Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates t4 an assembly providing low
resistance connections between electrical conductors and more
particularly to an improved assembly for establishing a low
resistance connection between conductors adapted to carry high
current.
PRIOR ART
Connections between conductors carrying high currents
such as 400 amps and above are subject to blow apart forces due
to constricting current paths and opposing large magnetic fields.
Various attempts have been made to improve such connec-
tions and reduce resistance as well as blow apart forces. One
approach in avoiding the blow apart forces at the connection
utilizes a jaw-like assembly with one end of the assembly
secured to opposite sides of a bus bar and the ot~rend projec-
ting forwardly to reeeive therebetween another bus bar. The jaw
members are biased together by heavy springs to hold them
tightly against the connected bus bars and to resist the blow
apart forces. The contact surfaces of eaeh jaw member at the
point of contaet with eaeh bus bar may be rounded to make the
contact angle of current flow less acute which will tend to
lessen blow apart forces. However, portions of such eonneeting
jaws are still substantially parallel to both the source-side
and load side bus bars and in relatively close proximity so
magnetic fields of eurrent paths in such connecting jaws and
parallel bus bars still create substantial blow apart foree.
The aforementîoned arrangement is also quite expensive, and
imperfections in the engaged surfaces give rise to poor or high
resistanee eontact and heating effects.
Arrangements to secure multiple current paths between
associated conductors have used helical or coil springs. The
10'34~g
turns of the springs provide a multiplicity oE engaged surfaces
acting in parallel which are free to adjust themselves independ-
ently to make good contact. This approach, as set out in British
Patent 29,822, uses a hard drawn copper or phosphor bronze
helical coil with the turns set at an angle of 60 to 80 from
the axis of the helix to the points of engagement or contact.
This angle can provide high resistance to insertion or connecting
forces, and phosphor bronze is inherently a high electrical
resistance material with conductivity usually in the neighborhood
of 18% of that of copper.
Copper, on the other hand, while providing low resist-
ivity does not generally retain its resiliency in the high heat
environments, such as that occurring in high current connections
adapted to carry 400 amps or more. Temperatures in such en-
vironments may be maintained at 100Cand may reach a maximum
transient temperature of 150C for a 30 cps current.
It has, therefore, not been previously proposed to
utilize a coil spring to establish connections between conductors
adapted to carry currents of 400 amps or more.
SUMMARY OF THE INVENTION
This invention utilizes a coil spring for establishing
low resistance connections between conductors adapted to carry
currents of 400 amps or more. The problem of high insertion
forces is avoided by substantially decreasing the angle between
the turns of the spring and the axis of the helix or coil and by
utilizing a joint compound and an angle of less than 50. This
angle is preferabLy chosen as 45 and a coil-holding-trough is
provided in one of the conductors, which ensures two points of
engagement for the spring with the conductor.
According to one aspect of the present invention,
there is provided, ~
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an assembly for use .in establishing a low resistance
electri.cal connection comprising, a pair of conductors
each including aluminum and sized to carry either 400
amperes or more amperes of electrical current with each
conductor having a planar surface and movable relative
each other in a first direction parallel to each planar sur-
face to place said surfaces in overlapping positions, the
planar surface of one conductor of said pair of conductors
having an elongate recess extending in a direction transverse
to said first direction and having a bottom surface in said
recess, said recess having longitudinal edges extending
transverse to said first direction to define an opening
communicating with the respective planar surface of said
one conductor, a helical coil spring fcrmed of a copper
cadmium alloy having a conductivity of at least 60% of
that of pure copper adapted to remain resilient at a con-
tinuous temperature of at least 100C located in said
recess with each turn of said spring having an arcuate
periphery formed about an axis of rotation located in
the respective recess and having a diameter greater than
the distance between said longitudinal edges and between
said edges and said bottom surface whereby each turn of
said spring engages said bottom surface at a respective
tangent position to locate each turn of said spring in a
plane having an angle of less than 50 to said axis of
rotation, each periphery projecting from the respective
recess through said openi:ng to a respective position
spaced from the planar surface of said one conductor,
means operative during th~e relative movement of said
conductors in said first Idirection to space the planar
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surfaces of said conductors apart by a distance less than
the projecting periphery of each turn projects from the
planar surface of said one conductor whereby each turn is
engaged by the planar surface of the other conductor along
the arcuate periphery and in a direction transverse to
said axis of rotation in response to the relative movement
between said conductors in said first direction to place
said surfaces in said overlapping positions, the arcuate
periphery of each turn lying in a plane having an angle of
less than 50 to a respective planar surface of said
one conductor for enabling a planar surface of the other
conductor to facilely deflect each turn toward a respective
planar surface of said one conductor and establish an
electrical connection between said conductors in response
to relative movement between said conductors in said first
direction to place said surfaces in said overlapping
.positions, and a joint compound on each planar surface
and on the arcuate periphery of the turns of said spring.
