Neutral grounding method and protection co-ordination on several direct-connected generators in parallel

There is a power micro grid composed of several diesel generators, cables, step-down transformers and motors. The similar grid scheme is applied to airports, mining plant, and oil platforms etc. In the micro grid, the generating system needs to meet the demands not only for supplying stable electricity, but also for keeping the islanding operation. As we know, damages of generator stator insulation easily happen due to the generator arcing ground current beyond the limit. In this paper, naturally it is available that high resistance grounding is used at one of several direct-connected generators neutral in a micro grid, and to keep only one generator grounding at a time among them in parallel, there is one automatic isolator at each generator neutral by the generator control system. Further, the protection co-ordination basing on this grounding method that is reliable earth-fault protection scheme has been used to this micro grid. The neutral grounding method, the protection configuration of feeders, generators and buses, and partly the settings calculation of the relay device are introduced and analyzed in this paper, and the available complete scheme has been adopted.