Evaluating the detail level of reliability analyses used in the investment planning at Fortum Distribution AB

Sammanfattning: This master thesis project is a cooperation between Fortum Distribution AB and The Royal Institute of Technology (KTH). When maintaining and operating a power distribution system, which is the task of Fortum Distribution AB, the aim is to always be able to deliver electric energy to the customers. A 100% reliability is however not a realistic goal since too high reliability would cost too much. The net planners at Fortum have to choose the most cost effective investments. Due to the complexity of the power system, grid analyses are expensive and simplifications have to be made. In this master thesis it is examined if Fortum Distribution AB’s methods for prioritizing between different reliability investments for the rural power distribution system are detailed enough to give the same result as more complex methods. This is done by creating theoretical models of two 11 kV lines out of two different substations in a rural part of Fortum’s grid. The fault management process at Fortum Distribution AB is thoroughly described and implemented in the theoretical models of the two case lines. The time it takes to perform specific tasks in the fault management are listed for future reference. A couple of investments for better reliability are applied to the case lines. The effect on reliability and cost efficiency of different investments allow for the investments to be prioritized after which are better to implement. One of the case lines is in an area where reliability investments have already been performed. This line is chosen because the results from the analysis then can be compared to the real investments. To test and apply the result the other case study is performed on an area that has not yet been renovated. For this case line cost-efficient investments are recommended. The conclusion of the analyses is that the detail level of the analyses made by Fortum Distribution AB most likely are sufficient for today’s grid. However, because of the ongoing project to weather-secure the grid, changing overhead lines for underground cables is the number one priority. The analysis in this thesis could have reflected the effect of extreme weather better, but even so, the result shows such a significantly lower cost-efficiency for investing in cables that it might be favorable for Fortum Distribution AB to review the benefits of changing overhead lines for underground cables. In some cases other investments might be more beneficial.