Due to the characteristics of large volatility and strong uncertainty

wind power ramp events(WPREs)are likely to cause the active power imbalances of power systems and even load loss accidents. Based on the analysis on characteristics and prediction status of WPREs

a WPREs model is proposed to establish the quantitative relationship between charactering quantities and wind power curves. The uncertainties of WPREs and load forecasting are simultaneously considered

and the scenario reduction method is used to generate the typical scenarios set of net load during WPREs. With the derivation of mathematical calculating method of buffered load loss probability based on scenario reduction

an indicator system is established

by which the system status can be categorized as being adequacy

load loss and marginal

and the corresponding probability of each status and severity of load loss can be calculated respectively. The assessment results of typical events based on the Gansu power grid verify the effectiveness and rationality of the proposed assessment method and indicator system. The roles of ramp rate of conventional units and proportion of reserve capacity in preventing the adverse effects of WPRE are further analyzed. This work is supported by National Basic Research Program of China(973 Program)(No. 2012CB215101).