- This is the first step in the process to ensure a reliable supply of electricity to the capital and surrounding areas in the future, says senior vice president Håkon Borgen in Statnett. 

The power cables between Smestad and Sogn in Oslo are old and need renewing to meet future requirements for security of supply, urban development and environmental solutions. The current cables, which date from 1955 and 1977, are nearing the end of their technical lifespan, and capacity is about to run out. Since 1990, electricity consumption has increased by 30 percent, and it is expected to continue to increase in line with the population growth and new consumption.

- In order to secure the supply of electricity to Greater Oslo in the years to come, we urgently need to replace these interconnectors and upgrade the Smestad substation. This must take place regardless of how much electricity consumption increases, says Borgen.

Smestad substation was built in 1952. The substation has reached the end of its lifespan and needs upgrading. Capacity at the substation must be increased to provide a better supply of electricity to residents in Oslo in the future.

Proposes cables in a separate tunnel

Statnett has thoroughly assessed two possible solutions to replace the cable interconnectors between Smestad and Sogn: cable in tunnel and cable in trench. For both solutions we have mapped buildings, infrastructure, roads and the environment, assessed repair time if a fault occurs on a cable, risk for the surrounding areas and made economic calculations. Throughout the process, we have had meetings with local authorities and public agencies to receive their input.

- Based on a comprehensive assessment, a tunnel was considered to be the best solution for security of supply and the surroundings. We have therefore applied for a licence from the authorities to build a new tunnel for the new cables between Smestad and Sogn.  A tunnel is a secure, robust and forward-looking solution for the Oslo main grid, says project manager Hans Herlofsen.

A tunnel has many advantages compared with a trench. Cables in a separate tunnel are less exposed to damage, easier to inspect and easier to maintain and repair. They provide greater flexibility, have less impact on the environment, are generally more profitable and have a shorter installation period.

Statnett has also assessed alternatives for Smestad substation.

- Overall, we consider a compact station facility (SF6) to be the best solution here. We have therefore applied to the authorities for a licence to construct such a facility inside a mountain hall as an extension of the underground facility, says Herlofsen

Consultation comments to the NVE

Statnett has applied to the authorities for a licence to construct a new tunnel for new cables between Smestad and Sogn, and to upgrade Smestad substation.  During the consultation, there will be opportunities to provide input to the NVE. The NVE will conduct public meetings in connection with the licence application, and Statnett will attend these meetings.

The overall Greater Oslo Grid Plan for the future main grid consists of 30 different measures. When all measures have been completed, the grid will have capacity to transport about 60 percent more electricity. At the same time, we can demolish around 300 kilometres of power lines.

- This will facilitate sound climate solutions. Furthermore, it will free up areas and give a more energy-efficient power grid where less electricity is lost on its way to the consumers, says Herlofsen.

Facts about the Greater Oslo Grid Plan

In 2010, Statnett prepared the Greater Oslo Grid Plan because we wanted an open process and early dialogue with the surrounding community during the work on an overall plan for how the main grid can be developed in the future.

The Greater Oslo Grid Plan has analysed the power requirement for Oslo and Akershus and assessed various alternatives for how the capital region can be supplied with a reliable power supply in the years to come. In February 2015, the Greater Oslo Grid Plan project launched the overall plan which consists of 30 different measures that will be realised during the period leading up to 2030.

Facts about Smestad substation

- New 420-kV compact station installation (SF6) in underground facility at Smestad

- The station is the largest substation in Norway for general consumption

Facts about the Smestad – Sogn cable interconnector

- Cables in tunnel will replace earth cables in a trench

- Approximately 4.5 km tunnel for cables

- Will increase the transmission capacity between Smestad and Sogn substations

The application and environmental report are available at NVE here