CA2046682A1 - High voltage insulator - Google Patents
High voltage insulatorInfo
- Publication number
- CA2046682A1 CA2046682A1 CA 2046682 CA2046682A CA2046682A1 CA 2046682 A1 CA2046682 A1 CA 2046682A1 CA 2046682 CA2046682 CA 2046682 CA 2046682 A CA2046682 A CA 2046682A CA 2046682 A1 CA2046682 A1 CA 2046682A1
- Authority
- CA
- Canada
- Prior art keywords
- core
- strip
- high voltage
- silicone
- insulator
- 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.)
- Abandoned
Links
Landscapes
- Insulating Bodies (AREA)
Abstract
HIGH VOLTAGE INSULATOR
ABSTRACT
A process for making a high voltage insulator extrudes a silicone rubber high voltage insulator stock into a parallelogram shaped strip having the minor surfaces at an angle of less than 45°C. to the major surfaces. The outer major surface can have a shed formed on it. The strip is spirally wound around a core, having its outer surface coated with a primer, so that adjacent surfaces of the strip overlap each other to give a continuous, homogeneous, uniformly thick covering over the core. A pressure roll is applied to the cover at the point where adjacent turns overlap to slightly work the surfaces together. When the core is completely covered, it is placed into an oven to vulcanize the silicone high voltage insulation stock.
ABSTRACT
A process for making a high voltage insulator extrudes a silicone rubber high voltage insulator stock into a parallelogram shaped strip having the minor surfaces at an angle of less than 45°C. to the major surfaces. The outer major surface can have a shed formed on it. The strip is spirally wound around a core, having its outer surface coated with a primer, so that adjacent surfaces of the strip overlap each other to give a continuous, homogeneous, uniformly thick covering over the core. A pressure roll is applied to the cover at the point where adjacent turns overlap to slightly work the surfaces together. When the core is completely covered, it is placed into an oven to vulcanize the silicone high voltage insulation stock.
Description
HIGH VOLTAG~ INSULATOR
This invention relates to composite high voltage insulators and bushings.
Insulators and bushings for use at high voltages have been developed which are manufactured using a number of different materials in the same unit. Current practice forms a central rod or tube of fiber reinforced resin, such as a tube of epoxy resin reinforced with glass fibers. The rod or tube provides physical strength to the unit. The outer surface of the rod or tube is then covered with a layer of insulation material to provide the surface electrical characteristics which are required for high voltage insulators and to protect the core tube or rod from the effects of weathering, moisture and electrical arcing on the surface of the insulator. The surface layer is usually shaped so as to form a series of sheds on the insulator surface to provide an extended leakage distance. The insulation layer has been applied to the rod or tube by direct molding, forming of sheds and then applying the sheds over the rod or tube and by forming a strip and spirally winding the strip over the rod or shed.
U.S. Patent No. 3,484,938, issued December 23, 1969, teaches an electrical insulator formed of a resili,ent strip of insulating material having at least one shed extending from one surface thereof and having a keyway extending along the other surface near the other edge whereby ad~acent turns are interlocked with each other and a spiral shed is formed which extends along the length of the insulation structure.
Swiss Patentschrift CH 659 907 A5, published on February 27, 1987, claims an insulator consisting at least , ~ .
, ~ .
partly of plastic and a cover consisting of an elastic material with at least one premanufactured part with a screen profile which with one contact surface lies adjacent to the outer surface of the carrier, the premanufactured part being a longitudinal screen profile which runs in several sequential windings around the carrier. A bonding agent is used to adhere the sequential windings together where they contact each other.
A process for producing a composite high voltage insulator is described. The process extrudes a silicone high voltage insulation material into a parallelogram having a shed on one surface and wraps the extrusion around an insulating core over a silicone primer surface, the joint between the wraps is compressed with a roller and the covered core assembly is placed in an oven and cured.
It is an ob~ect of this invention to produce a high voltage insulator comprising a core covered with a continuous coating of silicone high voltage material with sheds on the outer surface, there being no seams or voids present in the cured coating.
Figure 1 of the drawings is a view of a tubular insulator made in accordance with this invention, partly in 8 ection, showing the construction.
Figure 2 is a cross section of the extruded strip used to form the covering on the insulator core in accordance with this invention.
Figure 3 is a view of the method of this invention for extruding the strip and spirally winding it around the cylindrical core and of a pressure roll means used to help seal the ~oint between turns.
Figure 4 is a cross section of the insulator of this invention being formed in Figure 3.
.
' . " . , . ,. . . ..
. :
,,. ' ~ '' ' ~:
- ., ~ 3~
This invention relates to a high voltage insulator comprising a cylindrical, electrically insulating core, the core having a covering adhered to its outer surface from one end to the other and completely covering the outer surface, the covering being a silicone high voltage insulation material which is extruded into the form of a parallelogram shaped strip having a shed formed upon one surface of the strip, the edges of the strip being at an angle of less than 45C., with the strip being wound in a spiral from one end of the core to the other to completely cover the core surface, the angled edges of the strip being overlapped so that the thickness of the strip is uniform and the surface of the strip having the shed being on the outer surface, so that the shed forms a spiral from one end of the core to the other and the parallelogram shaped strip forms a uniform covering over the core; and to a method for producing the insulator. The method comprises (A) extruding a silicone high voltage insulation stock into a strip in the form of a parallelogram with a shed formed on the upper major surface of the strip and the parallel minor surfaces of the strip at an angle of less than 45C. to the ma~or surfaces, (B) immediately after extruding and simultaneously with the extrusion process, spirally winding the strip being extruded over the outer surface of the core, the core having been coated with a silicone primer, the core being rotated at a rate equal to the extrusion rate of the strip and being advanced past the extruder at a rate 90 that the core advances a distance equal to the width of the strip with each revolution of the core, beginning the winding at one end of the core and winding in a manner such that the shed is on the outer surface and the minor surfaces of the strip overlap each other to give a uniform thickness along the surface of the core, the strip being wound smoothly against the core surface so that no air , . - .. . .: ~, " j ,.. ... ...
is entrapped between the core surface and the lower major surface of the strip, (C) applying a pressure means against the strip in the space between the sheds and applying pressure to .he strip at the joint between turns of the strip to assure that there is no air entrapped in the joint, then, when the core is completely covered, (D) placing the covered core into an oven and heating to vulcanize the silicone rubber covering.
