Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ROLLER EXPANSION JOINT
Field of the Invention
This invention relates to support structures
for current carrying conductors and to expansion joints
for enabling longitudinal changes of dimension within
the conductor and movement of the conductor relative to
other objects, without affecting the conductor's current
carrying capability. The roller expansion joint of the
present invention includes an electrically conductive,
flexible expansion loop for affixation to an end of the
conductor and roller means for rollably supporting the
conductor as it moves.
~ e _ nd of the Invention
Current carrying conductors are often subject
to thermal expansion and contraction caused by changes
in ambient temperature, by changes in heat generated
within the conductor by load currents, or by radiant
energy imparted to the cGnductor by the sun or other en-
ergy sources. Such expansion or contraction may cause
longitudinal movement of the conductor relative to the
ends of the conductor which are typically connected to
electrical apparatus. Longitudinal movement of a con-
ductor such as a high voltage electric power bus bar may
also be caused by the weight of foreign material such as
; ~ ice which may adhere to the conductor. If no compensa-
tion for such movement is provided, the conductor may
break or pull away from a point of connection, inter-
rupt1ng the transmission of electric current by the
conductor. It has been found, for example, that a
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high voltage electric power bus bar exposed to typical
outdoor conditions encountered in the Province of
Saskatchewan, Canada, may be subject in an average year
to expansion or contraction of as much as 4 inches (lO0
mm.) over every lO0 feet (30 m.) of its length. Simi-
larly, relatively low voltage current carrying conduc-
tors such as those used to power electric arc furnaces
may be subject to significant thermal expansion or con-
traction, at least in the immediate vicinity of the
furnace.
In situations where conductor expansion or
contraction is expected, expansion joints are typically
inserted at regular intervals in the current carrying
conductor to enable the conductor to expand or contract
without stretching beyond its tensile capacity, without
permitting excessive sagging of the conductor, and with-
out stressing components to which the conductor may be
connected.
Conventional conductor expansion joints have
suffered from a number of disadvantages. Typically,
conventional conductor expansion joints enable limited
sliding movement of a conductor segment relative to a
fixed support. However, frictional forces at the point
of sliding contact frequently result in jamming which
disables the expansion joint.
; Another disadvantage of conventional conductor
expansion joints is the widespread use of compression
connections ln which parts are compressed together to
form a connection by using elements such as bolts.
Bol~ed connec~ions are unreliable because they tend to
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loosen and reduce the current-carrying capacity of the
expansion joint. ~olted connections also have inter-
stices which may be contaminated by dirt buildup or cor-
rosion, inhibiting the ability to pass electric current
across the bolted connections.
A further disadvantage o conventional expan-
sion joints has been the use of expansion joint compo-
nents which are formed of a different metal than that
used to form the conductor. This use of dissimilar met-
als results in galvanic action and consequent electroly-
tic corrosion at the point of connection between the
conductor and the expansion joint which, again, reduces
the current-carrying capacity of the expansion joint.
~ the Invention
The invention is directed to an expansion
joint for enabling longitudinal changes of dimension
within a current carrying conductor. The expansion
joint comprises an electrically conductive expansion
loop for affixation to an end of the conductor and rol-
ler means for rollably supporting the conductor. The
expansion loop comprises a plurality of spaced-apart
l m inations. The roller means comprises a pair of rol-
lers for positioning adjacent vertically opposed sides
of the conductor for rollably supporting the conductor.
The rollers substantially reduce frictional forces at
the point of;contact with the conductor, thus minimizing -
the potential for jamming of the expansion jaint.
The expansion loop may include a first end for
affixation to an end of the conductor and a second end
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expansion loop may include a first end for aEixation to
an end of a first conductor segment and a second end for
affixation to an end of a second conductor segment.
Preferably, the expansion loop is welded to
the conductor ends and is formed of the same material as
the conductor. Welded connections are less likely to
work loose as the conductor moves than compression con-
nections. By forming the expansion joint of the same
material as the conductor, the potential for electro-
lytic corrosion is reduced.
Advantageously, a conductor extension memberis affixed between the conductor end and the expansion
loop end to simplify on-site welding of the expansion
joint to a conductor segment.
In a preferred embodiment, adjacent lamina-
tions of the expansion loop are spaced apart by at least
1.6 mm. "
The invention also provides a roller support
for an electrical conductor, the support comprising a
pair of rollers for positioning adjacent vertically
opposed sides of the conductor for rollably supporting
the conductor.
t~ _ I tb~ De~ ol~
FIGURE 1 is a side elevation view of a roller
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expansion joint for connection between a current carry-
ing conductor and a piece of normally immovable equip-
ment.
FIGURE 2 is a sectional view taken with res-
pect to section line 2-2 of FIGURE 1.
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FIGURE 3 is a top plan view of the base plate
24 showing the holes provided for bolted connection
thereof to a piece of terminal equipment.
FIGURE 4 is a side elevation view of a roller
S expansion joint for connection between adjacent long-
itudinally aligned conductor segments.
