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Traditionally, most generation plants are based on hydro or and thermal generating units. It is essential to recognize the critical role played by these unit generator controls in maintaining system adequate performance, its stability, voltage and frequency control. In the last years, renewable generation integration has increased to supply new markets and in several countries mainly to displace thermal power plants, in order to face environmental societal pressure by energy “more clean”. In many power systems, the amount of renewable generation connected to the grid system has been low so far. However, this scenarium is all changing. Renewable generation, in particular wind power plants, is now becoming a major contributor to power systems and its contributions will increase even more in the next years. To give an idea of this, the European Wind Energy Associated estimated that in 2020 around 180 GW of wind power plants will be operational - 35 GW will be offshore. Some power systems predict that by 2020 up to 50% of installed capacity will be based on renewable generation. This considers both on-shore and off-shore generation. It is important to remark that in several countries this generation is used to displace traditional generation showing good performance, however due to environmental concerns the society does not tend to welcome this king of source. The impact of wind generation on power system performance should be assessed face to their effects considering time and space. Thus, short and long-term effects should be considered. The short term effects are caused by system balancing at the operational timescale (minutes to hours), whereas the long term effects are related to the contribution wind power can provide to reliably meet peak load and assure energetic security. Concerning the operation of renewable generation units together with traditional generation ones in terms of guaranteeing that such new generation units will not be shut off - uring disturbances which provoke underfrequency or voltage sags, as well as the calculation of the spinning reserve, are examples of the challenges to be faced in this new environment. In other words, under normal conditions, the objective is to operate the system as economically as possible with sufficient security margin, and all system variables within acceptable limits. When a disturbance occurs and abnormal conditions develop, the objective is to minimize the impact of the disturbance and to restore normal conditions as quickly as possible. In order to assure the system operation as economically as possible with adequate security margin, ONS has been working hard, developing several actions to enable the integration of this new kind of generation with security This paper describes the Brazilian experience on the integration of this kind of energy source, emphasizing lessons learned and new challenges to be faced.