Superconducting rotational generators are a promising application of the high temperature superconductor (HTS). Typically, superconducting rotating generators use HTS coated conductors to form the DC coils in the rotor as they experience lower AC loss compared to the stator windings. However, in the actual operation, the AC loss produced by the harmonic magnetic field is inevitable. Other transient electromagnetic disturbances in the operating generator environment can also cause the AC loss. This paper introduces a fully coupled numerical method for coated conductor HTS coils in operating generators based on the T-A formulation, which is verified by almost the same simulation results with the A-H formulation model. Using this method, the simulation results show that the ferromagnetic stator teeth will increase the AC loss caused by the harmonic magnetic field and the load change, while the shielding layer can decrease the AC loss in a certain amount.