Arrester housing with weak section

Information

  • Patent Grant
  • 6667871
  • Patent Number
    6,667,871
  • Date Filed
    Friday, February 16, 2001
    23 years ago
  • Date Issued
    Tuesday, December 23, 2003
    21 years ago
Abstract
An electrical device includes a housing with first and second portions. Each of the first and second portions has a first insulative layer and a second conductive layer. The first and second layers define an inner cavity. The second portion has opposing first and second lateral sides with the first layer defining a first thickness at the first lateral side and a second thickness at the second lateral side. An electrically conductive member is received within the inner cavity in the first portion. At least one electrical component is received within the inner cavity at the second portion. A weak section is defined by the first thickness at the first lateral side being substantially less than the second thickness at the second lateral side diametrically opposite it at given points along a longitudinal axis of the second portion.
Description




BACKGROUND OF THE INVENTION




Conventional protective electrical devices, such as surge arresters, provide protection for equipment of power distribution systems during fault conditions caused by a system disturbance, such as a lighting strike. An overload of current resulting from a system disturbance can damage and/or destroy electrical equipment because the amount of current is much greater during the disturbance relative to during normal operating conditions.




Conventional surge arresters include an outer housing with two end terminals for connecting the arrester between a conductor device, such as a bushing insert, and ground. Held within the housing of a conventional arrester is a stack of arrester elements or metal oxide varistor (MOV) blocks. The MOV blocks allow the arrester to divert the overload current through the arrester to ground, thereby protecting the electrical equipment. In particular, as the voltage applied to the MOV blocks is increased, due to a system disturbance, the impedance of the MOV blocks decreases towards zero and the blocks become highly conductive thereby conducting the resulting current overload to ground.




Typically during fault conditions, conventional surge arresters rupture and separate from the bushing insert of the electrical equipment, to which it was connected. Arcing typically occurs within the arrester resulting in the generation of gas and heat as the internal arrester elements vaporize. During such a catastrophic failure, the arrester will rupture due to the generated gases that cannot be vented quickly enough from the arrester housing. Commonly, the housing ruptures in random areas, particularly near the connection of the bushing insert and the arrester, thereby forcing the arrester away from the bushing insert such that the arrester separates from the bushing insert. The conventional arresters fail to provide a mechanism for preventing separation of the arrester from the bushing insert during a fault event.




Examples of conventional arresters are disclosed in U.S. Pat. Nos. 6,014,306 to Berlovan et al.; 6,008,975 to Kester et al.; 5,633,620 to Doerrwaechter; 5,309,313 to Yaworski et al.; 5,088,001 to Yaworski et al.; 5,043,838 to Sakich; and 4,463,405 to Koch et al.




SUMMARY OF THE INVENTION




Accordingly, an object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides protection for the system equipment during a fault condition.




Another object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides a mechanism for limiting separation of the electrical device from an electrical connector of the system.




Yet another object of the present invention is to provide an electrical device for a power distribution system and a method of making same that provides a weak section in the housing of the device that allows controlled venting of internal gases upon rupture of the housing.




The foregoing objects are basically attained by an electrical device, comprising a housing including first and second portions with each of the first and second portions having a first insulative layer and a second conductive layer. The first layer defines an inner cavity, and the second portion has opposing first and second lateral sides. The first layer defines a first thickness at the first lateral side and a second thickness at the second lateral side. An electrically conductive member is received within the inner cavity in the first portion. At least one electrical component is received within the inner cavity at the second portion. A weak section in the first lateral side of the second portion of the housing is defined by the first thickness at the first lateral side that is substantially less than the second thickness at the second lateral side diametrically opposite thereto at given points along a longitudinal axis of the second portion.




The foregoing objects are also basically attained by a method of making an electrical device, comprising the steps of forming an outer conductive layer, forming the inner cavity in first and second portions thereof and placing a mandrel in the inner cavity of the second portion of the conductive layer. The mandrel has a teardrop cross sectional shape. Molding an inner insulative layer by injecting a substantially resilient insulative material into the inner cavity at a second portion of the housing and around the mandrel, thereby forming an inner cavity in the insulative layer into teardrop cross-sectional shape that is substantially identical to the tear drop cross-sectional shape of the mandrel.




