Wind power fluctuations cause frequency deviation from the 60-Hz standard. Using the composite transfer function G (fw) of a small system of thermal power plants, it is estimated that power fluctuation of 5% of the total thermal plant capacity can be tolerated without exceeding 1% frequency deviation. The technology to filter out the power fluctuations by wind turbine generators for increasing wind power penetration already exists. However, perfect filtering sacrifices as much as 27.6% of the wind power that can otherwise be utilized. The paper presents a method of quantifying wind penetration based on the amount of fluctuating power that can be filtered by wind turbine generators and thermal plants. For optimal wind power acquisition, the penetration level is conservatively estimated to be 50%.