Top 5 Longest Overhead AC Transmission Lines in the World

 

Top 5 Longest Overhead AC Transmission Lines in the World

High-voltage engineering, record-setting distances, and the innovations that made them possible

This list EXCLUDES HVDC and includes only pure overhead AC transmission systems, 220 kV to 765 kV and above.

If you want the Blogger-ready HTML version, just tell me.

🌍 TOP 5 LONGEST OVERHEAD AC TRANSMISSION LINES IN THE WORLD

⚡ 1. Belo Monte – Estreito – Miracema 500 kV AC Transmission System (Brazil)

Length: 2,400 km (approx.)
Voltage: 500 kV AC
Type: Overhead
Utility: Eletrobras / ISA CTEEP

Although Belo Monte is famous for its UHVDC link, it also has the longest AC overhead backbone in Brazil feeding load centers and stabilizing the AC grid.

Key Engineering Challenges

1. Very Long AC Corridor Stability

Over 2,400 km of uninterrupted AC overhead line required:

  • series compensation

  • shunt reactors

  • controlled switching

  • advanced protection (distance + differential)

2. Tropical Lightning Belt

Lightning density up to Ng = 15/km²/year →

  • double OPGW protection

  • ultra-low tower footing resistance (≤10 Ω)

3. Tower Design for Hilly + Forest Terrain

Required:

  • multi-circuit 500 kV towers

  • heavy-duty crossarms

  • Corten steel for corrosion resistance

⚡ 2. Grand Ethiopian Renaissance Dam (GERD) 500 kV AC Transmission Network (Ethiopia → Sudan)

Length: ~1,000 km total
Voltage: 500 kV AC
Type: Overhead
Operator: Ethiopian Electric Power

This is East Africa’s largest 500 kV AC project, built to export hydropower and interconnect grids.

Technical Challenges

1. Desert + Mountain Terrain

The line spans:

  • deep river gorges

  • cliffs

  • hot desert plains (>45°C)

This required:

  • high-temperature low-sag (HTLS) conductors

  • reinforced foundations

  • increased insulator creepage distance

2. Grid Synchronization

Long AC export corridors need:

  • power system stabilizers

  • dynamic reactive support

  • FACTS devices (SVC, STATCOM)

⚡ 3. Rio Madeira 600 kV / 500 kV AC Transmission System (Brazil)

Length: >1,900 km
Voltage: 500 kV AC
Type: Overhead
Operator: Madeira Energia / Eletrosul

Although the Madeira project uses HVDC for bulk transfer, the parallel 500 kV AC system is one of the world’s longest AC overhead corridors.

Major Challenges

1. Crossing the Amazon Basin

  • swamp zones

  • floodplains

  • heavy vegetation → requires helicopter tower erection

2. High Lightning Performance Requirements

  • double shield wires

  • target grounding ≤ 5–8 Ω

  • long-span towers with improved geometry

3. Voltage Stability on Long AC Lines

AC lines above 1,500 km face serious stability risks:

  • Ferranti effect

  • reactive power fluctuations

  • voltage rise at no-load

Solutions:

  • shunt reactors every 200–300 km

  • series compensation

  • intelligent line switching

⚡ 4. Queensland–New South Wales Interconnector (QNI), 330 kV AC (Australia)

Length: ~915 km combined 330 kV overhead lines
Voltage: 330 kV AC
Type: Overhead
Operators: Powerlink Queensland, TransGrid

This is Australia’s longest continuous 330 kV AC interconnection, serving as the backbone of the National Electricity Market (NEM).

Technical Challenges

1. Extreme Bushfire and Heat Conditions

Summer temperatures reach 45–47°C →

  • high-temp conductor ratings

  • anti-galloping systems

  • fire-resistant structures

2. Very Long AC Stability Requirements

Over 900 km requires:

  • reactive power compensation

  • wide-area protection relays

  • controlled power oscillation damping

⚡ 5. Nelson River 500 kV AC Transmission System (Canada)

Length: ~900 km (AC portion)
Voltage: 500 kV AC
Type: Overhead
Operator: Manitoba Hydro

Mostly known for its HVDC bipoles, the Nelson River also includes a long AC 500 kV overhead corridor used for regional transfer and grid stability.

Engineering Challenges

1. Arctic Winters & Icing Loads

Temperatures drop to –40°C, with:

  • heavy icing

  • ice shedding

  • galloping

Required:

  • aerodynamic spacers

  • ice-resistant bundles

  • weathering steel towers

2. Long-Distance AC Control

Cold-weather high-resistivity soil →

  • high tower footing resistance

  • compensated by double shield wires + LSAs

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