CA1106008A - High current electrical bushing - Google Patents
High current electrical bushingInfo
- Publication number
- CA1106008A CA1106008A CA281,153A CA281153A CA1106008A CA 1106008 A CA1106008 A CA 1106008A CA 281153 A CA281153 A CA 281153A CA 1106008 A CA1106008 A CA 1106008A
- Authority
- CA
- Canada
- Prior art keywords
- stud
- bushing
- working fluid
- section
- fluid
- 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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- Insulators (AREA)
Abstract
HIGH CURRENT ELECTRICAL BUSHING
Abstract A high current electrical bushing for an electrical transformer immersed in a dielectric fluid within a housing, the bushing including a hollow stud mounted on the housing and having a terminal on the outside of the housing and a heat radiating surface immersed in the dielectric fluid on the inside of the housing. A heat pipe structure within said stud in-cluding a fluid medium and a wick within said stud for transferring the fluid medium from a one section of the stud to another section of the stud whenever a differential in temperature exists within the bushing stud. The dielectric fluid within the transformer absorbs heat from the radiating sur-faces of the stud such that the temperature of the stud will remain substan-tially the same as the temperature of the dielectric fluid.
Abstract A high current electrical bushing for an electrical transformer immersed in a dielectric fluid within a housing, the bushing including a hollow stud mounted on the housing and having a terminal on the outside of the housing and a heat radiating surface immersed in the dielectric fluid on the inside of the housing. A heat pipe structure within said stud in-cluding a fluid medium and a wick within said stud for transferring the fluid medium from a one section of the stud to another section of the stud whenever a differential in temperature exists within the bushing stud. The dielectric fluid within the transformer absorbs heat from the radiating sur-faces of the stud such that the temperature of the stud will remain substan-tially the same as the temperature of the dielectric fluid.
Description
Background of the Invention The current carrying capabilities of electrical bushings are limited by the temperature rise of the conducting member due to the resistance of that member to current flow.
A common criterion for establishing the current rating of an electrical bushing is generally defined as follows: the current carrying capacity is that current which causes the temperature of the hottest part of the bushing to rise 10C. above the temperature of the cooling insulating medium of the device in which the bushing is installed.
There are two common methods of increasing the current carrying capacity of an electrical bushing and still remain within the criterion set forth above. The first method is to increase the conductor size and thereby decrease its resistance.
The second is to increase the radiative surface of the bushing so that the heat is dissipated at a faster rate to the cooling media to thereby maintain the temperature within the required criterion.
The first of these methods is limited by the expense of the material and the increasing effect of skinning at higher currents, to lower current leveis. The second requires a substantial increase in the size of the bushing in order to increase the surface area sufficiently to dissipate heat at a rate which would stay within the above criterion. However, ; in order to accomplish this by this method alone, the size ~ of the bushing becomes very large and as a consequence, expensive.
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A common criterion for establishing the current rating of an electrical bushing is generally defined as follows: the current carrying capacity is that current which causes the temperature of the hottest part of the bushing to rise 10C. above the temperature of the cooling insulating medium of the device in which the bushing is installed.
There are two common methods of increasing the current carrying capacity of an electrical bushing and still remain within the criterion set forth above. The first method is to increase the conductor size and thereby decrease its resistance.
The second is to increase the radiative surface of the bushing so that the heat is dissipated at a faster rate to the cooling media to thereby maintain the temperature within the required criterion.
The first of these methods is limited by the expense of the material and the increasing effect of skinning at higher currents, to lower current leveis. The second requires a substantial increase in the size of the bushing in order to increase the surface area sufficiently to dissipate heat at a rate which would stay within the above criterion. However, ; in order to accomplish this by this method alone, the size ~ of the bushing becomes very large and as a consequence, expensive.
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- 2 -6~(~8 It is generally known that the center section of a high current bushing stud is not effectively carrying much of the total current because of the "skinning" effect of the current. Therefore, the center section can be removed without affecting temperature rise. The rate of heat transfer has been increased between the hottest portion of the bushing stud and the coolest portion by using the center section space to house a heat pipe structure.
