A control method for a pressure relief device in a water supply system with back pressure technology

Abstract

This invention relates to a control method for a pressure relief device in a water supply system with back pressure technology. A first pressure switch is set to a pressure value of P1, and a second pressure switch is set to a pressure value of P2. When the switching quantity provided by the first pressure switch and the analog quantity provided by the pressure transmitter simultaneously reach the operating pressure P1 + (P2 - P1) × 95%, the electric flow regulating valve remains open for 30 seconds. If the pressure transmitter pressure is still higher than the operating value during this period, the control cabinet controls the electric flow regulating valve to execute an opening procedure. When the pressure transmitter pressure drops to P1 + (P2 - P1) × 20% during valve opening, the control cabinet controls the electric flow regulating valve to stop opening. When the electric flow regulating valve is fully open, and the system pressure still cannot reach below P1 + (P2 - P1) × 95%, the electric flow regulating valve remains fully open. This invention improves the stability and reliability of the technical water supply system of hydropower station units, preventing accidental shutdowns caused by excessive pressure in various technical water supply systems of hydropower stations, such as damage to air coolers, three-bearing oil coolers, chillers, main transformers, and air conditioning systems.

Description

Technical Field

[0001] This invention belongs to the field of hydro-generator operation and maintenance technology, and relates to a control method for a pressure relief device applicable to a water supply system with back pressure technology. Background Technology

[0002] A hydropower station's technical water supply system uses gravity flow. Water is drawn in through a spiral casing, passes through a water filter, two-stage pressure reducing valves, and a four-way directional valve, and is supplied to cooling equipment such as three bearing oil coolers and air coolers. Failures such as the four-way directional valve switching or the pressure reducing valve malfunctioning can cause system pressure to rise, jeopardizing the stable operation of the technical water supply system and the turbine generator units. In such cases, a pressure relief valve is needed to accurately and stably release some high-pressure water, reducing the water supply system pressure and ensuring its stable operation. This hydropower station has a mechanical hydraulic pressure relief valve installed after the two-stage pressure reducing valve. The mechanical hydraulic pressure relief valve's operation can discharge a portion of the system water to the tailrace, reducing system pressure. However, because the tailrace water level is higher than the pressure relief valve's position, the pressure after the valve changes with the tailrace water level. The mechanical hydraulic pressure relief valve installed at this power station suffers from inaccurate unloading pressure, is unsuitable for conditions with changing tailrace water levels, and has difficulty operating.

[0003] The reason for this situation is that the mechanical hydraulic pressure relief valve uses a hydraulic pilot valve to drain or replenish water in the main valve control chamber, thereby controlling the opening and closing of the pressure relief valve. This control method has two major drawbacks:

[0004] First, the back pressure after the valve is prone to change, which can lead to inaccurate control of the pressure relief valve opening and closing, and even difficulty in opening the valve when the back pressure is large.

[0005] Secondly, when opening the valve, it is impossible to adjust the opening degree in time according to the pressure in front of the valve to ensure that the opening degree of the pressure relief valve is in the optimal state with the current pressure, so as to avoid the system pressure being too low or too high due to the opening being too large or too small. Summary of the Invention

[0006] To address the problems raised in the background technology, this patent aims to design a control method for a pressure relief device suitable for a water supply system with back pressure technology, solving the problems of inaccurate pressure relief valve unloading, unsuitability for tailwater level changes, and difficulty in valve operation.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a pressure relief device suitable for a water supply system with back pressure technology, comprising a water supply pipe connected between the water inlet of a volute and the tailwater pipe, an electric flow regulating valve installed on the water supply pipe, the electric flow regulating valve being electrically connected to a control cabinet, a pressure transmitter installed on the pipeline between the electric flow regulating valve and the water inlet of the volute, and a first pressure switch and a second pressure switch installed on the pipeline between the pressure transmitter and the water inlet of the volute, wherein the first pressure switch, the second pressure switch, and the pressure transmitter are all electrically connected to the control cabinet.

[0008] Preferably, the first pressure switch is used to control the electric flow valve to open, and the second pressure switch is used to control the electric flow valve to close.

[0009] Preferably, the pressure transmitter is used to compare with the first pressure switch and the second pressure switch to avoid measurement errors by the first pressure switch or the second pressure switch, which could lead to malfunction of the electric flow regulating valve.

