Note: Descriptions are shown in the official language in which they were submitted.
` 1 334300
POLYMER HOUSED ELECTRICAL ASSEM~LIES
USING MODULAR CONSTRUCTION
Related Applications
This application is related to Canadian
5application Serial No. 488,845 filed August 16, 1985.
Field of the Invention
The invention relates to polymer housed electrical
assemblies which are formed as modules and which are
selectively coupled together to vary the overall electrical
rating of the device. Each electrical assembly is formed
from electrical components that are wrapped in a
nonconductive filament winding. The components can be
varistors, resistors, capacitors, insulators, or any
combination thereof.
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Backqround of the Invention
A surge protector or arrester is commonly connected
across a comparatively expensive piece of electrical
equipment to shunt over-current surges. Such over-current
sur~es occur, for example, when lightning strikes. When
this happens, the surge arrester shunts the surge to ground,
thereby protecting the piece of electrical equipment and the
circuit from damage or destruction
Present day surge arresters commonly include an
elongated, hollow cylindrical housing made of porcelain or
the like, and a plurality of non-linear resistive blocks
within the housing. Some of these structures also include
spark gaps, the blocks and gaps being electrically
interconnected to handle voltage and current surge
conditions arising on a power line. The bloc~s commonly
contain silicone carbide (SIC) or metal oxide varistors
(MOV), and are usually in the shape of relatively short
cylinders stacked within the arrester housing. The number
of blocks employed is a function of the material (SIC or
MOV) and the voltage and current ratings of the assembly.
For a surge arrester to function properly, intimate
contact must be maintained between the MOV or SIC blocks.
This necessitates placing an axial load on the blocks within
the housing. Prior art arresters utilize bulky contact
springs within the housing to provide this axial load.
Typically, these springs can provide only relatively small
loads, for example, abo~t sixty pounds. As a result, prior
art surge arresters experience one or more problems- such as
poor heat transfer between the MOV or SIC blocks and
arrester terminals; non-uniform current distribution; and
high contact resistances at joints. Furthermore, units
having low contact force sputter and the ionized metal which
is produced can cause axial flashover at high currents.
An additional pro~lem with surge arresters of the prior
art i~ that they, on rare occasions, fail in a dangerous
fashion. When these arresters fail and experience high
fault currents, the bursting unit may throw parts and cause
property damage. --
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~_ In addition, some of the prior art devices are difficult to
assemble, have poor dielectric design, are susceptible to water
invasion and require totally different devices to provide varied
voltage ratings.
Examples of prior art surge arresters are disclosed in the
following U.S. patents: 2,587,587 to Bellezza et al; 2,947,903
to Westrom; 2,997,529 to Fink; 3,018,406 to Innis; 3,261,910 to
Jacquier; 3,412,273 to Kennon et al; 3,524,107 to Reitz;
3,566,183 to Olsen; 3,567,541 to Kaczerginski; 3,586,934 to
Nakata; 3,706,009 to Reitz; 3,725,745 to Zisa; 3,850,722 to
Kreft; 3,973,172 to Yost; 3,987,343 to Cunningham et al;
4,029,380 to Yonkers; 4,092,694 to Stetson; 4,100,588 to Kresge;
4,107,567 to Cunningham et al; 4,161,012 to Cunningham;
4,218,721 to Stetson; 4,404,614 to Koch et al; 4,467,387 to
Bergh et al; 4,491,687 to Kaczerginski et al and U.S. Defensive
Publication T102,103, as well as U.K. patents 730,710; 1,109,151
and 1,505,875.
Summary of the Invention
Accordingly, the invention seeks to provide electrical
devices, particularly surge arresters, which are relatively
simple to assemble, have good dielectric design, resist water
invasion and have modular components and housings to simply vary
voltage ratings.
Further the invention seeks to provide electrical
assemblies, such as surge arresters, having high axial loadings,
thereby resulting in uniform current distribution, low contact
resistances at joints and excellent heat transfer to the
arrester terminals.
Still further the invention seeks to provide an electrical
assembly, such as a surge arrester, having a shatter-proof
housing which has a high-impact strength and which does not fail
in a dangerous fashion.
Further still the invention seeks to provide an MOV block
assembly with greatly improved tensile and cantilever strengths.
Further still the invention seeks to provide a surge
arrester which i8 forgiving of dimensional variations in
associated parts, thereby reducing the need for expensive close
tolerances.
Briefly the inve~tion pertains to an electrical device, the
combination comprising a plurality of electrical assemblies,
each having first and second ends and substantially cylindrical
outer surfaces with substantially similar diameters, the
assemblies being oriented in an end-to-end serial array, a
connector, coupled to each pair of adjacent electrical
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assemblies, for electrically and mechanically coupling each
adjacent pair of electrical assemblies, a weathershed housing,
enclosing the assemblies, for protecting the assemblies, the
weathershed housing having a substantially cylindrical
throughbore with substantially the same diameter as the
diameters of each of the electrical assemblies' outer surfaces
and terminals, coupled to each of the two electrical assemblies
at opposite ends of the serial array.
