Abstract—Efficient use of energy, the increase in demand of energy and also with the reduction of natural energy sources, has improved its importance in recent years. Most of the losses in the system from electricity produced until the point of consumption is mostly composed by the energy distribution system. In this study, analysis of the resulting loss in power distribution transformer and distribution power cable is realized which are most of the losses in the distribution system. Transformer losses in the real distribution system are analyzed by CYME Power Engineering Software program. These losses are disclosed for different voltage levels and different loading conditions. Keywords—Distribution system, distribution transformer, power cable, technical losses. I. INTRODUCTION ODAY’s increasing demand for energy and new energy sources on the initiative of environmental awareness of the more efficient energy system has entered the next research objectives. Thus, alleviation of the loss that occur in the power system has gained importance. A large part of the losses in the power distribution system consists of the power distribution line. These losses are examined mainly as technical and non- technical losses. Technical losses occurring due to current are expressed as the loss occurring in cables, lines, transformers, phase imbalance, harmonics, measuring instruments and so on devices [1]. The non-technical losses are non-invoiced electricity use, incorrect energy meters, incorrect billing, and so on. [2]. Technical losses constitute a large part of the transformer losses. As known, transformers have two types of losses which are called no-load and load losses. In literature there are many studies regarding the identification and estimation of transformer losses. Real system data using the load profile, loading condition and the load factor, etc. for the no load and loaded status of transformer losses, technical losses of the feeder have been analyzed [1]-[6]. In the condition that New-type transformers like amorphous transformer are used in the distribution system, changes of technical losses are explored [7]. In this study, in Bogazici Electricity Distribution Inc. (BEDAS) at the same voltage level in power transformer A. Bozkurt is with Electrical Engineering Department, Yildiz Technical University, Istanbul, Turkey (corresponding author to provide phone: +90- 212-3835834; fax: +90-212-3835858, e-mail: abozkurt@yildiz.edu.tr). C. Kocatepe and R. Yumurtaci are with Electrical Engineering Department, Yildiz Technical University, Istanbul, Turkey (e-mail: kocatepe@yildiz.edu.tr, ryumur@yildiz.edu.tr). I. C. Tastan and G. Tulun are with Boğaziçi Electricity Distribution Inc, Istanbul, Turkey (e-mail: ibrahim.tastan@bedas.com.tr, gizem.tulun@bedas.com.tr). depends on different balanced loading conditions, no-load and load losses are explored. By CYME Power Engineering Software program and the handled region was modeled and analyzed. Then these transformers losses’s changes have been analyzed with different voltage level instead of the same loading conditions and using the distribution transformers which have same powers. II. TRANSFORMER LOSSES In General, balanced three-phase systems it is sufficient to examine the one phase equivalent circuit of a transformer. Equivalent circuit of one phase transformer is given in Fig. 1. Fig. 1 Equivalent circuit of one phase transformer Here, respectively R p and X p primary winding resistance and leakage of the reactants, R s ' and X s ' primer degrade winding resistance and leakage of reactants, R fe iron loss of resistance, X m reactance providing magnetization, I 0 no-load current, I m refers to the current of the magnetization [8]. Transformers total loss is expressed like, P TR = P 0 + P LL (1) where P 0 no-load loss, P LL states load loss. No-load losses, induced at the core of the transformer, depends the voltage and does not change depending on the load changes, are constant. Load losses can be expressed like, P LL = I 2 R + P EC + P OSL (2) This loss is the total of the “losses that belongs to a current based the joule (ohmic) losses (I 2 R), winding with eddy losses (P EC ) and leakage losses (P OSL )” [8]. Total cable losses (P L ) occurred in the distribution system are taken into account, the total loss in transformer and cable would be; P T = P TR + P L (3) found by this relation. Loss Analysis by Loading Conditions of Distribution Transformers A. Bozkurt, C. Kocatepe, R. Yumurtaci, Đ. C. Tastan, G. Tulun T World Academy of Science, Engineering and Technology International Journal of Energy and Power Engineering Vol:9, No:8, 2015 869 International Scholarly and Scientific Research & Innovation 9(8) 2015 scholar.waset.org/1307-6892/10002203 International Science Index, Energy and Power Engineering Vol:9, No:8, 2015 waset.org/Publication/10002203