This thesis considers how an assessment method for reinvestments in the distribution grid can be designed and implemented. The assessment method was created to give long-term estimations of the amount overhead lines that could be substituted with underground cables and how to prioritize between different areas. The regulation of power grid companies was reviewed to highlight important factors for profitable reinvestments. The assessment method was implemented for overhead lines in Ellevio´s distribution grid using the database program FME and validated against real reinvestment decisions in a case study area called Sinntorp. The resulting reinvestment proposals mainly consist of replacing older grid sections and sections where expensive maintenance is planned in the future. The script show similar results as real reinvestment decisions but small differences are noticed related to the script’s hard focus on older grid sections. The script has potential to be used on Ellevio´s entire overhead line network but this requires work to complete essential data. Further validation on new areas are also desired to see if results are reasonable and if the script can be developed to consider more reinvestment factors.

Svenska kraftnät is responsible for the operation and development of the Swedish transmission grid. A large number of substations in the transmission grid are approaching their expected service lifetime and must be renewed in the coming years. When renewing substations, total and partial outages in operation are often unavoidable. These outages may cause downtime for any party connected to the substation, whether it be an electricity generation or consumption. A solution is to build a new substation while the old is still in operation. Upon completion, a transfer of operation can be done from the old to the new substation. This however requires laying claim to new land, which affects the local environment and can be a time-consuming process. In an effort to minimise the need for planned outages during substation renewals, Svenska kraftnät wants to investigate techniques for bypassing substations while also allowing the connected party to remain in operation. This thesis has evaluated two differing techniques that allow for substations and any connecting parties to remain mostly in full operation during station renewals. One technique involves constructing a temporary switchgear compartment using air-insulated apparatuses to bypass the station and connect the third party. The other technique uses a mobile gas-insulated switchgear to achieve essentially the same arrangement.  After studying cases where either technique has been employed in station renewals, it was concluded that a solution utilising air-insulated apparatuses is better in several aspects. While the two technologies achieved similar results, the air-insulated technology did so at a lower cost, offered more flexibility, and was easier to integrate into pre-existing stations. Furthermore, the gas-insulated technology required more specialised competence, possibly limiting the availability of qualified contractors. It was concluded that bypassing stations during renewal projects could provide several benefits in terms of less downtime and economical losses, while also minimising the need to claim new land. In order to optimise the method a supply of air-insulated apparatuses and construction materials necessary for the bypassing of a station should be established by Svenska kraftnät. This, mostly reusable, equipment would then be on stand-by, ready to use in future station renewals.