Patent Description:
Sewage or wastewater collection systems for wastewater treatment plants typically comprise one or more wastewater pits, wells or sumps for temporarily collecting and buffering wastewater. Typically, wastewater flows into such pits passively under gravity flow and/or actively driven through a force main. One, two or more pumps are usually installed in or at each pit to pump wastewater out of the pit. If the inflow of wastewater is larger than the outflow for a certain period of time, the wastewater pit or sump will eventually overflow. Such overflows should be prevented as much as possible in order to avoid environmental impact. Therefore, any pump fault or clogging, pipe clogging, leakage or other type of faulty operating scenario should be identified as quickly as possible for maintenance staff to take according action, like cleaning, repairing or replacing as quickly as possible.

<CIT> describes a wastewater treatment system and a method for reducing energy used in operation of a wastewater treatment facility. <CIT> describes a method for determining faults during operations of a single pump unit. Similarly, <CIT> describes a method that serves for monitoring a single pump. The paper "<NPL>, describes a model based approach for fault detection and isolation in a single centrifugal pump. <CIT> describes a multi-pump system in which the wire-to-water efficiency is monitored.

It is a challenge for known wastewater pumping station management systems of wastewater pumping stations with two or more pumps to reliably identify the cause for a certain problem in order to give an operator or maintenance staff a clear indication for the appropriate action, e. where or what needs to be cleaned, repaired or replaced.

In contrast to known systems, the present invention provides a wastewater pumping station with two or more pumps as defined in claim <NUM> and a method for identifying an operating scenario in the wastewater pumping station as defined in claim <NUM> with more specific and more reliable information.

In accordance with a first aspect of the present invention as defined by claim <NUM>, a wastewater pumping station comprising two or more pumps arranged for pumping wastewater out of a wastewater pit into a pipe and a monitoring module for identifying an operating scenario in the wastewater pumping station is provided.

The group of predefined operating scenarios may include faulty and/or non-faulty operating scenarios. For example, faulty operating scenarios may be a clogging of the pipe downstream of the pump(s), a clogging in one or more of the at least one pump(s), a leak in a non-return valve for one or more of the at least one pump(s), and/or a leak in a connection between one or more of the at least one pump(s) and the pipe. The combination of at least two criteria, the first one of which is based on the at least one load-dependent pump variable and the second one of which is based on the at least one model-based pipe parameter, may be interpreted by the monitoring module as a "scenario signature".

Optionally, the group of operating scenarios may be predefined in a selection matrix unambiguously associating each operating scenario with a unique combination of the at least one first criterion, the at least one second criterion, and the at least one third criterion. For instance, in case of a wastewater pumping station with only one pump, which is not part of the present invention, three different operating scenarios may be identified based on the combination of the two criteria as follows:.

According to the present invention, for a wastewater pumping station with two or more pumps, a first criterion for each pump is used to distinguish between operating scenarios in which a specific pump is clogged or pump connection is leaking, for example. For instance, five different operating scenarios may be identified based on the combination of the two criteria as follows:.

According to the present invention, for a wastewater pumping station with two or more pumps, only one pump is typically running at a time as long as one pump suffices for pumping enough wastewater out of the wastewater pit into the pipe. In order to evenly distribute the operating hours and wear, the pumps may be running in turns. In contrast to operating all or several pumps simultaneously, the overall operating hours, and thus wear, and the overall energy consumption may be reduced by this. Only in case more pump power is needed during times of high inflow, e.g. at heavy rain incidents, all or several pumps may run simultaneously in order to prevent an overflow. For the alternating normal operation of only one pump at a time, non-return valves may be installed for each pump to prevent the active pump from pumping wastewater through the passive pump(s) back into the wastewater pit. A leak in such a non-return valve of a passive pump may have a different scenario signature than a leak in the pump connection of the active pump when a further second criterion is used based on another model-based pipe parameter as follows:.

