Abstract: A three-dimensional electromagnetic field finite element calculation model with the transverse crescent groove as the focus was established in this paper.The distribution of eddy current losses of the 300 Mvar air-cooled condenser under different negative sequence state was analyzed.Due to the difficulty in setting boundary conditions for local three-dimensional temperature field analysis, it is difficult to accurately simulate the maximum temperature value of the rotor.The negative sequence capacity test of the 412 MVA air-cooled turbogenerator, which is identical in terms of structure and cooling method to the 300 Mvar air-cooled condenser, was completed in the factory.Therefore, the steady-state negative sequence capacity of the 300 Mvar air-cooled condenser was determined in this paper by means of finite element comparative analysis of the negative sequence eddy current field and the 412 MVA air-cooled generator test.