Distance Protection in Distribution Systems: How It Assists With Integrating Distributed Resources

The integration of distributed generation (DG) or distributed resources in the distribution system poses technical constraints for the electrical power system owner or manager. The addition of relatively large amounts of generation to the distribution system can potentially challenge the historical setting principles and design assumptions made in developing protection and control strategies based on overcurrent protection. The necessity and complexity of additional protection and control measures increase as the aggregate DG capacity within a potential island approaches or offsets the load within that island. In addition, the varying nature of DG availability and fault current capability must also be considered. The key issues discussed and associated with DG on the distribution feeder include anti-islanding, temporary overvoltages during fault conditions, and loss of sensitivity of feeder overcurrent protection for long feeders. As the distribution system evolves to accommodate more DG, the design and implementation of the feeder protection must also evolve. This paper presents the use of distance relays for distribution protection to solve some of the DG integration problems. This paper provides real-world event report data to further demonstrate the performance of distance protection on the distribution system. A relative cost comparison between various feeder protection solutions is presented along with a discussion on options for education of distribution companies challenged with implementing distance protection for the first time.