Study On Runner Stress Measurement Of Large-Capacity Turbine

With the continual enlarged of dimension and capacity of hydroelectric units in recent years, the problem of vibration and runner cracks caused by turbine hydraulic stability had become more and more salient. The runner crack is a serious and kernel problem related to the unit safe and stability operation that had become a focus of commom concern in hydroelectric domain, and it is also one of the key tasks that should be urgently resolved during the hydropower project constructed. After investigated of overseas field dynamic stress measurement and equipment of turbine runner in recent years, in allusion to the specific requirement of dynamic stress measurement of turbine runner, the onboard runner dynamic stress measurement system, which is advanced in the world and can independently run without PC, had be integrated and developed in the study. According to the characteristics of hydropower unit, the reasonable methods of measurement and data analysis are presented, including the sensors selection, location, and installation, reasonable sampling rate, sampling time, and analysis methods etc. In order to solve the contradiction of frequency resolution and time domain signal precision during turbine natural frequency tests, the signal sampling and frequency response function with varying time base (VTB) are put forward, namely, selected higher sampling rate for excitation force sampling in order to improve its time domain signal precision, and selected lower sampling rate for vibration response measurement in order to ensure the frequency resolution of response signal. In addition, aimed at the problem of runner crack, the runner dynamic stress and unit stability measurement of HUANENG XUCUN and FUJIAN MIANHUATAN hydropower station are carried out, including runner natural frequency measurement, runner blade strain gauge measurement, pressure fluctuation, unit vibration and shaft displacement measurement etc. The level of static and dynamic stresses on runner blade during the different loads operating condition including the transient operating condition such as unit start up and coast down and the correlativity between the dynamic stresses and pressure fluctuation are analyzed, the cause of runner blade cracks are researched according to the test results. Finally, the method of runner damage accumulation evaluation and the reliability evaluate standard of turbine is discussed. Runner dynamic stress measurement of large-capacity turbine is an important content of hydropower project safeguard study, which is very significant in analysis and solution the problem of large-capacity units safe and stability operation. The research achievements in this paper could be offered the necessary means for analyzing and studying the runner crack problem of large-capacity units, and it is also a highly valuable information to deepen the study for turbine safe and and stability operation.