Note: Descriptions are shown in the official language in which they were submitted.
10799S3 36-CA-3289
This invention relates to a dielectric liquid composition
suitable for use as an insulating medium in electrical devices,
and more particularly, to an improved halogen containing
ester type dielectric liquid composition particularly
adaptable for use as a dielectric liquid impregnant for
electrical capacitors.
U.S. Patent 3,363,156 dated January 9, 1968, Cox,
discloses and claims various types of dielectric liquid
impregnated electrical capacitors. The dielectric liquid
composition described in Cox is a chlorinated hydrocarbon,
more particularly a halogenated aromatic hydrocarbon
and specifically a chlorinated diphenyl. The
chlorinated diphenyl impregnants for electrical capacitors
are commercially available under the trademark Aroclor, a
trademark of the Monsanto Company, and a specific example
being Aroclor 1242 or Aroclor 1016. The chlorinated diphenyls,
referred to as PCs's,have recently been associated
with ecological problems and their continued use in
applications other than electrical has been limited.
Accordingly there is a continuing search for new and
improved impregnants in the eIectrical capacitor field.
In U.S. Patent 3,754,173 dated August 21, 1973
Eustance, there is disclosed an epoxide stabilized
liquid aromatic ester impregnant which does not
have many of the PCB ecological disadvantages. Of
the problem associated with the aromatic ester kind of impregnant
is the fact that the flammability point, i.e. the level
at which the liquid will sustain combustion, is relatively
low and many of these ester materials are classified as
flammable under some failure conditions of an electrical
capacitor.
It has also been disclosed that the aromatic esters in
- 1 -
1079953 36-CA-3289
accordance with the Eustance patent will provide very high
corona start voltages ICSV) and therefore favourably
compare with the Aroclor liquid for capacitors, However,
a further important voltage level or criteria of a cap-
acitor i~ referred to as the corona extinction voltage
(CEV) of a capacitor, The corona start voltage and the
corona extinction voltage are the voltages at which de-
leterious corona discharge may commence in a capacitor
and be extinguished respectively during a rising and de-
creasing voltage level across the capacitor, In highvoltage power factor corxection capacitors, the corona ex-
tinction voltage for the ester impregnants has been found
to be significantly less than the corona extinction voltage
for the Aroclor type impregnant ,
In addition to the foregoing problems~ many of the
ester impregnants, particularly those of higher molecular
weights, are otherwise desirable for capacitor impregnants
but have an increased viscosity which creates a problem in
essentially completely impregnating a capacitor in ac-
cordance with the teachings of the above noted Cox patent,
Additive liquids used to minimize the foregoing problems
have been found in many cases to have adverse ef~ects on
other characteristics of the impregnant such as lowering
the dielectric constant (DK).
