CompactLine

Context

Bastian Bohm

Asset & Operation

Together with industrial and scientific partners, 50Hertz is developing a new compact technological design for alternating current overhead lines called compactLine©. CompactLine is a research and development project for the development of an innovative 380-kV-overhead line on the basis of technological studies and tests implemented from 2013 to 2017. The overhead line is marked by solid wall towers and an innovative conductor suspension. Both features contribute to a lower height and smaller corridors compared to conventional overhead lines of 380 kV.

50Hertz conducted a research on compact overhead lines and developed a brand new design called compactLine. In 2015 mechanical and electrical tests had been carried out. They resulted in a global novelty. After a test period in 2018 and 2019 compactLine could enrich the possibilities for electricity transmission.

The compactLine pilot stretch near Jessen in Saxony-Anhalt. Photo: Vis-à-vis

Approach

The space saving overhead line compactLine is aiming to enlarge the spectrum of technical solutions to use existing 220-kV corridors for the more powerful 380-kV overhead lines. In general the compactLine needs a smaller corridor than a conventional overhead line. With a total height of 30-36 meters the towers of compactLine are approximately 20 meters lower than Donau-type towers. Thus, compactLine is less visible in wide landscapes. Impacts on the local residents’ perception of the line had also played a role during the technical design. Compactness and design reduce the depth of impact. They might have a positive influence on public acceptance of overhead line constructions.

compactLine offers an alternative for future grid expansion projects when:

the space for corridors is very limited in width
the design of the towers supports significantly the impairment of landscapes
existing corridors of 220-kV overhead lines shall be used for increasing the lines’ capacity to 380 kV

Prerequisites: the compact high-voltage transmission towers and lines available on the market today cannot reduce 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 concentrated not just on the size of the tower, but also on the entire system of the power transmission line.

Comparison between a conventional tower "Donau" (r.) and the new overhead line concept called compactLine.

Description

Project progress

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. From September 2017 to August 2018 a compactLine pilot stretch of two kilometers was built at Jessen/Nord substation in Saxony-Anhalt. The pilot was commissioned in the third quarter of 2018. Now, monitoring takes place for about a year to prove the practical suitability of the line.

For more information on the pilot line please visit: 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. They have a strong impact on the perception of the landscape. 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 had to be researched and modified: for compactLine, the transmission tower, the conductor arrangement, conductors and earth wires are all being reimagined.

The tower

The tower is a conical solid wall construction with an innovative suspension of the conductors. The basic compactLine has a tower height of 30-36 meters and a corridor width of 55-60 meters. The basic height of a Donau-type tower is 50-60 meters and the corridor of a Donau-tower-overhead-line is approximately 72 meters wide. Distances between compactLine towers will reach up to 400 meters, just as for conventional overhead lines. The final distance depends on the terrain und the corridor route

Conductor arrangement

A conventional tower usually has multiple crossarms as the different conductor bundles need to be kept at a certain distance. This construction is made for the absorption of mechanical forces and the optimization of electrical effects (e.g. electrical and magnetic fields). Regular tower distances of 400 meters lead to a tower height of 55-60 meters. These distances made it so far impossible to build low, slender tower types using current technology.

For compactLine the suspension of the conductors at the tower has been reimagined. So called suspension ropes are being installed between two towers. They serve to attach the conductors every 20 meters. The sag and the swing of the conductors are thus reduced. The tower can be lower and the corridor can be smaller.

Results

Three different new suspension types were studied and tested during the research. The pilot stretch was built with the so called “Havel”-type, which is characterized by a single level arrangement of the conductors. The other two types had a two-level arrangement of the conductors – bringing along effects on height and width of tower and crossarm. One of the results of the acceptance study was the preference of the Havel-type by the majority of the respondents.