Technical condition of large power transformers has large impact on reliability of a power system since they are the connection points for generators and distribution system. Power transformers can experience various faults that can disrupt their reliable operation such as mechanical defects caused by magnetostriction or electrodynamic forces. Magnetostriction is a phenomenon occurring in transformer core in normal operation mode, yet in time it can cause the delamination of magnetic core resulting in higher vibrations and noise. Mechanical defects are complicated to detect with indirect measurements. Therefore, modelling elastic deformations of the magnetic core caused by magnetostriction combined with vibration measurements on the tank surface would create a more beneficial approach to mechanical defect diagnosis. The aim of this paper is to create model for magnetic core elastic deformation simulation and provide a case study. Authors developed this model in Matlab and COMSOL software.