The hydroelectric generator is an asset of central importance in hydroelectric plants. Permanent damage, operation accidents or just non-planned halts caused by failure in that equipment have high costs to the power generation company. Regular assessment of the hydroelectric generator condition, which is strongly related to the quality of its isolation system, allows minimization of such losses. Therefore, following the machine condition provides the means to organize scheduled actions by maintenance teams.
During operation, intense electric and magnetic fields inside the generator cause discharges (called partial discharges, PD) to happen. Moreover, aging and mechanical vibration deteriorate the isolation system, increasing even more the intensity of PD. Thus, the integrity of the isolation system can be inferred by monitoring and analysing PD. Such an approach reduces the frequency of direct inspection of the machine isolation system, which is time and money consuming.
The process of monitoring PD comprises mainly two phases: measurement and interpretation. The first step includes procedures and apparatus to effectively measure partial discharge signals. To succeed in this task, in-depth knowledge on partial discharge phenomenon, principles of electrical machines and signal processing techniques is critical. In turn, interpretation aims at classification of fault patterns and pinpointing the location of PD. Feature extraction and machine learning techniques are of particular interest here.
In this book we discuss a rather broad field of PD problems in high voltage generators. The book addresses the measurement, pinpointing and interpretation of PD in hydrogenerators, covering key topics such as physics of the partial discharge phenomenon, types of defects and corresponding PD patterns, sensors and acquisition procedures, applied signal processing techniques, automatic classification of discharge types, and correlation between partial discharge occurrence and ozone generation.
In the introduction, we consider the main types of failures in the high voltage rotating machines, and, principally, in the electrical insulation of the stator windings providing description of terms and concepts of PD. Further, a short description of electromagnetic sensors for PD detection is given. Then, signal processing techniques and an overview of PD online monitoring systems are presented. Thus, we give below a brief review of state of the art of the PD problems in high voltage generators.
