Stabilizing the Operation Modes of a Modern Multi-Machine Power System after Large Disturbances

Abstract

Operational experience has shown that the tuning of stabilization channels of automatic excitation controllers (AEC) adopted in the UES of Russia improves steady-state stability in the power system both for long power lines and through weak connections, as well as in the event of small fluctuations in parameters. However, situations may occur in a multi-machine power system during transients after large disturbances and loss of synchronism between generators with large power fluctuations when the adopted (standard) tuning does not provide rapid suppression of these fluctuations. In an emergency situation, a prolonged transient with large power fluctuations can cause a local damage to evolve into a system accident. The article describes a method for stabilizing the operation modes in a multi-machine power system, according to which it is proposed to produce stabilizing AEC signals based on the difference of deviations between the shaft rotation frequency of each unit and the voltage frequency on the power plant busbars. Such signals will contribute to fast synchronization of generators with respect to one another and prevent power overflows between them during oscillations. In addition, with the stabilizing signals formed in this way, there will be no need for repeatedly retuning the AEC in the course of power system development and as changes are made in the electrical network structure; moreover, a widespread introduction of the proposed approach will significantly reduce the risk of torsional vibration of the turbine unit shaft. The results of the discussion of the proposed stabilization method by the UES Scientific and Technical Council are presented.