Accordingly it i~ an object of this invention to provide
an improved ester dielectric liquid composition,
It i8 a further object of this invention to provide
an improved capacitor dielectric liquid ester impregnant
having increased corona extinction voltage characterstics,
It is another object of this invention to provide an
improved capacitor dielectric liquid ester impregnant
having improved dielectric constant characteristics,
It is a specific object of this invention to provide
36-CA-3289
~079953
an electrical capacitor which ha~ been impregnant with a
dielectric liquid composition compri~ing a mixture of a
dielectric liquid aromatic ester, a chlorine containing
compound, and an epoxide stabilizer,
This invention will be better understtod when taken
in connection with the following descriptions and the
drawings in which--
Fig, 1 is a curve showing the increase in the corona
extinction voltage ~CEV) of capacitors containing DOP-TCB
mixtures,
Fig, 2 is a curve showing the increase in dielectric
constant of DOP-TCB mixtures,
Fig, 3 is a curve showing the viscosity of DOP-TCB
mixture~,
Fig. 4 is an exemplary roll section comprising al-
ternate electrode fail strips and dielectric strips,
Fig, 5 is a cross sectional view of a part of a
capacitor roll section utilizing solely synthetic resin
film as a dielectric,
Fig, 6 is a view of a part of a capacitor roll section
utilizing mixed synthetic resin film and paper as a die-
lectric,
Fig, 7 is a cross sectional view of a part of a
capacitor roll section utilizing a syn~hetic resin film
in a different dielectric paper and film arrangement in a
capacitor,
Fig, 8 is a complete capacitor in the form of sealed
can containing the roll section of Fig, 5,
Fig, 9 is a greatly reduced drawing of an exemplary
power capacitor utilizing multiple rolls, a structure
common to the large size power factor correction, induction
heating, and high frequency capacitorC,
107~ 3 36-CA-3289
It has been discovered that the aromatic ester im-
pregnants i~ accordance with the Eustance patent may be
qreatly improved when a chlorine containing compound is
added to the ester. The chlorine contribute-~ improved
anti_flammable characteristics to the impreynant while
at the same time advantageously raising its corona ex-
tinction level, increasing its dielectric constant, and
reducing its viscosity~
In high voltage capacitor applications the aromatic
esters evidence a very high corona start voltage, a
critical requirement of this impregnant. It is expected
that capacitors~ during their operating life, are subjected
to certain transient overvoltage conditions which could
cause a corona discharge within the dielectric. However,
with an impregnant such as a chlorinated diphenyl, this
corona i8 extinguished as soon as the transient voltage has
passed or as soon as the transient has reduced to a certain
degree In an effective impregnant, such as chlorinated
diphenyl, the voltage level at which the corona is ex-
tinguished (CEV) i8 very close to that level at which
corona originates This is known as a high corona ex-
tinction voltage and a high corona ectinction voltage is
required in order to prevent the lingering corona from
ser~ou~ly injuring the capacitor~ but more importantly,
to extinguish the corona when the voltage drops to the
ordinary operating voltage of the capacitor
When 1, 3, 4 trichlorobenzene ~TCB) is added to
dioctyl phthalate (2_ethyl hexyl) impregnant (DOP), there is
an increase in the corona extinction value of capacitors
containing mixtures More specifically, it was found that
the addition of at least about 10% of chlorine, by weight,
to DOP, where the chlorine is an admixture and is not ir
_ 4 --
1073953 36-CA_328g
combined with the DOP, is a ~ufficient amount to provide
a significantly improved corona extinction voltage of the
mixture which is close to that of Aroclor 1016: one of the
more common chlorinated diphenyl impregnant~ utilized in
the capacitor industry As low a8 an added amount of
5% chlorine by weight still results in a measured improve-
ment to the corona extinction voltage of capacitors con-
taining the phthalate.
Representative mixtures of this invention were utilized
as impregnants in capacitor embodiments and their corona
extinction values (CEV) were obtained as more cleaxly
shown in Fig. 1. Referring to Fig.l, the curve of the
CEV ver~us the weight percent of chlorine in a DOP/TCB
blend is illustrated as a curve which rises from about
1500 volts to about 2350 volts to about 2350 volts at the
highest point. It is to be noted that the increase in
CEV is most pronounced at about 8% through 12% with very
little increase after about 20% of TCB has been added to
the mixture The 10% chlorinate by weight provides a
sîgnificant increase in the overall CEV, which approaches
that of the Aroclor 1016. TCB which is a chlorinated fluid
is electronegative and this characteristic may be of sign-
i~icant assistance in the quenching of a corona arc. The
character of the corona pulses noted during these tests
is also improved by the addition of TCB In DOP capacitors,
the corona pulses break in every suddenly at high level
(ab. 100 picocoulombs). In capacitors with the DOP/TCB
blend, on the other hand, the corona breaks in at a low
level which increases in a controlled fashion as the
voltage is increased. As the voltage is decreased, the
level of the DOP/TCB pulses decrease rapidly and extin-
guish about the same point at which it appeared, while on
iO79953 36--CA_3289
the other hand, the DOP pulses per~ist at a high level up to
the extinguishing voltage. Corona extinction voltage i8
measured much in the same way and by the same equipment
which is used to measure corona start voltage. It usually
involves an amplified testing circuit which di~play~ the
presence of electrical discharges within the insulation
system on a cathode ray oscilloscope. The corona measuring
equipment utilized in the invention has a sensitivity of
one (1 0) picocoulomb.
