Impact of Distributed Resources on Distribution Line Protection

This report covers how the addition of distributed resources will impact the distribution relay protection of the system. The issues covered include protective device coordination problems due to infeed and bi-directional current flow; effects on synchronizing and autoreclosing; the potential for forming small islanded systems; and issues related to ground fault detection. The types of interface transformer connections are compared. Their influence on the protection of the system is based on the type of connections. Changes to relay protection in response to the problems encountered and other solutions that have been applied are also covered. The protection of the generators and the interface protection are specifically omitted from this report. Some issues related to control of voltage levels and capacitor switching are included.