[0010] This invention also provides a control method for a pressure relief device in a water supply system with back pressure technology, defining a set pressure value of P1 for a first pressure switch and a set pressure value of P2 for a second pressure switch:

[0011] When the switching quantity provided by the first pressure switch and the analog quantity provided by the pressure transmitter simultaneously reach the operating pressure P1+(P2-P1)×95%, the electric flow regulating valve remains for 30 seconds. If the pressure of the pressure transmitter is still higher than the operating value at this time, the control cabinet controls the electric flow regulating valve to execute the valve opening procedure.

[0012] During the valve opening process, when the pressure transmitter pressure drops to P1+(P2-P1)×20%, the control cabinet controls the electric flow regulating valve to stop opening the valve.

[0013] When the electric flow control valve is fully open, and the system pressure still cannot reach below P1+(P2-P1)×95%, the electric flow control valve remains fully open.

[0014] Preferably, when the pressure of the second pressure switch and pressure transmitter drops to P1+(P2-P1)×5%, the electric flow regulating valve remains for 1 minute. If the pressure is still lower than P1+(P2-P1)×5% at this time, the control cabinet controls the electric flow regulating valve to close.

[0015] During the valve closing process, when the pressure of the pressure transmitter exceeds P1+(P2-P1)×5% again, the electric flow control valve stops closing and remains in place; when the pressure of the second pressure switch and the pressure transmitter drops to P1+(P2-P1)×5%, the valve closing procedure continues to be executed, and the above valve closing process is repeated until the electric flow control valve is fully closed.

[0016] Preferably, during the valve closing process, if the electric flow regulating valve is in a stopped state for more than 10 minutes, the control cabinet exits the valve closing process and issues an alarm signal to remind maintenance personnel to adjust the technical water supply system.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. In this invention, the opening degree of the electric flow regulating valve can be adjusted in real time according to the system pressure, and the closing rate of the flow regulating valve can be adjusted to adapt to different system pressures.

[0019] 2. In this invention, the system pressure is not affected by back pressure, the electric pressure relief method is accurate, highly adaptable, and highly automated. When the system pressure is abnormal, the maintenance personnel can detect it in time and adjust the system pressure through the pressure reducing valve, resulting in higher system reliability.

[0020] 3. The device and control method of the present invention improve the stability and reliability of the technical water supply system of the hydropower station unit, the technical water supply system of the main transformer, and the technical water supply system of the air conditioning system. It avoids accidental shutdowns caused by excessive pressure in the various technical water supply systems of the hydropower station, which could lead to damage to the air cooler, the three bearing oil coolers, the chiller unit, the main transformer, and the air conditioning system. This is of great significance for the safe and stable operation of the unit, the main transformer, and the air conditioning system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the present invention.

[0022] In the diagram: 1. Volute water intake; 2. Tailwater pipe; 3. Water supply pipe; 4. Electric flow regulating valve; 5. Control cabinet; 6. Pressure transmitter; 7. First pressure switch; 8. Second pressure switch. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The technical water supply line of the hydropower station unit has various operating conditions in actual operation. In order to analyze in detail the impact of pressure and flow fluctuations caused by the closure of the pressure relief valve on the safe operation of the water supply system and the water hammer protection measures, the inventors of this application selected the normal and fault conditions of the pressure reducing valve as the control conditions and conducted an analysis of the transition process of the pressure relief valve closure, based on the technical water supply operation of the unit.

[0025] Under normal operating conditions, due to the relatively low pressure in the pipeline, the maximum water pressure rise caused by different closing patterns of the pressure relief valve is not significant. Furthermore, the maximum water pressure rise decreases with increasing closing time, reaching only about 2% to 3% of the rated working pressure. The maximum water hammer pressure caused by the hydraulic oscillation during the opening of the pressure reducing valve is approximately 7% to 8% of the rated working pressure, and the decay time of this oscillation is 2 to 3 seconds. Only when the pressure relief valve closing time is short (e.g., 2 seconds) will the hydraulic oscillation processes of the two processes overlap, affecting the maximum water hammer pressure, but this effect is relatively small. Regarding the change in total pipe flow, since the pressure reducing valve is open and operating normally, the total pipe flow first decreases, with a maximum decrease of approximately 50% of the rated flow. The time it takes to recover to the rated flow is related to the pressure relief valve closing time; the faster the pressure relief valve closes, the smaller the decrease in total pipe flow and the shorter the time to recover to the rated flow.