Large high voltage insulators and bushings have been conventionally produced by forming them of clay and firing to give a homogeneous structure of glass or porcelain.
As voltages increased, the size of the required insulators increased and the porcelain insulator construction and weight became ma~or problems. Composite insulators have been constructed using a fiberglass reinforced resin rod or tube as the body. This is protected from the effects of weather by covering with a resinous or elastomeric cover. The cover is applied to completely enclose the core. The cover can be formed on the outer surface so that it contains sheds to increase the leakage distance of the insulator. This cover and the associated sheds have been applied in many ways, for example, by molding elastomeric rings containing sheds and tightly fitting them over the core. This procedure means that the surface between the core and the ring and the ~oints between rings are potential failure points. In an attempt to eliminate the ~oints, insulators have been made by ln~ection molding the covering and sheds onto a core placed inside a mold. This procedure requires a very expensive and complicated mold for every different size desired. A method of production whereby a premanufactured part with a screen profile runs in several sequential windings around the outer surface of a carrier is also known. The profile is bonded to the surface of the carrier and the boundary surfaces of .
- - . . .: . , , :, ..
: ~ . . . .
- ~ :
adjacent windings are cemented along the joint formed between them. The discontinuities of the cemented joint provide a source of potential failure due to water ingress.
The process herein described was developed to eliminate any discontinuities in the covering so that there would be no potential failure points. A strip is extruded of silicone high voltage insulation stock. This uncured strip is then spirally wrapped around an insulative core which has been coated on the outer surface with a silicone primer. The joint between the adjacent windings is shaped at an angle of less than 45C. so that as the strip is wound, each succeeding winding falls over the preceding one to give a uniform thickness to the covering between any sheds. There i~ no adhesive applied to the joint. The unvulcanized silicone stock used to form the strip bonds to itself without the use of an adhesive. When the windings have been applied to the core, the joint between them is subjected to mild pressure with a pressure means such as a roller to ensure that there are no voids present between the surfaces. After the core to completely covered, the insulator is placed in an oven to vulcanize the silicone high voltage insulation material. The result is a core completely covered with a homogenou~ sheet of silicone high voltage insulation rubber, which is bonded to the core in a void free manner.
The process can be better explained by reference to the drawings. Figure 3 is an illustration of the process.
The silicone high voltage insulation stock used in this invention is placed into the extruder 20 and extruded through the die to give the strip 14. This extruded strip 14 is shown in cross section in figure 2. The strip is in the shape of a parallelogram with ma~or surfaces 18a and 18b.
The minor surfaces are shown as 17a and 17b. The ma~or surface which is to the outside when wrapped around the core s has at least one shed 15 formed on it to increase the flashover distance of the finished insulator. The angle 16 between the major and minor surfaces is less than 45C., for example, 30C. It has been found that when the angle is greater than 45C., it is more difficult to obtain a homogeneous joint which does not contain any voids. The lower ma~or surface 18b of strip 14 is shown in Fig. 2 as flat. It can also be crowned with the center of the strip being 1 mm thicker for a strip having a width of 45 mm for instance. This crowned shape helps to force the air between the strip and the primed core out as the strip is being wound onto the primed core. Another means to aid in removing the air at this interface has been found to be the addition of a series of small ridges on the under major surface 18b.
Triangular ribs about 1/2 mm high and 3 mm apart across this surface were found to aid the removal of air at this surface during the rolling of the joint with a pressure roller means.
The shape and size of the shed 15 is dictated by the design of the finished insulator. A taller shed, for example, would result in a longer leakage distance, while a thicker shed would re9ult in a stiffer construction, but require more material to be used. The desired shape and size of the shed is determined by taking into consideration these various factors. The strip 14, consisting of the parallelogram shaped base and the shed 15 is wound around the electrically insulative core 11 by rotating the core 11 as shown in Fig. 3 90 that the surface speed of the core 11 is the same as the extrusion rate of the strip 14. The strip 14 is placed onto the surface of the core 11 so that the bottom of the strip 14 fits tightly against the silicone primer 13 which has been previously placed on the outer surface of the core 11. When the covered core is placed in an oven and vulcanized in step (D) of the process, the strip 14 is firmly bonded to the core .
.. ~ . .
,. ,. . :
, 11 through the silicone primer 13 with no voids between them.
As the core 11 is being rotated, it is also moved laterally at a rate so that the core moves forward in one revolution a distance equal to the width of the strip 14. The minor surface of the strip 17a fits over the corresponding minor surface 17b so that the result is a covering having a uniform thickness. The angle of the minor surfaces 17a and 17b to the corresponding major surfaces 18a and 18b is shown as <
16. This angle is less than 45C., for example 30C. As the strip 14 is wound, it has been discovered that the number of voids trapped in the joint between the surfaces 17a and 17b is greatly reduced or eliminated by making the angle less than 45C. so that as the strip is wound there is a natural tendency for any air between the turns to be expelled along the ~oint by the force of the outer turn bearing against the inner turn at the ~oint. There is no adhesive or bonding agent present at the joint between minor surfaces 17a and 17b. The absence of any adhesive at this point results in a homogeneous covering over the core 11. As a further means of insuring that there are no voids in the joint between minor surfaces 17a and 17b, a pressure means is applied over the ~oint. A pressure means is shown in figures 3 and 4 as a pre~sure roller 21. A pressure roller 21 is applied as shown in Figures 3 and 4 to the outer surface of the insulator, at least one revolution away from the point of applying the strip 14 to the core 11, to further force minor surfaces 17a and 17b tightly together. The force applied by the pressure roller 21 is ~ust sufficient to cause the ~oining and smoothing of the silicone high voltage insulation stock together at the ~oint between minor surfaces 17a and 17b.