DOP_TCB mixtures were also studied to determine their
dielectric constants Dielectric constant (DK) is the ratio
of the capacitance of a given structuxe with the dielectric
liquid as compared to the capacitance of that structure with
air as the dielectric medium The value obtained i~ qualified
with reference to the conditions of measurement (voltage,
frequency, and temperature). The dielectric constant ~DK)
of the preferred aromatic esters, the Aroclors, and TCB
are desirably high so that the expected result of mixing
these liquids would be a somewhat average DK Surprisingly
enough, it was discovered that the mixture of this invention
exhibited a dielectric constant which was significantly
greater of the dielectric constant of either DOP alone or
the TCB alone The dielectric constant of a mixture is
usually calculated by the use of a linear dielectric constant
mixing rule or a logarithmic dielectric constant mixing
rule 1,2. However, the behavior of the mixtures of the present
invention appears to be an exception to both rules This
synergism which is noted to be most significant for the
dioctyl phthalate and trichlorobenzene mixtures is not
readily explained by previous experiences with dielectric-
mixture~. The synergism of an increased dielectric constant
~'or~ ne~C
A above the expected mixing rule value w~s -~ef~hi~Kff~by testing
36-CA_3289
1079953
of DOP mixtures with other chlorinated compunds.
The linear dielectric constant mixing rule as defined
in both cited reference~ by apprc>priate equations i8 in-
tended to mean the straight line function, i.e. the dash
A line of Fig 2 As hereinafter ~ to in the claims,
Dielectric Constant Mixing Rule refers to the rules noted
in the above cited references and in thi~ specification.
A DK higher than that calculated by the Dielectric Constant
Mixing Rule is a DK whose value is above that indicated by
the dash line regardless of the slope or initial height of
the dash line. ~he basis for the straight line function
is derived from the equations given and whether or not the
line is precisely str3ight is of no importance. This in-
vention describes a DK greater than that predicted by the
noted equations.
Several mixtures were studied under conditions of 25C
f and at a frequency of 100 Hertz, and their dielectric con-
stants are more clearly shown in Fig. 2 Re~erring now
to Fig. 2, there is disclosed a volume percent TCB in DOP/TCB
mixtures as compared with the DK value of the mixtures
It can be seen that at about 20% of TCB in the mixture a
maximum DK of about 5.5 is reached This DK does not ~eem
to be affected by further increases in the amount of TCB.
The DK expected, from linear or logarithmic mixing rules for
these mixtures, would be about 5.15 as indicated by the dash
line The high DK figure of 5.5 is compared to the DK of
about 5.15 to 5 2 for either of the TCB or the DOP material
alone.
The curve of Fig. 2 shows a DK higher than either com-
ponent. However, when one of the components has an initial
DK which is much lower than the other component, the DK
curve will be higher than the noted mixing rules predict
10799S3 ~ 6 -CA 3 2 8 9
although the mixture will not exhibit a DK higher than
either component.
Variou~ mixtures of DOP ~ TCB were made up and utilized
in representative type capacitors. It wa8 noted during the
course of this work that the TCB reduced the viscosity of
the DOP and thus facilitated impregnation particularly in
all film capacitors Accordingly, where many of the estèrs
are more undesirable because of their high viscosity, the
addition of TCB may reduce that viscosity to more desirable
and appropriate levels
One example of the viscosity lowering ability of TCB
in DOP is shown in FIG. 3. In Fig. 3, the curves show that
the viscosity of the mixture decreases quite rapidly with
increasing amount~ of TCB at room temperature conditions
or 2sC. At 70 C it is noted that the viscosity decreases
less rapidly with increasing amounts of TCB since at this
temperature the viscosity of the DOP is already low. By
comparison, the viscosity of the more common chlorinated
diphenyl impregnant, Aroclor 1016, is about 45 centistokes
at 25C.
