A Design Guide for Conventional Underground Distribution Systems

Conventional underground electric distribution systems, installed in ducts and vaults, can be designed many ways. This paper offers a design guide based on safety, reliability, and economic considerations. Considering safety at all times, the basic design is derived to meet requirements for restoration time, reliability level, and contingency level. Economy is realized by efficient use of cable and equipment, and a favorable comparison to network systems is shown. In the resulting design, feeders are divided into five, load-bearing, fused branches, each with independent backup. Loads of all sizes are accommodated by the various branch designs presented.