Bare over head alminum conductors midal(revised)
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Transcript of Bare over head alminum conductors midal(revised)
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.