Mixtures of DOP and TCB were also tested for their
flame retardant characteristics These tests show that the
ability of the DOP to sustain combustion i~ lessened by
the addition of the TCB, and, therefore, the TCB addition
is quite ~avourable for capacitor operation where a high
degree of inflammability is desired. For example, it was
found that DOP has a fire point, the point at which DOP will
sustain flame at about 240 C. However a 70% DOP + 30% TCB
mixture had no fire point up to about 265 C
Preferred capacitor structures embodying this invention
are illustrated in Pigs. 4 through 9. Referring now to Fig
4 here is disclosed a typical roll section 10 comprising
1079953 36-CA-3289
alternate electrode foils 11 and 12 and dielectric strips
13 and 14. Strips 13 and 14 may be single strip~ of paper
or a synthetic resin, plural strip of the~e materials, or
composite strips. The electrode foilR 11 and 12 may also
be formed as metallized coatings on the strips 13 and 14,
or on separate and additional stripc of various dielectric
material~. Suitable electrical connectors in the form of
tabs 15 and 16 are utilized to connect the electrode 11 and
12 to appropriate capacitor terminals.
The dielectxic structures for roll section 10 may
include any of the composites of Fig. 5, 6 and 7 as
illustrated Referring to Fig. 5, there is illustrated
what may be referred to as an all ~ilm roll structure 17
In this structure, only a synthetic resin film such as
polypropylene film is used as the 901e dielectric between
electrodes 11 and 12. A typical all polypropylene film
capacitor will utilize one or more polypropylene film strips
18 between electrodes 11 and 12.
Referring to Fig 6, there is illustrated one form of
a mixed dielectric roll structure 19 or a capacitor using
dissimilar dielectrics, such as a synthetic resin film and
a paper strip, although different resin films may be employed
as a composite, such as polypropylene film and a polyester
film. As illustrated in Pig. 6, roll structure 19 has
been described as a semi-~andwich construction and uses one
or more paper strips 20 with one or more synthetic resin
film ~trips 18.
Referring to Fig. 7, there is illustrated a further
mixed dielectric roll structure 21. Structure 21 has been
referred to as an inverted sandwich -~tructure whose primary
characteri~tic is that a synthetic resin film is used ad-
jacent each foil 11 and 12 and there is one or more in-
_ g _
36-CA-3289
1079953
termediate dissimilar strips 20 l~hich are usually employed
as a combined dlelectric and wiclcing #trip. In a preferred
form of the invention as illu~trated, the intermediate
strip i8 a single paper strip 20 and the synthetic resin
strips are single polypropylene strips 18,
One or more of the roll sections 10 of Fig. 1, in-
A cluding the ~a~ structure of one or more structures ofFigs, 5,6, and 7, are assembled in cans or casings, im-
pregnated with the impregnant of this invention, and then
sealed. Typical capacitor constructions are illustrated
in Figs, 8 and 9,
Referring to Fig. 8, there is illustrated what may be
referred to as a motor start or motor run capacitor 22,
Such a capacitor usually includes a single roll section 10
of Fig. 4, which is inserted into a metal casing 23 and
Realed therein. The tabs 15 and 16 of roll section 10
are connected to external capacitor terminals 24 and 25,
The metal casing 23 is filled with the impregnant of this
invention through fill hole means 26 which is illustrated
as being solder sealed,
Plural and larger roll sections are u~ed in capacitors
referred to as power capacitors or power factor correction
capacitors, One such typical capacitor is illustrated in
Fig, 9. Refexring now to Fig, 9, there i~ illustrated
a high voltage power factor correction capacitor 27,
Capacitor 27 usually includes a large rectangular steel cas-
ing 28 which may be form ~ to 1 meter in the longer dimen-
sion shown, Casing 28 includes therein a row of longer
roll sections 10 whose connectors 15 and 16 are suitably
connected to external capacitor terminals 29 and 30,
Casing 28 may be filled with the impregnant of this inven-
tion in a manner similar to that as described for Fig, 9,
-- 10 --
.
