LIFE-CYCLE COST EVALUATION OF UNDERGROUND DISTRIBUTION SYSTEMS.

The paper describes the following five underground distribution systems suitable for supplying suburban commercial and industrial load: radial, open loop, loop with automatic throwover, primary selective, and spot network. A cost-reliability index (CRI) is defined by the inverse of the product of the system cost per customer c and system average interruption duration index d as: CRI equals 1/cd. This index is a measure of the merit of a distribution system design in terms of combined cost and reliability. The larger the cost reliability index or CRI number is, the better the system design. The CRI is used to evaluate the designs considered. It is observed that the spot network has the lowest average interruption duration index but highest cost among the five designs. In terms of cost reliability index, the primary selective design is superior to others. On the basis of cost reliability index and annual revenue consideration, an application guide of underground distribution system design for supplying commercial and industrial loads is proposed.