Synchronous generator is the most common generator type used in power systems. Modern control and diagnostic systems require information of the excitation winding temperature. This winding is located on the rotor and therefore conventional temperature measurement requires slip-rings or wireless data transfer. IR thermography can be used to obtain average temperature of the surface of excitation winding while rotating and 3D FEM models can give temperature distribution. Laboratory model included synchronous hydro-generator (400 kW), IR thermometer and Bluetooth ® wireless temperature acquisition system with temperature sensors placed on rotor. Two measurement systems were compared and experimental results are presented.