Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
PRIOR ART
U.S. Patent 3,955,417 lssued May 11, 1976~ discloses
thermoparticulating greases for use in generators.
Canadlan Patent 1,079,165 issued June 10, 1980 to
D. C. Phillips et al, titled "Mhltiple Signal mermoparticulat-
ing Coating", discloses (Example 1) a mixture o~ a thermopartic-
ulating grease, two thermoparticulating compounds, a resin, and
a solvent for use in generators.
The following U.S. Patent , all o~ which were issued
to James D. B. Smith and David C. Phillips, disclose thermo-
particulating compounds for use in generators: 3,973,439
issued August 10, 1976; 4,016,745 issued April 12, 1977;
3,979,353 issued September 7, 1976; 3,995j489 issued December 7,
1976; 3J957,014 issued May 18, 1976; and 3,973,438 issued
August 10, 1976.
BACKGROUND OF THE INVENTION
Electrical apparatus, such as motors and turbine
generators, occasionally overheat due to shorts or other
malfun~tions. The longer the o~erheating continueæ the more
damage is done to the apparatus. A malfunction detected
immediately may mean only a ~uick repair but if the over-
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heating continues, the entire machine may be damaged.
Large rotating electrical apparatus is usuallycooled with a hydrogen gas stream. The organic compounds in
the apparatus are first to be affected by the overheating
and they decompose to form particles which enter the gas
stream. Monitors then detect particles in the gas stream
and sound a warning or shut down the apparatus when too many
particles are detected. Special coatings, however, may be
applied to the apparatus which contains compounds which de-
compose and form detectable particles at a lower temperaturethan the usual organic compounds found in the apparatus.
Until now most thermoparticulating compositions
consisted of a thermoparticulating compound in a solution of
an air-dryable resin. The composition was applied to an
area inside a generator and when the solvent had evaporated
a solid coating was formed.
However, there are certain locations in a gener-
ator, such as where flaking may block passages (e.g., the
inside of parallel rings), where resinous coatings cannot be
used. Also, the residual solvent emanating from a resinous
coating may occasionally give a false signal in th monitor.
~ho ~r~e~onea~
For these reasons the greases described in~U.S.
Patent 3,955,417 may be more suitable, because the greases
do not flake and do not contain a solvent. The principal
disadvantage of using those greases, however, is that they
do not thermoparticulate at very low temperatures. Thus, a
warning signal may not be given until considerable damage
has already occurred.
SUMMARY OF TXE IN~ENTION
We have discovered that compounds whlch thermo-
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part~culate can be incorporatecl directly into ~reases, with-
out the use of a solvent or a resin in the final composi-
tion. The compounds thermoparticulate ~rom the grease as
easily and at the same temperature as they did from the
resin. In addition, if a thermoparticulating grease is
used, it will also thermoparticulate, giving an additional
signal.
The mixed grease of this invention can be easily
applied to inside portions of the generator. It does not
flake or give off solvent vapors.
DESCRIPTION OF THE INVENTION
me compositions of this invention comprise a com-
pound which is stable at 600C and thermoparticulates between
80C and 200C, and a grease which is stable at 600C and is
unreactive with the thermoparticulating compound. A suit-
able composition is about 10 to about 300 parts by weight
thermoparticulating compound per 100 parts by weight of
grease, and a preferred composition is about 150 to about
250 parts by weight thermoparticulating compound per 100
parts by weight grease. A ratio which has been used experi-
mentally and has been found to work well is 2 parts by
weight thermoparticulating compound per part by weight of
grease.
Compounds which thermoparticulate between 80 and
200C are now well known in the art. An extensive list of
such compounds can be found in the aforementioned U.S. Patent
3,957,014, Canadian Patent 1,079,165 and U.S. Patent 4,179,926
issued December 25, 1979 to D. C. Phillips et al. Families
of such compounds include diazonium salts, malonic acid and
its deri-
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~ ~18 15 ~
vatives, metal acetyl acetonates, blocked isocyanates, sulfonic
acids (Canadian Patent 1,085,276 issued September 9, 1980 to
J. D. B. Smith et al), and metal dithiocarbamates (Canadian
Patent 1,074,485 issued March 25, 1980 to J. D. B. Smith et al).
A particularly useful thermoparticulating compound is zinc
acetylacetonate because it thermoparticulates at a low temper-
ature with a strong signal. Mixtures of thermoparticulating
compounds can also be used to provide a series of signals as
the temperature rises.
