CA1111523A - Electrical bushing - Google Patents
Electrical bushingInfo
- Publication number
- CA1111523A CA1111523A CA365,578A CA365578A CA1111523A CA 1111523 A CA1111523 A CA 1111523A CA 365578 A CA365578 A CA 365578A CA 1111523 A CA1111523 A CA 1111523A
- Authority
- CA
- Canada
- Prior art keywords
- bushing
- metallic
- bodies
- end flanges
- conductor
- 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
A bushing for leading an electrical connector through a wall with an intermediate flange for attachment in or to the wall and metallic end flanges on either side of the intermediate flange and two hollow insulating bodies clamped respectively between the intermediate flange and the end flanges. A conductor runs the whole length of the bushing and is movable relatively to at least one of the end flanges with a drawing member comprising two elongated metallic bodies connected between the end flanges.
The metallic bodies connect respectively to a corresponding end flange at one end and overlap one another for a predetermined distance with a pressure transmitting and power transmitting connection between those ends of the metallic body not connected to the end flanges. The insulating bodies are typically ceramic material with the pressure transmitting member having a greater average thermal expansion per unit length than the first and second metallic body. The pressure transmitting member may also be metallic. The assembly is such that the coefficient of thermal expansion of the bushing conductor and drawing member assembly is approxi-mately equal to the coefficient of thermal expansion of the insulating body assembly.
A bushing for leading an electrical connector through a wall with an intermediate flange for attachment in or to the wall and metallic end flanges on either side of the intermediate flange and two hollow insulating bodies clamped respectively between the intermediate flange and the end flanges. A conductor runs the whole length of the bushing and is movable relatively to at least one of the end flanges with a drawing member comprising two elongated metallic bodies connected between the end flanges.
The metallic bodies connect respectively to a corresponding end flange at one end and overlap one another for a predetermined distance with a pressure transmitting and power transmitting connection between those ends of the metallic body not connected to the end flanges. The insulating bodies are typically ceramic material with the pressure transmitting member having a greater average thermal expansion per unit length than the first and second metallic body. The pressure transmitting member may also be metallic. The assembly is such that the coefficient of thermal expansion of the bushing conductor and drawing member assembly is approxi-mately equal to the coefficient of thermal expansion of the insulating body assembly.
Description
BACKGROUND OF THE INVENTION
The present invention relates to electrical bushings.
More particularly, the present invention relates to bushings such as gas filled bushings for introducing high voltage conductors into a housing, such as a gas filled circuit breaker.
In bushings of the foregoing type, the central conductor serves both a mechanical and electrical function. In addition to providing an electrical connection between the conductive flanges on either side of the hollow dielectric ~152~
housing, the conductor provides the mechanical connection for holding the bushing together. In order to be certain that the central conductor serves both functions properly, it is necessary to design the bushings to accommodate relative expansion or dimensional changes between the metallic central conductor and the porcclain insulative housing due to thermal expansion and contraction. This is a major problem since bushings of the present type are ordinarily subjected to wide ranges of temperatures and since the coefficients of thermal expansion of the metallic conductor and porcelain housin~ are r quite divergent.
The standard solution of this problem has been to provide a spring assembly connecting the central conductor to one of the two conductive flanges. Bushings of this type are illustrated in U.S. Patent No. 3,566,001 and will be described in some detail with reference to Figure 1, below.
The apparatus dlsclosed eliminates the need for s~ring type systems of the prior art by providing a unique through-rod assembly, the effective coefficient of thermal expansion of which is approximately equal to the coefficient of thermal expansion of the hollow insulator column within which the through-rod assembly is s-ituated.
The through-rod assembly comprises first, second and third coaxial cylinders which cooperate to bias first and second conductive flanges, located adjacent first and second ends of a hollow insulator column, against their respective ends of the insulator column. The innermost of the three cylinders is connected at one end to the first conductive flange and extends internally into the insulator column.
