The selection of the grounding of the interconnection
transformer is one of the most important decisions in the
development of the DG interconnection project. In the U.S.,
distribution systems range from 4 to 34.5 KV and are multigrounded
4-wire systems as shown in Fig. 4. The use of this type of
system allows single-phase, pole-top transformers, which typically
make up the bulk of the feeder load, to be rated at line-to-neutral
voltage. Thus, on a 13.8 KV distribution system, single-phase
transformers would be rated at 13.8 KV/1.73~8 KV. Fig. 4 shows a
typical feeder circuit. For synchronous generator DGs
interconnections, line-to-neutral rated transformers and lightning
arrestors can be subjected to damaging overvoltages depending on
the choice of DG interconnection transformer.