A power system should keep the its frequency for supplying the high quality electricity. Most wind generators (WGs) operate for maximizing the active power rather than responding to the frequency of the power system. As increasing the wind power penetration level, the frequency stability problem might arise. Modern WGs are forced or encouraged to participate in frequency control in the form of inertial and/or primary control to improve the frequency stability of power systems. To participate in primary control, WGs should perform deloaded operation that maintains reserve power using rotor speed and/or pitch-angle control. This paper proposes an optimization formulation that allocates the required reserve to WGs to maximize the kinetic energy (KE) stored in a wind power plant (WPP). The frequency support capability of WPP could increase if the WPP have more kinetic energy and reserve power. Normally, an amount of reserve power is assigned by the system operators. To improve the frequency support capability of WPP, this paper has focus on maximizing the kinetic energy. The proposed optimization formulation considers the rotor speed margin of each WG to the maximum speed limit, which is different from each other because of the wake effects in a WPP. As a result, the proposed optimization formulation allows a WG with a lower rotor speed to retain more KE in the WPP. The performance of the proposed formulation was investigated in a 100-MW WPP consisting of 20 units of 5-MW permanent magnet synchronous generators using an EMTP-RV simulator. The results show that the proposed formulation retains the maximum amount of KE with the same reserve. In addition, the pitch angle movement is the smallest. The frequency nadir in a power system successfully increases by releasing the stored KE in a WPP in the case of a disturbance.