Ferroresonance and Loading Relationships for DSG Installations

Self-excitation of induction generators or small synchronous generators connected to distribution feeders is analyzed during the transient period following the islanding of a generator on the feeder. The relationship of feeder load after separation and the occurrence of ferro-resonance with an isolated induction, synchronous or single-phase generator are developed. The results indicate that an isolated distribution system generator (DSG) can theoretically support as much as three times the generator's rated power output in a ferroresonant mode provided the prime mover has the needed inertia or torque available at the abnormal isolated speed. The abnormal voltage and frequency operation during separation modifies load, generator, and prime mover characteristics and may result in an energy balance, although such balance is not obvious before separation.