Overhead power lines are easily affected by storms and other weather extremes leading to interruptions in the power supply and putting residents to risk. Due to this and their unsightly appearance, many areas have switched from overhead cables to underground cable connections. Estonian capital Tallinn decided to improve power supply safety and rid visual pollution by taking overhead power lines on a stretch of 10-km underground. The construction company Connecto Eesti and wholesaler SLO chose Pipelife Estonia to supply the cable protection pipes that are for a good part installed trenchless.
Overhead power lines are not just highly vulnerable to weather extremes but are unsightly and take up space that could be used otherwise. By opting for underground infrastructure, Tallinn chooses to free the land for developers and new infrastructure.
Electricity and gas transmissions system operator Elering oversees the extensive project for which the more densely populated areas of Tallinn will be gradually freed from high-voltage lines that have reached the end of their service life. Also, the replacement of overhead cables opens up new living spaces under the otherwise protected zones.
The project, taking place from Veskimetsa to Kadaka and Harku, is divided into three stages. 37.5 km of 110 kV power lines between Veskimetsa to Harku have been installed in the first stage, implemented from October 2019 to October 2020. During the second stage, from February to September 2020, 43.5 km of 110 kV cable protection pipes were laid between Veskimetsa to Kadaka. Currently, the third stage that started in spring 2019 and is still in progress, is planned to install 10.2-km-long power lines from Kadaka to Harku.
During all three stages, the installation of underground cable protection pipes was done for a great part trenchless by horizontal directional drilling. Next to cost benefits, the greatest advantage of trenchless installation methods is that they minimize nuisance and disruptions to traffic, inhabitants, and the environment. However, trenching could not be avoided in some sections where old, unmarked pipes were discovered during the drilling procedure and had to be carefully bypassed. Regardless of the unexpected drawback, the pipes could be installed according to plan.
The OD 160 pipes were supplied in 12 m and 13.5 m lengths and OD 75 pipes were delivered in 200-meter-coils. Pipes in longer lengths require less welding, saving on time and resources. The ends of the PE cable protection pipes were securely welded by electrofusion in the receiving pits. Coupling of conduits was done by using the buttfusion method and some parts were done with the electrofusion method.
The cable line was installed in the ground at a depth of 1.5-6 meters along the entire route. Since the protective pipes used for the cables are produced with a nominal stiffness (SN) of 12.5, they can be installed securely with relatively little coverage beneath highly frequented roads. Due to their flexible and durable qualities, the PE pipes are suitable for challenging terrain and can withstand ground pressure and mechanical stress from demaning installation methods such as directional drilling.
Once all the pavements, roads, and greenery in the construction area are restored, thousands of square meters of land are ready to be used for building projects.
From the planning phase in November 2018, Kairit Lootus, Key Account and Product Manager Pipelife Estonia, has been accompanying the project. Also, SLO representatives and Kaspar Järve, Key Account Manager from Pipelife Estonia, were on-site for support and to makes sure the project runs smoothly.
Due to a previous successful trenchless project with the electricity, gas, and telecommunication design and construction company Connecto in 2019 where Pipelife provided a OD 140 HDPE drilling pipe and a long and great partnership with wholesaler SLO, Pipelife's piping solutions were once again selected for the project. Apart from high product quality to local specifications, it was of great importance to the client to opt for a local producer benefiting from better cooperation and optimal product availability.
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