A double-suction centrifugal pump control system with cavitation protection function

Abstract

This invention relates to the field of double-suction centrifugal pump control system technology, and more particularly to a double-suction centrifugal pump control system with cavitation protection function, comprising a monitoring module, a triggering module, a booster capacity judgment module, a fault type judgment module, a cavitation analysis module, and a control execution module. This invention analyzes the differential changes in inlet and outlet pressures, the temporal variation of outlet pressure, and the fluctuation amplitude of drive motor current, progressively identifying three causes: normal operating response, gradual wear, and operating condition cavitation. This allows the control system to distinguish the true cause of the outlet pressure drop and execute control actions most closely matching the current actual state of the double-suction centrifugal pump based on the nature of the actual fault. This effectively solves the technical problems of existing technologies that struggle to accurately distinguish the causes of double-suction centrifugal pump outlet pressure drops and cannot effectively identify and implement targeted control for gradual wear and operating condition cavitation.

Description

Technical Field

[0001] This invention relates to the field of double-suction centrifugal pump control system technology, and in particular to a double-suction centrifugal pump control system with cavitation protection function. Background Technology

[0002] Double-suction centrifugal pumps are widely used in large-scale cascade water pumping stations due to their large flow rate and stable operation. During the operation of the pumping station, the inlet water level will fluctuate periodically due to factors such as upstream water inflow and downstream water consumption. The operating conditions of the double-suction centrifugal pump are closely related to the inlet water level of the pumping station forebay. A drop in the inlet water level will lead to a decrease in the pressure at the suction inlet of the double-suction centrifugal pump, thereby reducing the effective net positive suction head (NPSH) of the double-suction centrifugal pump and increasing the risk of cavitation.

[0003] However, in actual operation, when a drop in outlet pressure is detected, the existing control system cannot distinguish whether this pressure drop is a normal physical response to changes in inlet conditions or a sign of performance degradation in the double-suction centrifugal pump itself due to cavitation and impact wear from flowing sand in the water. The performance degradation of the double-suction centrifugal pump mainly takes two forms: first, progressive wear of the impeller and other flow components due to long-term scouring by abrasive materials such as silt carried in the water flow, leading to a permanent decrease in its pressurization capacity; second, operational cavitation caused by changes in operating conditions such as excessively low inlet water levels. The causes and consequences of these two types of performance degradation are completely different. The former is permanent damage accumulated over a long period, while the latter is a temporary phenomenon related to the current operating conditions. Existing pump protection systems typically trigger alarms or shutdowns based on absolute thresholds for outlet pressure, flow rate, or vibration, making it difficult to effectively distinguish between these situations. Simple low pressure alarms cannot identify the root cause of the pressure drop, easily misinterpreting normal operating conditions as faults, or responding to early cavitation reactions that are occurring and can be suppressed through adjustment. Furthermore, existing technologies often employ timed inspection diagnostic methods, whose diagnostic timing is disconnected from the actual point of risk occurrence, resulting in insufficient diagnostic efficiency and specificity. Therefore, there is an urgent need for a dual-suction centrifugal pump control method and system capable of accurately distinguishing the causes of outlet pressure drops and identifying progressive wear and condition-related cavitation. Summary of the Invention

[0004] To address the technical problem mentioned in the background art, where existing technologies struggle to accurately distinguish whether a drop in outlet pressure of a double-suction centrifugal pump is caused by changes in inlet conditions or by performance degradation of the pump itself, thus failing to effectively identify and implement targeted control for progressive wear and operational cavitation, this invention provides a double-suction centrifugal pump control system with cavitation protection function.

[0005] To achieve the above objectives, the present invention provides a dual-suction centrifugal pump control system with cavitation protection function, comprising: The monitoring module is used to obtain the inlet water level, inlet pressure, outlet pressure, and drive motor current of the double-suction centrifugal pump. The trigger module is used to trigger the diagnostic process when a preset drop in the inlet water level is detected. The boosting capacity judgment module is used to determine whether the boosting capacity of the double-suction centrifugal pump has decreased based on the changes in inlet and outlet pressures after the diagnostic process is triggered. The fault type determination module is used to respond to the decrease in the boosting capacity of the double-suction centrifugal pump. Based on the time-series change pattern of the outlet pressure, it determines whether the performance degradation is dominated by progressive wear or by condition-related cavitation. The cavitation analysis module is used to classify the severity of cavitation in response to performance degradation being dominated by operating condition cavitation, based on the fluctuation range of drive motor current associated with changes in outlet pressure pattern. The control execution module is used to perform corresponding protective control actions or early warning actions based on the severity of cavitation.

[0006] The system uses the natural operational event of a drop in inlet water level as a natural trigger signal for diagnosis. Through progressive logical judgment, it achieves accurate identification of the causes of performance degradation in dual-suction centrifugal pumps.

[0007] Furthermore, the triggering module includes a water level threshold detection unit, which is used to trigger the diagnostic process when the inlet water level is detected to drop below a preset attention level or when the inlet water level is detected to drop below a preset danger level.

[0008] The water level threshold detection unit uses an event-driven triggering method to ensure that the diagnosis is initiated only when the risk of cavitation actually increases, avoiding ineffective periodic inspections and improving the targeting and efficiency of the diagnosis.

[0009] Furthermore, the boosting capacity judgment module includes a differential pressure comparison unit, which is used to compare the decrease in outlet pressure with the decrease in inlet pressure during a water level drop event. When the decrease in outlet pressure is greater than the decrease in inlet pressure, it is determined that the boosting capacity of the double-suction centrifugal pump has decreased.

[0010] The differential pressure comparison unit's judgment method is based on the basic working principle of the double-suction centrifugal pump. If the boosting capacity remains unchanged, the decrease in inlet pressure and outlet pressure should be basically equal. Any excessive decrease in outlet pressure indicates a weakening of the double-suction centrifugal pump's own boosting capacity, providing a clear basis for subsequent diagnosis.

