Method and device for detecting a leak in a supply network

Abstract

The invention relates to a method for detecting a leak, and to a device suitable therefor, in a supply network that comprises a pipeline system through which a fluid is conveyed, wherein a pressure (p(t)) of the fluid and a volumetric flow (V(t)) of the fluid are detected as a function of time by measuring at various locations (x1, x2, ...xN) of the pipeline system. The invention is characterised in that, at a first location (x1), for a first defined duration (T1), the pressure in the pipeline system is modulated using a first predefinable reference signal (M1), and curves of the modulated pressure signal and volumetric flow signal are preferably recorded at this first location (x1) and, if a time difference (Δt1) is detected between defined signal portions of the pressure signal and the volumetric flow signal, a first distance of a leak from this first location (x1) is determined from this time difference (Δt1). The method according to the invention and appropriately designed devices are in particular applicable for detecting supply network leaks.

Description

[0001] Description

[0002] Method and device for detecting a leak in a supply network

[0003] The invention relates to a method for detecting a leak in a supply network having a piping system through which a fluid is conveyed, wherein a pressure of the fluid and a volume flow of the fluid are measured at various locations in the piping system as a function of time. The invention further relates to devices suitable for the method.

[0004] Loss of drinking water due to dilapidated piping systems is a major problem in many countries around the world. Enormous quantities of drinking water are lost through undetected leaks. There is a global need for action here, as climate change, the growing world population, and increasing industrialization are making water an increasingly scarce and expensive resource.

[0005] A variety of methods for detecting leaks in water distribution networks are known from the state of the art. Leak detection techniques can generally be divided into two categories: external and internal methods. External methods detect leaks by looking for signs of leaks outside the piping system. One example is visual inspection. Another method is listening to the flow noise at various points along the pipe, from which the location of the leak can be determined. Internal methods, such as internal inspection, attempt to find leaks using sensors that measure state variables within the pipes. This category includes a variety of mathematical, computational, and signal processing methods.

[0006] Silva et al., JAFR 1996 "Pressure wave behavior and leak detection in pipelines", Comp. And Chemical Eng. Proceedings 6th Eur. Symp. (Rhodes) 20, pp. 491-6, discloses an online computing technique in which data on transients caused by a leak are recorded by a computer, which displays the pressure transient curve and enables the leak location to be identified. This method is based on the fact that the pressure wave generated by a leak is accompanied by a sudden drop in pressure. GB2444955A discloses a leak detection device for underground water distribution pipes in which a pressure wave is transmitted from a hydrant to the underground pipe. A pressure sensor detects pressure fluctuations in the fluid in the pipe caused by the pressure wave reflected by discontinuities ( e . g . leaks ) in the system .A control unit records the measured pressures, analyses them and calculates the distance between the pressure sensor and a detected discontinuity. A disadvantage of the leak detection approach described in GB2444955A is that a significant pressure surge is required to generate reflections at the leak point, which puts a strain on the piping system. Furthermore, it is a temporary measurement setup that requires personnel and cannot be permanently integrated into existing infrastructure. The measurement setup only works for large leaks, and other fault points (e.g. branches or changes in cross-section) lead to misinterpretations. The detection range is also very limited.

[0007] WO2019 / 160433A1 discloses a method for processing transient events in a distribution network with a specific network topology based on wavefront characteristics that are recorded at high speeds by a large number of sensors at specific measuring locations in the distribution network. In the method, an arrival time of a wavefront caused by a specific transient event is recorded at least at a subset of the measuring locations by a respective sensor of the N sensors. A location of the specific transient event in the distribution network is then determined depending on differences in the detected arrival times of the wavefront detected by the sensors at the subset of the measuring locations.Subsequently, an event type of the transient event in the distribution network is classified using the specific location of the transient event in the distribution network, using the detected arrival times of the wave fronts, and using the specific network topology of the distribution network. The approach described in W02019 / 160433A1 also has the disadvantage that very strong pressure gradients (e.g. caused by a pipe burst) place a strain on the piping system. Furthermore, many closely distributed measuring points are necessary, which often leads to difficulties, particularly with regard to the power supply of the measuring points. All measuring points require a very precise time and must be precisely synchronized.

[0008] In particular, both of the aforementioned methods are unsuitable for continuous monitoring of existing leaks integrated into the piping system of a water supply network. It is therefore an object of the present invention to overcome the disadvantages of the prior art and to provide an improved method and device for detecting leaks, in particular existing leaks, in a supply network, in particular a water supply network.

[0009] This object is achieved by a method having the features of claim 1. Furthermore, the object is achieved by a device according to claim 15 and a computer-aided processing unit according to claim 16. Advantageous further developments emerge from the dependent claims.

