UNIT 1 OVERHEAD LINES
Overhead lines are electrical power transmission and distribution lines that are
installed above the ground, supported by poles or towers.It is a structure used
in electric power transmission and distribution to transmit electrical energy along
large distances. They are used to transmit electrical power from generating stations
to substations and from substations to consumers over long distances.
In short, Overhead lines are
1. electrical power transmission and distribution lines
2. installed above the ground
3. supported by poles or towers.
USES
They transmit electrical power from
1. Generating stations to substations
2. Substation to substation
3. Substation to consumer over long distances
Features of Overhead Lines
The term "features of overhead lines" can also be referred to as "components of
overhead lines." This term encompasses the various parts and elements that make up
the overhead power line system, ensuring it functions effectively and reliably. When
discussing the features or components of overhead lines, we are talking about the
individual elements that are essential for the construction, operation, and maintenance
of these lines. we are addressing the structural and functional elements that make up
the entire system used to transmit and distribute electrical power above ground. These
components are designed to ensure the safe, efficient, and reliable delivery of
electricity from power generation stations to end users. This involves understanding
how each part works, how they interact with each other, and the specific roles they
play in the overall infrastructure of electrical power distribution and transmission. This
includes
1. LINE SUPPORTS
Line supports, also known as support structures or simply supports, are the physical
structures that hold up overhead power lines and keep the conductors (wires) elevated
above the ground. They play a crucial role in ensuring the stability, reliability, and
safety of the electrical transmission and distribution network. There are various types
of line supports, each designed to handle specific loads and environmental conditions.
The main requirements of the line supports are:
1. High mechanical strength to withstand the weight of conductors and wind load etc.
2. Light in weight without the loss of mechanical strength.
3. Cheaper in cost.
4. Low maintenance cost.
5. Longer life.
6. Good looking
7. Easy accessibility for painting and erection of line conductors.
8. Flexibility to introduction of other customers
Functions of Line Supports
Elevation-The primary function of line supports is to keep the conductors elevated
above the ground to prevent contact with the ground, vegetation, buildings, and other
structures.
Safety-By maintaining a safe distance between conductors and the ground or other
objects, line supports help prevent electrical hazards, including accidental contact by
people or animals.
Mechanical Stability-Supports must withstand various mechanical forces, including
the weight of the conductors, environmental loads such as wind, ice, and snow, and
dynamic forces from electrical faults.
Electrical Clearance-Line supports ensure that there is adequate clearance between
conductors and the ground, as well as between different conductors, to prevent short
circuits and electrical arcs.
Types of Line Supports
Overhead power lines rely on various structures to support and elevate the conductors
above the ground, ensuring safe and reliable transmission and distribution of
electricity. The main types of structures include
Poles
Various types of poles are used to support and elevate the conductors above the
ground. The selection of pole type depends on factors such as load capacity, durability,
environmental conditions, and cost
Wooden Poles
Commonly used for lower voltage distribution lines,
Advantages
wooden poles are
• cost-effective
• relatively easy to install.
They are, however, susceptible to decay, insects, and weather conditions, which can
shorten their lifespan.
Concrete Pole
Concrete pole gave greater strength and used in place of a wood pole.
Advantages
• It has a longer life than that of a wood pole because of little degradation.
• Their maintenance cost is low.
Disadvantages
• Concrete poles are very heavy and are liable to damage during loading,
unloading, transportation and erection due to their brittle nature.
• Difficult to Handle and transport
• Rigid. Once produced, it’s difficult to tee off and introduce other customers
because holes can’t be easily done on concrete.
Steel Poles
For low and medium voltage tubular steel poles or Grider steel supports are used.
Longer spans are possible with steel poles. The poles need to be galvanised or painted
periodically to prevent them from corrosion. Their maintenance expense is high.
Advantages
• Steel poles are at least 30% lighter than woods poles – lighter weight can
reduce the cost of transportation, handling, and construction unlike concrete
poles.
