arylnaphthalenes, and
aralkylnaphthalenes. Halogenated polyaromatic hydrocarbons such as PCB are
also included.
Accordingly, the electrical insulating oils in item (a) are exemplified by
monoaromatic hydrocarbons, aliphatic olefin oligomers, organic acid
esters, animal or vegetable oils, mineral oils, silicone oils, and
aromatic ethers.
More particularly, the above-mentioned monoaromatic hydrocarbons are
exemplified by alkylbenzenes such as dodecylbenzene, cycloalkylbenzenes
such as cyclohexylbenzene, partially hydrogenated condensed aromatics such
as alkylindanes or tetralin.
The above-mentioned aliphatic olefin oligomers are exemplified by
polybutenes or poly-.alpha.-olefins.
The aforementioned organic acid esters are more exemplified by aromatic
esters such as diethyl phthalate, dibutyl phthalate, dioctyl phthalate
including di-(2-ethylhexyl)phthalate, diisodecyl phthalate, nonyl
benzoate, trioctyl trimellite, and triisodecyl trimellite; cycloaliphatic
acid esters such as di-(2-ethylhexyl) tetrahydrophthalate and diisodecyl
tetrahydrophthalate; aliphatic acid esters such as dioctyl adipate,
diisodecyl adipate, dibutyl adipate, and dioctyl sebacate.
The aforementioned animal or vegetable oils are exemplified by castor oil,
soybean oil, and cotton seed oil.
Although the foregoing aromatic ethers are exemplified by alkyl-aryl ethers
such as anisole, the aromatic ethers having two condensed or noncondensed
aromatic nuclei are preferable because of their appreciable synergistic
effect. Those aromatic ethers are exemplified by diaryl ethers such as
phenyl tolyl ether, ditolyl ether, phenyl xylyl ether, phenyl cumenyl
ether, and phenyl sec-butyl ether; aryl aralkyl ethers such as ethylphenyl
benzyl ether, propylphenyl benzyl ether, cumenylphenyl benzyl ether, and
phenyl phenylpropyl ether; diaralkyl ethers such as dibenzyl ether,
diphenethyl ether, bis(.alpha.-methylbenzyl) ether, and benzyl phenethyl
ether; alkoxy or cycloalkoxy diaryl alkanes such as methoxydiphenyl
methane, ethoxydiphenyl methane, and propoxydiphenyl ethane; alkoxy or
cycloalkoxy diaryls such as methoxy biphenyl, ethoxy biphenyl, propoxy
biphenyl, and isopropoxy biphenyl; alkoxy or cycloalkoxy naphthalenes such
as methoxynaphthalene, methoxymethylnaphthalene, ethoxynaphthalene,
propoxynaphthalene, isopropoxynaphthalene, butoxynaphthalene,
sec-butoxynaphthalene, and isobutoxynaphthalene.
As the electrical insulating oils except polyaromatic hydrocarbons of item
(a), the above oils can be used singly or in a mixture of two or more
kinds and the viscosity of the oil is preferably not higher than
3.times.10.sup.-5 m.sup.2 /s (30 cSt) at 40.degree. C., and more
preferably not higher than 10.sup.-5 m.sup.2 /s (10 cSt) at 40.degree. C.
The compounds that are used together with the foregoing electrical
insulating oils of item (a) are aromatic monoolefins and/or diolefins each
having two aromatic nuclei of item (b). As these aromatic olefins, they
are derivatives of aliphatic olefins and derivatives of alicyclic olefins
such as cyclopentene and cyclohexene, which are exemplified by the
following compounds represented by general formulae (I) to (VII). The
general formulae (I) to (IV) represent monoolefins and formulae (V) to
(VII) represent diolefins.
General formula:
##STR1##
wherein R.sub.1 is an alkenylene group or a cycloalkenylene group having
an unsaturated double bond, each of m and n is an integer from zero to 3,
inclusive, and R.sub.2 of m in number and R.sub.3 of n in number are
respectively the same or different from one another and each of them is a
hydrogen atom or an alkyl group.
