CA1100586A - Application of conductive porcelain to electrical insulators - Google Patents
Application of conductive porcelain to electrical insulatorsInfo
- Publication number
- CA1100586A CA1100586A CA306,188A CA306188A CA1100586A CA 1100586 A CA1100586 A CA 1100586A CA 306188 A CA306188 A CA 306188A CA 1100586 A CA1100586 A CA 1100586A
- Authority
- CA
- Canada
- Prior art keywords
- insulator
- porcelain
- clay
- ferric oxide
- conductive
- 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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Abstract
ABSTRACT OF THE DISCLOSURE
A ceramic body such as a porcelain insulator is provided with a conductive porcelain layer which can be fired on to the body without diffusion into a contiguous insulative or semiconductive glaze layer. The conductive porcelain layer consists of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture, and is fired on to the porcelain body of the insulator for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
A ceramic body such as a porcelain insulator is provided with a conductive porcelain layer which can be fired on to the body without diffusion into a contiguous insulative or semiconductive glaze layer. The conductive porcelain layer consists of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture, and is fired on to the porcelain body of the insulator for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
Description
110(158~i The invention relates to conductive porcelain and to applications of conductive porcelain layers, as distinguished from glazes.
An electrically conductive porcelain in accordance with the present invention consists of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15%
to 50% by dry weight of the mixture, and the porcelain being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C.
One application of the invention is to the manufacture of electrical components such as ceramic resistors. Such a resistor may comprise a unitary ceramic body having an elongated insulative core and a conductive layer thereon extending continuously between end regions of the body, the core being .., of insulator clay and the conductive layer being of the same insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50~ by dry weight of the mixture, and the body being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C.
Another important application of the invention is to high voltage electrical insulators. Such insulators are presently made radio and television interference free by the application of a highly conductive ferric oxide glaze. The glaze is applied to the body of the insulator in the vicinity of the conductor support saddle and the neck of the insulator so as to make an electrical contact with the line conductor and an associated tie wire. The equipotential region formed between the însulator, conductor and the tie wire prevents local sparking, and prevents radio and television interference.
However, as the conductive glaze extends the high voltage on to the body of the insulator, electrochemical attack of the glaze occurs during wetting by rain, dew and fog. As the surface is subject to accumulated contamination which provides --2-- ~
1~00586 a hygroscopic surface, glaze deterioration progresses until the equipotential region is lost and the insulator begins to spark. In the presence of sparking the glaze deteriorates very rapidly and sparking increases. By providing an electrically insulating surface, glaze deterioration is reduced and the useful life of the insulator is greatly increased.
The insulating layer in this case must withstand spark erosion which occurs on the surface of the insulator during wetting.
Normal porcelain glazes are well known to stand up to such harsh environments~ However, the two-layer glazing techniques presently in use tend to cause mixing of the glazes by diffusion during firing. As a result, conductive filaments ; appear at the surface of the insulator, which are prone to electrochemical attack, and this process spreads quickly to the lower conductive glaze layer and causes extensive damage as well as radio and television interference.
In order to solve this problem the present invention contemplates a porcelain insulator having an integral terminal region of conductive porcelain consisting of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture, the surface of the body being covered by an insulative glaze layer extending to the conductive region and leaving an exposed region thereof, the conductive region and said glaze layer being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C. As there is no diffusion of the ferric oxide into the insulating glaze the latter retains its protective properties.
Another Lmportant application of the invention is to high voltage electrical insulators of the type provided with a semiconductive glaze surface wherein it is necessary to make good electrical contact between the glaze and the insulator hardware. Thus, the invention provides an electrical insulator ~lOOS~36 comprising a unitary ceramic structure having a body of electrical porcelain consisting of insulator clay an~
- 3a -1~0(~5l~6 ha~ing fixst and second terminal regions, the en~ire surface of the body between said texminal regions being coyered b~ a semiconductive glaze layer and each of said terminal xegions being covered by a conductive porcelain layer extending to the semiconductive glaze layer, the conductive porcelain layer consisting of said insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% b~ dry weight o~
the mixture, and the structure being fired at a temperature for a time of foux to eight hours in the range 1115C to 1365C.
In this way good electrical contact can be made between the terminal regions and the insulator hardware, thus xeducing high potential gradients and reducing the likelihood of glaze deterioration by sparking and electrochemical attack.
