CA1079165A - Multiple signal thermoparticulating coating - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A composition is disclosed of a solution of a resinous carrier and at least two compounds which thermoparticulate at different temperatures between 60 and 200°C. A coating is made by applying the com-position to a portion of an electrical apparatus ex-posed to a gas stream. As the temperature of the coating increases the compounds therein thermoparticulate. The time between which the compounds thermoparticulate indi-cates the rate of rise of the temperature and analysis of the products of thermoparticulation indicates the location of the coating in the electrical apparatus. Alternatively, the coating can consist of several layers with a thermo-particulating compound in each layer which thermoparticulates at different temperatures.

Description

CROSS-R~F~RENCES TO RELATED PAT~MTS
This application is related to the follo.r~ng U.S. Paten's:
U.S. Patent No. 3,972,225 issued Augus~ 3, 1976 to Emil M. Fort, Thomas D. Kaczmarek, and David Colin Phillips.
U.S. Patent No. 3,973,439 issued August 10, 1976 to J. D. B. Smith and D. C. Phillips.
U.S. Patent No. 4,100,121 issued July 11, 1978 to J. D. B. Smith and D. C. Phillips.
U.S. Patent No. 3,955,417 issued May 11, 1976 to J. D. B. Smith and Do C. Phillips.
UOSo Patent No. 3,979,353 issued September 7~ 1976 to J. D~ B. Smith, Do C. Phillips and K. ~;1. Grossett~
U.SO Patent No. 4,016,745 issued April 12, 1977 to J. D. B. Smith, J. F. Meier, and D. C. Phillips.