By fashioning the electrical device in this manner, a controlled venting of internal gases is provided through the weak section. Arranging the weak section rupture in a direction away from an electrical connector device to which the electrical device is connected to avoid disconnection.











Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with annexed drawings, discloses a preferred embodiment of the present invention.




BRIEF DESCRIPTION OF THE DRAWINGS




Referring to the drawings which form a part of this disclosure:





FIG. 1

is a side elevational view in section of a surge arrester in accordance with an embodiment of the present invention;





FIG. 2

is a top plan view in section of the surge arrester taken along line


2





2


of

FIG. 1

, showing a housing of the surge arrester with a weak section after insertion of a module of MOV blocks within the housing;





FIG. 3

is a top plan view in section of the surge arrester similar to

FIG. 2

, showing the housing of the surge arrester with the weak section, before insertion of the module of MOV blocks within the housing;





FIG. 4

is a side elevational view of the surge arrester illustrated in

FIG. 1

, showing the surge arrester mated with a bushing insert; and





FIG. 5

is a top plan view in section of the surge arrester similar to

FIG. 3

, showing the housing of the surge arrester with a teardrop mandrel inserted within the housing.











DETAILED DESCRIPTION OF THE INVENTION




Referring to

FIGS. 1-4

, a surge arrester


10


in accordance with the present invention generally includes housing


14


having a bushing interface portion


16


for connection with an electrical connector, such as a bushing insert


12


, and a shank portion


18


for connection to a ground. Bushing interface portion


16


and shank portion


18


form a substantially elbow shaped arrester, as is well known in the art. Shank portion


18


has a weak section


20


that provides a controlled rupture of the housing to vent or release internal gases that develop during a fault closure. The controlled rupture assists in preventing separation of arrester


10


and bushing insert


12


.




Housing


14


has the general shape of an elbow with bushing interface or first portion


16


extending along a first central longitudinal axis


22


and shank or second portion


18


extending along a second central longitudinal axis


24


, with the first axis being angularly disposed with respect to said second axis, preferably at generally ninety degrees. A conventional housing for a surge arrester is disclosed in U.S. Pat. No. 6,014,306 to Berlovan et al., the subject matter of which is hereby incorporated by reference.




A conductive jacket


26


forms the outer layer of housing


14


and an insulative layer


28


forms an inner lining, as is conventional in the art. The outer conductive jacket


26


is preferably made of conductive EPDM rubber, and the inner insulative layer


28


is preferably made of insulating EPDM rubber. Insulative layer


28


forms an inner cavity


30


at the shank portion


18


of housing


14


that receives an electrical component or module


34


. At the bushing interface portion


16


of the housing


14


, insulative layer


28


forms inner cavity


32


that includes a centrally disposed conductive member or probe


36


that mates with contacts of bushing insert


12


.




With respect to bushing interface portion


16


of housing


14


, a conductive insert


38


, formed of conductive EPDM rubber, sits within inner cavity


32


and provides an electrical connection between conductive probe


36


and electrical module


34


. A bushing port


40


for receiving the end of bushing insert


12


in a telescoping arrangement is defined between conductive insert


38


and an end opening


42


of inner cavity


32


. Conductive insert


38


includes a copper portion


39


that accepts a threaded end


44


of conductive probe


36


with its opposing end


46


extending through end opening


42


. An albative member


48


is included with opposing end


46


of probe


36


, as is known in the art.




As to shank portion


18


, electrical component


34


fits within inner cavity


30


. Electrical component forms a module that particularly includes first and second end terminals


50


and


52


with conventional metal oxide varistor (MOV) blocks


54


stacked and axially aligned between first and second end terminals


50


and


52


. Surrounding first and second end terminals


50


and


52


and MOV blocks


54


is a fiberglass weave casing


56


that tightly secures the blocks


54


and end terminals


50


and


52


together forming a generally tubular module having a right circular cylindrical shape. Springs


58


are applied on each of first and second end terminals


50


and


52


, respectively, to further compress the elements of electrical component


34


, thereby ensuring an electrical path through end terminals


50


and


52


and blocks


54


.




