Information
-
Patent Grant
-
6667871
-
Patent Number
6,667,871
-
Date Filed
Friday, February 16, 200123 years ago
-
Date Issued
Tuesday, December 23, 200321 years ago
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Inventors
-
Original Assignees
-
Examiners
Agents
- Hoffman; Tara L.
- Bicks; Mark S.
- Goodman; Alfred N.
-
CPC
-
US Classifications
Field of Search
US
- 361 111
- 361 127
- 361 117
- 361 118
- 361 119
- 361 56
- 361 58
- 361 120
-
International Classifications
-
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)