Because the strip 14 is made of silicone rubber stock which i8 soft and plastic at this point, the two strips bond to each other at the point of overlap and the joint between the .,~
' ' ' ' ' ~ ~ ' ' ' ' ,'"" , ' , '' .' ~, ~'' ,. ,' . ' , ' , .' ' ':
: , '~ ''~''.". ' '" ".;, minor surfaces 17a and 17b essentially disappears after being worked slightly by the presence of the pressure means, for example pressure roll 21. The pressure roll 21 preferably has a surface coating, such as a silicone resin or Teflon, which prevents the roll from adhering to the silicone rubber stock of strip 14. Several light passes of pressure roll 21 could be used if desired, particularly if the silicone rubber stock is soft and easily flowable. If an insulator being constructed is removed from the process and a section of the covering is cut away to reveal the joint between minor ~urfaces 17a and 17b, it is no longer possible to locate the joint after the joint area has been subjected to the action of the pressure roller 21, since the strip 14 is then a homogeneous cover 12. An alternate means of applying pressure to the joint wraps a smooth polymeric tape, such as Mylar, over the joint with enough tension to apply pressure to the ~oint. The tape is held in place until the cover has been vulcanized in step (D) of the method. This process of applying the strip 14 to the core 11 and applying a pressure means to the joint at surfaces 17a and 17b is continued in a continuous manner until the entire core 11 is completely covered. The covered core is then placed into an oven and heated for the time and at the necessary temperature to completely cure the silicone high voltage insulation stock to give a core 11 covered by a silicone rubber cover 12 The covered core can also be vulcanized by placing into a steam autoclave or into a pressurized container of hot fluid, a silicone oil for example.
The core 11 used in this invention has a rotational shape, that is, it i9 has a circular cross section, such as a hollow cylinder or solid rod. Using a properly designed machine, the process could also be used with a non-uniform rotational shape such as a segment of a cone or a barrel ": ' ~ . ' ''' ; :
:~:
,, shape. The preferred shape is a cylinder (tube) or rod.
Since the psrt being made is a high voltage insulator, the material used to make the core must be capable of acting as an insulator at the design voltage of the insulator. The core must be a high quality insulator, having a high electrical resistivity under the use conditions. A preferred core material is a glass fiber reinforced plastic where the plastic used is capable of providing high electrical resistivity under the use conditions. Preferred are thermosetting plastics such as polyester resins and epoxy resins. The glass fiber reinforcement can be in the form of fabric or filaments. In the case of a rod as the core, the construction is preferably unidirectional fibers extending the length of the core and bound together in a void free manner by an epoxy resin. The glass fiber can be treated with a coupling agent to improve the bond between the glass fiber and the resin. Either glass fabric or glass roving is commonly used to produce hollow cylinders or tubes.
The silicone primer 13 used in this invention is used to ensure a void free bond between the outer surface of the core and the silicone high voltage insulation material used to form strip 14. The choice of primer will depend upon the selection of materials used for the core 11 and the strip 14. When a fiber glass reinforced epoxy resin tube was used as the core and a peroxide cured, vinyl-containing polydi-methyl9iloxane was used in the high voltage silicone insulation stock, a useful primer was found to be a solvent dispersed silicone primer comprising a 20 percent solids dispersion in trichloroethane of vinyl-containing polydimethylsiloxane having a Williams Plasticity Number of about 150 and reinforced with fumed silica and aluminum trihydrate which was curable through a platinum catalyzed hydrosilation reaction.
,:
A silicone high voltage insulation material is chosen so that it has the necessary functional characteristics both in the uncured state and in the cured state. In the uncured state the stock needs sufficient green strength and a high enough Williams plasticity at ambient temperature to be able to hold the die shape and not sag or droop, but still be pliable enough to allow winding tightly against the core and to allow the surfaces 17a and 17b to form tightly together. A silicone insulation stock that was shown to be useful in this process had a Williams Plasticity Number of about 225, measured in accordance with ASTM D 926.
The compo~ition of the high voltage insulation stock used is such that the stock used is capable of giving the necessary electrical properties to the finished insulator. The stock needs to have high arc resistance and low water absorption.
A suitable high voltage insulation stock is discussed in U.S.
Patent No. 4,749,824, issued June 7, 1988, to show preferred high voltage insulation stock and examples of suitable tests which determine the suitability of the stock for use in high voltage insulators from an electrical standpoint.
The silicone high voltage insulation material used in this method i8 preferably one comprising a mixture of 100 parts by weight of polydiorganosiloxane having dimethylvinyl-siloxy endblocking and predominantly methyl groups as the organo groups, from 10 to 20 parts by weight of fumed silica having a surface area of greater than 50 m2/g, from 90 to 220 parts by weight of aluminum trihydrate and a curing means for the polydiorgano8iloxane.
The insulator produced by the method described above iY particularly suitable for use at high voltage because the method produces a core covered by a homogeneous covering which iY attached to the core without any voids being present. The silicone high voltage insulation stock . .; .
: .
:: .. . . .
cures to give a homogeneous material which has been shown to be particularly suitable for high voltages, for example, 220 Rv and higher. The absence of voids, or of discontinuities due to the use of differing materials in the covering, insures that the covering will provide the protection desired for the core even in the presence of long time weathering and exposure to high voltages.
Example 1 A core 11 was obtained in the form of a fiber glass reinforced epoxy tube, having an outer diameter of 147 mm and a length of 820 mm. The surface of the tube was coated with a silicone primer. The primer was a 20 percent solids dispersion in trichloroethane comprising 100 parts of a silicone base of 100 parts of hydroxyl endblocked polydiorganosiloxane having about 0.15 mole percent vinyl radicals with the remainder methyl radicals, 55 p~rts of fumed silica, 7 parts of hydroxyl endblocked polydimethylsiloxane fluid having a viscosity of about 0.04 Pa-s at 25C. and about 4 weight percent silicon-bonded hydroxyl radicals, 5 parts of diphenylsilanediol and 1 part of hydroxyl endblocked polymethylvinylsiloxane having about 4 weight percent hydroxyl radical; 5 parts of aluminum trihydrate, .8 part of trimethylsiloxy endblocked polydiorganosiloxane having an average of five methylhydrogensiloxane units and three dimethylsiloxane units per molecule with a silicon-bonded hydrogen atom content in the range of about 0.7 to 0.8 weight percent, .15 part of methyl butynol and .55 part of a platinum catalyst mixture having about .22 percent platinum.