• They require little maintenance, greatly reducing the costs associated with
upkeep – there is little need for tightening hardware to compensate for pole
shrinking.
• Due to the strength of steel, in most circumstances, steel poles involved in
vehicle impacts can be repaired or changed during normal working hours,
reducing the high cost of overtime pay.
• At the end of its long service life, a steel pole can be sold to scrap dealers and
completely recycled – eliminating the costs of pole disposal.
• Steel poles can be taller and carry heavier loads, permitting longer spans and
requiring fewer poles.
Disadvantages
• Steel is subject to the corrosive effects of chemicals and pollution.
Composite Poles
Made from materials such as fiberglass or other composites, these poles are
lightweight yet strong, resistant to corrosion and decay, and ideal for harsh
environments. They are more costly than traditional materials.
Towers
Towers are a critical component of overhead power lines, providing the necessary
support and elevation to conductors for the transmission and distribution of electrical
power over long distances. These robust structures are designed to withstand various
environmental conditions and mechanical loads, ensuring the reliability and safety of
the electrical grid.
Typically made of steel, towers come in different designs and configurations, each
tailored to specific applications and requirements. The primary types of towers include
lattice towers, tubular steel towers, guyed towers, and monopoles. Each type offers
unique advantages in terms of strength, durability, cost, and environmental impact.
Lattice Towers
Large, steel structures commonly used for high voltage transmission lines, designed
to carry heavy loads over long distances. These towers are highly configurable and
vary significantly in height and shape.
Tubular Steel Towers
These towers are made from tubular steel sections and offer a cleaner appearance
compared to lattice towers. They can be designed to blend in better with the
environment.
Guyed Towers
Supported by guy or stay wires (tensioned cables), these towers provide additional
stability in areas with high winds or other environmental stresses. They are often used
for both transmission and taller distribution lines.
Monopoles
Single, tall poles typically made of steel or concrete, used in urban areas or where
space is limited. They have a smaller footprint and less visual impact compared to
lattice towers.
Poles
Wooden Poles: Commonly used for lower voltage distribution lines, these poles are
relatively inexpensive and easy to install but may have a shorter lifespan due to
susceptibility to decay and insect damage.
Concrete Poles: More durable than wooden poles, these are resistant to rot, insects,
and fire. They are often used in areas where higher strength and durability are
required.
Steel Poles: Known for their high strength and long lifespan, steel poles are used in
areas where high loads are expected or where poles need to be taller. They are
resistant to environmental factors but can be more expensive.
Towers:
Lattice Towers: These are large, steel structures commonly used for high voltage
transmission lines. They are designed to carry heavy loads over long distances and
can vary significantly in height and configuration.
Tubular Steel Towers: Similar to lattice towers but made from tubular steel sections,
these towers offer a cleaner appearance and can be designed to blend in better with
the environment.
Guyed Towers: These are supported by guy wires (tensioned cables) and are often
used in areas where additional stability is needed due to high winds or other
environmental factors.
2. Conductors
Wires made from materials like aluminum, copper, or aluminum conductor steel-
reinforced (ACSR), which carry the electrical current over distances.
A conductor is one of the most important components of overhead lines. Selecting a
proper type of conductor for overhead lines is as important as selecting economic
conductor size and economic transmission voltage. A good conductor should have the
following properties:
▪ high electrical conductivity
▪ high tensile strength in order to withstand mechanical stresses
▪ relatively lower cost without compromising much of other properties
▪ lower weight per unit volume
Conductor Materials
Copper was the preferred material for overhead conductors in earlier days, but,
aluminum has replaced copper because of the much lower cost and lighter weight of
the aluminum conductor compared with a copper conductor of the same resistance.
Following are some materials that are considered to be good conductors.
