In order to improve the utilization rate and power generation of wind turbines

and reduce the cost of maintenance and replacement of wind turbines

it is necessary to monitor the operating conditions. In this paper

five state curves of the unit

including the wind speed-power curve

the wind speed-rotor speed curve

the wind speed-pitch angle curve

the rotor speed-power curve

and the rotor speed-pitch angle curve

are introduced theoretically. Then

they are analyzed combining with the actual operational data. The results show that

due to the randomness of wind speed and the inertia of wind turbines

the first three curves does not allow the wind turbine to distinguish normal operation status from a fault status. However

the rotor speed-power curve and rotor speed-pitch angle curve are able to accurately monitor the abnormal conditions of the wind turbine. On the basis of the last two state curves

the distribution of different operating conditions of the unit is analyzed

and corresponding evaluation systems are established for each operating condition. The fault case study indicates that

this method can sense the unit's abnormal situation in advance

and effectively improve the state monitoring accuracy of the system.