This paper proposes a calculation model and method of output power loss of wind farms and wind turbines. An expert system database with large amounts of historical data is established to represent the relationships among wind speed

wind direction and power output. The power loss model is built on the expert database. The loss of the real time power and generating capacity of the wind farms can be measured according to the observed wind speed and wind direction when the wind turbines are broken or curtailed. Experimental results demonstrate that the model can accurately measure the power output loss caused by various reasons

and thus verify the validity of the model. More importantly

the proposed method not only improves the operation and management level of the wind farms

but also provides accurate data reference for peak regulation and frequency modulation.