Bare Over Head Aluminum Conductors

Introduction

Aluminum Conductors form an integral part of an over head transmission and

distribution system. An over head transmission and distribution system is preferred by

the utilities owing to the fact that an over head system is the lowest cost involved setup

to realize for transmitting high volume of power over long distances. In an over head

line, the surrounding air act as the insulating medium and hence the bare conductor

can be used for different voltage levels without much difficulty.

There are many different type of conductors in use for over head transmission. In

general these conductors are manufactured by stranding aluminum or aluminum alloy

wire concentrically in helical shape around a core wire. Or in other words in a concentric

stranded conductor strands are arranged in a circular pattern. Each layer alternates

direction and has an increasing lay length (the center strand is longest). Concentric

stranding is characterized by its mechanical strength and crush resistance.

Concept of Conductor Stranding

Stranded conductors are composed of non insulated “strands” of wire twisted together. The advantages of stranded conductor over a single strand of equal cross-section are increased flexibility and flex-fatigue life. Stranded conductor can be manufactured in a variety of configurations, the most common being concentric (true concentric, equilay concentric, unidirectional concentric, and unilay concentric), bunched and rope.

Concentric

When the term “concentric stranding” is used, it refers to the definition of the word “concentric”, which is having a “common center”. Concentric conductor may be defined as: a central wire (strand) surrounded by one or more layers of helically laid wires in a geometric pattern.

The geometric pattern requires that concentric constructions can only be produced with 7, 19, 37, 61, (etc.) strands or members, following the pattern that each successive layer has 6 more strands than the layer below it.

In all types of concentric constructions, the geometric pattern of the strands is consistent for the entire length of the conductor. That is, the central strand, and the strands in each layer remain in their respective positions from the beginning to the end of its length.

The main advantage of concentric constructions is the close/tight diameter tolerances that can be maintained on the conductor. Concentric constructions have very smooth uniform surfaces that are suited for thin wall insulation in high performance applications.

Concentric Stranding

There are four common types of “concentric” constructions manufactured for the high performance wire and cable industry. Although there are four distinct types, the industry normally refers to “Concentric” as “True Concentric” and will use the terms interchangeably. The other types are referenced as noted.

Concentric - or True Concentric characterized by a central wire surrounded by one or more layers of helically laid wires in a geometric pattern, with alternately reversed lay direction and increasing lay length.

Equilay - or Equilay Concentric characterized by a central wire surrounded by one or more layers of helically laid wires in a geometric pattern, with alternately reversed lay direction and the same lay length.

Unidirectional - or Unidirectional Concentric characterized by a central wire surrounded by one or more layers of helically laid wires in a geometric pattern, with the same lay direction and an increasing lay length.

Unilay - or Unidirectional Equilay Concentric characterized by a central wire surrounded by one or more layers of helically laid wires in a geometric pattern, with the same lay direction and the same lay length.

Bunched Stranding - Bunch strand wire contains any number of strands in random pattern. Twisted in one operation, all strands have the same lay direction and same lay length, however, the result is a rougher surface and lower dimensional tolerance than the concentric constructions. The number of strands is determined by the size of the individual strands and the total cross-sectional area required.

Rope Stranding - Wire constructions consist of single strands assembled together into concentric or bunched configurations. Rope constructions consist of concentric or bunched members stranded together into the final concentric or bunched configuration. Rope stranding has the advantage of increasing flexibility by using a larger number of finer strands while maintaining a tighter diameter tolerance than a simple bunched construction. Ropes are more evident in the larger AWG sizes, such as 8 AWG and larger, but there are also many applications that require the flexibility of rope constructions in the smaller gauges. Constructions vary and can contain hundreds or thousands of strands.

Conductors used in Over Head Transmission / Distribution system

The Conductors used in over head transmission / distribution system are concentric lay stranded conductors.The bare conductors usually used in over head lines are designated as Class AA. The ASTM standard defines a concentric lay conductor as one constructed with a central core surrounded by one or more layers of helically laid wires. A conventional Class AA conductor is constructed with a round central core surrounded by one or more layers of helically laid round wires. The direction of lay is reversed in successive layers, and generally with an increase in length of lay for successive layers.