[0011] In one embodiment, the boosting capacity judgment module further includes an auxiliary verification unit, which is used to selectively perform auxiliary verification after determining that the boosting capacity of the double-suction centrifugal pump has decreased. The auxiliary verification includes fine-tuning the outlet valve when the inlet water level is relatively stable, and confirming whether the boosting capacity of the double-suction centrifugal pump has indeed decreased based on the response of the outlet pressure.

[0012] The auxiliary verification step can provide secondary confirmation when the judgment result is in a critical state. By observing the response capability of the dual-suction centrifugal pump to minor changes in operating conditions, the robustness of the judgment is enhanced.

[0013] Furthermore, the fault type determination module includes a morphology determination unit, which determines that when the temporal change pattern of the outlet pressure is approximately linear and the rate of decrease remains stable, the performance degradation is dominated by progressive wear; and when the temporal change pattern of the outlet pressure is characterized by a pressure decrease inflection point and the rate of decrease after the inflection point is higher than the rate of decrease before the inflection point, the performance degradation is dominated by operating condition cavitation.

[0014] The morphology determination unit utilizes the differentiated characteristics exhibited by different failure modes during dynamic response: Progressive wear-dominated pressure reduction, where the degree of damage remains constant throughout the inlet water level decline, has a uniform and continuous impact on outlet pressure; operational cavitation-dominated pressure, on the other hand, exhibits spontaneous acceleration. When the inlet pressure drops below a certain critical value, cavitation is triggered. The generation and collapse of bubbles further exacerbate the local pressure distribution, leading to more bubble formation and a positive feedback acceleration effect. This is represented on the outlet pressure curve as a sudden shift from uniform to accelerated decline—an inflection point. This differentiated characteristic allows the two failure modes to be distinguished by the temporal variation of the outlet pressure.

[0015] Preferably, the cavitation analysis module includes a current swing detection unit, which is used to determine the severity of cavitation based on the fluctuation amplitude of the drive motor current before and after the inflection point of accelerated decrease in outlet pressure, and based on whether the current has a continuous downward trend, so as to determine whether it is in a stage that can be suppressed by operation adjustment or a stage that is difficult to suppress by operation adjustment.

[0016] The fluctuation of motor current directly reflects the stability of the shaft power of a double-suction centrifugal pump. The generation and collapse of bubbles during cavitation are the main reasons for unstable shaft power. Therefore, by analyzing the fluctuation range of the drive motor current, the development stage of cavitation can be accurately and sensitively determined.

[0017] Furthermore, the control execution module includes an adjustment control unit and an alarm shutdown unit.

[0018] The regulation and control unit is used to perform protective control actions, including speed regulation and / or valve regulation, in response to cavitation being in a stage that can be suppressed by operational regulation.

[0019] The alarm shutdown unit is used to respond to the stage where cavitation is difficult to suppress through operation adjustment, to perform shutdown protection and output an alarm signal.

[0020] The adjustment control unit and the alarm shutdown unit constitute a hierarchical processing strategy, which realizes precise response to faults. It can both promptly suppress early cavitation and prevent damage from spreading, and decisively deal with severe cavitation to prevent catastrophic accidents.

[0021] Furthermore, the adjustment and control unit includes a speed adjustment subunit, an effect judgment subunit, and a correction adjustment subunit.

[0022] The speed regulation subunit is used to reduce the speed of the double-suction centrifugal pump according to the degree to which the fluctuation of the drive motor current deviates from the normal operating state.

[0023] The effect judgment subunit is used to determine whether the current adjustment measures are effective after speed adjustment, based on the direction of change in the fluctuation amplitude of the drive motor current relative to the normal operating state, so as to determine whether further adjustment of the double-suction centrifugal pump is needed.

[0024] The correction adjustment subunit is used to close the outlet valve or further reduce the speed when the effect judgment subunit determines that the current adjustment measures are insufficient, and to re-trigger the effect judgment subunit for evaluation after the correction operation is performed.

[0025] The speed regulation subunit, effect judgment subunit, and correction regulation subunit constitute a closed-loop control, which adaptively responds to different degrees of cavitation conditions, avoiding the continued development of cavitation due to insufficient regulation or the impact on the normal output of the double-suction centrifugal pump due to excessive regulation.

[0026] Optionally, the dual-suction centrifugal pump control system with cavitation protection function described in this invention further includes a damage verification module, which is used to verify whether the dual-suction centrifugal pump has suffered permanent damage by comparing the current outlet pressure with the outlet pressure under the initial calibration state when the water level returns to the normal zone after a complete cycle of water level drop and rise, under the same operating conditions of the same rotation speed and the same valve opening.

[0027] The damage verification module can distinguish between reversible performance degradation caused by cavitation under operating conditions and permanent damage caused by cavitation erosion or wear, providing key data for equipment maintenance decisions and health status assessments.

[0028] To address the issue that progressive wear may be overlooked for a long time in some pumping stations with low sediment content and stable inlet water levels due to the lack of water level drop events, the triggering module of this invention may also include a time backup detection unit.

[0029] The time backup detection unit is used to trigger a diagnostic process once when the cumulative running time of the double-suction centrifugal pump reaches the preset maintenance interval and no diagnostic process is triggered due to water level changes during this period.

[0030] The time-backup detection unit serves as an effective supplement to the event-driven mechanism, ensuring that even under stable operating conditions, slow and cumulative performance degradation can be detected in a timely manner.

[0031] Compared with the prior art, the present invention has the following beneficial effects: By analyzing the differential change of inlet and outlet pressure, the temporal change pattern of outlet pressure, and the fluctuation amplitude of drive motor current, the present invention progressively isolates the different causes of three types of outlet pressure drop: normal operating condition response, progressive wear, and operating condition cavitation. This enables the control system to distinguish the true cause of the outlet pressure drop and execute the control action that best matches the current actual state of the double-suction centrifugal pump based on the nature of the actual fault. This effectively solves the technical problems of the prior art, which is unable to accurately distinguish the cause of the outlet pressure drop of the double-suction centrifugal pump and cannot effectively identify and take targeted control measures for progressive wear and operating condition cavitation.