Detailed Descri~tion of Three Embodiments of the Invention
The preferred embodiments to be described con-
template roller expansion joints and roller support
structures for a high voltage electric power bus bar.
However, it is not intended that the invention be limit-
ed to high voltage applications. It is expected that
the invention may alleviate problems caused by conductor
expansion or contraction in a wide range of applications
including, for example, conductors for powering electric
arc furnaces or electroplating apparatus - either of
which may be subject to significant thermal expansion or
contraction in the vicinity of the powered apparatus.
One of two different roller expansion joint
constructions may be selected depending upon the indi-
vidual application. The two types of roller expansion
joints are herein referred to as the "single roller ex-
pansion joint" and the "double roller expansion jointn;
the principal difference between the two types being the
number of roller pairs provided. The single roller
~; expansion joint is used where a conductor segment is to
be connected to a rigid terminal point. The double
roller expansion joint is used to interconnect two long-
itudinally aligned conductor segments. The roller sup-
port structure may also be used separately from the
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expansion joint elements to support a conductor segment
at points where allowance for longitudinal movement need
not be made.
Single R lle E pansion J_ nt
Figure 1 depicts a single roller expansion
joint. The single roller expansion joint includes an
electrically conductive expansion loop 10 which compris-
es a plurality of spaced-apart laminations. Expansion
loop 10 has a first end 12 for affixation to an end of
a conductor extension member such as stub connector 20,
and a second end 16 for affixation to base plate 24.
Base plate 24 may then be bolted to a piece of normally
immovable equipment such as a disconnect switch (not
shown).
Conductor 14 is circumferentially welded at 18
to stub conductor 20. Conductor 14 will typically com-
prise a section of aluminium pipe (such as Alcan B505~
aluminium alloy conductor pipe) in which case stub con-
nector 20 may comprise a short length of the same pipe.
An insert 22 comprising a short length of pipe having an
outside diameter slightly less than the inside diameter
of either conductor 14 or stub connector 20 is placed
inside conductor 14 and stub connector 20 to overlap
welded connection 18, providing rigidity at the point of
connection.
Base plate 24 supports a pair of roller brac-
kets 26 which extend vertically upward from base plate
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24 ad~acent opposite sides of stub connector 20 (best
seen in Flgure 2). Roller brackets 26 are drilled to
provide relatively loose support for rollers 28 which
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are positioned adjacent vertically opposed sides of stub
connector 20 to rollably support stub connector 20.
The ends of rollers 28 which are fitted within roller
brackets 26 should be coated with a suitable lubricant
such as MOLYKOTE~ 321R, a product of Dow Corning.
A first pair of backing plates 30 are welded
together around their outer edges to sandwich the lamin-
ations comprising expansion loop first end 12. Backing
plates 30 provide reinforcement and enable welded con-
nection of expansion loop first end 12 to stub connector
20. Advantageously, stub connector 20 is welded to
backing plate 30 in a production environment before the
expansion joint is welded to a conductor segment in the
field. Stub connector 20 protrudes from the roller ex-
pansion joint and facilitates relatively simple on-site
welding of the expansion joint to a conductor segment.
A second pair of backing plates 30 sandwich expansion
loop second end 16 to provide reinforcement and to `~
facilitate welded connection of expansion loop second
end 16 to base plate 24. Base plate 24 is then con-
nected (by means of bolts - not shown) to whatever
terminal equipment may be provided. The bolts are
passed through holes 23 in base plate 24 (best seen in
Figure 3).
A guide means such as a pair of guide plates
32 is welded to rol~ler brackets 26 to prevent rotational
movement of conductor 14 if it is used in conjunction
with a rotating stack device of the type commonly found
in electric power line disconnect switches. Figure 1
shows only a single guide plate 32. In practice, guide
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plates are provided in pairs, as shown in Figure 2, on
opposite sides of stub connector 20, one guide plate
being welded to each of the roller brackets 26. Without
a suitable yuide means, operation of the disconnect
switch may impart a torque to the conductor, causing it
to rotate and possibly misaligning the conductor and/or
subjecting it to undesirable stresses which may cause
physical damage to the conductor or to equipment
connected to the conductor. `
Preferably, all sharp edges and welds on all
components of the expansion joint assembly are ground
smooth to limit undesirable corona discharge. Inso-
far as practically possible all expansion joint compon-
ents should be constructed of the same material as con-
ductor 14 to eliminate the possibilty of electrolytic
corrosion at points of contact between dissimilar met-
als. Welded connections should be used in preference to -
compression (bolted) connections since compression con-
nections are subject to contamination by dirt buildup or
corrosion and may tend to loosen, thus reducing the
current carrying capacity of the expansion joint.
The single roller expansion joint is normally
supported on an insulated terminal pad. As conductor 14
expands or contracts it forces stub connector 20 to move
to either the right or the left as viewed in FIGURE 1.
