JPS5936367B2 - Electrical devices containing dielectric fluids - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical devices containing dielectric fluids that are readily biodegradable.

More particularly, this invention relates to certain chlorinated aromatic compounds that have excellent fire resistance and biodegradability and are particularly useful as dielectric fluids or impregnants in electrical capacitors and transformers. Modern dielectric currents must have a unique combination of electrical and physical properties while minimizing adverse effects on the surrounding environment.

Fire resistance is a highly desirable property to avoid collateral damage should a failure of an electrical device cause electrical sparks or overheating. Chlorinated aromatic compounds have long been well known and preferred as dielectric fluids for electrical devices.

The most familiar soft fluid of this kind is “Askarel” (Askarel).
karels). Askarel dielectric fluids are fire resistant, have a relatively high dielectric constant, and are by far the most widely accepted fluids today for use in electrical capacitors and transformers. Askarel fluids consist primarily of polychlorinated biphenyl, often mixed with chlorobenzene to impart specific viscosity properties. However, certain polychlorinated biphenyls are resistant to natural degradation, and if released into the surrounding environment, these materials enter the life cycle and can be ecologically harmful.

Even though capacitors and transformers are typically sealed units and leakage of dielectric fluid (or impregnating agent) into the surrounding environment can be largely prevented, they still contain major components that are persistent in the surrounding environment. It has become desirable to provide alternative fluids that do not require Halogenated aromatic compounds other than polychlorinated biphenyl have previously been disclosed as dielectric fluids for electrical devices.

U.S. Pat. No. 2,617,770 discloses halogenated compounds of naphthalene, toluene, benzene, nitrodiphenyl, diphenyl oxide, diphenyl ketone, diphenylmethane, diphenylethane, terphenyl and quarterphenyl. Similarly, US Pat. No. 2,410,714 discloses chlorinated benzenes, chlorinated diphenyl oxides, chlorinated diphenylmethanes, chlorinated diphenylbenzenes and their alkyl derivatives. Despite the disclosures of the prior patents mentioned above, commercial acceptance of halogenated aromatic compounds as dielectric fluids has been limited to polychlorinated biphenyls for several years. Other known halogenated aromatic compounds with possible utility as dielectric currents have no commercial significance for one or more technical or economic reasons. Efforts published in recent years to provide alternative dielectric fluids for capacitors and transformers have therefore largely moved away from halogenated aromatic compounds, which have been modified by certain polychlorinated biphenyls. This is because of its persistence in the surrounding environment. It is an object of the present invention to provide an electrical device containing a dielectric fluid that is easily biodegradable.

Yet another object of the present invention is to provide improved electrical capacitors and transformers containing dielectric fluids that are fire resistant and readily biodegradable.
Yet another object of the present invention is to provide a fire resistant, yet easily biodegradable dielectric fluid having excellent viscosity properties for use in capacitors and transformers. Other objects of the invention will become apparent from the description below. It has now been found that certain halogenated diphenylmethanes are excellent dielectrics for electrical equipment because they combine the necessary electrical and physical properties with excellent biological resolution and fire resistance.

The dielectric fluid of the present invention has a structural formula (in the formula, each X is chlorine,
Bromine or fluorine, n is an integer from 1 to 4,
each R is an alkyl group having 1 to 5 carbon atoms, and m is o or an integer from 1 to 3)
It consists of at least one kind of halogenated diphenylmethane compound represented by.

Surprisingly, it has been found that only those halogenated diphenylmethanes having one unsubstituted phenyl group can be readily biodegraded.

Diphenylmethane in which both phenyl groups are substituted with halogen, or diphenylmethane in which one phenyl is substituted with halogen and the other phenyl is substituted with alkyl, has been found to be resistant to decomposition by microorganisms. This result was unexpected and the reason has not yet been fully elucidated. The halogenated diphenylmethanes described herein, ie those having one unsubstituted phenyl ring, are particularly useful as capacitor impregnants and as dielectric fluids for transformers. It has been found desirable to use certain additives in such applications, such as stabilizers, such as epoxide stabilizers. This fluid is also useful in power transmission cables, rectifiers, electromagnets, circuit breakers, etc. Electrical capacitors containing the halogenated diphenylmethane of this invention are constructed and impregnated by standard procedures.