General formula:
##STR2##
wherein R.sub.4 is an alkenyl group or a cycloalkenyl group, R.sub.5 is an
alkylene group or a cycloalkylene group having no olefinic unsaturation,
each of m and n is an integer from zero to 3, inclusive, and R.sub.2 of m
in number and R.sub.3 of n in number are respectively the same or
different from one another and each of them is a hydrogen atom or an alkyl
group.
General formula:
##STR3##
wherein R.sub.4 is an alkenyl group or a cycloalkenyl group, each of m and
n is an integer from zero to 3, inclusive, and R.sub.2 of m in number and
R.sub.3 of n in number are respectively the same or different from one
another and each of them is a hydrogen atom or an alkyl group.
General Formula:
##STR4##
wherein R.sub.4 is an alkenyl group or a cycloalkenyl group, each of m and
n is an integer from zero to 3, inclusive, and R.sub.2 of m in number and
R.sub.3 of n in number are respectively the same or different from one
another and each of them is a hydrogen atom or an alkyl group.
General Formulae:
##STR5##
wherein R.sub.6, R.sub.7 and R.sub.8 are hydrocarbon residual groups,
respectively, each of m and n is an integer from zero to three, inclusive,
R.sub.6 of m in number, R.sub.7, and R.sub.8 of n in number are either the
same or different substituent groups, and the total number of double bonds
in the substituent groups is two in each formula.
In the foregoing general formula (I), the alkenylene group or
cycloalkenylene group of R.sub.1 is a substituent group which is made by
removing two hydrogen atoms from a compound such as ethylene, propylene,
butene, isobutene, pentene, methylpentene, hexene, cyclopentene,
cyclohexene, or alkylcyclohexene. The alkyl groups of R.sub.2 and R.sub.3
are exemplified by methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,
sec-butyl, tert-butyl and amyl groups.
The compounds represented by formula (I) are exemplified by stilbene,
4-methylstylbene, 1,2-diphenylpropene, 1,3-diphenylpropene,
1,4-diphenylbutene-1, 1,4-diphenylbutene-2, 1,1-diphenylethylene,
1-phenyl-1-(4-ethylphenyl)ethylene, 1,1-diphenylpropene-1,
2,3-diphenylpropene, 1,2-diphenylbutene-2, 1,3-diphenylbutene-1,
2,4-diphenyl-4-methylpentene-1, 1,2-diphenylcyclohexene, and
phenylbenzylcyclohexene.
These compounds can be prepared by dimerization or codimerization of
styrenes such as styrene, .alpha.-methylstyrene and vinyltoluene in the
presence of an acid catalyst.
Further, 1,2-diphenylethylene is prepared by reacting benzaldehyde with
benzylmagnesium bromide and then dehydrating the reaction product.
1,2-diphenylpropene is prepared in a similar manner. Furthermore,
1,1-diphenylethylene is prepared by reacting diphenylketone with a
Grignard reagent such as methylmagnesium iodide which is followed by
dehydration.
The symbol R.sub.4 in formula (II) is an alkenyl group or a cycloalkenyl
group such as vinyl, propenyl, isopropenyl, allyl, butenyl, cyclopentenyl
or cyclohexenyl group. R.sub.5 is a divalent substituent group which is
made by removing two hydrogen atoms from a saturated aliphatic hydrocarbon
or a saturated alicyclic hydrocarbon such as cyclopentane, cyclohexane or
cycloheptane. R.sub.2 and R.sub.3 of alkyl groups are the same as those in
formula (I).
The compounds represented by formula (II) are exemplified by
1-phenyl-1-(4-vinylphenyl)ethane,
1-(4-methylphenyl)-1-(4-vinylphenyl)ethane,
1-phenyl-1-(4-isopropenylphenyl)ethane, phenyl-(4-vinylphenyl)methane, and
phenyl(cyclohexenylphenyl)methane.
These compounds can be prepared through various chemical synthesis methods.
