CA1145926A - Elastomeric composition for providing electrical stress control - Google Patents
Elastomeric composition for providing electrical stress controlInfo
- Publication number
- CA1145926A CA1145926A CA000372227A CA372227A CA1145926A CA 1145926 A CA1145926 A CA 1145926A CA 000372227 A CA000372227 A CA 000372227A CA 372227 A CA372227 A CA 372227A CA 1145926 A CA1145926 A CA 1145926A
- Authority
- CA
- Canada
- Prior art keywords
- composition
- base material
- effect
- dielectric constant
- finely divided
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G15/00—Cable fittings
- H02G15/08—Cable junctions
- H02G15/10—Cable junctions protected by boxes, e.g. by distribution, connection or junction boxes
- H02G15/103—Cable junctions protected by boxes, e.g. by distribution, connection or junction boxes with devices for relieving electrical stress
- H02G15/105—Cable junctions protected by boxes, e.g. by distribution, connection or junction boxes with devices for relieving electrical stress connected to the cable shield only
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/22—Conductive material dispersed in non-conductive organic material the conductive material comprising metals or alloys
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B1/00—Conductors or conductive bodies characterised by the conductive materials; Selection of materials as conductors
- H01B1/20—Conductive material dispersed in non-conductive organic material
- H01B1/24—Conductive material dispersed in non-conductive organic material the conductive material comprising carbon-silicon compounds, carbon or silicon
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02G—INSTALLATION OF ELECTRIC CABLES OR LINES, OR OF COMBINED OPTICAL AND ELECTRIC CABLES OR LINES
- H02G15/00—Cable fittings
- H02G15/02—Cable terminations
- H02G15/06—Cable terminating boxes, frames or other structures
- H02G15/064—Cable terminating boxes, frames or other structures with devices for relieving electrical stress
- H02G15/068—Cable terminating boxes, frames or other structures with devices for relieving electrical stress connected to the cable shield only
Landscapes
- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Dispersion Chemistry (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Compositions Of Macromolecular Compounds (AREA)
Abstract
ELASTOMERIC COMPOSITION FOR PROVIDING
ELECTRICAL STRESS CONTROL
Abstract A permanently elastic dielectric composition com-prising a resilient dielectric base material, an electrically polarizable component having low electrical conductivity to increase the relative dielectric constant of the composition, and a component displaying metal conductivity for maintenance of the relative dielectric constant at high power frequencies.
ELECTRICAL STRESS CONTROL
Abstract A permanently elastic dielectric composition com-prising a resilient dielectric base material, an electrically polarizable component having low electrical conductivity to increase the relative dielectric constant of the composition, and a component displaying metal conductivity for maintenance of the relative dielectric constant at high power frequencies.
Description
z~
Description ELASTOMERIC COMPOSITION FOR PROVIDING
ELECTR CAL STRESS CONTROL
Technical Field The invention relates to a dielectric material of permanent resilience, for influencing electrical fields in power current and high voltage systems, the material ccntaining a dielectric base material having permanent resilience, pre~erably silicone rubber or polyethylene or EPDM, with a content:of a finely distributed effect ~ material increasing the relative dielectric constant : ~ (permittivity).
Background Art A description of the general prior art with respect 15 to stress control can be found, for example, in the :
~ German Offenlegungsschrift 28 21 017.
:~ Mater-lals of the general kind indicated above are known, for example, from U.S. Patent No. 4,053,702. They : contain titanium dioxide as the effect material. That known substance makes possible, inter alia, the manufac-~: ture of permanently resilient stress control elements ~ of definite ~eometric configuration, which may be simply : ~ shifted on, while yielding resiliently, at the site of - application, typically a cable connection. Due to thelr resllience, they then fit in a gap free manner That strong and gap-free fitting is retaired, due t~o the per-manently resilient properties, over very long time : periods, for instance many years, and particularly over ~: ~ the usual operational li~e of power~current systems. ;:~
30 The application~of such permanently resilient stress ~:~
control elements requ~res less knowledge and skill than ~:
: the application of other stress control devices, such asg : for example, metallic stress control cones, the gap-fre0 wrapping of tapes Or stress-controlllng material, the : 35 molding or modelling and subsequent hardening of flowable ?
~. ' ,, 3'~
Description ELASTOMERIC COMPOSITION FOR PROVIDING
ELECTR CAL STRESS CONTROL
Technical Field The invention relates to a dielectric material of permanent resilience, for influencing electrical fields in power current and high voltage systems, the material ccntaining a dielectric base material having permanent resilience, pre~erably silicone rubber or polyethylene or EPDM, with a content:of a finely distributed effect ~ material increasing the relative dielectric constant : ~ (permittivity).
Background Art A description of the general prior art with respect 15 to stress control can be found, for example, in the :
~ German Offenlegungsschrift 28 21 017.
:~ Mater-lals of the general kind indicated above are known, for example, from U.S. Patent No. 4,053,702. They : contain titanium dioxide as the effect material. That known substance makes possible, inter alia, the manufac-~: ture of permanently resilient stress control elements ~ of definite ~eometric configuration, which may be simply : ~ shifted on, while yielding resiliently, at the site of - application, typically a cable connection. Due to thelr resllience, they then fit in a gap free manner That strong and gap-free fitting is retaired, due t~o the per-manently resilient properties, over very long time : periods, for instance many years, and particularly over ~: ~ the usual operational li~e of power~current systems. ;:~
30 The application~of such permanently resilient stress ~:~
control elements requ~res less knowledge and skill than ~:
: the application of other stress control devices, such asg : for example, metallic stress control cones, the gap-fre0 wrapping of tapes Or stress-controlllng material, the : 35 molding or modelling and subsequent hardening of flowable ?
~. ' ,, 3'~
- 2 -or shapeable masses having stress-controlling propertles at the site o~ operation, etc.
Materials of the kind described inltially therefore have made possible a considerable advance in the field of stress control ln power current and high voltage systems.
The materials described inltially act, together with cable insulating materials of low dielectric constant, upon electric fields in the sense of a refraction. For the sake of completeness, it should be mentioned that for the manufacture o~ stress-controlling devices, other materials are known which mainly act-in a resistive manner; they contain electrically conductive or semi-conductive effect materials which provide to the material a desired (mostly voltage-dependent) electrical conduc-tivity (U.S. Patent Nos. 3,673,305; 3,666,876). In these cases, permittivity is also increased by the embedding of particles of electrically conductive or semi-conductive e~ect material; for example, it may be up to 11 (U.S.
