In accordance with the aim of increasing the renewable energy sources in Turkish power system, the optimum wind power generation capacity in the power system shall be maximized. Since 52,6% of raw materials for operation of conventional electricity generation sources (e.g. natural gas) are imported, the integration of wind power plants to the Turkish power system plays a critical role in Turkish economy. In order to maximize the capacity of wind power plants and keep the stability constant in the system, Turkish Grid Code also needs to be detailed and expended. There are several requirements defined in transmission and distribution system grid codes in the World and in our country for stable connection of renewable energy sources. In this paper grid codes of several countries is examined and afterwards simulation models and connection assesment of wind power plants are explained.