Transmission line upgrade to 420 kV, Norway

Norway's electrical transmission company, Statnett, took on a large voltage increase project on its transmission system. The company's research has shown that the capacity of existing 300 kV lines can be increased by almost 30% by upgrading them to 420 kV and delaying the construction of new lines. Thereby it is possible to respond, in a relatively short time, to a significant increase of energy demand in Norway. By using accurate engineering methods, it is possible to uprate the existing 300 kV lines to 420 kV with relatively small visual changes. To be able to use accurate engineering methods, several R&D projects were performed. This project means that it is possible to save NOK 7bn in the upgrade of Statnett’s transmission system to 2030.


Mannvit, together with the engineering firm Ramböll, signed a framework agreement with Statnett. Mannvit is part of a team of three Statnett consultants that are working on the voltage upgrade on approximately 1500 km of 300 kV transmission lines. The existing towers and conductors will be used. The design of the uprated line is divided into three parts: First the existing line is analysed and an accurate model of it created in PLS-CADD. The second phase comprises a first proposal for uprating using deterministic methods and the identification of ‘problem’ towers. Finally, the third phase involves a more detailed design, including fine-tuning and accurate engineering using probabilistic methods and final implementation.

Before implementation, the consultants, in co-operation with Statnett, are responsible for the purchase of materials and follow-up of material orders together with the preparation of specifications prior to construction. The consultants will also be responsible for providing consultancy services during the construction period, on-site follow-ups and the preparation of a final report on the project.


First phase includes modelling original lines. First uprating proposal is where standard insulator configuration is used and problem towers were identified, followed by final uprating proposal, technical specifications, drawings and procurement. Mannvit then provides consulting during construction phase; follow up work on site, ending with a final report.

420 kv 
7bn NOK 
1500 km 
HV lines

“It is a unique opportunity to be a part of the one of the most extensive voltage uprating projects in the world. We are following a unique path in the upgrade of current high voltage transmission lines and significantly increasing transmission capacity at relatively low cost. “

Daníel Scheving Hallgrímsson

Project Manager