Countermeasures for Increasing the Stability of Francis Turbines

摘要

The problems of vibration and blade cracks on Francis turbines have had serious impact on the stable operation, which consequently affects the economic benefits. As turbine size and capacity increasing, the issue of the stability becomes even more acute and tougher. This article makes an exploration on the countermeasures for increasing the stability of Francis turbines in five aspects. First, an appropriate head variation range should be selected, the ratio between the maximum head and the design head should be controlled under 1.2. Second, an excellent hydraulic design is required, it is unfavorable to set the specific speed on the high side, and a smaller value for the relative height of the guide vane should be appropriate, which will reduce the unit flow and decrease the pressure pulsation at the draft tube, so as to exclude the blade passage vortexes from the operating range, and to avoid the resonance caused by the vortex band frequencies during the low-load modes. Third, to optimize the runner mechanical design and the runner rigidity and strength should be strengthen, and to reduce the Max. local stress of runner. Forth, to increase the manufacturing quality, adopt the VOD vacuum deoxygenating stainless steel refining method, runner to be machined by NC machining, try possible means to adopt the integral runner, improve the welding technique, and to reduce the residual stress. Fifth, taking scientific management and operating the units according to the specifications and regulations, to avoid operating in the vibrating zones, and make a quick crossing over the unstable zones.