Note: Descriptions are shown in the official language in which they were submitted.
-
~0452Z'~
BACKGROUND OF THE I~VENTION
The principle of using aluminum upon steel as an over-
head conductor has been widely used in recognition of the high
conductivity of the former and the high strength of the latter.
The designation by which this type of conductor is usually known
in technical and trade literature is "ACSR" for Aluminum Conductor, -`~
Steel Reinforced. The industry-recognized manufacturing speci-
fication for conventional ACSR is ASTM Specification B 232,
"Standard Specification for Aluminum Conductors, Concentric-Lay-
Stranded Steel Reinforced (ACSR)." The principle is also employed ~ -
with the type conductor described by Edwards (U.S. Pat. No.
3,378,631).
Aluminum and aluminum-steel overhead conductors are
traditionally made in tempers that provide a tensile strength as
high as commercially feasible. Normally overhead lines are
designed to utilize this strength to the greatest practical-degree, ~
therefore the operating stresses upon the aluminum component of ` `
these conductors are substantial. The temper and the magnitude
of operating stresses relate directly to the problem of loss of
strength at high operating temperatures and long-time creep. For
example, when wires of different metals, such as steel and
EC-Hl9 aluminum, are pulled in unison, as they are in a composite
stranded conductor, the metal having the least ductility will
be the first to break. In conventional composite conductors
wherein aluminum is the current carrying metal, such as ACSR,
aluminum wires have the least ductility and fail at an extension
as low as one percent. For this reason, strength in the steel
core of ACSR beyond one percent extension is not useful for
rating the strength of the conductor.
-- 2 --
: . ,,, ~ : . . :
1045Z2'~
When conventional ACSR composite conductors (having a
hard drawn EC aluminum component) are strung-in overhead
between spaced ports the amount of sag in the cable at installa-
tion is calculated by taking into consideration the tensile
strengths and elongations of both the steel core and the aluminum
component. However, at elevated temperatures the hard drawn
alumimum component will begin to anneal, thereby gaining elonga-
tion and losing strength, consequently causing the steel core to
carry a greater percentage of the load. This will cause an
increase in the amount of sag of the cable beyond the amount of
sag at installation. Because the amount of sag in an overhead
cable is not permitted to exceed a predetermined maximum, it
should be apparent that conventional ACSR type cable cannot be
utilized at temperatures beyond that which causes unacceptable -
annealing of the aluminum component.
U.S. Patent No. 3813481 represents one attempt to over-
come the foregoing problems with ACSR type cable. The conductor
described in U.S. Patent No~ 3813481 consists of a fully-annealed
aluminum component supported by a steel core. Because the
aluminum is fully annealed, it has increased elongation charac-
teristics and thus the cable can be utilized at higher operating
temperatures than ACSR conductors. At installation the aluminum
component is elongated beyond its yield point such that the steel
core carries substantially the entire load of the composite con-
ductor. Inasmuch as the sag at installation is calculated solely
on the basis of the tensile strength and elongation of the steel
core, there will be no further sag at elevated operating tempera-
tures because the steel core is already carrying the entire load
at installation.
However, because the aluminum component does not
:
.' ,, ' ' , '. , :
1(~452ZZ
contribute to the load-carrying capability of the composite
conductor in the aforementioned prior art cable, the steel must
be of a greater cross-sectional dimension than conventional
ACSR cable in order to make up for the lack of load-carrying
capability of the aluminum. This increased cross-section of the
composite conductor has presented problems in joining the cable
at conventional connectors which are sized to accept the smaller
cross-sectional dimensions of ACSR conductors. On the other hand,
if the steel cross-section is maintained the same as in conven-
tional cable, then the ultimate tensile strength of the cable
is reduced as compared with that of conventional cable.
SUMMARY OF THE INVENTION
In view of the foregoing, it should be apparent that
there is still a need in the cable-making art for an effective
cable which will operate at high temperatures while maintaining
its strength and sag and tension properties. Accordingly, there
has been provided in accordance with this invention a novel
composite conductor wherein the aluminum component is formulated
from an aluminum alloy which has a high tensile strength in the
annealed condition which is equivalent to the tensile strength
of EC hard drawn. Consequently, the aluminum component can carry
a portion of the load which permits:
1. The use of less steel and consequently
more aluminum in a cross-section equivalent to the
cross-sectional dimension of the aforementioned
prior art U.S. Patent No. 3813481, and therefore
a greater current-carrying capability than said
prior art cable; or
.. . . . . . . .
