Note: Descriptions are shown in the official language in which they were submitted.
~9602
BACKGROUND OF THE INVENTI0N
This invention relates to a dielectric liquid impregnant for electrical
devices and more particularly to an electrical capacitor utilizing an
improved non-toxic dielectric liquid impregnant theretofore.
Liquid impregnants for electrical capacitors should have a high
dielectric constant, maintain a low dissipation factor, and be compatible
with the other materials utilized in capacitor structure. At the same
time, the impregnant must withstand elevated and fluctuating temperature,
pressure, and voltage stress conditions with excellent electrical
characteristics for a long operative life of the capacitor.
The polycholorinated biphenyls as capacitor impregnants meet these
requirements and they were eminently satisfactory for several decades.
The polychlorinated biphenyls are broadly referred to as PCBs. The poly-
chlorinated biphenyls have recently been associated with ecological
problems, restrictive use limitations, and rising costs. These problems
have spurred the search for a suitable non-toxic replacement capacitor
impregnant which would have some advantageous impregnant characteristics
comparable to those of the chlorinated diphenyls, and still provide
outstanding electrical and compat;bility performance with the two most
important present day capacitor solid dielectrics, paper and polypropylene.
It has been found that soybean oil provides good electrical
characteristics as a dielectric fluid impregnant as well as being non-toxic.
A useful soybean oil for example, would be of a refined, low acid grade
with a flash point of about 325C, which is available in commercial
quantities. However, one of the problems of using soybean oil is its
fluidity or its otherwise mobility. More specifically the mobility of any
conductive ions or impurities of the soybean oil could coat the
metal foil in capacitors or cause hot spots in the capacitor.
~ ~9~(~2
FEATURES OR OB~ECTS OF THE INVENIION
_ . _
It is, therefore, a feature of the ;nvention to pr~vide a dielectriC
impregnating fluid that is non-toxic. Another feature of the invention is
to provide such an impregnating flud that includes soybean oil. Another
feature of the invention is the provision of such a dielectric impregnating
fluid that includes an additive which causes the soybean oil to gel. Still
another feature is the provision of such an additive ~ihich includes a
phenolic antioxidant. Another feature of the invention is the provision
of such a dielectric impregnating fluid that includes an antioxidant
compound of alkylhydroxyphenylalkanoyl-hydrazine. These and other features
of the invention will become apparent from the following description taken
in conjunction with the accompanying drawings.
SUMMARY OF THE INVENTION
Generally speaking, the present invention pertains to an a-c
capacitor having a dielectric fluid including soybean oil and an additive
of an alkylhydroxyphenylalkanoyl-hydrazine compound in an amount of
from 0.1% to 10% by weight of the total weight of the dielectric
fluid to gel the soybean^oil.
BRIEF DESCRIPTION OF THE DRA~IINGS
FIGURE 1 of the drawing illustrates a convolutely wound a-c capacitor
body partially unwound to show the dielectric plastic film and foil
electrode structure.
FIGURE 2 of the drawing illustrates the convolutely wound a-c
capacitor body of FIGURE 1 to which leads are attached.
FIGURE 3 of the drawing illustrates the a-c capacitor body suitably
encased and sealed in a housing.
DISCUSSION OF THE INYENTION
Referring now to Figure 1 of the drawing, there is illustrated a
convolutely wound a-c capacitor body 10. The capacitor body 10 includes
a pair of dielectric film layers 11 and 12 and overlying electrodes 13 and 14
_ c _
t ~
960Z
respectively. Electrodes 13 and 14 are of a suitable metal such as
aluminum for example. Margins 15 and 16 are provided for preventing
electrical short circuit between the electrodes. As shown in Figure 2,
suitable terminal leads 23 and 24 are attached to the electrodes 13 and
14 from opposite ends 21 and 22 of the capacitor body 10. Suitable
lead material could be solder coated copper for example.
The dielectric plastic films or layers 11 and 12 should have high
dielectric strength, low dissipation factor to prevent thermal runaway,
broad temperature range capabilities, resistance to the dielectric fluid7
and freedom from pinholes and conductive particles. Suitable dielectric
film layers 11 and 12 may be paper, a paper and polymeric film combination,
or polymeric films.
