Temperature rise is one of the limiting factors in generator design. Bearings and windings failure are the two most prominent cause of generator failure in the wind turbine application. The generator is mostly converter-fed in the wind turbine application, and operation with converter brings specific challenges. Insulation of generator system should be designed in such a way to withstand these challenges. Two immediate problems with converter-fed wind generators are winding temperature rise due to harmonic losses and voltage peaks. Voltage peaks generated by converter can create a winding hotspot and eventually destroy the insulation system of generator winding, which leads to reducing the lifetime of the insulation system. Turbine availability study from a commercial point of view is presented. For selecting the winding insulation system, it is essential to know the environment generator is going to operate. Specific voltage peaks from different converter systems can damage windings insulation. Damage insulation brings the downtime of the turbine, which affects the LCOE and AEP of the wind turbine. The electrical voltage between motor terminals and ground can be generated due to the different converter output circuit, longer feeder cables (when converter being placed on the basement and not in the nacelle) on the and unfavorable grounding conditions. Paper discusses voltage peaks due to operation with converter and make a recommendation for the winding insulation system, for a particular case. A better selection procedure for a generator winding insulation system is recommended.