~n external shoulder extends from the distal end oE the first cyLinder and supports one end of the second cylinder. The remaining end oE the second cylinder terminates at an internal flange extending from the distal end of a third cyclinder which is connected to the second conductive flange.
The coefEicient of thermal expansion of the through-rod assembly is chosen such that the effective coefficient of thermal expansion thereof is approximately equal to the coefficient of thermal expansion of the ho]low insulator column. By way of example, the coefficient of thermal expansion of the second cyclinder will be slightly less than twice as great as the coefficient of thermal expansion of the first and third cylinders.
Since the coefficient oE thermal expansion of the hollow insulator column is typically low, the effective coefficient of thermal expansion of both elements will be approximately equal and both elements will expand or contract an equal distance during normal temperature excursions.
A significant feature of the apparatus disclosed is that any suitable flexible conductor may be utilized to electrically connect the first and second conductive flanges on either end of the insulator column.
When such an arrangement is utilized, the conductor is not subjected to any mechanical load and can be made from the most suitable material in terms of current carrying capacity.
More particularly in accordance with the invention there is provided a bushing for leading an electrical connector through a wall or the like, comprising an intermediate flange for attachment in the wall, two metallic end flanges arranged on either side of the intermediate flange and two hollow insulating bodies clamped between the intermediate flange and the end flanges, and abushing conductor running ~he length of the whole bushing, saidbushing conductor being movable in relation to at least one of the end flanges, and a drawing member connected between the 1~1152;3 end flanges comprising a first and a second elongated metallic body, each of which is attached at one end to a corresponding end flange, said bodies overlapping each other for a certain distance, and a pressure-transmitting member forming a power-transmitting connection between the ends of the metallic bodies which are not connected to the end flanges. The insulating bodies may be of ceramic material with the pressure transmitting member made of a material of greater average thermal expansion per unit of length than the first and second metallic bodies. There may be a third elongated metallic body constituting the pressure transmitting member, and the first, second and third metallic bodies may be coaxial cylinders with the third body radially interposed between the other two. The bushing may be a tube surrounding the drawing member and the tube together r with a metal cylinder included in the drawing member may define a hollow cylindrical space communicating with a space radially outside the tube for circulation of coolant.
Specific embodiments of the invention will now be described having reference to the accompanying drawings in which:
- 3a -- ' `` l~l~SZ~
Figure 1 is a plan cross-sectional view of a prior art bushing.
Figure 2 is a plan cross-sectional view of a novel bush-ing constructed in accordance with the teaching herein.
Figure 3 is a cross-sectional view of the bushing of Figure 2 taken along line 3-3 of Figure 2.
Referring now to the drawings wherein like numerals indi-cate like elements there is shown in Figure 1 a typical prior art gas-filled bushing 10. Bushing 10 consists of an insulator housing 12, a pair of conductive flanges 14 and 16 and a central conductor 18.
Insulator housing 12 comprises two conical insulator columns 20 and 22 which are separated by an annular mounting flange 24. The sections of insulator housing 12 are biased together by centrla conductor 18 which applies a tensile force to conductive flanges 14 and 16.
Central conductor 18 is threaded at 26 and connected to conductive flange 16 in a manner described below. The distal end of conductor 18 is provided with an external flange 28 which is electrically connected to conductive flange 14 by flexible conduct-ors 30. External flange 28 is mechanically connected to conductive flang 14 by a spring assembly comprising studs 32, rings 34 and springs 36. Studs 32 depend from conductive flange 14 and termin-ate at expanded heads 38. Head 38 of each stud 32 supports a ring 34 of sufficient size to seat one end of spring 36. Springs 36 are compression springs and force conductive flanges 14 and 16 inwardly towards annular mounting flange 24. The particular force exerted as well as the distance "A" between external step 28 and conductive flange 14 is adjusted by tightening conductive flange ~ .
`
16 about the threaded end 26 of central conductor 18.
