Interconnection of a "Green Power" DG to the Distribution System, A Case Study

The majority of the electric utility distribution systems in the USA are designed for radial flow of power from distribution substations to the electric customer. Today, throughout the country, distributed generation(DG) is being added to this system. This paper describes an example of a relatively large distributed "green power" generator interconnected to a rural electric system. A case study is presented that summarizes the steps taken to analyze this DG connection and it's impact on the system design and protection. Design decisions are made to provide methods to best achieve the utility and DG owner's goals. The choice of DG interconnect transformer grounding has a major impact on the design of the protection scheme. Problems with coordination of protective devices are reviewed and the final system protection design is presented