Optionally, the at least one load-dependent pump variable may comprise a specific energy consumption Esp of the at least one pump. There are different ways to determine the specific energy consumption Esp of the at least one pump. For example, the specific energy consumption Esp may be defined by Esp=E/V, wherein E is an average energy consumed by the at least one pump during a defined time period and V is the volume of wastewater pumped during said defined time period by the at least one pump. The average energy consumption may be determined by integrating or summing the current power consumption P(t) over the time t between an end of a delay period after pump start and pump stop: <MAT>. Analogously, the pumped wastewater volume may be determined by integrating or summing the current flow q(t) over the same time period: V = <MAT>. The delay period may be useful to skip an initial period of high fluctuations after start-up of the pump(s). The monitoring module may be signal connected wirelessly or via a cable with the pump(s) to receive a signal indicative of the power or energy consumption. Furthermore, the monitoring module may be signal connected wirelessly or via a cable with a flow sensor to receive a signal indicative of the flow through the pipe.

A current specific energy consumption Esp(t) of the at least one pump may be defined by Esp(t)=P(t)/q(t), wherein P(t) is a current power consumption of the at least one pump and q(t) is a current flow of wastewater pumped by the at least one pump. The current specific energy consumption Esp(t) may be monitored as the at least one load-dependent pump variable as an alternative to the averaged specific energy consumption Esp as defined above. If the current specific energy consumption Esp(t) fluctuates too much to the at least one first criterion on it, a low-pass filtering may be applied as explained later herein. Even in case of a specific energy consumption Esp that is averaged for each pump cycle, it can fluctuate between the pump cycles so much that a low-pass filtering may be advantageous.

As a flow meter may be quite expensive and may require regular maintenance, it may be preferable to estimate the outflow q of wastewater through the pump(s) based on a measured pressure differential Δp and power consumption P. For instance, the outflow q of wastewater through the pump(s) may be estimated by <MAT> <MAT>, wherein s is the number of running pumps, ω is the pump speed (e. constant), Δp is the measured pressure differential, P is the power consumption of the running pump(s), and λ<NUM>, λ<NUM>, λ<NUM> and λ<NUM> are pump parameters that may be known from the pump manufacturer or determined by calibration. Accordingly, the monitoring module may be signal connected wirelessly or via a cable with a pressure sensor, which is located at or downstream of the pump(s), to receive a signal indicative of the pressure differential Δp. So, optionally, the monitoring module may be configured to receive a measured pressure pm at or downstream of an outlet of the at least pump. Alternatively or in addition, the monitoring module may be configured to receive a measured flow qm through the pipe or to process an estimated wastewater flow qe through the pump.

It is important to note that the "scenario signature" may depend on whether a flow q through the pipe is measured or a flow q through the pump(s) is estimated. For instance, a leak in a pump connection or in a non-return valve may result in a rising specific energy consumption Esp when the flow q through the pipe is measured. However, if a flow q through the pump(s) is estimated, the specific energy consumption Esp may turn out to be falling. Therefore, the monitoring module may be configured to apply one of at least two predefined selection matrices dependent on whether a flow q through the pipe is measured or a flow q through the pump(s) is estimated. Each of the at least two selection matrices unambiguously associate each operating scenario with a unique combination of the at least one first criterion, the at least one second criterion, and the at least one third criterion.

Optionally, one of the at least one model-based pipe parameter may be a pipe clogging parameter A in a pipe model polynomial p=Aq<NUM> + B, wherein p is a pressure at or downstream of an outlet of the at least pump, q is a wastewater flow through the pipe and/or the at least one pump, and B is a zero-flow offset parameter. The zero-flow offset parameter B may be a second one of at least two model-based pipe parameters, wherein the pipe clogging parameter A may be a first one of the at least two model-based pipe parameters.

Alternatively or in addition, one of the at least one model-based pipe parameter may be a residual r=pm-pe=pm-Aq<NUM> - B between a measured pressure pm at or downstream of an outlet of the at least pump and an estimated pressure pe according to a pipe model polynomial pe=Aq<NUM> + B, wherein A is a pipe clogging parameter of the pipe, q is a wastewater flow through the pipe and/or the at least one pump and B is a zero-flow offset parameter. The residual r may be considered as a pipe model testing parameter. If the residual r deviates from zero by more than a certain threshold, e.g. <NUM> Pa, one of the at least one second criterion may be fulfilled, otherwise not. Such a fulfilled second criterion may mean a "model mismatch", indicating a pipe clogging, whereas a non-fulfilled second criterion may mean a "model match", indicating a pump problem rather than a pipe clogging. As described above, a leak in a pump connection or in a non-return valve may show a model mismatch when the flow through the pump(s) is estimated, but a model match if a flow q through the pipe is measured.