1045ZZ2
2. The same steel cross-sectional
dimension as in the priol art cable while achieving
a higher operating temperature than conventional
EC ACSR cable.
At the same time, the annealed aluminum component of
the instant invention has greater elongation than the aluminum
component in conventional ACSR cable and will thus continue to
carry a portion of the load at elevated temperatures, thereby
mitigating the tendency to increase the sag in the cable as occurs
with conventional ACSR composite conductors at elevated tempera-
tures where the hard drawn aluminum component loses its strength.
In its broadest aspect, therefore, the instant invention
is directed to an electrical conductor for an overhead power line
comprising a steel core and an aluminum component stranded about
the core having an electrical conductivity of at least 61% IACS,
said aluminum component being in an at least partially annealed
condition; characterized in that said at least partially annealed
aluminum component is an aluminum alloy having yield strength
and elongation characteristics when at least partially annealed
such that the aluminum component will act as a load-carrying
element when the conductor is strung-in between spaced supports
and tensioned in excess of tensile loads beyond which the annealed
aluminum components of prior art composite conductors exceed their
yield point, thus achieving improved qualities of fatigue re-
sistance as compared with prior art at least partially annealed
aluminum components which are adapted to carry none of the load
under comparable tensile stresses, while at the same time pre-
venting sag in the conductor at elevated temperatures.
More particularly, the aluminum alloy component of this
invention has a yield strength of from 13,000 PSI for an elonga-
-- 5 --
~, . . . .. . .. .
1~45ZZ2
tion of 5~ when partially annealed to a yield strength of at
least 8500 PSI for an elongation of 15~ when fully annealed.
In one embodiment of the invention the aluminum alloy
component consists essentially of from 0.30 to 0.95 weight percent
iron; from 0.01 to 0.15 weight percent silicon; and the remainder
aluminum with associated trace elements not exceeding 0.05 weight
percent.
In a second embodiment of the invention the aluminum
alloy component consists essentially of from 0.20 to 2.00 weight
cobalt; from 0.10 to 1.30 weight percent iron; from 0.0001 to
1.00 weight percent magnesium; from 0 to 1.75 weight percent of
at least one additional alloying element selected from the group
consisting of: nickel, copper, silicon, zirconium, niolium,
tantalum, yttrium, scandium,thorium, carbon, rare earth metals;
and the remainder aluminum with associated trace elements.
In a third embodiment of the invention the aluminum
alloy component consists essentially of from 0.20 to 1.60 weight
percent nickel; from 0.30 to 1.30 weight percent iron; and the
remainder aluminum with associated trace elements.
The composite multistrand electrical conductor of this
invention is particularly adaptable and useful in those environ-
ments where a conductor of composite construction not only must
have overall characteristics of relatively high electrical con-
ductivity ~ut at the same time a relatively high strength to
weight ratio, a relatively high strength to operating temperature ~;~
ratio, and a relatively high current carrying capacity. These ~ -
and other objects, features and advantages of the present ~ ~
invention become more apparent in a review of the following speci- -
fication when taken in conjunction with the accompanying drawings
which are shown for purposes of illustration only.
1045Z22
BRIEF DESCRIPTION OF THE_DRAWINGS
Fig. 1 is a transverse cross-sectional view of a
steel supported aluminum alloy overhead conductor comprising a
sheath of aluminum wires helically stranded over a core of
stranded steel wires.
Fig. 2 is a transverse cross-sectional view of a
steel supported aluminum alloy overhead conductor comprising a
seamless tube of aluminum alloy provided about a core of stranded
steel wires;
Fig. 3 is a transverse cross-sectional view of a steel
supported aluminum alloy overhead conductor comprising a welded
seam tube of aluminum alloy provided about a core of stranded
steel wires;
Fig. 4 is a transverse cross-sectional view of a steel
supported aluminum alloy overhead conductor comprising a sheath
of keystone-sectioned aluminum alloy strips about a core of
stranded steel wires;
Fig. 5 is a transverse cross-sectional view of a
steel supported aluminum alloy overhead conductor comprising
a sheath of flat, round-edged aluminum alloy strips helically
stranded about a core of stranded steel wires.
Following a practice which is common in the wire and
cable industry, the entire article of the invention is referred
to herein as a "conductor" even though the aluminum alloy portion
thereof would in a strictly technical sense be more accurately
designated the conductor. ~;^
Unless otherwise indicated or obvious from the context,
absolute valves of dimensions given herein are for illustrative
purposes only, to enable a more concise discussion of the
preferred embodiments.
1(~45ZZZ:
With reference to FIG. I, there is depicted a steel
supported aluminum alloy overhead conductor 10 comprising a
stranded steel core 12 and an electrically conductive helically
stranded aluminum alloy component 14 received over the core 12.
In the instance depicted, the aluminum alloy component is in
the form of two superimposed layers 16 and 18 of helically
wound layers of aluminum alloy wires 20.
The steel core 12 may be of any desired kind but is
preferably made of stranded steel wires. They may, for example,
be identical in composition and fabrication to the cores used
in stranded ACSR conductors; see AS~M B 232 "Aluminum Conductors,
Steel Reinforced, Concentric-Lay Stranded (ACSR)," B 341
"Aluminum-Coated (Aluminized) Steel Core Wire for Aluminum
Conductors, Steel Reinforced (ACSR)," B 502 "Aluminum-Clad Steel
Reinforced (ACSR-/AW)" and B 498 "Zinc-Coated (Galvanized) Steel
Core Wire for Aluminum Conductors, Steel Reinforced (ACSR)."
As illustrated, the steel core 12 consists of seven
0.1360 diameter steel strands 22 helically stranded to produce
a core having an O.D. of 0.4080 inch.
Aluminum alloy wires 20 are then either partially
annealed to half-hard temper or fully annealed, and then stranded
directly upon the core 12 to form the conductor of the present
invention. As can be seen by examining Table I, below, the
conductors X, Y and Z of the present invention, while having a ~ .
slig~tly lower average tensile strength and yield strength when
compared to EC-H-l9 aluminum, their tensile strenths and yield
strengths exceed those of prior art annealed aluminum steel
composite conductors by more than 200 percent. Moreover, the
aluminum alloy wires 20 of the present invention have an elonga-
tion sufficient to offer the advantages of less sag and higher
operating temperatures.
-- 8 --
-
1(~)45ZZZ
~--oo o o o -
Z ~ -- N 1~ ~'i O ~ ~
` ~1 00 O O
~ ~ 00 U~ _l O .,
0~ ~1 ~ ~ ~ ~ O ~i
-- I ~ ~
_ _ O O ~
_ O N O O
H
_ ~
O O O O O ,` ~'
_ H U ~:
U~ H O 3
1~ ~! æP ~u~
~; H a H ~ H
o ~! æ 1i3 æ æ
. ... E~ E~ ~ IY :~
1045;~Z2
When annealed aluminum alloy wires are used, the rated
strength of ACSR type conductors is calculated differently than
if hard drawn wires are used. This is because the elongation of
the hard drawn aluminum wires (on the order of 2 percent) is sub-
stantially less than that of the steel wires (on the order of 5
percent), whereas the elongation of annealed aluminum alloy wires
is substantially greater than the elongation of steel. With
hard drawn aluminum wires having low elongation, the rated
strength of a conductor is calculated on the basis of the full
strength of the aluminum wires plus the strength of the steel at
only 1 percent elongation. With the annealed aluminum alloy wires
having greater elongation and high strength the full strength of
the steel wires can be used for calculating the rated strength,
thereby providing a conductor of higher strength which can with-
stand sustained operation at 150 to 200C without substantial
decrease in its mechanical properties.
In one embodiment of the present invention, identified
in Table I as Alloy X, the aluminum component 14 of the overhead
conductor 10 is preferably fabricated from an aluminum alloy
which consists essentially of from about 0.30 to about 0.95 `
percent iron, 0.01 to about 0.15 percent silicon, 0.0001 to about
0.05 percent of trace elements selected from the group consisting
essentially of vanadium, copper, manganese, magnesium, boron and
titanium. In the preferred form of this embodiment the aluminum
alloy component 14 of overhead conductor 10, the iron to silicon
ratio must be at least 1.99:1 or greater and is preferably 8:1
or greater. In the most preferred form after annealing aluminum
alloy component 14, iron alumnate inclusions are formed therein,
a majority of these iron alumnate inclusions have a particle size
less than 2,000 angstrom units when measured in a direction
-- 10 --
. . .
, . ' . ,
1~45ZZZ
perpendicular to the longitudinal axes of said inclusions. These
inclusions are substantially evenly distributed throughout the
aluminum alloy component 14.
In a second embodiment of the present invention,identi-
fied in TAsLE I as Alloy Y, the aluminum component 14 of the
overhead conductor 10 is preferably fabricated from an aluminum
alloy which consists essentially of from about 0.20 to about
2.00 percent cobalt, about 0.1 to about 1.3 percent iron, about
0.001 to about 1.00 percent magnesium and up to about 1.75 percent
of an additional alloying element selected from a group consisting
of: nickel, copper, silicon, zirconium, niobium, tantalum,
yttrium, scandium, thorium, carbon, rare earth metals and mixtures
of two or more of the foregoing,the remainder being aluminum with
associated trace elements.
In a third embodiment of the present invention, identi-
fied in TABLE I as alloy Z, the aluminum component of overhead
conductor 10 is preferably fabricated from an aluminum alloy which
consists essentially of nickel, iron, other optional alloying
elements and aluminum. It has been found that suitable results
are obtained when nickel is present in a weight percentage of from
about 0.20 percent to about 1.60 percent. Superior results are
obtained when nickel is present in a weight percentage of from
0.50 percent to about 1.00 percent and particularly superior and
preferred results are obtained where nickel is present in a weight
percentage of from about 0.60 to about 0.80 percent.
Suitable results are obtained with iron present in
amounts of from about 0.30 percent to about 1.30 percent.
Superior results are obtained when iron is present in amounts of
from about 0.40 percent to about 0.80 percent and pa~ticularly
superior and preferred results are obtained when iron is present
in amounts of from about 0.45 percent to about 0.65 percent.
.~.... . . ... . . . .
... . . . ...
1~45ZZZ .:
The aluminum content of the aluminum alloy component
14 may vary from about 97.00 peraent to about 99.50 percent by
weight with superior results being obtained when the aluminum
content varies between about 97.80 percent and about 99.20 percent
by weight. Since the percentages for maximum and minimum aluminum
do not correspond with the maximums and minimums for the alloying
elements, it should be apparent that suitable results are not
obtained if the maximum amounts of all alloying elements are used.
If commercial aluminum is employed in preparing the aluminum
alloy component 14 of the present condùctor 10, it is preferred
that the aluminum, prior to addition of the recited alloying
elements, contain no more than about 0.10 percent total impuri-
ties.
Optionally the present aluminum alloy component 14 may
contain an additional alloying element or group of alloying
elements. The total concentration of the optional alloying
elements may be up to about 2.00 percent by weight, preferably
from about 0.10 percent to about 1.50 percent by weight is used.
Particularly superior and preferred results are obtained when -
from about 0.10 to about 1.00 percent by weight of total addi-
tional alloying elements is employed.
Superior results are obtained when the additional
alloying elements shown in TABLE II are used.
TABLE II
ELEMENT PERCENT BY WEIGHT
Magnesium 0.001 to 1.00
Cobalt 0.001 to 1.00
Copper 0.05 to 1.00
Silicon 0.05 to 1.00
, ... . . . ,, . . ~ .
.. .: , ~. . : - , .
. - ~::: .
1045ZZ2
TABLE II (Cont.)
ELEMENT PERCENT BY WEIGHT
Zirconium 0.01 to 1.00
Niobium 0.01 to 2.00
Tantalum 0.01 to 2.00
Yttrium 0.01 to 1.00
Scandium 0.01 to 1.00
Thorium 0.01 to 1.00
Rare Earth Metals 0.01 to 2.00
Carbon 0.01 to 1.00
Preferred results are obtained when either cobalt or
magnesium is used as the additional alloying element. Suitable
results are obtained when either magnesium or cobalt is used in
amounts of from about 0.001 to about 1.00 percent by weight with
superior results being obtained when from about 0.025 to about
0.50 percent of either cobalt or magnesium is used. Particularly
preferred results are obtained when from about 0.03 to about
0.10 percent by weight of either cobalt or magnesium is used.
The rare earth metals may be present either individually
within the range shown in TABLE II or as either a partial or ;
total group, the total amount present as a group being within
the range shown for rare earth metals in TABLE II.
It should be understood that the additional alloying
elements may be present either individually or as a group of
two or more elements. It should be understood, however, that
if two or more of the additional alloying elements are employed,
the total concentration of additional alloying elements should
not exceed about 2.00 percent by weight.
