Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND OF THE IN~ENTION
Field of the Invention:
The invention relates generally to electrical
apparatus, and more particularly to high-current sliding
contact assemblies.
Descri~tion of the Prior Art:
Many devices used in the transmission and distri-
bution of electrical energy require sliding contact current
transfer members. Such devices include gas insulated or air
type disconnect switches, grounding switches, high-current
bus switches, and gas insulated transmission bus Joints.
Each of these devices includes two members relatively movable
between an open position wherein the members are physically
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- separated and a closecl position wherein the members are ln
mechanical engagement, allowing electrical energy to flow
therebetween.
The problem to be solved in all of these devices
is that of reducing electrical resistance at the point of
mechanical engagement. This resistance produces a joule
neating effect as current passes therethrough, thereby
limiting the maximum amount of current which can b,e safely
transferred. Methods for reducing this resistance include
providing a large number of separate points of engagement
between the separable members and providing contact pressure
urging the two members together. While increasing the
contact pressure and increasing the number of points of
engagement between the separable members reduces the resist-
ance, it also means that the mechanism for moving the
members between the open and closed positions must generate
considerable force, thereby increasing the cost of the
mechanism.
Prior art devices have included a plurality of
spring-loaded contact fingers to provide a multiplicity of
contact points upon each of which is exerted a spring force
in a direction perpendiculr to the direction of relative
movement between the separable members. While the contact
resistance and therefore the temperature rise was within
tolerable limits in such prior art devices~ the resulting
force required for actuation of the contacts required a
costly high-energy actuating mechanism or was otherwise
obJectionable from a cost standpoint.
It is therefore desirable to provide a contact
3 assembly exhibitng minimum contact resistance at a lower
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- cost.
SUMMARY O~ THE INVENTION
In accordance with the preferred embodiment of the
present invention, there is provided a resilient sliding
contact assembly comprising a housing, a contact member
adapted for sliding electrical contact with an associated
conductor, resilient biasing means acting upon the contact
member, and means attached to the housing lor loading the
biasing means to produce a spring force along said contact
member, the spring force having a line of action generally
parallel to the direction of relative motion between the
contact member and an associated conductor, thereby urging
the contact member against the surface of the housing to
produce electrical contact therebetween. The point of
contact between the contact member and the housing surface
is offset from the line of action of the spring force. The
spring force is thus resolved into a component parallel to
the direction of relative motion between the center con-
ductor and the housing, and a component perpendicular to the
direction of relative motion between the conductor and the
housing.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a perspective view of a telescoping
contact assembly employing the principles of the present in- -
vention;
Figure 2 is an end view of the contact sheath
shown in Figure l;
Figure 3 is a partial sectional view of the contact
assembly of Figures 1 and 2, showing the construction of the
indi~idual contact fingers; and
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- Figure 4 is a partial sectional view similar to
Figure 3 of a telescoplng contact employing an alternate
embodiment of the present invention, with the center con-
ductor withdrawn.
DESCRIPTI~N OF THE PRE~ERRED EMBO~MENT
Throughout the drawings and specifications, llke
reference characters refer to corresponding components.
Referring now to Figure 1, there is shown a tele-
scoping contact assembly 10 incorporating the principles of
the present invention. The assembly 10 includes a movable
cylindrical center conductor 12 and a cooperating contact
sheath assembly 14. When the conductor 12 is inserted into
the assembly 14, the outer walls of the conductor 12 form
electrical contact with a plurality of contact finger
members 18 arranged around the inner circumference of the
housing 16. The fingers 18 are held against a contact
surface 19 by a plurality of coil springs 20, one of which
is attached to each of the fingers 18. The other ends of
the springs 20 are seated in a channel 22 of a metallic
` 20 holder ring 24 and secured by a flexible adhesive.
A retainer ring 26 is seated around the inner
circumference of the housing 16 (axially spaced from the
fingers 18) and held there by set screws 28 engaging the
inner surface of the housing 16. Loadlng screws 30 are
threaded into the retainer ring 26 and are tightened against
the holder ring 24 to load the springs 20 to provide the de-
sired spring force upon the contact fingers 18.
As can be seen more readily in Figure 3, each of
- the contact fingers 18 includes an aperture 32 through which
extends a circular metallic stabilizer ring 34. The orienta-
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~ion o, the stabilizer ring 3LI can be seen more clearly in
Figure 2. During const.ruction of' the sheath assembly 14,
the fingers 18 are strung upon the stabilizer ring 34 like
beads upon a necklace. The ends of the stabilizer ring 34
are then crimped to sllghtly enlarge them and prevent the
contact fingers 18 from sliding off. In addition to aiding
in the assembly of the de~ice, the stabilizer ring 34, by
maintaining the contact fingers ,L8 in close proximity to
each other, provides lateral stability and prevents the
fingers 18 from sliding out of place during operation of the
assembly 10.
