Method for checking properties of conveying medium of centrifugal pump, in particular for dry operation detection
By changing the speed of the centrifugal pump and detecting torque changes, the problem of difficult to identify dry operation at low speeds is solved, and reliable identification of dry operation and evaluation of the characteristics of the conveying medium are achieved, thereby improving the operating reliability and efficiency of the pump.
Patent Information
- Application Number
- CN202380090712.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2023-01-09
- Filing Date
- 2023-12-12
- Publication Date
- 2025-08-12
AI Technical Summary
The prior art is difficult to reliably identify the dry operation status of centrifugal pumps at low speeds, resulting in an increased risk of pump wear and equipment damage.
By briefly or periodically changing the target speed of the centrifugal pump, detecting torque changes and comparing them with reference values, evaluating the characteristics of the conveying medium and identifying dry operation.
Reliable identification of dry operation at low speeds is achieved, the risks of pump wear and equipment damage are reduced, and the operation reliability and efficiency of the pump are improved.
Smart Images
Figure CN120476261A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a method for checking the properties of a conveying medium of a centrifugal pump, in particular for dry-running detection. Background Art
[0002] Centrifugal pumps are used to convey various conveying media. Information about the conveying media can be important for the proper and, in particular, energy-efficient operation of the centrifugal pump. Changes in characteristic properties of the conveying media, such as temperature changes and density changes, can be particularly important for efficient pump control or regulation. Therefore, there is a legitimate interest in suitable methods for determining these characteristic parameters of the conveying media during pump operation.
[0003] Another important aspect of pump operation in wet-running centrifugal pumps is dry-run detection. Since the medium being pumped is often used to lubricate rotating machine components of the pump assembly or to cool the pump, dry-running during pump operation can lead to increased pump wear or even overheating. A dry-running pump is also an indicator of a dry-running hydraulic system, which can damage the system. For this reason, dry-run detection is also very important in non-wet-running pumps. Therefore, to avoid potential subsequent damage to the pump itself or the hydraulic system, it is desirable to detect such situations early and reliably, especially regardless of the operating point.
[0004] If the lines in a hydraulic system are insufficiently filled with liquid, that is, with the pumped medium, the torque acting on the impeller is lower than with filled lines. This fact can be exploited to reliably detect dry running. To this end, the torque is recorded in the laboratory at different speeds with the valve closed but the lines filled. The measured speed / torque value pairs are stored in the pump as a table. Operation with the valve closed and the resulting zero delivery flow corresponds to the "worst-case" scenario, where the torque is as low as possible for a filled line. The stored torque values are the lowest possible values for a filled line. As soon as the torque during operation falls below the reference torque stored in the table, dry running is inferred, and the pump can issue a corresponding notification.
[0005] This method works reliably at medium and high rotational speeds, but at lower rotational speeds the torque difference between a filled unit (with closed valves) and an unfilled unit is so small that a reliable distinction at such operating points is difficult.
[0006] Against this background, it is also meaningful to optimize the method mentioned in order to make it possible to reliably detect dry running for every operating point. Summary of the Invention
[0007] The stated problem is solved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject matter of the dependent claims.
[0008] According to the present invention, for a process to check or detect dry-running, it is proposed to briefly change the target speed of a centrifugal pump used for speed regulation. Particularly preferably, the target speed is briefly increased. For the changed speed, a motor variable characteristic of the pump torque is then determined and evaluated taking into account at least one reference value. Based on the result of the evaluation, a statement regarding a change in a characteristic property of the pumped medium can then be made and / or the presence of dry-running can be detected.
[0009] Characteristic properties that can be determined using the method according to the present invention include, for example, the density and / or temperature of the conveying medium or changes in the temperature and / or density of the conveying medium relative to initial values. Since the density or temperature of the conveying medium influences the viscosity of the liquid and thus the required torque of the pump, the change in torque detected for a specific rotational speed can be used to indicate deviations or changes in the consistency of the conveying medium. This also applies if there is a pressure drop or dry running on the suction side, so that the torque to be applied by the pump motor is reduced accordingly.
