This paper describes methods to monitor partial discharges (PDs) of important power plant components, such as generator stator windings, generator circuit-breaker, and step-up transformer. Two methods have been evaluated under practical conditions, using various sensors: (i) time-domain measurements followed by signal-processing to discriminate between PDs and interference, and (ii) a tunable narrow-bandwidth filter which can be tuned to a frequency where PDs are strong and interference is weak. For several generators, abnormal PD activity was observed. In all cases, the source of these PDs could be located, by means of the transit-time between various sensors. Examples of identified abnormal discharge activity are: (i) discharge activity between phase separations of a statorwinding, (ii) sparking inside a step-up transformer, and (iii) large PDs in a generator circuit-breaker. Copyright © 2006 John Wiley & Sons, Ltd.