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BACKGR~UND OF 1~ INVENTION
Electrical apparatus, such as motors and tur-blne generators, occasionally overheat due to shorts or other malfunctions. The longer the overheating continues the more damage i8 done to the apparatus. A malfunc-tion detected immediately may mean only a quick repair but if the overheating contlnues, the entire machine may be damaged.
Large rotating electrical apparatus is usually cooled with a hydrogen gas stream. The organic compounds in the apparatus are rlrst to be affected by the over-heating 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 appara-tus when too many particles are detected.
Descriptions of such monitors and h~ they function may be found in U.S. Patent ~,427,880 titled "Overheating Detector For Gas Cooled Electrical Machine"
and in U.S. Patent 3,573,460 titled "Ion Chamber For 45,718 107gl65 Submicron Partlcles." Another monitor, "The Condensa-tion Nuclel Detector, ~! iS described by F. W. VanLuik, Jr.
and R. E. Rippere, in an article titled "Condensation Nuclei, A New Technique For Gas Analysis," in Analytical Chemistry 34, 1617 (1962) and by G. F. Skala, in an article titled "A New Instrument For The Continuous Detection Of Condensation Nuclei," in Analytical Chemis-try 35, 702 (1963) .
As U.S. Patents 3,427,880 and 3,807,218, and - 10 the hereinbefore-cited related U.S. Patents dis-close, special coatings may be applied to the apparatus which decompose to form detectable particles (i.e., thermo-particulate) at a lower temperature than the usual organic compounds found in the apparatus. However, merely knowing that an area in the generator is being overheated may not be enough information on which to base a decision to shut down the generator. Since shuttlng down a generator means the loss of the electricity which would have been generated plus the cost of inspecting, disassembling, and reassembling the generator, such decisions are not made lightly.
SUMMARY OF THE INVENTION
We have discovered that the rate at which the temperature rises in a particular area of a generator can be determined by applying to a surface in the gas stream of the generator a coating which contains at least two compounds which thermoparticulate at different temperatures between 60 and 200C. If the rate or temperature increase is rapid, a runaway situation is probably occurring and the generator must be shut down. On the other hand, if the temperature rise is slow, the load on the generator can be reduced while :10791 65 the generator is checked and analyzed. Also, because various combinations of thermoparticulating compounds can be used in the coating, the location of the over-heating in the generator can be determined by analyzing the products of thermoparticulation. The location of over-heating can also be determined visually because the thermo-particulating compounds described herein (except for the grease) blister and darken when they decompose.
DESCRIPTI ON OF THE INVENTION
A composition is prepared of at least two thermoparticulating compounds (hereinafter "TPC's") in a solution of a resinous carrier. The TPC's may be dis-persed if they are insoluble in the solvent (e.g., tolu-ene) or they may be in solution if they are soluble in the solvent (e.g., ethyl alcohol ar diethyl ether).
Dispersions are preferred as they produce much more particulation than do solutions. A particle size of the dispersed IPC's of about 25 to about 1000 microns is suitable.
A suitable composition is a resinous carrier, about 20 to about 250 phr (parts by weight per hundred parts of resinous carried not including solvent) total of the TPC's and about 25 to about 75% (by weight based on the resinous carrier) of a solvent for the resinous carrier. If the total amount of the TPC is less than about 20 phr, the quantity of particles given off during decomposition may be too low to be detected by presently existing detectors. However, the construction or more sensitive detectors would permit a lower amount of TPC.
If the amount of TPC exceeds about 250 phr, the composition is thick, difficult to apply, and does not bond well.
The preferred amour,t of TPC, which generally gives the best results, is about 40 to about 60 phr. If the amount of solvent is less than about 25%, the composition is generally too viscous to apply easily and if the amount of solvent is greater than 75%, the composition is unne-cessarily dilute and the coating may be too thin to pro-duce ar. adequate number of particles during decomposition, at least while the malfunction is highly localized. Best resul~s are usually obtained with about 45 to about 55%
solvent.
The resinous carrier performs the function of bonding the TPC to the apparatus since a coating of a TPC by itself does not adhere well. The resinous carrier should be compatible with the other resins used in the apparatus ar,d therefore it is usually advantageous to use the same resin used elsewhere. The resinous carrier is curable at 60 C, and is preferable air-dryable since it cannot be easily cured in place with heat. Also, it should be stable after curir,g for several years at 60C. l`he resin must be unreactive with the TPC for otherwise suitable thermoparticulation will not occur. The TPC and the resin from a mixture and the TPC does not catalyze the cure of the resin. Epoxy resins are preferred as they are usually used elsewhere in the apparatus, but polyester, silicone rubber, styrene, etc. could also be used.
The solvent for the resinous carrier depends on the particular resinous carrier used. Toluene, xylene, benzene, methyl ethyl ketone, ethyl alcohol, diethyl ether, acetone ? cellosolve, etc. are common solvents that 45,718 ~,o79~65 may be used. Toluene is preferred as it is inexpensive and dissolves most resins.
The composition also preferably contains about 0~1 to about 3 phr of a drier when the resinous carrier is an epoxy resin or similar resin, to promote its room temperature cure. Lead naphthenate or cobalt naphthenate is preferred although stannous octoate, zinc stearate, etc. could also be used. Resins such as polyesters may also require the presence of an organic peroxide as is known in the art. Mixtures of various resins, solvents, or driers are also contemplated.
The composition may be prepared by simply mix-ing the ingredients, but it is preferable to mix the drier, resinous carrier, and solvent first and then add the TPC to prevent the occlusion of the drier in the TPC
and thereby to obtain a more homogeneous dispersion of the TPCc Certain TPCIs, such as the greases described herein, can be applied directly and need not be mixed into a com-position wlth a solvent and reslnous carrier.
The TPC's of this invention are compounds which are stable solids or greases at 50C, but which decompose at 60 to 200~C to produce detectable particles. With pre-sently-existing monitors particles must be larger than about 25A in order to be detected, but future monitors may be capable of detecting smaller particlesO The previously cross-referenced patents, de~cribe many suitable TPC's. Br~efly~ these com-pounds include diazonium salts, malonic acid and its deri-vatives, metal acetyl acetonates, blocked isocyanates, and certain greases. The following tables are lists of useful l~5,71~

1~)7916S

therrnoparticulating compounds from those previously cross referenced applications.
Thermoparticulating Metal Days Aged Temperature Range Acetylacetonate At 60C (c) Zn(C5H7020) o 2H2 110 95-100 Al(CsH702) 3 44 159-161 Fe( C5H702) 3 6 171-174 Mg(C5H702)2O2H2o 6 192-195 Mn(C5H702)3 1 132-133 Mn(C5H702) 2 1 182-185 Co ( C 5H7 2) 2 1 128- 131 Co ( C5H702) 3 1 150-152 Co ( C5H702) 2 ~ H20 1 165-168 Cr(C5H702) 3 1 179-183 Ni (C5H702)2~ 2H2 1 169-173 Agin~ Time at 120C (days) Grease 3 59 _ ~ 4 A mixture of about 20%
telomer of polytetrafluoro- 194-198C 191-198C 200-207c ethylene and about 80% per-fluoroalkyl polyether, sold by DuPont under the trademark "Krytox 24 0-AD"
The above table gives the thermoparticulation temperature after various periods of aging~

45, 718 Llterature Concentra- Additlonal Thermopartlcula-Temperature Support tlon in b lleat tlon Temperature Diazonlum Salt C) Materlal ~poxy (phr) Treatment (C) 3-chloro - 4-diethyl Dacron ~?elt 26.2a None None an~nobenzene diazc~ 113 lum chlorozlncate Copper 20.0 20 days ~ at 80C 190 p-diethylamlno- Dacron relt 4o.5a None None 0 benzene-dlazonium 117 chlorozlncate Copper 20 0 20 dayS 190 ~ at 0 C
p-diethylamino- Dacron felt 3o.8a None 120 benzene dlazonium lOB Copper 20.0 1 day at ~OvC 125 rluoroborate Copper 20.0 20 days at ~O"C 190

2, 5-dietho~- 3 d2ys at 80C
4-morphollnobenzene 120 Copper 20.0 (sample diazonium chlorozincate _ deca~osed) 4-diethylamlno-2-- 3 days at 80C
n~thylbenzene- diazon- 120 Copper 20.0 (sample Ium chlorozincate à~composed) 4-dlethylarnino -2-ethoxybenzene - dia- 140 Copper 20.0 24 days at 80C 180 zoni~n chlorozlncate 4-ethylamlno -3- 2 days at 80C
methylben ene - dia~ 125 Copper 20.0 (sample zonlwn chlorozlncate decomposed) ~amino-N-benzyl-N~ethylbenzene - dia- 160 Copper 20.0 24 daya at 80C 159 31) zonlum chlorostannate p-dlmethylamino- 2 days at BOC
benzene- diazonium 145 Copper 20.0 (sample chloroz1 ncate 7~77 decomposed) p-chlorobenzene- Dacron felt 63.5 None 110 diazonium penta- 150 fluorophosphate Copper 20.0 3 days at Booc _ decomposed) ~i probably due to decomposltlcn Or epoxy resin.
a This flE;ure is the wel~t % on the Dacron felt -no resin was used.
b "phr" includea solvent.

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45,718 1l)79165 ChemicalAging Thermoparticulating Compound FormulaCondition Temperature Range (C) Malonic Acid CH2(COOH)2 140 days at 60C 132 - 142 Methylmalonic Acid CH3CH(COOH)2 140 days at 60C 132 - 138 Dimethylmalonic Acid (CH3)2C(COOH)2180 days at 80C 152 - 158 Ethylmalonic Acid C2H5CH(COOH)2140 days at 60C 119 - 127 10 Diethylmalonic Acid (C2Hs)2(COOH)23 days at 80C 168 - 180 Di-n-Propylmalonic Acid (C3H7)2C(COOH)2 120 days at 80 C 155 - 160 Benzy~E~onic Acld C6H5CH2CH(COOH)2 50 days at 60C 143 - 151 Phenylmalonic Acid C~HsCH(C05H)2 1 day at 60c 150 - 157 The thermoparticulating temperatures given in the abo~Je tables are approximate and may vary depending on the resin used, aging time, and other factors In preparing the composition at least two TPC's are included which thermoparticulate at different tem-peraturesO More than four TPC's may be included, but lr this is done, resolution of the separate signals may be dif~icult~ Preferably, the temperatures at which the TPC's thermoparticulate should be separated by at least 25C to provide a clear resolution of the signals~
If two TPC's are included in the composition, the first preferably thermoparticulates at about 125 co about 175C (first stage) and the second at about 175C to about 200C (second stage)~ Preferably, how-ever, the composition contains three TPC's, the first preferably thermoparticulating at about 80 to about 125C (~irst stage), the second at about 125 to about 45,718 175C (second stage), and the third at about 175C to about 200C (third stage). If two stages are used, the first stage can serve as a warning that something may be wrong, and after the second signal is detected, the machine can be shut down or the load reducedO If three stages are used, the first can function as a warning, the second to reduce load or shut down, and the third for an automatic shutdown.
Whether to shut down or reduce load depends on a number of factorsO If the second signal is received within a few hours of the first, a runaway condition may be occurring which would make a shutdown advisableO
On the other hand, if the power is badly needed, a deci-sion may be made to accept the risk of damage to the machine while operating at a reduced loadO Also, after checki.ng it may be determined that the malfunction is correcta~le -- for example, it may be due to a reduced cool:ing gas pressure~ Analysis of the products of thermo-particulation may also aid in deçiding whether a shut-down or a reduced load is advisable since different areasof the machine can be coated with compositions contaln-ing different TPC's and the products of thermoparticula-ting may indicate whether the area being overheated is criticalO
Consecutive signals may, of course, be due tc two separate first stages from different parts of the machineO While analysis of the thermoparticulation pro-ducts would determine if this is occurring, a coinciden-tal occurrence of two first stages is not likely because overheating in these machines is fairly infrequentO

