IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 39, NO. 1, JANUARY/FEBRUARY 2003 53 LCC Design Criteria in Electrical Plants Oriented to the Energy Saving Aldo Canova, Francesco Profumo, Senior Member, IEEE, and Michele Tartaglia Abstract—In this paper, a life-cycle cost (LCC) approach is pro- posed to design electric installations suitable to industrial and civil applications. The structure of the electric system under study is supposed radial, as in most cases, and composed by transformers and lines, while users are simply represented by means of their load diagrams. The LCC procedure allows us to evaluate the main char- acteristics of transformers (rated power) and lines (rated current) and it can be adapted to also choose particular loads like induction motors. The paper shows an improvement of the standard proce- dures to design electric lines constituted by cables also including the case of their parallel connections and the most convenient types of bus bars. A similar concept is also applied to transformers taking into account their thermal behavior to establish their limit perfor- mance, starting from the supplied system load characteristics. In the case of induction motors, the mechanical load is considered in the evaluation of the most convenient solution. The procedure has been applied to the case of a real industrial plant and the results reported in the paper are related to it. Index Terms—Cables, energy saving, induction motors, life-cycle cost, transformers. I. INTRODUCTION T HE design of electrical installations requires the satisfac- tion of many technical constraints like electrical, thermal, and mechanical taking into particular consideration the system operating costs. It is well known that usually the solution corre- sponding to the lower initial cost could be quite different from the solutions which optimize both the initial cost and the energy saving. Because of the relatively long “life” duration in time of electrical installations (more than 20–30 years), the design pro- cedure can be conveniently based on the choice of design pa- rameter values which satisfy the technical limits and minimize the life-cycle cost (LCC), which is defined as follows: (1) where initial cost of investment [current unit (c.u.)]; operating cost (c.u.); set of design parameters. Paper ICPSD 34–4, presented at the 2001 Industry Applications Society An- nual Meeting, Chicago, IL, September 30–October 5, and approved for publi- cation in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Energy Systems Committee of the IEEE Industry Applications Society. Manuscript sub- mitted for review October 15, 2001 and released for publication November 1, 2002. The authors are with the Dipartimento di Ingegneria Elettrica Industriale, Po- litecnico di Torino, I-10129 Turin, Italy (e-mail: canova@polel1.polito.it; pro- fumo@polito.it; tarmich@athena.polito.it). Digital Object Identifier 10.1109/TIA.2002.807216 The first term is the cost necessary to build the electric installations and it depends on chosen materials, manufacturing costs, used technologies, etc. The second term can be split as the sum of different terms like energy consumption cost (c.u.); maintenance cost (c.u.); nonoperating time cost (c.u.). As a first simplification, the term due to the cost of the energy consumption can be considered as the prevalent, thus, (1) can be written in the form (2) The design criteria summarized by (2) can be applied to the choice of the main components of an ac electric plant as lines and transformers for a defined system structure and for fixed system rated voltages. In such a way, the design of the main components of the electrical system mainly depends on load waveforms. The cost of the complete system is the sum of costs of each branch and, under the frequent hypothesis of a radial network structure, the of each component mainly depends on its own design parameters and is weakly influenced by the design parameters of other branches. Therefore, the optimum solution for the complete system is found when the best solution of each component is gotten. In fact, one can start from the terminal branches nearest to the users and design them independently one from another and go back up to the generator side. A simple power summation can be performed according to the Boucherot rules, neglecting the voltage variations in the network depending on each branch electrical parameters and usually are lower than 4%. In the present paper, the well-known criterion standardized in [1] is used to choose electric cables having negligible dielec- tric losses. This criterion has been improved to also consider the case of power lines with multiple conductors connected in par- allel, as proposed in [2], and it has also been extended to the case of bus bars. Similar considerations have been applied to the choice of induction motors [3] and power transformers ac- cording to [4]. In the case of the induction motors the main electric pa- rameter is the rated power: the optimal solution can be found starting from prospective mechanical load and considering the mechanical, the Joule, the iron and the excess losses of these systems, comparing machines having different rated power and comparing also traditional motors and high-efficiency machines. A similar method can be applied to the choice of transformers. As a first step, the network power flow is evalu- ated to select the minimum size of transformer (rated power), thus evaluating the most convenient solution according to (2). 0093-9994/03$17.00 © 2003 IEEE