In the foregoing bushing, the force applied to flanges 14 and 16 by springs 36 varies for different operating temperatures particularly when the length of the insulator column increases for increased voltage rating. As the operating temperature increases, the length of central conductor 18 increases at a faster rate than the length of insulator housing 12 causing the length of springs 36 to increase. The converse is, of course, also true. Since the spring rate is a function of the length of the spring and the length of the spring is a function of temperature, the spring rate will vary for varying operational temperatures. In practical applications, this requires that the force exerted by the springs be excessively high when the conductor 18: is at its shortest length to insure adequate force when the conductor 18 is at its maximum length.
In the prior art design the central conductor 18 also serves both a mechanical and electrical function. Thus its material must be chosen such that the central conductor can with-stand both the tensile forces applied thereto during the normal operation and at the same time, have the highest possible conduct-ivity.
Referring now to Figures 2 and 3, there is illustrated a new bushing design designated generally as 40. Bushing 40 comprises five major components; insulator housing 42, conductive flanges 44 and 46, through-rod assembly 48 and conductor 50. Insulator hous-ing 42 consists of two insulator columns 52 and 54 which may be of any standard configuration and which are joined in end-to-end re-lation through an annular . --5--~1152;3 mountin~ flange 56. Columns 52 and 54 are normally made of porcelain but may be constructed of any other suitable insulative material. The annular mounting flange 56 is of the standard type and contains numerous bolt hole openin~s, such as bolt hole 58, which permit bushing 40 to be mounted to any suitable enclosure such as the fragmentarily shown enclosure 6~ which could, for example, represent the sealed housing of a gas circuit breaker. When so mounted, the entire insulator column 54 is immersed within the enclosure, and the insulator housing 42 may also be gas filled.
Bushings of the type disclosed herein may be rated at extremely high voltages, for example 550 k~' and above.
For this reason, it is desirable to fill bushing 40 with an insulation gas such as sulfur hexafluoride to pro~erly insulate annular mounting flange 56 (which will normally be grounded) From the high voltage conductor 50. To this end, conductive flange 46 may be provided with an aperture 64 which permits gas to communicate between the enclosure 60 into bushing 40.
Since insulator column 5Z is positioned above the exterior of enclosure 60, seals 68 are provided between flanges 44 and 56 and insulator column 52. Suitable seals are described in U.S. Patent No 3,566,001, assi~ned to ~ould Inc , the assignee of the present invention.
Conductive flanges 44, 46 are situated adjacent opposite ends of insulator housing 42 and are biased towards each other by througll-rod assembly 48 ~hrough-rod assembly 48 comprises three cylindrical rods 70, 72 and 74 which clamp the two flanges 44, 46 to insulator housing 42 .~ith a sufficiently high force to insure a sound mechanical design.
Specifically, the force which must be exerted by the through-rod assembly 48 must be sufficiently great to overcome the following loads~ load due to gas pressure ~ithin bushing ~S.l lSZ3 r 40, (2) load due to wind forces, (3) load due to line pulls, (4) load due to short circuit forces, and ~5) load imposed during a seismic event.
The innermost cylindrical rod 70 is fitted into an appropriately threaded opening 76 in conductive flange 44 and extends internally into insulator housing 42. The distal end 78 of cylindrical rod 70 is provided with an external flange 78 which supports cylindrical rod 72. Cylindrical rod 72 is coaxial with cylindrical rod 70 and, as will be shohn below, cooperates with cylindrical rods 70 and 74 to act as a spring member which biases conductive flanges 44, 46 together. The upper end 80 of cylindrical rod 72 abuts an internal flange 82 on the distal end of cylindrical rod 74. The proximal end 84 of cylindrical rod 74 is externally threaded and mates with ~n internally threaded aperture 85 in conductive flan~e 46.
