The Ultimate Guide to Choosing Overhead Line

Overhead power lines (also known as transmission lines, power lines, power cables, and coaxial cables) are groups of suspended cables and wires used to transport electrical power between two or more separate locations so it can be processed for use by consumers safely and efficiently.

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What is an overhead power line?

An overhead power line operates as a channel to transfer electromagnetic waves of varying voltage levels across a variety of distances, environments, and landscapes to supply electrical power where it is needed.

Power line cables are structurally supported by utility poles or steel towers, which are designed to keep the lines suspended at a safe height. This ensures that there is a sufficient amount of ground clearance ' minimizing the risk of the live lines being disturbed or damaged.

Overhead power lines come in different types and lengths to accommodate varying voltage loads. This enables them to serve the entire spectrum of industrial and residential electrical supply purposes.

How does an electrical power transmission system work?

The electrical power transmission system of overhead lines enables electricity to be moved nationwide ' creating a seamless, speedy power supply across all corners of a country. The network is vital in ensuring a reliable and regular supply of power to our homes, workplaces, and other amenities.

Overhead power lines are of two types: transmission lines and distribution lines. Transmission lines carry high-voltage 'primary' power between generators and substations, where it can be later safely 'stepped down' to a lower voltage level using a transformer before being distributed publicly.

Distribution lines are the cables that then carry this decreased 'secondary' electricity supply to individuals, businesses, and other premises for everyday use.

Types of power lines

Power lines can use two forms of current flow: alternating current (AC) and direct current (DC). With direct current, the electrical current flows in only one direction, whilst with alternating current, the power can periodically change direction.

Due to its superior ability to work with higher voltages and the ease with which the power can be transformed as required, AC current is most commonly used in power lines today.

For ease of assessing performance, AC power lines can be classified according to voltage and length:

Voltage Classification

• Low Voltage: Lines transmitting 1 kV or less;
• Medium Voltage: Lines transmitting between 1-69kV;
• High Voltage: Lines transmitting between 69 kV ' 345V;
• Extra-High Voltage: Lines transmitting around 345-800kV; and
• Ultra-High Voltage: Lines transmitting 800 kV and over.

Length Classification

Short Lines

Short power lines are those which cover a distance up to 50 miles (80 km). These lines carry a voltage flow of between 11-33 Kv and are often used to supply electricity to homes and other low-demand power networks.

Medium Lines

Lines spanning between 50-100 miles (80-160km) are classified as medium power lines and usually transmit between 66-132 Kv through its cables. This category can be further sub-divided into Pi-Models and T- Models. In a Pi-Model line, the capacitance (ability to store an electrical charge) is concentrated equally at each end, whereas in a T-Model line the capacitance is concentrated at its center.

Long Lines

A long power line covers a distance of 100+ miles (over 160km) with a voltage capacity of 132 Kv or above. Only in these lines are all four parameters used for determining performance (resistance, inductance, capacitance, and leakage conductance) equally distributed across the entire power line.

Components of overhead power lines

Line Supports

Line supports keep power lines suspended above the ground, minimizing the safety risk and maximizing their power transmission. There are 2 main types of line supports ' poles and towers. The type used will depend on various factors, such as the voltage level and distance coverage required.

Poles

Poles transport power over shorter distances. Commonly used for distribution lines, they usually carry low-high voltage levels. The most common pole materials are wood, concrete, and steel.

Wooden Poles: Often used to cover shorter distance spans, wooden poles are a cost-effective option for transporting low-medium voltage levels. However, as a natural material, wooden poles have a shorter life span and are considerably more vulnerable to environmental conditions than their man-made counterparts.

Concrete (RCC) Poles: Low maintenance with a superior loading capacity, concrete poles are a prime choice for supporting structures requiring an extra boost of strength or resilience, such as areas hosting extreme climatic conditions. Unfortunately, their weightier construction also makes them expensive and awkward to transport.