A die was prepared for a 3 inch Davis Standard extruder which extruded a strip 14 having a ma~or surface of 45 mm and a minor surface of 20 mm with a thickness of 10 mm.
., ! " ' ~
,, ~ " .. ''~ :
`' " ' ~ ' " : ' A shed 15 was formed at the center of the major surface with a thickness of 5 mm and a height of 35 mm.
A winding machine was constructed which turned the core 11 at 0.5 revolutions per minute and moved it past the extruder 20 at a rate of 45 mm per revolution.
A high voltage silicone rubber insulation stock was prepared by mixing 100 parts by weight of dimethylvinylsiloxy endblocked polydimethylsiloxane having a Williams plasticity number of about 150, 15 parts of fume silica having a surface area of about 250 m2/g, 8 parts of hydroxyl endblocked polydimethylsiloxane fluid having a viscosity of about 0.04 Pa-s at 25C. and about 4 weight percent silicon-bonded hydroxyl radicals, 1 part of hydroxyl endblocked polydiorganosiloxane having methyl and vinyl radicals and having about 10 weight percent vinyl radical and about 16 weight percent hydroxyl radical and 200 parts of aluminum trihydrate. This mixture was heated after mixing for about 1 hour at a temperature of about 175C., then cooled to give a base material. The base was catalyzed with 1.5 parts of catalyst paste of 50 percent 2,4-dichlorobenzoyl peroxide in polydiorganosiloxane fluid per 100 parts of base to give the high voltage insulation stock.
The high voltage insulation stock was fed to the extruder and the extruder adjusted so that the strip 14 as shown in Fig. 2 was extruded at a rate of 230 mm per minute.
The extrusion pressure was about 70 kg/cm2. The extruded strip wa9 then fed to the revolving core 11 so that it wound around the outer top surface. The width of the strip 14 was 45 mm and the core 11 was moved past the extruder at a rate of 45 mm per revolution so that each succeeding wrapping exactly overlapped at minor surfaces 17a and 17b and these surfaces fit tightly together. A pressure roller 21 was applied to the ~oint formed by surfaces 17a and 17b with a , ' , . : .
. .
...
.
force against the joint of about 1.75 kg/cm2. The roller had a diameter of 130 mm and a thickness of 42 mm. The surface of the roller had been coated with a silicone resin which prevented the uncured silicone rubber from adhering to the roller. The pressure roller exerted just enough pressure on the 30int to force the surfaces 17a and 17b tightly together, but not enough pressure to cause the plastic material to flow away from under the roller. After pressing, the joint was no longer visible. This process was continued until the entire core wa9 completely covered with the extruded strip.
The covered core was then suspended in an air circulating oven at 150C. for 1/2 hour to vulcanize the cover of silicone rubber. The cover consisted of 7850 mm of the extrusion, which weighed 115 g per 100 mm, to give a total cover weight of about 9 kg. The finished insulator was evaluated and found to perform as expected.
.
: . ' ~ ';. . . :
. . . :
. . -: . . , .::
- . ~ - ,:. :
This invention relates to composite high voltage insulators and bushings.
Insulators and bushings for use at high voltages have been developed which are manufactured using a number of different materials in the same unit. Current practice forms a central rod or tube of fiber reinforced resin, such as a tube of epoxy resin reinforced with glass fibers. The rod or tube provides physical strength to the unit. The outer surface of the rod or tube is then covered with a layer of insulation material to provide the surface electrical characteristics which are required for high voltage insulators and to protect the core tube or rod from the effects of weathering, moisture and electrical arcing on the surface of the insulator. The surface layer is usually shaped so as to form a series of sheds on the insulator surface to provide an extended leakage distance. The insulation layer has been applied to the rod or tube by direct molding, forming of sheds and then applying the sheds over the rod or tube and by forming a strip and spirally winding the strip over the rod or shed.
U.S. Patent No. 3,484,938, issued December 23, 1969, teaches an electrical insulator formed of a resili,ent strip of insulating material having at least one shed extending from one surface thereof and having a keyway extending along the other surface near the other edge whereby ad~acent turns are interlocked with each other and a spiral shed is formed which extends along the length of the insulation structure.
Swiss Patentschrift CH 659 907 A5, published on February 27, 1987, claims an insulator consisting at least , ~ .
, ~ .
partly of plastic and a cover consisting of an elastic material with at least one premanufactured part with a screen profile which with one contact surface lies adjacent to the outer surface of the carrier, the premanufactured part being a longitudinal screen profile which runs in several sequential windings around the carrier. A bonding agent is used to adhere the sequential windings together where they contact each other.
A process for producing a composite high voltage insulator is described. The process extrudes a silicone high voltage insulation material into a parallelogram having a shed on one surface and wraps the extrusion around an insulating core over a silicone primer surface, the joint between the wraps is compressed with a roller and the covered core assembly is placed in an oven and cured.
It is an ob~ect of this invention to produce a high voltage insulator comprising a core covered with a continuous coating of silicone high voltage material with sheds on the outer surface, there being no seams or voids present in the cured coating.
Figure 1 of the drawings is a view of a tubular insulator made in accordance with this invention, partly in 8 ection, showing the construction.
Figure 2 is a cross section of the extruded strip used to form the covering on the insulator core in accordance with this invention.
Figure 3 is a view of the method of this invention for extruding the strip and spirally winding it around the cylindrical core and of a pressure roll means used to help seal the ~oint between turns.
Figure 4 is a cross section of the insulator of this invention being formed in Figure 3.
.
' . " . , . ,. . . ..
