Basic Research On Acquisition Of AE Signal Of Cracks In Francis Turbine Runner Blades

The Francis turbine has high water-head and big power, which has been used in many large scale hydropower station. However, mass cracks frequently appeared in the runner blade of Francis turbine. As some datum shows: mass trans-cracks appeared in the runner blade of all Francis turbine after running a period of time, it has a major impact to the operation stability and safety of the hydroelectric power station.At present, it can only judge trans-cracks through the regular maintenance in the hydroelectric power station, which brought very big economic loss to the hydroelectric power station. In order to carry on the service to the runner blade of the Francis turbine according to the present situation, enhance the economic efficiency, guarantee the safety production of the hydroelectric power station, the on-line monitoring technique should be used in the runner blade of the Francis turbine. Using AE technique, it can be earlier and more efficiently to discovery the generation of cracks, to evaluate the position and the spreading of cracks and to master the position and the degree of damage, as well as, it can be more accurate to evaluate the running condition of the runner.In big background noise and strong electromagnetic interference environment, it is very difficult to receive the AE signal of the runner crack. In this paper, first, the detection system's request was analyzed, and the overall concept of detection system was designed. Some kind of domestic and foreign AE sensor were compared, the method of choosing and installing the AE sensor was confirmed, the selected AE sensor was proved correct by comparing experiment. The interference of AE monitor system was analyzed in the hardware and the software aspects.The metal crack acoustic emission signal was acqured in the laboratory condition; Three time-frequency analysis methods ware used to analyze and process the cracked metallic acoustic emission signal, and the method of analyzing the metal crack acoustic emission signal was determined.Because the online monitor system rotates along with the runner, the city electricity can not be used for it. So a small generating system was designed, and it can provide the monitor system with commercial power. It is proved the system working stability by the experiment . The research goal of generating system was achieved.