[0032] Furthermore, this invention can not only identify the occurrence of cavitation but also classify its severity and implement differentiated protection strategies, ranging from online adjustment to alarm shutdown. This avoids a one-size-fits-all approach to control, effectively suppressing early cavitation, extending equipment life, and preventing unnecessary downtime, thus ensuring the continuity and economy of the water supply system.

[0033] Furthermore, by comparing the performance of the double-suction centrifugal pump after the water level rises, this invention can determine whether a single cavitation event has caused permanent damage, enabling long-term tracking and evaluation of the equipment's health status and providing a scientific basis for maintenance decisions.

[0034] Furthermore, the monitoring parameters relied upon by this invention are all conventional configurations of pumping stations, requiring no additional, invasive, and expensive sensors. Its event-driven diagnostic logic is activated only when necessary, with low computational load, high reliability, and easy modification based on existing control systems. Attached Figure Description

[0035] Figure 1 This is a system diagram of a dual-suction centrifugal pump control system with cavitation protection function in an embodiment of the present invention.

[0036] Figure 2This is a logic flowchart of the boosting capacity judgment module in an embodiment of the present invention.

[0037] Figure 3 This is a logic flowchart of the cavitation analysis module in an embodiment of the present invention.

[0038] Figure 4 This is a flowchart of the closed-loop control logic of the control unit in an embodiment of the present invention. Detailed Implementation

[0039] To make the objectives and advantages of the present invention clearer, the present invention will be further described below with reference to embodiments; it should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0040] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0041] To address the difficulty in accurately distinguishing between operational cavitation and progressive wear in existing technologies when performance degradation in dual-suction centrifugal pumps is caused by cavitation degradation, this invention provides a dual-suction centrifugal pump control system with cavitation protection. This invention utilizes an existing edge computing system, using the monitoring of the inlet water level drop—a natural process during pump station operation—as a diagnostic trigger and information carrier. It performs a progressive, local, and rapid analysis of the dynamic evolution of multi-dimensional physical parameters of the dual-suction centrifugal pump in response to water level changes. This enables precise identification of the root cause of the fault and differentiated execution of countermeasures, effectively distinguishing between operational cavitation and permanent damage, and executing corresponding protection and control strategies accordingly.

[0042] In this invention, some terms have specific technical meanings. Among them, operating condition cavitation is a cavitation phenomenon caused by changes in operating conditions, such as a drop in inlet water level, which can be alleviated or eliminated by adjusting the operating conditions, such as reducing the speed or closing the valve. It is different from the permanent performance decline caused by the impeller being subjected to long-term cavitation and abrasive wear, resulting in structural incompleteness. In contrast, permanent damage is a decline in the performance of a double-suction centrifugal pump or physical damage to components caused by long-term erosion of cavitation or abrasive wear, which cannot be recovered even after returning to good operating conditions. For example, erosion pits or material peeling on the blade surface.

[0043] The technical solution of the present invention will be described in detail below. Please refer to [link / reference]. Figure 1As shown, the present invention provides a control system for a double-suction centrifugal pump with cavitation protection function, comprising: a monitoring module, which acquires the inlet water level, inlet pressure, outlet pressure, and drive motor current of the double-suction centrifugal pump from existing sensors that can be installed at the pumping station site. For example, a level gauge can be installed in the forebay, a pressure transmitter can be installed at the inlet and outlet flanges of the double-suction centrifugal pump, and a current transformer can be installed above the motor power supply line; a triggering module, which triggers a diagnostic process when a preset drop in the inlet water level is detected; and a booster capacity judgment module, which, after the diagnostic process is triggered, determines the booster capacity based on the inlet water level... The system uses several modules: a pressure and outlet pressure change module to determine if the boosting capacity of the double-suction centrifugal pump has decreased; a fault type determination module to determine whether the performance degradation is dominated by progressive wear or operational cavitation based on the temporal variation of the outlet pressure; a cavitation analysis module to classify the severity of cavitation based on the fluctuation of the drive motor current associated with the outlet pressure change, in response to performance degradation dominated by operational cavitation; and a control execution module to execute corresponding protection control actions or early warning actions based on the severity of cavitation.

[0044] Specifically, this invention analyzes the differential changes in inlet and outlet pressures, the temporal changes in outlet pressure, and the fluctuations in drive motor current. By progressively identifying the different causes of outlet pressure decline—normal operating response, progressive wear, and operating condition cavitation—the invention enables the control system to distinguish the true cause of the outlet pressure decline and execute control actions that best suit the current actual state of the double-suction centrifugal pump based on the nature of the actual fault. This effectively solves the technical problems of existing technologies that make it difficult to accurately distinguish the causes of outlet pressure decline in double-suction centrifugal pumps and cannot effectively identify and implement targeted control for progressive wear and operating condition cavitation.

[0045] In this embodiment, the temporal variation of the outlet pressure is the curve shape of the outlet pressure changing with time or with the inlet water level throughout the entire time period of the inlet water level decline. This invention focuses on whether it decreases approximately linearly or exhibits nonlinear characteristics of accelerating decline after a specific inflection point.

[0046] In this embodiment, the fluctuation range of the drive motor current refers to the difference between the maximum and minimum values ​​of the input current of the motor driving the double-suction centrifugal pump within a certain time window, or the ratio of the difference to the average value, which is used to indirectly identify the stability of the shaft power of the double-suction centrifugal pump, and thus reflect the severity of cavitation bubble formation and collapse.

[0047] Based on the above scheme, the triggering module includes a water level threshold detection unit.