Patent No. 3,666,876). With resilient materials having resistive stress control properties, however, the active current, which due to the function flows continuously, rnay gra~ually ~ive rise to changes of electrical conduc-tivity, and to a premature agein~ of the materlal. Thus, other modes of operation are preferred for permanently resilient materials, particularly the refractive mode of operation which also applied to the material of the present invention.
It will be appreclated that a relatively hlgh per-mittivity o~ the material i8 desirable. Thus, lt is desired to use substances having a permittivity as high as possible as the e~fect material for materials showing ; refractive stress control action, e.g. the titanium dioxide already mentioned, but also other known substances o~very high permittivity, e.g. barium titanate. The use of such materials as an effect material for materials having a refractive stress-controlling action has been known for a long time, but without paying part~cular attention to the requirement Or permanent resilience (U.S. Patent Nos 3,673,305; 3,823,334; 3,287,489). In .. . . .
: :
this connection, however, it was found also that when utilizing effect materials o~ very high permittlvity, e.g.
barium titanate having permittivities of appro~imately lO,000, the permittivity of the material cannot be increased beyond approximately 25 if the material is to retain the permanently resillent propertles of the base material. The reason for this therefore is that in mixtures of that kind, the permittivity ~r mix f the mixture has to be calculated according to a logarithmic, and not according to an additive~ mixture formula from the permittivities ~rn f the components of the mixture:
log ~r mix = ~Xn log ~rn in which Xn is the volume ratio, and ~rn is the relative dielectric constant (permittivity) of the component ~L.
Accordingly, that formula shows particularly that with a material consisting of two components, namely, Component l: Elastomeric base material havlng an ~r f about 3, Component 2: Barium titanate having an ~r of about lO,000, one would have to employ a proportion of abouk 35 volume percent or about 75 weight per cent barium titanate to obtain a permittivity of the mixture of about 50. Wi.th the proportion o~ er~ect rnaterial bein~ so high, the resilient properties, however, of the material are insufficient to permit the manufacturing there~rom of practicable gap-free fitting stress control elements having permanent resilience. The resilience itself, as well as the maintenance in time of an elastic tension once produced in the material (the so-called permanent resetting force), are insufficient. It was generally true for the prior art (e.g., U.S. Patent No. 4,053~702) that permanently re~ilient materials of the kind initially described could bc manufactured with permittivities of .~
. -.
. ~ .
..
only up to about 25, even when employing the kno~n e~fectmaterials having ve~y high permittivitie~. The permanent reslliency of dielectric materials can only be observed and malntained for the technical practice of testing results achleved i~ th~ residual stress (permanent set) under constant deflection according to the specification DIN 53517 (ISO-STANDARD R 815-69), particularly after accelerated ageing for 72 hours at 150C are always less than about 35~ and results Or SHORE-A Hardness according to the spec~fication DIN 53505 (ISO~STANDARD R 868-68) are less than 65. If these requirements characterizing permanent resiliency cannot be met it cannot be warranted that such materials can be used to produce elastic stress control elements. All described materials known until now, which have a permittivity above 25 do not pass this important criteria of permanent resiliency.
Disclosure of Invention The present invention provides a dielectric, perman-ently resilient material which is suitable for a highly effective refractive stress control.
According to the invention, there is provided a material o~ the kind initially described, wherein the effect material comprises strongly structurized dust-fine particles of an electrically polarizable material, such as carbon black, in a concentration at which in the range Or usual power frequencies, e.g. 50 cycles per second, the following properties of the material are present in combination:
a) The volume reslstivity has at least a
Materials of the kind described inltially therefore have made possible a considerable advance in the field of stress control ln power current and high voltage systems.
The materials described inltially act, together with cable insulating materials of low dielectric constant, upon electric fields in the sense of a refraction. For the sake of completeness, it should be mentioned that for the manufacture o~ stress-controlling devices, other materials are known which mainly act-in a resistive manner; they contain electrically conductive or semi-conductive effect materials which provide to the material a desired (mostly voltage-dependent) electrical conduc-tivity (U.S. Patent Nos. 3,673,305; 3,666,876). In these cases, permittivity is also increased by the embedding of particles of electrically conductive or semi-conductive e~ect material; for example, it may be up to 11 (U.S.
Patent No. 3,666,876). With resilient materials having resistive stress control properties, however, the active current, which due to the function flows continuously, rnay gra~ually ~ive rise to changes of electrical conduc-tivity, and to a premature agein~ of the materlal. Thus, other modes of operation are preferred for permanently resilient materials, particularly the refractive mode of operation which also applied to the material of the present invention.
It will be appreclated that a relatively hlgh per-mittivity o~ the material i8 desirable. Thus, lt is desired to use substances having a permittivity as high as possible as the e~fect material for materials showing ; refractive stress control action, e.g. the titanium dioxide already mentioned, but also other known substances o~very high permittivity, e.g. barium titanate. The use of such materials as an effect material for materials having a refractive stress-controlling action has been known for a long time, but without paying part~cular attention to the requirement Or permanent resilience (U.S. Patent Nos 3,673,305; 3,823,334; 3,287,489). In .. . . .
: :
this connection, however, it was found also that when utilizing effect materials o~ very high permittlvity, e.g.
barium titanate having permittivities of appro~imately lO,000, the permittivity of the material cannot be increased beyond approximately 25 if the material is to retain the permanently resillent propertles of the base material. The reason for this therefore is that in mixtures of that kind, the permittivity ~r mix f the mixture has to be calculated according to a logarithmic, and not according to an additive~ mixture formula from the permittivities ~rn f the components of the mixture:
log ~r mix = ~Xn log ~rn in which Xn is the volume ratio, and ~rn is the relative dielectric constant (permittivity) of the component ~L.
Accordingly, that formula shows particularly that with a material consisting of two components, namely, Component l: Elastomeric base material havlng an ~r f about 3, Component 2: Barium titanate having an ~r of about lO,000, one would have to employ a proportion of abouk 35 volume percent or about 75 weight per cent barium titanate to obtain a permittivity of the mixture of about 50. Wi.th the proportion o~ er~ect rnaterial bein~ so high, the resilient properties, however, of the material are insufficient to permit the manufacturing there~rom of practicable gap-free fitting stress control elements having permanent resilience. The resilience itself, as well as the maintenance in time of an elastic tension once produced in the material (the so-called permanent resetting force), are insufficient. It was generally true for the prior art (e.g., U.S. Patent No. 4,053~702) that permanently re~ilient materials of the kind initially described could bc manufactured with permittivities of .~
. -.
. ~ .
