Main Causes of Water Turbine Spill Cone Failure

What are the main reasons for the failure of hydraulic turbine drainage cones? Turbine drainage cones will not be treated in time if they fail. This will leave considerable safety hazards and severely affect the normal operation of the generator set. Therefore, this article briefly introduces the main reasons for the failure of the water discharge cone and provides power for the majority of power. Workers reference.

First, the operation mode is irrational. In the daily work, due to the rotating water flow at the outlet of the runner and the effects of off-flow vortex and cavitation, water pressure pulsation will be caused in the tail water pipe, especially in the tail water pipe. Afterwards, the vortex belt rotates within the tube at a frequency close to a fixed frequency, causing a low-frequency pressure pulsation in the water flow, thereby causing vibration of the draft tube wall, the runner, the water guiding mechanism, the volute, and the pressure piping. When its frequency is close to the natural vibration frequency of the generator or power system, resonance will occur, eventually resulting in loosening of the drain cone fixing bolts and cracking of the weld joint.

Second, the daily inspection is not perfect, the accuracy of the hydropower oscillation monitoring system is not enough, after the drainage cone falls off, in theory, the unit vibration should have a certain increase, but the unit vibration monitoring does not reflect, thus further expanding the accident.

Third, the design defect, the water leakage between the cone and the wheel body using ordinary Q235A steel bolt connection, the hole is drilled without further treatment, so that there may be a certain gap after the bolt tightening, so that the screw to withstand additional bending stress Due to insufficient strength, the bolt eventually breaks.

4. Disturbance of the water flow and the turbulence of the water flow in the draft tube after the discharge cone falls off are bound to result in an irregular, spiral-shaped eccentric vortex zone. Due to the uneven distribution of the pressure in the draft tube due to the detachment of the condensate cone, irregular pressure pulsation is formed on the wall of the draft tube or the bottom plate when the vortex belt rotates. When the drainage cone breaks off, under the action of the eccentric vortex belt and the water flow, it rotates and rushes toward the bottom plate of the draft tube. Under the impact of the drainage cone, the bottom plate of the draft tube is bound to be cracked. After the drainage cone fell off, the water at the outlet of the runner could not turn into axial flow and become disordered, which exacerbated the hydraulic pulsation and cavitation in the tail water flow channel, and also increased the impulse water hammer pressure.

V. Installation quality problems. After the bolts are tightened, they have not been subjected to measures such as retrofitting, retreating, and spot welding. At the same time, improper selection of welding materials, it can be seen from the cracked area of ​​the welding seam that the welding rod is a stainless steel rod, and the stainless steel rod Due to the different shrinkage coefficients after the welding of the runner (stainless steel) and the drainage cone (Q235A steel), the weld is subjected to local stress. When the pressure pulsation aggravates the resonance, the discharge cone fixing bolt loosens.

There are many reasons for the failure of the water turbine's water discharge cone in the power station. In the daily work, the electric power worker should do the appropriate equipment maintenance to ensure the normal operation of the generator set, and at the same time make a corresponding record, after the next failure. Corresponding references can be made to improve the speed of fault detection.