[0048] The water level threshold detection unit is pre-set with at least two key water level thresholds: a higher warning water level and a lower danger water level. Both the warning water level and the danger water level are set based on the required net positive suction head (NPSH) curve of the double-suction centrifugal pump and the design minimum operating water level of the pumping station. Specifically, based on the required NPSH of the double-suction centrifugal pump at rated flow, combined with the design minimum operating water level of the pumping station forebay, the lowest inlet water level that ensures the pump does not cavitation is calculated and used as a reference for setting the danger water level. At least one safety margin is reserved above the danger water level as a reference for setting the warning water level. The safety margin is determined based on the historical operating data of the pumping station to provide an early warning window before the risk of cavitation materializes.

[0049] When the real-time inlet water level obtained by the monitoring module drops below the preset warning water level for the first time from the normal area, or further drops below the preset danger water level from the warning area, the water level threshold detection unit is activated, which determines that a preset drop event has occurred and immediately triggers the subsequent diagnostic process.

[0050] Specifically, this invention avoids the problem of excessively frequent traditional timed inspections leading to a large number of invalid diagnoses when the water level is stable, while excessively lenient inspections result in the loss of monitoring effectiveness for the dual-suction centrifugal pump. By precisely focusing computing resources and diagnostic logic on the moment when the risk of cavitation actually increases, the invention increases the pertinence and actual efficiency of the diagnostic process.

[0051] Based on the above solutions, such as Figure 2 As shown, this is the internal logic flow of the boosting capacity judgment module, which includes a differential pressure comparison unit.

[0052] Once the diagnostic process is triggered, the differential pressure comparison unit records and calculates the total decrease in outlet pressure and the total decrease in inlet pressure during the inlet water level drop event.

[0053] Ideally, if the impeller of the double-suction centrifugal pump is intact and its boosting capacity remains constant, then the decrease in inlet pressure will be equally transmitted to the outlet; that is, the decrease in outlet pressure should be approximately equal to the decrease in inlet pressure. However, when the differential pressure comparison unit finds, through statistical analysis and calculation, that the decrease in outlet pressure is significantly greater than the decrease in inlet pressure, it is determined that the boosting capacity of the double-suction centrifugal pump itself has decreased. Thus, the boosting capacity judgment module completes its preliminary judgment, confirming that there is a problem with the double-suction centrifugal pump itself, providing the necessary premise for subsequent fault type determination.

[0054] In practical engineering applications, the comparison between the outlet pressure drop and the inlet pressure drop is made by comparing the difference between the two with a preset allowable deviation value. During the pump station commissioning phase, under the conditions of normal water level and steady-state operation of the double-suction centrifugal pump, the allowable deviation value is determined by continuously collecting inlet and outlet pressure data, calculating the fluctuation amplitude of the two within the same time window, and taking the larger of the inlet pressure fluctuation amplitude and the outlet pressure fluctuation amplitude as the allowable deviation value. The allowable deviation value is used to determine the inherent noise level of the measurement channel and the parameter fluctuation range under normal operating conditions, so as to eliminate the interference of measurement error and normal fluctuation on the judgment.

[0055] When the deviation between the outlet pressure drop and the inlet pressure drop is less than or equal to the allowable deviation value, the two are considered to be approximately equal, and the boosting capacity has not decreased. When the portion of the outlet pressure drop that exceeds the inlet pressure drop is greater than the allowable deviation value, the boosting capacity is considered to have decreased.

[0056] As a preferred implementation method, please continue reading. Figure 2 The boosting capacity judgment module also includes an auxiliary verification unit.

[0057] The auxiliary verification unit is used to provide an optional auxiliary verification step to enhance the reliability of the judgment after the differential pressure comparison unit determines that the boosting capacity has decreased. The auxiliary verification step performs a more accurate secondary judgment when the difference between the outlet pressure drop and the inlet pressure drop is close to the preset allowable deviation value, or when the complex on-site working conditions cause fluctuations in the measured value.

[0058] When the auxiliary verification unit performs auxiliary verification, when the inlet water level is temporarily stable at a certain position, the control system actively and slightly closes the outlet valve. Subsequently, the auxiliary verification unit closely monitors the response of the outlet pressure: if the outlet pressure can rise significantly after the valve is closed, it indicates that the impeller's pressurization capability is reliable, and the pressure difference judged by the pressure difference comparison unit is too large, which may be caused by measurement error or instantaneous fluctuation; conversely, if the outlet pressure does not rise significantly or even continues to drop after the valve is closed, it indicates that there is indeed a flow deterioration such as cavitation bubbles or severe wear inside the impeller flow channel, and the pressurization capability has indeed decreased. For example, the outlet valve is closed by a small fixed angle, which can be 2% to 3% of the opening. This adjustment amount is only an example value. Its specific value is determined according to the size of the outlet valve and the characteristics of the pipeline, with the standard that the adjustment amount can cause an observable response in the outlet pressure, while not significantly affecting the water flow rate of the double-suction centrifugal pump.

[0059] The auxiliary verification unit provides a means of secondary verification for the system through simple operations that do not require modification to the pump body structure, thereby improving the accuracy of diagnosis.

[0060] After confirming a decrease in boost capacity, the fault type determination module starts working. In a preferred embodiment, the fault type determination module includes a morphology determination unit.

[0061] The morphology determination unit is used to distinguish different performance degradation characteristics corresponding to the decrease in pressurization capacity. The morphology determination unit makes its determination by analyzing the temporal change pattern of the outlet pressure during the entire inlet water level decline. During the water level decline, if the outlet pressure decreases approximately linearly with time or the inlet water level, and there is no significant acceleration in the rate of decrease during the decline, then the current performance degradation is determined to exhibit characteristics corresponding to progressive wear, and the performance degradation is determined to be dominated by progressive wear. If the outlet pressure remains relatively flat in the initial stage of the decline, and then shows a clear inflection point after the inlet water level further declines to a certain level, and the rate of decrease in outlet pressure after the inflection point is significantly increased compared to before the inflection point, then the current performance degradation is determined to exhibit characteristics corresponding to operating condition cavitation, and the performance degradation is determined to be dominated by operating condition cavitation.

