**Abstract**

In the analysis of transient electromechanical and electromagnetic transients one of the most important things is the selection of the synchronous generator with adequate mathematical model. In general, the modeling approaches are divided into two types. For a detailed analysis of the auto-matic generator control system, the research group created a detailed mathematical model that takes into account all the control circuits, their characteristics and physical properties of the machine. However, this approach is justified for the detailed study of a single machine. In the analysis of complex industrial systems modes excessive detailed description of processes sometimes has no significance for the study network modes but significantly complicates the simulation process and increases the duration of the calculation. In order to analyze the long transient processes in the electromechanical generator, it is recommended to set simplistic transitional constant values. However, this approach can lead to calculation errors. One reason for this is the change in internal resistance of the generator because the change of currents and voltages cause a change in the saturation level of the machine including its individual parts. Thus, when calculating the electromechanical and electromagnetic processes synchronous generator, we should take into account the external characteristics of the excitation controller and velocity with the corresponding time constants but also the change of contact resistances affecting the currents in emergency and after emergency mode, and also the magnitude of rotating electromagnetic moments determining the balance of power on the shaft. Accounting for changes in excess transient, transient and synchronous inductive resistance in view of the machine in saturation mode, short circuit is expected to make in the development of software system to calculate and analyze transient electromechanical modes. Calculations have shown that taking into account the transient changes in resistance has a significant effect on the currents at the moment fault current generator and synchronization with the network. The developed mathematical model makes it possible to correctly detect the currents during long short circuits and disconnections in a complex configuration networks.

**Keywords**

Contact resistance, industrial synchronous generator, short-circuit, transient electromechanical mode, software, automatic excitation regulator, saturation of the synchronous machine, electric remoteness, mathematical model.

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