Transient stability of small plant generators connected to a weak utility system - a case study

Small generators connected through a large impedance and operating in synchronism with a weak utility system are more likely to pull out of step on a large perturbation, i.e. a fault in the utility´s system. Under an incident impact, which will be distributed unevenly amongst various machines, every machine will be retarded or accelerated, and undergo damped or divergent oscillations. The paper demonstrates that the small machines are more vulnerable and may fall out of step. This may plunge the entire process plant into a complete power outage on system separation. A case study of two small generating units and the improvements in the transient stability by fast system separation and load shedding is demonstrated.