Abstract. The modern electric power systems (EPS) are large, multiparameter, stiff, non-linear and dynamic systems. Control and protection of such systems are extremely complex and urgent tasks. It is confirmed by the statistic of accidents in EPS: about 25 % of severe accidents are caused by wrong actions of relay protection (RP) and automation of EPS. The 30 % of these incorrect actions are caused by inadequate setting. The goal of this work is to solve the problem of RPs setting through the usage of detailed models that take into account specific features of the RPs and processes in transducers. The paper focused on the solution of the problem for the transformer differential protection (TDP), based on the impulsetime principle -DZT-21/DZT-23. The presented research results confirm the effectiveness of the usage of the appropriate mathematical models for the problem solution. The presented fragments are a part of a single project aimed at the problem' solution for all the RPs devices.

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Abstract. Numerical relay protection devices (NRP) are a promising area for the development of protection equipment for electric power systems. For its development, research and, in some cases, setting mathematical models are used. At the same time, the converting part of the NRP, which realizes the analog-to-digital conversion (ADC) of the analog input signal to the digital one, with which the microprocessor of the NRP works directly, is often ignored in models. The purpose of this work is to study the characteristics and parameters of the ADC, as well as to evaluate its impact on the operation of the ADC itself and need to take into account those or other characteristics in the simulation. To develop the ADC model, the C programming language was used. The ADC model is takes into account the cutoff frequency of the analog signal, sampling period, and number of samples required. The characteristics and parameters of the ADC are studied, their effect on the operation of the ADC is estimated. The result of this study -the ADC must be modeled as completely as possible, since its operation depends on the correct functioning of the NRP algorithm.