The use of wind power to generate electricity is probably the most widely used renewable energy sources around the globe. The major reason may well be of its well developed technology in comparison with other form of renewable. The percentage of wind power installation with respect to the total power generation, also known as the penetration factor, is increasing rapidly year by year in many countries. As wind speed varies randomly and which means that the output of wind generators is intermittent. When a wind farm is connected to a transmission network its effects on the network can be quite different from that of connecting a conventional power station even when connected at the same point. When analyzing the effects of the conventional generator on the network under different load profiles the operator can assume that the generator operates at its maximum capacity. In the case of wind power the situation is more complex as the output of the generator is intermittent. The analysis could be even more complex when more than one wind farm is connected at more than one location. In this paper a method is proposed to analyze the effects of wind power on transmission network. In the study the Weibull Distribution Function is used to represent the stochastic wind speed distribution. The method of Monte Carlo simulation will also be introduced to solve the problem of wind turbine output calculation and the system reliability studies. To estimate the reserve capacity of the transmission line when wind power participated, Monte Carlo Simulation method will be used a second time. The results of the calculation are then used to estimate an Economic Transmission Capacity on transmission lines affected after wind power is introduced. This can be used for transmission lines reinforcement implementation. The IEEE-9bus system will be used an example. The study will include 3 scenarios and will consist of 1 and 2 wind farms participation.