Effect of synchronous generator regulation on the subsynchronous resonance phenomenon in power systems

Since the potential consequences of the subsynchronous resonance phenomenon were encountered in 1970, concern has escalated among those electric utilities which rely upon series compensation to seek reliable methods for determining the existing power systems subsynchronous stability margins. In the several publications available on this subject, no attempt has been made to represent the synchronous machine governing and excitation control systems in the mathematical models devised, particularly when the torsional dynamics of the shaft are considered. It is the main objective of this paper to present a rigorous mathematical technique for the evaluation of the subsynchronous resonance stability limits of regulated synchronous machines connected through series compensated transmission systems. The results of a digital simulation of the suggested mathematical technique is also presented. The investigations presented show that properly designed electrohydraulic governors can improve considerably the subsynchronous resonance stability limits. On the other hand, practical voltage regulators seem to be unable to achieve such an improvement.