More particularly, the invention in one broad aspect
provides an electrical device, the combination comprising a
plurality of conductive electrical assemblies, each electrical
assembly having first and second ends and substantially
cylindrical outer surfaces with substantially similar diameters,
the assemblies being oriented in an end-to-end serial array.
lS Means i8 coupled to each pair of adjacent electrical assemblies,
for electrically and mechanically coupling each adjacent pair of
electrical assemblies, the mechanical coupling resisting
relative axial movement between the electrical assemblies.
Weathershed means completely encloses the assemblies and the
means for electrically and mechanically coupling and protects
the assemblies and the means for electrically and mechanically
coupling. The weathershed means has a substantially cylindrical
throughbore with substantially the same diameter as the
diameters of each of the electrical assemblies outer surfaces.
2S Terminal means, coupled to each of the two electrical assemblies
is at opposite ends of the serial array.
Another aspect of the invention provides an electrical
device in combination comprising a plurality of conductive
electrical assemblies, each electrical assembly having first and
second ends, the assemblies being oriented in an end-to-end
serial array and means, coupled to each pair of adjacent
electrical assemblies, for electrically and mechanically
coupling each adjacent pair of electrical assemblies, the
mechanical coupling resisting relative axial movement between
the electrical asse~blies. Weathershed means, completely
encloses the assemblies and the means for electrically and
mechanically coupling, protects the assemblies and the means for
electrically and mechanically coupling and terminal means is
coupled to each of the two electrical assemblies at opposite
ends of the serial array. Each of the electrical assemblies
includes a plurality of conductive electrical components aligned
in a row and having axially-directed ends, the electrical
components being in electrical connection with one another via
the axially-directed ends. Means is wrapped around the
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components, for applying an axially-directed compressive force
on the plurality of electrical components to maintain the
electrical connection thereof and the means for applying an
axially-directed compressive force includes a non-conductive
filament winding.
Still another aspect of the invention provides a modular
electrical assembly, in combination comprising a plurality of
conductive electrical components aligned in a row, the
electrical components having axially-directed ends and being in
electrical connection via their axially-directed ends. A first
electrically conductive terminal is located at a first end of
the row, the first terminal having first and second axially-
directed ends and being in electrical connection with the
electrical components via the first axially-directed end thereof
and having an axially-directed surface facing in a direction
opposite the first axially-directed end thereof. A second
electrically conductive terminal is located at a second end of
the row, the second terminal having first and second axially-
directed ends and being in electrical connection with the
electrical components via the first axially-directed end thereof
and having an axially-directed surface facing in a direction
opposite the first axially-directed end thereof. Connecting
means is in the second end of at least one of the terminals, for
electrically and mechanically coupling the one terminal to an
adjacent, similarly constructed modular electrical assembly, the
mechanical coupling resisting relative axial movement between
- coupled modular electrical assemblies. Compression means,
coupled to the first and second terminals, axially compresses
the electrical components and the first and second terminals
together as a unit,~ the compression means comprising a non-
conductive filament winding enclosing and axially compressing
the electrical components and engaging the axially-directed
surfaces.
Further still, there is provided an electrical device, in
combination comprising a plurality of substantially identical
and interchangeable modular conductive electrical assemblies in
an end-to-end serial array, the electrical assemblies each
having a substantially cylindrical lateral outer surface with
substantially similar diameter. Each electrical assembly has
first and second terminals at opposite ends thereof and
weathershed means, completely encloses the lateral outer
surfaces of the electrical assemblies for protecting the
electrical assemblies. First means is coupled to adjacent pairs
of terminals for internally electrically and mechanically
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1 334300
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coupling adjacent electrical assemblies, the mechanical coupling
resisting relative axial movement between the electrical
assemblies. Second means is coupled to the two terminals at
opposite ends of the serial array for establishing an external
electrical and mechanical connection of the device. The
weathershed means also completely encloses the lateral outer
surface of the first means for protecting the first means and it
has a substantially cylindrical throughbore of a diameter
corresponding to the diameters of each of the electrical
assemblies outer surfaces.
A still further aspect of the invention provides a surge
arrester, comprising a modular unit having a plurality of
substantially cylindrical metal oxide varistor blocks with
opposite, substantially planar ends, the blocks being
substantially axially aligned and in end-to-end electrically
conductive relationship forming a substantially cylindrical
block stack of desired electrical surge arresting
characteristics and having a stack length. First and second
substantially cylindrical, conductive terminals are at opposite
ends of the stack and have axially-directed surfaces facing in
directions opposite to the stack. Electrically non-conductive
stack loading means, extending along the stack length and
circumferentially around all of the blocks and engaging the
axially-directed surfaces on the terminals, axially compresses
the stack and maintains electrical contact between the blocks.
The loading means encloses the block stack therein and forms a
~ generally cylindrical, non-conductive cover over the block stack
having an outer diameter. An elongated housing of elastomeric
material, having an axial, substantially cylindrical, interior
bore opening at opposite ends thereof, receives the block stack
enclosed in the cover through one of the ends of the housing,
the bore defining an inner diameter of the housing relative to
the outer diameter of the cover for providing close fit
therebetween for minimizing gaps between the cover and the
housing.
