A water turbine is a machine that converts the potential energy of water into mechanical energy. Using this machine to drive a generator, the water energy can be converted into
Electricity This is the hydro-generator set.
Modern hydraulic turbines can be divided into two categories according to the principle of water flow and structural characteristics.
Another type of turbine that utilizes both the kinetic energy and potential energy of water is called an impact turbine.
Counterattack
The water drawn from the upstream reservoir first flows to the water diversion chamber (volute), and then flows into the curved channel of the runner blade through the guide vane.
The water flow produces a reaction force on the blades, which makes the impeller rotate. At this time, the water energy is converted into mechanical energy, and the water flowing out of the runner is discharged through the draft tube.
Downstream.
The impact turbine mainly includes Francis flow, oblique flow and axial flow. The main difference is that the runner structure is different.
(1) Francis runner is generally composed of 12-20 streamlined twisted blades and main components such as wheel crown and lower ring.
Inflow and axial outflow, this type of turbine has a wide range of applicable water heads, small volume and low cost, and is widely used in high water heads.
Axial flow is divided into propeller type and rotary type. The former has a fixed blade, while the latter has a rotating blade. Axial flow runner is generally composed of 3-8 blades, runner body, drain cone and other main components. The water passing capacity of this kind of turbine is larger than that of Francis flow. For the paddle turbine. Because the blade can change its position with the load, it has high efficiency in the range of large load change. The anti-cavitation performance and the strength of the turbine are worse than those of the mixed-flow turbine, and the structure is also more complicated. Generally, it is suitable for the low and medium water head range of 10.
(2) The function of the water diversion chamber is to make the water flow evenly into the water guiding mechanism, reduce the energy loss of the water guiding mechanism, and improve the water wheel.
machine efficiency. For large and medium-sized turbines with a water head above, a metal volute with a circular section is often used.
(3) The water guide mechanism is generally arranged evenly around the runner, with a certain number of streamlined guide vanes and their rotating mechanisms, etc.
The function of the composition is to guide the water flow into the runner evenly, and by adjusting the opening of the guide vane, to change the overflow of the turbine to suit the
The requirements of the generator load adjustment and change can also play the role of sealing water when all of them are closed.
(4) Draft pipe: Since some of the remaining energy in the water flow at the outlet of the runner is not used, the function of the draft pipe is to recover the
Part of the energy and drains the water downstream. Small turbines generally use straight-cone draft tubes, which have high efficiency, but large and medium-sized turbines are
The water pipes cannot be dug very deep, so elbow-bend draft pipes are used.
In addition, there are tubular turbines, oblique flow turbines, reversible pump turbines, etc. in the impact turbine.
Impact turbine:
This type of turbine uses the impact force of high-speed water flow to rotate the turbine, and the most common is the bucket type.
Bucket turbines are generally used in the above high-head hydropower plants. Its working parts mainly include aqueducts, nozzles and sprays.
Needle, water wheel and volute, etc., are equipped with many solid spoon-shaped water buckets on the outer edge of the water wheel. The efficiency of this turbine varies with load
The change is small, but the water passing capacity is limited by the nozzle, which is much smaller than the radial axial flow. In order to improve the water passing capacity, increase the output and
To improve the efficiency, the large-scale water bucket turbine has been changed from a horizontal axis to a vertical axis, and developed from a single nozzle to a multi-nozzle.
3. Introduction to the structure of the reaction turbine
The buried part, including the volute, the seat ring, the draft tube, etc., are all buried in the concrete foundation. It is part of the water diversion and overflow parts of the unit.
Volute
The volute is divided into a concrete volute and a metal volute. The units with a water head within 40 meters mostly use a concrete volute. For turbines with a water head greater than 40 meters, metal volutes are generally used due to the need for strength. The metal volute has the advantages of high strength, convenient processing, simple civil construction and easy connection with the water diversion penstock of the power station.
There are two types of metal volutes, welded and cast.
For large and medium-sized impact turbines with a water head of about 40-200 meters, steel plate welded volutes are mostly used. For convenience of welding, the volute is often divided into several conical sections, each section is circular, and the tail section of the volute is due to The section becomes smaller, and it is changed into an oval shape for welding with the seat ring. Each conical segment is roll formed by a plate rolling machine.
In small Francis turbines, cast iron volutes that are cast as a whole are often used. For high-head and large-capacity turbines, a cast steel volute is usually used, and the volute and the seat ring are cast into one.
The lowest part of the volute is equipped with a drain valve to drain the accumulated water during maintenance.
Seat ring
The seat ring is the basic part of the impact turbine. In addition to bearing the water pressure, it also bears the weight of the entire unit and the concrete of the unit section, so it requires sufficient strength and rigidity. The basic mechanism of the seat ring consists of an upper ring, a lower ring and a fixed guide vane. The fixed guide vane is the support seat ring, the strut that transmits the axial load, and the flow surface. At the same time, it is a main reference part in the assembly of the main components of the turbine, and it is one of the earliest installed parts. Therefore, it must have sufficient strength and stiffness, and at the same time, it should have good hydraulic performance.
The seat ring is both a load-bearing part and a flow-through part, so the flow-through surface has a streamlined shape to ensure minimal hydraulic loss.
The seat ring generally has three structural forms: single pillar shape, semi-integral shape, and integral shape. For Francis turbines, an integral structure seat ring is usually used.
Draft pipe and foundation ring
The draft tube is a part of the flow passage of the turbine, and there are two kinds of straight conical and curved. A curved draft tube is generally used in large and medium-sized turbines. The foundation ring is the basic part that connects the seat ring of the Francis turbine with the inlet section of the draft tube, and is embedded in the concrete. The lower ring of the runner rotates within it.
Water guide structure
The function of the water guide mechanism of the water turbine is to form and change the circulation volume of the water flow entering the runner. The rotary multi-guide vane control with good performance is adopted to ensure that the water flow enters uniformly along the circumference with a small energy loss under different flow rates. runner. Ensure that the turbine has good hydraulic characteristics, adjust the flow to change the output of the unit, seal the water flow and stop the rotation of the unit during normal and accident shutdown. Large and medium-sized water guiding mechanisms can be divided into cylindrical, conical (bulb-type and oblique-flow turbines) and radial (full-penetrating turbines) according to the axis position of the guide vanes. The water guide mechanism is mainly composed of guide vanes, guide vane operating mechanisms, annular components, shaft sleeves, seals and other components.
Guide vane device structure.
The annular components of the water guiding mechanism include a bottom ring, a top cover, a support cover, a control ring, a bearing bracket, a thrust bearing bracket, etc. They have complex forces and high manufacturing requirements.
Bottom ring
The bottom ring is a flat annular part fixed to the seat ring, most of which are cast-welded construction. Due to the limitation of transportation conditions in large units, it can be divided into two halves or a combination of more petals. For power stations with sediment wear, certain anti-wear measures are taken on the surface of the flow. At present, anti-wear plates are mainly installed on the end faces, and most of them use 0Cr13Ni5Mn stainless steel. If the bottom ring and the upper and lower end faces of the guide vane are sealed with rubber, there shall be a tail groove or a pressure plate type rubber seal groove on the bottom ring. Our factory mainly uses brass sealing platen. The guide vane shaft hole on the bottom ring should be concentric with the top cover. The top cover and the bottom ring are often used for the same boring of the medium and small units. The large units are now directly bored with a CNC boring machine in our factory.
Control loop
The control ring is an annular part that transmits the force of the relay and rotates the guide vane through the transmission mechanism.
Guide vane
At present, guide vanes often have two standard leaf shapes, symmetrical and asymmetrical. Symmetrical guide vanes are generally used in high specific speed axial flow turbines with incomplete volute wrap angle; asymmetric guide vanes are generally used in full wrap angle volutes and work with low specific speed axial flow with a large opening. turbines and high and medium specific speed Francis turbines. The (cylindrical) guide vanes are generally cast in whole, and cast-welded structures are also used in large units.
The guide vane is an important part of the water guide mechanism, which plays a key role in forming and changing the water circulation volume entering the runner. The guide vane is divided into two parts: the guide vane body and the guide vane shaft diameter. Generally, the whole casting is used, and large-scale units also use casting welding. The materials are generally ZG30 and ZG20MnSi. In order to ensure the flexible rotation of the guide vane, the upper, middle and lower shafts of the guide vane should be concentric, the radial swing should not be greater than half of the diameter tolerance of the central shaft, and the allowable error of the end face of the guide vane being not perpendicular to the axis should not exceed 0.15/1000. The profile of the flow surface of the guide vane directly affects the water circulation volume entering the runner. The head and tail of the guide vane are generally made of stainless steel to improve the cavitation resistance.
Guide vane sleeve and guide vane thrust device
The guide vane sleeve is a component that fixes the diameter of the central shaft on the guide vane, and its structure is related to the material, seal and the height of the top cover. It is mostly in the form of an integral cylinder, and in large units, it is mostly segmented, which has the advantage of adjusting the gap very well.
The guide vane thrust device prevents the guide vane from having upward buoyancy under the action of water pressure. When the guide vane exceeds the dead weight of the guide vane, the guide vane lifts upward, collides with the top cover and affects the force on the connecting rod. The thrust plate is generally aluminum bronze.
Guide vane seal
The guide vane has three sealing functions, one is to reduce energy loss, the other is to reduce air leakage during phase modulation operation, and the third is to reduce cavitation. Guide vane seals are divided into elevation and end seals.
There are seals in the middle and bottom of the shaft diameter of the guide vane. When the shaft diameter is sealed, the water pressure between the sealing ring and the shaft diameter of the guide vane is tightly sealed. Therefore, there are drainage holes in the sleeve. The seal of the lower shaft diameter is mainly to prevent the entry of sediment and the occurrence of shaft diameter wear.
There are many types of guide vane transmission mechanisms, and there are two commonly used ones. One is the fork head type, which has a good stress condition and is suitable for large and medium-sized units. One is the ear handle type, which is mainly characterized by a simple structure and is more suitable for small and medium-sized units.
The ear handle transmission mechanism is mainly composed of guide vane arm, connecting plate, split half key, shear pin, shaft sleeve, end cover, ear handle, rotary sleeve connecting rod pin, etc. The force is not good, but the structure is simple, so it is more suitable in small and medium units.
Fork drive mechanism
Fork head transmission mechanism is mainly composed of guide vane arm, connecting plate, fork head, fork head pin, connecting screw, nut, half key, shear pin, shaft sleeve, end cover and compensation ring, etc.
The guide vane arm and the guide vane are connected with a split key to directly transmit the operating torque. An end cover is installed on the guide vane arm, and the guide vane is suspended on the end cover with an adjusting screw. Due to the use of a split-half key, the guide vane moves up and down when adjusting the gap between the upper and lower end faces of the guide vane body, while the positions of other transmission parts are not affected. influences.
In the fork head transmission mechanism, the guide vane arm and the connecting plate are equipped with shear pins. If the guide vanes are stuck due to foreign objects, the operating force of the relevant transmission parts will increase sharply. When the stress increases to 1.5 times, the shear pins will be cut first. Protect other transmission parts from damage.
In addition, at the connection between the connecting plate or the control ring and the fork head, in order to keep the connecting screw horizontal, a compensation ring can be installed for adjustment. The threads at both ends of the connecting screw are left-handed and right-handed respectively, so that the length of the connecting rod and the opening of the guide vane can be adjusted during installation.
Rotating part
The rotating part is mainly composed of a runner, a main shaft, a bearing and a sealing device. The runner is assembled and welded by the upper crown, the lower ring and the blades. Most of the turbine main shafts are cast. There are many types of guide bearings. According to the operating conditions of the power station, there are several types of bearings such as water lubrication, thin oil lubrication and dry oil lubrication. Generally, the power station mostly adopts thin oil cylinder type or block bearing.
Francis runner
The Francis runner consists of an upper crown, blades and a lower ring. The upper crown is usually equipped with an anti-leakage ring to reduce water leakage loss, and a pressure-relief device to reduce axial water thrust. The lower ring is also equipped with an anti-leakage device.
Axial runner blades
The blade of the axial flow runner (the main component for converting energy) is composed of two parts: the body and the pivot. Cast separately, and combine with mechanical parts such as screws and pins after processing. (Generally, the diameter of the runner is more than 5 meters) The production is generally ZG30 and ZG20MnSi. The number of blades of the runner is generally 4, 5, 6, and 8.
Runner body
The runner body is equipped with all the blades and the operating mechanism, the upper part is connected with the main shaft, and the lower part is connected with the drain cone, which has a complex shape. Usually the runner body is made of ZG30 and ZG20MnSi. The shape is mostly spherical to reduce volume loss. The specific structure of the runner body depends on the arrangement position of the relay and the form of the operating mechanism. In its connection with the main shaft, the coupling screw only bears the axial force, and the torque is borne by the cylindrical pins distributed along the radial direction of the joint surface.
Operating mechanism
Straight linkage with operating frame:
1. When the blade angle is in the middle position, the arm is horizontal and the connecting rod is vertical.
2. The rotating arm and the blade use cylindrical pins to transmit the torque, and the radial position is positioned by the snap ring.
3. The connecting rod is divided into inner and outer connecting rods, and the force is evenly distributed.
4. There is an ear handle on the operation frame, which is convenient for adjustment during assembly. The matching end face of the ear handle and the operation frame is limited by a limit pin to prevent the connecting rod from being stuck when the ear handle is fixed.
5. The operation frame adopts the “I” shape. Most of them are used in small and medium-sized units with 4 to 6 blades.
Straight linkage mechanism without operating frame: 1. The operating frame is canceled, and the connecting rod and the rotating arm are directly driven by the relay piston. in large units.
Oblique linkage mechanism with operating frame: 1. When the blade rotation angle is in the middle position, the swivel arm and the connecting rod have a large inclination angle. 2. The stroke of the relay is increased, and in the runner with more blades.
Runner room
The runner chamber is a global steel plate welded structure, and the cavitation-prone parts in the middle are made of stainless steel to improve the cavitation resistance. The runner chamber has sufficient rigidity to meet the requirement of uniform clearance between the runner blades and the runner chamber when the unit is running. Our factory has formed a complete processing method in the manufacturing process: A. CNC vertical lathe processing. B, profiling method processing. The straight cone section of the draft tube is lined with steel plates, formed in the factory, and assembled on site.
Post time: Sep-26-2022