" 1094659
1 I3RIEE' D~:SCRIP'LION OE' TIIE' D~`1Il`lGS
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2 Fig. 1 is a side eleva-tion view of one embodiment of this
3 invention in the form of a helical coil of conductive wire.
4 Fig. 2 is an exploded perspective view of a bus bar having
conductive helical coils as shown in Fig. 1 restrainingly seated
6 ¦ transversely therein on opposite sides with portions projecting
7 outwardly from the contact surfaces of the bus bar for contact
8 with another conductor.
~ Fig. 3 is a side elevation view of the bus bar and an end
view of the conductive helical coil shown in Fig. 2 with a second ¦
11 bus bar shown in connected contacting relationship therewith.
12 Fig. 4 is a perspective view of a modified form of the low
13 resistance connecting device in accordance with -this invention,
14 comprising axially aligned conductive discs in nested relation-
ship to each other and restrainingly seated transversely in a
16 bus bar with a surface portion of each disc projecting outwardly
17 from the contact surface of the bus bar for contact with another
18 conductor.
19 Fig. 5 is a side elevation view of one ring element of the
low resistance helical coil shown in Fig. 1 with the respective
21 adjacent ring elements on each side being broken away.
22 Fig. 6 is a side elevation view of the conductive discs
23 shown in Fig. 4.
24 Fig. 7 is an exploded perspective view of helical coils
embodying this invention shown seated in a round socket con-
26 ducting member of a plug-~in connection.
27 Fig. 8 is a section taken on line 8-8 of Fig. 3.
28 Fig~ 9 is a perspeclive view of a conductive contact arm of
29 a circuit breaker having a pivot end seated in a bus bar of the
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1 circuit brea};er, and a helica:L coil oL- conductive wire in
2 accordance with this inven-tion seated in a recess of the bus bar.
3 Fig. 10 is an exploded perspective view of helical coils
4 embodying this invention shown seated in recesses formed around
the circumference of a plug member of a plug-in type connec~ion.
6 Fig. 11 is a generally schematic isometric view of an
7 1 embodiment of the invention utilized in a high current applica-
8 tion~
9 Fig. 12 is a sectional view taken through a spring recess,
and
11 Fig. 13 is a longitudinal sectional view of a recess and
12 coil.
13 DESCRIPTION OF PR~FERRED ~MBODIMENT
14 A low resistance electrical connec-tin~ device in accordance
with this invention may be embodied in the form of a helical coil
16 1 of conductive wire 2 such as copper cadmium. The wire should
17 be at least 60% IACS. It may be relatively thin and is preferablyj
18 silver plated for improved conductivi-ty. The rings 3 of -the coil j
19 ¦1 are arranged so close together in this invention, and the
20 ¦diameter of the coil is sufficiently small, whereby sufficient~
21 Isupport and rigidity is provided for the coil.
22 l! Each ring 3 of helical coil 1 comprises one conductive
23 element 4 in accordance with this invention. The invention is
24 described as being embodied in a helical coil for convenience of
description, but the invention may be embodied in a wide variety
26 of resilient elements of suitable conductivi-ty. I
27 Each conductive element 4 includes a pair of outwardly con- ¦
28 ~vex surfaces 5 and 6, each supported on opposite sides of an
29 ~equatorial or latitudinal plane 7 between them as illustrated in
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Fig. 5. ~he plane between convex surfaces 5 and 6 may be at the
equator dividing each into equal halves, but it need not be. It
may be any latitudillal plane naving some part of an outwardly
convex surface on each opposite side of the plane. The poles of
such spnerical or convex surfaces 5 and 6 on opposite sides oL
such plane need not be axially aligned. They may be axially
offset, or their axes may be randomly directed, but they are
preferably conductively associated to provide parallel current
paths between a source-side conductor 8 in contact with one set of
said convex surfaces 5 and a load-side conductor 9 in contact with
the opposite set of convex surfaces 6.
