The paper presents the method of working with the DIGSI 5 software package, with the use of a numerical relay device type 7UT85 from the company Siemens, when creating a project for adjusting the differential protection of a two-winding power transformer. In addition to differential protection, low-adjustable and high-adjustable overcurrent protection and thermal protection of the transformer have been implemented. When adjusting the differential protection parameters, additional stabilization and cross-blocking functions were used, as well as the blocking of action when engaging in idling (detection of the 2nd harmonic) and overexcitation of the transformer (detection of higher harmonics). The work with the DIGSI 5 program when connecting the relay device to current transformers, as well as the method of implementing the signal and switching matrix, is presented in detail. Input data on the specific two-winding power transformer from the distribution network were used.