..
only up to about 25, even when employing the kno~n e~fectmaterials having ve~y high permittivitie~. The permanent reslliency of dielectric materials can only be observed and malntained for the technical practice of testing results achleved i~ th~ residual stress (permanent set) under constant deflection according to the specification DIN 53517 (ISO-STANDARD R 815-69), particularly after accelerated ageing for 72 hours at 150C are always less than about 35~ and results Or SHORE-A Hardness according to the spec~fication DIN 53505 (ISO~STANDARD R 868-68) are less than 65. If these requirements characterizing permanent resiliency cannot be met it cannot be warranted that such materials can be used to produce elastic stress control elements. All described materials known until now, which have a permittivity above 25 do not pass this important criteria of permanent resiliency.
Disclosure of Invention The present invention provides a dielectric, perman-ently resilient material which is suitable for a highly effective refractive stress control.
According to the invention, there is provided a material o~ the kind initially described, wherein the effect material comprises strongly structurized dust-fine particles of an electrically polarizable material, such as carbon black, in a concentration at which in the range Or usual power frequencies, e.g. 50 cycles per second, the following properties of the material are present in combination:
a) The volume reslstivity has at least a
3 minimum value which i8 still sufficient rOr purposes of electrical insulation~
b) The relative dielectric constant (permittivity) ~s greater than 30, and up to about 300, and c) The dielectric loss factor is not greater than approximately 1.5 and further comprises a supplemental effect material in the form of finely divided particles possessing metal .
.
.
conductivity to improve the electric stre~s d-issipation and consequently the dielectric strengths at high f~equen-cies as they are typical for impulse waves 5 and to hold the permittivity at high ~requencies (e.g. 105 Hz) to at 5 least about 20.
Detailed Description The composition accordlng to the invention utilizes the fact that ~ith effect materials like carbon black, which comprise strongly structurized or cleft dust-fine lO polarizable particles~ a relatively small range of mean concentrations in the base material can be found in whlch there is no disturbing electrical conductivity and a relatively high permittivlty with satisfactory properties of permanent resilience. The material further comprises a 15 supplemental effect material of metal conductivity which performs in such a way that the impulse resistance required for high voltage accessories is maintained. It is surprising that in this manner, permanently resilient insulating materials can be produced which are dielectrics, 20 i.e. insulators, and which have substantially higher permittivities than hitherto possible, and which exhibit the necessary high electric impulse strength required for high voltage equipment.
rrrue, it is known that the permittivity of an insul- ?
25 ating material can be increased by the incorporation of finely divided particles of electrically conductlve or semi~conductive material, as long as excessive concen-trations Or such particles are avoided because they can provide an excessive specific electrical conductlvity 30 which is not suitable for the use as an insulating material. Ilowevcr~ it has been stated in respect thereto that by the addition of finely divided titanium dioxide or carbon black, the permittivity of natural or synthetic rubber could be increased to values from lO to about 25, 35 and that it would be appropriate to use titanium dioxide because that material had a less adverse effect upon the dielectric strength and the specific volume resistivity (U.S Patent No. 3~2871489). That statement is in .
, . , , . i , .~ :
~, ~ , . , correspondence with the known te~ching stated in ~.S.
Patent No. 4,053,702 that elastomeric materials o~ the kind indicated compr~sing titanium dioxide, titanates or the like as ef~ective materials, can be produced with a permittivity of up to only about 25~ and that, ~or example, a permlttivity of at least 50 could not be reached with elastomeric materials.
Furthermore, stress-controlling materials are known which contain carbon black as a filler for improving the mechanical properties of the material (U.S. Patent Nos.
2,515,7~8; 3,349,164), or as an effect material for obtaining a desired electrical conductivity ~U.S. Patent No. 3,673,305); however, no suggestions towards the present invention can be found in this connectionO
The composition according to the invention in prin-ciple is very simple and can be produced at minimum expense. In combination, it shows good properties of permanent resilience, good chemical durability, good electrical insulating capability, fully satisfactory dielectric and impulse strength, and high values of permittivity which had not been thought possible hitherto with compositions displaying permanent resilience. Thus~
the composition according to the invention can particu-larly be employed at great advantage in stress control elements whlch then can have substantially smaller dlmensions as compared with elements made of known re-frac~ive materlals of lower permittivlty. Such a stress control element, e.g. ln the ~orm of a shaped body, like a sleeve, which can be shifted-on reslllently, ls designed with respect t,o its electrical properties and its geometric con~iguration, in correspondence with the desired modification o~ an electric field existing at its slte of application. Additionally, depending upon the strength of the electric field, a constltuent of elec-tr1cally conductive resilient material may be insertedin the stress control element to make contact with a cable shield.
The composition according to the invention preferably has a permittivity between about 50 and 150, at low '` ~.
., .
, ..
. , !~h6 frequencies (e.g., 50 Hz) and at least about 20 at hlgh frequencies (e.g., 105 Hz). In this range, the properties of permanent resilience are particularly good~ at a good electrical insulating capabili~y.
The effectiveness of the strongly structurized of cleft dust-flne polarizable particles employed in accor-dance with the invention is dependent upon the morphology of the particles. Therefore, the concentration of effect material to be employed in the production of the compo-sition is determined by producing for every given charge o~ unitary quality of the effect material, a plurality of test compositions having different contents of effect material, determining the permittivity ~r at low fre-quencies ~e.g. 50 Hz) and the specific electrical volume resistivity ~ for each of the test compositions, and determining the concentration of effect material at which a desired pair of values ~r~ ~ is present. It is parti-cularly advantageous to determine a concentration as the optimum one which is associated in the function log ~r = f (log ~) with a medium range in which the absolute value of the slope is higher than in the area adJacent on both sides. In this manner, the suitable concentrations and particularly also the optimum concentrations in the base materials can be evaluated for every charge of an effect materlal exhlbiting a macroscopically unitary quality.
It has been found that with the preferred ef~ect material, i.e carbon black, the commercially available qualities show very dlfferent effectiveness in the sense of the present invention. For example~ the optimum concentration may be approximately 3 parts by weight, bu~ also approximately 30 parts by weight per 100 parts by weight base material. Thus~ the teaching to determine the concentrations to be used separately for every charge of an effect material exhibiting a macroscopi-cally unitary quality constitutes an essential part of the present invention.
The minimum value of the specific electrlcal volume reslstivity of the composition according to the invention ~ , . . . .
. . - , : , . .
.
. : -3~6 should be approximately 106 ohm,cm ln order for the compo-sition to still be considered an insulating material;
preferably, the minimum value is approximately 10 ohm.cm.
