The article presents experimental and theoretical studies concerning the possibility of using a controlled hydrodynamic clutch in a wind power plant’s drive system. The hydrodynamic clutch is controlled by changing the distance between the hydrodynamic clutch rotors. The control system is supposed to maintain a constant angular velocity of the electric generator shaft. The considered method of control has not been used so far in power plant's drive systems. The advantages of using a controlled hydrodynamic clutch is simple structure, high durability and low weight of the entire drive system. The equations of the mathematical model for the drive system are formulated on the basis of: the balance of torques and the equations of the hydrodynamic clutch with retractable rotors. The equations are based on the one-dimensional flow of the working fluid along the mean line of the stream. The model calculations are conducted numerically. In order to be able to determine the coefficients of the mathematical model, experimental research is conducted on a test bench designed specifically for this purpose. The research determines how the rotation direction and size of the gap between rotors influences the torque transferred by the hydrodynamic clutch, for selected values of the clutch’s filling degree and the working fluid’s temperature. On the basis of the model calculations results it was determined that a hydrodynamic clutch controlled by increasing the distance between rotors may be successfully used in drive systems of wind power plants to maintain a constant angular velocity of the electric generator shaft.