Steel Poles: Commonly used in urban areas, steel poles are durable and allow for a high level of flexibility in their manufacture ' making them an attractive option adaptable to a range of transmission purposes. Though galvanized poles boast good longevity, they can still fall foul to rusting and are costly.

Towers

For the transmission of higher voltage levels across larger areas, steel towers are the go-to line supports. As mighty steel constructions with a considerable level of mechanical strength, their design offers robust resilience to the elements and a higher quality of transmission.

However, as with steel poles, towers are expensive and more vulnerable to lightning strikes than other materials.

Power Line Conductors

Conductors are components attached to power lines to promote the passage of electricity from one location to another. They also help to boost the safety of the electrical network.

The four main types of conductors used on overhead lines are AACs (All Aluminium Conductors); AAACs (All Aluminium Alloy Conductors); ACARs (Alloy Reinforced Aluminium Conductors), and ACSRs (Steel Reinforced Aluminium Conductors).

ACSR conductors ' and to a lesser degree, AAACs ' are the most frequently used conductors on modern power lines. As lightweight conductors with high capacitance ACSRs and AACs are also cost-effective ' making them ideal for use in high voltage lines requiring multiple or bundled conductors.

Power Line Insulators

Insulators restrict the power flow at defined points of an electrical network. They are used on power lines to assist in the safety and support of the structure by reinforcing the line and keeping the conductors separated.

Power line insulators can be loosely split into two categories depending on the installation process: pin insulators (installed above the line) and suspension insulators (installed to hang below the line).

For higher-voltage lines, modular (multiple units) suspension insulators are often used to handle the higher level of resistance required. Made from a series of adjustable insulator disks, they can be easily increased or decreased as needed.

Power Line Earth Anchors

Earth anchors (also known as ground anchors) are heavy-duty engineering devices used to reinforce and stabilize the poles or towers installed to support power lines.

Driven or corkscrewed into the surrounding foundations, earth anchors help to protect the structural integrity of the lines against adverse or extreme weather conditions, as well as any subsequent natural or man-made changes to the local landscape.

Power Line Fittings

A variety of hardware accessories are fixed to power lines, poles, and towers to assist in the smooth transition of electricity from one place to another. Some of the most common fittings used on power lines and supports include:

• Cross arms: A bar attached horizontally to a pole to support its insulators and other hardware;
• Guy wires: Strong steel cables that reinforce the structure of a utility pole;
• Spacers: Components that keep live conductors on a line a safe distance apart;
• Dampers: Devices that protect fragile cables and wires in an outdoor environment;
• Earth Wires: Provide a layer of shielding between the line and harsh climatic conditions;
• Lightning Arrestors: Safety devices that redirect lightning away from the live line into the ground.

Conclusion

When genius pioneer Nikola Tesla designed the AC system during the Industrial Revolution, perhaps even his visionary mind could not have predicted the unrivaled impact his discovery would have in reinventing how this powerful energy could be utilized.

Nearly 150 years on, AC current remains the undisputed worldwide standard for electrical transmission ' and, thanks to our state-of-the-art network of overhead lines which carry this radiant resource far and wide, we have been able to achieve a level of technological advancement which has enriched all areas of our lives.

Thanks to the development of long-distance power transmission, our humble planet Earth has been illuminated within the vast expanse of inky space ' and our future looks brighter still.

Frequently Asked Questions (FAQs)

What is an overhead power line?

An overhead power line operates as a channel to transfer electromagnetic waves of varying voltage levels across a variety of distances, environments, and landscapes to supply electrical power where it is needed.

How does an electrical power transmission system work?

The electrical power transmission system of overhead lines enables electricity to be moved nationwide ' creating a seamless, speedy power supply across all corners of a country. The network is vital in ensuring a reliable and regular supply of power to our homes, workplaces, and other amenities.

Types of transmission lines

Power lines can use two forms of current flow: alternating current (AC) and direct current (DC).

