Subsynchronous resonance countermeasure using phase imbalance

Since the discovery in 1970 that subsynchronous resonance (SSR) was the main cause of the shaft failures at the Mohave plant in Southern Nevada, extensive research and development efforts have been devoted to the development of effective SSR mitigation measures. This paper presents a contribution to these efforts by providing a new concept for simple and reliable SSR mitigation. The basic idea is to reduce the energy exchange between the two sides of turbine-generator sets at subsynchronous oscillations by weakening the electromechanical coupling. This is attained by creating phase imbalance at subsynchronous oscillations. The imbalance diminishes the capability of the three phase currents to develop interacting electromagnetic torques and, therefore, suppresses energy exchange between the electrical and mechanical sides of turbine-generator sets. The objective of this paper is to study the influence of having the phase imbalance associated with the generator to be protected from potential torsional interaction problems