The desired force between conductive flanges 44 and 46 is adjusted by rotating conductive flange 46 on the tllreaded end 84 of cylindrical rod 74. ~s conductive flange 46 is rotated, cylindrical rod 74 is drawn away from conductive flange 44 and cylindrical rod 72 is compressed between flanges 78 and 82. This increases the tensile force applied to conductive flanges 44, 46 by through-rod assembly 48 and makes it possible to adjust the force with ~hich flanges 44, 46 press against housing 42.
Significantly, the effective length of through-rod assembly 48 is approximately three times the length of the bushing. This length provides an effective spring rate which, although relatively high, keeps the force to be used on assembly to an acceptable level. Particularly, the force required is such that under the worst temperature conditions the force generated by through-rod assembly 48 is the minimum required to overcome the externally applied loads described above.
S;~3 Although through-rod assembly 48 is normally metallic, and therefore provides an electrical connection between conductive flanges 44 and 46, it is pTeferable to provide a separate conductor, such as cylindrical conductor 50, to electrically connect flanges 44, 46. In the strueture illustrated in the drawings, conductor 50 is a cylinder of extremely high conductivity which is coaxial to rod assembly 48. One end of cylindrical conductor 50 includes an external flange 86 which is bolted to conductive flange 46 by appropriate fasteners 88. As best seen in Figure 3, flange 86 is provided with a notch 90 which is coextensive with aperture 64. Although conductor 50 serves no mechanical function, it still must accommodate dimensional changes in the bushing structure. Accordingly, a plurality of flexible connectors 92 connect conductor 50 to conductive flange 44. While conductor 50 has been shown as a cylindrical conductor, any other suit-able arrangement could be utilized without departing from the spirit of scope of tlle present invention.
It should be obvious from the foregoing, that the full mechanical load between flanges 44 and 46 is applied to through rod assembly 48 and that conductor 50 may be designed with only electrical characteristics in mind. Accordingly, conductor 50 may be made of any material exhibiting high conductivity regardless of the relative strength of such material. Similarly, through-rod assembly 48 can be designed with only mechanical cha~acteristics in mind. Accordingly, the cylindrical rods 70, 72, 74 can be made from any material exhibiting high tensile strength.
As noted above, bushing 40 will normally be subjected to large temperature excursions due to both ambient conditions and I2R losses within the bushing itself. Since bushings of the type described herein are often used in high voltage l~lSZ;~
applications in the 550 kV range and above in hostile environments, tl-e temperature excursions can be quite extreme.
The insulator housing 42 is normally ma~le of porcelain for its good insulative characteristics. The through-rod assembly will normally be made of metallic elements for their strength and good sprin~ characteristics. The coefficient of thermal expansion of procelain is relatively low while that of metals is relatively high. If this variance is not compensated for, the structural integrity of the bushing will be jeopardized.
To avoid this possibility, the thermal coefficients of expansion of cylindrical rods 70, 72, 74 are chosen such that the overall coefficient of thermal expansion of through-rod assembly 48 is approximately equal to the coefficient of thermal expansion of insulator housing 42. In this manner, the pressure applied by conductive flanges 44 and 46 against the ends of insulator housing 42 will remain approximately constant over the entire range of operating temperatures of bushing 40. In the embodiment illustrated in Figure 2, cylindrical rod 72 is chosen to have a coefficient of thermal expansion which is slightly less than twice the coefficient of thermal expansion of cylindrical rods 70 and 74, the co-efficient of thermal expansion of the latter two rods being essentially identical. By this arrangement, the distance between conductive flanges 44 and 46 will be permitted to increase an amount approximately equal to the distance between the two ends of insulator housing 42 during any temperature excursion and the force applied by flanges 44 and 46 against insulator housing 42 will remain approximately constant.
~lthough this invention has been described with respect to a preferred embodiment, it should be understood that many variations in modifications will now be obvious to those skilled in the art, and, therefore, the scope of this invention is limited not by the specific disclosure - herein, but only by the appended claims.