[0010] As a motor parameter to be detected, for example, the current torque of the electric motor can be determined. Direct detection of the torque by a torque sensor or, alternatively, derivation of the torque from other motor parameters is conceivable. The torque can also be estimated, particularly by using a motor model. It is also conceivable to determine or estimate the electrical power consumption and / or the consumed motor current of the motor. Since the electrical power consumption or the motor current, particularly the current component that generates the motor torque, directly influences or is proportional to the generated torque, the method according to the present invention can also be implemented by evaluating these operating parameters.
[0011] As mentioned above, dry-running detection works reliably at medium and higher speeds. Only at lower speeds is the change in torque often too small to be reliably determined. Against this background, it is sensible to implement the proposed method only when the centrifugal pump is currently operating at a speed that is too low. Only in this case is it necessary to manually change or increase the target speed in order to reliably detect dry-running or check the properties of the pumped medium. Therefore, the method can be implemented only when the currently set target speed is less than a definable threshold value.
[0012] In the simplest case, the speed change proposed by the present invention can be limited to a brief increase in the target speed. Motor parameters are determined for the current increased speed and compared with reference values associated with the increased target speed. To determine the associated reference values in advance, operating parameters (e.g., torque with a closed valve but a filled line) are recorded for different speeds in a laboratory or under real operating conditions, for example, and the measured speed or torque value pairs are stored in the pump as a table. The stored reference values are the lowest values that can occur with a filled line. As soon as an operating parameter (e.g., torque during running operation) falls below the reference value stored in the table, dry running is inferred, and the pump can issue a corresponding notification.
[0013] It is particularly preferred if the speed increase sets the target speed to the maximum speed or to a value between 50 and 90% of the maximum speed, preferably between 65 and 85% of the maximum speed.
[0014] However, depending on the application of the pump, the above-mentioned speed increase may not be allowed. Therefore, it is alternatively proposed to superimpose the current target speed with a time-variable signal, which leads to a limited temporal change or fluctuation of the target speed over a certain time period, but preferably only with a limited quantitative increase in the speed. The dynamic change of the target speed forces a dynamic change of the motor parameters to be evaluated. For further evaluation, in particular the correlation between the time course of the target speed and the time course of the motor operating parameters is studied. Based on this correlation, the physical properties of the conveying medium, in particular the changes in these properties, can be inferred and / or the presence of dry running can be identified. Since the system pressure at the suction connection and the properties of the conveying medium influence the mass inertia of the pump unit, by evaluating the time course between the reactively generated torque or the detected motor parameters and the target setting of the speed, the existing mass inertia can be inferred and based on this the properties of the conveying medium or possible dry running can be identified.
[0015] For example, it is preferred to superimpose the target rotational speed on a periodic signal, so that a periodic variation of the target rotational speed occurs during the observation period. However, superimposition of an alternative time-varying signal is also conceivable.
[0016] Due to mass inertia, a time delay of the torque change process or the motor parameter relative to the time change process of the target speed usually occurs. In this context, it is meaningful to evaluate the phase offset between the time change process of the target speed and the time change process of the detected motor parameter. If the viscosity of the conveying medium increases, the phase offset increases; conversely, if the viscosity decreases, the phase offset must also decrease. In the dry running scenario, the phase offset is minimal due to the lack of conveying medium in the area of the impeller. Alternatively or in addition to this, the amplitude value of the motor parameter, in particular the torque, can also be determined and evaluated during the fluctuation of the target speed due to superposition. When the mass inertia is large, the torque amplitude or the amplitude of the motor parameter increases by a certain amount. It is meaningful to compare the determined amplitude value with a reference value or to determine the amplitude ratio to the reference amplitude.