Furthermore, khe composltion according to the invention is characterized in that it has, as a rule~ a positive tem-perature coefficient o~ specific electrical volume resis-tivity. In other words, the temperature coefficient of the specific electrical volume resistivity should be at least approximately zero in the temperature range of from about 0 to 100C. This of~ers the known advantage that the proportion of losses caused by action currents becomes smaller with an increasing temperature of tha composition;
this counteracts undesirable heating up. Preferably~ the temperature coef~icient of the specific electrical volume resistivity is approximately 0.01 per degree wlthin the temperature range o~ about 0 to 100C.
Within the range of permittivities stated, the dielectric loss factor at low and high rrequencies ls not ~reater than about 1.5, and not greater than about 1 in the range Or the permittivities preferably employed. Thls is completely suf'ficient for the intended use as stress control elements for high voltage accessories.
Furthermore~ it has been found that the addition of a conductive material showing metal conductivity, as known per se from the German Offenlegungschri~t, 28 21 017, in the form o~ ~inely divided particles, the load carrying capabllity and the st,ress control action are strongly improved at high frequencies, e.g,, as may occur with loads produced b~ shock waves or lightening strikes in high voltage llnes. Experiments with impulse voltage loads o~
a duration of 1.2 per 50 ~s have shown that the stability against such impulses can be increased by up to 100 per cent by the additional use of platelet-shaped conductlve matérial. The conductive material may consist simply o~
aluminum which is easily and commercially available in form of thin platelets or flakes. The conductive material may also consist of vacuum metalized microspheres based on glass spheroids or plastic spheroids. In the latter case, it is generally sufficient if the microspheres are only ., .
, -' ,' ' " ' , ' - ', , 3~
g super~icially conductive. The area size of the conductive microspheres should ~e ln the same range as the area of conductive platelets, which means that the conductive surface of both types Or particles will be comparable.
In order to increase the dielectric strength of the composition accordlng to the invention, it may be advan-tageous to additionally intermix, as an additional effect material, an insulating material which is different from the base material, in finely divided form as platelet-shaped particles ~See German OLS 2821017). Thereby, the concentration of bridges between directly contacting par-ticles of the e~fect material and of the additional con-ductive ef~ect material is strongly reduced. Preferably, the insulating material has a higher dielectric strength than the base material to thereby increase dielectric strength of the composition. In order to not adversely affect, and possibly increase the refractive action of the composition, it is advantageous to use an insulating matcrial havin~ a permlttlvity which is at least equal to that of the base material. An insulating material which is particularly suited as an additional effect material is mica which inherently is of platelet structure. Also, when employing an insulating material different from the base material, the boundary conditions stated above are maintained.
The size of the platelets of the additional effect materlal is o~ ~mportance ~or dielectric homogeneity of the composition ln relation to the dimensions of the structural parts made therefrom, With the dimensions and flash-over distances whlch are appropriate for alternating voltages from about 3 k~, the platelets of the conductive material may have a transverse dlmension~ measured trans-verse of their thickness, of about 5 to 75 ~m; an advantageous intermediate range is 10 to 40 ~m. The thickness of the platelet-shaped particles should be not more than about one tenth of the trans~erse dimension to retain the character of a platelet. Of course~ the same also holds for the platelets of insulating material, and they may be somewhat larger than plakelets of conductlve .
.. .. . .
-, . ~ :
material, particularly with respect to their trans~e~se dimensions.
It is particularly advantageous that, as known from German Offenlegungsschrift 28 21 017, the platelets of conductive material need not be oriented in definite directions but, rather, may be distributed with an essen-tially random-dlstribution orientation of their platelet planes. Thus, particular manufacturing steps to orient the platelets~ e.g., calendering, pasting-on, and the like, are not necessary when compositions containing platelet-shaped particles according to the invention are produced.
The dielectric composition according to the invention can be prepared by inter-mixing the effect material, the conductive ef~ect material and, where desired, the addi-t~onal insulating effect materials with a liquid or pasteof flowable or die-castable base compound which is capable of being hardened to the permanently resilient composition, for example by cold or hot vulcanizing.- The hardening can be performed in molds, whereby permanently resilient bodies of a desired shaped configuration can be directly obtained which are suitable as stress control elements.
Injection mol~ing, casting, die casting, etc., are also satisfactory manufacturing techniques.
With particular kinds of carbon black which are particularly suited for the purposes of the present inven-tion, i e. which even at low concentrations cause a strong increase in permlttivity, it has been found to be appropriate to introduce the carbon black in a phase of the preparation process where the viscosity is as low as possible. Then, the dispersion of the carbon black is more uniform.
Brief Description of Drawings Figs. 1 to 5 illustrate the properties o~ dielectric composi~ions which have been prepared with the e~fect material carbon black, type N 75~, as set forth below.
Figs. 6 to 9 illustrate the properties Or dielectric compositions according to the invention, which contain an additional ef~ect material in the form o~ conductive platelets.
- , ,: . .
. :
.
- ~ -:
t~ 6 ~ig. 10 illustrates composltions according to the invention, prepared with silicone rubber type 101~30 and as the e~fect material carbon black, type N 762, as set forth below.
The invention will now be more speclfically illus- !
trated by the following examples, wherein all parts are by weight unless otherwise specified, and whlch are discussed in conjunction with the attached drawings.
Examples One hundred parts by weight of silicone rubber base material of the type S 2351 of Dow Corning were intermixed with different parts by weight carbon black ~N 754 of Columbian Carbon Company, New York) and various parts by weight aluminum platelets (No-. 4-501 of Reynolds Metal Company, Richmond, Va., USA.).
In each case, the mixtures were intermixed wlth 0.4 parts by weig~lt of the catalyst dicumylperoxide ~of the type~'Dicup R" Or Herkules~, and cured in molds to form permanently resilient test bodies of about 3 mm thickness.
Fig. 1 lllustrates the relationship between the logarithms of the relative dielectric constant (permit-tivity) and the electrical volume resistivlty for different proportions of carbon black. It is apparent that in the medium range of curve A, i.e., with the proportion of carbon black where the absolute value of the ~lope i5 higher than in the adJacent ranges (i.e. the ~irst deriva~ive ha~ an extremum), relatively high permittivities are evident at still very high volume resistivitles, for instance ~r = 5 at ~ = lolor~ cm. Only from ~r = 200 does the volume reslstivlty commence to drop to values which are critical with respect for use as an insulating material; the readily useful range extends to about ~r = 150.
Fig. 2 illustrates that at higher frequencies, permittivity decreases relatively rapidly. Curve B
designates 1.0 kHz, Curve C 24 kHz and Curve D 53 Hz.
