Distributed generation systems incorporate a distribution network and typically a number of distributed generators. It is possible that power islands may be created in substations incorporating a generator when that substation and generator is isolated from the distribution network by a circuit breaker. A problem arises when the power island is re-connected to the distribution network when the phase of electrical power supply in the previous power island is not synchronized with the power supply on the distribution network. Identifying such an out of phase nature is achieved utilizing application of test reactances, both capacitative and inductive, across the whole distribution network such that such test reactances are substantially unbalanced within a particular substation and in particular a distribution path for a generator so that there is a test reactance load imbalance which will identify out of phase operation and therefore control activation of the circuit breaker.