Optionally, the monitoring module may be configured to apply a low-pass filtering to the at least one load-dependent pump variable and/or the at least one model-based pipe parameter before selecting an operating scenario dependent on the at least one first criterion, the at least one second criterion, and the at least one third criterion. This may be very helpful to cope with fluctuations of the load-dependent pump variable, e.g. the specific energy consumption Esp, and/or the pipe parameter, e.g. the pipe clogging parameter A or the residual r.

For instance, the monitoring module may be configured to sequentially process a multitude of samples of the at least one load-dependent pump variable, wherein the at least one first criterion is based on whether a cumulative sum of deviations between the actual sample and an average of past samples of the at least one load-dependent pump variable exceeds a predetermined maximum or falls below a predetermined minimum. Such a low-pass filtering may follow a so-called iterative CUSUM (cumulative sum) algorithm such as: <MAT> <MAT> wherein Sup and Sdown are decision variables summing up deviations using a test variable x. The test variable x may, for instance, be defined as the deviation of the specific energy consumption in the i-th pump cycle from an average specific energy consumption Esp, i.e. x = Esp - Esp. The average specific energy consumption Esp may be a predefined value or a value statistically determined over several previous pump cycles during normal faultless operation. For instance, it may be useful to identify non-faulty operating scenarios to statistically determine an average specific energy consumption Esp. Dependent on the variance of x, the decision variables may be tuned by gain parameters Gup and Gdown. Fluctuations below a certain number n, e.g. n=<NUM>, <NUM> or <NUM>, of standard deviations σ may be suppressed for the decision variables. Similar to the average specific energy consumption Esp, the standard deviation σ may be statistically determined over several previous pump cycles during normal faultless operation.

A first one of the at least one first criterion based on the specific energy consumption Esp may be whether the decision variable Sup is above or below an alarm threshold indicating that the specific energy consumption Esp is rising. A second one of the at least one first criterion based on the specific energy consumption Esp may be whether the decision variable Sdown is above or below an alarm threshold indicating that the specific energy consumption Esp is falling. An estimation of the flow through the pump based on pressure and power consumption of the pump(s) has, compared to a flow measured by a flow meter, not only the advantage that a flow meter can be spared with, but also that the scenario signature is different in cases of a leakage of a pump connection or a non-return valve. In those cases, the specific energy consumption Esp would appear as falling if the flow through the pump is estimated. If the flow through pipe is measured, the specific energy consumption Esp would be rising in case of pipe clogging, pump fault/clogging and leakage of a pump connection or a non-return valve. In case of a wastewater pumping station with m ≥ <NUM> pumps, there may be two first criteria per pump, i. <NUM> times m first criteria to identify the operating scenario.

A similar low-pass filtering may be applied to the at least one model-based pipe parameter before selecting an operating scenario dependent on the at least one second criterion. So, optionally, the monitoring module may be configured to sequentially process a multitude of samples of the at least one model-based pipe parameter, wherein the at least one second criterion is based on whether a cumulative sum of deviations between the actual sample and an average of past samples of the at least one model-based pipe parameter exceeds a predetermined maximum or falls below a predetermined minimum.

For instance, the evolvement of the pipe clogging parameter A may be monitored by decision variables Sup and Sdown with a test variable x being defined as the deviation of the pipe clogging parameter A in the i-th pump cycle from an average pipe clogging parameter A, i.e. x = A - A. Kalman filters may be applied to calculate the mean and variance of the pipe clogging parameter. As an alternative or in addition, the residual r for testing whether the pipe model still matches with reality may be used as test variable x, i.e. x = r. In this case, a combined decision variable S = Sup + Sdown may be used to indicate a model mismatch, because there is no need to distinguish between upward and downward fluctuations.

According to the invention, the monitoring module is configured to process a first of at least two model-based pipe parameters and a zero-flow offset parameter as a second of the at least two model-based pipe parameters, wherein the negative-flow parameter is indicative of how the wastewater flows through the pipe and/or the at least one pump when the at least one pump is stopped, wherein the monitoring module may be configured to identify an operating scenario in the wastewater pumping station by selecting an operating scenario from a group of predefined operating scenarios further dependent on at least one third criterion that is based on the negative-flow parameter. Optionally, the negative-flow parameter may show as a decay of the zero-flow offset parameter B in a pipe model polynomial p=Aq<NUM> + B, wherein p is a pressure at or downstream of an outlet of the at least one pump, q is a wastewater flow through the pipe and/or the at least one pump, and A is a pipe clogging parameter.