4~, 718 107916~

An alternative to mixing two or more TPCIs into a single composition is to apply two or more separate coatings to the machine one atop the other, each containing a TPCo In this case, the resin is preferably the same in each coating to avoid problems of adherence and compatabilityD A
thickness of about 1 to about 3 mils per layer is preferred~
Three layers having stages as described for the mixture would be preferred and more than four layers may make it difflcult to resolve the separate signalsO A layer con-taining a compound which thermoparticulates at a lowertemperature than a compound in an adjacent layer is pre-ferably on top of the ad~acent layer so that when the layer thermoparticulates, it does not cause the adjacent layer to flake off before the compound therein has thermoparticu--latedO Layers may contain more than one TPC. A mixture of TPC's is preferred to a layered structure because it is less expensive to apply it to the machineO The layered structure does offer an advantage over a mixture, however, in that a physical examination or chemical analys~s of the layers after thermoparticulation may indicate the maximum tempera-ture to which the area was exposed since the lower layers may not be as severely damaged This information is useful in determining the extent of damage to the inslllation in the generator.
The compositlon is applied to portions of the electrical apparatus which are exposed to the gas stream The coating formed does not function as insulation and is usually applied on top of insulation, but can also be applied to conductorsO The greases are usualiy applied to conductors. The application may be made by painting, 45,/18 1079~65 spray~nK, dipping, grease gun, or other techniquesO A
suitable coating thickness (after drying) is about 1/16 inch The particles of TPC should not be covered with excessive resinous carrier as that may prevent the decom-position particles from escaping into the gas stream.
After evaporation of the solvent and room temperature cure of the resinous carrier, if necessary, the apparatus ls ready to be operated.
The following examples further illustrate this invention.
~; EXAMPLE I - A MIXTURE
~ The following composition was prepared~
Parts by Weight Zinc acetyl acetonate 2 (Zn(C5H702)~2H2o) ~tmethyl malonic acid ( (C2H5)2(COOH)2) "Krytox 240-AD" grease 2 Epoxy resin (50% solids in toluene) 20 made from 200 pbw (parts by weight) linseed fatty acids, 200 pbw styrene and 300 pbw diglycidyl ether of Bisphenol A, sold by Westinghouse Electric Corporation as "B-276"
Varnish (See Example I of U.S~
Patent 2,909,497 for detailed description) 10 6% sollltion ln low-boiling hydrocarbons of cobalt naphthenate 0O15 30 24% solution in low-boiling hydro-carbons of lead naphthenate 0O38 r14~htf) e n ~ t~
The cobalt and lead ~a~he~at-e solutions were ,dded to the epoxy resin prior to the addition of t;he TPC's.

A sample was prepared by brush~ng the above composition onto a 3 inch by 1 inch aluminum sheet to a thickness of about 1/8 to about 1/4 inch. The sample was placed in an oven at 60 for 3 days to determine if it was stable and would functior. after aging.
The sample was placed in a stainless steel boat within a 1 inch stainless steel tube. Hydrogen was passed over the sample at a flow rate of 7 l/min.
A phase-controlled temperature regulator and programmer controlled the temperature in the boat. The temperature in the bot 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 monitored on a two-pen potentiostatic recorder.
A 5 C/min. heating rate was maintained in each experi-ment after the insertion of the sample in the boat.
The threshold temperature at which considerable particu-lation occurred ~as taken from the chart produced by the recorder. Ihe "alarm" temperature at which consi-derable particulation occurred corresponded to a 50%
decrease in the initial ion current of the detector (usually from 0.8 to 0.4 mA). The occurrence of particula-tion was detected using a Ger,erator Condition Monitor, sold by Environment One Corporation.
Three distinct signals were obtained, one at 92C (due to the zinc acetyl acetonate), one at 145 C
(due to the dimethyl malonic acid), and one at 200 C
(due to the fluorinated hydrocarbon grease).
EXAMPL ~ AAYERED STRUCTURE
The following composition was prepared using the procedure of Example 1:

45,718 Parts by Weight Dimethyl malonic acid 4 B-276 resin 5 6% solutlon ln low-bolling hydrocarbons of cobalt naphthenate 0.08 24% solutlon ln low-boillng hydrocarbons of lead naphthenate 0.019 An alumlnum foil was smeared wlth a layer about 2 mlls thlck of "Krytox 240-AD" grease and the above compositlon was applled to the grease to form a layer about 1/16 to about 1/8 lnches thick. The layer was dried for one hour at 60C to form a tack-free coating.
The followlng composition was prepared uslng the procedure of Example 1:
Parts by Welght Zinc acetyl acetonate B-276 resin 5 6% solution in low-boiling hy~rocarbons o~ cobalt naphthenate OoO8 20 24% solution in low-boillng hydrocarbons of lead naphthenate 0.019 The above composition was applied over the dimethyl malonic acid layer on the alumlnum foil to a thickness of about 1/16 to about 1/8 lnch~
The foil was aged for three days at 60C and tested as in Example lo Three distinct slgnals were detected, one at 83C from the zinc acetyl acetonate, one at 140C from the dimethyl malonic acid, and one at 185C from the grease.
The thermopartlculation temperatures ln this example were slightly lower than in Example 1 and the 45,718 1~)7gl6S

signals appeared to be slightly stronger, but the reason for these dlfferences has not as yet been ascertainedO
In both examples the coatings were dark brown and hea-v.lly pitted, and appeared to be more distinctly marked than coatings containing only one TPCo

Claims (21)

We claim:

1. A composition comprising at least two com-pounds which thermoparticulate at different temperatures at least 25°C apart between 60° and 200°C.

2. A composition according to Claim 1 which contains two compounds, one of which thermoparticulates between about 125 and about 175°C and the other of which thermoparticulates between about 175 and about 200°C.

3. A composition according to Claim 1 which contains three compounds, one of which thermoparticulates between about 80 and about 125°C, one of which thermo-particulates between about 125 and about 175°C, and one of which thermoparticulates between about 175 and about 200°C.

4. A composition according to Claim 1 which includes a solution of a resinous carrier curable and stable at 60°C and unreactive with any of said compounds which thermoparticulate.

5. A composition according to Claim 4 wherein the amount of said compounds totals about 20 to about 250 phr and the amount of solvent in said solution is about 25 to about 75% (by weight based on the resinous carrier).

6. A composition according to Claim 5 wherein the amount of said compounds totals about 40 to about 60 phr and the amount of said solvent is about 45 to about 55% (by weight based on said resinous carrier).

7. A composition according to Claim 4 wherein said resinous carrier is an epoxy resin.

8. A composition according to Claim 7 which includes about 0.1 to about 3 phr of a drier for said epoxy resin.

9. A composition according to Claim 8 which is prepared by first mixing said solution of resinous carrier and said drier and then mixing in said compounds which thermoparticulate.

10. A composition according to Claim 4 where the solvent in said solution is toluene.

11. A composition according to Claim 4 wherein said compounds which thermoparticulate are dispersed in said solution.

12. A composition according to Claim 4 wherein said resinous carrier is air-dryable.

13. A thermoparticulating coating comprising a solid layer which comprises at least two compounds which thermoparticulate at different temperatures at least 25°C
apart between 60° and 200°C.

14. A thermal detection system for electrical apparatus cooled by a gas stream, comprising a coating according to Claim 13 on a portion of said electrical apparatus exposed to said gas stream and a monitor for detecting the presence of particles in said gas stream.

15. A thermoparticulating coating comprising at least two solid layers one atop the other, each layer comprising at least one compound which thermoparticulates the thermoparticulating temperature of the compound in one layer differing on the thermoparticulating temperature of the compound in the other layer by at least 25°C and both temperatures lying between 60 and 200°C.

16. A thermoparticulating coating according to Claim 15 wherein each compound thermoparticulates at a lower temperature than does the compound in the layer below it.

17. A thermal detection system for electrical apparatus cooled by a gas stream, comprising a coating according to Claim 15 on a portion of said electrical apparatus exposed to said gas stream and a monitor for detecting the presence of particles in said gas stream.

18. A method of determining the rate of temperature rise in an electrical apparatus which includes a cooling gas stream and a monitor for detecting particles in said gas stream and for emitting a signal when said particles are detected comprising:
(A) applying at least one composition according to Claim 1 to said electrical apparatus at positions exposed to said gas stream;
(B) monitoring said gas stream for the presence of particles therein; and (C) timing the interval between successive signals emitted by said monitor.

19. A method according to Claim 18 including the additional last step of inspecting said apparatus visually for blistered and darkened areas, after a signal has been emitted, to locate the area of overheating.

20. A method according to Claim 18 including the additional last steps of collecting a sample of said gas stream after a signal has been emitted, and chemically analyzing said sample.

21. A method according to Claim 18 including the additional last step of measuring the interval of time between signals emitted from said monitor.