Applications of electrically conductiYe porcelain will now be described by way of example wlth reference to the accompanyin~ drawings, in which:
Figure 1 is a graph illustrating the variation in surface resistivity with ferric oxide content for different conducti~e porcelain layers;
Figure 2 is a graph illustrating the variation in volume resisti~ity with ferric oxide content;, Figure 3 is a half-sectional ele~ational Yiew of a portion of a high voltage electrical insulatox according to one embodiment of the invention;
Figure 4 is a half-sectional elevational ~iew of a portion of a high voltage electrical insulator according to another embodiment of the invention; and Figure 5 illustrates an application of the in~ention to a porcelain electrical xesistor.
' In each of the em~odiments described herëin the porcelain elements of the structures are of electrical porcelain consisting of an insulator clay fired at the appro-priate temperature. A typical insulator clay consists llO(;~S86 essentiallY of ball clay, alumina and nepheline syenite, for example:
Component % by Dry Weight Ball Clay 33.5-42.5 Alumina 35-~5 Nepheline Syenite 18-22.
A specific insulator clay used by the inventors yielded the following analysis:
Ball Cl.ay 38 Alumina 40 Nepheline Syenite 20~
The conductive porcelain referred to below consists of insulator clay having the above composition admixed with ferric oxide, the ferric oxide constituting from 20% to 30% by dry weight of the mixture, This is the preferred amount of ferric oxide for most applications-, although the proportion of ferric oxide may be from 15% to 50% for some applications depending upon requirements, In general, if the proportion of ferric oxide is less than about 15% the conductivity of the porcelain is too low to be useful, whereas if the proportion o~ ferric oxide is higher than about 50%
the mechanical strength of the resultant porcelain is poor.
In the preparation of the conductive porcelain coatings, the necessary insulator clay mix with ferric oxide is prepared in accordance with the ranges outlined and then water is added to form a conductive clay slip.
This slip can be applied to the desired portions of the insulator by spraying or brushing, or the insulator can be dipped into the slip. The conductive porcelain can ~ ,??~
be used with or without glaze covering materials. Glaze forming materials provide an insulating glassy layer free of conductive protrusions. The clay body, with conductive porcelain layer with or without a glaze covering, is fired and soaked in a kiln at a temperature and for a time in the ranges specified herein.
Figure 1 illustrates the variation in surface resistivity of a conductive porcelain with ferric oxide concentration, the porcelain being applied to a substrate by dipping for 15 seconds in the case of curve A, and 2 ; seconds in the case of curve B. The slurry had viscosity of 130 mPa.s, and firing was at 1240C for 6 hours in each case.
Figure 2 illustrates the variation in volume resistivity with ferric oxide concentration of a conductive porcelain in accordance with the invention.
Referring now to Figure 3, this figure illustrates the upper portion of a typical pin-type distribution insulator having one or more bell-shaped porcelain members 10. The figure also shows an upper terminal member 11 which is formed by a unitary body of porcelain cemented to the member 10 and having a terminal region 12. The terminal region 12 is integral with the body 11 and is itself of conductive porcelain.
An insulating porcelain glaze 13 covers the surface of the body 11, extending to and partially over the conductive region 12 so as to leave an exposed conductive surface to which an electrical contact has to be made, as by a high voltage conductor.
In forming the body 11 a clay slip formed from the clay of the insulator body but containing ferric oxide in the required amount is applied to the upper end of the insulator body and around the neck 14. An insulating glaze is next applied to the entire surface of the insulator body up to the neck 14, leaving an exposed terminal portion. The composite body so formed is next fired at 1240C for six hours.
~10C~5~36 In the firing an amalgamation of the conductive clay and the insulator clay to which it is applied results, forming a - unitary porcelain body with a conductive surface at the exposed terminal portion. As there is no diffusion of the ferric oxide into the insulating glaze, the latter retain~ its protective properties.
The technique is applicable to all porcelain insulators, including bushings, post insulators and suspension insulators.
