The challenges of undergrounding of 4th  Annual Symposium of the Hellenic Association for Energy Economics (HAEE)   The challenges of undergrounding of high and ultra-high voltage cables in SE Europe Georgia ILIOPOULOU Surveying Engineer, Beng, MEng National Technical University of Athens, Greece Prodromos PSARROPOULOS Structural & Geotechnical Engineer, BEng, MEng, MSc, PhD Athens – 8 May 2019  

Electricity projects in SE Europe Large-scale electricity production projects have been constructed and planned in SE Europe ( onshore and offshore ) New power-plant in north Greece Submarine cables to connect Israel, Cyprus and Greece

Transmission of electricity The transmission of electricity from onshore production sites to various consumers takes mainly place via high and ultra high voltage above ground ( overhead ) cable grids, which consist Critical Infrastructures Above ground ( overhead ) cable grids

Transmission of electricity The above ground ( overhead ) grids are generally unacceptable for the general public because of their social and environmental impact. More specifically: visual pollution electromagnetic radiation structural vulnerability

Social and environmental impact Examples of visual pollution Visual pollution may be detrimental for the culture and tourism

Social and environmental impact Electromagnetic Radiation Electromagnetic Radiation may have an impact on the public health and safety

Social and environmental impact Structural Vulnerability Structural vulnerability due to earthquakes, storms etc

Undergrounding cable grids The most modern way to eliminate optical pollution and/or reduce electromagnetic radiation is via the undergrounding of high and ultra-high voltage grids. A buried cable grid

Undergrounding cable grids Installation Techniques The new manufacturing and installation techniques Include (ICF, 2003): Reducing the dimensions and weights of HV and UHV (UltraHighVoltage) cables by using materials such as cross-linked polyethylene (XLPE). Mechanical placement methods that avoid extensive excavation and material transfer. Methods of installing cables without "defects" that respect the preservation of the characteristics of the environment into which they are imported. There are many different methods of installing cables. Each method used depends on a number of factors Including land use and different environmental characteristics.

Example of underground cables in Europe It is noted that in some EU countries ( e.g. Germany ) the usage of buried cables has already been started. SuedLink project is a 700 km HVDC underground cable that will transport energy generated in wind parks in northern Germany to southern Germany.

Implications of undergrounding cable grids However, the “solution” of undergrounding cable grids involves some technical or techno-economical implications. More specifically: a) overheating of cables b) exposure to human interference ( unintentional or intentional ) potential geohazards relatively high cost

Geohazards & undergrounding cable grids Depending on the local geological, topographical ( and seismological ) conditions, various geohazards may be present geohazards under static conditions ( karstification, landslides, rockfalls, ground settlements, erosion, river crossings, etc.) b) earthquake-related geohazards ( active seismic faults, earthquake-triggered landslides, and soil liquefaction phenomena )

Examples of geohazards special soils ( turf ) in Greece erosion in Israel sinkhole in Guatemala mud volcanoes in Azerbaijan

Examples of geohazards landslide in California landslide in Taiwan landslide in California

A hypothetical case study Route optimization of an underground cable in north Peloponnese, Greece taking into account the potential geohazards

A hypothetical case study Route optimization of an underground cable in north Peloponnese, Greece taking into account the potential geohazards Map of seismicity of the Corinthian Gulf in the period 1900-1999 Map of landslides of the Corinthian Gulf

A hypothetical case study Route optimization of an underground cable in north Peloponnese, Greece taking into account the potential geohazards Map of susceptibility to liquefaction of the geological formations of the Corinthian Gulf General view of a seismic fault

A hypothetical case study Route optimization (and cost analysis) was based on a GIS-based tool that has been developed for this purpose

General conclusions Above ground ( overhead ) electrical cables may have a social and environmental impact. Undergrounding of electrical cables has been used in various countries as an alternative to overhead cables. It is evident that the construction cost of undergrounding is higher than the corresponding cost of aerial cables ( depending on the local conditions and the geohazards ). Nevertheless, the total cost of undergrounding is not that high since the direct and indirect environmental benefits and economic impacts may be very important.

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