Such capacitors are characterized by low dissipation factors, high dielectric constants, good low temperature performance, fire resistance and good biological resolution of the impregnating agent itself. The halogenated diphenylmethane of the present invention is characterized in that only one aromatic ring is substituted with halogen.

Alkyl substitution in the molecule is also permissible, but must be in the same ring on which the halogen substitution is made. The other phenyl rings must be unsubstituted. Although not to be construed as limiting, examples of compounds with desired biological degradability with fire resistance and good electrical and physical properties include o-chlorodiphenylmethane, p-chlordiphenylmethane, 3 , 4-dichlorodiphenylmethane,
2,4-dichlorodiphenylmethane, a mixture of the 2,4- and 3,4 monoisomers of dichlorophenylmethane, and the 2,4,5- and 2- and 2-isomers of trichlorodiphenylmethane.
, 4,6-isomer. Chlorine is the preferred halogen because of its lower cost compared to bromine and fluorine. Tetrahalogenated diphenylmethanes having all halogens in one aromatic ring are also within the scope of this invention. Up to three identical or different alkyl groups having 1 to 5 carbon atoms may be present in the halogenated ring. Examples of alkyl-substituted halogenated diphenylmethanes are o-chlorotolylphenylmethane and p-chlorotolylphenylmethane. A capacitor device employing the present invention has the general structure and arrangement shown in FIG. This is a capacitor 10 that has been designed.

The terminal connectors 15 and 16 are connected to electrode foils 11 and 12.
and has an enlarged surface (not shown) in contact with. Electrode foils 11 and 12 are generally metallic and comprised of one or more of a number of different materials including, for example, aluminum, copper and stainless steel. Dielectric spacer 1
3 and 14 generally consist of paper and/or polymeric film. Therefore, the dielectric spacer 13 and the metallic electrode foils 1.1 and 12 together constitute a capacitor element structure. The dielectric spacer material and the apertures within and between the material and the electrode foil are impregnated with a dielectric fluid.
Continuing with reference to FIG. 1 of the accompanying drawings, dielectric spacers 13 and 14 may be made of a solid, flexible, porous material such as highly refined cellulose paper, or a substantially non-porous material such as polyolefin. It may be comprised of a composite film material or a combination of paper and polymeric materials.

In a preferred embodiment, the paper material has an individual sheet thickness of no greater than about 1.0 mil and preferably about 0.3 mil to accommodate the intended voltage of the capacitor. Two or more sheets of kraft capacitor paper having a suitable total combined thickness are preferred. Such paper has a relatively good dielectric strength and a relatively high dielectric constant compared to other dielectrics. The polymeric material is preferably a biaxially oriented polypropylene film, but other polyolefin films, particularly polyethylene and 4-methylbenzene-1, are also frequently used in capacitors. Other useful polymeric materials include polyester,
Included are polycarbonate, polyvinylidene fluoride and polysulfone. Either paper or polymeric film may be used alone, but combinations of both are often used. The paper is positioned adjacent to the polymeric membrane and has an impregnating agent for passing a dielectric liquid impregnating agent into an area that coexists with the area of contact between the porous paper and the substantially non-porous polymeric material. It acts as. Referring to FIG. 2, an assembled capacitor unit 18 is shown containing a spirally wound capacitor of the type shown in FIG.

The assembled unit includes a container 19, a sealed cover 20 containing a small dielectric fluid filling hole 21, and a pair of terminals 22 and 23 projecting from the cover 20 and insulated therefrom. Terminal 22 and',2
3 is connected in container 19 to terminal connectors 15 and 16 shown in FIG. Although not shown, the unit 18 shown in FIG. 2 further includes a dielectric fluid composition, which fills the remaining space in the container 19 not occupied by the capacitor elements. occupying and also impregnating dielectric spacers 13 and 14. Impregnation of the capacitor is carried out by conventional operations.

For example, in one common impregnation method, a capacitor unit enclosed in an assembly, such as capacitor 18 of FIG. 2, is vacuum dried to remove any remaining moisture. The drying temperature varies depending on the length of the drying cycle, but is usually about 60-150°C. If the temperature is too low, the drying period will be too long, while if the temperature is too high, it will cause the polymeric film used as the dielectric spacer to crack or decompose. The holes 21 allow moisture and gases to escape from the interior of the container 19 during the drying process. The impregnating dielectric liquid is preferably introduced into the capacitor assembly through hole 21 while the dried capacitor assembly is surrounded and under a suitable vacuum.

