Examples of protective relaying interface of distributed generation with automatic transfer between two CenterPoint Energy distribution feeders

Industrial load customers want economical and reliable electric power and more are looking into the benefits of distributed generation (DG) as a solution. Some of the utility concerns with connecting DGs to the utility distribution system are (a) back feeding into a feeder during a faulted feeder condition and (b) providing power to other customers on the feeder when the DG is running their generator and the utility substation feeder breaker is open (“island”). This paper describes how the transfer trip requirement was implemented by Centerpoint Energy (CNP) at two DG sites (DG "A" and DG "B"). Prior to these two projects other DG sites connected to CNP which required transfer trip were connected to a single circuit as represented in Figure 1.