Investment Cost Analysis with Structural Design of Concrete Duct Bank Power Cables

Abstract

Capital investment in underground duct bank cables is very expensive. Therefore, the design and planning for underground power cables is important. It is often done with analysis of the power demands minimizing costs over the lifetime of the cables. This work presents an evaluation of underground power cable ampacity and the total costs during the anticipated operational life of the equipment. It was evaluated with variation of concrete duct bank dimensions. Analysis of ampacity depends on temperature. The thermal model of the current study uses a finite element method. The total costs evaluated by the economic model in terms of net present value analysis consist of the initial investment costs and the value of losses over the life of the cable. These were based on installation costs, load factors, annual load growth, the price of energy, the price of demand charges and the forecast discount rate. The results show that cable spacing parameters are a significant factor that influences ampacity. Ampacity can be improved while reducing the losses in power cables. This is because appropriate cable spacing can reduce the effect of Joule heating from neighboring cables. However, this leads to increased construction costs. The total costs of power cables over their lifetime can be reduced by decreasing the horizontal distance between the center of a casing pipe and the side edge of the concrete layer. This is because the contribution of reduced construction costs is more than that of the effect of increased losses. Therefore, the dimensions of the concrete duct bank significantly influence ampacity, the construction costs and the losses of power cables in an analysis of total costs over the lifetime of power cables.