For example, phenyl(vinylphenyl)ethane is prepared by reacting
diphenylethane with acetyl chloride in the presence of Friedel-Crafts
catalyst to obtain phenyl(acetylphenyl)ethane, then it is reduced with
sodium borohydride and dehydrated. Phenyl(isopropenylphenyl)ethane is
prepared by reacting phenyl(formylpheny)ethane with a Grignard reagent
such as methylmagnesium iodide, which is followed by dehydration.
In formula (III), R.sub.4 is an alkenyl group or a cycloalkenyl group the
same as R.sub.4 in formula (II), and R.sub.2 and R.sub.3 of alkyl groups
formula (III) are also the same as those in formula (II).
The compounds represented by formula (III) are exemplified by
2-isopropenylbiphenyl, 4-isopropenylbiphenyl,
2-isopropenyl-4'-isopropylbiphenyl, cyclohexenylbiphenyl, and
cyclopentenylbiphenyl. Among these compounds, for example,
isopropenylbiphenyl prepared by dehydrogenation of isopropylbiphenyl.
In formula (IV), R.sub.4 is an alkenyl group or a cycloalkenyl group is the
same as those of formula (II) and R.sub.2 and R.sub.3 of formula (IV) are
the same as those of formula (II).
The compounds represented by formula (IV) are exemplified by
.alpha.-vinylnaphthalene, isopropenylnaphthalene, allylnaphthalene, and
1-cyclopent-2-enylnaphthalene. Among them, for example, vinylnaphthalene
is prepared by reacting formylnaphthalene with a Grignard reagent such as
methylmagnesium iodide, which is followed by dehydration.
In the foregoing general formulae (V) to (VII), in the case where R.sub.6
or R.sub.8 is an unsaturated group, it is an alkenyl or cycloalkenyl
group, and is exemplified by vinyl, propenyl, isopropenyl, allyl, butenyl,
and cyclohexenyl group.
In the case where R.sub.6 or R.sub.8 is a saturated group, it is an alkyl
or cycloalkyl group, and is exemplified by a methyl, ethyl, n-propyl,
isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl and cyclohexyl
group.
In the case where R.sub.7 is an unsaturated group, it is an alkenylene or
cycloalkenylene group, and is exemplified by a divalent substituent group
which is obtained by removing two hydrogen atoms from an olefinic
hydrocarbon such as ethylene, propylene, butene, cyclopentene, and
cyclohexene.
Furthermore, in the case where R.sub.7 is a saturated group, it is an
alkylene or cycloalkylene group, and is exemplified by divalent
substituent groups which are obtained by removing two hydrogen atoms from
a saturated hydrocarbon such as methane, ethane, propane, butanes and
cyclohexane.
The following compounds are exemplified as those represented by the
foregoing formulae (V), (VI) and (VII).
Compounds represented by formula (V):
1-phenyl-1-(4'-vinylphenyl)ethylene;
1,1-diphenylbutadiene;
2,4-diphenyl-1,3-pentadiene;
bis(4-isopropenylphenyl)methane;
1,1-bis(4-isopropenylphenyl)ethane;
1,2-bis(4-isopropenylphenyl)ethane; and
1,1-bis(vinylphenyl)ethane.
Compounds represented by formula (VI):
2,2'-divinylbiphenyl and 4,4'-diisopropenylbiphenyl.
Compounds represented by formula (VII):
divinylnaphthalene and diisopropenylnaphthalene.
The above compounds are shown as examples of the components which can be
used in the preparation of the insulating oil composition of this
invention, and the materials which may be used for the present invention
are by no means restricted to the above exemplary compounds.
Still further, the aromatic monoolefin and/or diolefin used in this
invention are prepared by employing reactions of dehydrogenation,
oxidative dehydrodimerization and decomposition.
More particularly, in a method employing dehydrogenation, a saturated
aromatic hydrocarbon corresponding to the aromatic monoolefin of the
invention, or a saturated aromatic hydrocarbon or an aromatic monoolefin
corresponding to the aromatic diolefin of the invention is dehydrogenated
in the presence of a suitable dehydrogenation catalyst with suppressing
side reactions of decomposition and polymerization.
