In the paper out-of-step operation of distributed generation units (DG) is considered with construction features of generation units taken into account. Impact of DG out-of-step operation on other generation units and consumers is investigated taking equivalent impedance into account. National standards on islanding algorithms and devices are considered. Consequences of DG fast out-of-step operation clearance are considered and proposals are state for islanding algorithms improvement. Possibility of resynchronization is important feature should be considered for designing islanding algorithms. Novel approaches are proved to be effective for DG out-of-step operation clearance.