Transmission towers are crucial structures supporting overhead power lines and ensuring the efficient transmission of electricity over long distances. These high voltage towers are built with durable materials such as steel and aluminium to withstand environmental conditions and maintain the stability of power lines, preventing sagging and contamination. Their strategic placement is key to creating a reliable transmission network, ensuring electricity reaches both urban and remote areas, thereby aiding economic development and the integration of renewable energy sources. As global electricity demand grows, transmission towers play an increasingly vital role in modernising power grids and supporting the transition to sustainable energy.
Tower technologies
Lattice towers
Lattice towers are the most widely used type of transmission towers, characterised by steel frameworks that form triangular or square structures. They are durable, versatile and relatively easy to assemble and transport. Capable of supporting multiple circuits and spanning long distances, lattice towers are well suited for various terrains and weather conditions. However, they come with certain disadvantages, including higher maintenance costs, a noticeable visual impact on landscapes and vulnerability to corrosion and bird collisions.
Tubular towers
Tubular towers are constructed from hollow steel tubes that are either welded or bolted together. Compared to lattice towers, they are more compact and visually appealing, and have better resistance to corrosion. However, they are also costlier, heavier and more challenging to transport and install. These towers can accommodate single or double circuits and are commonly used in urban areas where space constraints and aesthetics are key considerations.
Concrete towers
Concrete towers are constructed from reinforced or prestressed concrete, either cast on-site or prefabricated. They are known for their durability, stability and low maintenance needs, but are also bulky, inflexible and challenging to modify or relocate. These towers can support single or double circuits and are typically used in regions prone to high seismic activity, strong winds or corrosive soil conditions.
Hybrid towers
Hybrid towers are constructed using a combination of materials, such as steel and concrete or steel and wood, to leverage the strengths of each material while mitigating their drawbacks. Their design allows for greater flexibility, efficiency and sustainability compared to traditional towers, making them adaptable to the specific requirements of a project. However, hybrid towers present greater challenges in terms of design, fabrication and installation.
Emerging trends
Monopoles
One energy transmission tower requires approximately 25 sq m of land space. Because of this, it has become crucial to deploy a structure that requires less space. The use of monopole towers has become imperative because they require less space than transmission towers. While a transmission tower is made of one truss, a monopole tower is made of tubes. Monopoles have distinct advantages over lattice towers with regard to space, speed of erection, delivery time and more. The benefit of a smaller base installation space, even while rising when they are taller than 40 to 50 metres, makes monopoles an eco-friendly alternative. Bajaj Electricals Limited was the first to design, manufacture and erect steel monopoles.
Multicircuit towers
Multicircuit towers are engineered to support three, four or even six circuits, allowing them to transmit larger amounts of power over a given distance. Designed with robust operating systems, these towers help reduce the overall right-of-way (RoW) requirements for transmission lines, making them particularly effective in challenging areas such as forests, densely populated urban centres, and substation entry and exit points. Despite their advantages, multicircuit towers remain underutilised due to concerns that a fault in one connection could compromise the entire circuit network.
Emergency restoration towers
Emergency restoration system (ERS) towers are modular and reusable transmission tower systems that offer exceptional versatility. They are widely used by line crews from national grids, utility companies and other power transmission and distribution organisations. ERS towers serve various purposes, such as restoring power after disasters such as floods, hurricanes or conflicts; enabling scheduled maintenance on existing towers with minimal service disruption; providing temporary line extensions quickly without the need for civil engineering work; and connecting remote locations or villages, such as mining sites, to the main grid.
When transmission lines are interrupted due to damaged towers, the resulting economic impact on transmission and utility companies can be significant. ERS towers provide a fast and efficient solution to minimise these disruptions. The Power Grid Corporation of India (Powergrid) has used ERS towers to quickly, safely and efficiently restore power interrupted by natural disasters, sabotage or vandalism. It has indigenously developed ERS sets up to the 400 kV level.
Other types
Guyed towers are supported by guy wires for added stability. These towers consist of a central mast with multiple guy wires extending outward, anchored to the ground. They are often used in locations with limited space or uneven terrain, where conventional self-supporting towers may not be practical. Additionally, they serve as a cost-effective solution for medium to high voltage transmission lines.
