This paper proposes equivalent circuits and a method for the estimation of the peak transient voltages at generator terminals in wind turbines equipped with back-to-back converters. Equivalent circuits as well as a way of phase-to-phase and phase-to-ground voltages estimation in back-to-back converter are presented. Proposed theoretical background is well confirmed by small-scale measurements. It is shown and proven that phase-to-ground voltages represent a dominating threat for the wind turbine generators insulation. Copyright © 2014 John Wiley & Sons, Ltd.