Tail water system of water turbine and pressure regulating method

Abstract

The invention discloses a tail water system of a water turbine and a pressure regulating method. The tail water system comprises a tail water pipe, and a tail water air supply system is arranged on the tail water pipe to replace a surge shaft to form the water turbine tail water system. The tail water air supply system comprises a forced air supply device. According to the pressure regulating method, when the working condition of great load reduction or load shedding occurs in the water turbine, the tail water gas supplementing system connected with the tail water pipe is started, and gas is supplemented into the tail water pipe through the tail water gas supplementing system. The water hammer and reverse water hammer phenomena in the draft tube can be effectively restrained, complex civil engineering is not needed, pressure regulation and control are directly achieved through combination of a pipeline and a valve, and the construction cost and layout difficulty of a power station are remarkably reduced; accumulated water in a connecting pipeline can be emptied within several seconds, negative pressure rise can be rapidly restrained, part damage caused by response lag of a traditional surge shaft is avoided, the natural air supplementing device supplements air passively through a mechanical structure, extra energy consumption is not needed, balance of emergency regulation and energy-saving operation is achieved, and water turbine parts are effectively protected against damage.

Description

TECHNICAL FIELD

[0001] The present application relates to a water turbine tail water system and a pressure regulating method, and belongs to the technical field of water turbines and pumped storage. BACKGROUND

[0002] In a hydroelectric generator station and a pumped storage power station, water pressure stability and water pressure peak value within a safe range are crucial to unit stability and safety. In the past three decades, water turbine large shaft center hole air supplement technology has emerged, which supplements about 1-3% of the rated flow of natural air to the tail water through the water turbine large shaft center hole, effectively reducing pressure pulsation and improving power stability. For example, for a unit in Baihetan, by increasing the supplement amount to the center hole, the power fluctuation problem is solved. However, when the unit is in sudden operating conditions such as load reduction and emergency shutdown, the flow rapidly decreases from 100% to zero, and only relying on the water turbine center hole to supplement about 1-3% of the rated flow of natural air will still form an excessively high negative pressure in a short time due to water flow inertia, as shown in FIG. 1. Figure 3

[0003] To avoid the extrusion damage of the negative pressure to the key components such as the water turbine drainage cone, the pipeline interface and the sealing element, in a long tail water system of a Francis turbine, the existing technology generally adopts a solution of setting a surge tank. The traditional surge tank balances the pressure between the water body stored inside and the water flow in the tail water pipe, buffers the pressure fluctuation caused by water hammer impact, suppresses the negative pressure exceeding the standard, and thus guarantees the unit operation safety. However, this solution has significant limitations: from the construction cost, the surge tank needs to rely on specific terrain to excavate or cast large concrete structures, involving complex geological survey, impermeable structure design and deep foundation pit construction control, especially in power stations in complex terrains such as mountains and valleys, the excavation is difficult and the construction material consumption is large, resulting in a high proportion of the construction cost of a single surge tank in the total investment of the power station; from the engineering cycle, the construction process of the surge tank is complicated, from foundation pit excavation, steel bar binding to concrete pouring and water testing and debugging, which needs to consume months or even years of time, seriously restricting the overall construction progress of the power station; in addition, the surge tank occupies a large space, which will limit the flexibility of the overall layout of the power station, especially in power stations with narrow sites, it is difficult to adapt to the compact unit layout requirements. With the expansion of hydropower projects to high parameters and complex terrain areas, the cost and construction bottlenecks of the traditional surge tank solution are increasingly prominent.

[0004] ​Besides the situations mentioned above, the tailrace system of low-head axial-flow turbines is often short and straight, with relatively low water inertia. The negative pressure amplitude generated by backwater hammer is not large, and there is no need to use a surge tank to buffer water pressure changes. During normal operation, the axial thrust of the water flow on the runner is downward, which is balanced with the weight of the runner, main shaft, and other rotating components, as well as some electromagnetic axial loads. Due to the low head of the axial-flow propeller, the axial projected area of ​​the blades is large. Although the water hammer amplitude is not large, it accounts for a large proportion compared with the head. Under the action of the huge axial projected area of ​​the blades, it will also generate a large upward thrust. When this upward thrust exceeds the total weight of the rotating parts of the unit and the downward constraint force provided by bearings and other components, it will lift the runner, main shaft, and even some rotating components upward, resulting in turbine lift-up. Usually, the turbine lift-up problem can be solved by installing a vacuum breaker valve on the turbine top cover to allow natural air replenishment. However, for some models, natural air replenishment alone is not enough. For example, at the Luodong Hydropower Station in Guangxi, although there is a vacuum breaker valve, turbine lift-up of more than 10 mm has occurred multiple times. Not only will it disrupt the normal clearances between unit components, but it may also damage critical components such as the main shaft seal and thrust bearing. In severe cases, it can lead to structural deformation of the unit and threaten overall operational safety.