The heat dissipation rate has been further increased by providing the bushing stud with a large heat radiating surface and immersing the heat radiating surface of the bushing in the cooling medium of the device upon which the bushing is mounted. Since the criterion, as pointed out above, of rating the current carrying capacity of the bushing is its rise in temper-ature over the cooling medium, locking the temperature of the bushing stud closely to the temperature of that cooling medium can greatly extend the current rating. By positioning a heat pipe structure within the bushing stud to transfer heat from the hot portion of the bushing to the cool portion, the bushing stud temperature can be kept very close to that of the cooling medium. ;
According to the present invention, there is provided a high current electrical bushing for an electrical device immersed in a dielectric fluid within a housing, said bushing comprising: a hollow electrically conductive stud having a terminal at one end and having the other end elec-trically connected to the electrical device, electrically insulating means mounting said stud on said housing with a portion of the stud immersed in said dielectric fluid, said terminal being located outside of said housing, means mounted on said portion of said stud immersed in said dielectric fluid for transferring heat from a first section of said stud to said dielectric fluid, a working fluid within said stud, and means positioned within said stud for conducting the working fluid from said first section of the stud to a second section of the stud whenever the temperature in said second section exceeds the temperature of said first section; hence evaporating said working fluid and removing heat energy from said second section, where-
The heat dissipation rate has been further increased by providing the bushing stud with a large heat radiating surface and immersing the heat radiating surface of the bushing in the cooling medium of the device upon which the bushing is mounted. Since the criterion, as pointed out above, of rating the current carrying capacity of the bushing is its rise in temper-ature over the cooling medium, locking the temperature of the bushing stud closely to the temperature of that cooling medium can greatly extend the current rating. By positioning a heat pipe structure within the bushing stud to transfer heat from the hot portion of the bushing to the cool portion, the bushing stud temperature can be kept very close to that of the cooling medium. ;
According to the present invention, there is provided a high current electrical bushing for an electrical device immersed in a dielectric fluid within a housing, said bushing comprising: a hollow electrically conductive stud having a terminal at one end and having the other end elec-trically connected to the electrical device, electrically insulating means mounting said stud on said housing with a portion of the stud immersed in said dielectric fluid, said terminal being located outside of said housing, means mounted on said portion of said stud immersed in said dielectric fluid for transferring heat from a first section of said stud to said dielectric fluid, a working fluid within said stud, and means positioned within said stud for conducting the working fluid from said first section of the stud to a second section of the stud whenever the temperature in said second section exceeds the temperature of said first section; hence evaporating said working fluid and removing heat energy from said second section, where-
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by the working fluid is evaporated and heat energy from said second section is removed to said first section.
The invention will now be described in greater detail with ref0rence to the accompanying drawing which shows a high current electrical bushing accordin~ to the invention with a portion broken away to show the heat pipe structure within the center section of the bushing stud.
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Description of the Invention The high current electrical bushing 10 is shown mounted in an opening 12 in the wall 14 of a transformer (not shown) which is immersed in a dielectric fluid or medium 16. The bushing generally includes a tubular member or stud 18 having a spade terminal 20 at one end. The stud 18 is sup-ported in the opening 12 in the wall 14 by means of a dielectric member 22, which is secured to the wall by a clamp assembly 24 and is sealed by means of a gasket 26.
The bushing stud 18 is in the form of a tubular member having a blind bore 28. The bore 28 is closed at its open end by means of a tube ex-tension 30. Means are provided on the extension 30 in the form of a number of heat radiating fins 32 to dissipate heat from the bushing. The open end of the extension is closed by a cap 34 having a filling tube 36.
Means are provided within the blind bore 28 for transferring heat from one end of the bore to the other at a rate sufficient to maintain the stud at a temperature approximating the temperature of the dielectric fluid 16. Such means is in the form of a heat pipe structure 38 which includes a fluid medium 40 and wick 42.
The wick 42 is in the form of a sleeve which covers the inside sur-20 faces of the blind bore 28 and the tube extension 30. The wick functions asmany capillary tubes to transfer the fluid from the cool end of the conductor to the hot portion of the conductor. The wick 42 can be formed of a number of wick materials that are capable of withstanding the contemplated system temperature without deterioration. In the form shown, a woven fiber glass sleeve 41 is positioned in the bore. The sleeve 41 is retained in position by means of a stainless steel expander spring 43 inside of the fiber glass to hold the sleeve against the wall of the tube.
The working fluid 40 can be selected from a number of liquids and must have a heat of vaporization and a vapor pressure range which allow rapid 30 heat energy transfer and low internal operating pressures. One such liquid is water. Ethylene glycol has also been used because of its higher vapor pressure and hence, higher potential temperature operating range.
On assembly, the wick 42 is inserted into the blind bore 28. The tube extension 30 is inserted partially into the bore 28 and soldered into position. The tube is evacuated and while the vacuum is maintained a small amount of the fluid medium is injected through tube 36 into the bore 28.