Referring now to Figure 4, an element of a pin-type high voltage insulator consists of a porcelain body 20 having an upper metallic terminal 21 and a pin 22 serving as a lower terminal. The upper terminal 21 and pin 22 are cemented to the porcelain body 20 by conductive cement 23, 24 in the manner well known in the art. The entire surface of the ~ody 20 is covered by a semiconductive glaze layer 25 which provides a semiconductive path between the upper and lower terminals, this layer serving either to reduce the local potential gradients in the vicinities of the terminals, or to provide surface heating for minimizing condensation, or both. In order to provide good electrical contact between the metallic terminals and the semiconductive glaze layer 25, via the conductive cement 23, 24 a conductive porcelain layer having the composition hereinbefore described is applied to each of the terminal regions of the body 20, the conductive porcelain layer 26, 27 in each case extending to the semi-conductive layer and being fired on to the body at a temperature o~ 1240C for six hours.
~ eferring now to Figure 5, which illustrates another embodiment of the invention, a porcelain resistor is formed as a unitary ceramic body 30 of cylindrical shape extending between terminal caps 31, 32. The body has an elongated insulative core 33 formed of insulator clay having llO~S~36 the composition hereinbefore described. A conductive porcelain layer 34 covering the core extends continuously between the terminal caps 31, 32, this layer consisting of the same insulator clay admixed with ferric oxide in the amount necessary to provide the required resistivity, and being fired on to the body at the appropriate temperature for a time of four to eight hours in the range 1115C to 1365C. An insulating glaze 35 may be applied to encase the conductive layer. Also in this embodiment of the invention the whole ceramic body 30 can be made of conductive porcelain and covered with an insulating glaze.
An electrically conductive porcelain in accordance with the present invention consists of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15%
to 50% by dry weight of the mixture, and the porcelain being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C.
One application of the invention is to the manufacture of electrical components such as ceramic resistors. Such a resistor may comprise a unitary ceramic body having an elongated insulative core and a conductive layer thereon extending continuously between end regions of the body, the core being .., of insulator clay and the conductive layer being of the same insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50~ by dry weight of the mixture, and the body being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C.
Another important application of the invention is to high voltage electrical insulators. Such insulators are presently made radio and television interference free by the application of a highly conductive ferric oxide glaze. The glaze is applied to the body of the insulator in the vicinity of the conductor support saddle and the neck of the insulator so as to make an electrical contact with the line conductor and an associated tie wire. The equipotential region formed between the însulator, conductor and the tie wire prevents local sparking, and prevents radio and television interference.
However, as the conductive glaze extends the high voltage on to the body of the insulator, electrochemical attack of the glaze occurs during wetting by rain, dew and fog. As the surface is subject to accumulated contamination which provides --2-- ~
1~00586 a hygroscopic surface, glaze deterioration progresses until the equipotential region is lost and the insulator begins to spark. In the presence of sparking the glaze deteriorates very rapidly and sparking increases. By providing an electrically insulating surface, glaze deterioration is reduced and the useful life of the insulator is greatly increased.
The insulating layer in this case must withstand spark erosion which occurs on the surface of the insulator during wetting.
Normal porcelain glazes are well known to stand up to such harsh environments~ However, the two-layer glazing techniques presently in use tend to cause mixing of the glazes by diffusion during firing. As a result, conductive filaments ; appear at the surface of the insulator, which are prone to electrochemical attack, and this process spreads quickly to the lower conductive glaze layer and causes extensive damage as well as radio and television interference.
In order to solve this problem the present invention contemplates a porcelain insulator having an integral terminal region of conductive porcelain consisting of insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture, the surface of the body being covered by an insulative glaze layer extending to the conductive region and leaving an exposed region thereof, the conductive region and said glaze layer being fired for a time of four to eight hours at a temperature in the range 1115C to 1365C. As there is no diffusion of the ferric oxide into the insulating glaze the latter retains its protective properties.
Another Lmportant application of the invention is to high voltage electrical insulators of the type provided with a semiconductive glaze surface wherein it is necessary to make good electrical contact between the glaze and the insulator hardware. Thus, the invention provides an electrical insulator ~lOOS~36 comprising a unitary ceramic structure having a body of electrical porcelain consisting of insulator clay an~
- 3a -1~0(~5l~6 ha~ing fixst and second terminal regions, the en~ire surface of the body between said texminal regions being coyered b~ a semiconductive glaze layer and each of said terminal xegions being covered by a conductive porcelain layer extending to the semiconductive glaze layer, the conductive porcelain layer consisting of said insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% b~ dry weight o~
the mixture, and the structure being fired at a temperature for a time of foux to eight hours in the range 1115C to 1365C.