[0005] Therefore, the industry urgently needs an effective water hammer or reverse water hammer control scheme that can reduce tailrace abnormalities, replace surge tanks, simplify tailrace system structure, and reduce construction costs, in order to adapt to the unit safety requirements under different operating conditions, solve the pain points of high cost, difficult construction, and long cycle in existing technologies, and promote the improvement of the economy and efficiency of hydropower engineering construction. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned problems by providing a turbine tailrace system and pressure regulation method that can reduce power plant construction costs. Under conditions of significant load reduction or load shedding, the tailrace aeration device can replenish air into the tailrace, thereby reducing or even eliminating the damage to the unit caused by water hammer or back water hammer.

[0007] The technical solution adopted in this invention is as follows: A turbine tailrace system includes a tailrace pipe, on which a tailrace aeration system is provided to replace a surge tank in the turbine tailrace system; the tailrace aeration system includes a forced aeration device.

[0008] Alternatively, the tailwater aeration system may also include a natural aeration device.

[0009] Alternatively, the natural aeration device includes a first connecting pipe connected to the tailwater pipe, the other end of the first connecting pipe being connected to the atmosphere, and a vacuum breaking valve being provided on the first connecting pipe to realize the connection and disconnection between the connecting pipe and the tailwater pipe.

[0010] Alternatively, the vacuum breaking valve is a float ball type or a spring type.

[0011] Alternatively, the vacuum breaking valve is a double float ball type.

[0012] Alternatively, the forced air supplement device comprises a second connecting pipeline in communication with the draft tube, the second connecting pipeline is provided with an air tank, the air tank and the second connecting pipeline are provided with a control valve, the control valve is an electromagnetic valve, the electromagnetic valve is electrically connected with an electrical control unit, and the opening and closing of the electromagnetic valve are controlled by the electrical control unit.

[0013] A method for regulating pressure of a draft tube of a water turbine, comprising the following steps: when the water turbine is in a load reduction condition, starting a draft tube air supplement system connected with the draft tube, and supplementing air into the draft tube through the draft tube air supplement system.

[0014] Alternatively, the forced air supplement device is used to supplement high-pressure air into the draft tube instantaneously, so as to rapidly compensate for the vacuum caused by emergency shutdown and flow cut-off, and reduce water hammer effect; when the air stored in the forced air supplement device is consumed, the draft tube has a small vacuum, and the natural air supplement device is used to further supplement air into the draft tube. Alternatively, when the air stored in the forced air supplement device can be supplemented to the allowable range of negative pressure, only the forced air supplement device is used to supplement air into the draft tube. Alternatively, when the maximum negative pressure value in the draft tube is within the allowable range, only the natural air supplement device is used to supplement air into the draft tube.

[0015] Alternatively, the step of starting the forced air supplement device comprises the following steps: when a load reduction instruction is sent by a water turbine monitoring system, an electrical control unit in the forced air supplement device outputs a control signal to open an electromagnetic valve connected with the air tank.

[0016] Alternatively, the step of starting the natural air supplement device comprises the following steps: a float ball type vacuum breaking valve in the natural air supplement device is opened under the action of negative pressure in the draft tube and no water in the valve body, so that the draft tube is in communication with the atmosphere through the connecting pipeline.

[0017] As described above, due to the adoption of the above technical solutions, the present application has the following advantages: 1. The water turbine tail water system and pressure regulating method provided by the application can effectively inject gas into the tail water pipe, effectively suppresses the tail water negative pressure or tail water abnormality under the condition of large load reduction or load rejection, thereby preventing the generation of water hammer phenomenon or reverse water hammer phenomenon; without complex civil engineering, the pressure regulation is realized by the combination of the air supplement system, the pipeline and the valve, thereby significantly reducing the power station construction cost and layout difficulty; meanwhile, the air supplement system adopts the combined design of forced air supplement and natural air supplement, cooperates with the linkage of the electromagnetic valve and the electrical control unit, can instantly start forced air supplement when the water turbine monitoring system issues a load reduction instruction, can empty the accumulated water in the connecting pipeline within a few seconds, quickly suppresses the negative pressure rise, avoids the damage of components caused by the response lag of the traditional surge tank, and the natural air supplement device relies on the passive air supplement of the mechanical structure, without additional energy consumption, realizes the balance of emergency regulation and energy-saving operation, and effectively protects the water turbine components from damage.

[0018] 2. The water turbine tail water system and pressure regulating method provided by the application, the two air supplement devices can be operated independently or in combination, can adapt to different negative pressure degrees in the tail water pipe, can provide targeted solutions from sudden high negative pressure to stable low negative pressure, and adapt to the tail water system characteristics of power stations of different scales and different terrains. The overall structure is mechanically linked with automatic control, reduces the dependence on electronic components, has lower failure rate in the humid and vibrating tail water environment, has lower maintenance cost, has strong long-term operation stability, and provides continuous guarantee for efficient and safe operation of the power station. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is an installation schematic diagram of the water turbine tail water system.

[0020] Figure 2 is a structural schematic diagram of the water turbine tail water system.

[0021] Figure 3 is a 100% load rejection tail water pipe inlet pressure process curve.

[0022] Marked in the figure: 1-natural air supplement device, 11-first connecting pipeline, 12-vacuum breaking valve, 2-forced air supplement device, 21-second connecting pipeline, 22-gas storage tank, 23-control valve. DETAILED DESCRIPTION

[0023] The application will be described in detail below with reference to the drawings.

[0024] In order to make the objects, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and not to limit the present application. It should be noted that, except for the dependent embodiments, any embodiment is independently existing, and the implementation or non-implementation does not affect the integrity of the solutions of the remaining embodiments, and the implementation or non-implementation of the dependent embodiments does not affect the integrity of the solutions of the original embodiments.

[0025] A water turbine tailrace system, as shown in Figure 1 、 2 , comprises a draft tube, wherein a draft tube air supplementing system is arranged on the draft tube to replace a surge tank to form the water turbine tailrace system; the draft tube air supplementing system comprises a forced air supplementing device 2.

[0026] The draft tube is a key channel for discharging water flow of the water turbine. When the unit suddenly stops, the water flow in the tubular Francis turbine continues to flow due to inertia, which is easy to cause water hammer effect, resulting in sudden pressure drop to form over-high negative pressure, and then the negative pressure value decreases. However, the high negative pressure will cause extrusion damage to the core components such as the water discharge cone of the water turbine. The guide vane mechanism of the axial flow turbine is quickly closed, and the water flow originally flowing in the positive direction along the water diversion system to the runner will be suddenly blocked. The water flow cannot stop moving immediately due to its own inertia, and will continue to impact the closed guide vane mechanism. The water flow that cannot move forward after the impact will flow back in the opposite direction to form a reverse water hammer, which will cause a sudden pressure rise in the water diversion system and the flow passage of the water turbine, and directly act on the runner of the axial flow turbine. The draft tube air supplementing system can keep the water flow in the draft tube stable by supplementing gas into the draft tube, directly inhibit the negative pressure value from exceeding the allowable range of the unit, and avoid the risk of component damage from the source. When the water turbine is normally operated, the water flow in the draft tube is stable, and the air supplementing system is in a standby state. When the water flow state suddenly changes due to load reduction and other conditions, and the pressure in the pipe decreases, the air supplementing system can input gas into the draft tube in time, use the compressibility of the gas to buffer the pressure fluctuation, quickly balance the pressure in the pipe by the pressure interaction between the gas and the water flow, replace the traditional mode of balancing the pressure by the water body through the surge tank, and realize efficient regulation and control of the pressure of the tailrace system. At the same time, the compressibility of the gas plays a buffering role, which can stabilize the water flow in the draft tube, buffer the water flow impact and weaken the pressure rise, and inhibit the lifting phenomenon of the low-head axial flow turbine. The forced air supplementing device 2 has active and rapid air supplementing capacity, and can quickly supplement a sufficient amount of gas into the pipe when a large negative pressure or a sudden negative pressure occurs in the draft tube, quickly inhibit the negative pressure rise, and avoid over-standard negative pressure.