[0062] The approximately linear decrease indicates a relatively stable degradation of the booster capacity of the dual-suction centrifugal pump as inlet conditions change, while the accelerated decrease after the inflection point characterizes a further rapid deterioration of the booster capacity under specific inlet conditions. Identifying the changing patterns during the outlet pressure decrease process can provide a basis for distinguishing between progressive wear and condition-related cavitation.

[0063] In this embodiment, the approximately linear descent pattern is generally consistent with the global and stable degradation loss characteristics of the double-suction centrifugal pump. Therefore, it is highly consistent with the progressive wear characteristics that occur after the impeller has been running for a long time. The presence of an inflection point and the accelerated descent pattern after the inflection point indicates that when the inlet pressure drops below a certain critical value, cavitation is triggered and develops rapidly. The generation and aggregation of bubbles lead to a reduction in the effective flow area of ​​the flow channel, which ultimately leads to a sharp deterioration in the pressurization capacity of the double-suction centrifugal pump. This is consistent with the typical outlet pressure change characteristics of working condition cavitation.

[0064] Specifically, by analyzing the temporal variation of outlet pressure, this invention successfully separates two completely different types of faults: progressive wear and condition-related cavitation.

[0065] When the fault type is determined to be performance degradation dominated by progressive wear, the system records this determination result in the health record of the double-suction centrifugal pump along with the current cumulative operating time, and accumulates the number of wear diagnoses for the double-suction centrifugal pump. When the cumulative number of wear diagnoses reaches the maintenance threshold, the system outputs a maintenance prompt, suggesting that the impeller be inspected or replaced during the planned shutdown window. Simultaneously, considering that after impeller wear, the blade inlet edge becomes blunt and the surface roughness of the flow channel increases, the pump's required net positive suction head (NPSH) is higher than in the healthy state, making cavitation more likely to occur under the same inlet water level conditions. The system will shift the set values ​​of the attention water level and the danger water level towards a preset safety margin at higher levels, so that subsequent diagnostic processes can be initiated earlier at higher water levels. The maintenance threshold and safety margin are determined by those skilled in the art during the pump station commissioning phase based on tests conducted according to different wear conditions and actual operating performance of the pump.

[0066] When the fault type is determined to be performance degradation dominated by operating condition cavitation, the cavitation analysis module will quantify the severity of cavitation as a preferred implementation method, such as... Figure 3 As shown, it is the logic flowchart of the cavitation analysis module, which includes a current swing detection unit.

[0067] The current swing detection unit is based on the obvious dynamic fluctuation characteristics of the generation, development and collapse of bubbles during cavitation. The generation and collapse of bubbles will cause pulsation of the fluid force on the impeller, which in turn will cause fluctuations in the torque and power of the double-suction centrifugal pump shaft. Therefore, by monitoring the fluctuation of the input current of the drive motor, the impact of the cavitation process on the operating stability of the double-suction centrifugal pump can be indirectly reflected.

[0068] The current swing detection unit is used to analyze the fluctuation amplitude of the drive motor current before and after the fault type determination module identifies the inflection point of accelerated decrease in outlet pressure, and compare the current fluctuation amplitude with the fluctuation amplitude benchmark under normal operating conditions to determine whether there is an identifiable deviation in the current fluctuation. When the current fluctuation amplitude has an identifiable deviation from the normal operating conditions, the unit further analyzes the changing trend of the average value of the drive motor current and determines the stage of cavitation accordingly.

[0069] When the current fluctuation amplitude does not deviate identibly from the normal operating state, it indicates that the disturbance caused by the current cavitation on the operating state of the double-suction centrifugal pump has not reached the preset significant level, and the system maintains the current operating state. When the current fluctuation amplitude deviates identibly from the normal operating state and the average current does not show a continuous downward trend, it is determined that the current cavitation is in a stage that can be suppressed by operation adjustment. When the current fluctuation amplitude deviates identibly from the normal operating state and the average current further shows a continuous downward trend, it is determined that the current cavitation has developed to the stage where the operation adjustment and suppression capability is insufficient, and the corresponding alarm or shutdown protection is triggered accordingly.

[0070] It should be noted that the above-mentioned stage judgment does not directly equate the decrease in the average current value with the severity of cavitation. Instead, it judges the current cavitation state and the degree of suppression of operation adjustment by combining the characteristics of the current fluctuation amplitude and the trend of the current average value change. In particular, considering that the physical meaning of the continuous decrease in the average current value is the continuous decrease in the shaft power of the double-suction centrifugal pump, and the decrease in shaft power means that the energy transferred by the impeller to the fluid is continuously reduced, the continuous decrease in shaft power under the condition of continuous decrease in inlet water level indicates that the effective flow area in the flow channel is constantly decreasing, and bubbles have begun to occupy a considerable proportion of the flow channel space. This makes the actual work of the impeller gradually become the gas-liquid mixture, the equivalent density of the fluid medium decreases, and the effective conversion rate of the impeller output power decreases accordingly. At this time, the bubbles are no longer limited to the vicinity of the impeller inlet, but gradually diffuse into the interior of the flow channel and continue to exist. Even if the required net positive suction head is reduced by reducing the speed, or the operating point is changed by closing the valve, the bubbles already existing in the flow channel will not disappear immediately due to the adjustment action. While the adjustment means change the bubble generation rate, the effect of clearing the gas clouds that have occupied the flow channel space is limited. Therefore, when the average current shows a continuous downward trend, the current swing detection unit determines that cavitation has entered a stage where it is difficult to effectively suppress through operational adjustments. At this point, relying solely on adjustment methods has limited effect, and continued operation may lead to cumulative damage. Conversely, when the average current does not show a continuous downward trend, it indicates that the shaft power has not experienced a trend of decline, and the bubbles in the flow channel are still mainly generated and collapsed locally, without causing continuous encroachment on the effective flow area. At this time, reducing the rotational speed to decrease the required net positive suction head (NPSH) or closing the valve slightly to change the operating point can improve the inlet conditions, help suppress further bubble formation, and potentially alleviate cavitation.