After the fluid medium has been put into the bore 28 in the bushing stud, the tube 36 is sealed by pinching the end of the tube 36 and sealing the end of the tube by solder. The interior is still below one atmosphere of pressure at that time in the case of water for a working fluid and with a bushing temperature below 100 Celcius.
In operation, the electrical bushing will conduct current and will normally build up heat in the portion of the bushing exterior to the wall 14.
As heat builds up, the fluid medium in the wick 42 will vaporize building up pressure within the blind bore 28 and removing heat from that portion of the conductor. Since the pressure of the medium in the bore 28 will attempt to ` equalize, the vapor will move from the hottest portion of the conductor to-ward the cooler portion. Upon reaching the cooler portion of the tube exten-sion, the vapor condenses giving up heat energy at that portion.
By immersing the tube extension 30 in the cooling medium as shown in the drawing, the heat will be absorbed at a greater rate off of the fins 32. Although the bushing is shown in a vertical position, it can also be mounted in a horizontal position with the entire internal end of the bushing ;~ immersed in the dielectric fluid. As long as the cooling medium can dissi-pate the heat from the fins at a rate sufficient to prevent complete dryout of the wick against the hot portion of the bore 28 of the bushing stud, or, in other words, at a rate that the wick 42 can transfer liquid 40 from the cool area to the hotter area, the vapor will continue to condense in the tube extension 30. ~he condensed liquid will then travel back to the hotter por--tion of the stud through the wick 42 thereby establishing a closed cycle.
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1~6~
by the working fluid is evaporated and heat energy from said second section is removed to said first section.
The invention will now be described in greater detail with ref0rence to the accompanying drawing which shows a high current electrical bushing accordin~ to the invention with a portion broken away to show the heat pipe structure within the center section of the bushing stud.
, ..~
;' -3a-6~
Description of the Invention The high current electrical bushing 10 is shown mounted in an opening 12 in the wall 14 of a transformer (not shown) which is immersed in a dielectric fluid or medium 16. The bushing generally includes a tubular member or stud 18 having a spade terminal 20 at one end. The stud 18 is sup-ported in the opening 12 in the wall 14 by means of a dielectric member 22, which is secured to the wall by a clamp assembly 24 and is sealed by means of a gasket 26.
The bushing stud 18 is in the form of a tubular member having a blind bore 28. The bore 28 is closed at its open end by means of a tube ex-tension 30. Means are provided on the extension 30 in the form of a number of heat radiating fins 32 to dissipate heat from the bushing. The open end of the extension is closed by a cap 34 having a filling tube 36.
Means are provided within the blind bore 28 for transferring heat from one end of the bore to the other at a rate sufficient to maintain the stud at a temperature approximating the temperature of the dielectric fluid 16. Such means is in the form of a heat pipe structure 38 which includes a fluid medium 40 and wick 42.
The wick 42 is in the form of a sleeve which covers the inside sur-20 faces of the blind bore 28 and the tube extension 30. The wick functions asmany capillary tubes to transfer the fluid from the cool end of the conductor to the hot portion of the conductor. The wick 42 can be formed of a number of wick materials that are capable of withstanding the contemplated system temperature without deterioration. In the form shown, a woven fiber glass sleeve 41 is positioned in the bore. The sleeve 41 is retained in position by means of a stainless steel expander spring 43 inside of the fiber glass to hold the sleeve against the wall of the tube.
The working fluid 40 can be selected from a number of liquids and must have a heat of vaporization and a vapor pressure range which allow rapid 30 heat energy transfer and low internal operating pressures. One such liquid is water. Ethylene glycol has also been used because of its higher vapor pressure and hence, higher potential temperature operating range.
On assembly, the wick 42 is inserted into the blind bore 28. The tube extension 30 is inserted partially into the bore 28 and soldered into position. The tube is evacuated and while the vacuum is maintained a small amount of the fluid medium is injected through tube 36 into the bore 28.
After the fluid medium has been put into the bore 28 in the bushing stud, the tube 36 is sealed by pinching the end of the tube 36 and sealing the end of the tube by solder. The interior is still below one atmosphere of pressure at that time in the case of water for a working fluid and with a bushing temperature below 100 Celcius.
In operation, the electrical bushing will conduct current and will normally build up heat in the portion of the bushing exterior to the wall 14.
As heat builds up, the fluid medium in the wick 42 will vaporize building up pressure within the blind bore 28 and removing heat from that portion of the conductor. Since the pressure of the medium in the bore 28 will attempt to ` equalize, the vapor will move from the hottest portion of the conductor to-ward the cooler portion. Upon reaching the cooler portion of the tube exten-sion, the vapor condenses giving up heat energy at that portion.
