At present, there is a general trend towards digitalization in electric power systems, a change in the principles of electricity and capacity market mechanisms and increasing penetration of low-carbon renewable energy sources. Such a transformation of power systems will lead to a decrease in the total inertia, stability margins and an increase in the irregular component of active power flows. Features of power systems after the transformation completion will be associated with an increase in the likelihood of the occurrence of non-design modes and a decrease of the emergency control laws correctness. These changes will require correction in traditional emergency control operation principle in terms of the fault detector speed. As a result, the importance of power system emergency control problem during the electromechanical transient process is increasing. Such an emergency control principle has a high requirement for the speed and accuracy of electric mode parameter estimation. The work is devoted to the study of electrical mode parameters express-estimation characteristics and the possibility of its applying in stationary conditions and the dynamic change of the input signal. The method of electrical mode parameters express-estimation is based on the signal approximation using a multi-parameter model, which is highly stable and reliable. The mathematically modeled signals in Matlab/Simulink were used as the initial data. A single-machine model of a test power system was used for the case study, taking into account the models of a synchronous generator, a steam turbine, an automatic voltage regulator, a turbine speed regulator, power lines and infinite bus. Because of the experiments, acceptable characteristics of express-method of electric mode parameters evaluation were obtained.