Advances in online monitoring and localization of partial discharges in large rotating machines

Some of the problems facing partial discharge (PD) measurements in rotating machines, especially during online measurements are: i) calibration of the measurements; ii) high noise levels interfering with both the measurement system and the winding under the test; as well as iii) attenuation and distortion of PD signals during transmission from the source point to the winding terminals. This paper presents a new technique and a measuring system for online PD monitoring of large rotating machines, developed by the authors. With this technique, the above mentioned problems are improved considerably. PD detection is implemented for every stator coil and the coil that PD comes from can also be identified. Inductive coils are used for decoupling of PD pulses and processing of the detected signals is in accordance with the developed technique, denoted "Intech". Remote monitoring and navigation via a telephone link is one of the system features. The system was tested on both hydro and turbo generators with good results. The detection sensitivity of the system for the conventional machines is about 1 nC under operating condition.