Fig. 3 illustrates that, as expected, the dielectric loss factor increases with increasing proportions of ,~lq ~D~ ~n,4p.f~, . .. ~ ,, ~ . - .
.
'.
~ ~5.~2~
carbon black; in contrast thereto, the dependence upon frequency is less distinct. Curves B, C and D relate to the same frequencies as ~ig, 2.
Fig, 4 illustrates - similarly as Fig. l - the relation between the relative dielectric constant (permit-tivity) ~r (,at 50 cps~ (Curve E) and the dielectric volume resistivity ~CCurve ~) when the proportions of the effect material carbon black (type N 754) are increasing. In this instance lO parts of Type 4-501 aluminum flake were also contained in the elastomer.
Fig. 5 illustrates the dependence of specific direct current conductivity ~the reciprocal of the volume resistivity) upon the field strength at various tempera-tures for a test body having 32 phr carbon black of the kype N 754. Curve G relates to 20C, Curve H 50C, Curve I 800C and Curve J 100C.
Fig. 6 illustrates for a dielectric compositlon having 32 phr carbon black of the type N 754 and lO phr aluminum platelets for the type 4-501 (REYNOLDS), that the direct current resistivity is not increased by the intro-duction o~ the conductive effect material; a similar dependence to that shown in Figure 5 exists. Curves G, H, I and J relate to the same temperatures as Fig. 5. Both figures, moreover, illustrate the posltive temperature coefficient of volume resistivity.
Figure 7 illustrates the dielectric loss factcr tan ~ and the dielectric constant (permittivlty) ~r dependence upon the ~requency f at various temperatures (same as F'ig. 5) for dielectric materials having 32 phr carbon black of the type N 754 and lO phr aluminum platelets of the type 4-50l. It can be recognized that ~t ls easily possible to adjust the dielectric loss factor close to values at least about l at low frequencies as well as at high ~requencies and that the permittivity at room, and even elevated temperatureg is characterized by values between 50 up to lOO at low ~requencies (e.g., 50 Hz) and to values at least about 20 at high frequencies (,e.g., 105 Hz~.
.
~ ~ ~ 5~
Flgure 8 illustrates that a dielectric mat~rial corl-taining 32 phr carbon black (type N 754) provides, due to the addition o~ 10 phr aluminum platelets an essentlal increase of the relative dielectric constant (permittivity) at low frequencies (e.g., 50 Hz) from about 250 up to 400 maximum, whereas at high frequencies (e.g., 105 Hz) the relative dielectric constant is held at about 25. Curve K represents 32 phr carbon black, and 10 phr aluminum, Curve L with no aluminum~ and Curve M with no aluminum and 30 phr carbon black.
Figure 9 illustrates that this increase in relative dielectric constant is only associated with a minor increase in dielectric loss factor.
Figure 10 illustrates, in a manner similar to Fig. 4, the properties of a dielectric material made with other components. As a base material, silicone rubber type 101/30 of the firm Wacker~Chemle, Munchen~ was used; as an ef~ect material carbon black of the brand N 762 of Columbian Carbon Company; and as an additional e~ect material, the already described aluminum platelets. One hundred parts by weight of the base materials were intermixed with 6 parts by weight o~ the aluminum platelets, different amounts of the carbon black, and 1.5 parts by welght of the above mentioned catalyst dicumyl peroxide ~ Vicup 40C~', filled into molds, and cured. It is apparent from Figure 10 that basically the same characteristics are obtained as illustrated in Figs. 1 to 9. However, the first derivative of the function log g - f (log ~r) reaches its extremum at a different, i.e,~ lower, carbon black concentration than shown ln ~ig. 4.
According to present understanding, it appears to be predominantly important for the described invention that the particles of ef~ect material have a surface area whi~h is large in relation to their mass, and capable of offering a certain resistance to the displacement of electrical charges. It may be imagined that other effective materials, which have properties similar to carbon black, may produce similar or perhaps even better results than carbon black, and the present invention provides a teac~ing to the skilled
b) The relative dielectric constant (permittivity) ~s greater than 30, and up to about 300, and c) The dielectric loss factor is not greater than approximately 1.5 and further comprises a supplemental effect material in the form of finely divided particles possessing metal .
.
.
conductivity to improve the electric stre~s d-issipation and consequently the dielectric strengths at high f~equen-cies as they are typical for impulse waves 5 and to hold the permittivity at high ~requencies (e.g. 105 Hz) to at 5 least about 20.
Detailed Description The composition accordlng to the invention utilizes the fact that ~ith effect materials like carbon black, which comprise strongly structurized or cleft dust-fine lO polarizable particles~ a relatively small range of mean concentrations in the base material can be found in whlch there is no disturbing electrical conductivity and a relatively high permittivlty with satisfactory properties of permanent resilience. The material further comprises a 15 supplemental effect material of metal conductivity which performs in such a way that the impulse resistance required for high voltage accessories is maintained. It is surprising that in this manner, permanently resilient insulating materials can be produced which are dielectrics, 20 i.e. insulators, and which have substantially higher permittivities than hitherto possible, and which exhibit the necessary high electric impulse strength required for high voltage equipment.
rrrue, it is known that the permittivity of an insul- ?
25 ating material can be increased by the incorporation of finely divided particles of electrically conductlve or semi~conductive material, as long as excessive concen-trations Or such particles are avoided because they can provide an excessive specific electrical conductlvity 30 which is not suitable for the use as an insulating material. Ilowevcr~ it has been stated in respect thereto that by the addition of finely divided titanium dioxide or carbon black, the permittivity of natural or synthetic rubber could be increased to values from lO to about 25, 35 and that it would be appropriate to use titanium dioxide because that material had a less adverse effect upon the dielectric strength and the specific volume resistivity (U.S Patent No. 3~2871489). That statement is in .
, . , , . i , .~ :
~, ~ , . , correspondence with the known te~ching stated in ~.S.
Patent No. 4,053,702 that elastomeric materials o~ the kind indicated compr~sing titanium dioxide, titanates or the like as ef~ective materials, can be produced with a permittivity of up to only about 25~ and that, ~or example, a permlttivity of at least 50 could not be reached with elastomeric materials.
Furthermore, stress-controlling materials are known which contain carbon black as a filler for improving the mechanical properties of the material (U.S. Patent Nos.