Still further, the invention provides a surge arrester
assembly, comprising a modular unit including a plurality of
substantially cylindrical metal oxide varistor blocks of
substantially equal diameter with opposite, substantially planar
ends, the blocks being axially aligned in end-to-end contact
forming a substantially cylindrical block stack with desired
electrical surge arresting characteristics. First and second
substantially cylindrical, conductive terminals are at opposite
ends of the block stack and have axially-directed surfaces
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facing in directions opposite to the block stack. The unit
further includes an elongated, electrically non-conductive
element having a substantially cylindrical outer surface, which
encloses the block stack, the element comprising a plurality of
axially disposed filament windings coupled to the axially
directed surfaces of the terminals and extending the length of
the stack for applying an axially-directed compressive force to
the blocks to hold the blocks and terminals in end-to-end
contact. There is a resilient housing having opposite ends and
a substantially cylindrical, interior bore opening at one end of
the housing, the bore being accessible for axial entry of the
modular unit into the one end of the housing. The bore has a
diameter relative to the outer diameter of the element, whereby
the element forms a close fit with the bore for reducing gaps
between the unit and the housing.
The invention in a still further aspect provides a surge
arrester assembly for protecting electrical circuits, comprising
a plurality of substantially cylindrical blocks having non-
linear voltage-current characteristics of substantially equal
diameter with opposite, substantially planar ends, the blocks
being axially aligned in end-to-end relationship to form a
substantially coaxial block stack. ~irst and second
electrically conductive terminal members are disposed at
opposite respective ends of the block stack in adjacency with
different ones of the blocks located at the opposite respective
ends of the stack, the terminal members having axially facing
~ surfaces. An elastomeric housing has opposite ends and an
axial, interior bore and non-conductive filament winding means
at least partially encloses the blocks and engages the surfaces
of the terminal members. The winding means applies an axially-
directed compressive force to the blocks and the terminal
members, the means applying the force independently of the
housing to maintain axial electrical contact between the blocks
and the terminal members with the means, the blocks and the
terminal members being received in the bore of the housing.
Still further, there is provided a surge arrester assembly
for protecting an electrical circuit, comprising a plurality of
substantially cylindrical blocks having non-linear voltage-
current characteristics of substantially e~ual diameter with
opposite, substantially planar ends, the blocks being axially
aligned to form a substantially cylindrical block stack and
first and second axially aligned, electrically conductive,
terminal members are disposed at opposite respective ends of the
block stack in adjacency with different ones of the blocks
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located at the opposite respective ends of the stack. There is
an elongated housing comprised of a polymeric electrical
insulation having opposite ends and a longitudinal cylindrical
bore intermediate the opposite ends. Elongate, non-conductive
filament winding means is coupled to the terminal members, for
applying and maintaining an axially-directed compressive force
to the blocks by way of the terminal members, the non-conductive
filament winding means having a substantially smooth and
cylindrical outer surface, whereby the non-conductive filament
winding means, blocks and terminal members form a substantially
right circular cylindrical module of axially compressed blocks
and terminal members of substantially constant diameter along
the entire length of the module. The module is mounted in the
bore of the housing with a close fit with portions of the
terminal members being accessible from opposite respective ends
of the housing for connection to the electrical circuit, whereby
the module maintains the compressive force on the blocks and
terminal members independently of the housing. An adhesive may
be applied to the winding means for rendering the module rigid.
The invention also comprehends a surge arrester comprising
a plurality of substantially cylindrical blocks having non-
linear voltage-current characteristics of substantially equal
diameter with opposite, substantially planar ends, the blocks
being axially aligned in end-to-end relationship to form a
substantially coaxial block stack. First and second
- electrically conductive terminals are disposed at opposite
respective ends of the block stack adjacent different ones of
the blocks located at the opposite respective ends of the stack.
Non-conductive filament winding means at least partially
encloses the blocks and terminals for applying an axially-
directed compressive force to the blocks and the terminals. A
housing has open opposite ends, an axial interior throughbore
and a plurality of weathersheds thereon, each of the
weathersheds having substantially the same outer diameter and
root diameter with the blocks and terminals being received in
the housing. There is a pair of disc-shaped end plates, each of
the end plates abutting one of the housing opposite ends and
having an outer diameter greater than the root diameter of the
weathersheds.
Further still, the invention provides a surge arrester
comprising first and second electrically conductive terminals
and at least one non-linear resisting block having first and
second axially-directed ends and positioned between the first
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and second terminals to form a substantially cylindrical
structure having a substantially uniform circumferential outer
surface. The first terminal has an axially-directed end thereon
in electrical connection with the first axially-directed end of
the block and includes a first surface facing in an axial
direction opposite the axially-directed end thereof. The second
terminal has an axially-directed end thereon in electrical
connection with the second axially-directed end of the block and
includes a second surface facing in an axial direction opposite
0 the axially-directed~ end thereof. A plurality of discrete
elongated tensile elements formed of an insulating material and
spaced circumferentially around and extending adjacent one
another the length of the outer surface engages the first and
second surfaces of the first and second terminals, the tensile
elements being under axial tension to thereby apply an
axially-directed compression force to the first and second
terminals and the block, whereby transverse bending of the
arrester is resisted and the first and second terminals and the
block are maintained in electrical connection. A housing having
a cylindrical bore with an inwardly facing substantially
cylindrical surface closely encloses the block, terminals and
tensile elements therein.