In the helical coil embodiment of this invention, the convex
surfaces 5 and 6 are conductively associated to provide parallel
current paths through the oppositely directed sides 4a and 4b each
ring 3 of the helical coil~
As illustrated in Fig. 3, one side 4a of a ring of the coil
1 provides one conductive path between a point where convex
surface 5 contacts source-side bus bar 8 an the points where
convex surface 6 contacts load-side bus bar 9 at 6b.
The opposite side 4b of the coil ring provides an electri-
cally parallel current path between the point where convex surface
5 contacts source-side bus bar 8 and the point 6d of convex
surface 6 in contact with load-side bus bar 9.
Thus a current path from bus bar 8, convex surface 5,
conductive path 4a, contact point 6a and bus bar 9 is electrically
in parallel with a current path from bus bar 8, convex surface 5,
conductive path 4b, contact point 6c and bus bar 9.
The conductive coils 1 may be seated in transv~rse recesses
10 and 11 formed in opposite sides of bus bar 9 opening to
109~6~9
1 respective surfaces 12 and 13. In this embocliment convex
2 surfaces 5 protruding outwardly from surfaces 12 and 13 respectiver
3 ly are proportionately smaller than their corresponding convex
4 surfaces 6 lying on the opposite side of respective planes
through coils 1 which are co-planar with respective surfaces 12
6 and 13 of bus bar 9.
7 The coils 1 are preferably sea-ted in recesses 10 and 11
8 with their rings 3 inclined in side elevation with respect to
9 the surfaces 12 and 13 of bus bar 9. This arrangement tends to
put the rings of the coil under a certain amount of tension or
11 tortional stress for better contact with the respective bus bars
12 8 and 9.
13 The width of the recesses 10 and 11 corresponds to the
14 circumferencial dimension of helical coils 1 to retain them
snugly therein. The depth of the recesses is less than the
16 diameter of the coils 1 whereby the convex surfaces 5 of each of
17 the coil rings 3 protrude outwardly from the surfaces 12 and 13
18 of bus bar 9.
19 The cross-sectional configuration of recesses 10 and 11
may be polygonal as shown, rectangular, square, ovular or
21 circular, as long as they retain the helical coils snugly therein
22 with a convex surface 5 pro~ecting outwardly from ~he surfaces
23 f the bus bar.
24 Only one helical coil 1 is shown recessed in each opposite
side of bus bar 9, in Fig. 2, but a plurality of recesses and
26 coils can be provided in each side of the bus bar throughout its
27 area which is in facing relation to a corresponding connected
28 bus bar.
29 ~ ~ modified embodiment of this invention ~s illustrated ln
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1 ~;`igs. ~ and 6. Ln this enlbodilllent eacll condllctive elernent 4'
2 consists of all indiviclual separate disk 3' is in nested engage-
3 ment and capable of flexure in response to engagement by a planar
4 surface of another conductor and, preferably silver plated. The
flexture may be provided by a bend in an equatorial plane to
6 enable resilient engagement witll the other conductor. The disks
7 may be in any of a variety of disk shapes, the only requirements
8 being that they have outwardly convex rim surfaces 5' and 6'
9 on opposite sides of a latitudinal plane between such surfaces,
and the disks should be relatively thin in cross-section to
11 enable stacking a large number closely adjacent to each other
12 to provide many contact points and current paths for a given
13 area of conductors with which they are used.
14 The disks 3' may be concavo-convex with concave and convex
side walls 14 and 15, respectively, for stacking in a nesting
16 relationship as illustrated in Fig. 6. Each disk may touch
17 adjacent disks or they may be slightly spaced apart.
18 Any number of other structural forms may be utilized to
19 embody this invention as long as they provide a multiplicity of
outwardly convex conductive surfaces on opposite sides of a
21 latitudinal plane between them and with the oppositely disposed
22 convex surfaces conductively associa~ed to provide parallel
23 current paths.
24 The structural embodiment of this invention is preferably
small in size relative to current carrying capacity, and easily
26 adapted for mounting across corresponding connecting surfaces of
27 respective source-side and load-side conductors. Fig. 7 illu-
28 strates a helical coil embodiment of this invention for use in
29 a plug and socket type of connection. Two helical coils 1 are
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1 shown seated in annular recesses 16 and 17 formed in the inner
2 conductive wall 18 of socket 19. Only one coil 1 in one recess
3 16 may be used, or a plurality of coils and recesses as shown.
