High Voltage AC Overhead Lines (OHL) are most commonly used for the transmission of energy. Thereby the current flows through conductors that are fixed through isolators to crossarms of the towers. The conductors are spanned between two towers. In order to increase the amount of energy transmitted the conductors are frequently bundled. The conventional conductors are characterised by linear dependence between current, conductor temperature and sag of the conductor. Conductors are aluminium-based and by maximal operating temperatures <100°C.
The major technology variations relate to the material used and build-up of conductor:
- All Aluminium Alloy Conductors (AAAC)
- Aluminium Alloy Conductor Steel Reinforced (AACSR)
- Aluminium Conductor Steel Reinforced (ACSR)
- All Aluminium Conductor (AAC)
- Aluminium Conductor Alloy Reinforced (ACAR)
The conductors are characterised by:
- maximal current currying capacity
- maximal operating temperature
- sag behaviour
- surface treatment
Components & enablers
Advantages & field of application
Aluminium-based conductors on HVAC overhead lines are a proven technology that is a century old. The first three-phase AC overhead line using conventional conductors was built in 1891 connecting the cities of Lauffen and Frankfurt in Germany. Today, the largest part of the transmission lines (exceeding 220 kV) on land are HVAC overhead lines and even with many new developments to be realized using HVDC technology and /or underground cables, its relative share will remain fairly stable the following decade in Europe.
The main advantage of the technology is its clear standardisation process and extended supply chain, which are optimized in terms of material, transportation, erection, maintenance, costs, lifetime, and appearance and minimizes risk of bottlenecks.
Technology Readiness Level
TRL 9 - System ready for full scale deployment
Research & Development
Current fields of research:
Best practice performance
Maximum capacity per circuit: 2600 MW
Current rating: 4.0 kA per phase of quad bundled conductor (AL/ST 550/70)
Maximal operating voltage: 420 kV
Best practice application
A specific AAAC conductor is used, which is considered to be the best technical optimization technique using Aluminium Alloy.
Two three-phase circuits on the same tower and four conductor bundle for each phase.
The energy losses are the lowest recorded for AAAC lines.
Netherlands – Germany
Commissioning of the 380 kV transmission line Dӧtinchem-Wesel which supports the expansion of the north-west European electricity market.
22 km of 380 kV OHL with 54 innovative tube wind-track pylons and an interconnector capacity of 2600 MW.
 e-Highway 2050. Modular Development Plan of the Pan-European Transmission System 2050. [Link]
 ABB. Feasibility study for converting 380 kV AC lines to hybrid AC/DC lines. [Link]
 TYNDP Project list. [Link]
 FNN (2014): FNN-Hinweis: Störungs- und Verfügbarkeitsstatistik Berichtsjahr 2013. [Link]
 TenneT. Doetinchem-Wesel 380 kV. [Link]
 Nexans. Bare Compact Overhead Aero-Z Conductors. [Link]