Stronger wind or higher rainfall – that is enough to keep hundreds or even thousands of Lithuanians without electricity. This is an increasingly recurring situation, especially well-known for people in rural and wooded areas. The reason is simple: it is most likely that falling trees or branches will damage overhead electricity lines in such areas.
Underground networks will serve 50 years
How to avoid such accidents? The only alternative is underground electrical cables. Some time ago, this was still considered a luxury, but the situation is changing rapidly as Lithuania decided to change the most troubled power lines. Therefore, do not be surprised if in Lithuania you see that the energy companies are digging around existing overhead lines. This means, that this electricity line will soon become an underground one, and the reinforced concrete supports will be dismantled and removed.
The underground cable network is not only more resistant to environmental impact, but also is generally less vulnerable to exploitation and more sustainable. In addition, maintenance and repair costs for underground cable networks are lower; the networks themselves are much safer and have a lifespan of at least 50 years. Meanwhile, the guarantee period for overhead power lines is 25 years.
Lithuanian electricity distribution operator AB “Energijos Skirstymo Operatorius” plans to have half of all electricity networks underground by 2026. Priority will be given to wooded areas; there will be no overhead lines left at all. Just last year, they replaced about 2,600 kilometres of overhead power lines to underground cables.
The contractor companies invest in expensive equipment
For some companies these changes mean new investment. In the case of construction works of overhead power lines power drills and mobile cranes are used, while underground cable lines require efficient ground excavation machinery (track, wheeled excavators), computerized mechanism for cable laying which regulates the pulling force of the cable, and trenchless construction technologies — controlled directional drilling equipment.
By using advanced trenchless technology, electric cables are laid under various roads, railroads, buildings, trees, rivers. The price of one new, trenchless machine for construction reaches EUR 300 000. Thus, companies that have invested considerable funds in the acquisition of such new equipment would like to use it all year round. However, there are no conditions for this in Lithuania. The construction of overhead power lines can take place in winter, and frozen ground even facilitates the work as the machinery can easily access any place. Meanwhile, the laying of cables is not possible in winter. In addition, the work also stops or considerably slows down at high rainfall as the heavy machinery can no longer enter the fields and cables cannot be laid in trenches full of water.
Only skilled specialists can work
According to Teodoras Bitinas, head of a construction company of energy objects, in electric cable laying work highly skilled professionals are required, who should have great thoroughness, accountability and show high quality works. People who install cable couplers must have received special training and have certificates for the installation of each type and each manufacturer’s couplings.
High voltage cables are tested on the ground by a raised very low frequency voltage. “After the installation of 10 kV cables a raised 19 kV voltage is transmitted from a special high voltage cable testing device and so it is checked if cable insulation is in good shape and if cable couplings are assembled in a qualitative manner. Such testing requires specialized and expensive equipment, as well as qualified and accordingly certified specialists”, Teodoras Bitinas emphasised.
The laying of an underground cable takes a particularly long time in cities and towns, where digging is made more difficult by underground communications, street pavement, coordination of work with municipalities and residents. Meanwhile, when laying cables in the fields, it is necessary to settle with farmers who, because of the crop, do not allow excavation work.
Thus, step by step Lithuania moves forward to more sustainable and safe way of power supply. Historically, from wooden poles to reinforced concrete pillars and now, finally, with the emergence of new technologies, the introduction of dry-type cables and having decreased prices of the cable, electric overhead lines are being changed to underground cable lines.
Source: Lietuvos elektros energetikos asociacija, 2018, link: http://www.leea.lt/naujienos/oro-linijos-keiciamos-pozeminiais-kabeliais/