One of the most popular conductor used in transmission system is the Aluminum Conductor Streel Reinforced Type ACSR. There are other type of conductors also commonly used by the transmission and distribution sector. These conductors and their salient features are discussed below.

AAC - All Aluminum Conductors

Concentric – Lay- Stranded Aluminum Conductor (AAC) is made up of one or

more strands of hard drawn 1350 Aluminum Alloy. Thess conductors are used in low,

medium and high voltage overhead lines. AAC has seen extensive use in urban areas

where spans are usually short but high conductivity is required. The excellent corrosion

resistance of aluminum has made AAC a conductor of choice in coastal areas. Because

of its relatively poor strength-to-weight ratio, AAC has had limited use in transmission

lines and rural distribution because of the long spans utilized.

Features:

High current carrying capacity.

Suitable for low and medium voltage lines in urban area

Excellent resistance to corrosion

Ideal for use in coastal area

Specifications

AAC manufactured by Midal meets or exceeds the requirements of all

international specification standards like ASTM, BS, CSA, DIN,IEC,NFC,AS,SS-

etc.

AAAC - All Aluminum Alloy Conductor

Concentric-Lay-Stranded Aluminum Alloy Conductors (AAAC) are made out of

high strength Aluminum-Magnesium-Silicon alloy. Midal manufactures and supply

AAAC with different variants of electrical grade Alloys type 6101 and 6201.

These conductors are designed to get better strength to weight ratio and offers

improved electrical characteristics, excellent sag-tension characteristics and

superior corrosion resistance when compared with ACSR. Equivalent

aluminum alloy conductors have approximately the same ampacity and

strength as their ACSR counterparts with a much improved strength-to-weight

ratio, and also exhibit substantially better electrical loss characteristics than

their equivalent single layer ACSR constructions. The thermal coefficient of

expansion is greater than that of ACSR.

As compared to conventional ACSR, lighter weight, comparable strength & current

carrying capacity, lower electrical losses and superior corrosion resistance have given

AAAC a wide acceptance in the distribution and transmission lines.

Features

High strength to weight ratio

Better sag characteristics

Improved electrical properties

Excellent resistance to corrosion

Specifications AAAC manufactured by Midal meets or exceeds the requirements of all international

specification standards like ASTM, BS, CSA, DIN, IEC,NFC,AS, SS -etc.

AACSR - Aluminum Alloy Conductor Steel Reinforced

AACSR is a concentrically stranded conductor composed of one or more layers of Aluminum-Magnesium-Silicon alloy wire stranded with a high-strength coated steel core. The core may be single wire or stranded depending on the size. Core wire for AACSR is available with Class A, B or C galvanizing; or aluminum clad (AW).

Additional corrosion protection is available through the application of grease to the core or infusion of the complete cable with grease

Features

Offers optimal strength for line design

Improved strength to weight ratio

Ideal for extra long spans and heavy load conditions

Excellent resistance to corrosion

Specifications

AACSR manufactured by Midal meets or exceeds the requirements of all international

specification standards like ASTM, BS, CSA, DIN, IEC,NFC,AS, SS -etc.

ACAR - Aluminum Conductor Alloy Reinforced

Aluminum Conductor Alloy Reinforced (ACAR) is formed by concentrically stranded

Wires of Aluminum 1350 on high strength Aluminum-Magnesium-Silicon (AlMgSi) Alloy core.

The number of wires of Aluminum 1350 & AlMgSi alloy depends on the cable design. Even

though the general design comprises a stranded core of AlMgSi alloy strands, in certain cable

constructions the wires of AlMgSi Alloy strands can be distributed in layers throughout the

Aluminum 1350 strands.

ACAR has got a better mechanical and electrical properties as compared

to an equivalent conductors of ACSR,AAC or AAAC. A very good balance

between the mechanical and electrical properties therefore makes ACAR

the best choice where the ampacity , strength , and light weight are the

main consideration of the line design. These conductors are extensively used in overhead

transmission and distribution lines.

