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Recently, the importance of supplying the reliable electric power is increasing. Insulation deterioration of stator winding is a major cause of faults in high voltage generators. Online partial discharge detection is useful technique to diagnose high voltage generators. Capacitive couplers have been the most widely used for on-line partial discharge detection in high voltage generators. However, interpretation of its result in time domain is very complex because of the mixed results with PD(Partial Discharges) and noises. In this paper, the partial discharge signals and noises were detected using 13[kV] class capacitive couplers at generator stator windings of hydro generators. Characteristics of the partial discharge signals and noises were analyzed. In addition, this paper presents system noise signals caused by sparks from slip rings, power tool operations, transformers and switchgears.