In the reaction, the dehydrogenation catalyst is not restricted to any
specific one. For example, the dehydrogenation catalysts are exemplified
by one or a mixture of oxides of metals such as Cr, Fe, Cu, K, Mg and Ca
or precious metals such as Pt and Pd, or these metal oxides or precious
metals which are supported on a carrier such as alumina.
The reaction temperature of the dehydrogenation is in the range of
350.degree. to 650.degree. C., preferably 400.degree. to 600.degree. C.
The LHSV (liquid hourly space velocity) of the dehydrogenation is in the
range of 0.2 to 10, preferably 0.5 to 3.0. In the dehydrogenation; steam,
nitrogen gas or hydrogen gas can be introduced into the reaction system in
order to reduce partial pressures and to avoid the formation of carbon.
Further, if necessary, a suitable diluent can be used. When the rate of
dehydrogenation is not so high, raw materials themselves conveniently
serve as a diluent.
Through the above procedures, for example, diphenylethylene is obtained
from diphenylethane; vinylphenyl-phenylethane, from
ethylphenyl-phenylethane; and vinylphenyl-phenylethylene, from
ethylphenyl-phenylethylene. Further, isopropenyl biphenyl is obtained from
isopropyl biphenyl; and isopropenyl-isopropylnaphthanene or
diisopropenylnaphthalene, from diisopropylnaphthalene.
The aromatic monoolefins used in the present invention can also be prepared
by oxidative dehydrodimerization method. In this method,
methyl-substituted monocyclic aromatic hydrocarbon such as toluene,
xylene, ethyltoluene and vinyltoluene are subjected to dimerization
(coupling) together with dehydrogenation.
For example, 1,2-diphenylethylene is obtained from toluene, and
1,2-di(methylphenyl)ethylene, from xylene. In this reaction, a saturated
aromatic hydrocarbon corresponding the obtained olefin, for example,
1,2-diphenylethane from toluene, is simultaneously obtained, which is
convenient for preparing the electrical insulating oil of the present
invention.
Any suitable catalyst can be used for this oxidative dehydrodimerization.
For example, usable catalysts are copper chromite catalysts containing Ni,
Ta or Ti as disclosed in Japanese Patent Publication No. 49-6312 (1974),
the catalysts of oxides of metals such as Bi, Pb, Te, Ba, Tl and Cd or
their mixture as disclosed in Japanese Patent Publication No. 49-20561
(1974), and composite oxide catalyst of Tl as disclosed in U.S. Pat. No.
4,243,825. Further, alkali metal oxides as promoters can be added to these
catalysts.
This reaction can be carried out in the presence of molecular oxygen with
the above-described catalyst. The molar ratio of oxygen/methyl-substituted
aromatic hydrocarbon is in the range of 0.01 to 5.0, preferably 0.05 to
1.0. Meanwhile, the reaction can be performed stoichiometrically without
the presence of molecular oxygen, in which oxidation treatment in addition
to usual treatment to remove deposited carbon, is necessary because the
oxide catalyst is reduced with the progress of reaction.
The reaction temperature is in the range of 300.degree. to 800.degree. C.,
and preferably 500.degree. to 700.degree. C. The contact time is in the
range of 0.01 second to several minutes, and preferably 0.1 to 30 seconds.
The pressure in this reaction is not restricted and can range from a
reduced pressure to 100 atmospheric pressure (98 bar), but preferably in
the range of 0.1 to 5.0 atmospheric pressure (0.098 to 4.9 bar).
Further, the aromatic olefins used in the present invention can also be
prepared by decomposition such as thermal cracking and catalytic cracking,
in which, for example, triarylalkanes, diaralkyl aromatic hydrocarbons and
polymers of styrenes are employed as raw materials.
In the thermal cracking of the above raw materials, the reaction
temperature is set in the range of 300.degree. to 700.degree. C., and
preferably in the range of 330.degree. to 600.degree. C. When the reaction
temperature is too low, the rate of decomposition becomes very low. On the
other hand, when the reaction temperature is too high, the raw material is
decomposed to monocyclic hydrocarbons. Accordingly, in order to obtain the
aromatic hydrocarbons used in the present invention at a higher yield, it
is advisable that the thermal cracking is performed at a relatively higher
temperature with a shorter retention time.