Features

Improved strength to weight ratio

Improved mechanical properties

Improved electrical properties

Excellent resistance to corrosion Specifications

Specifications

ACAR manufactured by Midal meets or exceeds the requirements of all international

specification

ACSR - Aluminum Conductor Steel Reinforced

Aluminum Conductor Steel Reinforced (ACSR) is concentrically stranded conductor with

one or more layers of hard drawn 1350-H19 aluminum wire on galvanized steel wire core. The

core can be single wire or stranded depending on the size. Steel wire core is available in Class

A ,B or Class C galvanization for corrosion protection. Additional corrosion protection is

available through the application of grease to the core or infusion of the complete cable with

grease.

The proportion of steel and aluminum in an ACSR conductor can be selected based on the mechanical strength and current carrying capacity demanded by each application.

ACSR conductors are recognized for their record of economy, dependability and favorable strength / weight ratio. ACSR conductors combine the light weight and good conductivity of aluminum with the high tensile strength and ruggedness of steel. In line design, this can provide higher tensions, less sag, and longer span lengths than obtainable with most other types of overhead conductors. The steel strands are added as mechanical reinforcements.

Features

High Tensile strength

Better sag properties

Economic design

Suitable for remote applications involving long spans

Specifications

ACSR manufactured by Midal meets or exceeds the requirements of

all international specification standards like ASTM, BS, DIN, IEC,NFC,AS, SS -etc.

.

ACSR/AS - Aluminum Conductor, Aluminum Clad Steel Reinforced

Aluminum Conductors, Aluminum Clad Steel Reinforced (ACSR/AS) are concentrically

stranded conductors with one or more layers of hard drawn 1350-H19 aluminum wires on

Aluminum Clad steel wire core. The core can be single wire or stranded depending on the size.

The mechanical properties of ACSR/AS conductors are similar to ACSR conductors but offers improved ampacity and resistance to corrosion because of the presence of aluminum clad steel wires in the core. These conductors are better replacement for ACSR conductors where corrosive conditions are severe.

Features Good mechanical properties Improved electrical characteristics Excellent corrosion resistance Better Sag properties Specifications

ACSR/AS manufactured by Midal meets or exceeds the requirements of all international

specification standards like ASTM, BS, DIN, IEC,NFC,AS, SS -etc.

ACSS - Aluminum Conductors Steel Supported

Aluminum Conductor Steel Supported (ACSS) is a composite concentric-lay stranded

conductor with one or more layers of hard drawn and annealed 1350-0 aluminum wires on a

central core of steel. In an ACSS ,under normal operating conditions, the mechanical load is

mainly derived from the steel core as aluminum in fully annealed stage does not contribute

much towards the mechanical strength. Steel core wires are protected from corrosion by

selecting an appropriate coating of the wire like galvanizing, mischmetal alloy coating or

aluminum clad. The type of coating is selected to suit the environment to which the conductor is

exposed and operating temperature of the conductor

ACSS are suitable for operating at high temperature without loosing the mechanical properties. The final sag-tension performance is not affected by the long term creep of aluminum.

Features Improved conductivity

High current carrying capacity Very low sag at high temperature High degree of immunity to vibration fatigue Better self damping property Specifications

Midal manufactures ACSS with Galvanized steel ( normal as well as high strength), Zn-

5Al mischmetal coated steel or Aluminum clad steel core.ACSS manufactured by

Midal meets or exceeds the requirements of all international specification standards like

ASTM.

ACSR/TW – Shaped wire Aluminum Conductor, Steel-Reinforced

Shaped Wire Compact Concentric-Lay-Stranded Aluminum Conductor, Steel-Reinforced

(ACSR/TW) is a concentrically stranded conductor , made with trapezoidal-shaped 1350-H19

wires over a high strength steel core. There are two possible design variants. In one case

ACSR/TW conductors are designed to have an equal aluminum cross sectional area as that of a

standard ACSR which results in a smaller conductor diameter maintaining the same ampacity

level but reduced wind loading parameters. In the second design, diameter of the conductor is

maintained to that of a standard ACSR which results in a significantly lower conductor

resistance and increased current rating with the same conductor diameter.