[0026] Under fault conditions, due to the high initial water pressure in the pipeline, the changes in main pipe pressure and flow rate during the hydraulic transition are significantly different from those under normal conditions. The maximum water hammer pressure is affected not only by the opening of the pressure reducing valve but also by the closing of the pressure relief valve, with the latter playing a dominant role. Under fault conditions, the maximum water pressure rise gradually decreases as the pressure relief valve closing time increases, reaching a maximum of approximately 40% of the rated working pressure. The hydraulic oscillations during the opening of the pressure reducing valve are the main cause of the reduced water hammer pressure, and the decay time of these oscillations is significantly slower than under normal conditions. Therefore, at different closing times of the pressure relief valve, the hydraulic oscillation processes of both will overlap, thus affecting the maximum water hammer pressure. Looking at the changes in the main pipe flow rate, the main pipe flow rate changes more smoothly, also related to the pressure relief valve closing time. Its minimum reduction is only about 25% of the rated flow rate (2-second closing rule), which is about 25% smaller than the flow rate reduction under normal conditions.

[0027] To obtain the optimal valve closing behavior, the inventors of this application analyzed the changes in water pressure and flow rate under different operating conditions and different hydraulic transition processes during valve closing. Regardless of whether it is under normal or fault conditions, the maximum increase in water pressure and the maximum decrease in flow rate caused by the pressure relief valve closing at a specific time are always mutually exclusive; that is, the larger the maximum increase in water pressure, the smaller the corresponding decrease in flow rate.

[0028] For fault conditions, the variation patterns of the maximum pressure increase and the maximum flow decrease during the hydraulic transition are as follows: the maximum water pressure increase decreases as the valve closing time increases, while the maximum flow decrease increases as the valve closing time increases.

[0029] Under normal operating conditions, as the valve closing time increases, the increase in maximum water pressure and the decrease in maximum flow rate also show opposite trends, which is similar to the pattern under fault conditions. Therefore, there exists an optimal valve closing rule that minimizes both the increase in maximum water pressure and the decrease in maximum flow rate.

[0030] Example 1

[0031] Based on the above research results, this embodiment proposes a pressure relief device suitable for a water supply system with back pressure technology, including a water supply pipe 3 connected between the volute water inlet 1 and the tailwater pipe 2. An electric flow regulating valve 4 is installed on the water supply pipe 3. The electric flow regulating valve 4 is electrically connected to a control cabinet 5. A pressure transmitter 6 is installed on the pipeline between the electric flow regulating valve 4 and the volute water inlet 1. A first pressure switch 7 and a second pressure switch 8 are installed on the pipeline between the pressure transmitter 6 and the volute water inlet 1. The first pressure switch 7, the second pressure switch 8, and the pressure transmitter 6 are all electrically connected to the control cabinet 5.

[0032] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0033] In the above embodiment, the first pressure switch 7 is used to control the electric flow valve 4 to open, and the second pressure switch 8 is used to control the electric flow valve 4 to close; the pressure transmitter 6 is used to compare with the first pressure switch 7 and the second pressure switch 8 to avoid measurement errors by the first pressure switch 7 or the second pressure switch 8, which could lead to malfunction of the electric flow regulating valve 4; the control cabinet 5 is used to receive data from the first pressure switch 7, the second pressure switch 8 and the pressure transmitter 4, and to determine and control the opening or closing of the electric flow regulating valve 4.

[0034] Example 2

[0035] A control method for a pressure relief device in a water supply system with back pressure technology, defining the set pressure value of the first pressure switch 7 as P1 and the set pressure value of the second pressure switch 8 as P2:

[0036] When the switching quantity provided by the first pressure switch 7 and the analog quantity provided by the pressure transmitter 6 simultaneously reach the operating pressure P1+(P2-P1)×95%, the electric flow regulating valve 4 remains for 30 seconds. If the pressure of the pressure transmitter 6 is still higher than the operating value at this time, the control cabinet 5 controls the electric flow regulating valve 4 to execute the valve opening procedure. Both signals are indispensable.

[0037] During the valve opening process, when the pressure of the pressure transmitter 6 drops to P1+(P2-P1)×20%, the control cabinet 5 controls the electric flow regulating valve 4 to stop opening the valve.

[0038] When the electric flow control valve 4 is fully open, and the system pressure still cannot reach below P1+(P2-P1)×95%, the electric flow control valve 4 remains fully open.

