Out-of-phase synchronization of a small alternator

In modern power systems with large amounts of dispersed generation the islanding of distribution networks is now a realistic possibility. Islanding can be implemented following system disturbances to improve the continuity of electricity supply and prevent blackout. Before this can become widespread many issues must be considered. One of the major concerns and the topic of this paper is out-of-phase synchronization and its effect on the system. To investigate this, a series of tests were preformed on a small 31.5 kVA alternator. The results show the differences in peak torque and current between synchronizations where the rotor either leads or lags the main system. They also let the authors propose a maximum acceptable synchronization angle for small generators that is higher than that used for larger plant. A simulation has been performed to give the expected system voltage deviations when re-connecting an island out-of-synchronously to the main system. © 2007 IEEE.