10 79953 36-CA-3289
A number of capacitors were made up for testing
purposes of this invention. A typical te~t capacitor in-
volved the r~ll section of Fig. 4 assembled a~ the motor
run capacitor of Fig. 8 In a f:irst test capacitor, the
strips 13 and 14 were composite strips comprising a pair
of polypropylene strips 18 and intermediate paper strip
20 (Fig. 7). In the examples as made up in this application,
the polypropylene comprised two strips 18 of about 0.47
mil. (12 mm) thick polypropylene and one sheet of 0 50
mil. (1.27 mm) paper. The overall capacitor height was
about 4 in. (10.16 cm) In a second capacitor structure
made up for the purposes of this invention~ the dielectric
strips 13 and 14 each comprised a pair of paper strips 20,
one of which was about 0.60 mil. (1 55 mm) thick paper and
the other which was 0.65 mil. (1.68 mm) thick paper. These
capacitors were impregnated in accordance with the general
impregnation cycle as set out in the Cox U S. patent No.
3,363,156 dated January 9, 1968 which comprised drying
the capacitors in a vacuum oven at temperatures up to and
including 105 C and then cooling the capacitors to less
than 100 so that they may be filled with a dielectric liquid
at about 65 to 75C. Thereafter, the capacitors were
sealed and permitted to heat soak overnight, i.e., about
14 to 16 hours, in a forced circulation oven at about 95 C
Testing of these capacitors of the first described kind in-
dicated the following corona start voltage levels as æet
out in Table I.
TABLE 1
Corona Start Voltage CSV (avg of 5) Minimum
95% DOP/5 TCB 3020 2900
9~% DOP/10 TCB 2912 2850
80% DOP/20 TCB 2870 2750
60% DOP/40 TCB 2950 2850
36-CA-3289
~79gS3
Ten of the capacitors from T~ble I which included the
60% DOP/ 40% TCB blend were put on life test at 2650 V~C
(volts, alternating current) at 70 C There were no
failures after 400 hours ac compared wqth three ~ailures
in DOP capacitors without TCB, and zero failures in cap-
acitors impregnated with Aroclor 1016
It has been found in the practices of thi-q invention
that some form of electrical stabilizer i~ de~irable in
the impregnant mixture Recently, the epoxide compounds
have been found to be particularly sffective with chlorinated
diphenyl compounds and also with ester compounds although
the reactions of neither addition are well understood. The
epoxides are the preferred stabilizer~ for the present in-
vention and they perform a stabilizing function in the
presence of both an ester liquid and a chlorinated com-
pound without any adverse effects from the component
mixtures. The liquid impregnant from the capacitors of Table
I above included about 0.3 percent of l_epoxyethyl_3, 4-
epoxycyclohexane.
While the power factor stabilizer is preferably an
epoxide material, other such stabilizers such as the anth-
roquinones may be utilized but with apparently less effect
than the epoxide as disclosed in the Eustance patent. On
the other hand, some of the anthrcquinones~ such as the
monochloroanthroquinones and the dichloroanthroquinones,
include a significant amount of the chlorine which appears
to be the necessary ingredient in the impregnant of this
invention.