Further still, the invention comprehends a surge arrester
comprising first and second electrically conductive terminals,
at least one non-linear resistive block, having first and second
axially-directed ends and a substantially cylindrical outer
surface, positioned between the first and second terminals and
a plurality of elongated tensile elements formed of an
insulating material positioned around the block at
circumferentially spaced locations. The first terminal has an
axially-directed end thereon in electrical connection with the
first axially-directed end of the block, the first terminal
including a first surface for engaging the tensile elements.
The second terminal has an axially-directed end thereon in
electrical connection with the second axially-directed end of
the block, the second terminal including a second surface for
engaging the tensile elements. The tensile elements engage the
first and second surfaces and are axially tensioned to thereby
apply an axially-directed compression force to the first and
second surfaces and the block to resist transverse bending of
the arrester and to maintain the first and second terminals and
the block in electrical connection. A housing having a through
passageway with an inwardly facing substantially cylindrical
surface has a diameter substantially equal to the diameter of
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thé block outer surface with the tensile elements positioned
therearound and receives the block and elements therein.
The invention also comprehends a surge arrester, comprising
a modular unit having a plurality of substantially cylindrical
metal oxide varistor~blocks with opposite, substantially planar
ends, the blocks being substantially axially aligned and in end-
to-end electrically conductive relationship forming a
substantially cylindrical block stack of desired electrical
surge arresting characteristics and having a stack length.
First and second substantially cylindrical, conductive terminals
are at opposite ends of the block stack and have axially
directed surfaces facing in directions opposite to the block
stack. Electrically non-conductive stack loading means extend
along the stack length and circumferentially around all of the
blocks and engage the axially directed surfaces of the terminals
for axially compressing the stack and for maintaining electrical
contact between the blocks. The loading means encloses the
block stack therein and forms a generally cylindrical, non-
conductive cover over the block stack having an outer diameter
whereby transverse bending is resisted. An elongated housing of
elastomeric material has an axial, substantially cylindrical,
interior bore opening at opposite ends thereof for axial entry
of electrical currents to the block stack enclosed in the cover
through one of the ends of the housing, the bore defining an
inner diameter of the housing which is such as to provide a
closely adjacent fit between the housing and the cover and
thereby minimize gaps between the cover and the housing.
Further still, the invention provides a surge arrester
assembly for protecting an electrical circuit, comprising a
plurality of substantially cylindrical blocks having non-linear
voltage-current characteristics of substantially equal diameter
with opposite, substantially planar ends, the blocks being
axially aligned to form a substantially cylindrical block stack.
First and second axially aligned, electrically conductive,
terminal members are disposed at opposite respective ends of the
block stack in adjacency with different ones of the blocks
having axial ends located at the opposite respective ends of the
stack and axially directed surfaces facing in an axial direction
opposite the ends of the blocks. An elongated housing comprised
of a polymeric electrical insulation has opposite ends and a
longitudinal cylindrical bore intermediate the opposite ends.
Elongate, non-conductive filamentary wrap means is coupled to
the axially-directed surfaces of the terminal members and
applies and maintains an axially-directed compressive force to
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the blocks by way of~the terminal members, the non-conductive
filament wrap means having a substantially smooth and
cylindrical outer surface and being sufficiently rigid whereby
the wrap means, blocks and terminal members form a rigid,
substantially cylindrical module of axially compressed blocks
and terminal members resistant to transverse bending. The
module is mounted in the bore of the housing with a closely
adjacent fit with portions of the terminals accessible from
opposite respective ends of the housing for connection to the
electrical circuit, whereby the module maintains the compressive
force on the blocks and terminal members independently of the
housing.
Further still, there is provided a surge arrester
comprising a plurality of substantially cylindrical blocks
having non-linear voltage-current characteristics of
substantially equal diameter with opposite, substantially planar
ends, the blocks being axially aligned in end-to-end
relationship to form a substantially coaxial block stack, first
and second electrically conductive terminals are disposed at
opposite respective ends of the block stack adjacent different
ones of the blocks located at the opposite respective ends of
the stack. Non-conductive filamentary wrapping, at least
partially encloses the blocks and terminals for applying an
axially-directed compressive force to the blocks and the
terminals. A housing has open opposite ends, an axial interior
bore and a plurality of weathersheds thereon, each of the
weathersheds having substantially the same outer diameter and
root diameter with the blocks and terminals being received in
the housing. There is a pair of disc-shaped end plates, each of
the end plates abutting one of the housing opposite ends and
having an outer diameter greater than the root diameter of the
weathersheds.
