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Some Suggestions On Improving Francis Turbine Stability
Sep 26, 2017

1. Reasonable choice of turbine range of Hmax / Hmin

Francis turbine is a fixed blade hydraulic machinery, the design and selection of the runner are to ensure that the design of the head at a relatively wide stable operation area, in order to reduce the vibration and cracks on the mixed flow Francis Turbine hazards, requiring large mixed flow Turbine head should not be too large. It is suggested that the ratio of the maximum head of the Francis Turbine and the design head should be controlled below 1.2, and the ratio of the maximum head to the minimum head should be controlled within 1.5.

2. Ensure the scientific and rationality of hydraulic design

First, a reasonable choice of Francis Turbine than the speed. Excessive than the speed, will weaken the strength of the turbine, affecting the cavitation and anti-sediment wear performance, the stability of the turbine. When the turbine stability index can not be met, a lower specific speed should be used and a lower guide vane relative height b should be selected. , Reduce the unit flow Q1. The second is to reduce the pressure of the draft tube pressure, control the occurrence of leaf vortex. Ye Da vortex from the occurrence to the development of a process, in the runner model test should be noted that as far as possible leaves the vortex line excluded from the scope of operation. The pressure fluctuation value of the draft pipe should be made according to the different head section and the different load section respectively.

The pressure fluctuation of the main operating area should be controlled below 3%; within the guaranteed operating range, the maximum value of the pressure pulse △ H / H (mixing) does not exceed 7% is not harmful to the stability of the unit; Of the other operating conditions pressure pulse value may be appropriate to relax. At the same time, to avoid the low load when the vortex frequency and the natural frequency of the draft tube resonance. Third, according to the characteristics of power plants, the correct design of the rotor type. The use of torsion blades or the use of large inlet diameter and small outlet diameter of the hydraulic design, the Francis Turbine can have a wide stable operation area; the use of long and short blades, but also to adapt to changes in the load of effective means; and leaves using Donalson type of water, To ensure the strength of the blade under the premise of the Carmen vortex excitation energy can be minimal.