Alternatively or in addition, the negative-flow parameter may be a leakage flow through one of the non-return valves or a pump connection, for instance, which will gradually lead to a pressure decay when the at least one pump is stopped. This may be formulated by Dṗ = -q, wherein D is the cross-sectional area of the pipe, <MAT> is the change in pressure at the outlet of a pump over time, and q is the leakage flow. Following Toricelli's law, the leakage flow may be calculated by <MAT>, wherein K is a constant, ρ is the density of the wastewater, p is the measured pressure at the pump outlet, h is the wastewater's height above a hydrostatic pressure sensor for level measurement at the bottom of the pit, and Δp<NUM> is a hydrostatic pressure of a difference in geodetic elevation between the pump outlet and the bottom of the pit. This leads to a differential equation as follows: Aṗ = <MAT>, which may be approximated by discrete test samples i as follows: <MAT>, so that a decision variable <MAT> may be tested as a third criterion for hypotheses H<NUM> and H<NUM>, wherein H<NUM>: γ = <NUM> and H<NUM>: γ ≠ <NUM>. If hypothesis H<NUM> cannot be rejected, there is probably a leak in the non-return-valve. If the decision variable y is above a threshold value, for instance <NUM>, the hypothesis H<NUM> may be rejected. The threshold value for this third criterion may be adjusted to an acceptable compromise between the sensitivity for a leakage and a false alarm rate.

In accordance with a second aspect of the present invention as defined by claim <NUM> and analogous to the monitoring module described above, a method is provided for identifying an operating scenario in a wastewater pumping station with two or more pumps arranged for pumping wastewater out of a wastewater pit into a pipe.

Optionally, the group of operating scenarios may be predefined in a selection matrix unambiguously associating each operating scenario with a unique combination of the at least one first criterion, the at least one second criterion, and the at least one third criterion.

Optionally, the at least one load-dependent pump variable may be a specific energy consumption Esp of the at least one pump.

Optionally, the specific energy consumption Esp of the at least one pump may be defined by Esp=E/V, wherein E is an average energy consumed during a defined time period and V is the volume of wastewater pumped during said defined time period by the at least one pump.

Optionally, the specific energy consumption Esp of the at least one pump may be defined by Esp=P/q, wherein P is a power consumption and q is a flow of wastewater pumped by the at least one pump.

Optionally, the at least one model-based pipe parameter may be a pipe clogging parameter A in a pipe model polynomial p=Aq<NUM> + B, wherein p is a pressure at or downstream of an outlet of the at least pump, q is the wastewater flow through the pipe and/or the at least one pump, and B is a zero-flow offset parameter.

Optionally, the at least one model-based pipe parameter may be a residual r=pm-pe=pm-Aq<NUM> - B between a measured pressure pm at or downstream of an outlet of the at least pump and an estimated pressure pe according to a pipe model polynomial pe=Aq<NUM> + B, wherein A is a pipe clogging parameter of the pipe, q is the wastewater flow through the pipe and/or the at least one pump and B is a zero-flow offset parameter.

Optionally, the method may further comprise a step of receiving a measured pressure pm at or downstream of an outlet of the at least pump.

Optionally, the method may further comprise a step of receiving a measured flow qm or processing an estimated wastewater flow qe through the at least one pump.

Optionally, the method may further comprise a step of applying a low-pass filtering to the at least one load-dependent pump variable and/or the at least one model-based pipe parameter before selecting an operating scenario dependent on the at least one first criterion, the at least one second criterion, and the at least one third criterion.

Optionally, the method may further comprise a step of sequentially processing a multitude of samples of the at least one load-dependent pump variable, wherein the at least one first criterion is based on whether a cumulative sum of deviations between the actual sample and an average of past samples of the at least one load-dependent pump variable exceeds a predetermined maximum or falls below a predetermined minimum.

Optionally, the method may further comprise a step of sequentially processing a multitude of samples of the at least one model-based pipe parameter, wherein the at least one second criterion is based on whether a cumulative sum of deviations between the actual sample and an average of past samples of the at least one model-based pipe parameter exceeds a predetermined maximum or falls below a predetermined minimum.

