To study the effect of voltage sag on the mechanical vibration of a wind turbine structure, a detailed model that considers the combined electrical, mechanical and aerodynamic aspects of the wind turbine must be used. A drawback of many previously published works in the area of wind turbine simulation is that they study either a very simple mechanical model with a detailed electrical model or vice versa. Therefore, the interactions between electrical and mechanical components are not accurately taken into account. In this paper, three simulation programs—TurbSim, FAST and Simulink—are used to model the wind, mechanical and electrical parts of a wind turbine and its controllers in detail. Simulation results obtained from the model are used to observe the interaction of all three factors affecting the operation of a wind turbine system. The focus of the paper is on the effect of the voltage sag on tower vibration, considering different power system characteristics (i.e. short circuit level and X/R ratio), mechanical parameter (i.e. mechanical tower damping) and wind turbine operating conditions. Copyright © 2008 John Wiley & Sons, Ltd.