AC power lines can be classified according to voltage and length:

Voltage Classification

• Low Voltage
• Medium Voltage
• High Voltage
• Extra-High Voltage
• Ultra-High Voltage

Length Classification

• Short Lines
• Medium Lines
• Long Lines

What is an Overhead Transmission Line?

An overhead transmission line is a crucial element in the electrical grid system. These lines carry high-voltage electrical power over long distances from power stations to substations, ultimately distributing electricity to consumers. Overhead transmission lines are the most common method of transmitting large amounts of electricity due to their ability to cover vast distances efficiently.

The setup consists of conductors, insulators, support structures, and various overhead line hardware. The design and components of these lines ensure that electricity reaches its destination without significant losses while minimizing the risk of system failure.

Understanding the components of an overhead transmission line is essential for suppliers, distributors, contractors, and engineers who are involved in electrical infrastructure projects.

Components of Overhead Transmission Line

The overhead transmission line is made up of several components, each serving a vital role in ensuring efficient and safe electricity transmission. Let's take a closer look at these key components:

#1. Line Supports (Poles and Towers)

The pole line supports are the structures that hold the transmission lines in place. Common types of utility poles are generally made from steel, concrete, or wood and are designed to elevate the conductors to the required height and maintain clearance for safe operation.

' Steel Poles/Towers: Our focus is on hot-dip galvanized steel utility poles, known for their superior strength, corrosion resistance, and longer lifespan compared to other materials. These are commonly used for high-voltage lines due to ability to withstand harsh weather conditions.

' Concrete Poles: Used in areas with high corrosion or environmental exposure.

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' Wooden Poles: Typically used for lower voltage transmission and in rural or less populated areas.

Hbcrownwealth Our steel utility poles are forged from high-quality carbon steel. The surface is evenly galvanized and is not easy to rust. The average service life can be more than 60 years.

#2. Insulators

Insulators are used to separate and support the conductors while preventing them from coming into contact with the support structures. These are crucial for maintaining the safety of the system and preventing electrical shorts.

' Porcelain: Traditionally used due to its durability and high electrical resistance.

' Toughened Glass: For insulation and suspension of conductors in high voltage and ultra-high voltage AC and DC transmission lines.

' Composite Materials: More modern materials that are lightweight and resistant to environmental degradation.

Based on the installation method, power line insulators can be roughly divided into two categories: Pin Insulators (installed on the line) and Suspension Insulators (installed under the line).

#3. Power Line Conductors

Overhead line conductors mainly carry transmission current. They are typically made from aluminum, copper, or aluminum-steel composites (ACSR), with the latter being the most common due to its strength and conductivity.

' ACSR (Aluminum Conductor Steel Reinforced): Often used for long-distance transmission because of its strength-to-weight ratio.

' Copper: Used for specific high-performance applications, although less common due to higher costs.

' Aluminum: Known for its light weight and good conductivity, ideal for various power lines.

#4. Grounding Systems and Earth Anchors

The grounding system ensures that any excess electrical charge, such as during a lightning strike or fault condition, is safely directed into the earth. Earth anchors are used to stabilize the transmission line poles and towers, ensuring their structural integrity under varying loads.

' Ground Conductors: Typically copper or aluminum wires used to connect the system to the ground.

' Earth Anchors: Also as No-Wrench acrew anchor, ensure the stability of the pole structure against forces like wind or ground movement.

#5. Overhead Line Hardware and Fittings

Overhead transmission lines require a range of line hardware to ensure they operate safely and efficiently. These components are designed to handle high tension, secure conductors, and prevent mechanical failure. Here are some of the most commonly used overhead line hardware:

' Pole Band: This is hardware accessories used to fix on poles. Hbcrownwealth has a variety of pole band with different appearances and structural designs for you to choose from.

' Cross Arm: The electrical cross arms a pole mounted horizontally on a utility pole to support insulators and other pole line hardware. Provide support for conductors and maintain their distance from each other.