The present invention relates to electrical bushings.
More particularly, the present invention relates to bushings such as gas filled bushings for introducing high voltage conductors into a housing, such as a gas filled circuit breaker.
In bushings of the foregoing type, the central conductor serves both a mechanical and electrical function. In addition to providing an electrical connection between the conductive flanges on either side of the hollow dielectric ~152~
housing, the conductor provides the mechanical connection for holding the bushing together. In order to be certain that the central conductor serves both functions properly, it is necessary to design the bushings to accommodate relative expansion or dimensional changes between the metallic central conductor and the porcclain insulative housing due to thermal expansion and contraction. This is a major problem since bushings of the present type are ordinarily subjected to wide ranges of temperatures and since the coefficients of thermal expansion of the metallic conductor and porcelain housin~ are r quite divergent.
The standard solution of this problem has been to provide a spring assembly connecting the central conductor to one of the two conductive flanges. Bushings of this type are illustrated in U.S. Patent No. 3,566,001 and will be described in some detail with reference to Figure 1, below.
The apparatus dlsclosed eliminates the need for s~ring type systems of the prior art by providing a unique through-rod assembly, the effective coefficient of thermal expansion of which is approximately equal to the coefficient of thermal expansion of the hollow insulator column within which the through-rod assembly is s-ituated.
The through-rod assembly comprises first, second and third coaxial cylinders which cooperate to bias first and second conductive flanges, located adjacent first and second ends of a hollow insulator column, against their respective ends of the insulator column. The innermost of the three cylinders is connected at one end to the first conductive flange and extends internally into the insulator column.
~n external shoulder extends from the distal end oE the first cyLinder and supports one end of the second cylinder. The remaining end oE the second cylinder terminates at an internal flange extending from the distal end of a third cyclinder which is connected to the second conductive flange.
The coefEicient of thermal expansion of the through-rod assembly is chosen such that the effective coefficient of thermal expansion thereof is approximately equal to the coefficient of thermal expansion of the ho]low insulator column. By way of example, the coefficient of thermal expansion of the second cyclinder will be slightly less than twice as great as the coefficient of thermal expansion of the first and third cylinders.
Since the coefficient oE thermal expansion of the hollow insulator column is typically low, the effective coefficient of thermal expansion of both elements will be approximately equal and both elements will expand or contract an equal distance during normal temperature excursions.
A significant feature of the apparatus disclosed is that any suitable flexible conductor may be utilized to electrically connect the first and second conductive flanges on either end of the insulator column.
When such an arrangement is utilized, the conductor is not subjected to any mechanical load and can be made from the most suitable material in terms of current carrying capacity.
More particularly in accordance with the invention there is provided a bushing for leading an electrical connector through a wall or the like, comprising an intermediate flange for attachment in the wall, two metallic end flanges arranged on either side of the intermediate flange and two hollow insulating bodies clamped between the intermediate flange and the end flanges, and abushing conductor running ~he length of the whole bushing, saidbushing conductor being movable in relation to at least one of the end flanges, and a drawing member connected between the 1~1152;3 end flanges comprising a first and a second elongated metallic body, each of which is attached at one end to a corresponding end flange, said bodies overlapping each other for a certain distance, and a pressure-transmitting member forming a power-transmitting connection between the ends of the metallic bodies which are not connected to the end flanges. The insulating bodies may be of ceramic material with the pressure transmitting member made of a material of greater average thermal expansion per unit of length than the first and second metallic bodies. There may be a third elongated metallic body constituting the pressure transmitting member, and the first, second and third metallic bodies may be coaxial cylinders with the third body radially interposed between the other two. The bushing may be a tube surrounding the drawing member and the tube together r with a metal cylinder included in the drawing member may define a hollow cylindrical space communicating with a space radially outside the tube for circulation of coolant.
