The use of electricity has been increasing constantly from past to now and there is a need of reliable transmission and distribution systems in order to provide continuous and balanced energy. Besides, traditional energy management systems have been forced to change as a result of increases in the usage of renewable energy resources and the efficiency of demand-side on the market. In this respect, power systems should be planned and operated, properly and the balance of generation-consumption should be ensured within the nominal voltage limits. In this study, initially, the current status of electricity infrastructure in Turkey is evaluated. Afterwards, the electricity transmission infrastructure of Ankara that is the capital city of Turkey is modelled by Digsilent program. The critical line scenarios are implemented on the electricity transmission infrastructure model developed. These scenarios are based on the period of maximum and minimum electricity demand and the effects of demand response in this period. As a result of grid analyses performed, several findings has been obtained about the impacts of different line scenarios on the transmission system, the optimization of grid voltage profile and the role of demand response on voltage regulation.