' Guy Wire: A strong steel cable used to reinforce the structure of a utility pole. Secure it firmly to the earth anchors with a guy wire clamp.

' Insulator Fittings: Secure insulators to the pole or tower.

' Vibration Dampers: Reduce the mechanical stress caused by wind and prevent line breakage.

' Lightning Arrester: A safety device that diverts lightning from a live line to the ground.

' Cable Clamps and Connectors: Used for securing and joining conductors cable, such as lashing wire clamp, span clamp, insulated piercing connector, etc.

' Tension & Suspension Clamp: Keeps the line under the correct tension and allows it to move freely during temperature changes, including anchoring clamp, guy grips, J suspension clamp and other types of preformed ADSS tension clamp and suspension clamp.

What Materials are Commonly Used in Components of Overhead Transmission Lines?

The materials used in overhead transmission lines are selected for their durability, strength, and ability to withstand the environmental stresses they face. Here are the most common materials:

' Aluminum: Widely used in conductors for its excellent conductivity and light weight.

' Copper: Known for superior conductivity, copper is used in specialized transmission lines.

' Steel: Often used in towers, anchors, and reinforced conductors due to its high tensile strength.

' Porcelain and Glass: Traditionally used in insulators for their ability to resist electrical breakdown and mechanical stress.

' Composite Materials: Used in modern insulators for their resistance to weathering and high performance under various electrical stresses.

The choice of materials for each component of the transmission line depends on factors like environmental conditions, voltage level, and budget. Ensuring that the right materials are used in the right applications is essential for the longevity and safety of the system.

Conclusion

For anyone involved in the planning, construction or maintenance of power infrastructure, it is important to understand the components of overhead transmission lines. From conductors to insulators and line hardware, they all play an important role in ensuring the safe and reliable transmission of power.

At Hbcrownwealth, as a reliable transmission line hardware manufacturer in China, we provide you with high-quality overhead power transmission line components that meet international standards and withstand the rigors of harsh environments.

If you are looking for overhead transmission line hardware, contact us today for expert advice and product recommendations for your specific needs.

FAQ

Types of Overhead Transmission Lines

By Voltage: Low Voltage ('1kV); Medium Voltage; (1-100kV); High Voltage (100kV'765kV); Ultra-high Voltage ('765kV);

By TransmissionDistance: Short Distance Line ('80 km); Medium Distance Line (80-160 km); Long Distance Line ('160 km);

By Circuit Type: Single Circuit; Double Circuit; Triple Circuit;

What are The Main Components Of An Overhead Transmission Line?

A: The main components include power line conductors, insulators, transmission poles, guy wires, and anchors.

What Role Do Insulators Play in an Overhead Transmission Line?

A: Insulators prevent the current from leaking to the ground, ensuring that electricity is transmitted safely and without loss through the line.

How are Transmission Line Conductors Selected?

A: Conductors are selected based on their material (typically aluminum or copper), voltage rating, and ability to handle the electrical load.

What is the Function Of a Transmission Pole in an Overhead Line?

A: Transmission poles support the conductors, keeping them elevated and separated to ensure safe transmission of electricity.

Why are Guy Wires Important for Overhead Transmission Lines?

A: Guy wires are used to stabilize transmission poles and prevent them from falling under the weight of the lines or during strong winds.

What are the Different Types Of Overhead Transmission Line Towers?

A: There are various types, including monopole, lattice, and guyed towers, each designed for different applications and environmental conditions.

What are Transmission Line Anchors and Why are They Necessary?

A: Anchors are used to secure guy wires and poles to the ground, ensuring the structural stability of the transmission line system.

How Does the Voltage Rating of an Overhead Transmission Line Affect Its Components?

A: Higher voltage lines require more robust components like stronger insulators and conductors that can handle greater electrical loads.

How Do Environmental Conditions Affect the Components of an Overhead Transmission Line?