[0071] Specifically, the current swing detection unit collects current data within a preset time window before and after the inflection point, calculates the difference between the maximum and minimum values ​​of the current sequence collected within the preset time window, and uses the ratio of this difference to the average current value within the preset time window as the quantified value of the fluctuation amplitude. This value is then compared with the benchmark value of the current fluctuation amplitude under normal operating conditions to determine whether the fluctuation amplitude deviates from the normal operating conditions. The length of the preset time window is determined based on the rated speed and number of blades of the double-suction centrifugal pump. The reciprocal of the impeller rotation frequency is used as the basic time unit, and the window length is taken as several to tens of times the basic time unit to ensure that a sufficient number of fluctuation cycles are captured to reflect the hydraulic pulsation characteristics caused by cavitation.

[0072] In this embodiment, the reference value of the current fluctuation amplitude under normal operating conditions is obtained through measured data during the pump station commissioning phase or when the water level is normal. The statistical envelope of the measured data is taken as the reference value to cover the inherent noise level of current fluctuation under normal operating conditions. When the currently measured current fluctuation amplitude is compared with the reference value, if there is no identifiable deviation, it indicates that the flow disturbance caused by cavitation is still in the stage where it has not yet produced obvious fluctuations in the current signal. When the current fluctuation amplitude shows an identifiable deviation, the current swing detection unit further combines the changing trend of the average current value to determine whether the current cavitation is still in the stage that can be suppressed by operation adjustment.

[0073] In this embodiment, the determination of a continuous downward trend adopts the sliding window comparison method. Under the conditions of normal water level and steady-state operation of the double-suction centrifugal pump during the pump station commissioning phase, time-series data of the average current are collected. The maximum rate of change of the average current due to normal load fluctuations within this period is calculated, and a multiple of this maximum rate of change is taken as the threshold for determining the downward trend. When the measured rate of decrease of the average current exceeds this threshold, it is determined that there is a continuous downward trend. The length of the sliding window should be as short as possible while ensuring coverage of a sufficient number of hydraulic pulsation cycles to reflect trend changes rather than instantaneous disturbances.

[0074] Specifically, by further clarifying the degree of cavitation development under the premise that cavitation has occurred, the system can distinguish between the early stage, which can still be suppressed by operational adjustments, and the severe stage, which has developed to the point where adjustment measures are ineffective. Based on the distinction, the system provides a direct basis for the control execution module to select adjustment control or alarm shutdown, so that the protection action can match the actual degree of cavitation damage and reduce the probability of premature shutdown affecting water supply or late intervention causing more serious equipment damage.

[0075] Based on the results of the cavitation classification, the control execution module will adopt differentiated response measures, as a preferred implementation method, such as... Figure 4As shown, it is a closed-loop regulation logic flowchart of the regulation control unit in response to moderate cavitation. The control execution module includes the regulation control unit and the alarm shutdown unit.

[0076] The adjustment and control unit is used to respond to the cavitation analysis module's determination that cavitation is in a stage that can be suppressed by operational adjustment, and to perform corresponding protective adjustment actions. Specifically, when the double-suction centrifugal pump is equipped with a frequency converter, the adjustment and control unit reduces the operating speed of the double-suction centrifugal pump; when the operating point needs to be adjusted, the adjustment and control unit can also appropriately close the outlet valve to change the operating point of the double-suction centrifugal pump, thereby changing the fluctuation amplitude of the drive motor current to the range corresponding to the normal operating state, and judging the suppression effect of the current adjustment on cavitation disturbance based on this.

[0077] The alarm shutdown unit is used in response to the cavitation analysis module determining that cavitation has reached a stage that is difficult to suppress through operational adjustments. It executes shutdown protection and outputs an alarm signal. Specifically, the alarm shutdown unit outputs a cavitation alarm signal of the corresponding level to the central control system and controls the dual-suction centrifugal pump to execute the shutdown procedure. If the pumping station is equipped with a standby pump, it can also send a standby pump switching command to the pumping station control system to reduce the impact of the continued operation of the damaged dual-suction centrifugal pump on the pumping station's water supply process.

[0078] In order to achieve closed-loop control of the adjustment process, in one specific implementation, the adjustment control unit includes a speed adjustment subunit, an effect judgment subunit, and a correction adjustment subunit.

[0079] The speed regulation subunit is used to determine the initial speed regulation amount based on the deviation of the fluctuation amplitude of the current drive motor current from the normal operating state when operation adjustment is required, and to reduce the operating speed of the double-suction centrifugal pump. The initial speed regulation amount can be determined according to the operating characteristics of the double-suction centrifugal pump at different speeds and the actual operating conditions of the pump station. For example, during the commissioning phase of the pump station, operating status data corresponding to different speeds are obtained, and the speed regulation range applicable to the current pump group is determined based on the operating status data, so that the speed regulation amount can meet the operating requirements of the pump station while suppressing cavitation disturbances.

[0080] The effect judgment subunit is used to reacquire the drive motor current after the speed adjustment is completed and compare the current fluctuation amplitude before and after the adjustment. When the deviation of the current fluctuation amplitude after adjustment from the normal operating state is reduced, the current speed adjustment is determined to be effective, and the current adjustment process is ended or the current operating state is maintained. When the current fluctuation amplitude after adjustment is not reduced or further increased, the current speed adjustment is determined to be insufficient, and further adjustment commands are output to the correction adjustment subunit.

[0081] The correction adjustment subunit responds to the further adjustment command output by the effect judgment subunit by performing a correction adjustment to close the outlet valve and / or further reduce the operating speed of the double-suction centrifugal pump. The adjustment amount of closing the outlet valve and further reducing the speed can be predetermined based on the operating characteristics of the double-suction centrifugal pump, the adjustment characteristics of the outlet valve, and the operating conditions of the pump station pipeline. After completing the correction adjustment, the effect judgment subunit reacquires the drive motor current and judges whether the current adjustment is effective based on the change in the current fluctuation amplitude before and after the correction adjustment, thus forming a closed-loop process of adjustment, judgment, and readjustment.