Another aspect of the invention provides an electrical
device wherein the combination comprises a plurality of
conductive electrical assemblies, each electrical assembly
having first and second ends, the assemblies being oriented in
an end-to-end serial array with means coupled to each pair of
adjacent electrical assemblies, for electrically and
mechanically coupling each adjacent pair of electrical
assemblies, the mechanical coupling resisting relative axial
movement between the electrical assemblies. Weathershed means
completely encloses lateral outer surfaces of the assemblies and
the means for electrically and mechanically coupling, for
protecting the assemblies and the means for electrically and
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mechanically coupling. Terminal means is coupled to each of the
two electrical assemblies at opposite ends of the serial array.
Each of the electrical assemblies includes a plurality of
conductive electrical components aligned in a row and having
axially-directed ends, the electrical components being in
electrical connection with one another via the axially-directed
ends. Non-conductive means is wrapped around the components
for applying an axially-directed, compressive force on the
plurality of electrical components to maintain the electrical
connection thereof, the means for applying an axially-directed,
compressive force including filamentary material which also
resists transverse bending of the device.
Still another aspect of the invention provides a surge
arrester wherein the combination includes at least one non-
linear resistive block having first and second axially-directed
ends. A first electrically conductive terminal has an axially
directed end thereon in electrical connection with the first
axially-directed end of the block and further has an axially-
directed surface thereon facing in a direction opposite the
axially-directed end thereof. A second electrically conductive
terminal has an axially directed end thereon in electrical
connection with the second axially-directed end of the block and
has an axially-directed surface thereon facing in a direction
opposite the axially-directed end thereof. A non-conductive
filament is wrapped around the block and wrapped around and
engages the axially-directed surfaces on the terminals, the
filament being axially tensioned to thereby apply an axially-
directed compression force to the terminals and the block to
resist transverse bending of the arrester and to maintain the
terminals and block in electrical connection.
A still further aspect of the invention provides a surge
arrestor, comprising a plurality of generally cylindrical, metal
oxide varistor blocks aligned in a row along an axis and having
axially directed ends, the varistor blocks being in electrical
connection with one another through the axially directed ends.
First and second generally cylindrical conductive terminals are
at opposite ends of the row, each terminal having a first axial
end in contact with one of the varistor blocks and an opposite
second axial end with an internally threaded socket. The
terminals have inner sections adjacent the first axial ends and
outer sections adjacent the second axial ends, the inner
sections being narrower than the outer sections. The varistor
blocks and the inner sections of the terminals have
substantially equal transverse diameters. A non-conductive
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filament winding is wrapped around the varistor blocks and inner
sections of the terminals and applies an axially-directed
compressive force on the varistor blocks and the terminals to
maintain electrical connection thereof, the winding having a
substantially constant diameter outer surface substantially
equal in diameter to the outer sections of the terminals.
Elastomeric weathershed means resiliently encloses the varistor
blocks, for protecting the varistor blocks, the weathershed
means having a substantially cylindrical throughbore with a
diameter substantially equal to transverse diameters of the
filament winding.
More particularly, other aspects, advantages and salient
features of the invention will become apparent from the
following detailed description, which, taken in conjunction with
the annexed drawings, discloses preferred embodiments of the
invention.
Drawings
Referring to the drawings which form a part of this
original disclosure:
Fig. 1 is a side elevational view, in longitudinal section,
showing a surge arrester constructed in accordance with the
principles of this invention;
Fig. 2 is a side elevational view, in section, of a
modified filament wrapped assembly comprising a plurality of MOV
blocks, spring washers and spacers which are filament wrapped in
several layers in accordance with the principles of this
invention;
1 334300
Fig. 3 i~ a s~de elev~tional view of a pre-cured
polymeric weathershed housing which is designed to receive
the filament wrapped ~OV blocks;
Fig. 4 is an enlarged transverse cross-sectional view
of a filament winding which may be used in accordance with
this invention and comprises a plurality of strands;
Fiq. S is a side elevational view of an electrical
device in accordance with the invention including a
plurality of modular and interchangeable filament wrapped
electrical assemblies enclosed ~n a weathershed housingS
Fig. 6 i8 a side elevational view in partial
longitudinal sect$on of the device shown in ~ig. 5 showing
the electrical assemblies including the filament windings
inside the weathershed hou~ingS
Fig. 7 is a side elevational view in longitudinal
section of the device shown in Fig. 5 and is similar to Fig.
6 but shows the inside of the electrical assemblies; and
Fig. 8 i~ an enlarged and exploded s'ide elevational
view in longitudinal section of one of the electrical
assemblies shown in Figs. 6 and 7.
Detailed Description of the Invention
As seen in Figs, 1, 2, and 3, the invention may take
the form of a surge arrester 10 comprising a filament wound
core of MOV blocks 11 and 12, first and ~econd terminal
p~ece~ 16 and 18, filament windings 14, and a polymeric
weat~ershed hou~ing 20, $he blocks 11 and 12 are separated
by a spring wa~her 13, and load and current distributing
washer~ 5 and 6.
