In this scientific study, an analysis of the modernization of the digital protection of AC traction substation electrical equipment in operation, in particular power transformers, the implementation of the basic provisions for the implementation of digital protection of power transformers, finding algorithms for the implementation of both measuring and logic elements of digital protection, mathematical models of digital protection of power transformers are obtained, a method for blocking current protection is implemented, a method is selected finding the setpoints of the stage, obtaining differential protection, the schemes of secondary switching of digital protection are considered, the results of the scientific research carried out in the microprocessor terminal of protection of power transformers.