[0082] When the fluctuation amplitude of the drive motor current deviates from the normal operating state to a preset acceptable range, it is determined that the current cavitation disturbance has been effectively suppressed, the adjustment process ends and the current operating state is maintained; when after a preset number of adjustments, or after the current adjustment amount reaches the preset adjustment upper limit, the fluctuation amplitude of the drive motor current still does not decrease to the acceptable range, or the average current continues to show a continuous downward trend, it is determined that the current operation adjustment is insufficient to suppress cavitation, and the control is transferred to the alarm shutdown unit.

[0083] The acceptable range characterizes the permissible deviation of the drive motor current fluctuation amplitude from the normal operating state. It can be determined during the pump station commissioning phase by collecting drive motor current data of the double-suction centrifugal pump under normal operating conditions. The preset adjustment number and preset adjustment upper limit are determined based on the operating capacity of the double-suction centrifugal pump, the pump station's water supply requirements, and the safe operating range.

[0084] Specifically, this embodiment re-detects the fluctuation amplitude of the drive motor current after each adjustment, using the change in drive motor current as feedback information to judge the adjustment effect. This allows the control execution module to determine whether to continue adjusting based on the actual adjustment result, rather than completing the control all at once according to a preset fixed adjustment amount. When the current fluctuation amplitude changes towards the range corresponding to the normal operating state and reaches an acceptable range, it indicates that the current adjustment measures can effectively reduce abnormal disturbances during operation, and the system ends further adjustment. When the acceptable range is still not reached after continuous adjustment, and the average current value further shows a continuous downward trend, it indicates that the adjustment measures under the current operating conditions are insufficient to maintain the stable operation of the double-suction centrifugal pump, and the system switches to alarm shutdown processing, thereby avoiding the double-suction centrifugal pump from operating in a continuous cavitation state.

[0085] To assess whether a cavitation event has caused permanent damage to the dual-suction centrifugal pump, as a preferred embodiment, the dual-suction centrifugal pump control system with cavitation protection function of the present invention further includes a damage verification module.

[0086] The damage verification module responds after a complete water level drop-rise cycle by comparing the current outlet pressure with the initial calibration pressure under the same operating conditions (same speed and valve opening) to verify whether the double-suction centrifugal pump has suffered permanent damage. Specifically, when the monitoring module detects that the inlet water level has risen from the previous warning or danger zone to the normal operating zone, the damage verification module controls the double-suction centrifugal pump to operate under the exact same conditions as before the water level drop, i.e., restoring the initial speed and valve opening. Under this baseline condition, the damage verification module measures and records the current outlet pressure and compares it with the outlet pressure stored in the system archive under the same conditions during new pump commissioning or the last verification of normal operation (i.e., the initial calibration pressure). If the difference between the pressure and the outlet pressure under healthy conditions is within the allowable measurement error range, the cavitation event is determined to be operational, without causing irreversible physical damage to the double-suction centrifugal pump, and the pump's performance has not permanently degraded. It can continue operating according to the original strategy. Conversely, if the current outlet pressure is significantly lower than the initial calibration pressure, creating an unrecoverable pressure difference, it is determined that components such as the impeller have suffered permanent damage. In this case, the system marks the double-suction centrifugal pump as damaged in its health record and adjusts its protection strategy accordingly. In future operation, attention will be paid to appropriately raising the thresholds for water level and dangerous water level to provide earlier warning triggering opportunities. This allows for early intervention and protection during subsequent water level drops, preventing further damage to the already damaged double-suction centrifugal pump due to cavitation impact.

[0087] Considering that in application scenarios where the sediment content of the water source is extremely low and the upstream water flow is extremely stable, the double-suction centrifugal pump may operate under a constant high water level for a very long time and will not trigger the diagnostic process driven by the drop in water level. In order to capture this long-term wear that is difficult to detect through conventional triggering mechanisms, as a preferred implementation, the triggering module also includes a time backup detection unit.

[0088] The time backup detection unit is used to forcibly trigger a diagnostic process when the cumulative running time reaches the preset maintenance interval and the system has never performed a complete diagnostic process due to water level changes during this period. The preset maintenance interval is determined according to the design overhaul cycle and maintenance plan of the double-suction centrifugal pump. For example, it can be set to half of an overhaul cycle or the duration of a maintenance interval.

[0089] To more fully demonstrate the preferred embodiments of the present invention, a complete embodiment including all technical features is described below.

[0090] Specifically, when the double-suction centrifugal pump was running stably at a pumping station in a Yellow River irrigation area, the cumulative running time had not yet triggered the backup detection unit. Due to upstream scheduling, the inlet water level of the pumping station began to drop slowly. When the water level dropped to the preset warning level, the trigger module activated the entire diagnostic process.

[0091] After collecting and comparing data, the boosting capacity assessment module found that the decrease in outlet pressure was significantly greater than the decrease in inlet pressure, indicating a decrease in boosting capacity. Due to the large difference, the system skipped the auxiliary verification step. Subsequently, the fault type assessment module analyzed the outlet pressure time-series data since the water level began to drop, clearly observing the appearance of an inflection point. After the inflection point, the pressure decreased at an accelerated rate, and the rate of pressure decrease after the inflection point was higher than before the inflection point. Therefore, the fault was determined to be primarily operational cavitation.

[0092] After cavitation was detected, the cavitation analysis module immediately analyzed the fluctuation characteristics of the drive motor current near the inflection point. The current fluctuation amplitude had deviated identibly from the normal operating state, but the average current had not yet shown a continuous downward trend. Upon receiving this signal, the control execution module immediately responded and executed the initial adjustment action: for example, the control execution module reduced the speed of the double-suction centrifugal pump by 10%. However, since the upstream water level was still continuously decreasing, shortly after the speed was reduced, the effect judgment subunit found that the fluctuation amplitude of the drive motor current had not been effectively reduced, but instead continued to rise. Therefore, the correction adjustment subunit was activated, and the outlet valve was closed by 3% on the basis of the already reduced speed. Despite this, the deterioration rate of the inlet conditions exceeded the adjustment capacity, the current fluctuation amplitude was further aggravated, and the average current began to show a continuous downward trend.

