High-Voltage Transmission Challenges

2025-4-18 Apr 16, 2025 by Ahmed Sheikh EE Power

High-Voltage Transmission Challenges

This article discusses challenges in high-voltage transmission, including insulation, corona discharge, and electromagnetic interference, while highlighting advancements like ultra-high voltage systems, HVDC technology, and smart grid integration.

High-voltage transmission systems face several technical challenges, such as ensuring proper insulation to prevent electrical arcing and managing corona discharge, which causes energy loss and noise at high voltages. Electromagnetic interference (EMI) can disrupt nearby communication systems, requiring specialized measures like shielding. Additionally, the cost of voltage conversion equipment, such as transformers and circuit breakers, is a significant concern due to the high voltages and fault currents involved. To address these challenges, advancements like ultra-high voltage (UHV) systems, high-voltage direct current (HVDC) transmission, and smart grid technologies are improving efficiency, reducing losses, and enhancing grid reliability.

Challenges in High-Voltage Transmission

While high-voltage transmission offers significant efficiency and economic benefits, it also introduces a range of technical and economic challenges that must be addressed in system design and operation. These challenges revolve around insulation, conductor behavior, electromagnetic effects, and the cost of specialized equipment.

Insulation Requirements

As voltage levels increase, the need for effective insulation becomes more critical. High-voltage systems require larger air clearances between conductors and grounded structures to prevent electrical arcing. Additionally, creepage distances—the shortest path along the surface of an insulating material between two conductive parts—must be extended, especially in polluted or humid environments where surface conductivity increases. Equipment such as transformers, insulators, and bushings must be rated to withstand not only normal operating voltages but also transient overvoltages from lightning or switching surges, demanding materials with high dielectric strength and robust design considerations.

Corona Discharge

At high voltages, especially above 200 kV, corona discharge becomes a prominent issue. This phenomenon occurs when the electric field around a conductor ionizes the surrounding air, leading to energy loss in the form of corona loss (typically measured in kW/km), audible hissing or buzzing noise, and visible blue-violet glow during nighttime. Corona generates ozone and other by-products that can degrade nearby equipment. To mitigate this, utilities often use bundled conductors, where two or more sub-conductors are used per phase to increase the effective conductor diameter, thereby reducing the electric field intensity and suppressing corona formation. Managing corona is essential not just for efficiency but also for compliance with environmental and noise regulations.

Figure 1. Corona discharge on an insulator string of a 500 kV overhead power line. Image used courtesy of Wikipedia

High-voltage transmission lines generate strong electromagnetic fields (EMF), which can cause interference with nearby communication lines, radio frequencies, and sensitive electronic equipment. EMI is especially problematic in densely populated areas or near infrastructure like railways and airports. Specialized shielding, grounding, and line routing strategies must be employed to minimize this interference. Additionally, regulatory bodies may impose strict EMI limits, requiring careful monitoring and mitigation efforts in the design phase of transmission projects.

Cost of Voltage Conversion Equipment

One of the major economic challenges of high-voltage transmission lies in the cost of voltage conversion infrastructure. Stepping up voltages for transmission and stepping them down for distribution and end-use requires high-cost transformers, circuit breakers, and switchgear capable of handling high voltages and fault currents. These devices are not only expensive to procure but also require significant space, maintenance, and insulation measures. Despite their high initial cost, they are justified over the system’s lifespan due to the efficiency and reliability gains achieved through high-voltage transmission.

Figure 2. Flow of electricity from a generating station through high-voltage transmission lines to substations and then to distribution networks. Image used courtesy of Wikipedia

Advancements in High-Voltage Transmission

As power demand grows and the need for long-distance transmission increases, high-voltage transmission systems have seen significant technological advancements. These innovations aim to increase capacity, reduce losses, improve reliability, and integrate with modern energy infrastructure. Key developments include ultra-high voltage systems, advanced conductor materials, smart grid technologies, and the rise of high-voltage direct current transmission.

Ultra-High Voltage AC and DC Systems

One of the most prominent advancements in the field is the deployment of ultra-high voltage (UHV) transmission systems. These systems operate at voltages beyond 765 kV for AC and up to 1100 kV for DC, allowing the transfer of massive amounts of power over extremely long distances with minimal losses. For example, China’s 1100 kV HVDC project, spanning over 3,000 km, is capable of transmitting more than 12 GW of power, equivalent to the output of several large power plants. These systems are crucial in countries with vast geographical areas or where renewable energy sources, such as large solar or wind farms, are located far from consumption centers. UHV technology reduces the need for multiple parallel lines, optimizing land use and infrastructure.