In the catalytic cracking, silica, silica gel, silica-alumina, kaolin,
zeolite (with or without de-aluminum treatment), and organic or inorganic
sulfonic acid can be used. The reaction is performed in a liquid phase or
gas phase, and the reaction temperature is in the range of 300.degree. to
700.degree. C., and preferably in the range of 330.degree. to 600.degree.
C.
The above-mentioned monoolefin and/or diolefin having two condensed or
noncondensed aromatic nuclei is/are employed as a mixture with the
electrical insulating oil of item (a). Accordingly, provided the
monoolefin and/or diolefin can be mixed and dissolved into the insulating
oil of (a) and produce a liquid mixture at ordinary temperatures, the
olefins themselves can be either liquid or solid. The above olefin having
two aromatic nuclei can be used singly or in a mixture of two or more
kinds.
In the present application, as described above, the electrical insulating
oil is prepared by mixing the electrical insulating oil except
polyaromatic hydrocarbon of item (a) and the aromatic olefin of item (b).
The viscosity of the thus prepared insulating oil of the invention is
preferably not higher than 30 cSt (3.times.10.sup.-5 m.sup.2 /s) and more
preferably not higher than 10 cSt (10.sup.-5 m.sup.2 /s) at 40.degree. C.
Accordingly, in order to obtain a mixture having a viscosity of the above
value, components are suitably selected from the foregoing electrical
insulating oils of item (a) and from the foregoing compounds of formulae
(I) to (VII) as aromatic olefins of (b).
According to the present invention, in spite of the mixing with the
unsaturated compounds of the aromatic olefins, no deterioration in
biodegradability, thermal stability and oxidation stability is observed in
practical uses, while various electrical properties can be improved.
The mixing ratio of the electrical insulating oil of (a) and the aromatic
olefin of (b) is arbitrary. However, a ratio of 0.01 to 50 wt % of the
aromatic olefin with respect to the mixture of both component materials is
preferable in view of their synergistic effects. The more preferable
quantity of the aromatic olefin is 1.0 to 30% by weight.
In order to improve further the oxidation stability, several known
antioxidants can be added to the electrical insulating oil of the present
invention. As such antioxidants, there are phenol compounds such as
2,6-di-tert-butyl-p-cresol,
2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methy
l-6-tert-butylphenol), 4,4'-thiobis(3-methyl-6-tert-butylphenol),
stearyl-.beta.-(3,5-di-tert-butyl-4-hydroxyphenol)propionate,
tetrakis[methylene-3(3',5'-di-tert-butyl-4'-hydroxyphenyl)-propionate]meth
ane, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene,
and 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenol)butane; sulfur
compounds such as dilauryl thiodipropionate, distearyl thiodipropionate,
laurylstearyl thiodipropionate, and dimyristyl thiodipropionate; and
phosphorous compounds such as triisodecylphosphite,
diphenylisodecylphosphite, triphenylphosphite, and
trinonylphenylphosphite.
These antioxidants can be added to the electrical insulating oil singly or
in combination of two kinds or more. The addition quantity of the
antioxidant is 0.001 to 5% by weight and preferably 0.01 to 2.0% by weight
of the electrical insulating oil.
Furthermore, in order to impart a nonflammable property and other desirable
effects to the electrical insulating oil of the present invention, several
known additives such as phosphoric esters and epoxy compounds can be added
to the electrical insulating oil.
The electrical insulating oil of the present invention is good for general
uses and, in particular, it is advantageous for the impregnation of
oil-filled electrical appliances such as electric capacitors, power cables
and transformers.
As described at the beginning of this specification, the requirements of
high-voltage withstanding and size reduction of such oil-filled electrical
appliances have become severe in recent years. In order to meet these
requirements, plastics are used to replace either partially or totally the
conventional insulating paper as insulating materials or dielectric
materials for the oil-filled electrical appliances. More particularly, as
electrical insulating materials (dielectric materials) of electric
capacitors, there is proposed the use of a combination of insulating paper
and plastic films such as stretched or nonstretched polypropylene,
polymethylpentene, or polyester film; the use of these plastic films
singly; the use of embossed films of these plastic films to facilitate
impregnation with the insulating oil; or the use of metallized plastic
films, wherein the metallic layer serves as an electrode. In the case of
oil-filled cables, the electrical insulating materials are made of
polyolefin film such as cross-linked or non-cross-linked polyethylene
film, stretched or nonstretched polypropylene film, and polymethylpentene
film; paper-polyolefin laminated film made by the extrusion of polyolefin
onto paper; composite film which is made by cross-linking insulating paper
with silane-grafted polyethylene in the presence of a silanol condensation
catalyst; or an artificial paper sheet which is made by mixing wood pulp
and polyolefin fiber.
The electrical insulating oil of the present invention is excellent in
compatibility with plastic materials. Accordingly, the electrical
insulating oil is quite suitable for use in oil-filled electrical
appliances such as electric capacitors and electric cables in which
plastic materials are used for either part or all of the insulating
material or dielectric material.
More particularly, when an electric capacitor is provided with an
insulating (dielectric) material that is partially or totally made of
plastics, especially polyolefin, and when it is impregnated with the
electrical insulating oil of the present invention, the insulating
material can be fully and completely impregnated with the electrical
insulating oil because swelling of the insulating material is slight, and
voids (unimpregnated portions) are not formed. Accordingly, corona
discharge due to the convergence of electric fields to the voids hardly
occurs, and dielectric breakdown can be well avoided. Furthermore, the
electrical insulating oil of the present invention has excellent hydrogen
gas absorbing capacity and corona discharge resistance under high-voltage
stress, so that it is possible to obtain both a long service life and
high-voltage use of the electrical appliances.
In the case of electric power cables, a change in dimensions of the
insulating material due to swelling is small, and resistance to the
insulating oil flow can be made low so that oil impregnation can be
performed in a short time. Of course, it will be understood that, because
of the ease of impregnation, voids are hardly formed and the dielectric
breakdown voltage becomes higher. When a cable is made by using an
insulating material of a laminated film or composite film made of plastic
material and paper, peeling, creasing and buckling of the insulating
material upon bending of the cable does not occur even when the insulating
material has been in contact with the electrical insulating oil for a long
time. Further, as in the case of the electric capacitor, a power cable
having a good corona discharge resistance can be obtained due to the
excellent hydrogen gas absorbing capacity of the electrical insulating
oil. Accordingly, it is also possible to obtain a long service life and
high-voltage use, as for the capacitors.
According to the present invention, the above-described advantageous
features can be improved by impregnation with the electrical insulating
oil consisting of a plurality of specific component materials, owing to
the synergistic effect between the component materials. Further, the good
electrical characteristics, biodegradability, thermal resistance, and
oxidation stability of each component material can be well maintained, and
at the same time, the viscosity and pour point of the electrical
insulating oil composition can be adjusted within desired ranges.
Therefore, the manufacture of oil-filled electrical appliances is
facilitated, and oil-filled electrical appliances exhibiting high
performance under any use conditions can be obtained.
In the following, the electrical insulating oil and electrical appliances
impregnated therewith according to the present invention will be described
in more detail with reference to several examples.
EXAMPLES
The monoolefins and/or diolefins having two condensed or noncondensed
aromatic nuclei used in the invention can be prepared by various known
methods as described above. For reference purpose, however, the
preparation of two compounds of item (b) employed in the following
examples will be described because they are hardly available in commercial
production.
PREPARATION EXAMPLE 1
Preparation of 1-phenyl-1-(4'-vinylphenyl)ethane
Synthesis of Ketone
To a 5 liter reaction vessel equipped with a stirrer, reflux condenser and
dropping funnel were added 2 liters of carbon tetrachloride and 475 g of
anhydrous aluminum chloride, and the contents were cooled by ice while
being stirred. This was followed by the addition of 275 g of acetyl
chloride through the dropping funnel and additional stirring for 1 hour.
To this was added 546 g of 1,1-diphenylethane, and the contents were
stirred for 4 hours. After the reaction, the aluminum chloride was
deactivated by diluted hydrochloric acid and the reaction mixture was
rinsed with an aqueous solution of sodium carbonate. The reaction medium
was then removed by distillation to obtain 502 g of ketone in a yield of
74.7%.
Synthesis of Alcohol
To a 2 liter reaction vessel equipped with a stirrer, reflux condenser and
dropping funnel were added 600 ml of isopropyl alcohol and 84 g of sodium
borohydride, and the isopropyl alcohol was refluxed by heating the vessel.
The ketone (500 g) was added dropwise for 1 hour to this mixture and the
reaction mixture was stirred further with refluxing of the isopropyl
alcohol.
After the reaction, the catalyst was deactivated by adding water. The
reaction product was separated by ether extraction and was dried by
anhydrous sodium sulfate. The ether was distilled off to obtain 480 g of
alcohol in a yield of 95.2%.
Synthesis of 1-phenyl-1-(4'-vinylphenyl)ethane
A 500 ml three neck flask was equipped with a dropping funnel, 40 g of
potassium hydrogensulfate was fed into the flask, and it was heated to
230.degree. to 240.degree. C. under a reduced pressure. The above-obtained
alcohol (480 g) was then added through the dropping funnel. The alcohol
was dehydrated to produce an olefin, which olefin was immediately
collected by distillation into an outer receptacle. By removing water from
the obtained olefin, 332 g of 1-phenyl-1-(4'-vinylphenyl)ethane was
obtained in a yield of 75.2% (b.p. 149.degree. C./10 mmHg, 113.degree.
C./2 mmHg).
The chemical structure of the final product was identified by elemental
analysis, IR spectrum analysis and NMR spectrum analysis.
PREPARATION EXAMPLE 2
Preparation of 1-phenyl-1-(4'-vinylphenyl)ethylene
A Grignard reagent was prepared by adding 14.6 g (0.601 mole) of magnesium
to 250 ml of dried tetrahydrofuran, heating the mixture to 65.degree. C.,
and adding dropwise 100 g (0.546 mole) of p-bromostyrene. This reagent was
then cooled to 20.degree. C. and 65.5 g (0.546 mole) of acetophenone was
added dropwise to the reagent. The reaction mixture was placed in a
mixture of 500 g of crushed ice, 500 g of water and 15 ml of 98% sulfuric
acid.
After that, a reaction product of alcohol was obtained by ether extraction.
This alcohol was then dehydrated by potassium hydrogensulfate to obtain
62.8 g of 1-phenyl-1-(4'-vinylphenyl)ethylene in a yield of 56%, which
compound was liquid at ordinary temperatures (b.p. 151.degree. C./10 mmHg,
114.degree. C./2 mmHg).
The chemical structure of the final product was identified by elemental
analysis, IR spectrum analysis and NMR spectrum analysis.
EXAMPLES OF ELECTRICAL INSULATING OILS
As indicated in the following Tables 1 to 3, electrical insulating oils
except polyaromatic hydrocarbon of item (a) were mixed with aromatic
monoolefins and/or diolefins of item (b) to prepare the electrical
insulating oils of the present invention.
In these tables, electrical insulating oil Nos. 1, 6, 10, 13, 16, 19, 27
and 28 are comparative examples and the others are examples of the
invention.
In connection with electrical insulating oil Nos. 1 to 15, capacitors were
prepared by using single-side metallized paper as electrodes and
dielectric materials, which capacitors were impregnated with the
electrical insulating oils. The capacitances of the capacitors which were
impregnated with electrical insulating oil Nos. 1 to 9 were 2.5 .mu.F and
those impregnated with oil Nos. 10 to 15 were 2.8 .mu.F.
The capacitors which were impregnated with electrical insulating oil Nos. 1
to 15 were applied with an electric voltage of 500 V for 100 hours and
capacitances and dielectric loss tangents before and after the voltage
application were measured. From these results, ratios of decrease in
capacitances and ratios of increase in dielectric loss tangents were
calculated, which are shown also in Table 1.