As ~een in Fig. 2, a modified filament wound electrical
assembly 15 may comprise three MO~ blocks 22, 24 and 26,
conducting ~pacer~ 28, 30, 32 and 34, ~pring washers 36 and
38, f~lament windings 14, and first and second terminal
pieceQ ~6 and 18, having first and second circumferential
grooves 1~ and 19. W~ndings 14 provide a plurality of
layers over the ~O~ block~.
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Fig. 3 show~ the pre-cured polymeric weathershed
housing 20, which is des~gned to receive the filament
wrapped assembly 15 shown in Fig. 2 as well as that shown in
Fig. 1.
The MOV blocks furnish a predetermined non-l$near
electrical characteristic between the ends thereof in a well
known fashion. The bloc~s themselves are usually in the
shape of relatively short cyl~nders and may be stacked
within the housing in a row either in intimate contact with
each other, or separated by one or more spring washers 36
and 38 and/or spacers 28, 30 and 32 as illustrated in Fig.
2. A preferred construction, which is shown in Fig. 1,
comprises placing a spring washer 13 and load and current
distributing washers 5 and 6 between the two MOV blocks 11
and 12, which are ad~acent to, and in intimate contact with
the terminal pieces 16 and 18. This provides an excellent
thermal path to ambient and improves operating
characteristics when thermal stability i8 a factor.
The filament windings 14 may be comprised of any
suitable continuous fiber such as nylon, rayon, glass and
polyethylene. Other fibers such as ceramic fibers may also
be used. A glass filament winding is preferred.
The filament windings 14 may be in the form of a single
fiber, or each winding may be comprised of many smaller
strands lS as depicted in Fig. 4.
The filament windings may optionally carry a resinous
material. The resin may be either natural or synthetic, and
may be in tbe partially cured or uncured state. While epoxy
resins are preferred, any other suitable resin may be used.
Tbe polymeric weathershed houslng 20 generally may be
of any shape and size which will ach~eve the desired effects
of providing a shatterproof enclosure having high impact
strength and good weather re~stance. ~he weathershed
housing may be comprisea of a r$gid or elastomeric polymer,
3s and may be either ~ynthet~c, natura~, or a combination
thereof. Examples of such polymers are natural and
synthet~c rub~ers, synthetic thermoplastic elastomers, such
_ 7 _ 1334300
.
as nylon, po~y~inylchlor~de, and polyethylene (linear), and
thermosetting elastomer~ such as polyethylene
(cro~s-linked), and polyester~. The preferred weathershed
elastomer i~ ethylene-propylene rubber (SPM).
The terminal pieces 16 and 18 may be comprised of any
conductive material, preferably a highly conductive metal,
and should preferably contain circumferential annular
groove~ to aid in the process of winding the filament.
In Fig~. 1 and 2, the circumferential grooves or
recesses I7 and 19 are shown as having vertical sidewalls
21, 23, 25 and 27, i.e., sidewalls whose surfaces are
perpendicular to the longitudinal central axis of the
aligned components and form shoulders that radially extend.
These sidewall~ are joined by annular curved bottom walls 29
and 31. In practice, these grooves may be of any
configuration which will serve the purpose of retaining the
windings or they may be merely substantially radially
extending shoulders.
~he spring washers and ~pacers themselves are
conventional and need not be described in detail.
While the discussion has centered on the use of MOV
blocks, it should be understood that the invention
contemplates and Figs. 1 and 2 also depict the use of other
electrical components such as resistors, capacitors, and
in~ulators in place of, or in addition to, MOV blocks. Such
arrangements will be useful for other types of electrical
assemblies.
It 6hould also be noted that while the drawings
illustrate components having a right circular cylindrical
configuration, "cylindrical", as defined for the purposes of
this invention is broadly defined as the surface traced by a
straig~t line Doving parallel to a f~xed straight line and
inter~ecting a fixed cur~e. A curve i5 the intersection of
two geometrical surfaces. Also, the ter~ ~axial~, for the
purpo~es of th~ invention, refers to the longitudinal
central aYis of the ~tructure. ~hus, while cylindrical
bloc~s are preferred, blocks hav~ng a polygonal cross
section may be used.
" .
1 3343~0
The method for making the surge arrester of this
- ~nvention comprises a first step of aligning a plurality of
MOV blocks, with or without $nterposed spacers and/or spring
washers, under an axial load. This invention contemplates
the use of any ax~al load from about 2n pounds per square
inch of bloc~ cross ~ection up to ~ust less than the
crushing Rtrength of the blocks employed. The preferred
; range is from about 50 pounds per square inch to 500 pounds
per square inch of block cross section.
10Any known manner for placing the aligned MOV ~locks
under an axial load would be acceptable provided it
facilitates the wrapping process. One acceptable method is
to align the block~ in a lathe-type apparatus capable of
providing an axial load.