. :
,,. ' ~ '' ' ~:
- ., ~ 3~
This invention relates to a high voltage insulator comprising a cylindrical, electrically insulating core, the core having a covering adhered to its outer surface from one end to the other and completely covering the outer surface, the covering being a silicone high voltage insulation material which is extruded into the form of a parallelogram shaped strip having a shed formed upon one surface of the strip, the edges of the strip being at an angle of less than 45C., with the strip being wound in a spiral from one end of the core to the other to completely cover the core surface, the angled edges of the strip being overlapped so that the thickness of the strip is uniform and the surface of the strip having the shed being on the outer surface, so that the shed forms a spiral from one end of the core to the other and the parallelogram shaped strip forms a uniform covering over the core; and to a method for producing the insulator. The method comprises (A) extruding a silicone high voltage insulation stock into a strip in the form of a parallelogram with a shed formed on the upper major surface of the strip and the parallel minor surfaces of the strip at an angle of less than 45C. to the ma~or surfaces, (B) immediately after extruding and simultaneously with the extrusion process, spirally winding the strip being extruded over the outer surface of the core, the core having been coated with a silicone primer, the core being rotated at a rate equal to the extrusion rate of the strip and being advanced past the extruder at a rate 90 that the core advances a distance equal to the width of the strip with each revolution of the core, beginning the winding at one end of the core and winding in a manner such that the shed is on the outer surface and the minor surfaces of the strip overlap each other to give a uniform thickness along the surface of the core, the strip being wound smoothly against the core surface so that no air , . - .. . .: ~, " j ,.. ... ...
is entrapped between the core surface and the lower major surface of the strip, (C) applying a pressure means against the strip in the space between the sheds and applying pressure to .he strip at the joint between turns of the strip to assure that there is no air entrapped in the joint, then, when the core is completely covered, (D) placing the covered core into an oven and heating to vulcanize the silicone rubber covering.
Large high voltage insulators and bushings have been conventionally produced by forming them of clay and firing to give a homogeneous structure of glass or porcelain.
As voltages increased, the size of the required insulators increased and the porcelain insulator construction and weight became ma~or problems. Composite insulators have been constructed using a fiberglass reinforced resin rod or tube as the body. This is protected from the effects of weather by covering with a resinous or elastomeric cover. The cover is applied to completely enclose the core. The cover can be formed on the outer surface so that it contains sheds to increase the leakage distance of the insulator. This cover and the associated sheds have been applied in many ways, for example, by molding elastomeric rings containing sheds and tightly fitting them over the core. This procedure means that the surface between the core and the ring and the ~oints between rings are potential failure points. In an attempt to eliminate the ~oints, insulators have been made by ln~ection molding the covering and sheds onto a core placed inside a mold. This procedure requires a very expensive and complicated mold for every different size desired. A method of production whereby a premanufactured part with a screen profile runs in several sequential windings around the outer surface of a carrier is also known. The profile is bonded to the surface of the carrier and the boundary surfaces of .
- - . . .: . , , :, ..
: ~ . . . .
- ~ :
adjacent windings are cemented along the joint formed between them. The discontinuities of the cemented joint provide a source of potential failure due to water ingress.
The process herein described was developed to eliminate any discontinuities in the covering so that there would be no potential failure points. A strip is extruded of silicone high voltage insulation stock. This uncured strip is then spirally wrapped around an insulative core which has been coated on the outer surface with a silicone primer. The joint between the adjacent windings is shaped at an angle of less than 45C. so that as the strip is wound, each succeeding winding falls over the preceding one to give a uniform thickness to the covering between any sheds. There i~ no adhesive applied to the joint. The unvulcanized silicone stock used to form the strip bonds to itself without the use of an adhesive. When the windings have been applied to the core, the joint between them is subjected to mild pressure with a pressure means such as a roller to ensure that there are no voids present between the surfaces. After the core to completely covered, the insulator is placed in an oven to vulcanize the silicone high voltage insulation material. The result is a core completely covered with a homogenou~ sheet of silicone high voltage insulation rubber, which is bonded to the core in a void free manner.
The process can be better explained by reference to the drawings. Figure 3 is an illustration of the process.
The silicone high voltage insulation stock used in this invention is placed into the extruder 20 and extruded through the die to give the strip 14. This extruded strip 14 is shown in cross section in figure 2. The strip is in the shape of a parallelogram with ma~or surfaces 18a and 18b.
The minor surfaces are shown as 17a and 17b. The ma~or surface which is to the outside when wrapped around the core s has at least one shed 15 formed on it to increase the flashover distance of the finished insulator. The angle 16 between the major and minor surfaces is less than 45C., for example, 30C. It has been found that when the angle is greater than 45C., it is more difficult to obtain a homogeneous joint which does not contain any voids. The lower ma~or surface 18b of strip 14 is shown in Fig. 2 as flat. It can also be crowned with the center of the strip being 1 mm thicker for a strip having a width of 45 mm for instance. This crowned shape helps to force the air between the strip and the primed core out as the strip is being wound onto the primed core. Another means to aid in removing the air at this interface has been found to be the addition of a series of small ridges on the under major surface 18b.
Triangular ribs about 1/2 mm high and 3 mm apart across this surface were found to aid the removal of air at this surface during the rolling of the joint with a pressure roller means.
The shape and size of the shed 15 is dictated by the design of the finished insulator. A taller shed, for example, would result in a longer leakage distance, while a thicker shed would re9ult in a stiffer construction, but require more material to be used. The desired shape and size of the shed is determined by taking into consideration these various factors. The strip 14, consisting of the parallelogram shaped base and the shed 15 is wound around the electrically insulative core 11 by rotating the core 11 as shown in Fig. 3 90 that the surface speed of the core 11 is the same as the extrusion rate of the strip 14. The strip 14 is placed onto the surface of the core 11 so that the bottom of the strip 14 fits tightly against the silicone primer 13 which has been previously placed on the outer surface of the core 11. When the covered core is placed in an oven and vulcanized in step (D) of the process, the strip 14 is firmly bonded to the core .
.. ~ . .
,. ,. . :
, 11 through the silicone primer 13 with no voids between them.
