Abstract: The use of on-line partial discharge (PD) measurements as an indicator of stator winding insulation condition, is well known. Trending results from on-line PD measurements over time, often allows maintenance personnel to become aware of developing stator insulation problems in motors and generators, and take corrective measures before failure occurs. However, partial discharge measurements on operating rotating machines can be inﬂuenced by conditions such as humidity, temperature, terminal voltage, and load. Thus, to provide reliable data which can be trended, it is important to take readings under similar machine operating conditions. In remote plants, or on pump storage units which are frequently cycled, it can be both time consuming and costly to ensure that personnel are available to take PD readings under ideal conditions occur. This paper describes the development of a automatic partial discharge monitoring svstem which is permanently connected to relevant machine sensors and can be conﬁgured to collect PD data when suitable conditions are met. The operating principles of the system are described, and some results are presented from data collected to date on 30 hydrogenerators.