[0010] A method is proposed which, in principle, is known from system analysis or the identification of dynamic systems, in which a dynamic system is suitably excited. According to the invention, the system is specifically excited with a pressure signal at one point within the supply system during a measurement campaign and, in response to this, the flow (and, for comparison, the pressure too) is measured at the point where the pressure is applied. The time offset between the change in pressure and the change in flow can be used to calculate the distance to the leak location. The exact location of the leak can be determined by carrying out several measurement campaigns at different locations. In particular, points where a fluid is fed into the piping system of a supply network can be used as measurement locations. However, any points in the supply network are also suitable as measurement locations.

[0011] The invention thus relates to a method for detecting one or more leaks in a supply network with a piping system through which a fluid is conducted, wherein a pressure of the fluid and a volume flow of the fluid are measured at different locations in the piping system as a function of time. The invention is characterized in that at a first location the pressure in the piping system is modulated with a first predeterminable reference signal for a first defined period of time, and preferably at this first location curves of the modulated pressure and volume flow signal are recorded and upon detection of a time difference between defined signal components of the pressure signal and the volume flow signal, a first distance of a leak from this first location is determined.

[0012] The method for leak detection according to the invention can advantageously be used in a wide variety of ways. In particular, the method can be used to detect existing leaks in supply networks. Even small leaks which become larger over time can be recorded. The normal operation of the supply network is not affected during the measurement campaigns, so that the method can be easily integrated into the existing operation of a supply network. The method is designed in such a way that a distinction can be made between normal operation, e.g. in a drinking water network, and a leak. This is because at a consumer point (= a point where fluid is taken from the network), it is fundamentally not possible to distinguish whether there is a leak or normal operation. In contrast, e.g.In a drinking water network, the consumer points (i.e. the house connections) have pressure reducers which decouple what is happening in the network from what is happening inside the house. All water withdrawal points downstream of the pressure reducer are not affected by the pressure change in the network. It should also be noted that the majority of the water consumption profile in the pipe network is statistically distributed. This means that the location, time and quantity of water used change at any given time. Leakage, on the other hand, is fixed in place, constant at all times and the leakage volume flow is pressure-dependent. By taking several measurements at different times, even over several days (especially at night), the method according to the invention can be used to differentiate the leak being sought from the rest of the consumption profile.

[0013] While only the distance to a leak can be determined by a measuring process, in a first advantageous embodiment of the invention the exact location of the leak in the piping system can also be determined. For this purpose the method according to the invention is repeated at other locations in the piping system at different times. For this purpose the pressure in the piping system is modulated at a second location in the piping system for a second defined period of time, which can be the same as the first period of time, with a second predefinable reference signal, which can be the same as the first reference signal. Preferably at this location the curves of the modulated pressure and volume flow signal are then recorded and when a time difference is detected between defined signal components of the pressure signal and the volume flow signal a second distance of a leak from this second location is determined from this time difference.The process is repeated at additional locations, and the position of the leak in the piping system is determined from a large number of distances thus determined. The greater the number of locations at which modulation and measurement are performed, the more accurate the leak location. By using different reference signals for pressure modulation, individual measurements can be better differentiated.

[0014] In a particularly advantageous embodiment, the distances from the leak to the measuring locations are determined at different measuring times. This allows for a high degree of flexibility in leak detection. For example, it is possible to carry out a first distance measurement of a leak to a first measuring location on one day and a second distance measurement of a leak to a second measuring location on a different day or, for example, during the night. Furthermore, different measuring times make it easier to separate individual measurements. This design is particularly advantageous for existing leaks.

[0015] In most cases, the locations at which the modulation is introduced into the piping system will be the same as the measuring locations for the pressure and volume flow. However, due to local conditions of the supply network, for example, it may be advantageous to introduce the modulation into the piping system at only one location or at a few locations and to measure at different locations. In this advantageous embodiment, the locations at which the pressure in the piping system is modulated are at least partially different from the locations at which the pressure and volume flow of the fluid are measured. This also applies to the metrological recording of the pressure and volume flow of the fluid at different locations in the same section of pipe. Structural conditions within the piping system or a section thereof may make it necessary to spatially separate the recording of the pressure and volume flow.

[0016] In a further advantageous variant of the method, the time periods during which the pressure in the piping system is modulated and the time periods during which the pressure and volume flow of the fluid are measured coincide, at least in part. In principle, the time periods of modulation and measurement must match to detect the time difference between the pressure and volume flow signals. However, in certain situations, it may be advantageous, for example, to apply the modulation signal before starting the actual measurement of the time shift, so that the system can settle.