Specific embodiments of the invention will now be described having reference to the accompanying drawings in which:
- 3a -- ' `` l~l~SZ~
Figure 1 is a plan cross-sectional view of a prior art bushing.
Figure 2 is a plan cross-sectional view of a novel bush-ing constructed in accordance with the teaching herein.
Figure 3 is a cross-sectional view of the bushing of Figure 2 taken along line 3-3 of Figure 2.
Referring now to the drawings wherein like numerals indi-cate like elements there is shown in Figure 1 a typical prior art gas-filled bushing 10. Bushing 10 consists of an insulator housing 12, a pair of conductive flanges 14 and 16 and a central conductor 18.
Insulator housing 12 comprises two conical insulator columns 20 and 22 which are separated by an annular mounting flange 24. The sections of insulator housing 12 are biased together by centrla conductor 18 which applies a tensile force to conductive flanges 14 and 16.
Central conductor 18 is threaded at 26 and connected to conductive flange 16 in a manner described below. The distal end of conductor 18 is provided with an external flange 28 which is electrically connected to conductive flange 14 by flexible conduct-ors 30. External flange 28 is mechanically connected to conductive flang 14 by a spring assembly comprising studs 32, rings 34 and springs 36. Studs 32 depend from conductive flange 14 and termin-ate at expanded heads 38. Head 38 of each stud 32 supports a ring 34 of sufficient size to seat one end of spring 36. Springs 36 are compression springs and force conductive flanges 14 and 16 inwardly towards annular mounting flange 24. The particular force exerted as well as the distance "A" between external step 28 and conductive flange 14 is adjusted by tightening conductive flange ~ .
`
16 about the threaded end 26 of central conductor 18.
In the foregoing bushing, the force applied to flanges 14 and 16 by springs 36 varies for different operating temperatures particularly when the length of the insulator column increases for increased voltage rating. As the operating temperature increases, the length of central conductor 18 increases at a faster rate than the length of insulator housing 12 causing the length of springs 36 to increase. The converse is, of course, also true. Since the spring rate is a function of the length of the spring and the length of the spring is a function of temperature, the spring rate will vary for varying operational temperatures. In practical applications, this requires that the force exerted by the springs be excessively high when the conductor 18: is at its shortest length to insure adequate force when the conductor 18 is at its maximum length.
In the prior art design the central conductor 18 also serves both a mechanical and electrical function. Thus its material must be chosen such that the central conductor can with-stand both the tensile forces applied thereto during the normal operation and at the same time, have the highest possible conduct-ivity.
Referring now to Figures 2 and 3, there is illustrated a new bushing design designated generally as 40. Bushing 40 comprises five major components; insulator housing 42, conductive flanges 44 and 46, through-rod assembly 48 and conductor 50. Insulator hous-ing 42 consists of two insulator columns 52 and 54 which may be of any standard configuration and which are joined in end-to-end re-lation through an annular . --5--~1152;3 mountin~ flange 56. Columns 52 and 54 are normally made of porcelain but may be constructed of any other suitable insulative material. The annular mounting flange 56 is of the standard type and contains numerous bolt hole openin~s, such as bolt hole 58, which permit bushing 40 to be mounted to any suitable enclosure such as the fragmentarily shown enclosure 6~ which could, for example, represent the sealed housing of a gas circuit breaker. When so mounted, the entire insulator column 54 is immersed within the enclosure, and the insulator housing 42 may also be gas filled.
Bushings of the type disclosed herein may be rated at extremely high voltages, for example 550 k~' and above.
For this reason, it is desirable to fill bushing 40 with an insulation gas such as sulfur hexafluoride to pro~erly insulate annular mounting flange 56 (which will normally be grounded) From the high voltage conductor 50. To this end, conductive flange 46 may be provided with an aperture 64 which permits gas to communicate between the enclosure 60 into bushing 40.