As with conductive probe


36


, conductive insert


38


is also electrically connected at copper portion


39


to electrical component or module


34


by a threaded connection


60


through first end terminal


50


. At the opposite or second end terminal


52


, a threaded fastener


62


engages terminal


52


and secures an end cap


64


to the end of shank portion


18


. As seen in

FIG. 4

, a grounding cable


63


can be connected to threaded fastener


62


at its bottom end


66


remote from terminal


52


, thereby providing an electrical connection between electrical module


34


and ground


67


.




Weak section


20


is located in the side of shank portion


18


of housing


14


, as best seen in

FIGS. 1 and 2

. Specifically, shank portion


18


has diametrically opposed first and second sides


68


and


70


laterally disposed from central longitudinal axis


24


. Inner insulative layer


28


defines a first thickness a in section transverse to central axis


24


at first lateral side


68


and similarly a second thickness b at second lateral side


70


of shank portion


18


with first thickness a being substantially less than second thickness b. Making housing


14


weaker at first lateral side


68


of shank portion


18


than at second lateral side


70


defines weak section


20


. Weak section


20


extends along and is substantially continuous along generally the entire length of shank portion


18


, as seen in

FIG. 1

, the length being generally defined between end cap


64


and the interface portion


16


of housing


14


. First thickness a being less than second thickness b laterally offsets electrical module


34


held in inner cavity


30


from central axis


24


, so that electrical module


34


is closer to first lateral side


68


than second lateral side


70


, and more of electrical module


34


is disposed on the side of central axis


24


that is near first lateral side


68


.




Assembly




Forming surge arrester


10


is generally a three step molding process of first molding outer conductive jacket


26


, then molding conductive insert


38


, and finally molding inner insulative layer


28


. Specifically, outer conductive jacket


26


is molded using a conventional mold including a solid generally L-shaped core mandrel. A conductive rubber is poured around the L-shaped core mandrel to form a one-piece unitary outer jacket


26


with a hollow interior. Jacket


26


can then be removed from the mold simply by removing it from the L-shaped core mandrel. Next, conductive insert


38


is separately formed in a conventional manner.




Once outer conductive jacket


26


and conductive insert


38


are each molded, both are placed in another mold for forming inner insulative layer


28


, with conductive insert


38


being placed within the hollow interior of jacket


26


at the junction point of the L-shaped jacket. First and second mandrels are then placed within the hollow interior of jacket


26


with conductive insert


38


being located between the mandrels. The first mandrel is placed in the interior at the part that will be the interface portion


16


of housing


14


. The second mandrel


80


is placed in the interior of the part that will be the shank portion of housing


14


as seen in FIG.


5


. Inner layer


28


is formed by injecting insulative material into jacket


26


and around the first and second mandrels, and conductive insert


38


, forming a one-piece unitary layer.




The first mandrel has a similar shape to the end portion


74


of bushing insert


12


, to thereby form bushing port


40


of housing


14


, which receives bushing insert


14


, as is known in the art. As seen in

FIG. 5

, the second mandrel


80


has a particular shape of a substantially teardrop cross-sectional shape to form weak section


20


in inner layer


28


of housing


14


. The material of inner layer


28


is injected through a funnel


72


formed in outer jacket


26


, into its interior, and around the first and second mandrels, thereby forming inner cavities


30


and


32


at shank portion


16


and interface portion


18


, respectively. The first and second mandrels can then be removed such that interface portion


16


of housing


14


is formed with inner layer


28


now defining inner bushing port


40


, and shank portion


18


of housing


14


is formed with inner layer


28


now defining inner cavity


30


. As seen in

FIG. 3

, inner cavity


30


has a substantially teardrop shape in section traverse to central axis


24


of shank portion


18


with the point


76


of the teardrop cross-section shape extending towards first lateral side


68


to create weak section


20


.