[0017] The modulation signal can be freely selected. Possible options are a brief pressure surge, a pressure jump, or even a sinusoidal pressure application at different frequencies. A downward pressure jump (e.g. 2 bar below operating pressure) is also conceivable. In a particularly advantageous design variant, a periodic signal with a specifiable amplitude, frequency, and phase is selected as the modulation signal for the pressure. Accordingly, the time differences between the pressure and volume flow signals determined at one location are phase differences that can be measured with particular precision.

[0018] With a periodic modulation signal, the phase between the pressure signal and the volume flow signal can be influenced by varying the frequency of the pressure signal. By tuning the frequency, the accuracy of the time difference measurement can be particularly advantageously increased.

[0019] In a further advantageous embodiment, the measured pressure signal is correlated with the measured volume flow signal. Based on the correlation, certain signal components can be amplified. This can be used particularly advantageously if the time periods during which the pressure and volume flow of the fluid are measured are selected to be as long as possible. By "long" here we mean periods of several hours. The amplitude and frequency of the modulation signal can be selected particularly advantageously depending on the properties of the piping system. Depending on the size of the piping system and the dynamics of the system, the frequencies of the modulation signal can be in the range of approximately 0.05...0.5 Hz.

[0020] By integrating the measurement of the pressure and volume flow of the fluid and / or the pressure modulation into a control system, the efficiency of the process can be significantly increased.

[0021] A further advantageous embodiment of the invention is that the supply network is a water distribution network, and the measuring points are water feed points into the pipeline system. The invention is applicable to all infrastructure networks in which fluids are transported and / or consumed. Examples of such infrastructure networks include gas supply and district heating networks, as well as hydrogen distribution networks.

[0022] In the following, the invention and its embodiments are described and explained in more detail with reference to the figures in which an embodiment of the invention is shown.

[0023] They show:

[0024] Figure 1 is a sketch of a first embodiment of a device according to the invention;

[0025] Figure 2 shows a graph with temporal courses of the modulated pressure and volume flow signal

[0026] Figure 1 shows a sketch of an embodiment of a device 1 according to the invention for detecting a leak in a pipeline system through which a fluid is conducted. The device 1 is arranged at a location xl of a pipe section R of the pipeline system. In this embodiment, the device 1 comprises a device 2 for modulating the pressure of the fluid, a computer-aided control unit 3 for controlling the device for modulation 2, a detection system 4 which has a pressure sensor 4A for metrologically detecting a pressure p(t) of the fluid and a flow sensor 4B for metrologically detecting the volume flow V(t) of the fluid, and a processing unit 5 which is communicatively connected at least to the control unit of the device for modulation 2 and the detection system 4.

[0027] The device for modulating 2 the pressure can, for example, be designed such that the speed of a pump is varied. This can be achieved by means of a booster pump or another mechanical arrangement such as, for example, a pump with a bypass feedback line with a throttle valve. The pump in Fig. 2 is connected to a computer-aided control unit 3 which, for example, varies the speed of the pump 2. The control signal corresponds to the reference signal with which the pressure of the fluid in the pipeline is modulated. A measuring transducer from the SITRANS P family from Siemens can be used as the pressure sensor 4A, for example. A measuring transducer from the SITRANS F family from Siemens can be used as the flow sensor 4B. The pressure sensor and the volume flow sensor are preferably placed in close proximity to one another.It is particularly advantageous if both sensors are arranged within the same pipe section of the piping system. In a water supply network, drinking water feed points are particularly suitable for this because pressure and flow sensors are usually present at these points anyway. The measuring transducers are often connected by fieldbus communication to a data processing unit 5, which in turn can be integrated into a higher-level data processing system 6 (e.g. a control system) in which the recorded process and diagnostic data are further processed. According to the invention, in order to determine a leak, the pressure in the piping system is modulated with a first predefinable reference signal for a first defined period of time TI at the location xl, and curves of the modulated pressure and volume flow signal are recorded preferably at this location xl.

[0028] To illustrate the invention, Fig. 2 shows a graph with temporal progressions of the modulated pressure and volume flow signals. In this embodiment, the pressure p(t) is modulated with a periodic reference signal and exhibits a sinusoidal progression.

[0029] The pressure change deliberately introduced into the pipeline by modulation propagates through the pipeline network at a limited speed (around 1000 m / s), depending on the fluid, and reaches the point of leakage with a corresponding time delay. At the location of the leak, the pressure change causes a change in the leakage volume flow. If the pressure in the pipeline increases or decreases, the volume flow also increases or decreases accordingly. This change can be recorded by a flow meter. If the flow meter is also placed at location xl, it records the increased volume flow V(t) with a time delay. Fig. 2 shows the sinusoidal curve of the volume flow signal V(t), which is delayed compared to the pressure signal p(t). Thus, approximately twice the propagation time in the pipeline passes until the corresponding increase in volume flow is measurable at location xl of the evoked pressure increase. Thus, upon detection of a time difference Δt (cf. Δt in Fig.2) between defined signal components of the pressure signal and the volume flow signal, from this time difference At a distance El (see Fig. 1) of the leakage to this location xl can be determined.