Stub~connector 20 rolls across rollers 28 which may
rotate, using the holes drilled in roller brackets 26 as
bearing surfaces. The laminations comprising expansion
loop 10 flex as stub connector 20 moves to the right or
to the left, enabling continuous electrical conductivity
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between conductor 14 and the terminal e~uipment (not
shown) to which it is connected via the expansion joint.
It has been found that an expansion loop suit-
able for use with a 1200 ampere current carrying conduc-
tor constructed of 3-inch inside diameter aluminium pipe
may be fabricated from ten aluminium laminations,
each measuring .032" in thickness. Preferably, adjacent
laminations included in such an expansion loop are
spaced apart by about 1/1~" to prevent binding or jam-
ming as the loop flexes. Temporary spacers may beplaced between adjacent laminations to hold them apart
while the laminations are welded in place between back-
ing plates 30. The loop radius "R" (see Figure 1) in
such an expansion loop is preferably at least 2 3/4" (70
mm.) so that loop 10 has ample capacity for flexing to
absorb expansion or contraction of the conductor.
Double Roller Expansion Joint
FIGURE 4 depicts a double roller expansion
joint. The double roller expansion joint provides an
electrically conductive expansion loop 33 for affixation
between a first conductor segment 34 and a second con-
ductor segment 36. An end of first conductor segment 34
is circumferentially welded to a first extension member
such as stub connector 38 which is rollably supported by
rollers 40 positioned adjacent vertically opposed sides
of stub connector 38. Rollers 40 are rotatably
supported by a pair of roller brackets 42 (only one of
which is visible in FIGURE 4). A first end 44 of
expansion loop 33 is welded to stub connector 38.
The right hand half of the double roller expansion
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joint depicted in FIGURE 4 is identical to the left hand
portion just described. A second roller pair 46 pro-
vides rolling support for a second conductor extension
member such as stub connector 48 which is circumferen-
tially welded to an end of second conductor segment 36.Rollers 46 are rotatably supported by a pair of roller
brackets 50 (only one of which is visible in FIGURE 3).
A second end 52 of expansion loop 33 is welded to stub
connector 48. Roller pairs 40 and 46 provide rolling
support for conductor segments 34 and 36 respectively as
they move to either the right or the left as viewed in
FIGURE 4. The laminations comprising expansion loop 33
flex to maintain electrical conductivity between conduc-
tor segments 34 and 36 as the segments move relative to
one another.
Installation
The spacing between consecutive expansion
joints will depend in most cases on the bus bar configu-
ration. In general, however, no segment of a high vol-
tage electric power bus bar should be fixed at both endswithout inaluding an expansion joint to allow for expan-
sion and contraction of the bus bar. In bus bar seg-
ments one might expect to employ an expansion joint
every 50 feet (15 m.) along the bus bar. This, however,
is a matter of judgment and will vary depending on the
expected range of temperatures to which the bus bar will
be subjected.
~; ~ When either single or double roller expansion
joints are installed in electric power bus bar, they
must be adjusted relative to ambient temperature
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conditions to ensure proper absorption of conductor
expansion or contraction. The expansion joints are
adjusted by varying the displacement "D" shown in
FIGURES 1 and 4 respectively. Note that displacement
"D" for a single roller expansion joint is the distance
between opposed backing plates 30 whereas the
displacement "D" for a double roller expansion joint is
one-half this distance. For Alcan B505~ aluminium alloy
conductor pipe, "D" is computed according to the
formula:
D = 1/2 + L(12)~.000023)~0C - TC)
where:
D = expansion joint adjustment displacement, mea-
sured in inches
L = the length of the conductor segment which the
expansion joint is to enable to expand or con-
tract. If the conductor segment is rigidly
fixed at one end, then one expansion joint
must absorb expansion or contraction along the
entire length "L~ of the segment. Otherwise,
if expansion joints are provided at both ends
of the conductor segment, then each expansion
joint need absorb only expansions or contrac-
tions expected along 1/2 of the length "L" of
the conductor segment.
T = the ambient bus bar temperature at the time of
installation of the expansion joint. ~-
For a single roller expansion joint used with
Alcan B505~ 3-inch inside diameter aluminium alloy con-
ductor pipe, "D" should be no greater than 3n. For a
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double roller expansion joint used with the same conduc-
tor pipe, "D" should be a maximum of 2".
Conductor Se ~ent Roller S~ t Structure
Base plate 24, roller brackets 26 and rollers
28 may be used separately from the expansion joint
elements to support a conductor segment at points where
allowance or longitudinal movement need not be made.
For example, it may be convenient to mount base plate
24, roller bracket 26 and rollers 28 at the top of an
insulator stack to rollably support a conductor segment
between the rollers at the top of the insulator stack.
As will be apparent to those skilled in the
art in the light of the foregoing disclosure, many
alterations and modifications are possible in the
practice of this invention without departing from the
spirit or scope thereof. Accordingly, the scope of the
invention is to be construed in accordance with the
substance defined by the following claims.
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