Inclined air cushion type pressure regulating chamber structure and its regulating method

Abstract

The present application relates to a kind of air cushion type surge chamber structure of inclined arrangement and its regulation method.Suitable for water conservancy and hydropower engineering field, especially suitable for high mountain gorge type hydropower station with limited terrain conditions, cannot be arranged conventional surge chamber.The technical scheme used in the present application is: a kind of air cushion type surge chamber structure of inclined arrangement, characterized in that, comprising: construction adit, and the water diversion tunnel between reservoir and unit is communicated, and the construction adit has inclined section in the vicinity of water diversion tunnel, the inclined section is inclined downward to the water diversion tunnel connection end;Closed surge chamber, be set in the inclined section of the construction adit, adopt inclined arrangement, the lower end of this surge chamber is connected by connecting pipe the pressure steel pipe in lower water diversion tunnel;Air cushion regulation mechanism, including the air supplement pipe and exhaust pipe communicated with the upper end of the closed surge chamber, wherein air supplement pipe is connected air compressor, and air valve is installed on exhaust pipe.

Description

Technical Field

[0001] This invention relates to an inclined air-cushion type surge tank structure and its control method. It is applicable to the field of water conservancy and hydropower engineering, and is particularly suitable for high-mountain and canyon-type hydropower stations where terrain conditions are limited and conventional surge tanks cannot be installed. Background Technology

[0002] In the water diversion system of a hydropower station, the core function of the surge tank is to buffer pressure fluctuations in the water diversion tunnel, prevent water hammer damage, and ensure stable system operation. Conventional surge tanks (such as cylindrical, impedance, and differential surge tanks) usually require open terrain conditions to accommodate vertical or near-vertical chambers. However, in terrain-constrained areas such as high mountains and canyons, they are often impossible to implement due to a lack of suitable terrain space.

[0003] While traditional air-cushion surge chambers can adapt to deeply buried cavern scenarios, they require the construction of dedicated caverns, resulting in drawbacks such as large excavation work, high costs, and long construction periods. Furthermore, the water level fluctuates significantly with water levels, making it difficult to meet the Thomas stability requirements at low water levels and maintain system stability. In addition, construction adits during the hydropower station construction phase are temporary facilities and are typically abandoned after completion, leading to a waste of cavern resources. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an inclined air cushion pressure regulating chamber structure and its control method to address the above-mentioned problems.

[0005] The technical solution adopted in this invention is: an inclined air cushion pressure regulating chamber structure, characterized in that it comprises: The construction adit is connected to the water diversion tunnel between the reservoir and the generating unit, and the construction adit has an inclined section near the water diversion tunnel, the inclined section being inclined downward towards the end connected to the water diversion tunnel; A sealed pressure regulating chamber is located in the inclined section of the construction adit and is arranged at an inclination. The lower end of the pressure regulating chamber is connected to the pressure steel pipe in the water diversion tunnel below via a connecting pipe. The air cushion control mechanism includes an air supply pipe and an exhaust pipe connected to the upper end of the sealed pressure regulating chamber, wherein the air supply pipe is connected to an air compressor and the exhaust pipe is equipped with an air valve.

[0006] Through the above-mentioned technical means, existing construction adits can be reused without the need to build new caverns, reducing excavation volume, costs, and construction period; the inclined section is adapted to the restricted terrain of high mountains and canyons, eliminating the dependence of conventional pressure regulating chambers on open sites; the inclined arrangement of the sealed pressure regulating chamber increases the water surface area and meets the Toma stability section; the connecting pipe realizes the transmission of water flow and pressure, and the air cushion control mechanism automatically adjusts the air pressure inside the chamber, buffering pressure fluctuations and preventing gas from entering the water diversion tunnel.

[0007] As a preferred embodiment, the inclination slope of the sealed pressure regulating chamber is 7° to 10°.

[0008] As a preferred embodiment, the cross-sectional area of ​​the connecting pipe is 25% of the cross-sectional area of ​​the water diversion tunnel.

[0009] By employing the aforementioned technical means, the water flow transmission requirements of the water diversion tunnel and the sealed pressure regulating chamber are matched, and the pressure fluctuations of the two are precisely balanced, ensuring the pressure regulating effect of the pressure regulating chamber and the stable operation of the water conveyance system.

[0010] As a preferred embodiment, concrete is backfilled into the construction adit between the lower end of the sealed pressure regulating chamber and the water diversion tunnel.

[0011] Through the above-mentioned technical means, a stable pressure-bearing foundation is formed at the bottom of the sealed construction adit, ensuring the airtightness and structural load-bearing stability of the sealed pressure regulating chamber.

[0012] A control method based on the inclined air cushion pressure regulating chamber structure, characterized in that it includes: Water filling process: When water flows from the reservoir to the unit, the water level in the sealed pressure regulating chamber rises, the internal air is compressed and concentrated at the top. After water filling is completed, if the gas pressure in the sealed pressure regulating chamber is insufficient, the air compressor will automatically replenish the air to the main body of the sealed pressure regulating chamber through the air replenishment pipe until the preset air pressure is reached. Water discharge process: When water flows to the unit through the connecting pipe, the air valve on the exhaust pipe is opened to discharge some gas and balance the pressure inside and outside the pressure regulating chamber; after the water discharge is completed, the air valve is closed to maintain the stable air cushion pressure inside the sealed pressure regulating chamber.

[0013] Through the above-mentioned technical means, the system automatically replenishes air to form a stable air cushion during water filling, ensuring pressure regulation capability; automatically vents air to balance pressure during water release, preventing gas from entering the water diversion tunnel; and automatically controls the entire process to maintain stable system operation.

[0014] The beneficial effects of this invention are: This invention utilizes the inclined section of the construction adit to set up a sealed pressure regulating chamber, eliminating the need for an open space to arrange a vertical chamber, perfectly adapting to the terrain conditions of deep burial and narrow mountain valleys, and solving the problem that conventional pressure regulating chambers cannot be implemented.

[0015] This invention directly reuses existing construction adits in hydropower stations without the need for large-scale excavation and construction of new caverns, significantly reducing project investment and shortening the construction period. At the same time, it revitalizes temporary construction cavern resources and avoids abandonment and waste.

[0016] The invention arranges the pressure regulating chamber at an angle, and the gentle slope of 7° to 10° can significantly increase the water surface area. It meets the requirements of the Thomas stability section throughout the entire water level range, effectively suppresses water level fluctuations, and ensures the stable operation of the water diversion system.

[0017] This invention achieves fully automatic air pressure regulation through an air cushion control mechanism. Combined with a specific ratio of connecting pipe design, it effectively buffers pressure fluctuations, prevents hazards such as water hammer, water column separation, and pipe bursts, and at the same time prevents gas from entering the water diversion tunnel, ensuring the safe operation of the unit. Attached Figure Description

[0018] Figure 1 This is an overall schematic diagram of the inclined air cushion pressure regulating chamber structure described in this invention.

[0019] In the diagram: 1-Reservoir, 2-Unit, 3-Connecting pipe, 4-Concrete, 5-Sealed pressure regulating chamber, 6-Air valve, 7-Exhaust pipe, 8-Make-up air pipe, 9-Air compressor, 10-Water diversion tunnel. Detailed Implementation

[0020] like Figure 1 As shown, this embodiment is an inclined air cushion pressure regulating chamber structure, including a construction support tunnel, a sealed pressure regulating chamber, and an air cushion control mechanism.

[0021] In this embodiment, the construction adit is an existing construction adit from the hydropower station construction phase. This construction adit is connected to the water diversion tunnel between the reservoir and the generating units. In this example, the layout of the construction adit was optimized in advance during the construction planning phase. The adit has an inclined section near the water diversion tunnel, which slopes downwards towards the end connecting to the water diversion tunnel, with an inclination slope of 8° to 10°.

[0022] In this example, the sealed pressure regulating chamber is located in the inclined section of the construction adit. The axis of the pressure regulating chamber is arranged parallel to the construction adit and inclined at 8° to 10°, thereby increasing the water surface area inside the pressure regulating chamber to meet the Thomas stability section and improve the stability of the water diversion system.

[0023] In this embodiment, the lower end of the sealed pressure regulating chamber is connected to the pressure steel pipe in the water diversion tunnel below via a connecting pipe. The cross-sectional area of ​​the connecting pipe is 25% of the cross-sectional area of ​​the water diversion tunnel. It is used to balance the water flow pressure fluctuations between the pressure regulating chamber and the water diversion tunnel and is a key connecting component between the pressure regulating chamber and the water conveyance system.

[0024] In this embodiment, the air cushion regulation mechanism is a fully automatic control structure that is linked with the unit control system. It includes an air compressor, an air supply pipe, an exhaust pipe, and an air valve. One end of the air supply pipe is connected to the air compressor, and the other end extends into the top of the sealed pressure regulating chamber for replenishing air after water filling. The exhaust pipe is fixedly installed on the inclined top of the chamber for discharging excess gas. The air valve is installed on the exhaust pipe and can adjust the opening to control the exhaust rate. The air compressor is arranged in the construction support hole outside the sealed pressure regulating chamber, which does not occupy additional space and is suitable for mountainous terrain.

[0025] In this example, the inner wall of the construction adit is lined with concrete, with a thickness of 60-80cm, which is tightly integrated with the sealed pressure regulating chamber to regulate the cross-section and provide foundation bearing capacity. Concrete is backfilled in the construction adit between the lower end of the sealed pressure regulating chamber and the water diversion tunnel to seal the lower part of the construction adit and form a stable pressure-bearing foundation.

[0026] The control method based on the air cushion pressure regulating chamber structure in this embodiment specifically includes: 1. Water filling process. When water flows from the reservoir to the generating unit through the water diversion tunnel, the water flows through the connecting pipe into the sealed pressure regulating chamber. The water level in the chamber gradually rises, and the internal air is compressed and concentrated in the inclined top area of ​​the chamber. After the water filling is completed, the system automatically detects the air pressure in the chamber. If the air pressure does not reach the preset value, the air compressor automatically replenishes air into the chamber through the air replenishment pipe until the air pressure reaches the standard. When the generating unit starts under no-load, the sealed pressure regulating chamber stabilizes the water supply flow through the connecting pipe to avoid a sudden drop in pipeline pressure and eliminate the risks of negative pressure and water column separation.

[0027] 2. Water Discharge Process. When the unit suddenly sheds its full load, water flows from the sealed pressure regulating chamber to the unit through the connecting pipe. The air valve on the exhaust pipe automatically opens, and the exhaust rate is controlled by adjusting the valve opening to discharge some gas from the chamber, balancing the pressure inside and outside the chamber and preventing gas from entering the water diversion tunnel with the water flow. After water discharge is complete and the water flow stabilizes, the air valve automatically closes, and the air compressor maintains stable air cushion pressure inside the chamber, preparing for the next operation. When the air pressure inside the chamber exceeds the maximum allowable value, the air valve automatically vents. When the water diversion system is emptied, the air valve opens to prevent a vacuum from forming inside the chamber. When the water level or control parameters inside the chamber fall below the minimum allowable value, the unit automatically shuts down to protect the equipment.

[0028] 3. Adaptive voltage regulation process In this embodiment, the air compressor and the unit's control system are linked. When the monitoring system detects that the unit's load change rate exceeds a preset threshold (e.g., ±10% / s), the control system immediately activates a feedforward intervention mechanism. Based on the direction (increase / decrease) and magnitude of the load change, the system predicts the pressure fluctuation trend using a built-in hydraulic transient model and proactively adjusts the air cushion pressure 0.5 to 2 seconds in advance: if a pressure increase is predicted, the air valve is opened to discharge and reduce pressure; if a pressure decrease is predicted, the air compressor is activated to replenish air and increase pressure. This proactive control strategy can counteract the water hammer wave before it has a significant impact, greatly improving system stability.

[0029] To ensure that the pressure regulating chamber structure of this invention maintains optimal stability across the entire water level range, this invention employs a specific parameter design method to determine its core geometric parameters.

[0030] The optimization objective is to maximize the water surface area during the operation of the sealed pressure regulating chamber. The constraint is that this water surface area must not be less than the Thomas stabilization cross-sectional area (A) required to maintain system stability.th The design variables are selected as the slope i and equivalent diameter D of the inclined section of the construction adit.

[0031] In this embodiment, the Thomas-stabilized cross-sectional area (A) th The formula for calculating ) is: ; Among them, A th The stable cross-sectional area of ​​the surge tank; L is the length of the pressure water diversion tunnel; A T ⍺ represents the cross-sectional area of ​​the pressure water diversion tunnel; ⍺ represents the head loss coefficient of the pressure water diversion tunnel. ;h w0 For head loss in the pressure water diversion tunnel; H r Why the water head; Q T The flow rate of the pressure water diversion tunnel.

[0032] In this embodiment, the slope is determined according to the key parameter design method provided by the present invention: The optimization objective is to maximize the water surface area during the operation of the sealed pressure regulating chamber, and the constraint is to ensure that the water surface area is not less than the minimum area required by the Thomas stability section. The slope i and the equivalent diameter D are used as key design variables. Under the boundary conditions of the existing spatial dimensions of the construction adit and the allowable slope of the terrain, different parameter combinations are solved and compared through hydraulic numerical simulation to obtain the optimal parameter combination {i, D} that maximizes the water surface area and the cross-sectional area of ​​the connecting pipe. Under the boundary conditions of the existing spatial dimensions of the construction adit (side length 7 meters), the allowable slope of the terrain (5°~15°), and spatial redundancy, the optimal slope range is found to be 8°~10°. Within this slope range, the water surface area in the entire water level range meets the Thomas stability section requirements, all data are optimal, and the amount of construction adit modification is minimized.

[0033] In this example, the lower end of the sealed surge tank is connected to the pressure steel pipe inside the water diversion tunnel via a connecting pipe, the cross-sectional area of ​​which is 25% of the cross-sectional area of ​​the water diversion tunnel. This ratio was determined through hydraulic transient simulation optimization: under the same boundary conditions, the maximum pressure drop rate at the volute inlet was calculated for load shedding conditions at area ratios of 10%, 15%, 20%, 25%, 30%, and 35%. The results show that the maximum pressure drop rate at the volute inlet is greatest at 25% (reduced by 5.23% compared to 10%, approximately 2.10% compared to 15%, approximately 0.71% compared to 20%, approximately 0.80% compared to 30%, and approximately 2.00% compared to 35%), and no negative pressure occurs under all conditions; therefore, this is determined to be the optimal design value. This connecting pipe is used to balance the water flow pressure fluctuations between the surge tank and the water diversion tunnel and is a key connecting component between the surge tank and the water conveyance system.

[0034] The following examples illustrate this: The basic situation is as follows: the reservoir has a low water level of 739m (T1 / T2 / T3 conditions) and a high water level of 742.8m (T4 / T5 conditions), with a fixed water level of 550m in the tailrace channel; the project needs to cope with 5 typical conditions (T1-T5). Without a surge tank, the maximum pipeline pressure reaches 216.81m (T5 condition) and the minimum pressure is only 0.27m (T3 condition), with the maximum speed increase rate of the unit reaching 55% (T4 condition), posing a risk of pipe burst and water column separation; the water pipeline runs through mountainous areas with no open space to arrange a conventional vertical surge tank, so an inclined air cushion surge tank will be constructed using existing construction adits for protection.

[0035] The control process is divided into two stages: water filling and water releasing, and is fully automated throughout. 1. Water filling stage (corresponding to T1 / T2 operating conditions) Start-up conditions: Reservoir water level reaches 739m (T1 / T2), tailrace channel water level is 550m, unit is not running (T2) or starts from no load (T1). Water flow process: Water flows from the reservoir into the water diversion tunnel, enters the main body of the pressure regulating chamber through the connecting pipe, and the water level gradually rises as water flows in, while the air in the air chamber is compressed. Air replenishment control: After water filling is completed, if the air chamber pressure is insufficient, the air compressor will automatically replenish air through the air replenishment pipe until the pressure stabilizes; Unit linkage (T1 condition): The unit guide vanes open in a straight line every 300 seconds, and the pressure regulating chamber stabilizes the water supply flow through the connecting pipe to avoid a sudden drop in pipeline pressure (minimum pressure of 0.83m in T1 condition, no negative pressure).

[0036] 2. Water discharge regulation (corresponding to T3 / T4 operating conditions) Start-up conditions: The unit operates at rated output, suddenly shedding all loads (T3 / T4), and the reservoir water level is 739m (T3) or 742.8m (T4). Venting control: When water is released, air at the top of the pressure regulating chamber may easily enter the pipeline with the water flow. At this time, the air valve will open automatically and some gas will be discharged through the vent pipe to ensure that no gas enters the water diversion tunnel. Stable completion: After the water flow stabilizes, the air valve closes, and the air compressor maintains the air cushion pressure in the pressure regulating chamber to prepare for the next operation.

[0037] This example, through the inclined air-cushion pressure regulating chamber, achieves the following effects: In terms of terrain, utilizing existing construction adits to arrange the inclined air-cushion pressure regulating chamber solves the problem of "the inability to arrange conventional pressure regulating chambers in mountainous terrain," eliminating the need for additional excavation and reducing project costs; in terms of pressure control, the maximum pipeline pressure under various operating conditions is 216.81 m and the minimum is 0.27 m, meeting the project's safe operation requirements and preventing pipe bursts or water column separation; in terms of unit protection, the maximum speed rise rate of the T4 operating condition unit is 55%, which does not exceed the allowable value specified in the standard, and the maximum pressure of the volute is 157.04 m, effectively protecting the unit from water hammer impact.

Claims

1. A tilted air cushion pressure regulating chamber structure, characterized in that, include: The construction adit is connected to the water diversion tunnel between the reservoir and the generating unit, and the construction adit has an inclined section near the water diversion tunnel, the inclined section being inclined downward towards the end connected to the water diversion tunnel; The sealed pressure regulating chamber is formed by modifying the inclined section of the construction adit and is arranged at an inclination. The lower end of the pressure regulating chamber is connected to the pressure steel pipe in the water diversion tunnel below via a connecting pipe. The air cushion control mechanism includes an air supply pipe and an exhaust pipe connected to the upper end of the sealed pressure regulating chamber, wherein the air supply pipe is connected to an air compressor and the exhaust pipe is equipped with an air valve.

2. The inclined air cushion pressure regulating chamber structure according to claim 1, characterized in that, The inclination slope of the sealed pressure regulating chamber is 7° to 10°.

3. The inclined air cushion pressure regulating chamber structure according to claim 1, characterized in that, The cross-sectional area of ​​the connecting pipe is 25% of the cross-sectional area of ​​the water diversion tunnel.

4. The inclined air cushion pressure regulating chamber structure according to claim 1, characterized in that, Concrete was backfilled into the construction adit between the lower end of the sealed pressure regulating chamber and the water diversion tunnel.

5. A control method based on the inclined air cushion pressure regulating chamber structure according to any one of claims 1 to 4, characterized in that, include: Water filling process: During water filling, water flows from the reservoir to the unit, the water level in the sealed pressure regulating chamber rises, and the internal air is compressed and concentrated at the top; after water filling is completed, if the gas pressure in the sealed pressure regulating chamber is detected to be lower than the preset pressure, the air compressor will automatically replenish the air in the sealed pressure regulating chamber through the air replenishment pipe until the preset pressure is reached. Water discharge process: During water discharge or unit load shedding, water flows through the connecting pipe from the sealed pressure regulating chamber to the unit, and the air valve on the exhaust pipe is opened to discharge some gas to balance the pressure inside and outside the pressure regulating chamber; after the water discharge is completed, the air valve is closed to maintain the stability of the air cushion pressure in the sealed pressure regulating chamber.

6. The control method according to claim 5, characterized in that, It also includes an adaptive voltage regulation process: Link the air compressor with the control system of the unit; When the load change rate of the unit is detected to exceed a preset threshold, the control system pre-calculates the required air cushion pressure compensation value based on the direction and magnitude of the load change. Before the water flow in the connecting pipe fluctuates significantly, the control system controls the air compressor to replenish air through the air replenishment pipe, or controls the air valve to exhaust air through the exhaust pipe, in order to actively adjust the air cushion pressure and counteract the impending water hammer pressure fluctuation.

7. The control method according to claim 5, characterized in that, The preset threshold is ±10% / s.

8. A design method for determining key parameters of the inclined air cushion pressure regulating chamber structure according to any one of claims 1 to 4, characterized in that, Includes the following steps: The optimization objective is to maximize the water surface area of ​​the sealed pressure regulating chamber during operation; The constraint condition is to ensure that the water surface area is not less than the minimum area required by the Thomas stability section. The slope i and equivalent diameter D of the construction adit are set as key design variables; Under the boundary conditions of the existing spatial dimensions of the construction adit and the allowable slope of the terrain, different parameter combinations are solved and compared through hydraulic numerical simulation to obtain the optimal parameter combination {i, D} that maximizes the water surface area and the cross-sectional area of ​​the connecting pipe.

9. The design method according to claim 8, characterized in that, The Thomas stable cross-sectional area (A) th The formula for calculating ) is: ； Among them, A th The stable cross-sectional area of ​​the surge tank; L is the length of the pressure water diversion tunnel; A T ⍺ represents the cross-sectional area of ​​the pressure water diversion tunnel; ⍺ represents the head loss coefficient of the pressure water diversion tunnel. ;h w0 For head loss in the pressure water diversion tunnel; H r Why the water head; Q T The flow rate of the pressure water diversion tunnel.

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