2,515,7~8; 3,349,164), or as an effect material for obtaining a desired electrical conductivity ~U.S. Patent No. 3,673,305); however, no suggestions towards the present invention can be found in this connectionO
The composition according to the invention in prin-ciple is very simple and can be produced at minimum expense. In combination, it shows good properties of permanent resilience, good chemical durability, good electrical insulating capability, fully satisfactory dielectric and impulse strength, and high values of permittivity which had not been thought possible hitherto with compositions displaying permanent resilience. Thus~
the composition according to the invention can particu-larly be employed at great advantage in stress control elements whlch then can have substantially smaller dlmensions as compared with elements made of known re-frac~ive materlals of lower permittivlty. Such a stress control element, e.g. ln the ~orm of a shaped body, like a sleeve, which can be shifted-on reslllently, ls designed with respect t,o its electrical properties and its geometric con~iguration, in correspondence with the desired modification o~ an electric field existing at its slte of application. Additionally, depending upon the strength of the electric field, a constltuent of elec-tr1cally conductive resilient material may be insertedin the stress control element to make contact with a cable shield.
The composition according to the invention preferably has a permittivity between about 50 and 150, at low '` ~.
., .
, ..
. , !~h6 frequencies (e.g., 50 Hz) and at least about 20 at hlgh frequencies (e.g., 105 Hz). In this range, the properties of permanent resilience are particularly good~ at a good electrical insulating capabili~y.
The effectiveness of the strongly structurized of cleft dust-flne polarizable particles employed in accor-dance with the invention is dependent upon the morphology of the particles. Therefore, the concentration of effect material to be employed in the production of the compo-sition is determined by producing for every given charge o~ unitary quality of the effect material, a plurality of test compositions having different contents of effect material, determining the permittivity ~r at low fre-quencies ~e.g. 50 Hz) and the specific electrical volume resistivity ~ for each of the test compositions, and determining the concentration of effect material at which a desired pair of values ~r~ ~ is present. It is parti-cularly advantageous to determine a concentration as the optimum one which is associated in the function log ~r = f (log ~) with a medium range in which the absolute value of the slope is higher than in the area adJacent on both sides. In this manner, the suitable concentrations and particularly also the optimum concentrations in the base materials can be evaluated for every charge of an effect materlal exhlbiting a macroscopically unitary quality.
It has been found that with the preferred ef~ect material, i.e carbon black, the commercially available qualities show very dlfferent effectiveness in the sense of the present invention. For example~ the optimum concentration may be approximately 3 parts by weight, bu~ also approximately 30 parts by weight per 100 parts by weight base material. Thus~ the teaching to determine the concentrations to be used separately for every charge of an effect material exhibiting a macroscopi-cally unitary quality constitutes an essential part of the present invention.
The minimum value of the specific electrlcal volume reslstivity of the composition according to the invention ~ , . . . .
. . - , : , . .
.
. : -3~6 should be approximately 106 ohm,cm ln order for the compo-sition to still be considered an insulating material;
preferably, the minimum value is approximately 10 ohm.cm.
Furthermore, khe composltion according to the invention is characterized in that it has, as a rule~ a positive tem-perature coefficient o~ specific electrical volume resis-tivity. In other words, the temperature coefficient of the specific electrical volume resistivity should be at least approximately zero in the temperature range of from about 0 to 100C. This of~ers the known advantage that the proportion of losses caused by action currents becomes smaller with an increasing temperature of tha composition;
this counteracts undesirable heating up. Preferably~ the temperature coef~icient of the specific electrical volume resistivity is approximately 0.01 per degree wlthin the temperature range o~ about 0 to 100C.
Within the range of permittivities stated, the dielectric loss factor at low and high rrequencies ls not ~reater than about 1.5, and not greater than about 1 in the range Or the permittivities preferably employed. Thls is completely suf'ficient for the intended use as stress control elements for high voltage accessories.
Furthermore~ it has been found that the addition of a conductive material showing metal conductivity, as known per se from the German Offenlegungschri~t, 28 21 017, in the form o~ ~inely divided particles, the load carrying capabllity and the st,ress control action are strongly improved at high frequencies, e.g,, as may occur with loads produced b~ shock waves or lightening strikes in high voltage llnes. Experiments with impulse voltage loads o~
a duration of 1.2 per 50 ~s have shown that the stability against such impulses can be increased by up to 100 per cent by the additional use of platelet-shaped conductlve matérial. The conductive material may consist simply o~
aluminum which is easily and commercially available in form of thin platelets or flakes. The conductive material may also consist of vacuum metalized microspheres based on glass spheroids or plastic spheroids. In the latter case, it is generally sufficient if the microspheres are only ., .
, -' ,' ' " ' , ' - ', , 3~
g super~icially conductive. The area size of the conductive microspheres should ~e ln the same range as the area of conductive platelets, which means that the conductive surface of both types Or particles will be comparable.
In order to increase the dielectric strength of the composition accordlng to the invention, it may be advan-tageous to additionally intermix, as an additional effect material, an insulating material which is different from the base material, in finely divided form as platelet-shaped particles ~See German OLS 2821017). Thereby, the concentration of bridges between directly contacting par-ticles of the e~fect material and of the additional con-ductive ef~ect material is strongly reduced. Preferably, the insulating material has a higher dielectric strength than the base material to thereby increase dielectric strength of the composition. In order to not adversely affect, and possibly increase the refractive action of the composition, it is advantageous to use an insulating matcrial havin~ a permlttlvity which is at least equal to that of the base material. An insulating material which is particularly suited as an additional effect material is mica which inherently is of platelet structure. Also, when employing an insulating material different from the base material, the boundary conditions stated above are maintained.
The size of the platelets of the additional effect materlal is o~ ~mportance ~or dielectric homogeneity of the composition ln relation to the dimensions of the structural parts made therefrom, With the dimensions and flash-over distances whlch are appropriate for alternating voltages from about 3 k~, the platelets of the conductive material may have a transverse dlmension~ measured trans-verse of their thickness, of about 5 to 75 ~m; an advantageous intermediate range is 10 to 40 ~m. The thickness of the platelet-shaped particles should be not more than about one tenth of the trans~erse dimension to retain the character of a platelet. Of course~ the same also holds for the platelets of insulating material, and they may be somewhat larger than plakelets of conductlve .
.. .. . .
-, . ~ :
material, particularly with respect to their trans~e~se dimensions.
It is particularly advantageous that, as known from German Offenlegungsschrift 28 21 017, the platelets of conductive material need not be oriented in definite directions but, rather, may be distributed with an essen-tially random-dlstribution orientation of their platelet planes. Thus, particular manufacturing steps to orient the platelets~ e.g., calendering, pasting-on, and the like, are not necessary when compositions containing platelet-shaped particles according to the invention are produced.