Finally, electrical module


34


is placed within inner cavity


30


. Upon insertion of module


34


, inner layer


28


at inner cavity


30


conforms to the shape of module


34


forming a friction or interference fit between module


34


and inner layer


28


, as best seen in FIG.


2


. Specifically, the cylindrical shape of module


34


forces the flexible and resilient material of inner layer


28


to conform to its shape, so that inner cavity


30


has a substantially right circular cylindrical shape defined by inner layer


28


. Since the point


76


is directed towards first lateral side


68


, in transforming from a substantially teardrop cross-sectional shape to a right circular cylindrical shape, first thickness a of inner layer


28


at first lateral side


68


is formed so that it is less than second thickness b at second lateral side


70


, thereby defining weak section


20


at first lateral side


68


.




The remaining assembly is conventional and therefore will not be described in detail. In general, module


34


and probe


36


are connected to conductive insert


38


by threaded connection


60


and threaded end


44


, respectively, so that an electrical path is created through probe


36


, insert


38


, and module


34


. End cap


64


is secured to the end of shank portion


18


by threaded fastener


62


which is connected to end terminal


52


of module


34


, and provides a ground connection.




Operation




Referring to

FIGS. 1 and 4

, surge arrester


10


connects to a bushing insert


12


of the electrical equipment for use with electrical equipment


82


of a power distribution system. During a fault event, weak section


20


of arrester


10


will provide a controlled venting of internal gases. The controlled venting will be directed away from bushing insert


12


and bushing interface portion


16


of arrester


10


, rather than in random directions or in a direction toward bushing insert


12


, thereby generally preventing separation of the arrester from the end portion


74


of bushing insert


12


.




In particular, as is known in the art, upon connection of arrester


10


and bushing


12


, end portion


74


of bushing insert


12


is received within bushing port


40


of arrester


10


in a telescoping manner. Probe


36


engages a female contact assembly


78


of bushing insert


12


, thereby forming an electrical connection between arrester


10


and bushing


12


.




During fault conditions, the overload of current results in the generation of gas and heat as the internal MOV blocks


54


of module


34


vaporize. This pressurized gas fills the inner cavities of arrester


10


until rupture occurs. The weak section


20


of shank portion


18


provides a controlled vent or rupture of the gases since the weak section will rupture first, thereby substantially preventing random ruptures in the arrester


10


. By disposing weak section


20


at first lateral side


68


of shank portion


18


opposite and remote from interface portion


16


and bushing insert


12


, arrester


10


is generally prevented from separating from bushing insert


12


because the force of the internal gases through weak section


20


tends to push arrester


10


toward bushing insert


12


, and the occurrence of ruptures near or towards bushing insert


10


are substantially eliminated since weak section


20


will always rupture first.




While a particular embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.



