Non-stationary processes in circuit of excitement or a stator of asynchronized hydrogenerator as the reasons causing an overvoltage on the distributed windings of excitement are considered. Analytical calculation of the overvoltage in system of imitating modeling of Matlab/Simulink is made. A comparative analysis of the results of the calculation of maximum voltage on the chosen sections of a rotor for the sudden short circuit, received by an analytical method and by means of modeling is carried out. Recommendations about a question of restriction of dynamic overvoltage are given.