As the core 11 is being rotated, it is also moved laterally at a rate so that the core moves forward in one revolution a distance equal to the width of the strip 14. The minor surface of the strip 17a fits over the corresponding minor surface 17b so that the result is a covering having a uniform thickness. The angle of the minor surfaces 17a and 17b to the corresponding major surfaces 18a and 18b is shown as <
16. This angle is less than 45C., for example 30C. As the strip 14 is wound, it has been discovered that the number of voids trapped in the joint between the surfaces 17a and 17b is greatly reduced or eliminated by making the angle less than 45C. so that as the strip is wound there is a natural tendency for any air between the turns to be expelled along the ~oint by the force of the outer turn bearing against the inner turn at the ~oint. There is no adhesive or bonding agent present at the joint between minor surfaces 17a and 17b. The absence of any adhesive at this point results in a homogeneous covering over the core 11. As a further means of insuring that there are no voids in the joint between minor surfaces 17a and 17b, a pressure means is applied over the ~oint. A pressure means is shown in figures 3 and 4 as a pre~sure roller 21. A pressure roller 21 is applied as shown in Figures 3 and 4 to the outer surface of the insulator, at least one revolution away from the point of applying the strip 14 to the core 11, to further force minor surfaces 17a and 17b tightly together. The force applied by the pressure roller 21 is ~ust sufficient to cause the ~oining and smoothing of the silicone high voltage insulation stock together at the ~oint between minor surfaces 17a and 17b.
Because the strip 14 is made of silicone rubber stock which i8 soft and plastic at this point, the two strips bond to each other at the point of overlap and the joint between the .,~
' ' ' ' ' ~ ~ ' ' ' ' ,'"" , ' , '' .' ~, ~'' ,. ,' . ' , ' , .' ' ':
: , '~ ''~''.". ' '" ".;, minor surfaces 17a and 17b essentially disappears after being worked slightly by the presence of the pressure means, for example pressure roll 21. The pressure roll 21 preferably has a surface coating, such as a silicone resin or Teflon, which prevents the roll from adhering to the silicone rubber stock of strip 14. Several light passes of pressure roll 21 could be used if desired, particularly if the silicone rubber stock is soft and easily flowable. If an insulator being constructed is removed from the process and a section of the covering is cut away to reveal the joint between minor ~urfaces 17a and 17b, it is no longer possible to locate the joint after the joint area has been subjected to the action of the pressure roller 21, since the strip 14 is then a homogeneous cover 12. An alternate means of applying pressure to the joint wraps a smooth polymeric tape, such as Mylar, over the joint with enough tension to apply pressure to the ~oint. The tape is held in place until the cover has been vulcanized in step (D) of the method. This process of applying the strip 14 to the core 11 and applying a pressure means to the joint at surfaces 17a and 17b is continued in a continuous manner until the entire core 11 is completely covered. The covered core is then placed into an oven and heated for the time and at the necessary temperature to completely cure the silicone high voltage insulation stock to give a core 11 covered by a silicone rubber cover 12 The covered core can also be vulcanized by placing into a steam autoclave or into a pressurized container of hot fluid, a silicone oil for example.
The core 11 used in this invention has a rotational shape, that is, it i9 has a circular cross section, such as a hollow cylinder or solid rod. Using a properly designed machine, the process could also be used with a non-uniform rotational shape such as a segment of a cone or a barrel ": ' ~ . ' ''' ; :
:~:
,, shape. The preferred shape is a cylinder (tube) or rod.
Since the psrt being made is a high voltage insulator, the material used to make the core must be capable of acting as an insulator at the design voltage of the insulator. The core must be a high quality insulator, having a high electrical resistivity under the use conditions. A preferred core material is a glass fiber reinforced plastic where the plastic used is capable of providing high electrical resistivity under the use conditions. Preferred are thermosetting plastics such as polyester resins and epoxy resins. The glass fiber reinforcement can be in the form of fabric or filaments. In the case of a rod as the core, the construction is preferably unidirectional fibers extending the length of the core and bound together in a void free manner by an epoxy resin. The glass fiber can be treated with a coupling agent to improve the bond between the glass fiber and the resin. Either glass fabric or glass roving is commonly used to produce hollow cylinders or tubes.
The silicone primer 13 used in this invention is used to ensure a void free bond between the outer surface of the core and the silicone high voltage insulation material used to form strip 14. The choice of primer will depend upon the selection of materials used for the core 11 and the strip 14. When a fiber glass reinforced epoxy resin tube was used as the core and a peroxide cured, vinyl-containing polydi-methyl9iloxane was used in the high voltage silicone insulation stock, a useful primer was found to be a solvent dispersed silicone primer comprising a 20 percent solids dispersion in trichloroethane of vinyl-containing polydimethylsiloxane having a Williams Plasticity Number of about 150 and reinforced with fumed silica and aluminum trihydrate which was curable through a platinum catalyzed hydrosilation reaction.
,:
A silicone high voltage insulation material is chosen so that it has the necessary functional characteristics both in the uncured state and in the cured state. In the uncured state the stock needs sufficient green strength and a high enough Williams plasticity at ambient temperature to be able to hold the die shape and not sag or droop, but still be pliable enough to allow winding tightly against the core and to allow the surfaces 17a and 17b to form tightly together. A silicone insulation stock that was shown to be useful in this process had a Williams Plasticity Number of about 225, measured in accordance with ASTM D 926.
The compo~ition of the high voltage insulation stock used is such that the stock used is capable of giving the necessary electrical properties to the finished insulator. The stock needs to have high arc resistance and low water absorption.
A suitable high voltage insulation stock is discussed in U.S.
Patent No. 4,749,824, issued June 7, 1988, to show preferred high voltage insulation stock and examples of suitable tests which determine the suitability of the stock for use in high voltage insulators from an electrical standpoint.
The silicone high voltage insulation material used in this method i8 preferably one comprising a mixture of 100 parts by weight of polydiorganosiloxane having dimethylvinyl-siloxy endblocking and predominantly methyl groups as the organo groups, from 10 to 20 parts by weight of fumed silica having a surface area of greater than 50 m2/g, from 90 to 220 parts by weight of aluminum trihydrate and a curing means for the polydiorgano8iloxane.