15Once the plurality of MOV blocks, with or without
spacers and spring washers, is aligned and placed under an
axial load, it is ready to be filament wrapped. Any
suitable method for filament wrapping the aligned components
is acceptable provided that it will retain the aligned
components under the specified ax$al load. The preferred
method for wrapping the aligned components comprises a
helical and overlapping wrapping at a relatively low helical
angle and is as follows. First, the filament winding is
secured over the shoulder of one terminal piece. Then the
2s components are rotated approximately 180, while the
filament is drawn axially along the surface of the assembled
components. Upon reaching the opposite terminal piece, the
filament is wound over the other shoulder for approximately
another 180-. The wind~ng machine then sends the filament
back to the ~tarting terminal while the components rotate
another 180. Again, the filament makes a half turn in the
terminal groove a~d this cycle is repeated as many times as
is desired. The degree of rotation and the axial traverse
are slightly out of synchronism so that subsequent cycles
will advance the windings aro~nd tbe ~rface of the
components. Multiple cycles will ult~mately cover the
entire surface with the filament. A partially covered
- 9 - 1 334300
as~embly u~ing this winding pattern is illustrated in Fig.
. Additional layers of winding may be added for additional
strength as shown in Fig. 2.
In practice, if the degree of rotation and the axial
traverse are approximately seven degrees out of synchronism,
twenty-five cycles will approximately cover the entire
~urface, and 100 cycles will provide four layer~ of winding
for additional strength.
It should be understood that this process does not
require axial rotations of 180. Rather, any axial rotation
is acceptable provided that a wrap results which will retain
the component~ under an axial load. In other words, upon
reaching a terminal end, the filament could be wrapped
around the shoulder for more or less than 180. Also, the
filament may be drawn axially along the aligned components
with lesser or greater rotational movement between the
components and the filament.
Also, lf a notched shoulder is used, no relative
rotation need be used thereby allowing for pure axial lay of
the filament wlthout slippage at the shoulder.
As previously mentioned, the filament winding may carry
a resinous compound. The resinous compound may be applied
to the filament w~nding by any number of means such as
pre-coating the filament in a resinous bath, or applying the
re~inous compound to the filaments after the components have
been wrapped. Additionally, the resinous compound may be
either in the semi-cured or uncured ~tate. If the resinous
compound i8 in the uncured state, curing will take place at
a later time, preferably during application of the polymeric
weathershed hou~ing.
Once the components have been wrapped, the weathershed
housing may be applied. A~ previou~ly mentioned, the
hou~ing preferabiy comprises a polymeric compound. ~his
application can be done in numerous ways, ~uch as by
inserting the f~lament wrapped asse~ly into a pre-cured
ela~tomeric polymer weather~bed. If the filament winding
carries an unc~red re~inou~ compound, the windings may be
~:.
1 3343~
-- 10 --
-
adhesively bonded to the pre-cured weathershed in an oven to
create a finished arrester. Other methods such as molding,
spraying, or dipping may be used to provide a polymeric
weathershed onto the filament wound components. Virtually
any method which achieves the desired resuLt i~ acceptable.
When a precured elastomeric weathershed is used, the
housing is straight walled inside as shown in Fig. 3. This
facilitates assembly. In practice, the outer end diameter
of the terminal pieces is made equal to the diameter of the
wound assembly. The diameter of the shoulder is less by the
thickness of glass over the shoulder. After the body of the
assembly is wound, any remaining groove is fillèd with
resin-wetted glass wound circumferentially at both ends.
The finished assembly should, to the extent possible,
approximate a smooth cylinder as shown in Fig. 2.
Again, while the invention has been illustrated in
terms of a surge arrester, the ~process for providing
filament windings can be applied to any suitable electrical
assembly comprising elements such as resistors, capacitors,
and insulators inste~ad of, or in addition to, MOV parts.
If other components are added to or substituted in
the assembly, a similarly shaped electrical assembly should
result. The length to radius ratio may be different than
that normally associated with surge arresters, however, the
concept of providing a filament wrapped electrical assembly
will remain.
Embodiment of Figs. S-8
Referring to Figs. 5-8, an electrical device 50 in
accordance with the invention is shown formed of a plurality
of modular electrical assemblies 52, 54 and 56 enclosed in a
polymeric, ela~tomeric weathershed hou~ing 58. ~ach of the
electrical assemblies is similar to those disclosed above
regarding Fig~ 4, is advantageously substantially
identical to and interchangeable with the other electrical
assemblies, and is in turn formed from a plurality of
cylindrical electrical components 60 and 62. These
~
- 11 - 1 3343~
.
component~ are aligned in a row, and are in electrical
connection with one another via thelr axially-directed ends
and under an axially-directed compressive force via a
nonconduct~ve fllament winding 64, as disclosed above
regarding Figs. 1-4. The electrical components can be
varistors, resistors, capacitors, insulators, or any
combination thereof. While only two electrical components
are shown in Figs. 5-7, more than two can be used.
In the case of varistors used to form a surqe arrester,
voltage rating~ can be enlarged merely by serially and
~electively coupling the plurality of modular electrical
assemblies together mechanically and electrically.
The weathershed housing 58 can be one section of
polymeric material or a plurality of sections 66, 68 and 70
lS in an end-to-end aligned serial array as seen in Figs. S-8.
