Studies in modern high-speed traction need to develop detailed equations to formulate a complete electromechanical model that represents the dynamic coupling of electrical and mechanical phenomena. Starting from Lagrange and Park theories, and after recalling the general criteria for the setup of the two distinct mechanical and electrical subsystems, the new formalization of a complete dynamic model with specific reference to a train dedicated to high-speed services is hereby presented. Simulations are carried out with relation to two conditions of particular interest in the application side, i.e., the steady-state condition and the three-phase short-circuit fault at a speed of 100 km/h. Representative of the dynamics of each single component, the investigation in particular focuses on the transmission organs (rotor, Cardan joint, and gear case) and the relevant torques associated with the short-circuit dynamics.