By immersing the tube extension 30 in the cooling medium as shown in the drawing, the heat will be absorbed at a greater rate off of the fins 32. Although the bushing is shown in a vertical position, it can also be mounted in a horizontal position with the entire internal end of the bushing ;~ immersed in the dielectric fluid. As long as the cooling medium can dissi-pate the heat from the fins at a rate sufficient to prevent complete dryout of the wick against the hot portion of the bore 28 of the bushing stud, or, in other words, at a rate that the wick 42 can transfer liquid 40 from the cool area to the hotter area, the vapor will continue to condense in the tube extension 30. ~he condensed liquid will then travel back to the hotter por--tion of the stud through the wick 42 thereby establishing a closed cycle.
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Claims (11)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A high current electrical bushing for an electrical device immersed in a dielectric fluid within a housing, said bushing comprising:
a hollow electrically conductive stud having a terminal at one end and having the other end electrically connected to the electrical device, electrically insulating means mounting said stud on said housing with a portion of the stud immersed in said dielectric fluid, said terminal being located outside of said housing, means mounted on said portion of said stud immersed in said dielectric fluid for transferring heat from a first section of said stud to said dielectric fluid, a working fluid within said stud, and means positioned within said stud for conducting the working fluid from said first section of the stud to a second section of the stud whenever the temperature in said second section exceeds the temperature of said first section;
hence evaporating said working fluid and removing heat energy from said second section, whereby the working fluid is evaporated and heat energy from said second section is removed to said first section.
a hollow electrically conductive stud having a terminal at one end and having the other end electrically connected to the electrical device, electrically insulating means mounting said stud on said housing with a portion of the stud immersed in said dielectric fluid, said terminal being located outside of said housing, means mounted on said portion of said stud immersed in said dielectric fluid for transferring heat from a first section of said stud to said dielectric fluid, a working fluid within said stud, and means positioned within said stud for conducting the working fluid from said first section of the stud to a second section of the stud whenever the temperature in said second section exceeds the temperature of said first section;
hence evaporating said working fluid and removing heat energy from said second section, whereby the working fluid is evaporated and heat energy from said second section is removed to said first section.
2. The bushing according to Claim 1 wherein said conducting means comprises a woven fiberglass sleeve.
3. The bushing according to Claim 2 including means for holding the sleeve in position within the stud.
4. The bushing according to Claim 3 wherein said holding means comprises a spring.
5. The bushing according to Claim 1 wherein said working fluid is water.
6. The bushing according to Claim 1 wherein the working fluid is ethylene glycol.
7. A high current electrical bushing for power apparatus immersed in a dielectric fluid comprising:
an electrically conductive member for connecting the power apparatus to a power source, said member having a bore in one end and a terminal at the other end, a dielectric housing surrounding a portion of said member, heat radiating means mounted on said one end of said member and adapted to be immersed in said dielectric fluid, an electrical terminal at the other end of said member, a working fluid within said bore, and a wick formed from a woven fiberglas sleeve positioned within said bore, said wick including a spring within said sleeve to hold the sleeve in position in said bore, said wick conducting said working fluid from said one end of said member toward the other end of said member whenever a temperature differential occurs in said member.
an electrically conductive member for connecting the power apparatus to a power source, said member having a bore in one end and a terminal at the other end, a dielectric housing surrounding a portion of said member, heat radiating means mounted on said one end of said member and adapted to be immersed in said dielectric fluid, an electrical terminal at the other end of said member, a working fluid within said bore, and a wick formed from a woven fiberglas sleeve positioned within said bore, said wick including a spring within said sleeve to hold the sleeve in position in said bore, said wick conducting said working fluid from said one end of said member toward the other end of said member whenever a temperature differential occurs in said member.
8. The bushing according to Claim 7 including a hollow tubular extension closing said bore.
9. The bushing according to Claim 8 wherein said heat radiating means comprises a plurality of fins mounted on said hollow extension.
10. The bushing according to Claim 7 wherein said working fluid is water.
11. The bushing according to Claim 7 wherein said working fluid is ethylene glycol.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US69952676A | 1976-06-24 | 1976-06-24 | |
| US699,526 | 1976-06-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1106008A true CA1106008A (en) | 1981-07-28 |
Family
ID=24809716
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA281,153A Expired CA1106008A (en) | 1976-06-24 | 1977-06-22 | High current electrical bushing |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1106008A (en) |
-
1977
- 1977-06-22 CA CA281,153A patent/CA1106008A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |