The invention generally relates to the area of overhead transmission cables. In particular, the invention relates to a new steel supported aluminum overhead transmission cable having low sag and a process for producing the same.

BACKGROUND OF THE INVENTION:
Overhead transmission cables lines are unique. They involve public safety directly both in terms of electrical clearances and structural adequacy. One of the fundamental limitations on power flow through overhead lines is limiting the conductor temperature to a level which neither causes a reduction in the conductor strength nor causes an increase in sag enough to infringe upon minimum electrical clearances to ground, buildings and other conductors.

Some of the steel supported aluminum overhead transmission cables produced by the Applicant and available in the market include:
• Aluminum Conductors Steel Reinforced (ACSR) Conductors: ACSR conductor consists of one or more layers of bare Aluminum wires 1350 (non-annealed Aluminum wires of EC grade) stranded over a high strength steel core. The core can be single or multiple strands depending on the application or requirement. There can be various stranding combinations of Aluminum and steel wires giving flexibility to obtain the suitable current carrying capacity and mechanical strength based on the application.
• Aluminum Conductor Steel Supported (ACSS) Conductors: ACSS conductor consists of one or more layers of annealed EC grade Aluminum wires stranded over a high strength steel core. ACSS conductor is a composite concentric lay-stranded conductor consisting of a stranded steel central core with one or more layers of 1350-O (High Temperature) aluminum wires.
• Aluminum Alloy Conductor Steel Reinforced (AACSR) Conductors: AACSR conductor consists of one or more layers of Aluminum-Magnesium-Silicon alloy wires stranded over a high strength steel core.
• Thermal-resistant Aluminum-alloy Conductor, Steel Reinforced (TACSR) Conductors: TACSR conductors are high ampacity conductors, wherein the inner core is composed of galvanized steel and the outer layers are composed of thermal resistant aluminum-alloy.
• Super Thermal Alloy Conductor Invar Reinforced (STACIR) Conductors: STACIR conductor has outer layers composed of Super Thermal Aluminum (STAL) alloy wires that can operate up to 210o C. The inner core is composed of aluminum clad INVAR wires. INVAR is a metal alloy with 36% Ni in steel.

It may be noted that these different types of steel supported aluminum overhead transmission cables have differing performance characteristics, which are reported and also well known to a person skilled in the art.

With the advancement in the industry, there has been a need for higher strength conductors, which can operate at high temperatures. There has been a need felt to provide a steel supported aluminum overhead transmission cable having low sag at high temperatures and a process for producing the same. Also, a need has been felt to provide a steel supported aluminum overhead transmission cable having increased the number of aluminum bundles. Furthermore, a need has been felt to provide a steel supported aluminum overhead transmission cable having improved transmission line feasibility. Last, but not the least, a need has been felt to provide a steel supported aluminum overhead transmission cable having a reduced total cost of ownership.

SUMMARY OF THE INVENTION:
This summary is provided to introduce a selection of concepts in a simplified format that are further described in the detailed description of the invention. This summary is neither intended to identify key or essential inventive concepts of the invention, and nor is it intended for determining the scope of the invention.

Accordingly, the present invention provides a steel supported aluminum overhead transmission cable (30) that may comprise a steel core (10) having plurality of steel wires, each of the steel wire having tensile strength in a range 2025- 2260 MPa; and plurality of EC grade aluminum wires (20) stranded around the steel core (10).

To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES:
In order that the invention may be readily understood and put into practical effect, reference will now be made to exemplary embodiments as illustrated with reference to the accompanying drawings, where like reference numerals refer to identical or functionally similar elements throughout the separate views. The figures together with a detailed description below, are incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention where:
Figure 1 illustrates a sectional view of a steel supported aluminum overhead transmission cable (30) constructed in accordance with the teachings of the invention.

It may be noted that to the extent possible, like reference numerals have been used to represent like elements in the drawings. Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the dimensions of some of the elements in the drawings may be exaggerated relative to other elements to help to improve understanding of aspects of the present invention. Furthermore, the one or more elements may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION OF THE INVENTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawing and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.

Reference throughout this specification to “an aspect”, “another aspect” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase “in an embodiment”, “in another embodiment” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

As used herein, and unless the context dictates otherwise, the terms "coupled to", “connected to”, “operably connected to”, “operatively connected to” are intended to include both direct connection / coupling (in which two elements that are coupled / connected to each other contact each other) and indirect coupling / connection (in which at least one additional element is located between the two elements). Therefore, the terms "coupled to" and "coupled with" are used synonymously. Similarly, the terms “connected to” and “connected with” are used synonymously.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The device, methods, and examples provided herein are illustrative only and not intended to be limiting.

The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.

Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

Referring to figure 1, the present invention provides an overhead transmission cable (30). The overhead transmission cable (30) as provided by the present invention is being referred to as steel supported aluminium overhead transmission cable (30). The steel supported aluminium overhead transmission cable (30) comprises a steel core (10) having plurality of steel wires, and plurality of EC grade aluminum wires (20) stranded around the steel core (10). In a preferred aspect of the invention, each of the steel wire has tensile strength in a range 2025- 2260 MPa.

The present invention also provides a process of producing a steel supported aluminum overhead transmission cable, which comprises providing a steel core (10) having plurality of steel wires; and standing plurality of EC grade aluminum wires (20) around the steel core (10). In an embodiment of the invention, each of the steel wire has tensile strength in a range 2025- 2260 MPa.

In an embodiment of the invention, the steel core (10) comprises a central steel wire and a plurality of peripheral steel wires stranded around the central steel wire.

In an embodiment of the invention, the central steel wire is round in shape.

In an embodiment of the invention, a shape of the peripheral steel wires is round or trapezoidal.

In an embodiment of the invention, the steel wires are made of (a) galvanized steel or (b) a steel alloy. In a preferred aspect of the invention, the steel wires are made of zinc–5% aluminum-mischmetal (Zn-5 Al-MM) alloy coated steel.

In an embodiment of the invention, the EC grade aluminium wires (20) are made of annealed aluminium.

In an embodiment of the invention, the aluminium wire (20) has electrical conductivity in excess of 63% IACS. In an embodiment of the invention, the aluminum wire provides electrical conductivity in the range of 63% to 63.5 % IACS.

In an embodiment of the invention, the EC grade aluminium wire have tensile strength in a range of 60 Mpa – 90 Mpa.

In an embodiment of the invention, a shape of the aluminum wire (20) is round or trapezoidal or a combination thereof.

The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the plurality of aluminium wires (20) are made of 1350 aluminium alloy having a maximum copper content of 0.04 wt.%.

In an embodiment of the invention, the plurality of aluminium wires (20) are made of Aluminium selected from a group comprising of Aluminium 1350-O; Aluminium1350-H12; Aluminium 1350-H22; Aluminium 1350-H14; Aluminium 1350-H24; Aluminium 1350-H16; Aluminium 1350-H26; Aluminium 1370-O; Aluminium 1370-H11; Aluminium 1370-H12; Aluminium 1370-H13; Aluminium 1370-H14; Aluminium 1120; Aluminium 6160; Aluminium 6201; Aluminium Magnesium-Silicon alloy; thermal resistant aluminium-alloy; Super Thermal Aluminium (STAL) alloy; AL57; and AL59.

In a furthermore embodiment of the invention the plurality of EC grade aluminum wires (20) are made of annealed aluminum of trapezoidal cross-section.

In an embodiment of the invention, the plurality of EC grade aluminum wires (20) are made of 1350 aluminum alloy having a maximum copper content of 0.04 wt. %. In a preferred aspect of the invention, the plurality of EC grade aluminum wires (20) are made of 1350 Aluminum alloy which has been subjected to annealing at about 400 Deg. C to provide an aluminum wire having conductivity in a range of above 63 % IACS and tensile strength in range of 60 Mpa – 90Mpa.

In a more specific embodiment of the invention, the process of producing a steel supported aluminum overhead transmission cable (30), comprises of:
• Hot-rolling a continuous cast alloy bar of 1350 aluminum alloy having a maximum copper content of 0.04 wt. % to form a rod;
• drawing the said rod to wire and further annealing the same at about 400 Deg. C to provide plurality of conductor strands of aluminum wire having conductivity above 63 % IACS and tensile strength in range of 60 Mpa – 90 Mpa; and
• Stranding the plurality of conductor strands of aluminum wire over a steel core comprising a plurality of steel wires to form the complete conductor for overhead transmission system; wherein the steel wires are made of galvanized or Zinc– 5% Aluminum-Mischmetal Alloy or any other steel alloy and the steel wires has tensile strength of about 2025 – 2260 MPa.

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has improved strength to weight ratio.

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has an operating temperature of about 180 to 250 Deg. C.

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has factor of safety of more than 2 with respect to regular ACSS.

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has reduced sagging. In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has maximum loading tension on tower thus reducing sag while stringing on overhead transmission line.

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable has the following properties as compared to existing ACSS overhead transmission cables (having tensile strength up to 1950 MPa):

Voltage /Span length
Parameters ACSS (Prior Art) Aluminum Conductor Steel
Supported Conductor of the Invention
400 KV /
400 mtr Steel mass (kg/km) 496 496
Sag (mtr) @ 180 Deg. C 14.02 13.24
220 KV/
350 mtr Steel mass (kg/km) 427 427
Sag (mtr) @ 150 Deg. C 10.69 10.13
132 KV/
335 mtr
Steel mass (kg/km) 361 361
Sag (mtr) @ 150 Deg. C 8.00 7.26

In an embodiment of the invention, wherein the steel supported aluminium overhead transmission cable allows for tension tower weight to be reduced by an extent in the range of around 5 to 10%.

Some of the properties of the steel supported aluminum overhead transmission cable of the present include:
• The steel supported aluminum overhead transmission cable of the present invention may be made of bare conductor, which has low sag with corresponding temperature.
• The steel supported aluminum overhead transmission cable of the present invention uses special steel core which has higher strength than another steel grade available;
• The steel supported aluminum overhead transmission cable of the present invention has a reduced working tension loading due to that reduction in tower material by which cost saving;
• The steel supported aluminum overhead transmission cable of the present invention may comprise an Aluminum conductor steel support low sag conductor, having trapezoidal / round aluminum or Round + Trapezoidal aluminum with special steel supported concentric lay stranded conductor;
• The steel supported aluminum overhead transmission cable of the present invention may comprise “O” temper (1350 Grade) of the aluminum, a fully annealed or soft temper, causes most or all of the mechanical load on the steel supported aluminum overhead transmission cable of the present invention to be carried by the steel.
• The steel supported aluminum overhead transmission cable of the present invention may comprise a steel core with strength of the steel is significantly more than regular or ultra- high strength steel. The steel strands form the central core of the cable, around which is stranded one or more layers of aluminum 1350-O wires. The steel core may consist of 7, 19, or more wires.
• The steel supported aluminum overhead transmission cable of the present invention may comprise trapezoidal shaped aluminum strands which minimize interstices, provide higher aluminum area compared to the equivalent diameter round-wire ACSR construction.
• The steel supported aluminum overhead transmission cable of the present invention may comprise aluminum strands that are annealed to with stand higher temperature operation.
• The steel supported aluminum overhead transmission cable of the present invention defines an operating temperature that can go as high as 180 to 250°C. The temperatures may be limited to 200°C when the conductor core uses ordinary hot-dipped zinc coatings.
• The steel supported aluminum overhead transmission cable of the present invention has low sag which is attained using special steel. Reduction on sag has more benefits in clearance point and reduction of tower material;
• The steel supported aluminum overhead transmission cable of the present invention has reduced loading on tower tension (i.e on both horizontal & vertical loading) for new transmission lines.
• The steel supported aluminum overhead transmission cable of the present invention has high strength to weight ratio, Low weight per unit length, high modulus & low linear expansion than all aluminum alloy conductor;
• The steel supported aluminum overhead transmission cable of the present invention has robust handling characteristic;
• The steel supported aluminum overhead transmission cable of the present invention has low electrical resistance (Better than ACSR) - can reduce the Power loss of a transmission line.
• The steel supported aluminum overhead transmission cable of the present invention increases Reliability of transmission grid.
• The steel supported aluminum overhead transmission cable of the present invention provides an Economic solution to utilities.
• The steel supported aluminum overhead transmission cable of the present invention provides high ampacity capability.
• The steel supported aluminum overhead transmission cable of the present invention has capacity to handle future load demands.
• The steel supported aluminum overhead transmission cable of the present invention reduces the conductor size.
• Some of the Areas of Application of the steel supported aluminum overhead transmission cable of the present invention include:
• Reconductoring of conventional conductor with same infrastructures.
• New line with optimized tower solution to reduce the cost of ownership.
• Operating to support the “n-1” contingency rating.
• Characteristics of the conductor are not affected under extreme ice loading condition.

While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein. The figures and the foregoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

We Claim:

A steel supported aluminium overhead transmission cable (30) comprising:
a steel core (10) having plurality of steel wires, each of the steel wire having tensile strength in a range 2025- 2260 MPa; and
plurality of EC grade aluminum wires (20) stranded around the steel core (10).

2. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the steel core comprises a round shaped central steel wire and a plurality of peripheral steel wires stranded around the central steel wire, shape of the peripheral steel wires being round or trapezoidal.

3. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the steel core (10) is made of (a) galvanized steel or (b) a steel alloy.

4. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the steel core (10) is made of zinc–5%-aluminum-mischmetal (Zn-5 Al-MM) alloy coated steel.

5. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the EC grade aluminium wires (20) are made of annealed aluminium.

6. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the aluminium wire (20) has electrical conductivity in excess of 63% IACS.

7. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the EC grade aluminium wire having tensile strength in a range of 60 Mpa – 90 Mpa.

8. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the shape of the aluminum wire (20) is round or trapezoidal or a combination thereof.

9. The steel supported aluminium overhead transmission cable as claimed in claim 1, wherein the plurality of aluminium wires (20) are made of Aluminium selected from a group comprising of Aluminium 1350-O; Aluminium1350-H12; Aluminium 1350-H22; Aluminium 1350-H14; Aluminium 1350-H24; Aluminium 1350-H16; Aluminium 1350-H26; Aluminium 1370-O; Aluminium 1370-H11; Aluminium 1370-H12; Aluminium 1370-H13; Aluminium 1370-H14; Aluminium 1120; Aluminium 6160; Aluminium 6201; Aluminium Magnesium-Silicon alloy; thermal resistant aluminium-alloy; Super Thermal Aluminium (STAL) alloy; AL57; and AL59.

10. A process of producing steel supported aluminium overhead transmission cable (30), comprising:
providing a steel core (10) having plurality of steel wires, each of the steel wire having tensile strength in a range 2025- 2260 MPa; and
standing plurality of EC grade aluminum wires (20) around the steel core (10).