4 The width of recesses 16 and 17 corresponds to the circumference
of helical coils 1 to retain them snugly therein. The depth
6 of the recesses is less than the diameter of helical coils 1
whereby the convex surfaces S of each of said coil rings 3
8 protrudes from the surface of inner conductive 18 for contact
~ with surface 20 of plug conductor 21. Fig. 10 illustrates a
plug and socket connection having the helical coils 1 mounted
11 on the plug conductor 21.
12 Since this invention includes a multiplicity of closely
13 adjacent individual elements each providing parallel current
14 paths, and minimal surface contact on the part of each element
for highly efficient low resistance transfer of current from one
16 conductor or another, it ls particularly useful in electrically
17 connecting conductors having irregular surface shapes and contours .
18 Fig. 9 illustrates one application of this type, involving
19 a movable contact arm 22 of a circuit breaker having a pivot
end seated in V-shaped recess 24 of conductor 25. A small
21 helical coil 1 in accordance with this invention, of preferably
22 silver plated wire, is seated in the vertex of V-shaped recess 24.1
23 Outwardly convex surfaces 5 project into the cavity of recess 24
24 for contact with the rounded surface edge 26 of the pivot end 23
f contact arm 22. The opposite outwardly convex surfaces 6 are
26 in contact with conductor 25. Prior to this invention, such
27 contact arm in this type of circuit breaker had only two contact
28 points at 27 and 28 along the respective side walls 29 and 30 of
29 the V-shaped recess 24. These were insuf-ficient when current
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increased beyond a given point to transfer the entire current
between conductor 25 and contact arm 22, and to prevent the
pivot end 23 from "popping" out of recess 24 due to blow apart
forces. A shunting conductor 31 had to be provided for such
increased current to prevent popping. The low resistance
connecting device comprising helical coil 1 seated in recess 24
for contact between conductor 25 and contact arm 22 is able to
transfer such increased current without the need of a shunting
conductor 31.
The connecting elements and assembly in accordance with
this invention may be embodied in a variety of different
structures using a variety of different conductive materials,
as long as the structure provides multiple parallel current
paths between a source-side conductor and a load-side conductor.
Preferable specifications for the conductive material,
whether it be a single element metal or an alloy, are tl)
electrical conductivity with a resistivity no greater than 1.12
michroms-centimeter at 20 Centigrade, and (2) structural
strength or stiffness equal to or greater than the modulus of
rigidity of copper, or alternatively a modulus of rigidity
equal to or greater than 15.0 X 106 pounds per square inch.
A preferred conductive material for use in this invention
is copper which may be silver plated for better conductivity.
Illustrative examples of other conductive materials that would
be suitable are alloys of beryllium copper, phosphor bron~e and
aluminum. Illustrative examples of other plating materials
which would be suitable for use with this invention include tin
plating and cadmium plating.
In E'ig. 11 a portion of a plug-in or switchboard unit 50
is schematically illustrated for extending a connection from a
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1¦ terminal 52 to a load termirlal 54. The line terminal 52 extends
21 from a bus bar, for example, and -typically may carry 400, 800 or
3 1200 amperes and is connected to a conductor or stab 56 pro-
4 jecting from the unit 50 in response to movement of the unit 50
toward the terminal 52. The stab 56 in turn extends a connection ¦
6 from the terminal 52 through a circuit breaker or switch generally
7 indicated at 58 of the plug-in unit to a conductor or jaw 60
8 adapted to receive the stab or load terminal 54 for extending
9 power to a load.
The line terminal 52 comprises a jaw or a pair of spaced
11 legs having spaced planar surfaces adapted to receive the spaced
12 planar surfaces of stab 56 therebetween. Each surface of stab
13 56 contains a plurality of elongated channels, troughs or
14 ¦recesses 62 extending transverse at an outer angle to the
direction of movement between the stab 56 and terminal 52. Each
16 recess retains a respective coil spring 64 for engaging the
17 surfaces of terminal 52. A crimp 65 in the recess edge adjacent
18 each end of a respective coil spring limits longitudinal movement j
19 of the spring.
