Costs Study of 69- to 345-Kv Overhead Power-Transmission Systems

With transmission voltages of long and heavy trunk lines having exceeded, in the case of the Boulder Dam line, the popular 230-kv voltage, it appears in order to investigate the cost of lines at a still higher voltage, particularly since the design and manufacture of the 345-kv equipment do not seem to present special difficulties. The study undertaken endeavors to find the economic relationship between voltage, block of power, and distance for the transmission of various blocks of power over distances up to 500 miles. The systems studied are made stable in the transient state by equipping them with devices which increase their transient-stability limit. The prices of equipment are those which were in force immediately prior to the outbreak of the second World War, and the costs of various system parts, as installed on foundations, have been obtained from the study of numerous actual construction projects in different parts of the country and reduced to the 1938-39 cost level. The system capital and annual costs are analyzed. The quantities of major equipment items in each system are given either by number or by weight, and the costs of major equipment groups and of items within a group are represented on a percentage basis. This representation permits the estimation of the cost of a transmission project based on cost of equipment and copper and steel prices other than those taken in the study. The cost of stability improvement is calculated, and this expenditure proves to be amply justified.