This paper introduces a novel risk assessment model for evaluating supply-demand imbalances in power systems utilizing reserves from wind power generators. Initially, the wind power reserves are characterized using the deloaded mode of wind power generators. Subsequently, the risk indices for supply-demand imbalance are formulated, along with an innovative index addressing the underutilization of wind power reserves, thereby enhancing the delineation of unused wind energy. A comprehensive risk assessment model that encompasses both economic dispatch decisions and wind power reserves is presented. The study concludes by examining the influence of wind power reserves on power system risks through illustrative numerical examples.