These sections receive the electrical assemblies therein via
a slight interference fit and therefore facilitate
construction and allow the practice of good dielectric
design by reducing radial gaps.
Each of the electrical assemblies 52, 54 and 56 are
substantially the same, so only a~sembly 52 seen in Figs.
6-8 will be described in detail. Assembly 52 has a
substantially cylindrical overall outer surface and
comprises first end member, or terminal 72, spring washer
74, contact disc 76, electrical component 60, contact disc
78, electrical component 62, contact disc 80, ~pring washer
82, and $econd end member, or terminal 84. The
nonconductive filament winding 64 is coupled to end members
72 and 84 via reception in peripheral grooves 73 and 85
respectively therein, enclo~es the electrical components,
and maintains them under an axially-directed force, which is
augmented by the ~pring was~ers. All of the parts
comprising electr~ca~ as~embly 52 are conductive except the
winding, u~les~ the component6 are insulators.
Advantageou~ly, end member~ 72 and 84 are fonmed from
alumlnum. The exposed outer surfaces of the filament
windlng 64 and the end members 72 and 84 are all
- 12 - l 3 3 4 3 00
substantially cylindrical and have substantially equal
diameters.
End members 72 and 84 form internal terminals, have
cylindrical exposed outer surfaces, and have opposite, first
and second axially-directed planar ends with internally
threaded soc~ets 86 and 88 formed respectively therein.
Socket 86 threadedly receives threaded end stud 90 which can
be connected to an electrical power source and is in the
form of a metallic, conductive shoulder bolt. End plate 92
is received on end stud 90, tightly engages an end of the
weathershed housing as seen in Figs. 5-8, and is held in
place via rigid shoulder 94 on the stud. A second end plate
96 is similarly positioned at the other end of the housing
and is received on end stud 98 which is connected to ground
and maintained thereon via shoulder 99 on the stud. Studs
90 and 9~ in essence form external terminals for the overall
device 50. Each weathershed housing as seen in Fiqs. 5-7
has a plurality of weathersheds thereon with substantially
t~e same outer diameter and root diameter, each of the end
plates 92 and 96 having an outer diameter greater than the
root diameter but less than the outer diameter of the
weathersheds.
Weathershed housing section 66 has a through passageway
in the form of a throughbore with an inwardly facing
2S cylindrical surface 100 which tightly receives therein the
outer cylindrical surface of the electrical assembly 52.
The same is true regarding sections 68 and 70 and assemblies
54 and 56. The reception of the assemblies in the
throughbore is preferably via an interference fit with the
assemblies having outer surface diameters that are
substantially equal to one another and from about 2% to
about 9% greater than the throughbore diameter, which is
substantially constant along its length. This reduces
radial gaps and thus provides advantageous dielectric
desig".
To mechanically and electrically connect the three
electrical assemblies 52, 54 and 56 together in an aligned,
straight end-to-end serial array, a pair of externally
threaded, metallic, and conductive studs 102 and 104 are
used, as seen in Figs. 6 and 7. These studs are
advantageously substantially identical and interchangeable,
as well as substantially rigid and formed of stainless
1 334300
steel. Stud 102 couples the adjacent ends of adjacent
assemblies 52 and S4 by being threadedly received in the
threaded sockets in each assembly's adjacent end member, and
the same is true regarding stud 104 and adjacent assemblies
54 and 56. The adjacent ends of adjacent assemblies are
screwed tightly together on the studs to provide a
substantially gap-free engagement between the facing planar
axially-directed outer ends of the end members thereon.
This provides an advantageous electrical and mechanical
interface by reducing possible separation during bending of
the device. If more assemblies are used, additional studs
are added to connect them, with the addition of any
necessary weathershed housing sections, or use of a larger,
; one-piece housing. As seen in Fig. 8, stud 102 is
receivable in socket 88.
To provide sealing against water invasion, preferably a
neoprene gasket is interposed between each adjacent stud
shoulder and end plate, and silicone grease is interposed
between each adjacent end plate and end member, between
adjacent end members, and between the outer surfaces of the
electrical assemblies and the inwardly facing surfaces of
the throughbore in each weathershed housing section. U6e of
grease between the weathershed housing section and the
electrical assembly aids in construction and assembly by
reducing friction and also reduces any radial gaps
therebetween.
Advantageously as seen in Figs. 5-8, the longitudinal
axes of the studs 90, 102, 104, and 98; the electrical
components in each assembly 52, 54 and 56; and the
weathershed housing 58 are coaxially aligned. Preferably,
the planar ends of the end members are perpendicular to
these aligned longitudinal axes.
Preferably, with regard to the electrical device 50
shown in Figs. 5-8, the axial load on the electrical
components before w~nding is about 750 pounds per s~uare
inch, and the filament is wet epoxy coated f$berglass which
i8 wound through about 100 turns and is cured for about two
hours at 150C.
1 334300
~_ - 14 -
Whi}e various embodiments have ~een chosen to
il~ustrate the invention, it will be understood by those
skilled in the art that var$ous changes and modifications
can be made t~erein without departing from the scope of the
invention as defined in the appended claims.
