TOP 5 LONGEST TRANSMISSION LINES IN THE WORLD

Engineering Challenges, Technical Innovations, and Why These Mega-Projects Are Power System Marvels

1. Belo Monte–Rio de Janeiro UHVDC Transmission Line (Brazil)

Length: 2,543 km
Voltage Level: ±800 kV DC
Power Capacity: 4,000 MW
Technology: UHVDC (Ultra High Voltage Direct Current)

Why It’s Extraordinary

This is one of the longest and most remote UHVDC lines on earth, carrying Amazon hydroelectric power to Brazil’s coastal cities.

Major Technical Challenges

a) Extreme Terrain (Amazon Rainforest)

• The line crosses dense rainforest, swamps, rivers, and mountainous areas.

• Foundation design required deep piles and corrosion-resistant structures.

b) Lightning & Storm Exposure

The Amazon basin is among the highest lightning activity regions on the planet (Ng > 12–15).
Required:

• Improved shielding design

• Ultra-low footing resistance

• Wide-phase spacing

c) Environmental Protection

Right-of-way design minimized deforestation through:

• Compact tower design

• Reduced corridor width

Key Engineering Innovations

• Use of hybrid steel–composite conductors to reduce sag in hot climates

• High-performance 800 kV converter stations

• Real-time wide-area protection systems (WAPS)

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2. Jinping–Sunan UHVDC Transmission Line (China)

Length: 2,090 km
Voltage: ±800 kV DC
Capacity: 7,200 MW
Region: Sichuan → Eastern China

Technical Challenges

a) Extreme Mountain Terrain

The route crosses mountains exceeding 4,000 meters elevation, requiring:

• High-altitude tower design

• Wind load design > 70–80 m/s

• Frost/icing conditions

b) Ultra-long spans

Spans exceeding 1,500 meters demanded:

• High-strength conductors

• High tension towers

• Special sag-tension studies

Innovations

• Composite insulators with high creepage

• High altitude corona mitigation

• Optimized tower geometries for steep slopes

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3. Xiangjiaba–Shanghai UHVDC Transmission Line (China)

Length: 1,907 km
Voltage: ±800 kV
Capacity: 6,400 MW

Why It’s Important

It was the world’s first commercial ±800 kV UHVDC line, marking China’s entry into large-scale UHV transmission.

Engineering Challenges

a) High Temperature Sag

China’s inland provinces experience summer temperatures > 40°C.

• Conductors had to meet strict HTLS requirements

• Special sag-tension control with PLS-CADD

b) Long Route, High Stability Requirement

• Earthquake-prone regions → seismic-resistant tower foundations

• Multi-climate zones: dry, humid, coastal, industrial

Engineering Innovations

• “Large bundle conductors” for corona loss minimization

• Strategic placement of line surge arresters

• Massive GIS converter stations

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4. Champa–Kurukshetra HVDC (India)

Length: 1,365 km
Voltage: ±800 kV
Capacity: 6,000 MW

Technical Challenges

a) Heavy Lightning Activity

Central and eastern India have Ng values up to 14–16 flashes/km²/year.

Required:

• Deep grounding (10 Ω targets across high-resistivity soils)

• Optimized shielding angle (12–15°)

• Double ground wires

b) Monsoon Season

Monsoon storms created:

• Tower overturning risks

• Conductor galloping

• High wind pressures

Innovations

• Flexible AC transmission systems (FACTS) at receiving ends

• Sag and tension real-time monitoring

• High-ampacity conductors (ACSR & ACCC combinations)

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5. Pacific DC Intertie (United States)

Length: 1,362 km
Voltage: ±500 kV HVDC
Capacity: 3,100 MW
Route: Oregon → Los Angeles

Why This Line Is Historic

Built in the 1970s, it remains one of the world’s longest and most reliable HVDC systems.

Technical Challenges

a) Crossing the Cascade Mountains

Required:

• Weather-resistant structures

• Snow + wind + ice loading checks

• Customized foundation design

b) Aging Infrastructure Upgrade

The line required:

• Conductor uprating

• Tower retrofits

• Converter station modernization

Key Innovations

• One of the earliest thyristor-controlled HVDC systems

• Use of wide-area monitoring systems (WAMS)

• Advanced converter station rebuild in the 2010s