The capacitor element in the container must be immersed in the impregnating liquid, and usually enough impregnating liquid is introduced to completely fill the container and displace all the air therein. The pressure of the envelope is increased to atmospheric pressure and the assembly is allowed to stand or soak for a number of hours to ensure complete penetration of the liquid impregnation agent. After impregnation, the capacitor unit is sealed by applying a suitable solder to the holes 21 or by using other sealing means. The capacitor assembly is then heated to increase the pressure within the capacitor assembly and aid the impregnation process. Heat and pressure will increase the impregnating capacity by changing the relative wettability, viscosity and solubility of the materials. In addition, the stretching and contraction of the individual components in the system as a result of heat and pressure acts as a driving force that induces liquid to move into the interstices of the dielectric spacer material. In addition to the presence of one or more halogenated diphenylmethane compounds, the dielectric fluids of the present invention may contain a number of other components in minor amounts.

In particular, it is often desirable to include stiffening components that act as stabilizers in impregnated dielectric systems. The stabilizer is present to neutralize certain ionizable contaminants or external substances that are present or formed in the system. Such contaminants include residual catalyst or catalyst activators remaining from the resin forming reaction. Contaminants can also include decomposition products caused by chemical reactions in the system that are induced by the ambient environment or by voltage. In some cases, the stabilizer may act as a scavenger for hydrogen chloride generated from the dielectric liquid, for example as a result of arc conditions during operation. These undesirable contaminants and extraneous products adversely affect the dissipation factor or power factor of the impregnated dielectric system, and the stabilizer reduces the low power factor in the impregnated dielectric system. It has been found to be highly effective in maintaining

The particular stabilizer depends in part on whether the electrical device, such as a capacitor, is used with alternating current (AC) or direct current (DC).

Anthraquinones give significantly better results for direct current applications. Particularly preferred stabilizers for AC applications are epoxides which are generally characterized by groups, examples of which include grindyl ether and derivatives of ethylene oxide. Other examples include 1-epoxyethyl-3,4-epoxy-cyclohexane, 3,4-epoxycyclohexylmethyl-
3,4-Eboxycyclohexanecarboxylate, 3,
4-epoxy-6-methylcyclohexylmethyl-3,
Examples include 4-epoxy-6-methylcyclohexanecarboxylate. These stabilizers are preferably used in the dielectric fluid compositions of the present invention in amounts generally ranging from 0.001 to about 8% by weight, and more preferably from about 0.1 to 3.0% by weight. The following examples illustrate the excellence of electrical devices containing dielectric currents of the present invention.

All parts and percentages herein are by weight unless otherwise specified. EXAMPLE 1 A number of electrical capacitors of the type shown in FIGS. 1 and 2 of the accompanying drawings were constructed of aluminum foil and paper separators and 3,4-dichlorodiphenylmethane 99
．． 7% and 3,4-poxycyclohexylmethyl
3,4-Epoxycyclohexanecarboxylate 0.
Impregnation as described above with a dielectric fluid composition consisting of 3%.

A group of eight of these capacitors, designated as "test capacitors", are subjected to service and life testing in a laboratory environment. The results of these tests are referred to as "control capacitors"
Compare the results obtained with a similar group of the same capacitors impregnated in a similar manner with electrical grade polychlorinated biphenyl containing about 42% chlorine, shown as . The impregnant for the control capacitor contains 0.3% 3,4-epoxycyclohexane carboxylate. The results of the test are presented in Table 1 below. The data in Table I demonstrate the superior electrical properties and reliability of capacitors impregnated with the dielectric fluid compositions of the present invention compared to similar capacitors of the prior art.

In particular, the test capacitors were
Table I shows that there were no failures when subjected to extreme test conditions of 0 volts. On the other hand, although the control capacitor survived to the final test conditions, it suffered an 87% failure at these conditions. That is, 7 out of 8 capacitors in the control group fail while all test capacitors are still operational. The halogenated diphenylmethanes of the present invention, ie, those having halogen substitution (and alkyl substitution if desired) on only one phenyl ring, are useful as dielectric currents in electrical transformers for cooling and insulation purposes.