According to the invention, the method further comprises the steps of.

The monitoring module described above and/or some or all of the steps of the method described above may be implemented in form of compiled or uncompiled software code that is stored on a computer readable medium with instructions for executing the method. Alternatively or in addition, some or all method steps may be executed by software in a cloud-based system, in particular the monitoring module may be partly or in full implemented on a computer and/or in a cloud-based system.

<FIG> shows a wastewater pit <NUM> of a wastewater pumping station. The wastewater pit <NUM> has a certain height H and can be filled through an inflow port <NUM>. The current level of wastewater is denoted as h and may be continuously or regularly monitored by means of a level sensor <NUM>, e.g. a hydrostatic pressure sensor at the bottom of the wastewater pit <NUM> and/or an ultrasonic distance meter for determining the surface position of the wastewater in the pit <NUM> by detecting ultrasonic waves being reflected by the wastewater surface. Alternatively or in addition, the wastewater pit <NUM> may be equipped with one or more photoelectric sensors or other kind of sensors at one or more pre-defined levels for simply indicating whether the wastewater has reached the respective pre-defined level or not.

The wastewater pumping station further comprises an outflow port <NUM> near the bottom of the wastewater pit <NUM>, wherein the outflow port <NUM> is in fluid connection with two pumps 9a, 9b for pumping wastewater out of the wastewater pit into a pipe <NUM>. The pumps 9a, 9b may be arranged, as shown in <FIG>, outside of the wastewater pit <NUM> or submerged at the bottom of the wastewater pit <NUM> in form of submersible pumps. A non-return valve 10a, 10b at or after each pump 9a, 9b prevents a backflow when one of the pumps 9a, 9b is idle and the other one of the pumps 9b, 9a is running. A monitoring module <NUM> is configured to identify operating scenarios and to output an according information and/or alarm on an output device <NUM>. The output device <NUM> may be a display and/or a loudspeaker on a mobile or stationary device for an operator to take notice of a visual and/or acoustic signal as the information and/or alarm.

<FIG> shows a chain of wastewater pumping stations being connected by respective pipes <NUM> through which a lower level wastewater pumping station is able to pump wastewater to the next higher level wastewater pumping station against gravity. Each of the wastewater pumping stations may be monitored by a monitoring module <NUM> in order to identify operating scenarios.

The monitoring module <NUM> is configured to identify an operating scenario in the wastewater pumping station by selecting an operating scenario from a group of predefined operating scenarios dependent on at least one first criterion that is based on at least one load-dependent pump variable and at least one second criterion that is based on at least one model-based pipe parameter. In order to do this, as shown in <FIG>, the monitoring module <NUM> is signal connected with the with power electronics of the pumps 9a, 9b and/or power sensors in the pumps 9a, 9b of the wastewater pumping station(s) to receive a power signal indicative of a power consumption of each of the pumps 9a, 9b via wired or wireless signal connection <NUM>. Depending on which sensors are available in the wastewater pumping station, further signal connections between the monitoring module <NUM> and available sensors are shown in <FIG> as options that may be implemented alone or in combination with one or two of other options. The first option is a wired or wireless signal connection <NUM> with a pressure sensor <NUM> at or downstream of the pump 9a. The second option is a wired or wireless signal connection <NUM> with the level sensor <NUM>. The third option is a wired or wireless signal connection <NUM> with a flow meter <NUM> at or downstream of the pump 9a. The signal connections <NUM>, <NUM>, <NUM>, <NUM> may be separate communication channels or combined in a common communication channel or bus. The monitoring module <NUM> is configured to receive a respective pressure, power and/or flow signal via the signal connections <NUM>, <NUM>, <NUM> and to process accordingly at least one load-dependent pump variable indicative of how the pumps 9a, 9b operate and at least one model-based pipe parameter indicative of how the wastewater flows through the pipe <NUM> and/or the pumps 9a, 9b.

