Voltage Sags and the Response of a Synchronous Distributed Generator: A Case Study

The dynamic behavior of a synchronous distributed generator connected to a distribution system during fault conditions is studied. A fault on an actual system was found to have a sag that was extended after the fault was cleared. It is shown that the combination of the generator and the load on the system contributes to the extended sag. The detailed simulation studies demonstrate that the primary factors are the reactive power drawn by the load during the fault and recovery along with the reaction of the generator. The prediction of such behavior requires proper modeling of the generator, the generator's controls, and the system and dynamic load. Operators of such generators need to be aware of this type of system and load response when synchronous DG is connected to a distribution network.