SSR. An condition involving energy exchange at natural frequencies below the synchronous frequency.
Subsynchronous Resonance (SSR)
Subsynchronous resonance is an electric power system condition where the electric network exchanges energy with a turbine generator at one or more of the natural frequencies of the combined system below the synchronous frequency of the system.
Subsynchronous resonance encompasses the oscillatory attributes of electrical and mechanical variables associated with turbine-generators when coupled to a series capacitor compensated transmission system, where the oscillatory energy interchange between the electric system and the turbine generator is lightly damped, undamped, or even negatively damped and growing. The terms subsynchronous and supersynchronous are used to denote frequencies below and above the synchronous frequency defined by rotor average speed.