Since insulator column 5Z is positioned above the exterior of enclosure 60, seals 68 are provided between flanges 44 and 56 and insulator column 52. Suitable seals are described in U.S. Patent No 3,566,001, assi~ned to ~ould Inc , the assignee of the present invention.
Conductive flanges 44, 46 are situated adjacent opposite ends of insulator housing 42 and are biased towards each other by througll-rod assembly 48 ~hrough-rod assembly 48 comprises three cylindrical rods 70, 72 and 74 which clamp the two flanges 44, 46 to insulator housing 42 .~ith a sufficiently high force to insure a sound mechanical design.
Specifically, the force which must be exerted by the through-rod assembly 48 must be sufficiently great to overcome the following loads~ load due to gas pressure ~ithin bushing ~S.l lSZ3 r 40, (2) load due to wind forces, (3) load due to line pulls, (4) load due to short circuit forces, and ~5) load imposed during a seismic event.
The innermost cylindrical rod 70 is fitted into an appropriately threaded opening 76 in conductive flange 44 and extends internally into insulator housing 42. The distal end 78 of cylindrical rod 70 is provided with an external flange 78 which supports cylindrical rod 72. Cylindrical rod 72 is coaxial with cylindrical rod 70 and, as will be shohn below, cooperates with cylindrical rods 70 and 74 to act as a spring member which biases conductive flanges 44, 46 together. The upper end 80 of cylindrical rod 72 abuts an internal flange 82 on the distal end of cylindrical rod 74. The proximal end 84 of cylindrical rod 74 is externally threaded and mates with ~n internally threaded aperture 85 in conductive flan~e 46.
The desired force between conductive flanges 44 and 46 is adjusted by rotating conductive flange 46 on the tllreaded end 84 of cylindrical rod 74. ~s conductive flange 46 is rotated, cylindrical rod 74 is drawn away from conductive flange 44 and cylindrical rod 72 is compressed between flanges 78 and 82. This increases the tensile force applied to conductive flanges 44, 46 by through-rod assembly 48 and makes it possible to adjust the force with ~hich flanges 44, 46 press against housing 42.
Significantly, the effective length of through-rod assembly 48 is approximately three times the length of the bushing. This length provides an effective spring rate which, although relatively high, keeps the force to be used on assembly to an acceptable level. Particularly, the force required is such that under the worst temperature conditions the force generated by through-rod assembly 48 is the minimum required to overcome the externally applied loads described above.
S;~3 Although through-rod assembly 48 is normally metallic, and therefore provides an electrical connection between conductive flanges 44 and 46, it is pTeferable to provide a separate conductor, such as cylindrical conductor 50, to electrically connect flanges 44, 46. In the strueture illustrated in the drawings, conductor 50 is a cylinder of extremely high conductivity which is coaxial to rod assembly 48. One end of cylindrical conductor 50 includes an external flange 86 which is bolted to conductive flange 46 by appropriate fasteners 88. As best seen in Figure 3, flange 86 is provided with a notch 90 which is coextensive with aperture 64. Although conductor 50 serves no mechanical function, it still must accommodate dimensional changes in the bushing structure. Accordingly, a plurality of flexible connectors 92 connect conductor 50 to conductive flange 44. While conductor 50 has been shown as a cylindrical conductor, any other suit-able arrangement could be utilized without departing from the spirit of scope of tlle present invention.
It should be obvious from the foregoing, that the full mechanical load between flanges 44 and 46 is applied to through rod assembly 48 and that conductor 50 may be designed with only electrical characteristics in mind. Accordingly, conductor 50 may be made of any material exhibiting high conductivity regardless of the relative strength of such material. Similarly, through-rod assembly 48 can be designed with only mechanical cha~acteristics in mind. Accordingly, the cylindrical rods 70, 72, 74 can be made from any material exhibiting high tensile strength.
As noted above, bushing 40 will normally be subjected to large temperature excursions due to both ambient conditions and I2R losses within the bushing itself. Since bushings of the type described herein are often used in high voltage l~lSZ;~
applications in the 550 kV range and above in hostile environments, tl-e temperature excursions can be quite extreme.