In Figures 2 and 3, a capacitor body 10 is preferable sealed to a
can or housing 40 to form a capacitor 41. Capacitor 41 includes the
metal housing or can 40 and terminals 42 and 43. The capacitor body 10
is contained within the housing 40 and terminal lead 23 makes electrical
contact with terminal 42 and the remaining terminal lead 24 makes electrical
contact with terminal 43.
As noted previously, fluid or liquid dielectric impregnants for
electrical capacitors should have a high dielectric constant, maintain a
low dissipation factor and be compatible with the other materials used in
capacitor structure. According to the present invention, the dielectric
fluid which is used to impregnate capacitor body 10 not only satisfies
these requirements, but is substantially non-toxic. The dielectric
fluid of the present invention includes refined soybean oil with an
additive which when the soybean oil is cool, gels the soybean oil to
arrest its fluidity or mobility. It has been found that phenolic antioxidant
compounds of alkylhydroxyphenylalkanoyl-hydrazine are useful in gelling
_ _ , . . . . . .. . .. . .
~9602
soybean oil. Such compounds are described in U.S. patent 3,773,722 issued
November 20, 1973 to Martin Dexter. A useful compound is sold in commercial
TM
quantities from Ciba-Geigy Co. under the brand name of Irganox MD-1024 and
bears the chemical name rl, r M -bis ~3-(3',5'-di-tert-butyl-~'-hydroxyphenyl)
propionyl~ hydrazine.
Over 50 additives were evaluated at high temperatures. The types of
additives used for gelation were: Phenylamines; Napthylamines; An-inophenols;
Monophenols; Polyphenols; Pulyhydroxbenzenes; Quinones; Thiobisphenols:
Epoxides and others.
From 0.1 to 10% by weight of the total weight of the soybean oil of
TM
such additives, including Irganox MD-1024, were added to soybean oil and
heated in an air circulated oven at 125C or higher for 16 hours or longer.
At all stages, with elevated temperatures, soybean oil and any of the
additives were in a liquid form. After heating, the samples were cooled
to room temperature. All remained in a liquid state except those which
TM
contained Irganox ~1~-1024. These haa gelled.
TM
These Irganox MD-1024 soybean gel samples were set back in the oven
and heated for a short time. The gel converted to a liquid. They were
again cooled to room temperature and again, the l;quid was converted to a
0 gel. Repeated heating and cooling produced the same results. Several
TM
samples with Irganox MD-1024 were set in a vacuum at 130C overnight, then
the heat was shut off with the vacuum still on. When these samples were
cooled to approximately 55C under vacuum, the soybean oil converted to a
gel. Thus, the rreSence of oxygen does not appear tc ir.fluer.ce sc'a'ion.
This phenomena is due to a physical reaction and partially responsible to
Van Der Walls forces.
When used as an additive in a dielectric fluid for capacitors of the
type described in Figures 1-3, the additive is mixed as a liquid with liquid
soybean oil at temperatures above about ~35C and then impregnated into the
B
~9602
capacitor. Upon cooling, the soybean oil gels in situ. The soybean oil
will remain a gel since there is very seldom, if any, prolonged capacitor
use above 85C.
On thousand hour life tests were perfonned on 4 electrical capacitors
of the type described in Figures 1-3 using soybean oil as a dielectric
fluid impregnant with an additive of 1.0% by weight of the total weight of
the dielectric fluid of Irganox MD-1024. The results are shown in Table II
which presents average capacity and dissipation -Factors.
Table I
ELECTRICAL CAPACITOR PROPERTIES
CAPACITANCE AND % DISSIPATION FACTOR (DF) STABILITY
DURING LIFE TEST
25uF 370VAC rated capacitor operated at 459VAC
80C LIFE TEST
DIELECTRIC-2 layers x 0.45 Mils + 2 layers x 0.40 Mil PAPER
CAPACITANCE-uF INITIAL 500 HRS 1000 HRS
25C 18.1 18.2 18.1
65C 17.8 17.9 17.9
85C 17.7 17.8 17.8
20DISSIPATION FACTOR ,0
25C 0.172 0.196 0.195
65C 0.212 0.288 0.304
85C 0.308 0.408 0.427
It is seen that over a life test of 1000 hours, the capacitor
exhibited good stability. There was no evidence of "hot spots" or other
failures.
--5--