[0017] Therefore, in order to detect changes in the physical properties of the conveying medium or to detect dry running, it can be provided that corresponding reference values are maintained for the phase shift or the amplitude ratio or the amplitude itself, wherein, if the currently determined phase shift and / or amplitude ratio changes relative to the reference value, a change in the conveying medium and, if necessary, dry running can be inferred.
[0018] One or more reference values for the implementation of the method can be obtained, for example, during a training run of the pump, in particular during commissioning or regularly during operation of the pump. It is also conceivable to determine and continuously update the reference value by corresponding previous measurements.
[0019] In addition to the method according to the invention, the present invention also relates to a centrifugal pump, in particular a heating circuit pump, with an integrated or external control / regulator designed to carry out the method according to the invention. Therefore, the centrifugal pump according to the invention exhibits the same advantages and properties as those described in detail with respect to the method according to the invention. For this reason, a repeated description will not be given. BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further advantages and features of the present invention will be described below with reference to the exemplary embodiments illustrated with the aid of the accompanying drawings.
[0021] Figure 1 : A graphical representation showing the torque of the pump drive unit versus the speed for different pump states,
[0022] Figure 2 : shows an exemplary diagram of the torque profile over time after superposition of a periodic signal for implementing the method according to the invention, and
[0023] Figure 3 : An exemplary comparative diagram of the target rotational speed superimposed on the periodic signal and the resulting torque variation over time is shown. DETAILED DESCRIPTION
[0024] Figure 1 The torque of the centrifugal pump assembly is shown as a function of the set target speed of the pump. The diagram shows a total of two curve profiles. The dashed line represents the torque P over the entire speed range for a completely filled suction line with conveying medium, but with the valve in the suction line closed. Q0 The solid line shows the torque P in the entire speed range when the pump is running dry. Dry process of change.
[0025] In general, it can be seen that the torque P during dry running Dry and torque P when the pump is filled as specified Q0 The deviation between becomes greater with increasing speed, so the method works very precisely at medium and higher speeds. Especially in the lower speed range, such as the speed indicated by reference numeral 1, the difference in torque or power consumption between a filled system with a closed valve and an unfilled system is very small or sometimes almost nonexistent. In this speed range, it is difficult to reliably distinguish whether dry running is actually occurring or whether the valve is simply closed.
[0026] Therefore, in order to solve the above problem, it is proposed according to the present invention to temporarily increase the target speed of the speed-regulated centrifugal pump, for example, to Figure 1 The speed value is marked with reference numeral 2 in the figure. Dry-running can be detected very reliably here. According to the diagram, the speed is significantly increased for dry-running detection, here by a factor of approximately three. In principle, it is believed that briefly increasing the speed to a value in the range of 50% to 100% of the maximum speed allows for the most reliable detection. The advantage of this method is that it is very simple to implement.
[0027] Since a temporary speed increase in the aforementioned range may not be permissible in certain processes, the method can alternatively provide for stimulating the target speed with a periodic signal, which not only enables dry-running detection but also thereby provides information about the conveyed medium.
[0028] It is proposed to apply the current target speed as a periodic signal within the framework of parameter identification in order to then observe the phase shift between the target speed profile and the occurring (measured or estimated) torque profile. Alternatively, the amplitude of the measured or estimated torque profile can also be observed.
[0029] In speed-controlled centrifugal pumps, the current actual speed and actual torque are used as estimated values for motor control. The phase shift or amplitude of the torque depends on the inertia of the moving machine parts (e.g., impeller, shaft, etc.) (known) and the pumped medium (to be determined). This method can be divided into two steps.
[0030] Step 1: Detecting the phase shift or torque amplitude in the normal state. Step 1 is performed in the laboratory. Different operating points (various speed / torque combinations) are run with a defined reference medium and reference temperature, and a target speed is superimposed with a high-frequency signal (e.g., 10 Hz). For each of these operating points, the phase shift between the target speed profile and the torque profile is recorded, or alternatively, the torque amplitude. The resulting characteristic field is stored in the pump.