Referring now to FIG 2, there is shown a steel sup-
ported aluminum alloy overhead conductor 30 which includes steel
core 12 as described above in relation to FIG. 1, and a tubular
- 13 -
- . : - ~ .
~ . .
1~45Z22
aluminum alloy component 32 extruded in an integral condition
over the core. The extrusion operation is performed at tempera-
tures which leaves the aluminum alloy component 32 in annealed
condition having the properties required for purposes of the
present invention.
Referring to FIG. 3, there is shown an alternative to
the construction depicted in FIG. 2 in that a steel supported
aluminum alloy overhead conductor 42 is provided with a tubular
aluminum alloy component 40 by wrapping a single broad strip 44
of electrically conductive annealed aluminum alloy about the steel
core 12 and welding its formerly laterally opposite edges to one
another at 46 utilizing conventional welding equipment and
techniques.
Aluminum alloy strands of other-than-circular cross- ~;~
sectional shape may be employed. By way of illustration (FIG. 4)
there may be used, upon a 7 X 0.1489 inch helically stranded steel
core 12 having an outer diameter of 0.4467 inch, a tube of
electrically conductive annealed aluminum alloy 27 having an
inside diameter at its fabrication of 0.4467 inch and consisting
of 10 trapezoidally shaped wires 29 having a thickness of 0.20
inch.
In FIG. 5, the first inner layer of the tubular aluminum
alloy conductor is provided by three helically stranded, round-
edge aluminum alloy strips each 0.1 inch thick and approximately
0.4 inch wide, this layer having an internal diameter of 0.399
inch at the time of fabrication, and an external diameter of
0.599 inch. The second, outer layer of the tubular aluminum alloy
conductor is helically stranded immediately upon the first, in an
opposite helical sense, and consists of four, round-edge alumimum
alloy strips each 0.1 inch thick and approximately 0.4 inch wide,
- 14 -
. .-, . . . .. : , ~
1~45Z2Z
this layer having an internal diameter of 0.599 inch at
the time of manufacture, and an external diameter of 0.799
inch. In each instance, the strips of aluminum alloy are
curved about the longitudinal axis of the tubular aluminum
conductor so that each is accurate as seen in transverse
cross-section.
The strips 20 are of electrically conductive aluminum
alloy and fully annealled before stranding. The layer 16
could be formed from a greater or a lesser number of strips
20.
In summary, the electrically conductive aluminum alloy
may have preferred weight ranges for composition elements
within the ranges earlier disclosed, wherein a preferred
weight range for iron is 0.55 to 0.65 weight per cent; and
that of silicon 0.01 to 0.7 weight per cent; and that of ~-
aluminum 99.10 to 99.40 weight per cent with of course ;
associate trace elements; alternatively the conductor may
be further characterized in that the aluminum alloy compon-
ent includes substantially that evenly distributed iron
aluminate inclusions with particulate size of less than
about two thousand angstrom units. In another variation
of the pre~erred form the electric conductor may consist
of 0.55 to 0.95 weight per cent cobalt and from 0.10 to
0.30 weight per cent of iron while the remainder volume
of the conductor is aluminum with associated trace elements;
alternatively the remainder of the volume of the conductor
may be aluminum with associated trace elements wherein the
the aluminum component is fully annealled and tempered
and has a yield strength of at least 10,000 p.s.i. for
an elongation of 15~ in 10 inches.
Further the aluminum aloide component in another
- 15 -
.~
1~4SZ2Z
embodiment has substantially evenly distributed cobalt
aluminate inclusions of a particle size less than 2 microns
in length and less than 1/2 microns in width. Further ~;
where the aluminum aloide component contains silicon its
preferred weight range may be from 0.01 to 0.07 weight
per cent of the composition of the aluminum alloy.
It should be apparent, integral or welded tubes, -
wire and strip may all alternatively be used in the
fabrication of the conductor in accordance with the ~ ~
invention disclosed herein. The particular mode which ~ -
would be preferably at any given point in time would
be the one that could most economically be produced at
the time of manufacture or meet other considerations
of design prejudice.
While present preferred embodiments of the present
invention have been illustrated and described, it will ~ -
.
be understood that the invention is not limited thereto
but may be otherwise embodied and practised without
departing from the spirit and scope of the invention
concept herein disclosed.
- 16--
C
. . .- . : .-.. . ~ - ~" -
.
