Economic aspects of D-C power transmission

Results of the study may be summarized as follows: 1. A number of d-c overhead and underground power-transmission systems were designed, with a-c generation and electronic power converters at both ends, operating on a constant-voltage principle. The d-c systems are designed for the same security and reliability conditions as the corresponding a-c systems, to the extent compatible with the particular characteristics of the two types of systems. The overhead and the underground buried lines are designed as 2-conductor systems with midpoints grounded. The underground systems are also designed on the single-conductor ground-return principle, for the ratio of direct-to-alternating operating voltages to ground k= 3.0, 4.5, and 6.0. 2. The capital cost of d-c systems, as estimated, includes the transmission line and the terminal substations equipment, but does not include the electronic converters. This cost is calculated as a percentage of the estimated capital cost of a-c transmission systems-transmission line and all equipment of the terminal and intermediate substations-transmitting same blocks of power over same distances as the d-c systems. This is shown in Figs. 1 and 2. The estimated capital cost of the d-c transmission lines alone, calculated as a percentage of the estimated capital cost of corresponding a-c lines, taken between the terminal substations, is represented in Figs. 3 and 4. 3. The percentage difference in the costs of a-c systems and thus estimated costs of corresponding d-c systems, as shown in Figs.