USING THE GROWTH MODELS FOR OPTIIIISATION OF ENERGY DISTRIBUTION SYSTEMS

Energy distribution systems were developed in the recent years due to increasing population, new technologies and toed demand. Alternative technical BITlIJlgemefltsare made trouble to choose the beet construction. On the other hand, syatem COlts are affected fur the new design and operating. That is, fur a new dilltribution design or operation of an exist syatem, both teclmical and economical constraints must be consider.

The purpo&e of this paper is a brief summary of rererence (1].Annual growth fBctors of load, 1088fuctor and energy costs were considered to obtain the sufficient system design.So, all the cost expressions depend on these factors can be obtained conectly.Moreover, these t8etonJ were modeled in twenty-sewn cases by the considered three models in "Present Worth Analysis" formulations.These cases can be used in such as exact COlt expressions, optimum system design, selection of the optimum design amongst the others (2,3,4,5,6], etc. in energy distribution syatems. The total cost (TC) expressions of an energy distribution system are compolled by two basic part: "Fixed costs" and "Variable Costs".Fixed costs (FC) are related to the investment costs.Variable COlts (VC) are operating costs.In other warda, operating costs are the cost of energy due to eR 10l8e8.The cost of investment is the 1algest cost component and it depends purchase cost, taxed, insuIance, depreciation, operation and maintenance, etc.
Since operating costs change from year to year, it is necessary to consider them over the expected lifetime (N) of the system.Therefore total cost of a syatem can be written by the following fonnula: In the following parts annual growth Iates must be considered, growth models and using these models in calculations will be preented for a dilJtribution sygtem.The expretilIions are derived by the Preient Worth Analysis fonnulations because of its simplicity using in optimization teclmiques.
Load growth in diBtribution systems is an unavoidable situation due to increasing population, increuing consumption, using new teclmologiea, migrations, etc.To obtain an efficient and economic system deaign in distnbution substation transfonners, high voltage primm:y feeders, diBtribution transformerll, low voltage feeders and service lines the load growth must be estimated.
The system experiences growth in load factor due to many mlSons such as increase in load diversity with load growth, increase in energy consumption per kW connected load with time, measures taken by the utilities to flatten load curves for improving system efficiency and to curb the growth in peak demand, etc. Due to depending on the load factor, l08S fiIctor also increases with load factor.
On the other hand, cost of energy also increases with time dependa on inflation.When the energy 10l1ell are chanced by the I2.R, the COlt of energy 10l1ell is subjected to the incnlased energy cost year by year.
In the next part of the study, considering the proceeding situations Sm, LF and EC will be modeled by the yearly growth rates gs, glf and gee using in three cases [
• There is a linear relation 8JTIOfI8st the annual growth Iates.• There is a nonlinear relation amongst the annual growth rates.In the cost expressions that are expre8lltld by subscript n; Sm, LF and EC are easily modeled by using with (2-4) in the following manner:

Sma=Smo
• The best model that SOOWll the growth trend is chosen.
• The lIIlJ1ual growth rate that is being used is detennined.The weighted cost of capital is taken into account U the interelrt rate.
That the three cases that determined in the preceding part amongst the three terms are revealed twenty-seven different possible arrangements.If there are two tenns, this number is 9; ifthere is only one term, there will be three arrangements.
That the constant case of Sm, LF and EC is shown by (C), the linear modeled case (L) and the nonlinear modeled case (N) is shown at Table I in twenty-seven diffilrent possible arrangements (I).
From table 1, the IlUitable model is chosen considering the problem and then its corresponding fonn (2-4) is substituted in the cost expressiOJl8with subscript n 81 (5).At the end, the case number C8 is detennined and for this number, the sum of the series Ten are constituted in the cost equatiOJl8.So, the expressiOJl8are obtained by depending on the lIIlJ1ualgrowth rates.In rererence (1), these twenty-seven cases were obtained with the generalized expressions fur Sm, LSF and EC.Therefore, required Tenvalues can be taken from there.