The insulator produced by the method described above iY particularly suitable for use at high voltage because the method produces a core covered by a homogeneous covering which iY attached to the core without any voids being present. The silicone high voltage insulation stock . .; .
: .
:: .. . . .
cures to give a homogeneous material which has been shown to be particularly suitable for high voltages, for example, 220 Rv and higher. The absence of voids, or of discontinuities due to the use of differing materials in the covering, insures that the covering will provide the protection desired for the core even in the presence of long time weathering and exposure to high voltages.
Example 1 A core 11 was obtained in the form of a fiber glass reinforced epoxy tube, having an outer diameter of 147 mm and a length of 820 mm. The surface of the tube was coated with a silicone primer. The primer was a 20 percent solids dispersion in trichloroethane comprising 100 parts of a silicone base of 100 parts of hydroxyl endblocked polydiorganosiloxane having about 0.15 mole percent vinyl radicals with the remainder methyl radicals, 55 p~rts of fumed silica, 7 parts of hydroxyl endblocked polydimethylsiloxane fluid having a viscosity of about 0.04 Pa-s at 25C. and about 4 weight percent silicon-bonded hydroxyl radicals, 5 parts of diphenylsilanediol and 1 part of hydroxyl endblocked polymethylvinylsiloxane having about 4 weight percent hydroxyl radical; 5 parts of aluminum trihydrate, .8 part of trimethylsiloxy endblocked polydiorganosiloxane having an average of five methylhydrogensiloxane units and three dimethylsiloxane units per molecule with a silicon-bonded hydrogen atom content in the range of about 0.7 to 0.8 weight percent, .15 part of methyl butynol and .55 part of a platinum catalyst mixture having about .22 percent platinum.
A die was prepared for a 3 inch Davis Standard extruder which extruded a strip 14 having a ma~or surface of 45 mm and a minor surface of 20 mm with a thickness of 10 mm.
., ! " ' ~
,, ~ " .. ''~ :
`' " ' ~ ' " : ' A shed 15 was formed at the center of the major surface with a thickness of 5 mm and a height of 35 mm.
A winding machine was constructed which turned the core 11 at 0.5 revolutions per minute and moved it past the extruder 20 at a rate of 45 mm per revolution.
A high voltage silicone rubber insulation stock was prepared by mixing 100 parts by weight of dimethylvinylsiloxy endblocked polydimethylsiloxane having a Williams plasticity number of about 150, 15 parts of fume silica having a surface area of about 250 m2/g, 8 parts of hydroxyl endblocked polydimethylsiloxane fluid having a viscosity of about 0.04 Pa-s at 25C. and about 4 weight percent silicon-bonded hydroxyl radicals, 1 part of hydroxyl endblocked polydiorganosiloxane having methyl and vinyl radicals and having about 10 weight percent vinyl radical and about 16 weight percent hydroxyl radical and 200 parts of aluminum trihydrate. This mixture was heated after mixing for about 1 hour at a temperature of about 175C., then cooled to give a base material. The base was catalyzed with 1.5 parts of catalyst paste of 50 percent 2,4-dichlorobenzoyl peroxide in polydiorganosiloxane fluid per 100 parts of base to give the high voltage insulation stock.
The high voltage insulation stock was fed to the extruder and the extruder adjusted so that the strip 14 as shown in Fig. 2 was extruded at a rate of 230 mm per minute.
The extrusion pressure was about 70 kg/cm2. The extruded strip wa9 then fed to the revolving core 11 so that it wound around the outer top surface. The width of the strip 14 was 45 mm and the core 11 was moved past the extruder at a rate of 45 mm per revolution so that each succeeding wrapping exactly overlapped at minor surfaces 17a and 17b and these surfaces fit tightly together. A pressure roller 21 was applied to the ~oint formed by surfaces 17a and 17b with a , ' , . : .
. .
...
.
force against the joint of about 1.75 kg/cm2. The roller had a diameter of 130 mm and a thickness of 42 mm. The surface of the roller had been coated with a silicone resin which prevented the uncured silicone rubber from adhering to the roller. The pressure roller exerted just enough pressure on the 30int to force the surfaces 17a and 17b tightly together, but not enough pressure to cause the plastic material to flow away from under the roller. After pressing, the joint was no longer visible. This process was continued until the entire core wa9 completely covered with the extruded strip.
The covered core was then suspended in an air circulating oven at 150C. for 1/2 hour to vulcanize the cover of silicone rubber. The cover consisted of 7850 mm of the extrusion, which weighed 115 g per 100 mm, to give a total cover weight of about 9 kg. The finished insulator was evaluated and found to perform as expected.
.
: . ' ~ ';. . . :
. . . :
. . -: . . , .::
- . ~ - ,:. :
Claims (5)
1. A high voltage insulator comprising a cylindrical, electrically insulating core, the core having a covering adhered to its outer surface from one end to the other and completely covering the outer surface, the covering being a silicone high voltage insulation material which is extruded into the form of a parallelogram shaped strip having a shed formed upon one surface of the strip, the edges of the strip being at an angle of less than 45°C., with the strip being wound in a spiral from one end of the core to the other to completely cover the core surface, the angled edges of the strip being overlapped so that the thickness of the strip is uniform and the surface of the strip having the shed being on the outer surface, so that the shed forms a spiral from one end of the core to the other and the rectangular strip forms a uniform covering over the core with no adhesive present between the overlapped edges of the strip.
2. The insulator of claim 1 in which the core is selected from the group consisting of a rod and a tube.
3. A method of producing a high voltage insulator comprising a cylindrical core, a uniform layer of silicone high voltage insulation material covering the outer surface of the core and a continuous shed of the same insulation material spiralling from one end of the insulator to the other, the method comprising (A) extruding a silicone high voltage insulation stock into a strip in the form of a parallelogram with a shed formed on the upper major surface of the strip and the parallel minor surfaces of the strip at an angle of less than 45°C. to the major surfaces, (B) immediately after extruding and simultaneously with the extrusion process, spirally winding the strip being extruded over the outer surface of a core, the core having been coated with a silicone primer, the core being rotated at a rate equal to the extrusion rate of the strip and being advanced past the extruder at a rate so that the core advances a distance equal to the width of the strip with each revolution of the core, beginning the winding at one end of the core and winding in a manner such that the shed is on the outer surface and the minor surfaces of the strip overlap each other to give a uniform thickness along the surface of the core, the strip being wound smoothly against the core surface so that no air is entrapped between the core surface and the lower major surface of the strip, (C) applying a pressure means against the strip in the space between the sheds and applying pressure to the strip at the joint between turns of the strip to assure that there is no air entrapped in the joint, then, when the core is completely covered, (D) placing the covered core into an oven and heating to vulcanize the silicone high voltage insulation material.
