Rotating electric machines with operating voltage greater than 12 [kV] are an integral part of the installed base of electric generators in different countries. These voltages incorporate new challenges to be solved in maintenance practices. One of the most important challenges is the identification of the condition of the stator winding. For many years, the most commonly used monitoring techniques in electrical generators were off-line insulation measurements, especially in direct current. More recently, the use of on-line insulation monitoring techniques has enabled problems to be detected in advance, such as partial discharge measurement. This article presents the measurement of on-line partial discharges, as a condition monitoring technique for high voltage electric generators. It is also used for risk assessment and decision support for corrective actions. In the case study, it was evidenced that periodic monitoring is key during the operating time of the evaluated generator unit, which can be extended to other generators. The monitoring of on-line partial discharges allowed to know its condition and evolution through the trend in time.Keywords: Partial discharge, electric generator, failure mode, predictive maintenance, void.