This master thesis is done within the Energy Systems Engineering program at Uppsala University and performed for Forsmarks Kraftgrupp, Vattenfall. The distribution grid for the outer area of the nuclear power plant at Forsmark is an old grid from the time during construction of the plant which later became permanent. Many changes have been made to the grid thus far and Forsmark’s need for an updated model to easily simulate upcoming changes to the system has increased. In this thesis, the distribution grid for the outer area of Forsmark is modeled and evaluated from the aspect of load and selectivity. The simulation software PowerFactory has been used to model and perform the necessary network calculations. The results from these calculations will serve as source material for a future system health report for the distribution grid. The results show that some components in the system are overloaded in some modes of operation. A few buses have a fault clearing time that is too long and the system is not selective. The problem with fault clearing time can be solved with new settings on a protection relay and swapping changing out a few fuses. The selectivity in the system would also be greatly improved by the new relay settings.

Vid ombyggnationer och utbyggnationer av elnät förändras dess karakteristik.Detta leder till att skyddsfunktioner kan behöva justeras för att passa elnätets nyakarakteristik. Justeringar kan medföra att selektiviteten mellan skydden försvinner.Selektivitet innebär att endast skyddet närmast felet bryter strömmen, så atten så liten del som möjligt av elnätet blir strömlöst. För att säkerställa att selektivitetråder mellan skydden utformas selektivplaner där selektiviteten visuellt kananalyseras och vid behov utförs justering av skydden. Rotebro mottagningsstation iSollentuna ägs och drivs av Sollentuna Energi & Miljö (SEOM). Stationen står införombyggnationer och selektivplanerna behöver därför ses över.Då problemställningen är att selektiviteten mellan skydden behöver kontrollerasblir målsättningen att skapa en selektivplan för Rotebro mottagningsstation. Dennabaseras på mottagningsstationens skyddsinställningar och det anslutna elnätetskarakteristik. Arbetet resulterade i att en modell av Rotebro mottagningsstationskapades i programmet PSS Sincal. Från denna genererades selektivplaner somvisar att små justeringar av skydden kan göras. Det utfördes även en generell analyssom visar att selektivplaner har stor betydelse för samhället. / In case of build out and rebuilding electricity grids, the electrical characteristicschange. This means that protection features may need to be adjusted to suit theelectrical grids’ new characteristics. Adjustments may lead to loss of selectivity betweenprotective relays. Selectivity means that only the protection device closest tothe fault break the current, so only the smallest possible part of the electrical gridgets disconnected. To assure selectivity, selective tripping schedule is created andprotective relays are adjusted if needed. Rotebro substation in Sollentuna is ownedand operated by Sollentuna Energi & Miljö (SEOM). The substation is facing rebuildingand its selective tripping schedule needs to be reviewed.Since the problem is that selectivity between the protective relays needs to bechecked the goal is to create a selective tripping schedule for Rotebro substation.This is based on the substation protective settings and the connected electricalgrids characteristics. The thesis resulted in a model of Rotebro substation createdin the computer program PSS Sincal. From this a selective tripping schedule weregenerated that shows that small adjustments of the protective relays can be made.A general analysis was also conducted which shows that a selective tripping scheduleis of great importance to the society.