This paper reports the operational experience from the Portuguese Power System during the 2009/2010 winter months when record wind penetrations were observed: the instantaneous wind power penetration peaked at 70% of comsumption during no-load periods and the wind energy accounted for more than 50% of the energy consumed for a large period. The regulation measures taken by the TSO are presented in the paper, together with the additional reserves operated for added system security. Information on the overall power system behavior under such extreme long-term wind power penetrations will also be addressed