The at least one load-dependent pump variable may be a specific energy consumption Esp of each of the two pumps 9a, 9b. There are different ways to determine the specific energy consumption Esp for each pump. For example, the specific energy consumption Esp for one pump may be defined by Esp=E/V, wherein E is an average energy consumed by said pump during a defined time period and V is the volume of wastewater pumped during said defined time period by said pump. The average energy consumption may be determined by integrating or summing the current power consumption P(t) over the time t between an end of a delay period after pump start and pump stop: E = <MAT>. Analogously, the pumped wastewater volume may be determined by integrating or summing the current flow q(t) over the same time period: <MAT>. Alternatively or in addition, a current specific energy consumption Esp(t) of each one of the two pumps may be defined by Esp(t)=P(t)/q(t), wherein P(t) is a current power consumption of said pump and q(t) is a current flow of wastewater pumped by said pump. If the current specific energy consumption Esp(t) fluctuates too much to the at least one first criterion on it, a low-pass filtering may be applied as explained later herein. Even in case of a specific energy consumption Esp that is averaged for each pump cycle, it can fluctuate between the pump cycles so much that a low-pass filtering may be advantageous.

In order to process the specific energy consumption Esp for each pump as the load-dependent pump variables, the monitoring module <NUM> receives, firstly, a power signal indicative of a power consumption of each of the pumps 9a, 9b via the signal connection <NUM> and, secondly, a pressure signal from the pressure sensor <NUM> via the signal connection <NUM> and/or a flow signal from the flow meter <NUM> via the signal connection <NUM>. As a flow meter may be quite expensive and may require regular maintenance, it may be preferable to estimate the flow q of wastewater through the pumps 9a,9b based on the pressure signal and the power signal. For instance, the outflow q of wastewater through the pumps 9a, 9b may be estimated by <MAT>, wherein s is the number of running pumps, ω is the pump speed (e. constant), Δp is the measured pressure differential, P is the power consumption of the running pump(s), and λ<NUM>, λ<NUM>, λ<NUM> and λ<NUM> are pump parameters that may be known from the pump manufacturer or determined by calibration.

<FIG> shows samples of the specific energy consumption Esp for each pump cycle over three days of operation. Each data point represents the specific energy consumption Esp averaged over one pump cycle. Typically, during normal faultless operation, only one of the pumps 9a, 9b is active at a time during a pump cycle and they are used in turns, i.e. in alternating order, to evenly distribute operating hours and corresponding wear among the pumps 9a, 9b. <FIG> shows that the first pump 9a has, on average over these three days, a higher specific energy consumption Esp than the second pump 9b. As can be seen, the specific energy consumptions Esp fluctuate for both pumps 9a, 9b around a respective average specific energy consumption Esp indicated by the horizontal lines.

The fluctuations are better visible in the plots shown in <FIG>, where the upper left plot shows the specific energy consumption Esp of the first pump 9a and the upper right plot shows the specific energy consumption Esp of the first pump 9a. In order to improve the identification of operating scenarios and reduce the rate of misidentifications, the monitoring module <NUM> is configured to apply a low-pass filtering to the at least one load-dependent pump variable. This is very helpful to cope with fluctuations of the specific energy consumption Esp. The monitoring module is thus, for each pump 9a, 9b, configured to sequentially process a multitude of samples of the specific energy consumption Esp and to determine a cumulative sum of deviations between the actual sample and an average of past samples of the specific energy consumption Esp. Such a low-pass filtering may follow a so-called iterative CUSUM (cumulative sum) algorithm such as: <MAT> <MAT> wherein Sup and Sdown are decision variables summing up deviations using a test variable x. The test variable x may, for instance, be defined as the deviation of the specific energy consumption in the i-th pump cycle from an average specific energy consumption Esp, i.e. x = Esp - Esp. The average specific energy consumption Esp may be a predefined value or a value statistically determined over several previous pump cycles during normal faultless operation. For instance, it may be useful to identify non-faulty operating scenarios to statistically determine an average specific energy consumption Esp. Dependent on the variance of x, the decision variables may be tuned by gain parameters Gup and Gdown. Fluctuations below a certain number n, e.g. n=<NUM>,<NUM> or <NUM>, of standard deviations σ may be suppressed for the decision variables. Similar to the average specific energy consumption Esp, the standard deviation σ may be statistically determined over several previous pump cycles during normal faultless operation. The lower left plot of <FIG> shows the decision variable Sup of the first pump 9a and the lower right plot of <FIG> shows the decision variable Sup of the second pump 9b. As can be seen, the decision variable Sup is more robust against fluctuations. A first one of the at least one first criterion based on the specific energy consumption Esp may be whether the decision variable Sup is above or below an alarm threshold, e.g. <NUM>, indicating that the specific energy consumption Esp is rising. A second one of the at least one first criterion based on the specific energy consumption Esp may be whether the decision variable Sdown is above or below the alarm threshold, e.g. <NUM>, indicating that the specific energy consumption Esp is falling. Although the fluctuations are sometimes above n·σ, the alarm threshold of <NUM> has not been reached in the example shown in <FIG>, so that the first criterion would not be fulfilled here. Once the alarm threshold of <NUM> has been reached and the first criterion is fulfilled, an alarm reset threshold at <NUM> is useful to reset the first criterion to "unfulfilled" when the decision variable Sup has dropped again below the alarm reset threshold at <NUM>. Thus, a hysteresis effect is achieved in order to reduce the risk of missing short operating scenarios.