These compounds are advantageous over mineral oil dielectrics because of their fire resistance. Furthermore, the advantages of good biological degradability and outstanding viscosity properties make these halogenated diphenylmethanes attractive for application in transformers. A representative electrical transformer in which the present invention is embodied is described in US Pat. No. 3,362,908.

Conveniently, an epoxyde stabilizer is used in the transformer together with the halogenated diphenylmethane. Although halogenated diphenylmethanes have been disclosed in the literature as dielectric or insulating fluids for electrical devices, little evidence of their industrial use is found. Polychlorinated biphenyl has for many years played the leading role among halogenated aromatic compounds with fire resistance and excellent electrical properties. Therefore, there was no understanding in the art as to the industrial potential of halogenated diphenylmethane. This is because these have been completely neglected due to the widespread acceptance of polychlorinated biphenyls. Upon discovery of biological degradation problems associated with certain polychlorinated biphenyls, those skilled in the dielectric fluid art immediately sought alternative fluids other than those in the halogenated aromatic compound family. Despite this pessimism, it is surprising that halogenated diphenylmethanes are excellent for use in electrical devices, depending on whether halogen substitution (and alkyl substitution, if desired) occurs on one or both phenyl rings. It was discovered that it can be a dielectric current. This discovery was completely unexpected and could not have been predicted from the prior art. for example,
While a mixture of 2,4- and 3,4-dichlorodiphenylmethane is highly biodegradable, the other 2,4'-
It could never have been foreseen that a mixture of and 4,4'-dichlorodiphenylmethane would be so resistant to biological degradation. Biodegradability has been established as an important factor in determining the persistence of organic compounds or mixtures thereof in the surrounding environment. Biodegradability is the susceptibility of a compound to degradation by a mixed population of bacteria in the presence of natural energy sources, such as wastewater. To illustrate the dramatic difference in biodegradability between mono- and double-ring substitutions of halogenated diphenylmethane compounds, biodegradability tests were conducted on a series of such compounds.

Biological degradation tests are conducted by the Soap and Cleaning Products Association (
SOapandDeter-NtAssOciatiO
n) Test method for surfactants presented by the Subcommittee on Biological Degradation Test Methods [J. Amer. OilChemis
tsSOc. 42, p. 986 (1965)] using a semi-continuous activated sludge test. In the semi-continuous activated sludge test, biological degradation capacity is measured using activated sludge from a wastewater treatment plant as the microbial source.

A predetermined level of test compound and synthetic sewage as an energy source are fed on a periodic basis to the activated sludge contained in the stirred vent chamber. Aeration of the mixed liquor (activated sludge and liquid) is carried out for "n-1" hours of an "n" hour cycle. Commonly used cycle times are 24, 48 or 72 hours. Representative samples of the mixture are taken immediately after feeding and near the end of the aeration period to determine the rate of disappearance of the test compound during the cycle. This cycle is repeated for as long as necessary to obtain consistent data on the rate of biological degradation. Semi-continuous activated sludge testing mimics secondary sewage treatment capacity. Example 2 below details biological resolution studies conducted on halogenated diphenylmethanes having monocyclic and bicyclic substitutions, respectively. Example 2 Activated sludge obtained from a typical treatment plant of the Metropolitan Sewerage District, St. Louis, Missouri, USA, is used in this example.

The mixed liquor obtained from the sewage treatment plant is passed through a 20 mesh stainless steel sieve to remove extraneous particulate matter. After adjusting the suspended solids content to 2500 m9/l with tap water, 1500 g of the mixed solution was filled into the ventilation chamber. The vent chamber was then connected to a source of compressed air and the mixture was pumped at a flow rate of 0.1 cubic feet per hour (ScFH) (
Aerate at a rate of 0.002877 z''/hr). Stirring of the mixture is also carried out using a magnetic stirrer during aeration. Compound to be tested in the form of either anhydrous ethanolic or aqueous solution and sludge microbial energy. The synthetic sewage used as a source is fed into the ventilation chamber at the beginning of each cycle.For substances with significant dissipation rates, a 24-hour cycle is used with a 72-hour cycle on weekends. A basic 48 hour cycle is used for the material. At the end of the aeration period or cycle, the sludge is allowed to settle and the clear soil liquid 11 is removed. The unit is re-fed and the mixed volume is replaced with tap water. 1
Adjust to 500 go and repeat the ventilation cycle again. A sample of the mixed liquid (e.g. 20ml) is divided into multiple 25ml samples.
! Samples are taken after one hour of feeding and at the end of the ventilation cycle through a side arm control valve with a graduated cylinder and analyzed for the two compounds or compounds of interest. The initial feed rate of chlorinated diphenylmethane is 1 mf7 per 24 hour cycle. Increased the rate to 3mf7 in the second week and 5W in the third week! Increases to F7. This level is then increased to 5 mf until constant loss rate data is obtained.
Keep it on i7. For those chlorinated diphenylmethanes that decompose rapidly at the 5mf7 level, the feed rate should then be reduced to 2.
Increase it to 0W9 and get more data.