The insulator housing 42 is normally ma~le of porcelain for its good insulative characteristics. The through-rod assembly will normally be made of metallic elements for their strength and good sprin~ characteristics. The coefficient of thermal expansion of procelain is relatively low while that of metals is relatively high. If this variance is not compensated for, the structural integrity of the bushing will be jeopardized.
To avoid this possibility, the thermal coefficients of expansion of cylindrical rods 70, 72, 74 are chosen such that the overall coefficient of thermal expansion of through-rod assembly 48 is approximately equal to the coefficient of thermal expansion of insulator housing 42. In this manner, the pressure applied by conductive flanges 44 and 46 against the ends of insulator housing 42 will remain approximately constant over the entire range of operating temperatures of bushing 40. In the embodiment illustrated in Figure 2, cylindrical rod 72 is chosen to have a coefficient of thermal expansion which is slightly less than twice the coefficient of thermal expansion of cylindrical rods 70 and 74, the co-efficient of thermal expansion of the latter two rods being essentially identical. By this arrangement, the distance between conductive flanges 44 and 46 will be permitted to increase an amount approximately equal to the distance between the two ends of insulator housing 42 during any temperature excursion and the force applied by flanges 44 and 46 against insulator housing 42 will remain approximately constant.
~lthough this invention has been described with respect to a preferred embodiment, it should be understood that many variations in modifications will now be obvious to those skilled in the art, and, therefore, the scope of this invention is limited not by the specific disclosure - herein, but only by the appended claims.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1 Bushing for leading an electrical connector through a wall or the like, comprising an intermediate flange for attachment in the wall, two metallic end flanges arranged on either side of the intermediate flange and two hollow insulating bodies clamped between the intermediate flange and the end flanges, and a bushing conductor running the length of the whole bushing, said bushing conductor being movable in relation to at least one of the end flanges, and a drawing member connected between the end flanges comprising a first and a second elongated metallic body, each of which is attached at one end to a corresponding end flange, said bodies overlapping each other for a certain distance, and a pressure-transmitting member forming a power-transmitting connection between the ends of the metallic bodies which are not connected to the end flanges.
2. Bushing according to Claim 1, in which said insulating bodies are of ceramic material and said pressure-transmitting member is made of a material with greater average thermal expansion per unit of length than said first and second metallic bodies.
3. Bushing according to Claim 2, in which said pressure-transmitting member consists of a third elongated metallic body.
4. Bushing according to Claim 3, in which said first, second and third elongated metallic bodies are in the form of three coaxial cylinders, of which said third metallic body is a hollow cylinder positioned radially between the other bodies.
5. Bushing according to Claim 1, in which said bushing conductor substantially consists of a tube which surrounds said drawing member.
6 . Bushing according to Claim 5, in which said tube together with a metal cylinder included in said drawing member limits a hollow-cylindrical space, which communicates, through circulation openings for coolant, with a space located radially outside said tube.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA365,578A CA1111523A (en) | 1976-09-08 | 1980-11-26 | Electrical bushing |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US721,379 | 1976-09-08 | ||
| US05/721,379 US4214118A (en) | 1976-09-08 | 1976-09-08 | Electrical bushing |
| CA283,057A CA1108256A (en) | 1976-09-08 | 1977-07-19 | Electrical bushing with thermal expansion compensation facilities |
| CA365,578A CA1111523A (en) | 1976-09-08 | 1980-11-26 | Electrical bushing |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1111523A true CA1111523A (en) | 1981-10-27 |
Family
ID=27165194
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA365,578A Expired CA1111523A (en) | 1976-09-08 | 1980-11-26 | Electrical bushing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1111523A (en) |
-
1980
- 1980-11-26 CA CA365,578A patent/CA1111523A/en not_active Expired
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