According to the results shown in Table 1, it will be understood that the
electrical insulating oils containing the foregoing aromatic monoolefins
and/or diolefins gave small ratios of changes in capacitances and
dielectric loss tangents and that the performance of the basic oils was
much improved.
In connection with electrical insulating oil Nos. 16 to 18 in Table 2,
capacitors were made by winding the following materials for electrode and
dielectric, and they were impregnated with the electrical insulating oils.
The capacitances of them were 0.68 .mu.F.
Electrode: Aluminum foil of 7.mu. in thickness and 50 mm in width.
Dielectric: Two-ply film of paper of 12.mu. thickness, 62 mm width and
polypropylene film of 28.mu. thickness, 62 mm width.
With regard to these capacitors, corona starting voltages (CSV) and corona
ending voltages (CEV) were measured, the results of which are shown in
Table 2.
From the results shown in Table 2, it will be understood that electrical
insulating oil Nos. 17 and 18 of the invention containing the aromatic
olefin gave higher values of CSV and CEV, and that the performance of the
electrical insulting oils was much improved.
In connection with electrical insulating oil Nos. 19 to 32 in Table 3,
which contain ethereal oils, capacitors were made by winding two-ply
capacitor-use polypropylene film (each 14.mu. thickness) as a dielectric
material and aluminum foil as electrodes. They were then impregnated with
the electrical insulating oils. The capacitance of them was 0.45 .mu.F.
With regard to these capacitors, corona starting voltages (CSV) and corona
ending voltages (CEV) were measured, the results of which are shown in
Table 3.
Breakdown times under a fixed voltage were also measured and the results of
this test are also shown in Table 3. In the test for breakdown times, each
value was calculated such that seven capacitors impregnated with the same
oil were tested and the maximum value and minimum value were neglected and
the average of the other five breakdown times was adopted as the resultant
value. Furthermore, the breakdown times were represented by the values
relative to the values of base oils having substantially no olefinic
unsaturation.
From the results shown in Table 3, it will be understood that the
electrical insulating oils of the invention containing the aromatic
olefins also exhibited better results and that the performance of the
electrical insulating oils was much improved. Incidentally, the electrical
insulating oil No. 27 containing hexadecene-1 was not good.
TABLE 1
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Ratio of
Ratio of
Insu- Kinematic
Decrease
Increase
lating
Electrical Insulating Oil Viscosity
in Capac-
in Dielec-
Oil Insulating Oil
Aromatic Olefin
(cSt itance
tric Loss
No. of (a) wt %
of (b) wt %
at 30.degree. C.)
(%) Tangent (%)
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1 Mineral oil
100 -- -- 11.6 2.3 30.0
2 " 90 1,3-diphenyl-
10 10.9 0.3 18.5
butene-1
3 " 90 2,4-diphenyl-4-
10 11.3 0.2 15.5
methylpentene-1
4 " 90 1,1-diphenyl-
10 10.4 0.1 13.3
ethylene
5 " 92 1-phenyl-1-(4'-
8 10.7 0.1 12.1
vinylphenyl)-
ethylene
6 Polybutene
100 -- -- 6000 6.8 29.5
7 " 90 2,4-diphenyl-4-
10 2060 0.7 15.8
methylpentene-1
8 " 90 1,1-diphenyl-
10 1650 0.3 11.3
ethylene
9 " 92 1-phenyl-1-
8 1720 0.2 11.0
(4'-vinylphenyl)-
ethylene
10 Dioctylphthalate
100 -- -- 43.7 1.3 30.9
11 " 90 1,1-diphenyl-
10 32.1 0.0 15.3
ethylene
12 " 92 1-phenyl-1-
8 34.6 0.0 15.6
(4'-vinylphenyl)-
ethylene
13 Castor oil
100 -- -- 250 1.6 28.7
14 " 90 2,4-diphenyl-
10 155 0.3 14.6
4-methylpentene-1
15 " 92 1-phenyl-1-
8 163 0.2 13.9
(4'-vinylphenyl)-
ethylene
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TABLE 2
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