As used herein, the term "disappearance rate" is synonymous with biodegradation rate or biodegradability.

The sample collection and analysis procedures used to measure biological degradation rates are as follows. Fifty samples of the mixture are taken after dispensing and at the end of the aeration cycle. The amount of chlorinated diphenylmethane in the concentrated extract is determined using fire-ionization gas chromatography. From the analytical data, the percentage of biological degradation is calculated using the following equation: (where CO = immediate number of test substances in the unit at the start of the aeration cycle after feeding the test substance; Cn = ~ number of test substances in the unit at the end of the aeration cycle) 15 halogenated diphenylmethanes of Example 2 Biological degradation data for the compounds are shown in the table below.

It can be observed that these halogenated diphenylmethanes with one unsubstituted phenyl ring, compounds A61-8, are highly biodegradable.

In contrast, compounds 9-15 with halogen or alkyl substitution on both rings resist biological degradation.
Surprisingly, it does not appear to be the mere presence of the halogen in the second phenyl group that prevents biological degradation.

Alkyl groups alone can cause the same effect. respectively, o-
See compounds considerations 14 and 15, which are chlorobenzylethylbenzene and p-chlorobenzylethylbenzene. The presence of the ethyl group in the second ring inhibits biological decomposition compared to, for example, compounds No. 7 and /I68, in which halogen and alkyl are present in one ring and the second ring is unsubstituted. It has further been discovered in the present invention that good biodegradability is not necessarily associated with unsubstituted phenyl rings in diaryl compounds.

For example, pentachlordiphenyl sulfide (compound 17), in which both phenyl rings are substituted with chlorine, was found to resist biological degradation, but this alone is not surprising. However, another diphenyl sulfide, 2,4,5-trichlorodiphenyl sulfide (compound 18), which has only a single ring substitution, was found to be equally resistant to biological degradation as compound 71617. Ivy. It has further been discovered that halogen substitution of a phenyl group in a monoaryl compound does not automatically render the group highly resistant to biological degradation.

For example, two different dichlorobenzene compounds, here compounds 21 and 22, respectively, exhibit excellent biodegradability. Example 3 To illustrate the unpredictability of biological degradation rates in various aromatic structures with 1-3 aromatic rings and different configurations of substitution, seven species other than halogenated diphenylmethane were prepared. The compound is tested according to the procedure of Example 2.

These compounds are compounds 16-22 and their biological degradation results are shown in the table below. The excellent electrical and biological decomposition properties of the monocyclic substituted halogenated diphenylmethanes of the present invention are evident from Tables 1 and 1, respectively.

Claims (1)

[Claims] 1 Structural formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, each X is chlorine, bromine, or fluorine, n is an integer from 1 to 4, and each R is 1 is an alkyl group having ~5 carbon atoms, and m is 0 or an integer from 1 to 3). An electrical device containing an improved dielectric current. 2. The electrical device of paragraph 1, wherein each X is chlorine and m is 0. 3. The electrical device of paragraph 1, wherein the dielectric fluid further contains about 0.001 to 8% by weight of a stabilizer. 4. The electrical device of paragraph 3 above, wherein the stabilizer is an epoxide. 5. The electrical device according to item 1 above, which is a transformer. 6. The transformer according to item 5 above, wherein the halogenated diphenylmethane compound is 3,4-dichlorodiphenylmethane. 7 The halogenated diphenylmethane compound is 2,4,5-
The transformer of item 5 above, which is trichlordiphenylmethane. 8 The halogenated diphenylmethane compound is 2,5,6-
The transformer of item 5 above, which is trichlordiphenylmethane. 9. The electrical device according to item 1 above, which is a capacitor.