Advanced Conductors

Traditional conductors are being replaced or supplemented with high-temperature low-sag (HTLS) conductors and composite core conductors to handle higher currents without excessive sag or thermal degradation. HTLS conductors can operate at temperatures up to 200–250°C, compared to conventional conductors rated around 90–100°C, which allows for increased current-carrying capacity. Composite core conductors, such as Aluminum Conductor Composite Core (ACCC), use materials like carbon fiber to reduce weight and thermal expansion, resulting in reduced sag under high load conditions. These materials improve reliability and enable the uprating of existing transmission corridors without needing taller towers or expanded rights-of-way.

Smart Grid Integration

With the evolution of the electrical grid into a smart grid, high-voltage transmission lines are increasingly equipped with real-time monitoring and control systems. Technologies such as Phasor Measurement Units (PMUs), dynamic line rating (DLR) sensors, and Wide Area Monitoring Systems (WAMS) provide real-time data on current, voltage, temperature, and mechanical stresses. This enables operators to optimize line loading, detect faults rapidly, and prevent outages, thus enhancing grid resilience and reliability. These systems also play a critical role in renewable energy integration, managing variability, and ensuring stable power delivery.

HVDC Transmission

While most power systems operate with AC transmission, high voltage direct current technology is increasingly being used for very long-distance transmission and for subsea power cables where AC is inefficient or impractical. HVDC systems have lower line losses over long distances and allow asynchronous interconnection of different power grids. Projects like the NordLink HVDC submarine cable between Norway and Germany highlight the role of HVDC in cross-border energy exchange.

Case Studies in High-Voltage Transmission

High-voltage transmission is not just a theoretical concept or confined to laboratory-scale advancements; it is a fundamental pillar of modern power grids worldwide. From intercontinental energy exchanges to rural electrification, high-voltage infrastructure has enabled reliable and efficient power delivery across vast distances and diverse terrains. Below are prominent real-world examples that showcase the strategic application and benefits of high-voltage transmission systems.

China’s Ultra High Voltage (UHV) Projects. 
www.sgcc.com.cn

China leads the world in UHV transmission deployment, both in terms of voltage levels and network scale. One standout project is the 1100 kV Changji–Guquan HVDC line, spanning over 3,000 kilometers, which can transmit more than 12 GW of power. This and other UHV AC and DC projects are designed to bridge the energy-rich western regions—home to extensive wind, solar, and hydro resources—with eastern industrial hubs that have massive energy demands.

These projects have significantly reduced transmission losses, optimized national grid balancing, and minimized the need for coal-fired generation near urban centers, supporting China’s broader decarbonization and air quality goals. Furthermore, by transmitting electricity at ultra-high voltages, the country has avoided building duplicate power plants near consumption areas, instead focusing on centralizing generation and maximizing transmission efficiency.

Figure 3. Changji-Guquan UHVDC Transmission Project. Image used courtesy of Guangdong Electric Power Design Institute (GEDI)

European High-Voltage Interconnectors

In Europe, high-voltage transmission is central to cross-border electricity trading and energy security. Countries are interconnected through a network of HVAC and HVDC lines, enabling power flow between nations based on demand, supply, and market conditions. Projects such as the NordLink (Germany–Norway) and IFA (UK–France) interconnectors operate at voltages around 320–525 kV DC, allowing the exchange of renewable energy like hydro and wind across regions.

These interconnectors not only enhance grid stability and reduce price volatility but also support the integration of intermittent renewable sources by spreading the load and supply over a larger geographical area. The European interconnection strategy is a model for regional energy cooperation, especially in the context of increasing electrification and decarbonization goals.

High-Voltage Networks in the United States

In the United States, extensive 500 kV HVAC transmission networks form the backbone of bulk power transfer, especially in the Western Interconnection and the Eastern Interconnection. Notable examples include the Pacific AC Intertie and Pacific DC Intertie (±500 kV HVDC), which transmit electricity from the hydroelectric plants in the Pacific Northwest to energy-demanding regions like Southern California.

These lines are vital for balancing seasonal load variations, facilitating the integration of renewable energy, and enhancing grid resilience. As the U.S. grid evolves to accommodate distributed energy resources (DERs) and an increasing share of renewables, there is a strong focus on expanding and modernizing existing high-voltage infrastructure to improve transmission efficiency, reduce congestion, and enhance interregional connectivity.

Advances in High-Voltage Transmission

The advancements in high-voltage transmission systems are essential to meeting the growing demand for reliable, efficient, and sustainable power delivery across long distances. Technologies like ultra-high voltage systems, HVDC, and smart grid innovations are crucial for minimizing transmission losses, improving grid stability, and enabling better integration of renewable energy sources. High-performance conductors and real-time monitoring systems further optimize line capacity and enhance resilience against faults or extreme conditions. These solutions not only improve the efficiency of energy distribution but also support efforts to reduce environmental impact and increase the resilience of power grids, which are becoming more complex and interconnected as energy needs evolve.