compactLine

Together with industrial and scientific partners, 50Hertz is developing a new technological design for alternating current overhead lines called compactLine©. CompactLine is a research and development project for the development of an innovative overhead line on the basis of technological studies and tests.

Project goal

The objective of the compactLine project is the development of a compact 380-kV overhead line suspended on innovative tower types. Contrary to conventional lines for this voltage level, the area and height occupied by the new line should be no greater than those of a 220-kV power line. This will allow us to upgrade many existing overhead line corridors to a higher transmission capacity. The compactLine overhead line concept shall reduce the effects on man and the environment resulting from the construction and expansion of high-voltage transmission grids.

After successful conclusion of all trials and tests, the compactLine can be offered as an alternative to traditional towers and lines. Depending on the requirements of a line construction project, different solutions will then be available. For this reason, the research team is particularly focussed on how the compactLine can help raise acceptance for the necessary expansion of the German power grid.

The compactLine will meet all safety-related criteria and shall also lead to lower grid expansion costs.

The compact high-voltage transmission towers and lines available on the market today meet various criteria with regard to the reduction of height or width compared to conventional towers. However, none of them reduces both the height AND width in comparison to traditional systems, as up to this day, this is technically not feasible. The development of the compactLine therefore concentrates not just on the size of the tower, but also on the entire system of the power transmission line.

The compactLine research and development project is led by 50Hertz. The following partners form the project team: 

• The Forschungsgemeinschaft für Elektrische Anlagen und Stromwirtschaft e.V. (FGH, research association for electrical installations and the electricity industry) from Mannheim, in charge of the electrical calculation and electrical trials


• RIBE Group from Schwabach, in charge of the development of new line fittings


• The institute for steel construction of the RWTH Aachen University, in charge of tower design, crossarm design, technical calculations


• SAG GmbH from Langen, in charge of technical coordination, development of new power lines, suspension ropes, earth wire, bundle spacers and bundle configuration


• The German Federal Institute for Materials Research and Testing is responsible for the scientific monitoring of the project. 


• CompactLine is supported by the manufacturer Lapp Insulators.


• The project is also fostered and co-funded by the Federal Ministry for Economic Affairs and Energy.

The compactLine research and development project has been ongoing since late 2013. In 2014, the first theoretical discussions, field calculations and simulations took place. Prototypes were built for new line fittings. Since January 2015, the line components have been undergoing various mechanical and electrical tests. At the same time, the planning of the final tower structure is underway. As of early 2015, the company City Analytics has started its work on the accompanying acceptance research. By the end of the year, all constructions and experimental research shall be concluded. After the conclusion of all tests, a pilot stretch of 2 kilometres will proof the line’s practicability. According to the current research progress, this pilot could go operational in 2017 if all upcoming tests are successful.

For more information on the pilot line please visit:

http://www.50hertz.com/en/Grid-Extension/Onshore-projects/-Grid-connection-of-the-Jessen-Nord-substation

Research and development subjects

Conventional high-voltage transmission lines sag considerably between towers. As the lowest point of sag needs to have a certain minimum distance to the ground depending on the terrain, conventional towers are very high. Furthermore, low-sag conductors can swing heavily to the side in case of strong winds, defining the width of the buffer strips along the line. The further the conductors swing, the wider the corridor. In order to reduce both sag and swing, every component of the electricity transmission system has to be researched and modified: for compactLine, the transmission tower, the conductor arrangement, conductors and earth wires are all being reimagined.

The tower will be a cylindrical or conical solid wall construction similar to those used for wind turbines. With a planned diameter of two metres at its most narrow point, it will take up considerably less space than conventional towers. These range from 49 to 144 square metres in size and occupy the same space as whole apartments and even single-family houses. At a planned height of 32 to 36 metres, the new pylons are only a few metres higher than the average tree height in Germany.
Distances between the compactLine towers will reach up to 400 metres.

A conventional tower usually has multiple crossarms as the different conductor bundles need to be kept at a certain distance. This prevents sound emissions such as humming as well as electrical and magnetic fields from exceeding legally predetermined limits. These distances made it so far impossible to build low, slender tower types using current technology. For the compactLine the configuration of the conductors is therefore altered at the towers. Three different new suspension types are being studied and will be tested for their mechanical and electrical functionality. All three meet the requirements of a compact design and low emissions.

As opposed to conventional lines, the conductors of the compactLine are supported by one or two so-called suspension ropes. Every 20 metres the conductors are attached to these lines in a festoon-like manner. This construction considerably reduces sag as well as any sideways swing as a result. The compactLine is planned to guarantee a minimum distance to the ground of 12.50 metres at the lowest point, which is still higher than the maximum legal requirement.