Dynamic transformer rating is a novel technology that has been showing high industry potential. This study uses dynamic rating on medium power transformer in the regional grid. The 63 MVA transformer is used for connecting the wind farm to the grid in Körsbärsdalen. The power system analysis evaluates how dynamic transformer rating (DTR) and increased share of wind power affect the grid performance with respect to reliability, voltage stability and active power losses. The actual rating has exceeded nominal capacity throughout the year, with larger margins during the winter. Rate of transformer lifetime is used as an input for economical analysis, with a trade-off between reliability and revenue from increased capacity and cheaper dispatch. Through the power system analysis procedure presented further, it is possible to sort out the most probable faults to cause severe violations. The fault probability is used for efficient reinforcement of the grid. The contingency and reliability analysis can help find the solutions that will decrease the probability of violations most efficiently. Furthermore, the developed procedure can also be used when expanding the grid and determining which grid alternative will be most reliable.