In this way good electrical contact can be made between the terminal regions and the insulator hardware, thus xeducing high potential gradients and reducing the likelihood of glaze deterioration by sparking and electrochemical attack.
Applications of electrically conductiYe porcelain will now be described by way of example wlth reference to the accompanyin~ drawings, in which:
Figure 1 is a graph illustrating the variation in surface resistivity with ferric oxide content for different conducti~e porcelain layers;
Figure 2 is a graph illustrating the variation in volume resisti~ity with ferric oxide content;, Figure 3 is a half-sectional ele~ational Yiew of a portion of a high voltage electrical insulatox according to one embodiment of the invention;
Figure 4 is a half-sectional elevational ~iew of a portion of a high voltage electrical insulator according to another embodiment of the invention; and Figure 5 illustrates an application of the in~ention to a porcelain electrical xesistor.
' In each of the em~odiments described herëin the porcelain elements of the structures are of electrical porcelain consisting of an insulator clay fired at the appro-priate temperature. A typical insulator clay consists llO(;~S86 essentiallY of ball clay, alumina and nepheline syenite, for example:
Component % by Dry Weight Ball Clay 33.5-42.5 Alumina 35-~5 Nepheline Syenite 18-22.
A specific insulator clay used by the inventors yielded the following analysis:
Ball Cl.ay 38 Alumina 40 Nepheline Syenite 20~
The conductive porcelain referred to below consists of insulator clay having the above composition admixed with ferric oxide, the ferric oxide constituting from 20% to 30% by dry weight of the mixture, This is the preferred amount of ferric oxide for most applications-, although the proportion of ferric oxide may be from 15% to 50% for some applications depending upon requirements, In general, if the proportion of ferric oxide is less than about 15% the conductivity of the porcelain is too low to be useful, whereas if the proportion o~ ferric oxide is higher than about 50%
the mechanical strength of the resultant porcelain is poor.
In the preparation of the conductive porcelain coatings, the necessary insulator clay mix with ferric oxide is prepared in accordance with the ranges outlined and then water is added to form a conductive clay slip.
This slip can be applied to the desired portions of the insulator by spraying or brushing, or the insulator can be dipped into the slip. The conductive porcelain can ~ ,??~
be used with or without glaze covering materials. Glaze forming materials provide an insulating glassy layer free of conductive protrusions. The clay body, with conductive porcelain layer with or without a glaze covering, is fired and soaked in a kiln at a temperature and for a time in the ranges specified herein.
Figure 1 illustrates the variation in surface resistivity of a conductive porcelain with ferric oxide concentration, the porcelain being applied to a substrate by dipping for 15 seconds in the case of curve A, and 2 ; seconds in the case of curve B. The slurry had viscosity of 130 mPa.s, and firing was at 1240C for 6 hours in each case.
Figure 2 illustrates the variation in volume resistivity with ferric oxide concentration of a conductive porcelain in accordance with the invention.
Referring now to Figure 3, this figure illustrates the upper portion of a typical pin-type distribution insulator having one or more bell-shaped porcelain members 10. The figure also shows an upper terminal member 11 which is formed by a unitary body of porcelain cemented to the member 10 and having a terminal region 12. The terminal region 12 is integral with the body 11 and is itself of conductive porcelain.
An insulating porcelain glaze 13 covers the surface of the body 11, extending to and partially over the conductive region 12 so as to leave an exposed conductive surface to which an electrical contact has to be made, as by a high voltage conductor.
In forming the body 11 a clay slip formed from the clay of the insulator body but containing ferric oxide in the required amount is applied to the upper end of the insulator body and around the neck 14. An insulating glaze is next applied to the entire surface of the insulator body up to the neck 14, leaving an exposed terminal portion. The composite body so formed is next fired at 1240C for six hours.
~10C~5~36 In the firing an amalgamation of the conductive clay and the insulator clay to which it is applied results, forming a - unitary porcelain body with a conductive surface at the exposed terminal portion. As there is no diffusion of the ferric oxide into the insulating glaze, the latter retain~ its protective properties.
The technique is applicable to all porcelain insulators, including bushings, post insulators and suspension insulators.