▪ Copper: Copper has a high conductivity and greater tensile strength. So, copper
in hard drawn stranded form is a great option for overhead lines. Copper has a
high current density which means more current carrying capacity per unit cross-
sectional area. Therefore, copper conductors have relatively smaller cross-
sectional area. Also, copper is durable and has high scrap value. However, due
to its higher cost and non-availability, copper is rarely used for overhead power
lines.
▪ Aluminum: Aluminum has about 60% of the conductivity of copper; that means,
for the same resistance, the diameter of an aluminum conductor is about 1.26
times than that of a copper conductor. However, an aluminum conductor has
almost half the weight of an equivalent copper conductor. Also, tensile strength
of aluminum is less than that of copper. Considering combined factors of cost,
conductivity, tensile strength, weight etc., aluminum has an edge over copper.
Therefore, aluminum is being widely used for overhead conductors.
▪ Cadmium-copper: Cadmium-copper alloys contain approximately 98 to 99% of
copper and up to 1.5% of cadmium. Addition of about 1% of cadmium to copper
increases the tensile strength by up to 50% and the conductivity is reduced only
by about 15%. Therefore, cadmium-copper conductors can be useful for
exceptionally long spans. However, due to high cost of cadmium, such conductors
may be uneconomical in many cases.
▪ Other materials: There are many other metals and alloys that conduct
electricity. Silver is more conductive than copper, but due to its high cost, it is
not practical in most of the cases. Galvanized steel may also be used as a
conductor. Although steel has very high tensile strength, steel conductors are not
suitable for transmitting power efficiently due to the poor conductivity and high
resistance of steel. High strength alloys such as phosphor-bronze may also be
used sometimes at extreme conditions.
3. Insulators
Components made from materials such as porcelain, glass, or polymers, used to
electrically isolate the conductors from the support structures and prevent current
leakage.
4. Crossarms
Horizontal members attached to poles or towers to support and space out the
conductors. These can be made of wood, steel, or composite materials.
5. Protective Devices:
Equipment such as lightning arresters, fuses, and circuit breakers designed to protect
the power lines from overvoltage, faults, and other electrical disturbances.
Ground Wires
Also known as earth wires or shield wires, these are installed at the top of poles or
towers to protect the power line from lightning strikes by providing a direct path to
the ground.
It should be known that all the above are installed by a linesman.
Who is a linesman then?
A linesman, also known as a lineman or lineworker, is a skilled tradesperson
responsible for installing, maintaining, and repairing overhead and underground power
lines and related equipment. They play a crucial role in ensuring the reliable
transmission and distribution of electrical power to homes, businesses, and industries.
Key Responsibilities
Installation
• Erect poles or towers
• string the overhead wires or cables.
• Install and maintain transformers, insulators, circuit breakers, switches, and
other equipment on the lines.
Maintenance
• Regularly inspect power lines and related equipment to identify wear, damage,
or potential faults.
• Perform routine maintenance to ensure the reliability and safety of the power
grid.
Repair
• Respond to power outages and other emergencies to quickly restore service.
• Repair or replace damaged components such as conductors, insulators, and
support structures.
Safety
• Follow strict safety protocols to protect themselves and the public.
• Use personal protective equipment (PPE) such as hard hats, gloves, and safety
harnesses.
• Ensure work areas are secure and safe from hazards.
Climbing and Working at Heights
• Climb poles and towers using ladders, climbing gear, or bucket trucks.
• Work at significant heights to perform installations, maintenance, and repairs.
Underground Work
• In addition to overhead lines, linesmen may work on underground cables,
requiring them to dig trenches and install conduit systems.
Skills and Qualifications
Technical Knowledge
• Understanding of electrical systems, circuitry, and power distribution.
• Proficiency in using various tools and equipment specific to line work.
Physical Fitness
• Ability to perform physically demanding tasks, including lifting heavy
equipment, climbing, and working in challenging conditions.
Problem-Solving
• Ability to diagnose and troubleshoot issues quickly and effectively.
Communication
• Ability to work as part of a team and communicate effectively with other crew
members and supervisors.