As can be seen in Figure 3, each of the springs 20
is seated in a notch 36, the height of which is indicated by
dimension A of Figure 3. The diameter of the spring 20 is
greater than the dimension A as indicated by dimension B of
Figure 3. Thus, when the spring 20 is inserted from the
side by an automated mechanical procedure (prior to stringing
the fingers 18 on the ring 34), the spring 20 is compressed
across its diameter and elongated in a direction perpendic-
ular to the plane of the drawing. The spring 20 is thussecurely retained by the notch 36 and will not fall out or
come loose during either assembly or operation of the contact
device.
Each of the contact fingers 18 has an end surface
38 and a bottom surface 40 which intersects at an angle C
less than 90. The force of the spring 20 causes the contact
finger 18 to bear against the housing 16 at the points 42
and 44. As can be seen the bearing point 42 is offset from
the line of action 46 of the spring 20. This causes the
force from the spring 20 to be resolved into a component 48
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- parallel to the direction of relative motion between the
conductor 12 and the sheath assembly 14 and a force
component 50 perpendicular to that direction. A contact
pressure is thus maintained between the finger 18 and the
housing 16 at the points 42 and 44, and another contact
pressure at the point 52 between a protruding surface of the
finger contact 18 and the center conductor 12. By ad~usting
the offset distance E between the spring force line of
action and the engagement point 42, the relative contact
pressures can be adjusted in any manner desired. For example,
a contact assembly for a high voltage gas insulated dis~
connect switch having a center conductor diameter of 2.36
inches and a total of 56 contact fingers can provide contact
pressures between the individual finger members 18 and
housing 16 of about 10 pounds and a contact pressure between
the center conductor 12 and contact finger 18 of about 3-1/2
pounds. This contact assembly has a capability of handling ~ `
4,000 amperes continuous current and a symmetrical fault
current of 63,000 amperes.
The walls 54 and 56 of the holder ring channel 22
are inclined at an angle to the axis of the spring 20. This
provides two important advantages. First, the lower angle F
aids in the assembly of the contact device. The upper angle
G allows the spring 20 to buckle slightly when the center
conductor 16 is disengaged, allowing the contact 18 to move
upward. The inner diameter of the holder ring 24 is slightly
larger than t;he outer diameter of the center conductor 12.
Thus, proper engagement of the center conductor 12 and
sheath assembly 14 is possible not only with a slight axial
displacement therebetween, but also with a slight axial
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- misalignment; that is, a degree of non-parallelism between
the axes of the center conductor 12 and the sheath assembly
14. It is the inward movement of the finger contacts 18
permitted by the angled wall 5'~ of the channel 22 which
permits such operation. ~or example, with an angle G equal
to 13, the axes of the conductor 12 and sheath assembly 14
can be misaligned by as much as 3. Proper operation under
these conditions is especially important since axial mis-
alignment is extremely di~ficult to correct, unlike axial
displacement which can be more easily corrected by adjust-
ment of components.
The use of contact fingers 18 having the disclosed
configuration also produces a wiping action at the points
~2, 42, and 44 during operation of the device 10. This is
especially important when the device 10 is operated in an
air environment which often tends to corrode exposed sur-
faces. Such corrosion occurring at the points o~ contact
acts to raise the resistance and produce high running temp-
eratures.
The individual contact fingers 18 can be formed by
either a fine blanking process or a three-step process
involving sintering, coining, and annealing to increase
conductivity. The disclosed device allows the use of almost
twice as many points of contact between the sheath assembly
14 and the center conductor 12 as would a device constructed
for the same cost according to the prior art. Performance
is thus substantially improved, allowing a reduced total
contact pressure between the fingers 18 and the center
conductor 12. This allows the use of a less costly operating
mechanism to provide motion for the center conductor 12.
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- Various means of loading the springs 20 can be
employed. For example, a unitary member 29 providing the
functions of both the holder ring 24 and the retainer ring
26 is shown in Fiæure 4. The spring seat channel 22 and set
screws 28 are both included in the single member 29. Other
means of loading the springs can also be employed.
The contact fingers cc,uld also be located on the
outer circumference of the movable condu¢tor 12 rather than
on the inner circumference of the sheath assembly 14. While
fewer fingers could be included for the same size contact,
this configuration may be desirable in some applications.
It can be seen therefore that the present invention
provides a high-current transfer contact assembly exhibiting
significant advantages over the prior art at substantially
reduced cost.
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