“…Well known examples of the hidden oscillations are nested limit cycles in 16th Hilbert problem (see, e.g., [20,28]) and counterexamples to the Aizerman and Kalman conjectures on the absolute stability of nonlinear control systems [24,27,7,28]. Hidden oscillations in the models of electrical machines are discussed, e.g., in [16,15,28,29,14] the trajectory of the system after transient processes is attracted to the stable limit cycle (Figs. 14,15), i.e., vibrations are arisen in the hydropower units.…”