Self-supporting towers have a mast structure that can support power lines independently, without the need for external supports such as guy wires. They come in various shapes, including triangular, square and hexagonal designs, each providing different levels of stability and load-bearing capacity. These towers are typically used in flat terrains or locations with few environmental restrictions, where space is not a major concern.
The “tower within tower” concept replaces existing transmission towers by constructing new towers within the space of the old ones. This approach reduces construction costs compared to traditional methods, speeds up project timelines and minimises land acquisition and compensation needs. Additionally, it helps avoid significant disruptions to the surrounding environment and infrastructure, making it an efficient and practical solution for upgrading transmission lines in densely populated or constrained areas. Tata Power Company Limited has set up four such towers in Kalyan and more are to be set up along the transmission corridor in the Diva and Mumbra areas.
Compact chainette towers are designed with a narrow footprint, making them ideal for challenging terrains, such as steep slopes and sharp angles, where traditional towers may not be feasible. The unique suspension system, where conductor bundles and insulator strings hang horizontally, allows for efficient load distribution and enhanced stability in such environments. Additionally, their minimal land requirement reduces environmental impact, making them a practical choice for areas with space or access constraints.
Further, ongoing research and development efforts are focused on incorporating composite materials such as fibre-reinforced polymers for tower construction. These materials offer a high strength-to-weight ratio, excellent insulation properties, affordability and low maintenance requirements. They are resistant to UV rays, rust and rot, and have flame-retardant properties.
Furthermore, transmission towers are exposed to harsh weather conditions such as cyclones, storms, earthquakes, floods, landslides and avalanches. To mitigate the impact of these events, key measures include reinforcing towers, shortening spans in existing lines, regular monitoring and maintenance, reconstructing damaged infrastructure and applying anti-corrosive coatings. To ensure the reliability of the line throughout its operation in challenging terrains and conditions, Indigrid has erected avalanche protection structures to protect the line from landslides and snow avalanches.
Digital solutions
Conventional surveying methods, such as walkover and detailed surveys, are manual processes that require significant time with a risk of inaccuracies. In contrast, modern techniques use advanced technologies for mapping and aerial monitoring, minimising errors and improving efficiency. Transmission tower patrolling apps are now being used by several state and private utilities.
For instance, at Madhya Pradesh Power Transmission Company Limited, using the Transmission Assets Management System app provides information on a number of assets (towers, feeders and substations) implemented in a particular administrative block that are readily available on a daily basis. This helps to keep track of the ground patrolling and maintenance report history on a regular basis with actual site photos, data and geographical coordinates.
Powergrid has developed the AMRIT app (Asset Management through ARtificial Intelligence in Transmission) for image processing-based identification of defects in transmission line towers along with geospatial defect tags. This has helped in the identification of more than 40 types of defects. It has a processing speed of 100 photographs per minute, and accuracy is over 70 per cent.
Drones equipped with light detection and ranging, RGB cameras and real-time kinematic systems provide high resolution 3D mapping at lower costs and greater safety. Drones significantly enhance maintenance by covering large areas quickly, performing detailed inspections and collecting comprehensive data in a fraction of the time compared to manual methods. This efficiency enables more frequent and thorough inspections, reducing the chance of unnoticed issues. Additionally, drones with advanced sensors and artificial intelligence provide real-time, accurate data that can be analysed to identify trends and improve maintenance planning.
Digital twin technology is an emerging solution for monitoring the health of transmission towers and lines by tracking all operational parameters. It offers real-time predictive data, improving operational flexibility and asset risk management.
Conclusion
The transmission tower industry is evolving rapidly to meet growing electricity demands, integrate renewable energy sources and minimise environmental and social impacts. To achieve this, the industry is employing lighter, stronger and more durable materials such as composite materials, high strength steel and aluminium alloys. Moreover, smart features such as sensors, cameras and communication devices are being incorporated to monitor and manage tower performance and condition. Green solutions are also being implemented, such as applying anti-corrosion or anti-icing coatings, planting vegetation around towers and installing bird deterrents or nesting platforms.
Aastha Sharma