Reassessment of Economic Current Density based on Life Cycle Cost under Market Economy Condition: a Case Study in Vietnam

Reasonable selection of cross-sectional area of conductors for overhead transmission lines has great effects on reaping economic benefits during the entire project's life cycle. Economic current density is an essential reference for the selection of conductor size. The traditional economic current density put forward in the 1950s and widely used in the electric power industry in Vietnam takes no account of the time value of money and assumes constant values of the marginal cost of electricity and wire price. These prices, however, can profoundly affect economic current density values. Therefore, these values need to be updated. This paper proposes a novel methodology based on life cycle cost (LCC) to scientifically and comprehensively determine economic current density values, complying with the current market economy conditions. The total LCC can be expressed as the sum of the initial capital investment cost (CIC) and the total cost of operation (TCO), comprising the cost of maintenance and electrical energy loss. Analytical function of CIC relating to conductor cross-sectional area and nominal voltage is obtained using available data from previously constructed overhead lines and regression analysis. The electrical energy loss is determined using equivalent hours of loss, which in turn depends on equivalent hours of utilization. Analytical expression of equivalent hours of loss with respect to equivalent hours of utilization is attained using the regression method from historical load data. Finally, a practical case study of a 110 kV overhead line in Vietnam is leveraged to validate the viability and effectiveness of the proposed approach. The calculation results show that the life cycle cost using the economic current density developed in this work is lower than that from the Vietnam standard.