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How to Choose Overhead Line?

Mar. 31, 2025

How to design overhead power lines for utility-scale green energy

Achieving the ambitious goals of a clean energy transition requires more than simply installing renewable power generation capacity. It also includes the associated infrastructure to transmit the electricity to where it is needed so that it can replace fossil fuel generation.

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Overhead lines are a key component of the power transmission and distribution grid, carrying wind and solar energy to homes and businesses, as well as to electric vehicle chargers and other electricity consumers. But overhead lines are often given little thought in discussions surrounding renewable power installations. What do you need to know about overhead lines and how to incorporate them into utility-scale project design?

What is an overhead power line?

An overhead line is the electrical cable and associated equipment that is used to transmit power between a generation plant and the transmission and distribution grid or to connect substations. The line is suspended overhead by towers or poles and can be part of the transmission network or distribution network.

Transmission lines transmit power at voltage levels of 46 kilovolts (kV) and above, which is too high to deliver to homes and businesses. The voltage is reduced via transformers and delivered through distribution lines.

The electrical performance of an overhead line is determined by four main parameters: resistance, inductance, capacitance, and shunt conductance.

Overhead line design considerations

The design of an overhead line will depend on whether it is a transmission or distribution line and needs to take into consideration several pieces of equipment, such as:

Towers or supports
Conductors of various types
Earth, or ground, wire to protect the conductors
Insulators
Accessories.

Overhead line design should go through several planning stages to guarantee the system’s reliability and availability. Components such as the conductor, earth wire, insulators, and circuits must all meet electrical and mechanical requirements.

The strength of the line should also be able to withstand different weather conditions depending on the location, such as heavy snowfall, high temperatures, or strong winds.

The choice of the tower or support design will also depend on the grid operator, the utility and the country where it is located.

How to design overhead lines

When designing an overhead line, you need to take into account several factors concerning the positioning of the components:

Geometry

The geometry of the tower top is crucial to the design of an overhead line. The dimensions are determined by minimum phase-to-earth, phase-to-phase and ground electrical clearances. There are several top tower types and geometries worldwide incorporating different safety clearances for various voltage levels and regulatory requirements.

Sag and span

The position of the conductors and earth wire at the tower and the sag of the line at mid span change with climatic conditions. The sag refers to the vertical distance between the highest point of the electrical pole or tower and the lowest point of the conductor between two electrical supports. The horizontal distance between supports is the span. The catenary curve of the conductor is described by its sag under different state changes while considering its clearance to the ground.

Connections

The forces on tower connection points are an important consideration because they can cause compression on one side of the tower and tension on the other side. Calculating forces takes into account wind and ice loads, maintenance and conductor tension.

Route

The spotting, or optimizing, of the towers is an important consideration from the start of the design stage, as the route of the overhead line is key to the project’s permitting and approval process.

Cost

The cost of installing an overhead line depends mainly on the cross-sections of the conductors and the height of the towers as well as their foundations.

Overhead line planning with RatedPower

The interconnection element is a crucial part of a solar project, and the application and engineering processes can be complicated and take a long time to complete.

Our solar design platform is one of the few applications that can automate the basic engineering of an overhead line to reduce the development time. In RatedPower, a user can manage the design and basic engineering of an overhead transmission or distribution line with just a few clicks.

From only an initial path, the results can provide an overview of utilities as well as the scope of the interconnection section of the project and the approximate cost.

Choosing the right PV structure for your project leads directly to greater efficiency, power output, and ROI. In this post, we outline the three main PV plant structures and share RatedPower analysis of their performance. Learn more on the blog post: Choosing PV structures: Trackers vs Fixed vs East-West (Case study inside!)

In the software, a user can import a path for the line and the algorithm will automatically evaluate the feasibility of the line. It will then spot the towers along the route, select the type of equipment needed, calculate the electrical and mechanical parameters, calculate the catenary and tower forces, design the top geometry of the towers, select towers from known manufacturers, and calculate the losses and the power factor at the receiving end of the line.

This enables you to design the interconnection between the plant’s substation and the point of interconnection with ease. Depending on the voltage level, the overhead will be designed as a distribution or transmission line.

The software generates complete PV system engineering documentation including a design report and a complete drawing of the line in .pdf and .dxf formats.

This overhead line feature in RatedPower opens the door for new users in electric utilities to be able to design optimized transmission and distribution lines in only a few minutes.

Project developers can also go beyond the plant and substation designs by adding more engineering design into the point of interconnection, giving users all the necessary results and data that they need for an overhead line.

Use RatedPower to optimize your solar plant interconnection

Overhead lines form an important part of the infrastructure that will enable utility-scale solar power projects to displace fossil fuel generation. If you are developing a large solar project, contact RatedPower to find out how we can help to automate and optimize your project.

Overhead Power Line and Components- The Ultimate Guide

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.

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.

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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.