The load terminal 54 comprises a parallelepiped stab whose
21 forward or engagement end is bevelled for sequentially engaging
22 Ithe coils or turns 66 of a coil spring 64 carried in a respective
23 lone of a plurality of recesses 68 of jaw 60. Contact between
24 Istab 54 and coils 66 is therefore gradual and limits the total
force necessary for engagement in a manner similar to tha-t
26 between springs 64 carried by stab 56 and terminal 52.
27 Each trolgh as seen in Fig. 12 is polygonally shaped having
28 sides a-g with relatively short sides b and f and the recess
29 extends substantially 270 about each spring to define an opening ¦
ll
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1 communicat~llg wi-th the adjacent planar surface. The opening
2 permits the spring to extend or project above the respective
3 planar surface for substantially .03". ~s can be seen in Fig. 13,¦
4 the conductive coils are positioned in the trough so that the
coil turns are at an angle less than 50 from the axis of the
6 coil or adjacent planar surfaces and preferably 45 as shown.
7 This angle is of critical importance as it reduces the force
8 necessary to secure engagement between the coils and the mating
~ surfaces, while retaining the necessary resilient engagement
between the opposing or mating conductors to ensure uniform
11 multiple current paths.
12 Fig. 12 shows the two points of contact or tangency between
13 each turn of conductive coil 64 and the surface of trough 62,
14 as occurs during engagement with a matiny surface. One point
f contact along side c and the other contact point along side e
16 each at substantially 135 to a normal N between a mating surface ¦
17 f terminals 52 or 54 and the respective turn to permit facile
18 deformation of the coil in the directions of sides b, d and f.
19 When the terminals 52 or 54 are disengaged from the respective
spring the turns expand so that they are also tangent to the
21 surfaces a and g terminate substantially at a respective point
22 of tangency with the spring to permit the spring to project from
23 the recess 62, however in fabrication the surfaces a and g
24 initially extend beyond the point of tangency as shown by dotted
lines D and are machined off, since the conductors or terminals
26 are yenerally formed from extruded aluminum and cannot be
27 accurately extruded to the desired dimension.
28 The coils have an outer diameter of substantially .250"
29 and are for ~d from cadmi~n copper alloy 162 wire of .02" diameter
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This wire has a resistance of less than 50 microhms per ineh,
with 25 turns per inch, and peak currents of 20 kiloamps per
inch can be safely carried. A silver plate of .00025" minimum
is applied to the wire and a similar plate is applied to the
planar terminal surfaces. The cadmium copper alloy has a
conductivity of substantially 82% of IACS and should not be
less than 60% IACS for use in the described arrange~ent. This
spring arrangement retains its resiliency or elasticity at
maximum transient temperatures of 150 C for 30 cps or at
continuous temperatures of 100C.
In addition a joint compound such as Cu-AlAid or No-Oxid,
or petroleum base compounds are provided on the springs and/or
adjacent surfaces to reduce friction and to protect against
chemical attack such as sulfides on the silver plate, or
oxidation and to enhance thermal eonduetivity.
To extend a eonnection from the line terminal 52 to the
load terminal 54, the plug-on unit 50 is moved relative the
terminals to engage the stab 56 between the spaced planar
surfaces of terminal 52 and the stab 54 is moved between the
spaced planar surfaces of terminals 60. As the planar surfaces
move into overlapping positions, the terminal 52 sequentially
engages the turns of coil 64 since the axis of the eoils are
positioned at an acute angle to the direction of movement.
This in eonjunetion with the angle of 45 between the plane of
the eoil turns and their axis or the planar surface and the
joint eompound substantially reduees the foree required for
engagement an facilitates re!petitive engagement with minimum
danger of damage. A similar result is achieved by the beveled
end of stab 54 engaging the coil turns in sequence.
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l As the planar surfaces of terminals 52 and 54 engage the
2 projecting springs the spring turns are compressed into the
3 respective recesses and the angle to the axis tends to be reduced
4 below 45 as the turns both slide relative each other and deform
51 into the recess. The spring turns move ffrom engagement with
6 surfaces a and g and are held tightly engaged under spring
7 pressure between surfaces c and e and the planar surface of the
8 mating terminal. The springs in this arrangement provide sub-
9 stantially equal engage~ent pressure at all points to ensure
multiple paths for current flow irrespective of tolerance
ll problems or minor differences in the spacing of the planar
12 surfaces.
13 The foregoiny is a description of the preferred embodiments
14 and the inventive concepts are believed set forth in the
16 accompanying claims. ¦'
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