Electricity generation, along with motor vehicles, is one of the biggest sources of pollution for the planet. Renewable energies are not able to replace massively polluting power plants but they can at least alleviate for it. Biomass and hydro power are the main source of renewable energy but wind power is developing to high extent, increasing by 30% its installed capacity every year in the world. Norway is increasing its wind power production since every hydro power areas are already used. The shallow Norwegian waters along with the increase of energy demand leads to offshore wind project.The aim of this thesis is to study the integration of large scale offshore wind farms into the grid. The biggest offshore wind farm is currently installed in the United Kingdom (Thanet) and its capacity is 300 MW. The wind farm studied here has a capacity of 1000 MW. HVAC and HVDC transmission are investigated in order to connect the wind farm to Norway. Case faults are performed in order to study the system stability. The connection points are located in the most populated areas of Norway, where there is a real need for new power plants: Sørlandet and Vestlandet.Statnett is the Norwegian transmission system operator and thus the focus was made on the connection with power flow and stability analysis and not on the full description of the wind farm. For simulations, Statnett is mainly using PSS®E (Power System Simulator) from Siemens but as much of the help was providing by SINTEF, the largest independent research organisation in Scandinavia, it was more convenient to use their tool: SIMPOW from STRI AB.