The dielectric composition according to the invention can be prepared by inter-mixing the effect material, the conductive ef~ect material and, where desired, the addi-t~onal insulating effect materials with a liquid or pasteof flowable or die-castable base compound which is capable of being hardened to the permanently resilient composition, for example by cold or hot vulcanizing.- The hardening can be performed in molds, whereby permanently resilient bodies of a desired shaped configuration can be directly obtained which are suitable as stress control elements.
Injection mol~ing, casting, die casting, etc., are also satisfactory manufacturing techniques.
With particular kinds of carbon black which are particularly suited for the purposes of the present inven-tion, i e. which even at low concentrations cause a strong increase in permlttivity, it has been found to be appropriate to introduce the carbon black in a phase of the preparation process where the viscosity is as low as possible. Then, the dispersion of the carbon black is more uniform.
Brief Description of Drawings Figs. 1 to 5 illustrate the properties o~ dielectric composi~ions which have been prepared with the e~fect material carbon black, type N 75~, as set forth below.
Figs. 6 to 9 illustrate the properties Or dielectric compositions according to the invention, which contain an additional ef~ect material in the form o~ conductive platelets.
- , ,: . .
. :
.
- ~ -:
t~ 6 ~ig. 10 illustrates composltions according to the invention, prepared with silicone rubber type 101~30 and as the e~fect material carbon black, type N 762, as set forth below.
The invention will now be more speclfically illus- !
trated by the following examples, wherein all parts are by weight unless otherwise specified, and whlch are discussed in conjunction with the attached drawings.
Examples One hundred parts by weight of silicone rubber base material of the type S 2351 of Dow Corning were intermixed with different parts by weight carbon black ~N 754 of Columbian Carbon Company, New York) and various parts by weight aluminum platelets (No-. 4-501 of Reynolds Metal Company, Richmond, Va., USA.).
In each case, the mixtures were intermixed wlth 0.4 parts by weig~lt of the catalyst dicumylperoxide ~of the type~'Dicup R" Or Herkules~, and cured in molds to form permanently resilient test bodies of about 3 mm thickness.
Fig. 1 lllustrates the relationship between the logarithms of the relative dielectric constant (permit-tivity) and the electrical volume resistivlty for different proportions of carbon black. It is apparent that in the medium range of curve A, i.e., with the proportion of carbon black where the absolute value of the ~lope i5 higher than in the adJacent ranges (i.e. the ~irst deriva~ive ha~ an extremum), relatively high permittivities are evident at still very high volume resistivitles, for instance ~r = 5 at ~ = lolor~ cm. Only from ~r = 200 does the volume reslstivlty commence to drop to values which are critical with respect for use as an insulating material; the readily useful range extends to about ~r = 150.
Fig. 2 illustrates that at higher frequencies, permittivity decreases relatively rapidly. Curve B
designates 1.0 kHz, Curve C 24 kHz and Curve D 53 Hz.
Fig. 3 illustrates that, as expected, the dielectric loss factor increases with increasing proportions of ,~lq ~D~ ~n,4p.f~, . .. ~ ,, ~ . - .
.
'.
~ ~5.~2~
carbon black; in contrast thereto, the dependence upon frequency is less distinct. Curves B, C and D relate to the same frequencies as ~ig, 2.
Fig, 4 illustrates - similarly as Fig. l - the relation between the relative dielectric constant (permit-tivity) ~r (,at 50 cps~ (Curve E) and the dielectric volume resistivity ~CCurve ~) when the proportions of the effect material carbon black (type N 754) are increasing. In this instance lO parts of Type 4-501 aluminum flake were also contained in the elastomer.
Fig. 5 illustrates the dependence of specific direct current conductivity ~the reciprocal of the volume resistivity) upon the field strength at various tempera-tures for a test body having 32 phr carbon black of the kype N 754. Curve G relates to 20C, Curve H 50C, Curve I 800C and Curve J 100C.
Fig. 6 illustrates for a dielectric compositlon having 32 phr carbon black of the type N 754 and lO phr aluminum platelets for the type 4-501 (REYNOLDS), that the direct current resistivity is not increased by the intro-duction o~ the conductive effect material; a similar dependence to that shown in Figure 5 exists. Curves G, H, I and J relate to the same temperatures as Fig. 5. Both figures, moreover, illustrate the posltive temperature coefficient of volume resistivity.
Figure 7 illustrates the dielectric loss factcr tan ~ and the dielectric constant (permittivlty) ~r dependence upon the ~requency f at various temperatures (same as F'ig. 5) for dielectric materials having 32 phr carbon black of the type N 754 and lO phr aluminum platelets of the type 4-50l. It can be recognized that ~t ls easily possible to adjust the dielectric loss factor close to values at least about l at low frequencies as well as at high ~requencies and that the permittivity at room, and even elevated temperatureg is characterized by values between 50 up to lOO at low ~requencies (e.g., 50 Hz) and to values at least about 20 at high frequencies (,e.g., 105 Hz~.
.
~ ~ ~ 5~
Flgure 8 illustrates that a dielectric mat~rial corl-taining 32 phr carbon black (type N 754) provides, due to the addition o~ 10 phr aluminum platelets an essentlal increase of the relative dielectric constant (permittivity) at low frequencies (e.g., 50 Hz) from about 250 up to 400 maximum, whereas at high frequencies (e.g., 105 Hz) the relative dielectric constant is held at about 25. Curve K represents 32 phr carbon black, and 10 phr aluminum, Curve L with no aluminum~ and Curve M with no aluminum and 30 phr carbon black.
Figure 9 illustrates that this increase in relative dielectric constant is only associated with a minor increase in dielectric loss factor.
Figure 10 illustrates, in a manner similar to Fig. 4, the properties of a dielectric material made with other components. As a base material, silicone rubber type 101/30 of the firm Wacker~Chemle, Munchen~ was used; as an ef~ect material carbon black of the brand N 762 of Columbian Carbon Company; and as an additional e~ect material, the already described aluminum platelets. One hundred parts by weight of the base materials were intermixed with 6 parts by weight o~ the aluminum platelets, different amounts of the carbon black, and 1.5 parts by welght of the above mentioned catalyst dicumyl peroxide ~ Vicup 40C~', filled into molds, and cured. It is apparent from Figure 10 that basically the same characteristics are obtained as illustrated in Figs. 1 to 9. However, the first derivative of the function log g - f (log ~r) reaches its extremum at a different, i.e,~ lower, carbon black concentration than shown ln ~ig. 4.