[0031] Step 2: Identify different parameters on site
[0032] During pump operation, at regular intervals or once upon request, the target speed is superimposed with the same high-frequency signal as previously used in the laboratory, and the phase shift between the target speed profile and the measured / estimated torque profile, or alternatively, the torque amplitude of the torque profile, is recorded. If the phase shift or torque amplitude falls significantly below the reference value for this phase shift recorded in the laboratory, this can be interpreted as a sign of dry running. Furthermore, this phase shift can indicate a density or temperature of the medium that deviates from a reference value or an incorrect mixing ratio.
[0033] Figure 2 The simulated torque profile of a centrifugal pump is shown as an example, in which a static target speed is superimposed on a periodic signal, resulting in a periodic torque profile indicated by reference numeral 10 (corresponding to a laboratory configuration). Curve 20 shows the torque profile for the same test configuration, with the simulated mass inertia of the pump's rotating components increased by 50%. The higher amplitude of curve 20 is clearly visible. The ratio of the amplitudes (here indicated by reference numeral 40) is equal to the ratio of the simulated mass inertia. The pump can detect a 50% deviation from the stored value recorded in the laboratory and infer a 50% change in mass inertia from this. Equal to the mass inertia, the density of the medium may also have changed.
[0034] The average value of the torque curve 30 is the same, which means that at a static target speed (without the application of a periodic signal), the information about the mass inertia cannot be recognized.
[0035] exist Figure 3 The time course of the target speed and the detected torque is shown in FIG. Curve 50 corresponds to the target speed superimposed with the periodic signal. Curve 60 shows the resulting torque course. Reference numeral 70 denotes the resulting phase shift between the two curve courses, which also becomes greater with increasing mass inertia. It is foresighted to point out that in Figure 3 In the illustration of FIG, the speed profile 50 and the torque profile 60 are shifted one on top of the other for a better understanding of the phase offset.
Claims
1. A method for checking the properties of a conveying medium of a centrifugal pump, in particular for dry-running detection, when using a speed-controlled centrifugal pump, wherein: For the check, the target speed of the centrifugal pump is briefly changed, in particular increased, and motor parameters characterizing the torque of the pump are determined and evaluated taking into account reference values in order to determine the properties of the conveying medium and / or detect the presence of dry running.
2. The method according to claim 1, characterized in that The method is used to determine a change in temperature and / or a change in density of the conveying medium relative to a reference value.
3. The method according to any one of the preceding claims, characterized in that As motor parameters characterizing the torque of the pump, the torque generated by the pump is determined, in particular estimated, and / or the electrical power consumption and / or the consumed motor current of the motor is determined or estimated.
4. The method according to any one of the preceding claims, characterized in that First, a check is performed to determine whether the current target speed lies below a minimum value, and only if the current target speed lies below the minimum value is the target speed changed or increased.
5. The method according to any one of the preceding claims, characterized in that The speed change provides for a brief increase in the target speed, a motor parameter is determined for the currently increased target speed, and is compared with a reference value associated with the increased target speed, wherein dry running is detected if the motor parameter is less than the reference value or less than the reference value by at least a limiting value.
6. The method according to any one of the preceding claims 1 to 4, characterized in that A target speed for the check is superimposed on a temporally variable signal, in particular a periodic signal, for certain time intervals.
7. The method according to claim 6, characterized in that Based on the correlation between the generated target speed profile and the time profile of the motor parameter, a property of the conveying medium or the presence of dry running is detected.
8. The method according to claim 7, characterized in that A phase shift between the time profile of the target rotational speed and the time profile of the motor parameter is evaluated and preferably compared with a reference value.
9. The method according to any one of claims 6 to 8, characterized in that During the superposition of the target speed, the amplitude of the motor parameter is determined and preferably compared with a reference value.
10. The method according to any one of the preceding claims, characterized in that One or more of said reference values are determined by a training program carried out under normal conditions. 11 . A centrifugal pump, in particular a heating circuit pump, with an integrated or external control system designed to carry out the method according to claim 1 .