Claims
  • 1. An electrical device, comprising:a housing including first and second portions, each of said first and second portions having a first insulative layer and a second conductive layer, said first and second layers defining an inner cavity, and said second portion having opposing first and second lateral sides with said first layer defining a first thickness at said first lateral side and a second thickness at said second lateral side; an electrically conductive member received within said inner cavity in said first portion; at least one electrical component received within said inner cavity at said second portion; and a weak section in said first lateral side of said second portion of said housing defined by said first thickness at said first lateral side being substantially less than said second thickness at said second lateral side diametrically opposite thereto so that a central axis of said electrical component is laterally offset from a central longitudinal axis of said second portion.
  • 2. An electrical device according to claim 1, whereinsaid weak section is disposed remotely from said first portion of said housing.
  • 3. An electrical device according to claim 2, whereinsaid weak section extends substantially continuously along an entire length of said second portion.
  • 4. An electrical device according to claim 1, whereina casing encloses said electrical component.
  • 5. An electrical device according to claim 4, whereinsaid electrical component comprises a plurality of axially aligned metal oxide varister blocks.
  • 6. An electrical device according to claim 1, whereinsaid first layer is an inner layer; and said second layer is an outer layer.
  • 7. An electrical device according to claim 1, whereinsaid first portion extends along a longitudinal axis substantially perpendicular to said central longitudinal axis of said second portion.
  • 8. An electrical device according to claim 1, whereinsaid electrically conductive member is an electrically conductive probe electrically connectable to an electrical connector.
  • 9. An electrical device according to claim 8, whereinsaid first portion of said housing includes an end opening for receiving said electrical connector in said inner cavity.
  • 10. An electrical device according to claim 1, whereinsaid first layer is a unitary, one-piece member; and said second layer is a unitary, one-piece member.
  • 11. An electrical device, comprising:a housing including a first portion extending along a first axis, and a second portion extending along a second axis oriented at an angle to said first axis, said second axis being a central longitudinal axis, each of said first and second portions having an inner insulative layer and an outer conductive layer, said inner layer defining an inner cavity, said second portion having opposing first and second lateral sides with said first lateral side being remote from said first portion of said housing so that said outer conductive layer at said first lateral side faces in a direction substantially opposite said first portion; an electrically conductive member received within said inner cavity at said first portion; an electrical component received within said inner cavity in said second portion; and a weak section of said inner insulative layer at said first lateral side of said second portion, said weak section being defined by a first thickness of said inner insulative layer in section substantially transverse to said second axis at said first lateral side, said first thickness being less than a second thickness formed by said inner insulative layer in section substantially transverse to said second central axis at said second lateral side of said second portions, so that a central axis of said electrical component is laterally offset from said second axis of said second portion.
  • 12. An electrical device according to claim 11, whereinsaid first thickness is substantially continuous along an entire length of said second portion.
  • 13. An electrical device according to claim 11, whereina casing encloses said electrical component.
  • 14. An electrical device according to claim 13, whereinsaid electrical component comprises a plurality of axially aligned electrical elements.
  • 15. An electrical device according to claim 14, whereinsaid electrical elements are metal oxide varistor blocks.
  • 16. An electrical device according to claim 11, whereinsaid inner insulative layer is a unitary, one-piece member; and said outer conductive layer is a unitary, one-piece member.
  • 17. An electrical device according to claim 11, whereinsaid first portion of said first electrical device includes an end opening; and an electrical connector is received in said end opening and said inner cavity electrically connecting said electrical device and said electrical connector, whereby said weak section controls venting of gas from said inner cavity of said first portion at said second portion of said electrical device upon rupture thereof during an overload of current through said electrical connector and said electrical conductive member and said electrical component of said electrical device.
  • 18. An electrical device according to claim 17, whereinsaid first axis is substantially perpendicular to said second axis.
  • 19. A method of making an electrical device, comprising the steps of:forming an outer conductive layer, including forming the inner cavity in first and second portions thereof; placing a mandrel in the inner cavity of the second portion of the conductive layer, the mandrel having a teardrop cross sectional shape; and molding an inner insulative layer by injecting a substantially resilient insulative material into the inner cavity at a second portion of the housing and around the mandrel, thereby forming an inner cavity in the insulative layer with a tear drop cross sectional shape that is substantially identical to the teardrop cross-sectional shape of the mandrel.
  • 20. The method of making an electrical device according to claim 19, further comprising the steps ofremoving the mandrel from the inner cavity of the housing; and inserting a right circular cylindrical electrical component into the inner cavity in the second portion of the housing, the electrical component having a transverse dimension, such that upon insertion into the inner cavity, the inner insulative layer conforms to the electrical component and the inner cavity has a substantially right circular cylindrical shape.
US Referenced Citations (11)
Number Name Date Kind
4456942 Bronikowski Jun 1984 A
4463405 Koch et al. Jul 1984 A
4609902 Lenk Sep 1986 A
4930039 Woodworth et al. May 1990 A
5043838 Sakich Aug 1991 A
5088001 Yaworski et al. Feb 1992 A
5128824 Yaworski et al. Jul 1992 A
5309313 Yaworski et al. May 1994 A
5633620 Doerrwaechter May 1997 A
6008975 Kester et al. Dec 1999 A
6014306 Berlovan et al. Jan 2000 A