[0039] Furthermore, in the valve closing procedure, when the pressure of the second pressure switch 8 and the pressure transmitter 6 drops to P1+(P2-P1)×5%, the electric flow regulating valve 4 remains open for 1 minute. If the pressure is still lower than P1+(P2-P1)×5% at this time, the control cabinet 5 controls the electric flow regulating valve 4 to close.

[0040] During the valve closing process, when the pressure of the pressure transmitter 6 exceeds P1+(P2-P1)×5% again, the electric flow regulating valve 4 stops closing and remains in place; when the pressure of the second pressure switch 8 and the pressure transmitter 6 drops to P1+(P2-P1)×5%, the valve closing procedure continues to be executed, and the above valve closing process is repeated until the electric flow regulating valve 4 is fully closed.

[0041] Furthermore, during the valve closing process, if the electric flow regulating valve 4 remains in a stopped state for more than 10 minutes, the control cabinet 5 exits the valve closing process and issues an alarm signal to remind maintenance personnel to adjust the technical water supply system.

[0042] It should be noted that the closing rate of the electric flow regulating valve 4 is calculated based on the characteristic compatibility equation of the water hammer calculation. Assuming that when the electric flow regulating valve 4 is fully open, the pressure of the pressure transmitter 6 is Pc=P1+(P2-P1)×5%, and the closing time t of the electric flow regulating valve 4 is given so that the maximum pressure at the pressure transmitter 6 is Pmax≈P2, the closing rate of the electric flow regulating valve 4 under this state is V=2π / t. Based on V, a suitable electric actuator is selected to control the opening and closing of the electric flow regulating valve 4.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A control method for a pressure relief device suitable for a water supply system with back pressure technology, wherein the pressure relief device includes a water supply pipe connected between a volute inlet and a tailpipe, an electric flow regulating valve installed on the water supply pipe, the electric flow regulating valve being electrically connected to a control cabinet, a pressure transmitter installed on the pipeline between the electric flow regulating valve and the volute inlet, the pressure transmitter being used to compare with a first pressure switch and a second pressure switch to avoid measurement errors by the first or second pressure switch, which could lead to malfunction of the electric flow regulating valve; a first pressure switch and a second pressure switch are installed on the pipeline between the pressure transmitter and the volute inlet, the first pressure switch being used to control the opening of the electric flow valve, and the second pressure switch being used to control the closing of the electric flow valve, the first pressure switch, the second pressure switch, and the pressure transmitter being electrically connected to the control cabinet; the set pressure value of the first pressure switch is defined as P1, and the set pressure value of the second pressure switch is defined as P2, characterized in that: When the switching quantity provided by the first pressure switch and the analog quantity provided by the pressure transmitter simultaneously reach the operating pressure P1+(P2-P1)×95%, the electric flow regulating valve remains for 30 seconds. If the pressure of the pressure transmitter is still higher than the operating value at this time, the control cabinet controls the electric flow regulating valve to execute the valve opening procedure. During the valve opening process, when the pressure transmitter pressure drops to P1+(P2-P1)×20%, the control cabinet controls the electric flow regulating valve to stop opening the valve. When the electric flow control valve is fully open, and the system pressure still cannot reach below P1+(P2-P1)×95%, the electric flow control valve remains fully open.

2. The control method for a pressure relief device in a water supply system with back pressure technology according to claim 1, characterized in that: When the pressure of the second pressure switch and pressure transmitter drops to P1+(P2-P1)×5%, the electric flow regulating valve remains for 1 minute. If the pressure is still lower than P1+(P2-P1)×5% at this time, the control cabinet controls the electric flow regulating valve to close. During the valve closing process, when the pressure of the pressure transmitter exceeds P1+(P2-P1)×5% again, the electric flow control valve stops closing and remains in place; when the pressure of the second pressure switch and the pressure transmitter drops to P1+(P2-P1)×5%, the valve closing procedure continues to be executed, and the above valve closing process is repeated until the electric flow control valve is fully closed.

3. The control method for a pressure relief device in a water supply system with back pressure technology according to claim 2, characterized in that: During the valve closing process, if the electric flow regulating valve remains in a stopped state for more than 10 minutes, the control cabinet will exit the valve closing process and issue an alarm signal to remind maintenance personnel to adjust the technical water supply system.

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