<FIG> shows a schematic pq-diagram for each of two pumps 9a, 9b. Analogous to <FIG>, each data point represents the flow q and the pressure q in one pump cycle. Each of the two clouds of data points correspond to one of the pumps 9a, 9b, which have different performance in this case. The parabola fitted to the data points indicates a pipe model characterized by a pipe model polynomial p=Aq<NUM> + B, wherein A is a pipe clogging parameter, p is the pressure measured at or downstream of an outlet of the at least pump, q is a wastewater flow through the pipe <NUM> and/or the pumps 9a, 9b, and B is a zero-flow offset parameter. The pipe clogging parameter A and/or the zero-flow offset parameter B may be used as model-based pipe parameters for the at least one second criterion.

However, in order to cope with fluctuations, similar low-pass filtering as described above for the specific energy consumption Esp may be applied to the model-based pipe parameters A, B before selecting an operating scenario dependent on the at least one second criterion. For instance, the evolvement of the pipe clogging parameter A may be monitored by decision variables Sup and Sdown with a test variable x being defined as the deviation of the pipe clogging parameter A in the i-th pump cycle from an average pipe clogging parameter A, i.e. x = A - A. Kalman filters may be applied to calculate the mean and variance of the pipe clogging parameter A.

Alternatively or in addition, as shown in <FIG>, one of the at least one model-based pipe parameter may be a residual r=pm-pe=pm-Aq<NUM> - B between a measured pressure pm at or downstream of an outlet of the at least pump and an estimated pressure pe according to a pipe model polynomial pe=Aq<NUM> + B, wherein A is a pipe clogging parameter of the pipe, q is a wastewater flow through the pipe and/or the at least one pump and B is a zero-flow offset parameter. The residual r may be considered as a pipe model testing parameter. If the residual r deviates from zero by more than a certain threshold, e.g. <NUM> Pa, one of the at least one second criterion may be fulfilled, otherwise not. Such a fulfilled second criterion may mean a "model mismatch", whereas a non-fulfilled second criterion may mean a "model match". As the residual r also fluctuates significantly, a similar low-pass filtering as described above for the specific energy consumption Esp may be applied to the residual r before selecting an operating scenario dependent on the at least one second criterion. The residual r for testing whether the pipe model still matches with reality may be used as test variable x, i.e. x = r, in the CUSUM algorithm described above. In this case, a combined decision variable S = Sup + Sdown as shown in the lower plot of <FIG> may be used to indicate a model mismatch, because there is no need to distinguish between upward and downward fluctuations.

<FIG> shows in the upper plot the pressure p over two pump cycles for a third criterion that, according to the invention, is applied to select an operating scenario. A negative-flow parameter as a basis for the third criterion may be a leakage flow through one of the non-return valves 10a, 10b, which will gradually lead to a pressure decay when the at least one pump 9a, 9b is stopped. This may be formulated by Dṗ = -q, wherein D is the cross-sectional area of the pipe, <MAT> is the change in pressure at the outlet of a pump over time, and q is the leakage flow. Following Toricelli's law, the leakage flow may be calculated by <MAT>, wherein K is a constant, ρ is the density of the wastewater, p is the measured pressure at an outlet of one of the pumps 9a, 10b, h is the wastewater's height above the level sensor <NUM>, and Δp<NUM> is a hydrostatic pressure of a difference in geodetic elevation between the pump outlet and the level sensor <NUM>. This leads to a differential equation as follows: <MAT>, which may be approximated by discrete test samples i as follows: <MAT>, so that a decision variable <MAT> <MAT> can be tested for hypotheses H<NUM> and H<NUM> as shown in the lower plot of <FIG>, wherein H<NUM>: γ = <NUM> and H<NUM>: γ ≠ <NUM>. As long as hypothesis H<NUM> is rejected, there is probably no leak in the non-return-valve 10a, 10b as shown in <FIG>. If the decision variable γ is below a threshold value, for instance <NUM>, the hypothesis H<NUM> cannot be rejected and a leakage in the non-return-valve 10a, 10b is identified. The threshold value may be adjusted to an acceptable compromise between the sensitivity for a leakage in one of the non-return-valves 10a, 10b and a false alarm rate.