4. The method of claim 3 in which the pressure means of step (C) is a pressure roller.
5. The method of claim 3 in which the pressure means of step (C) is a polymeric tape, applied under tension.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US56509190A | 1990-08-10 | 1990-08-10 | |
| US565,091 | 1990-08-10 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2046682A1 true CA2046682A1 (en) | 1992-02-11 |
Family
ID=24257175
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2046682 Abandoned CA2046682A1 (en) | 1990-08-10 | 1991-07-10 | High voltage insulator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2046682A1 (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19629796C2 (en) * | 1996-07-24 | 1998-07-16 | Ceramtec Ag | Plastic composite insulator with a spiral shield and process for its production |
| US6004416A (en) * | 1996-07-31 | 1999-12-21 | Pirelli Cavi S.P.A. | Shed-formed profile insulating covering and manufacturing method thereof |
| US6342679B1 (en) | 1996-07-31 | 2002-01-29 | Pirelli Cavi S.P.A. | Two-layered elastic tubular covering for electric components |
| WO2003003383A1 (en) * | 2001-06-29 | 2003-01-09 | Tyco Electronics Uk Limited | Helical shed |
| WO2020007871A1 (en) * | 2018-07-02 | 2020-01-09 | Abb Schweiz Ag | Insulator with resistivity gradient |
-
1991
- 1991-07-10 CA CA 2046682 patent/CA2046682A1/en not_active Abandoned
Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19629796C2 (en) * | 1996-07-24 | 1998-07-16 | Ceramtec Ag | Plastic composite insulator with a spiral shield and process for its production |
| US5925855A (en) * | 1996-07-24 | 1999-07-20 | Ceramtec Ag Innovative Ceramic Engineering | Plastic composite insulator with spiral shield and process for producing it |
| DE19629796C5 (en) * | 1996-07-24 | 2004-12-16 | Lapp Insulator Gmbh & Co. Kg | Plastic composite insulator with a spiral shield and process for its production |
| US6004416A (en) * | 1996-07-31 | 1999-12-21 | Pirelli Cavi S.P.A. | Shed-formed profile insulating covering and manufacturing method thereof |
| US6342679B1 (en) | 1996-07-31 | 2002-01-29 | Pirelli Cavi S.P.A. | Two-layered elastic tubular covering for electric components |
| US6576846B2 (en) | 1996-07-31 | 2003-06-10 | Pirelli Cavi S.P.A. | Two-layered elastic tubular covering for electric components, in particular terminations for electric cables, and related manufacturing method and mounting |
| WO2003003383A1 (en) * | 2001-06-29 | 2003-01-09 | Tyco Electronics Uk Limited | Helical shed |
| US6844503B2 (en) | 2001-06-29 | 2005-01-18 | Tyco Electronics U.K. Limited | Helical shed |
| WO2020007871A1 (en) * | 2018-07-02 | 2020-01-09 | Abb Schweiz Ag | Insulator with resistivity gradient |
| CN112384997A (en) * | 2018-07-02 | 2021-02-19 | Abb电网瑞士股份公司 | Insulator with resistivity gradient |
| US11798711B2 (en) | 2018-07-02 | 2023-10-24 | Hitachi Energy Switzerland Ag | Insulator with resistivity gradient |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1236965A (en) | High voltage resistant members and method for producing same | |
| US4196464A (en) | Semi-conductive layer-containing reinforced pressure hose and method of making same | |
| US3916488A (en) | Poly-polymer plastic device | |
| US3913625A (en) | Poly-polymer plastic material and device made therefrom | |
| US3481369A (en) | Reinforced plastic pipe | |
| US4343966A (en) | Electric line insulator made of organic material and having an inner semi-conductive part extending between end anchor fittings | |
| US4243628A (en) | Method for the manufacture of plastic insulators with screens for indoor and outdoor use | |
| CA2175917A1 (en) | Fluoropolymer coated elastomeric rollers and structures | |
| GB2102007A (en) | A semiconductor packing substance for an undersea cable, a cable containing said substance and a method of manufacturing such a cable | |
| US3988189A (en) | Method of constructing a hose | |
| AU730405B2 (en) | Two-layered elastic tubular covering for electric components,in particular terminations for electric cables and related manufacturing method and mounting | |
| US4853165A (en) | Method of using heat-recoverable articles comprising conductive polymer compositions | |
| CA2046682A1 (en) | High voltage insulator | |
| HU223912B1 (en) | Plastic bunch isolator with helical screen, method and apparatus for manufacturing thereof | |
| EP1261975B1 (en) | Method of producing a non-cylindrical component with ribs, particularly a high-voltage insulator, a thereby obtainable high-voltage insulator, and use of a silicon rubber having two curing catalysts or inhibitors, respectively | |
| KR100371066B1 (en) | Electric Isolator and Its Manufacturing Method | |
| EP0211505A2 (en) | Electrically insulating tape | |
| CH634683A5 (en) | Electrical insulator of vitreous resin and organic material for medium, high and very high tension, and process for the manufacture thereof | |
| EP0880302A2 (en) | Heating cable and method producing the same | |
| US3211598A (en) | Methods of coating pipe | |
| EP1008153B1 (en) | A method and an apparatus for manufacturing an electrical insulator | |
| CA1044866A (en) | Longitudinally watertight telecommunication cable and manufacture thereof | |
| US4971638A (en) | Method of manufacturing a sensing element | |
| CA1043717A (en) | Composite reinforced hose | |
| EP0088715A2 (en) | Method of making pressure hose |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |