Method for judging sensitivity of tail water pressure of pumped storage unit to flow asynchronization

Abstract

The application discloses a method for judging the sensitivity of tail water pressure of pumping storage unit to flow asynchronization, which is a method for judging the sensitivity of tail water pressure of pumping storage unit to flow asynchronization through water delivery system arrangement, that is, a method for connecting the water delivery system arrangement and the tail water pressure extreme value caused by flow asynchronization change in a transition process, that is, defining a flow asynchronization change inhibition coefficient for describing the tail water pressure extreme condition caused by flow asynchronization change of the pumping storage unit, and calculating the flow asynchronization change inhibition coefficient through the specific scheme of the water delivery system arrangement to judge the tail water pressure extreme condition. The method can judge the sensitivity of tail water pressure of the pumping storage unit to flow asynchronization change before the transition process calculation research is performed, and preliminarily judges the minimum pressure extreme condition of the tail water pipe, thereby providing a reference for the water delivery system arrangement design of the pumped storage power station.

Description

Technical Field

[0001] This invention relates to a method for determining the sensitivity of tailwater pressure of pumped storage units to asynchronous flow rates, belonging to the field of water conservancy and hydropower engineering. Background Technology

[0002] Pumped storage power stations are large-scale power sources for energy storage, peak shaving, frequency regulation, and spinning reserve. With the rapid development of intermittent energy sources such as wind and solar power, their important role in enhancing grid flexibility, improving overall efficiency, and ensuring safety and stability is becoming increasingly prominent. To prevent instability and accidents, some power stations have to implement operational restrictions, severely impacting their normal functioning. Many of these safety and stability issues occur during the transient processes of pumped storage power stations. Therefore, the design of high-head, high-flow pumped storage power stations requires in-depth research into the system's transient processes and a thorough understanding of the hydraulic characteristics to avoid safety accidents.

[0003] For high-head, high-speed pumped-storage power stations, the hydraulic transition process is often more dangerous due to the high head within the waterway system. Extremely low pressure is more likely to occur in the tailrace minimum pressure. The control conditions for the tailrace inlet minimum pressure are typically under asynchronous flow rate changes, such as successive load shedding, load shedding by both units, or a situation where one guide vane is closed and the other is closed. The occurrence of extreme low pressure in the tailrace system under asynchronous flow rate changes is more sensitive and complex than in conventional pumped-storage power stations. To ensure the safe and stable operation of the project and improve its efficiency, a detailed study and optimization of the water conveyance system layout is necessary. Summary of the Invention

[0004] The purpose of this invention is to address the problem that pumped storage power plants are more sensitive to extreme low pressure at the tailrace inlet than conventional pumped storage power plants when operating under asynchronous flow conditions. This invention provides a method for judging the sensitivity of the tailrace pressure of pumped storage units to asynchronous flow, providing a certain reference for the layout and design of water conveyance systems, and improving the safety and economy of pumped storage power plants.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for determining the sensitivity of tailwater pressure of pumped storage units to flow asynchrony is characterized by: when designing the water conveyance system layout scheme of a pumped storage power station, determining the sensitivity of tailwater pressure of pumped storage units to flow asynchrony before performing hydraulic transition process calculations, and determining the design direction of the water conveyance system layout scheme to ensure that the pumped storage power station experiences extreme low pressure during the transition process calculation.

[0007] The sensitivity of the tailwater pressure of the pumped storage unit to flow asynchrony is determined by the magnitude of the flow asynchrony suppression coefficient; the smaller the flow asynchrony suppression coefficient, the less sensitive the tailwater pressure of the unit is to flow asynchrony.

[0008] Furthermore, the method includes the following steps:

[0009] (1) Obtain the pipe section parameters of the water conveyance system layout and determine the expression for the minimum pressure at the tailrace pipe inlet of the unit;

[0010] (2) Determine the expression for the difference between the flow rate and pressure of the target water conveyance system;

[0011] (3) Determine the inhibition coefficients for asynchronous flow changes, including the upstream coefficient and the downstream coefficient;

[0012] (4) By comparing the inhibition coefficient of asynchronous flow rate change, the sensitivity of the tailwater pressure of the unit to asynchronous flow rate change under the water conveyance system layout scheme is determined.

[0013] Furthermore, for a pumped storage power station hydraulic unit containing two units, the expression for the minimum pressure at the inlet of the tailrace pipe in step (1) is derived based on the rigid water hammer theory:

[0014]

[0015]

[0016] In the formula, H td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L4 is the inlet pressure of the tailrace pipe of Unit 2; L5 is the length from Unit 1 to the tailrace branch pipe; L6 is the length from the tailrace branch pipe to the lower reservoir; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; A5 is the equivalent area of ​​the section from Unit 2 to the tailrace branch pipe; A6 is the equivalent area of ​​the section from the tailrace branch pipe to the lower reservoir; α4 is the head loss coefficient of the section from Unit 1 to the tailrace branch pipe; α5 is the head loss coefficient of the section from Unit 2 to the tailrace branch pipe; α6 is the head loss coefficient of the section from the tailrace branch pipe to the lower reservoir, which includes local head loss and friction head loss; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively; Q T1 Z represents the tailwater main flow rate. d This refers to the water level of the downstream reservoir.

[0017] Furthermore, based on the rigid water hammer theory, the expression for the difference between the flow rate change rate and the pressure in step (2) is derived as follows:

[0018]

[0019]

[0020] In the formula, H tu1 H represents the pressure at the end of the spiral casing of Unit 1. tu2 H represents the pressure at the end of the spiral casing of Unit 2. td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L2 is the inlet pressure of the tailrace pipe of Unit 2; L4 is the length from the water intake branch pipe to Unit 1; L5 is the length from Unit 1 to the tailrace branch pipe; A2 is the equivalent area of ​​the section from the water intake branch pipe to Unit 1; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively.

[0021] Furthermore, the upstream coefficient for suppressing asynchronous flow changes in step 3 is: (Equation (3))

[0022] Furthermore, the downstream coefficient for suppressing asynchronous flow changes in step 3 is: (4)

[0023] The theoretical basis of this invention is as follows: Equations (3) and (4) reflect the relationship between the flow rate change rate of the unit and the pressure difference between the units. The change of their coefficients will inevitably cause drastic changes in the flow rate. Equations (1) and (2) reflect the relationship between the minimum pressure at the tailwater inlet and the flow rate. Therefore, the sensitivity of the tailwater pressure of the pumped storage unit to the flow rate asynchrony can be judged by the flow rate asynchrony suppression coefficient.

[0024] Furthermore, when the minimum pressure at the tailrace pipe inlet occurs during the second wave of the flow rate of the first load-shedding unit dropping to zero, the positions of the upstream and downstream branch pipes are adjusted to reduce the sensitivity of the unit's tailrace pressure to asynchronous changes in flow rate, until the minimum pressure at the tailrace pipe inlet occurs during the first wave of the flow rate of the second load-shedding unit dropping to zero.

[0025] In a second aspect of the present invention, the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of the above-described method for determining the sensitivity of the tailwater pressure of a pumped-storage unit to flow rate asynchrony.

[0026] In a second aspect of the present invention, an electronic device is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, when the processor executes the program, it implements the steps of the method described above for determining the sensitivity of the tailwater pressure of a pumped-storage unit to asynchronous flow.

[0027] This invention proposes a method for determining the sensitivity of tailwater pressure of pumped-storage units to flow rate asynchrony. This method successfully solves the problem of extreme low pressure in the tailwater of pumped-storage units due to asynchronous flow rate changes. Furthermore, the method allows for the determination of the sensitivity of tailwater pressure to flow rate asynchrony during the water conveyance system layout design phase. This improves design efficiency and the operational safety of pumped-storage power plants, prevents excessively low pressure in the tailwater system, and ensures system safety. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method for determining the sensitivity of tailwater pressure of a pumped storage unit to asynchronous flow rate according to the present invention.

[0029] Figure 2 This is a schematic diagram of the layout of a pumped storage power station with two turbines in a tunnel, according to an embodiment of the present invention.

[0030] Figure 3 This is a curve showing the variation of the minimum pressure in the tailrace pipe with the upstream coefficient in an embodiment of the present invention.

[0031] Figure 4 This is a process line showing the change of flow rate of units with different upstream coefficients over time in an embodiment of the present invention.

[0032] Figure 5 This is a time curve showing the minimum pressure in the tailrace pipe of different upstream coefficient units in an embodiment of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described below with reference to the accompanying drawings. It should be understood that the embodiments provided below are only for the purpose of fully and completely disclosing the present invention and fully conveying the technical concept of the present invention to those skilled in the art. The present invention can also be implemented in many different forms and is not limited to the embodiments described herein.

[0034] This invention proposes a method for determining the sensitivity of pumped-storage unit tailwater pressure to flow asynchrony. This method involves deriving the expressions for the minimum inlet pressure of the unit's tailwater pipe and the difference between the flow rate and pressure under the given water conveyance system layout. Then, it calculates flow asynchrony suppression coefficients (upstream coefficient and downstream coefficient), and by comparing the magnitudes of these coefficients, determines the sensitivity of the pumped-storage unit's tailwater pressure to flow asynchrony. (Refer to...) Figure 1 The method for determining the sensitivity of tailwater pressure of a pumped storage unit to flow rate asynchrony includes the following steps:

[0035] Step A1: For a hydraulic unit containing two generating units, obtain the pipe section parameters of its water supply system layout and determine the expression for the minimum pressure at the tailrace pipe inlet of the generating unit.

[0036] Specifically, the expression for the minimum pressure at the tailrace pipe inlet is:

[0037]

[0038]

[0039] In the formula, H td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L4 is the inlet pressure of the tailrace pipe of Unit 2; L5 is the length from Unit 1 to the tailrace branch pipe; L6 is the length from the tailrace branch pipe to the lower reservoir; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; A5 is the equivalent area of ​​the section from Unit 2 to the tailrace branch pipe; A6 is the equivalent area of ​​the section from the tailrace branch pipe to the lower reservoir; α4 is the head loss coefficient of the section from Unit 1 to the tailrace branch pipe; α5 is the head loss coefficient of the section from Unit 2 to the tailrace branch pipe; α6 is the head loss coefficient of the section from the tailrace branch pipe to the lower reservoir, which includes local head loss and friction head loss; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively; Q T1 Z represents the tailwater main flow rate. d This refers to the water level of the downstream reservoir.

[0040] Step A2: Determine the expression for the difference between the flow rate change rate and the pressure of the target water conveyance system.

[0041] Specifically, the expression for the difference between the flow rate change rate and the pressure is as follows:

[0042]

[0043]

[0044] In the formula, H tu1 H represents the pressure at the end of the spiral casing of Unit 1. tu2 H represents the pressure at the end of the spiral casing of Unit 2. td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L2 is the inlet pressure of the tailrace pipe of Unit 2; L4 is the length from the water intake branch pipe to Unit 1; L5 is the length from Unit 1 to the tailrace branch pipe; A2 is the equivalent area of ​​the section from the water intake branch pipe to Unit 1; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively.

[0045] Step A3: Determine the inhibition coefficients for asynchronous flow changes—the upstream coefficient and the downstream coefficient.

[0046] Specifically, the upstream coefficient for suppressing asynchronous flow changes is: (Equation (3))

[0047] Specifically, the downstream coefficient for suppressing asynchronous flow changes is: (Equation (4))

[0048] Step A4: Compare the inhibition coefficients of asynchronous flow rate changes. If both the upstream and downstream asynchronous flow rate change inhibition coefficients are small, then the tailwater pressure of the unit under this water conveyance system layout scheme is not sensitive to asynchronous flow rate changes; otherwise, it is sensitive.

[0049] Because this invention can directly calculate the inhibition coefficient of asynchronous flow rate changes during the design phase of the water conveyance system layout, it can directly compare the sensitivity differences of the tailwater pressure of the units to asynchronous flow rate changes between different schemes. It does not require the calculation of the transition process for each water conveyance system layout scheme according to the traditional method, nor does it require drawing the time domain line of the minimum pressure at the tailwater pipe inlet and the time domain line of the unit flow rate, thereby determining the sensitivity of the tailwater pressure of the units in different water conveyance system layouts to asynchronous flow rate changes.

[0050] The method steps and effects of the present invention will be further described below through a specific example.

[0051] Figure 1 This diagram shows a simplified layout of the water diversion and power generation system of a pumped storage power station. The station uses a one-tunnel, two-unit configuration. The diagram includes sections 1, 2, 3, 4, 5, and 6 on the transmission pipeline. L1 represents the length of section 1 from the upper reservoir to the diversion branch pipe; L2 represents the length of section 2 from the diversion branch pipe to Unit 1; L3 represents the length of section 3 from the diversion branch pipe to Unit 2; L4 represents the length of section 4 from Unit 1 to the tailrace branch pipe; L5 represents the length of section 5 from Unit 2 to the tailrace branch pipe; L6 represents the length of section 6 from the tailrace branch pipe to the lower reservoir; T1 represents Unit 1; and T2 represents Unit 2. This is to study the upstream coefficient. The impact on the minimum pressure at the tailrace inlet is investigated. Keeping the total length of the water conveyance system constant, the upstream branch pipes are moved 40m to the upper reservoir and then moved to the upper reservoir (single upstream tunnel, single unit), respectively. The pipe diameter is adjusted to ensure the head loss of a single unit remains constant. The original scheme is denoted as S, and the adjusted schemes are denoted as S1 and S2. The asynchronous flow calculation condition is selected as the guide vane-closed-rejected condition. The accuracy of this invention is verified below using numerical simulation results of the transient process.

[0052] The pipe section parameters for the water conveyance system layout are shown in Table 1. Pipeline parameters for the water conveyance power generation system are also provided.

[0053]

[0054] Determine the expression for the minimum pressure at the tailrace inlet of the unit and the expression for the difference between the flow rate and pressure; then determine the inhibition coefficient for asynchronous flow rate changes—the upstream coefficient (Table 2) (the downstream coefficient is similarly determined), and the calculation results for the transition process under different upstream coefficients:

[0055]

[0056] By comparing the inhibition coefficients of asynchronous flow rate changes, the sensitivity of the unit tailwater pressure to asynchronous flow rate changes under this water conveyance system layout scheme is determined.

[0057] From Table 2 and Figures 2-4 It can be seen that as the flow rate asynchronous change suppression coefficient decreases, the flow rate alternation phenomenon caused by the flow rate asynchronous change is improved. When the upstream coefficient decreases, the minimum pressure at the tailrace pipe inlet is safer throughout the transition process, and the low pressure phenomenon in the tailrace pipe is gradually improved. That is, as the flow rate asynchronous change suppression coefficient decreases, the unit tailrace pressure is less sensitive to flow rate asynchronous changes.

[0058] When the minimum pressure at the tailrace pipe inlet occurs during the second wave of the flow rate of the first load shedding unit dropping to zero, the upstream branch pipe is moved to the upper reservoir and the downstream branch pipe is moved to the lower reservoir to reduce the flow rate asynchrony change suppression coefficient, thereby reducing the sensitivity of the unit's tailrace pressure to flow rate asynchrony changes, until the minimum pressure at the tailrace pipe inlet occurs during the first wave of the flow rate of the second load shedding unit dropping to zero.

[0059] From the above description of the embodiments, those skilled in the art will clearly understand that the facilities of the present invention can be implemented using software plus necessary general-purpose hardware platforms. Embodiments of the present invention can be implemented using existing processors, or by dedicated processors used for this or other purposes for suitable systems, or by hardwired systems. Embodiments of the present invention also include non-transitory computer-readable storage media, comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon; such machine-readable media can be any available medium accessible by a general-purpose or special-purpose computer or other machine with a processor. For example, such machine-readable media can include RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disc storage, disk storage or other magnetic storage devices, or any other medium that can be used to carry or store the required program code in the form of machine-executable instructions or data structures and is accessible by a general-purpose or special-purpose computer or other machine with a processor. When information is transmitted or provided to a machine via a network or other communication connection (hardwired, wireless, or a combination of hardwired and wireless), that connection is also considered a machine-readable medium.

[0060] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for determining the sensitivity of tailwater pressure of a pumped-storage unit to flow rate asynchrony, characterized in that: When designing the water conveyance system layout scheme for a pumped storage power station, the sensitivity of the tailwater pressure of the pumped storage unit to the asynchronous flow rate should be determined before the hydraulic transition process calculation, so as to determine the design direction of the water conveyance system layout scheme and ensure that the pumped storage power station does not experience extreme low pressure during the transition process calculation. The sensitivity of the tailwater pressure of the pumped storage unit to flow asynchrony is determined by the magnitude of the flow asynchrony suppression coefficient; the smaller the flow asynchrony suppression coefficient, the less sensitive the tailwater pressure of the unit is to flow asynchrony. The method includes the following steps: (1) Obtain the pipe section parameters of the water conveyance system layout and determine the expression for the minimum pressure at the tailrace pipe inlet of the unit; (2) Determine the expression for the difference between the flow rate change rate and the pressure of the target water conveyance system; (3) Determine the inhibition coefficients for asynchronous flow changes, including the upstream coefficient and the downstream coefficient; (4) By comparing the inhibition coefficient of asynchronous flow rate change, the sensitivity of the tailwater pressure of the unit to asynchronous flow rate change under the water conveyance system layout scheme is determined; For a pumped storage power station hydraulic unit containing two generating units, the expression for the minimum pressure at the tailrace inlet in step (1) is: In the formula, H td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L4 is the inlet pressure of the tailrace pipe of Unit 2; L5 is the length from Unit 1 to the tailrace branch pipe; L6 is the length from the tailrace branch pipe to the lower reservoir; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; A5 is the equivalent area of ​​the section from Unit 2 to the tailrace branch pipe; A6 is the equivalent area of ​​the section from the tailrace branch pipe to the lower reservoir; α4 is the head loss coefficient of the section from Unit 1 to the tailrace branch pipe; α5 is the head loss coefficient of the section from Unit 2 to the tailrace branch pipe; α6 is the head loss coefficient of the section from the tailrace branch pipe to the lower reservoir, which includes local head loss and friction head loss; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively; Q T1 Z represents the tailwater main flow rate. d This refers to the water level of the downstream reservoir. The expression for the difference between the flow rate change rate and the pressure in step (2) is as follows: （3） （4） In formula (3) Defined as the suppression coefficient for asynchronous flow changes upstream of the unit, in equation (4) Defined as the suppression coefficient for asynchronous changes in flow rate downstream of the unit, where H tu1 H represents the pressure at the end of the spiral casing of Unit 1. tu2 H represents the pressure at the end of the spiral casing of Unit 2. td1 H is the inlet pressure of the tailrace pipe of Unit 1; td2 L2 is the inlet pressure of the tailrace pipe of Unit 2; L4 is the length from the water intake branch pipe to Unit 1; L5 is the length from Unit 1 to the tailrace branch pipe; A2 is the equivalent area of ​​the section from the water intake branch pipe to Unit 1; A4 is the equivalent area of ​​the section from Unit 1 to the tailrace branch pipe; g is the acceleration due to gravity; Q1 and Q2 are the flow rates of Unit 1 and Unit 2, respectively. The method calculates the inhibition coefficients of asynchronous changes in upstream and downstream flow rates using the parameters of the water transmission pipeline. If the coefficients are small, it means that the tailwater pressure of the pumped storage unit is not sensitive to asynchronous flow rates, and vice versa.

2. The method for determining the sensitivity of tailwater pressure of a pumped-storage unit to flow rate asynchrony according to claim 1, characterized in that: When the minimum pressure at the tailrace pipe inlet occurs during the second wave of the flow rate of the unit that was first shedding load, adjust the positions of the upstream and downstream branch pipes to reduce the sensitivity of the tailrace pressure to asynchronous changes in flow rate, until the minimum pressure at the tailrace pipe inlet occurs during the first wave of the flow rate of the unit that was later shedding load.

3. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the computer program implements the steps of the method for determining the sensitivity of the tailwater pressure of a pumped storage unit to flow rate asynchrony as described in claim 1 or 2.

4. An electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the method for determining the sensitivity of the tailwater pressure of the pumped storage unit to the asynchronous flow rate as described in claim 1 or 2.

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