Referring now to Figure 4, an element of a pin-type high voltage insulator consists of a porcelain body 20 having an upper metallic terminal 21 and a pin 22 serving as a lower terminal. The upper terminal 21 and pin 22 are cemented to the porcelain body 20 by conductive cement 23, 24 in the manner well known in the art. The entire surface of the ~ody 20 is covered by a semiconductive glaze layer 25 which provides a semiconductive path between the upper and lower terminals, this layer serving either to reduce the local potential gradients in the vicinities of the terminals, or to provide surface heating for minimizing condensation, or both. In order to provide good electrical contact between the metallic terminals and the semiconductive glaze layer 25, via the conductive cement 23, 24 a conductive porcelain layer having the composition hereinbefore described is applied to each of the terminal regions of the body 20, the conductive porcelain layer 26, 27 in each case extending to the semi-conductive layer and being fired on to the body at a temperature o~ 1240C for six hours.
~ eferring now to Figure 5, which illustrates another embodiment of the invention, a porcelain resistor is formed as a unitary ceramic body 30 of cylindrical shape extending between terminal caps 31, 32. The body has an elongated insulative core 33 formed of insulator clay having llO~S~36 the composition hereinbefore described. A conductive porcelain layer 34 covering the core extends continuously between the terminal caps 31, 32, this layer consisting of the same insulator clay admixed with ferric oxide in the amount necessary to provide the required resistivity, and being fired on to the body at the appropriate temperature for a time of four to eight hours in the range 1115C to 1365C. An insulating glaze 35 may be applied to encase the conductive layer. Also in this embodiment of the invention the whole ceramic body 30 can be made of conductive porcelain and covered with an insulating glaze.
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrical insulator comprising a unitary ceramic structure having a body of electrical porcelain consisting of insulator clay, the body having first and second terminal regions, the entire surface of the body between said terminal regions being covered by a semiconductive glaze layer, and each of said terminal regions being covered by a conductive porcelain layer extending to the semiconductive glaze layer, the conductive porcelain layer consisting of said insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture and the structure being fired for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
2. A composite electrical insulator comprising a string of interconnected insulator members each comprising a unitary ceramic structure having a body of electrical porcelain con-sisting of insulator clay, the body having first and second terminal regions, the entire surface of the body between said terminal regions being covered by a semiconductive glaze layer, and each of said terminal regions being covered by a conductive porcelain layer extending to the semiconductive glaze layer, the conductive porcelain layer consisting of said insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50% by dry weight of the mixture, and the structure being fired for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
3. A porcelain insulator comprising a unitary ceramic structure including a body of electrical porcelain consisting of insulator clay and an integral terminal region of conductive porcelain consisting of said insulator clay admixed with ferric oxide, the ferric oxide constituting from 15% to 50%
by dry weight of the mixture, the surface of said body being covered by an insulating glaze layer extending to the conductive terminal region and leaving an exposed region thereof, and the structure being fired for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
by dry weight of the mixture, the surface of said body being covered by an insulating glaze layer extending to the conductive terminal region and leaving an exposed region thereof, and the structure being fired for a time of four to eight hours at a temperature in the range 1115°C to 1365°C.
4. An electrical insulator according to claim 1, the insulator clay consisting essentially of ball clay, alumina and nepheline syenite.
5. An electrical insulator according to claim 4, wherein the ferric oxide constitutes from 20% to 30% by dry weight of the mixture.
6. A composite electrical insulator according to claim 2, the insulator clay consisting essentially of ball clay, alumina and nepheline syenite.
7. A composite electrical insulator according to claim 6, wherein the ferric oxide constitutes from 20% to 30% by dry weight of the mixture.
8. A porcelain insulator body according to claim 3, the insulator clay consisting essentially of ball clay, alumina and nepheline syenite.
9. A porcelain insulator body according to claim 8, wherein the ferric oxide constitutes from 20% to 30% by dry weight of the mixture.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US90101578A | 1978-04-27 | 1978-04-27 | |
| US901,015 | 1978-04-27 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1100586A true CA1100586A (en) | 1981-05-05 |
Family
ID=25413473
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA306,188A Expired CA1100586A (en) | 1978-04-27 | 1978-06-26 | Application of conductive porcelain to electrical insulators |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1100586A (en) |
-
1978
- 1978-06-26 CA CA306,188A patent/CA1100586A/en not_active Expired
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| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |