Research On The Anylatical Expression And Verification Of Short Current's Thermal Effect Of Doubly-fed Induction Generators

Satisfying the thermal stability to the short current is a compulsory requirement to select the electrical equipments,thus the accurate calculation of the thermal effect is necessary.However,since the structures and the parameters of the doubly fed induction generators(DFIGs)are different from those of the SGs,the calculation of the DFIG's short current is more difficult,thus the research on the method of calculating the DFIGs' thermal effect of the short current has not been found yet.In this paper,the short current and the thermal effect of the DFIG are analyzed.The main research contents are as follows.(1)The analytical expression of the short current of the DFIG is derived to apply for the calculation of the thermal effect.To balance the accuracy of the analytical expression of the short current and the feasibility of calculating the thermal effect,the first-order model of the rotor flux is used with the steady-state component considered.(2)The short current is decomposed into four components and its square is integrated to get ten components to describe the thermal effect.The relatively small components are neglected to simplify the analytical expression of the thermal effect.The impacts of the voltage drop,the crowbar resistance,and the wind speed on the thermal effect are analyzed.(3)Considering the temperature rise,the mutual influence between the thermal effect and the crowbar resistance is studied.The heat of the fault can not be dissipated within the limited duration.As a result,it contributes to the temperature rise of the crowbar.The thermal effect will result the increased crowbar resistance and the reduced rotor current.The mutual influence between the heat and the increased crowbar resistance is investigated.(4)The check of the thermal stability based on the thermal effect is applied for the calculation of the temperature rise of the aluminum conductor.According to the curve and the analytical expression of the temperature rise of conductor,the temperature rise of aluminum conductor is calculated.