Optimum Design Return Period of EHV Lines Considering Reliability, Security and Availability

摘要

In overhead line design, reliability is provided by assigning a fixed return period to the extreme climatic loading events such as wind, ice and combined wind and ice. This implies some expected failure rate during the service life of a line. On the other hand, the security of a line is provided in two ways (1) designing structures for adequate longitudinal capacity and (2) inserting a number of containment structures (anti-cascading towers) at a fixed interval (e.g. normally every 20 to 25 structures). This study presents a basis for computing the optimum design return period of an overhead line considering initial line cost and the future failure cost. The optimization is done by balancing the initial line cost against the present value of the cost of losses due to line failures. The cost consists of two components; (1) expected cost of line replacement and (2) expected cost of energy not supplied considering unavailability of the line.