The dielectric liquid c~mpo~ition of this invention
i5 more specifically related for use in electrical devices
such as electrical capacitors. For that reason, the com-
ponents, particularly the halogen component, chould be
- 12 _
iot79953
36-CA-3289
chosen to be capacitor compatible with various capacitors
whether of the small motor run kind or the large power
factor correction kind. Compatibility means a material
A which is-~ct~ and stable not only under the operating
conditions and environment of the capacitor but also with
respect to capacitor materials such as copper, aluminum,
steel, paper, and synthetic re~ins as example~.
This invention may be separated into certain well-
defined categories, each of which relate to the addition
of a halogen containing compound to an ester ba~ed die-
lectric liquid impregnant, particularly adaptable as an
electrical capacitor impregnant. In a preferred embodiment
the ester is an aromatic, but it may be an aliphatic ester,
and it may also be a partially halogenated ester to which
a further halogen-containing compound i8 added. me further
halogen-containing compound i8 in the mixture in an ad-
mixture state, i.e., the added halogen-containing compound
is not combined in the ester molecule.
For example, best results have been obtained in the
practice of this invention when an aromatic ester, pre-
ferably a phthalate ester is the major component and a
separate component, such as trichlorobenzene, is mixed
therewith The chlorine is attached to the mixing component
and not to the base ester so that the chlorine compound is
in admixture relationship to the e~ter.
The halogen-containing compounds to this invention may
be suitable compounds from the chlorinated, fluorinated,
brominated, and the like, compounds Examples of such
halogenated compounds may include, for example, dichloro-
benzene, difluorobenzene, dibromobenzene, and mono-
chlorobenzene, including chlorinated aromatic and non aromatic
compounds .
- 13 _
36-CA-3289
~0~7~95~
It i~ a preferred concept of this invention that the
ester be the predominate liquid or component, i e., the
basic liquid for impregnation purposes Thi~ means that
ordinarily the ecter is the greater amount by volume or
weight in the mixture as compared to any other component.
In a capacitor environment, the basic electxical characteris-
tics, such as the dielectric constant and dissipation
factor, would be primarily based on the ester as the
predominate liquid. One or more ester~ make up one or more
components and a non ester chlorinated compound, such as
TCB, is another component. A stabilizer i8 not considered
as a component. While some mixtures may contain three or
more components, the foregoing description of a two com-
ponent system remains the preferred one.
In a preferred embodiment of the invention, the ester
based dielectric liquid is an aromatic ester, such as a
phthalate ester, and more particularly a branch chain
phthalate ester such as di-2_ethylhexyl phthalate and the
di-isophthalates. Corresponding to this preferred embodi-
ment, the halogen-containing compounds are the chlorinated,
and more particularly, the chlorinated benzenes such as
trichlorobenzene.
By the use of the preferred embodiment of this in-
vention, the particular desired, of increased dielectric
constant, a higher corona extinction voltage, and increa~ed
flame retardance, can all be programmed to the desirable
function of the capacitor
While this invention has been disclosed with respect to
particular embodiments thereof, numerous modifications may
be made by those skilled in the art without departing from
it~ true spirit and scope. Therefore, it is intended that
the appended claims over all such modifications and variations
_ 14 -
36-cA_32as
iO799~3
which come within the true 8pirit and scope of the pre~ent
invention.
1 C P Smyth, "Dielectric Behavior and Structure", page 23,
McGraw-Hill, 1955. ,~
( ~ - 1) (2 ~ + 1) M = 4 ~ ~o +
g L d 3 3KT
Where ~ i8 the dielectric constant, M is the molecular weight~
N is the number of molecules per mole, ~ o i8 the polariz-
ability, ~ is the molecular dipole moment in the liquid,
is the sum of the molecular dipole moment and the moment
induced as the result of hindered rotation, and d is the
density
2 A Von ~ipple, "Dielectrics and Waves", page 231,
John Wiley & Sons, 1954.
Log km" = ~1 loq Kl + e2 log K2 '
Where km' is the dielectric constant of the mixture of k 1
and k2' and el and e2 are the volume ratio8 of the compon_
ents.
- 15 -
