Damping Shaft Torsional Oscillations in Dual Excited Turbo Generators

Abstract

Technical advantages of utilizing the two field systems of the Dual Excited Synchronous Generator (DESG) for damping inertial and unstable torsional modes of steam turbo-generators (T-G) are considered. This is achieved by adding two auxiliary controllers, one on each field system. The d- axis auxiliary controller is designed to enhance the stability of the inertial oscillatory mode while the q-axis controller is designed to damp the unstable torsional modes. A comparison is made between using either generator or high-pressure turbine speed deviations as the stabilizing signals for the two controllers. The study is conducted on system-1 of the second IEEE benchmark for the simulation of the sub-synchronous oscillations. A rigorous state space mathematical model has been developed and simulated using MATLAB to carry the sought investigations. The pole placement method is used to determine the controller parameters. The results indicate that coordination of the two controllers can significantly increase the power system damping for the inertial and torsional oscillatory modes.