Midal manufactures ACSR/TW with Galvanized steel ( in Class A, Class B & Class C), Zn-5Al

mischmetal coated steel or Aluminum clad steel core

Features

High Tensile strength

Better sag properties

Reduced drag properties

Low wind and ice loading parameters

suitable for remote applications involving long spans

Specifications

ACSR/TW manufactured by Midal meets or exceeds the requirements of all international

specification standards like ASTM.

ACSS/TW - Shaped Wire Aluminum Conductors Steel Supported

Shaped Wire Compact Concentric-Lay-Stranded Aluminum Conductor, Steel-Supported

(ACSS/TW) is a concentrically stranded conductor with one or more layers of trapezoidal

shaped hard drawn and annealed 1350-0 aluminum wires on a central core of steel. ACSS/TW

can either be designed to have an equal aluminum cross sectional area as that of a standard

ACSS which results in a smaller conductor diameter maintaining the same ampacity level but

reduced wind loading parameters or with diameter equal to that of a standard ACSS which

results in a significantly higher aluminum area, lower conductor resistance and increased

current rating.

ACSS/TW is designed to operate continuously at elevated temperatures, it sags less

under emergency electrical loadings than ACSR/TW, excellent self-damping properties, and its

final sags are not affected by long-term creep of aluminum. ACSS/TW also provides many

design possibilities in new line construction: i.e., reduced tower cost, decreased sag, increased

self-damping properties, increased operating temperature and improved corrosion resistance.

The coating of steel core is selected to suit the environment to which the conductor is exposed

and operating temperature of the conductor

Features

High Operating temperature

Improved current carrying capacity

Better sag properties

Excellent self-damping properties

Reduced drag properties

Low wind and ice loading parameters

Specifications

Midal manufactures ACSS/TW with Galvanized steel ( normal as well as high strength),

Zn-5Al mischmetal coated steel or Aluminum clad steel core. ACSS/TW manufactured

by Midal meets or exceeds the requirements of all international specification standards

like ASTM.

HTLS ( High Temperature Low Sag ) CONDUCTORS

The HTLS high temperature low sag conductors are the latest development for the transmission

line applications. There are different variants of conductors in HTLS family and Midal Cables is

specialized in manufacturing of these special designed conductors. An HTLS conductor can

operate at very high temperature but retaining the mechanical strength and there by the sag

characteristics at elevated temperature. In a normal Gap Type Conductor , the high thermal

resistance alloy wires are stranded around a high strength steel core or INVAR with a small

gap between the steel core and the aluminum layer. The gap is filled with a heat resistant

grease.This facilitates the easy slide of aluminum strands over the core when it expands but the

strength is still supported by the steel core. The low thermal expansion characteristics of the

INVAR keeps the extension to the minimum level and helping to reduce the sag.

Features

High operating temperature

Enhanced power transfer capacity

Very low sag at high temperature

Excellent damping properties

Effect of creep on final sag is minimal.

Specifications :

Midal Manufactures the HTLS conductors of Types TACSR , GzTACSR , ZTACIR , ACCC for

operating temperatures 150oC and 210oC meeting national and international standards like

IEC/ASTM/JCS & JEC as well as customer specific requirements..

ACCC - Aluminum Conductor Composite Core

Aluminum Conductor Composite Core (ACCC) is a concentrically stranded conductor with one

or more layers of trapezoidal shaped hard drawn and annealed 1350-0 aluminum wires on a

central core of high strength Carbon and glass fiber composite. The ACCC Conductor uses a

carbon fiber core that is 25% stronger and 60% lighter han a traditional steel core. This allows

with the help of trapezoidal shaped strands the ability to increase the conductor’s aluminum

content by over 28% without increasing the conductor’s overall diameter or weight.

Features

Excellent Sag properties

Increased current carrying capacity

High operating temperature

Excellent strength to weight ratio

Highly energy efficient.

Specification

Midal manufactures ACCC under license from CTC Cable Corporation, USA. The

conductors manufactured by Midal satisfies all the technical requirements of M/s CTC

Corporation as well as the general requirements given in the international specification

standards like ASTM.