Although greases which do not thermoparticulate
can be used, preferably the grease is a thermoparticulating
grease which preferably thermoparticulates at a temperature
at least 20C higher than the thermoparticulating compound,
so that two distinct signals are received, thereby providing
additional conformation that overheating is occurring.
Descriptions of thermoparticulating greases can be found in
the aforementioned U.S. Patent 3,955,417. Mixtures of greases
are also contemplated.
me thermoparticulating grease composition of this
invention can usually be made by simply blending the thermo-
particulating compound and the grease together until a
homogeneous blend is produced. However, some thermoparticu-
lating compounds, such as, for example, zinc acetylaceton- -
ate, do not blend well. As to these compounds it may be
necessary to dissolve the compound, and preferably also the
grease, in a solvent such as FreonTM 113 (CC12F-CClF2). me
solvent is then evaporated so that the final composition
contains no solvent, nor does it contain any organic resin.
The absence of solvents in the composition eliminates the
problems of residual solvent vapors in the generator. me
absence of resins eliminates problems with resin flakes
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clogging ducts and signals resulting from the decompositionof the resin. The composition may contain a small amoun~
(up to about 20%, and preferably about 3 to about 5%, of a
B thixotrope such as finely-divided silica (e.g., "Cab-O-Sill)
if the composition is too liquid to stay in place. The
composition is applied by wiping or other means to areas
inside the generator which are exposed to the cooling hydro-
gen gas stream. The composition is particularly applicable
to those areas of the generator where only greases can be
used, such as the inside surfaces of parallel rings, or
where flaking from decomposing resins could clog passage
ducts, or where solvents are not easily evaporated. The
following example further illustrates this invention:
EXAMPLE
Compositions of various thermoparticulating greases
and various thermoparticulating compounds were prepared
using a ratio of 2 parts by weight thermoparticulating
compound to 1 part by weight grease. The compositions were
prepared by blending until homogeneous, except for the
composition containing zinc acetylacetonate, which was
prepared by forming an 80% solids solution of the grease and
zinc acetylacetonate in Freon 113 and evaporating the Freon
113. The compositions were coated on 10 mil thick~ 4 inches
x 1 inch aluminum straps to a depth of about 1 to 3 mils and
aged for 16 hours at 60C, except for the compositions which
contained benzene sulfonic acid and benzene disulfonic acid
which were not aged as they tended to flow at 60C.
The samples were placed one at a time in a stain-
less steel boat within a l-inch stainless steel tube.
Hydrogen was passed over the samples at a flow rate of 7
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l/min. A phase-controlled temperature regulator and pro-
grammer controlled the temperature in the boat and the tem-
perature in the boat was measured by mounting a hot Junction
chromel-alumel thermocouple within a small hole in the boat.
The output of the thermocouple and the detector were moni-
tored on a two-pen potentiostatic recorder. A 6C/min.
heating rate was maintained in each experiment after the
insertion of the sample in the boat. The threshold tempera-
ture at which considerable particulation occurred was taken
from the chart produced by the recorder. The occurrence of
particulation was detected using a Generator Condition
Monitor or a Condensation Nuclei Monitor. Both instruments
are sold by Environment One CorporationO
The following table gives the results:
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ThermoparticulatingOrganoparticulation
Grease Compound Temperature Range (C)
A mixture of about 20%
(by weight) telomer of
polytetrafluoroethylene
and about 80% perfluoro- None 194-198
alkyl polyether, sold by
DuPont under the trade-mark
"Krytox 240-AD"
A polyurea-thickened
hydrocarbon oil sold
by Chevron Oil Co. None 181-184
under the trademark
"Chevron BRB2"
A grease made of colloidal
copper, molybdenum, sulfide,
and a hydrocarbon oil sold None 174-178
by Fel-Pro Company under
the trademark "Fel-Pro C-100"
"Krytox 240-AD" Zinc acetylacetonate 132-142
"Krytox 240-AD" Malonic acid 133-140
:
"Krytox 240-AD" p-chlorobenzene-
diazonium penta-
fluorophosphate, sold 125-129
by Ozark-Mahoning Co.
under the trademark
"Phosfluorgen 'A"'
"Krytox 240-AD" Benzene sulfonic acid 125-128
"Krytox 240-AD" Benzene disulfonic acid 147-153
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The first number in the organoparticulation range
is the temperature of the sample when the alarm sounded on
the ion chamber monitor. The second number in the organo-
particulation range is the temperature of the sample when
the current in the ion chamber had dropped to about half its
normal value (i.e., from about 0.8mA to about 014mA).
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