Abstract: In view of the abnormal phenomenon that the magnetic pole T-shaped platen in a pumped-storage power plant is cocked up, the force on the platen is calculated in the operating condition that the unit is in open-phase running and the electric brake is in the false forced excitation operation. The influence of the change of electromagnetic and centrifugal forces on the platen is studied by using the finite element simulation, and the cause of the fault is determined to be the electric brake with false forced excitation. So that the centripetal force on the magnetic pole T-shaped platen exceeds the limits of bending and warping, which results in deformation. And some suggestions that prevent from the similar incidents are put forward.