Improving Power System Stabilization in Response to Grid Disturbance

Abstract

The stability of the parallel operation of the generators in the power system is ensured by automatic excitation controllers (AEC). In case of disturbances in the power system and the frequency drop at the generator, the AEC provides a controlled signal to reduce excitation, which leads to a decrease in the braking electromagnetic moment on the shaft and provides acceleration of the generators, and when the frequency increases, a signal is sent to increase the excitation, which increases the braking moment. Obviously, this can only be effective if the phase deviation of the frequency at the terminals of the stator coincides with the frequency of rotation of the shaft of the generator. However, in parallel operation of numerous generators in a complex multi-machine system with strong electrical connections, the amplitude and phase of the deviations of the frequency of the generator can differ significantly from the amplitude and phase of the deviations of the frequency of rotation of its shaft. It is fundamentally impossible to compensate for this difference by choosing the gain and time constants of the elements of the control channels, since this difference varies depending on the number of units operating in parallel, the degree of their connection in the power system, and other dynamically changing factors. The phase shift of the signals with respect to the deviation and the frequency derivative can lead instead to increase of the oscillations, in amplitude and time. The paper discusses a method of stabilizing the modes by the difference between the rotational speed of the generator shaft and the voltage frequency on busbars of power plants. The results of full-scale system tests carried out to verify the effectiveness of this method are presented, which confirmed transient processes improvement. Suggestions for using the proposed stabilization method are provided.