[0093] The alarm shutdown unit of the control execution module was triggered by the continuous downward trend of the average current. The system immediately executed the shutdown protection and sent a shutdown alarm and switchover command to the central control system, thereby avoiding catastrophic damage that might have been caused by the double-suction centrifugal pump operating for a long time under severe cavitation.

[0094] After the upstream water flow resumes and the inlet water level rises back to the normal range, the system automatically triggers the damage verification module. It restarts the double-suction centrifugal pump at its initial rated speed and with the valve fully open, and measures its outlet pressure. When the measurement results show that the current outlet pressure is lower than the pressure recorded under the same operating conditions in the initial calibration state of the double-suction centrifugal pump, and the difference exceeds the allowable range of measurement error, the damage verification module determines that the double-suction centrifugal pump has suffered permanent damage. The system automatically adds a damaged mark to its health record and appropriately raises the "dangerous water level" alarm threshold for the next run, for example, by a preset safety margin. At the same time, it generates a detailed diagnostic report and maintenance work order to prompt maintenance personnel to carry out maintenance.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A control system for a double-suction centrifugal pump with cavitation protection function, characterized in that, include: The monitoring module is used to obtain the inlet water level, inlet pressure, outlet pressure, and drive motor current of the double-suction centrifugal pump. The trigger module is used to trigger the diagnostic process when a preset drop in the inlet water level is detected. The boosting capacity judgment module is used to determine whether the boosting capacity of the double-suction centrifugal pump has decreased based on the changes in inlet and outlet pressures after the diagnostic process is triggered. The fault type determination module is used to respond to the decrease in the boosting capacity of the double-suction centrifugal pump. Based on the time-series change pattern of the outlet pressure, it determines whether the performance degradation is dominated by progressive wear or by condition-related cavitation. The cavitation analysis module is used to classify the severity of cavitation in response to performance degradation being dominated by operating condition cavitation, based on the fluctuation range of drive motor current associated with changes in outlet pressure pattern. The control execution module is used to perform corresponding protective control actions or early warning actions based on the severity of cavitation.

2. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, The trigger module includes: The water level threshold detection unit is used to trigger a diagnostic process when the inlet water level is detected to drop below a preset warning level or when the inlet water level is detected to drop below a preset danger level.

3. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, The boost capacity judgment module includes: The differential pressure comparison unit is used to compare the decrease in outlet pressure with the decrease in inlet pressure during a water level drop event. When the decrease in outlet pressure is greater than the decrease in inlet pressure, it is determined that the boosting capacity of the double-suction centrifugal pump has decreased.

4. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, The fault type determination module includes: The progressive wear determination unit is used to determine whether the performance degradation is dominated by progressive wear or operating condition cavitation based on the difference in the temporal change pattern of the outlet pressure as the inlet water level decreases. Specifically, when the rate of decrease of the outlet pressure does not change trend during the water level decrease, it is determined to be dominated by progressive wear. When the rate of decrease of the outlet pressure has an inflection point during the water level decrease and changes from being basically constant to accelerating, it is determined to be dominated by operating condition cavitation.

5. The dual-suction centrifugal pump control system with cavitation protection function according to claim 4, characterized in that, The cavitation analysis module includes: The current swing detection unit is used to determine the severity of cavitation based on the fluctuation range of the drive motor current before and after the inflection point of accelerated decrease in outlet pressure and the changing trend of the average value of the drive motor current, so as to determine whether the cavitation is in a stage that can be suppressed by operation adjustment or a stage that is difficult to suppress by operation adjustment.

6. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, The control execution module includes: The regulation control unit is used to perform protective control actions, including speed regulation and / or valve regulation, in response to cavitation being in a stage that can be suppressed by operational regulation. The alarm shutdown unit is used to respond to the stage where cavitation is difficult to suppress through operation adjustment, to perform shutdown protection and output an alarm signal.

7. The dual-suction centrifugal pump control system with cavitation protection function according to claim 6, characterized in that, The adjustment and control unit includes: The speed regulation subunit is used to reduce the speed of the double-suction centrifugal pump when the double-suction centrifugal pump is equipped with a variable frequency speed control device, based on the degree of deviation of the current fluctuation amplitude from the normal operating state. The effect judgment subunit is used to respond to the reduction of the speed of the double-suction centrifugal pump. Based on the change in the deviation of the current fluctuation amplitude from the normal operating state, it judges whether the current adjustment is effective and determines whether further adjustment of the double-suction centrifugal pump is needed. The adjustment subunit is used to respond to the need for further adjustment of the double-suction centrifugal pump, close the outlet valve and / or further reduce the speed of the double-suction centrifugal pump, and reassess the effectiveness of the current adjustment to determine whether the current operating adjustment is sufficient to suppress cavitation.

8. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, Also includes: The damage verification module is used to verify whether the double-suction centrifugal pump has suffered permanent damage after a complete cycle of water level drop and rise, when the water level returns to the normal zone, by comparing the current outlet pressure with the outlet pressure under the same operating conditions of the same rotation speed and the same valve opening.

9. The double-suction centrifugal pump control system with cavitation protection function according to claim 1, characterized in that, The trigger module also includes: The time backup detection unit is used to trigger the diagnostic process when the cumulative running time of the double-suction centrifugal pump reaches the preset maintenance interval and the diagnostic process is not triggered due to water level changes during this period.

10. The double-suction centrifugal pump control system with cavitation protection function according to claim 3, characterized in that, The boost capacity judgment module also includes: An auxiliary verification unit is used to selectively perform auxiliary verification after determining that the boosting capacity of the double-suction centrifugal pump has decreased. This verification is based on the response of the outlet pressure when the inlet water level is relatively stable, by fine-tuning the outlet valve.

Images