<FIG> and <FIG> illustrate, by way of selection matrices, how the operating scenario is identified by selecting an operating scenario from a group of seven predefined operating scenarios (seven rows of the selection matrix) dependent on four first criteria (column <NUM> to <NUM> of the selection matrix) that are based on the specific energy consumption Esp, one second criterion (column <NUM> of the selection matrix) that is based on the residual r, and one third criterion (column <NUM>) based on the decision variable γ for the negative-flow parameter.

Each of the selection matrices in <FIG> and <FIG> unambiguously associate each operating scenario with a unique combination of the four first criteria, the second criterion and the third criterion. An "x" in the matrices means that the criterion of this column is fulfilled. The difference between the selection matrices in <FIG> and <FIG> is that the selection matrix of <FIG> is applied when a flow q through the pump(s) is estimated and the selection matrix of <FIG> is applied when a flow q through the pipe is measured. This is, because the "scenario signature" depends on whether a flow q through the pipe is measured or a flow q through the pump(s) is estimated. For instance, a leak in a pump connection or a non-return valve 10a, 10b may result in a rising specific energy consumption Esp when the flow q through the pipe is measured. However, if a flow q through the pump(s) is estimated, the specific energy consumption Esp may turn out to be falling. Therefore, the monitoring module may be configured to apply one of the two predefined selection matrices of <FIG> and <FIG> dependent on whether a flow q through the pipe is measured or a flow q through the pump(s) is estimated. An estimation of the flow through the pumps 9a, 9b based on pressure p and power consumption P of the pumps 9a, 9b has, compared to a flow q measured by a flow meter <NUM>, not only the advantage that the flow meter <NUM> can be spared with, but also that the scenario signature is different in cases of a leakage of a pump connection or a non-return valve 10a, 10b. In those cases, the specific energy consumption Esp would appear as falling if the flow through the pump is estimated. If the flow through the pipe <NUM> is measured, the specific energy consumption Esp would be rising in case of pipe clogging, pump fault/clogging and leakage of a pump connection or a non-return valve. The number of applied criteria may overdetermine one or more of the selection scenarios, which may provide a beneficial redundancy for better differentiating between the operating scenarios at a lower rate of misidentifications.

Claim 1:
A wastewater pumping station comprising:
- two or more pumps (9a, 9b) arranged for pumping wastewater out of a wastewater pit (<NUM>) into a pipe (<NUM>), and
- a monitoring module (<NUM>) for identifying an operating scenario in the wastewater pumping station,
characterized in that the monitoring module (<NUM>) is configured to process at least one load-dependent pump variable for each running pump of the pumps (9a, 9b) indicative of how the respective running pump (9a, 9b) operates,
to process a first of at least two model-based pipe parameters indicative of how the wastewater flows through the pipe (<NUM>) and/or the pumps (9a, 9b), and to process a negative-flow parameter as a second of the at least two model-based pipe parameters, wherein the negative-flow parameter is indicative of how the wastewater flows through the pipe and/or non-running pump(s) of the pumps (9a, 9b) when at least one of the pumps (9a, 9b) is stopped,
wherein the monitoring module is configured to identify an operating scenario in the wastewater pumping station by selecting an operating scenario from a group of predefined operating scenarios dependent on at least one first criterion for each running pump of the pumps (9a, 9b) that is based on the at least one load-dependent pump variable, at least one second criterion that is based on at least the first of the at least two model-based pipe parameters and at least one third criterion that is based on the negative-flow parameter.