CALCULATION OF DISTRIBUTION TRANSFORMER LEAKAGE REACTANCE USING ENERGY TECHNIQUE A. Naderian-Jahromi, Jawad Faiz and Hossein Mohseni Department of Electrical Engineering University of Tehran, IRAN Naderiya@ece.ut.ac.ir Abstract Energy technique procedures for computing the leakage reactances in distribution transformers are presented. This method is very efficient compared with the use of flux element and image technique and is also remarkably accurate. Examples of calculated leakage inductances and the short circuit impedance are given for illustration. For validation, the results are compared with the results obtained using test. List of symbols: form solution often provides more insight about critical physical parameters than a computer-based numerical solution. λ Leakage flux N No. of turn of winding I current L mt Mean length of one turn of winding L c length of window of core d Width of winding s 1 Distance between core and LV windings In this paper a closed form solution technique applicable to the leakage reactance calculations for transformers is presented. Emphases is on the development of a simple method to characterize the leakage reactance of the transformers. Leakage reactance calculations play an important role in designing geometry of transformers. The design parameters my be varied as such that the required short circuit impedance is determined. A 2D representation proves to be satisfactory in determining the leakage reactance. Final expressions are developed on a per-unit-of-length basis for the third dimension. Certain assumptions have been made in this calculation. End effects introduced by the terminations in 3D configurations are not evaluated here. s,s 2 Distance between LV and HV windings r ave1 , r ave2 Mean radius of HV and LV winding respectively X Reactance of transformer f frequency of current of windings W Electromagnetic energy stored in active part L eq Equivalent inductance of transformer H x Magnetic field intensity in a distance x of first layer of primary winding I. INTRODUCTION Determination of transformer leakage reactance using magnetic cores has long been an area of interest to engineers involved the design of power and distribution transformers. This is required for predicting the performance of transformers before actual assembly of the transformers. A method has been presented [1] for estimating the leakage reactance by flux tube in order to include in an electric circuit model of transformer. Computer-based numerical solution techniques using finite elements analysis, boundary element method and boundary-integral method are accurate and form an important part of the design procedures but require rather elaborate computer resources and a somewhat lengthy setup before a solution can be obtained. Also a closed- There are different techniques for the leakage- reactance evaluation in transformer. The most common technique is the use of the flux leakage elements and estimation of the flux in different parts of the transformer [1-6]. The images technique can be also used. The base of this method is considering the image of every turn of the winding where the magnetic potential vector [7,8] is employed to compute the mutual and leakage inductances. Although the technique is effective, the computation result depends on the current of the image conductor [7]. This paper presents a novel technique for calculation of the leakage inductance in different parts of the transformer using the electromagnetic stored energy.