According to present understanding, it appears to be predominantly important for the described invention that the particles of ef~ect material have a surface area whi~h is large in relation to their mass, and capable of offering a certain resistance to the displacement of electrical charges. It may be imagined that other effective materials, which have properties similar to carbon black, may produce similar or perhaps even better results than carbon black, and the present invention provides a teac~ing to the skilled
4 expert how to test substances which may be suitable as . ....
:
~ ~ .
' ' ' ..
_ lL~ _ e~ect materials. In cases where respectlve materlal data for the effect materials are known whi¢h characterize the structure and performance of its particles, and where these data are useful also to characterize the effectiveness of the present invention in accordance with the rating criteria described in this specification, it may be su~ficlent to simply apply such data for repeat orders for commercially available brands of suitable effect materials. In the above examples, the carbon black brands are characterized by ASTM designations according to US standards, under which they are also commercially available.
.
, ' ; - . ~ , , ;
,, : , . -, ~ . .
~ . ~
''' ' ~ ':
:
~ ~ .
' ' ' ..
_ lL~ _ e~ect materials. In cases where respectlve materlal data for the effect materials are known whi¢h characterize the structure and performance of its particles, and where these data are useful also to characterize the effectiveness of the present invention in accordance with the rating criteria described in this specification, it may be su~ficlent to simply apply such data for repeat orders for commercially available brands of suitable effect materials. In the above examples, the carbon black brands are characterized by ASTM designations according to US standards, under which they are also commercially available.
.
, ' ; - . ~ , , ;
,, : , . -, ~ . .
~ . ~
''' ' ~ ':
Claims (20)
1. A permanently elastic dielectric composition for influencing electrical fields in power current and high voltage systems, comprising a permanently resilient dielectric base material, a content of a finely divided effect material to increase the relative dielectric constant, the effect material comprising strongly struc-turized dust-fine particles of an electrically polarizable material of low electrical conductivity, in sufficient concentration to provide, within the range of normal power frequencies, the following properties of the composition in combination:
a) An electric volume resistivity of a minimum value which is still sufficient for purposes of electrical insulation, b) A relative dielectric constant is between about 30 and about 300, c) A dielectric loss factor of less than about 1.5, and a content of a supplemental effect material comprising finely divided particles possessing metal conductivity, in sufficient concentration to maintain the relative dielectric constant at not less than about 20 at high power frequencies.
a) An electric volume resistivity of a minimum value which is still sufficient for purposes of electrical insulation, b) A relative dielectric constant is between about 30 and about 300, c) A dielectric loss factor of less than about 1.5, and a content of a supplemental effect material comprising finely divided particles possessing metal conductivity, in sufficient concentration to maintain the relative dielectric constant at not less than about 20 at high power frequencies.
2. The composition of claim 1, wherein said effect material is carbon black.
3, The composition of claim 1, wherein said minimum value of electric volume resistivity at room temperature is about 106 ohm.cm.
4. The composition of claim 1, wherein said minimum value of electric volume resistivity at room temperature is about 108 ohm.cm.
5. The composition of claim 1, wherein said electric volume resistivity has a temperature coefficient in the temperature range of about 0 to 100°C of about zero.
6. The composition of claim 1, wherein said relative dielectric constant is between 50 and 150 at low power frequencies and not less than about 20 at high frequencies.
7. The composition of claim 1 wherein said dielectric loss factor is about l at low and high frequencies at room temperature.
8. The composition of claim 1, wherein said supple-mental effect material consists of finely divided micro-spheres.
9. The composition of claim 9, wherein said micro-spheres are only superficially conductive.
10. The composition of claim 8, wherein said micro-spheres have a diameter of at least 2 µm.
11. The composition of claim l, wherein said supplemental effect metal consists of finely divided platelets.
12. The composition of claim 1, wherein said supple-mental effect material is aluminum.
13. The composition of claim 12, wherein said aluminum is present at a concentration of about 3 to 15 parts by weight per 100 parts by weight of said base material.
14. The composition of claim 1, additionally comprising an insulating material different from said base material in finely divided form as platelet shaped particles.
15. The composition of claim 14, wherein said insulating material has a dielectric strength not less than said base material.
16. The composition of claim 14, wherein said insulating material is mica.
17. The composition of claim 16, wherein said mica is present at a concentration of about 5 to 30 parts by weight per 100 parts by weight of said base material.
18. The composition of claim 1, in the form of a shaped body capable of functioning as a refractive stress control element.
19. The composition of claim 18, wherein said body is a sleeve capable of resiliently sliding on a cable termination.
20. The composition of claim 17 wherein said base material is selected from the group consisting of silicone rubber and EPDM.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP3008264.5 | 1980-03-04 | ||
| DE19803008264 DE3008264C2 (en) | 1980-03-04 | 1980-03-04 | Permanently elastic dielectric material for influencing electrical fields, as well as its use in field control elements |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1145926A true CA1145926A (en) | 1983-05-10 |
Family
ID=6096234
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000372227A Expired CA1145926A (en) | 1980-03-04 | 1981-03-03 | Elastomeric composition for providing electrical stress control |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1145926A (en) |
| DE (1) | DE3008264C2 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4404125A (en) * | 1981-10-14 | 1983-09-13 | General Electric Company | Polyphenylene ether resin compositions for EMI electromagnetic interference shielding |
| US4508640A (en) * | 1981-11-24 | 1985-04-02 | Showa Denko Kabushiki Kaisha | Electromagnetic wave-shielding materials |
| GB8805556D0 (en) * | 1988-03-09 | 1988-04-07 | Dowty Seals Ltd | Sealing member |
| DE3943296C2 (en) * | 1989-12-29 | 1994-08-11 | Minnesota Mining & Mfg | Sleeve for covering a connection or an end of an electrical cable |
| DE102011101579B4 (en) * | 2011-05-12 | 2015-03-05 | Otto Bock Healthcare Gmbh | Use of conductive polymer material for medical and orthopedic applications |
| CH710800B1 (en) * | 2015-08-27 | 2016-08-31 | Gramespacher Hansjörg | Prefabricated socket body for the connection of two high-voltage polymer cables for DC. |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE2118135C3 (en) * | 1971-04-14 | 1980-01-24 | Kabel- Und Metallwerke Gutehoffnungshuette Ag, 3000 Hannover | Conductive polymer mixture |
| GB1602372A (en) * | 1977-05-18 | 1981-11-11 | Hotfoil Ltd | Electrically conductive rubber composition |
-
1980
- 1980-03-04 DE DE19803008264 patent/DE3008264C2/en not_active Expired
-
1981
- 1981-03-03 CA CA000372227A patent/CA1145926A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| DE3008264A1 (en) | 1981-09-10 |
| DE3008264C2 (en) | 1983-01-05 |
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