Electricity can be transmitted or distributed using an overhead wire. The mechanical design of an overhead line has a significant impact on its ability to operate successfully. When building an overhead line, it's important to make sure that the power cable’s mechanical strength is sufficient to withstand the worst-case weather scenarios.
The conductor is one of the most significant things because it
receives the majority of the capital investment. As a result, selecting the
right material and size for the conductor is critical. The conductor material
used for electric power transmission and distribution should have the following
characteristics:
1. Electrical conductivity should be high
2. It must have a high tensile strength to endure mechanical
loads
3. It should be low-cost, allowing it to be used across large
distances.
4. Should have low specific gravity, resulting in a low weight
per unit volume.
All of the requirements listed above are not met by anyone. As a
result, when choosing a conductor material for overhead wire cables, a trade-off is made between cost and required
electrical and mechanical attributes.
Electricity is defined as the physical phenomena of electric
charge flow in a very concentrated form. From a subatomic perspective, this
refers to the passage of electrons from one atom to the next, resulting in a
chain effect known as an electric current.
Good conductors of electricity have atoms that allow electrons
to flow freely through them, whereas bad conductors have atoms that make this
flow problematic. Insulators are materials with atoms that refuse to allow
electrons to flow through them.
Aluminium ranks fourth among known metals in terms of electrical
conductivity. Silver and gold, which are far too expensive to contemplate for
most regular uses, take first and third position on this list, respectively.
As a result, aluminium is the second most conductive material available in a
practical sense, trailing only copper.
Aluminium is less expensive and lighter than copper, but it has
lower conductivity and tensile strength. The following is a brief comparison of
the two materials:
1. Aluminium has a conductivity of 60 percent that of copper.
Because aluminium has a lower conductivity than copper, the X-sectional area of
the conductor must be bigger in aluminium for given transmission efficiency.
The diameter of the aluminium conductor is approximately 126 times that of the
copper conductor with the same resistance. Because aluminium's enlarged
X-section exposes a larger surface to wind pressure, supporting towers must be
constructed for greater transverse strength. This frequently necessitates the
installation of higher towers, resulting in increased sag.
2. Aluminium has a lower specific gravity (271 gm/cc) than
copper (809 gm/cc). As a result, the weight of an aluminium conductor is nearly
half that of a copper conductor. As a result, the supporting structures for
aluminium conductors do not need to be as robust as those for copper
conductors.
3. Because aluminium conductors are light, they are prone to
higher swings, necessitating the use of larger cross-arms.
4. Aluminium conductors sag more because of their lower tensile
strength and higher coefficient of linear expansion.
Aluminium outperforms copper in terms of cost, conductivity,
tensile strength, weight, and other qualities. As a result, it is commonly used
as a conductor material. Aluminium is especially cost-effective for
heavy-current transmission overhead lines where the conductor size is big and
the conductor cost is a significant fraction of the total installation cost.
Aluminium conductors sag more due to their poor tensile
strength. This makes them unsuitable for long-distance transmission and
prevents them from being used for bigger spans. The aluminium conductor is
strengthened with a core of galvanised steel wires to boost tensile strength.
The resulting composite conductor is called steel cored aluminium and is
abbreviated as ACSR conductor
(aluminium conductor steel reinforced).
A central core of galvanised steel wires is surrounded by
several aluminium strands in a steel-cored aluminium conductor. Steel and
aluminium wires have the same diameter in most cases. As a result of the
composite conductor's design, the steel core receives a higher percentage of
mechanical strength, while the aluminium strands carry the majority of the
current.
This is why aluminium is used for overhead transmission lines.
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