In the coordination of power source and grid, the issues of grid-related protection of generator will exert an increasing significant on running of power grid and network equipment. For the unreasonable setting problems of low excitation limit, phase advance capacity and loss excitation, coordination principles among them are provided. In power system protection, the loss of excitation protection is one of the most important and complex protections. Loss of excitation protection and out-of-step protection both use the variation of the measured impedance as the operation criterion of the operation, and there is an overlap operation area in the impedance plane, so loss of excitation protection and out-of-step protection exist confliction in coordination. For the measurement of power angle is real-time, on-line, and automatic adaptive, a method of solving loss excitation protection and out-of-step protection is provided based on the power angle locking. Simulation verifies the correctness of the conclusion.