By simulating the appropriate power distribution network operating points the analysis of their exploitationcapabilities is significantly improved. Beside the methodology used in the analyses, the greatest impact to thequality of results obtained has the accuracy of the model itself, or in other words it is necessary to respect thereal driving conditions of each element being modeled.Since extreme operating conditions such as minimum and maximum network load are usually modeled, whencalculating power flow and voltage distributon across the network, it is important to take into account theambient temperature influence and the operating temperature of the network elements. For transmission lines,ambient temperature and load heating are usually taken into account by calculating electrical resistance for eachtype of conductor. Due to the complexity of the construction and non-linearity of the processes that take placeduring the heating and cooling of the transformer windings, it is necessary to define the appropriate practicalthermal model for power transformers.Since the most of the power transformer stations in the distribution network are integrated into the somedistributed remote measurement and control system, electrical values sampled after fifteen minute interval aswell as the ambient temperature, transformer windings and oil temperature are readily available. Using these dataand developed software tools to identify the process, a simple practical thermal models of power transformerscan be identifed, without performing a detailed power transformer nonlinear thermal analysis.For the purpose of analysis whose results are presented in this paper, the ARX mathematical model and softwaretool for identification of the processes of the software package MATLAB are used.

XI CONFERENCE ON ELECTRICITY DISTRIBUTIONwith regional participationSerbia, Kopaonik, Grand HotelSeptember 24-28, 2018 Izdavač / Publisher: Nacionalni komitetCIRED SrbijaCIRED Liaison Committee of SerbiaElektrovojvodina, 21000 Novi SadBulevar Oslobođenja 100, Tel/Fax: +381(0)21 528556e-mail: cired.serbia@ev.rs, web: www.ciredserbia.org.rsGlavni i odgovorni urednik: dr Zoran SIMENDIĆEditor in ChiefPriprema i tehnička obrada: BBN Congress Management, Deligradska 9, 11000 BeogradPrepress Tel/Fax: +381(0)11 3629405, 3629402, 2682318e-mail: bbn@bbn.co.rs, web: www.bbn.co.rsDizajn korica / Cover Design: Sanja MiloševićŠtampa / Printing Office: Štamparija RadunićTiraž / Print run: 550