Considering Reliability in the Design of Mixed Overhead and Underground Distribution Feeders

Many utility companies are converting overhead (OH) main line feeder sections to underground (UG) to improve reliability, system resiliency, or other local customer demands. A Hybrid distribution feeder is one with a mixture of OH and UG main line sections. Conventional protection philosophies for hybrid feeders normally result in lower overall feeder reliability. This paper will examine an example feeder to demonstrate the impact of protection and isolation system improvements on predicted reliability for Hybrid distribution feeders.