[0027] In the long tail water system of Francis turbine, the traditional scheme for dealing with negative pressure of tail water pipe needs to set a surge tank, and the surge tank needs large concrete structure, which has high construction cost, long construction period and large space occupation; at the same time, for low head axial flow turbine, at present, when the load is greatly reduced, there is still no effective anti-lifting machine measure due to the effect of water hammer. The air supplement system in the prior art is set at the water turbine shaft, and its core function is to assist the mechanical operation of the unit, reduce the rotating resistance of the shaft by air supplement, improve the rotating stability, and solve the problem of unit operation. Therefore, the application scene of the air supplement system is fixed in the water turbine shaft area, and the function is limited to assisting the rotating stability, and it is generally believed in the industry that the negative pressure of the tail water pipe needs to be solved by the surge tank, and there is no technical idea of combining the air supplement system with the tail water pipe to regulate and control the negative pressure. The present scheme shifts the air supplement system to the tail water pipe, and the function focuses on the regulation of tail water pressure, replaces the traditional tail water surge tank of Francis turbine, significantly reduces the construction cost and layout difficulty of power station; for axial flow turbine, it effectively solves the lifting machine problem, specially deals with the negative pressure damage caused by water hammer effect and the lifting machine phenomenon caused by the effect of water hammer, realizes the precise switching of the application scene and function target of the air supplement system, avoids the technical bottleneck of the surge tank in the implementation of air supplement, and breaks away from the functional limitations of the existing air supplement system, forming a new technical path for solving the tail water problem of different water turbines.

[0028] As another specific embodiment, the tail water air supplement system further comprises a natural air supplement device 1. The natural air supplement device 1 is supplemented by atmospheric pressure passively, and is suitable for a scene with a small negative pressure value, and can stably maintain the pressure balance in the pipe under low load. When the two devices are used in combination, the forced air supplement device 2 is first used quickly to respond to the significant negative pressure in the initial stage by using its strong air supplement capacity, and after the pressure is preliminarily controlled and the forced air supplement device 2 stops, the natural air supplement device 1 continues to work to maintain the pressure stable in a more energy-saving manner. If the natural air supplement device 1 can control the negative pressure in the normal range alone, the forced air supplement device 2 does not need to be started, and unnecessary energy consumption is reduced. For the axial flow water turbine, the natural air supplement device 1 is mainly used for the case where the working condition changes slowly and the negative pressure and the reverse water hammer strength are low. This kind of device does not need additional power, and automatically absorbs air by relying on the pressure difference between the tail water pipe and the atmospheric pressure, and has simple structure and low maintenance cost. The forced air supplement device is used for the case where the working condition changes sharply and the reverse water hammer and the negative pressure are serious. When the unit encounters extreme working conditions such as emergency shutdown and large load shedding, a strong negative pressure and a high-strength reverse flow will be formed in the tail water pipe instantaneously, and the air suction speed and the air suction amount of the natural air supplement device 1 cannot balance the pressure change in time. At this time, the forced air supplement device 2 actively injects a large amount of gas into the tail water pipe quickly to ensure that the pressure peak value and the axial thrust are weakened in a very short time. In terms of adaptability, the air supplement scheme can be adapted to different working conditions, avoiding the problem of insufficient capacity or resource waste of a single device under extreme working conditions. In terms of efficiency, the staged air supplement mode can accurately regulate the air supplement amount and the air supplement time according to the actual demand, which ensures the rapid response in emergency and realizes the energy-saving operation in the normal state. In terms of economy, the natural air supplement device 1 does not need additional power, and the combination of the forced air supplement device 2 can minimize energy consumption and reduce the long-term operation cost of the system. At the same time, the optional combination of the two devices also provides more flexible configuration options for power stations of different scales and different working conditions, further improving the practicality and universality of the technical scheme.

[0029] As another specific embodiment, the natural air supplement device 1 comprises a first connecting pipeline 11 communicated with the tail water pipe, the other end of the first connecting pipeline 11 is communicated with the atmosphere, and a vacuum breaking valve 12 is arranged on the first connecting pipeline 11, and the connection pipeline and the tail water pipe are opened and closed through the vacuum breaking valve 12. The arrangement of the first connecting pipeline 11 in the natural air supplement device 1 forms a direct gas flow path between the tail water pipe and the atmosphere, so that the atmosphere can enter the tail water pipe through the pipeline to provide a physical channel for air supplement under negative pressure. One end of the first connecting pipeline 11 is communicated with the tail water pipe, and the other end is directly connected with the atmosphere. This structure design ensures the stability of the air supplement source, and passive air supplement can be realized relying on atmospheric pressure without additional power support. The vacuum breaking valve 12 arranged on the first connecting pipeline 11 bears the key function of opening and closing control. When negative pressure occurs in the tail water pipe, the vacuum breaking valve 12 will automatically open according to the pressure change, so that the atmosphere flows into the tail water pipe through the first connecting pipeline 11 to supplement the gas to balance the pressure; when the pressure in the tail water pipe returns to the normal range, the vacuum breaking valve 12 is automatically closed to cut off the communication between the tail water pipe and the atmosphere, so as to avoid the interference of irregular gas into the water flow during normal operation, or to prevent the water in the tail water pipe from leaking through the pipeline. Both ensure the effectiveness of natural air supplement and realize precise control of the air supplement process.

[0030] As another specific embodiment, the structure of the vacuum breaking valve 12 is a floating ball type or a spring type. The floating ball type vacuum breaking valve 12 realizes action through the balance of the gravity and buoyancy of the floating ball in the valve body. When negative pressure occurs in the tail water pipe, the floating ball falls under the action of atmospheric pressure, opens the valve passage to allow gas to enter; when the pressure returns to normal, the water in the pipe or the positive pressure pushes the floating ball to rise, and the valve is sealed to block the gas flow. This structure has high tolerance to a small amount of water in the pipe, which can reduce the influence of water backflow on the sealing performance of the valve. The spring type vacuum breaking valve 12 relies on the balance of spring force and pipe pressure to control the opening and closing. Under negative pressure, the spring pushes the valve core to open the passage, and when the pressure rises, the valve core compresses the spring to close the valve. From the air supplement effect, the floating ball type relies on the direct balance of the gravity of the floating ball and the pressure in the tail water pipe to realize opening and closing. When negative pressure occurs in the pipe, the floating ball falls smoothly under the action of atmospheric pressure, and the process of opening the valve passage is gradual and controllable, which can automatically adjust the air according to the degree of negative pressure. The greater the negative pressure, the greater the falling amplitude of the floating ball, and the more unobstructed the air supplement passage, which can quickly supplement sufficient gas. When the pressure rises to the normal range, the water in the pipe or the positive pressure slowly pushes the floating ball to rise, gradually reduces the passage until completely sealed, avoids the pressure rebound caused by the sudden interruption of air supplement, and makes the whole air supplement process and the pressure change in the tail water pipe accurately matched, the air supplement amount is more balanced, and the pressure regulation is more stable.

[0031] As another specific embodiment, the vacuum breaking valve 12 is a double-ball type. The double-ball design realizes precise regulation of the valve through the coordinated action of two independent balls. The main ball bears the main pressure response function. When negative pressure occurs in the draft tube, the main ball acts first under atmospheric pressure to open the air supply channel. The auxiliary ball forms a secondary seal at the same time as the main ball acts to prevent gas leakage due to wear or impurities on the sealing surface of the main ball.

[0032] As another specific embodiment, the forced air supply device 2 includes a second connecting pipeline 21 connected to the draft tube. The second connecting pipeline 21 is provided with a gas storage tank 22, and a control valve 23 is arranged between the gas storage tank 22 and the second connecting pipeline 21. The gas storage tank 22 reserves a certain amount of high-pressure gas in advance, so that the forced air supply device 2 does not need to produce gas temporarily in case of a sudden situation in the draft tube, and can directly release the pre-stored gas, greatly improving the air supply response speed and meeting the demand for rapid air supply in emergency conditions. When the draft tube needs forced air supply, the control valve 23 is opened to allow the gas in the gas storage tank 22 to flow into the draft tube through the second connecting pipeline 21; when the negative pressure drops to a safe range or there is no need for continuous air supply, the control valve 23 is closed to terminate gas delivery. This control method can flexibly adjust the air supply time and amount according to the actual pressure changes, avoiding excessive gas delivery that causes abnormal pressure rise in the pipe, and preventing insufficient air supply that cannot effectively suppress negative pressure.

[0033] The control valve 23 is an electromagnetic valve, and the electromagnetic valve is electrically connected with an electrical control unit for controlling the opening and closing of the electromagnetic valve. The electromagnetic valve relies on electromagnetic force to drive the valve core to act, and has faster opening and closing speed than mechanical valves, and can complete state switching within milliseconds. The electrical control unit as the core control center can receive water turbine operation state signals in real time, determine whether forced air supply is needed according to the preset logic, form a closed-loop control from signal sensing to action execution, and respond quickly to instructions to output control signals to trigger the electromagnetic valve to open, so that the pre-stored gas in the gas storage tank 22 quickly enters the draft tube through the second connecting pipeline 21. This linkage control mechanism skips the manual judgment and operation link, compresses the delay time of air supply start to the shortest, and ensures timely intervention in the early stage of negative pressure formation to minimize the negative pressure peak.

[0034] As an implementable way, when the tail water air supplement system is composed of two kinds of natural air supplement device 1 and forced air supplement device 2 in combination, the natural air supplement device 1 and the forced air supplement device 2 are connected after confluence and then connected to the preset position of the tail water pipe. The confluence design makes the high-pressure gas of the forced air supplement preferentially supplement the tail water, and after the high-pressure gas is consumed, a certain negative pressure is generated in the confluence pipe to open the natural air supplement device 1 to supplement the tail water naturally. When the forced air supplement device 2 stops supplying air, if there is still negative pressure in the tail water pipe, the floating ball is opened under the attraction of the negative pressure of the tail water pipe at this time, so that the atmosphere enters the tail water pipe through the first connecting pipeline 11, and seamlessly switches to the natural air supplement mode. The automatic isolation and switching of the two air supplement modes are realized through the linkage of the mechanical structure, without the need for additional electrical control elements to avoid gas waste during forced air supplement and channel blockage during natural air supplement, which not only ensures the precise control of the air supplement path under different working conditions, but also simplifies the control logic of the system, improves the air supplement efficiency, enhances the reliability of the overall structure, and is more suitable for the complex and variable pressure environment of the tail water system. At the same time, the confluence method can reduce the number of openings on the tail water pipe, reduce the sealing difficulty of the connection part of the pipeline and the tail water pipe, simplify the overall layout of the system, save installation space, and is especially suitable for power stations with compact structure or limited wall strength of the tail water pipe.

[0035] A water turbine tail water pressure regulating method, comprising the following steps: when the water turbine appears a load reduction condition, starting a tail water air supplement system connected with the tail water pipe, and supplementing air into the tail water pipe through the tail water air supplement system.

[0036] By starting the tail water air supplement system connected with the tail water pipe and supplementing air into the pipe, the water hammer effect and the anti-water hammer effect caused by water flow inertia during load reduction are directly regulated. Under the load reduction condition, the sudden stop of the water turbine causes the water flow state in the tail water pipe to change dramatically, which is easy to form a local vacuum due to the continuous flow of water flow, causing excessive negative pressure. By actively supplementing air, the compressibility of the air can be used to fill the pressure gap in the pipe, quickly buffer the pressure drop trend, and from the source, inhibit the negative pressure from exceeding the allowable range of the unit, avoiding damage to the core components such as the water turbine drain cone due to negative pressure extrusion; or the anti-water hammer effect lifts the runner, main shaft and even part of the rotating parts upwards, causing the unit structure to deform. This scheme abandons the traditional idea of relying on the pressure regulating well to balance the pressure of the water body, and instead uses the direct intervention of gas, greatly improving the pressure regulating response speed. When the load reduction condition occurs, the air supplement system can be started immediately without waiting for the water body in the pressure regulating well to complete the pressure conduction, and can intervene in the regulation at the early stage of load reduction; at the same time, this method does not need to build a large concrete pressure regulating well, saving the complex civil construction link, significantly reducing the construction cost and engineering period of the power station; in addition, the air supplement system is directly related to the tail water pipe, and the supplemented air can directly reach the pressure change area, the regulation is more targeted, avoiding the pressure regulating lag problem caused by the water body flow delay of the pressure regulating well, further ensuring the safe operation of the water turbine under sudden conditions.

[0037] As another specific embodiment, first, the forced air supplement device 2 is used to supplement air into the draft tube at high pressure and instantaneously to quickly make up for the vacuum caused by the emergency shutdown and to reduce the water hammer effect; when the air stored in the forced air supplement device 2 is consumed, a small vacuum appears in the draft tube, and then the natural air supplement device 1 is used to further supplement air into the draft tube; Or, when the air stored in the forced air supplement device 2 can supplement air to the allowable range of negative pressure, only the forced air supplement device 2 is used to supplement air into the draft tube; Or, when the maximum negative pressure value in the draft tube is within the allowable range, only the natural air supplement device 1 is used to supplement air into the draft tube.

[0038] The forced air supplement device 2 can quickly intervene in the initial stage of the negative pressure rise in the draft tube, quickly suppress the rising trend of the negative pressure, and avoid the negative pressure exceeding the standard in a short time, by virtue of the pre-stored gas and the active delivery capability. After the forced air supplement device 2 stops supplying air, the natural air supplement device 1 passively supplements air relying on the atmospheric pressure, can continuously balance the pressure in the pipe in a low energy consumption state, prevent the secondary rise of the negative pressure, and ensure that the pressure is stable in the safe range. When the air storage capacity of the forced air supplement device 2 alone can control the negative pressure to the normal range, the natural air supplement device 1 does not need to be started. When the maximum negative pressure value in the initial stage of the draft tube is small, the threat of the negative pressure to the unit is small, the natural air supplement device 1 does not need additional power to complete the air supplement relying on the atmosphere, and only the natural air supplement device 1 is used to supplement air, which avoids unnecessary energy consumption and mechanical loss, simplifies the control process, makes the air supplement process more direct and efficient, and focuses on economy and simplicity. It can not only meet the pressure balance demand, but also reduce the system operation cost to the greatest extent and reduce the fault risk caused by complex control links.

[0039] As another specific embodiment, the step of starting the forced air supplement device 2 includes: when the water turbine monitoring system issues a load reduction instruction, the electrical control unit in the forced air supplement device 2 outputs a control signal to open the electromagnetic valve connected with the air storage tank 22. When the water turbine operates in the working condition that requires forced air supplement to reduce the corresponding load, once the water turbine monitoring system issues a load reduction instruction, it means that the water flow state in the draft tube will change dramatically in a short time, and the risk of water hammer and negative pressure will increase sharply. At this time, the electrical control unit as the instruction processing center can quickly receive and analyze the signal, immediately output the corresponding control signal to trigger the electromagnetic valve to act, skip the manual judgment and operation link, compress the delay of the instruction transmission and execution to the minimum, ensure that the air supplement action is almost synchronous with the high negative pressure, and effectively inhibit the water hammer phenomenon and the negative pressure.

[0040] As another specific embodiment, the step of starting the natural air supplement device 1 specifically comprises: the float ball type vacuum breaking valve 12 in the natural air supplement device 1 is opened under the action of negative pressure in the draft tube and the absence of water in the valve body, so that the draft tube is connected with the atmosphere through the connecting pipeline. When negative pressure is formed in the draft tube and there is no water in the valve body, the two conditions jointly act on the float ball: the suction force generated by the negative pressure breaks the original force balance of the float ball, and the absence of water in the valve body causes the float ball to lose the support of the buoyancy, and under the double action, the float ball falls, driving the vacuum breaking valve 12 to open. This action directly opens the channel of the draft tube to the atmosphere, allowing external air to flow into the draft tube through the connecting pipeline, supplementing the gas in the pipeline with atmospheric pressure, and gradually balancing the negative pressure. The float ball type structure directly and sensitively senses the pressure change and the state of the water body, can accurately capture the critical state of the draft tube that needs to be supplemented with air, and ensures that the valve is opened only when negative pressure is formed and there is no water body to hinder the flow of gas, which not only avoids the air flow disorder caused by air supplement when there is still water in the draft tube, but also prevents the misoperation when the negative pressure does not reach the required air supplement threshold. At the same time, the whole process does not need electrical control or manual intervention, and is completed only through the linkage of mechanical structure and physical force.

[0041] An example of an application scenario of the present application is as follows: Figure 3 : When starting to shed 100% load after 2 seconds, the negative pressure reaches-2m, after 4 seconds, it reaches-9.8m, and after 10 seconds, the negative pressure decreases to the allowable range. While the allowable negative pressure of the water turbine is-8m, causing the water turbine to be damaged.

[0042] When the power station monitoring system issues a load shedding instruction, the draft tube is still in the water filling state and maintains positive pressure, the float ball is floated up under the action of the water body buoyancy, and the float ball valve remains closed. At the same time, the electromagnetic valve of the air tank 22 receives the opening instruction and starts to act, and within 2 seconds, the air released by the air tank 22 can completely drain the accumulated water in the draft tube connecting pipe, and the high-pressure air is continuously released in the following few seconds to correspond to the pressure sudden decrease period of the draft tube. After the air in the air tank 22 is exhausted, negative pressure is gradually formed in the draft tube, at which time the float ball falls due to the loss of water body buoyancy and the disappearance of the positive pressure in the shell, and the float ball valve is opened, so that the draft tube is naturally connected with the atmosphere, and external air can continuously enter the draft tube. This continuous process can greatly reduce the negative pressure value in the draft tube to below the allowable range, thereby effectively preventing the water turbine from being damaged due to excessive negative pressure.

[0043] The above merely describes preferred embodiments of the present application and is not intended to limit the present application. The present application extends to any novel features or any new combinations disclosed in the specification and any modifications, equivalent replacements and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the details of the technical features not disclosed in the embodiments are all prior art, which can be obtained by those skilled in the art from the prior art. The connection mode can be fixed connection, detachable connection or integral; it can be fixed connection, movable connection or hinged connection, and it can be directly connected or indirectly connected through an intermediate medium. Those skilled in the art can understand the specific mode of the above terms in the embodiments of the present application according to the specific situation, and the embodiments of the present disclosure do not specifically limit the above terms.

Claims

1. A turbine tailrace system, characterized in that: The system includes a tailrace pipe, on which a tailrace aeration system is provided to replace the surge tank and constitute the turbine tailrace system; the tailrace aeration system includes a forced aeration device.

2. The turbine tailrace system as described in claim 1, characterized in that: The tailwater aeration system also includes a natural aeration device.

3. The turbine tailrace system as described in claim 2, characterized in that: The natural aeration device includes a first connecting pipe that is connected to the tailwater pipe. The other end of the first connecting pipe is connected to the atmosphere. A vacuum breaking valve is provided on the first connecting pipe to realize the connection and disconnection between the connecting pipe and the tailwater pipe.

4. The turbine tailrace system as described in claim 3, characterized in that: The vacuum breaker valve has a float-type or spring-type structure.

5. The turbine tailrace system as described in claim 4, characterized in that: The vacuum breaker valve is a double float type.

6. The turbine tailrace system as described in claim 1, characterized in that: The forced air replenishment device includes a second connecting pipe connected to the tailwater pipe. An air storage tank is provided on the second connecting pipe. A control valve is provided between the air storage tank and the second connecting pipe. The control valve is a solenoid valve. The solenoid valve is electrically connected to an electrical control unit, which controls the opening and closing of the solenoid valve.

7. A method for regulating the pressure of a turbine tailrace, characterized in that: Includes the following steps: When the turbine experiences a significant load reduction or load shedding, the tailrace gas supply system connected to the tailrace pipe is activated to supply gas into the tailrace pipe.

8. The turbine pressure regulation method as described in claim 7, characterized in that: First, high-pressure instantaneous air is injected into the tailwater pipe through the forced air injection device to quickly make up for the vacuum caused by the emergency shutdown and flow interruption, and reduce the water hammer effect. After the air stored in the forced air injection device is consumed, a small vacuum appears in the tailwater. Then, the natural air injection device is used to further inject air into the tailwater. Alternatively, when the air stored in the forced air supply device is sufficient to supply air to the negative pressure allowable range, air is supplied to the tailwater pipe only through the forced air supply device. Alternatively, when the maximum negative pressure in the tailwater pipe is within the allowable range, air is supplied to the tailwater pipe only through the natural air supply device.

9. The turbine pressure regulation method as described in claim 7, characterized in that: The steps for activating the forced air supply device include: when the turbine monitoring system issues a command to significantly reduce or shed load, controlling the electrical control unit in the forced air supply device to output a control signal to open the solenoid valve connected to the air storage tank.

10. The turbine pressure regulation method as described in claim 7, characterized in that: The steps for starting the natural aeration device specifically include: the float-type vacuum breaker valve in the natural aeration device opens under the action of negative pressure in the tailwater pipe and no water in the valve body, so that the tailwater pipe is connected to the atmosphere through the connecting pipe.

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