[0030] If this measuring method is repeated at several measuring locations in the branched pipeline network, the location of the leak can be determined using correlation. Since the measured signals are probably noisy and superimposed with all kinds of interference, it is also sensible to use a method related to correlation. A lock-in amplifier is proposed that multiplies the signals p(t) (=reference signal) and V(t) (=measurement signal). This eliminates statistical interference and amplifies the signal components that correlate with the reference signal. By adjusting the phase shift of the reference signal at the lock-in input, the output signal of the lock-in amplifier is at its greatest when the reference and measurement signals are in phase. The phase shift is a measure of the distance of the leak from the measuring location.

[0031] Alternatively, methods from the identification of dynamic systems can be used that can explicitly estimate a dead time. This dead time corresponds exactly to the phase shift above, or the delay.

Claims

Patent claims 1. Method for detecting a leak in a supply network with a piping system through which a fluid is conducted, wherein at N different locations (xl, x2, ...xN) of the piping system, a pressure (p(t) ) of the fluid and a volume flow (V (t) ) of the fluid in the pipeline system are measured, characterized in that at a first location (xl) for a first defined period of time (TI) the pressure in the pipeline system is modulated with a first predeterminable reference signal (Ml), and preferably at this first location (xl) profiles of the modulated pressure and volume flow signal are recorded and upon detection of a time difference (Atl) between defined signal components of the pressure signal and the volume flow signal, a first distance (El) of a leak to this first location (xl) is determined from this time difference (Atl).

2. Method according to claim 1, characterized in that at a second location (x2) for a second defined period of time (T2), which may be equal to the first period of time (TI), the pressure in the pipeline system is modulated with a second predeterminable reference signal (M2), which may be equal to the first reference signal (M1), and preferably at this second location (x2) profiles of the modulated pressure and volume flow signal are recorded and upon detection of a time difference (At2) between defined signal components of the pressure signal and the volume flow signal, a second distance (E2) of a leak to this second location (x2) is determined from this time difference (At2) and the method is repeated at further locations (x3, x4, ...) and the position of the leak in the pipeline system is determined from a plurality of the distances (E3, E4, ...) determined in this way.

3. Method according to claim 1 or 2, characterized in that the determination of the distances of the leakage to the locations (xl, x2, ...xN) takes place at different measuring times (tl, t2, ...tM).

4. Method according to claim 2 or 3, characterized in that at least partially the locations at which the pressure in the pipeline system is modulated are different from the locations at which the pressure and the volume flow of the fluid are measured.

5. Method according to one of claims 1 to 4, characterized in that the measurement devices for detecting the pressure and the volume flow of the fluid are positioned at different locations in the same pipeline section.

6. Method according to one of the preceding claims, characterized in that the time periods (Ti) during which the pressure in the pipeline system is modulated and the time periods during which the pressure and the volume flow of the fluid are measured coincide at least partially.

7. Method according to one of the preceding claims, characterized in that the modulation of the pressure can be a periodic signal with a predeterminable amplitude, frequency and phase and accordingly the time differences between the pressure and volume flow signal determined at a location are phase differences.

8. Method according to claim 7, characterized in that in the case of a periodic modulation signal, the phase between the pressure signal and the volume flow signal is influenced by varying the frequency of the pressure signal.

9. Method according to one of the preceding claims, characterized in that the measured pressure signal with is correlated with the measured volume flow signal.

10. Method according to one of the preceding claims, characterized in that in order to improve the signal-to-noise ratio, the time periods during which the pressure and the volume flow of the fluid are measured are selected to be as long as possible. 11 . Method according to one of the preceding claims, characterized in that the amplitude and frequency of the modulation signal are selected as a function of properties of the pipeline system.

12. Method according to one of the preceding claims, characterized in that the metrological detection of the pressure and the volume flow of the fluid and / or the pressure modulation are controlled. 13 . Method according to one of claims 1 to 12, characterized in that the supply network is a water distribution network and the locations are feed points for water into the pipeline system.

14. Method according to one of claims 1 to 12, characterized in that the supply network is a hydrogen distribution network and the locations are feed points for hydrogen into the pipeline system.

15. Device (1) for detecting a leak in a supply network with a pipeline system through which a fluid is conducted, comprising - a modulation device (2) which is designed to modulate the pressure of the fluid with a predeterminable reference signal, - a computer-aided control unit ( 3 ) for controlling the modulation device ( 2 ), - a detection system (4) which can be coupled to the piping system at a location (xl) and has a pressure sensor (4A) for measuring the pressure of the fluid and a flow sensor (4B) for measuring the volume flow of the fluid, - a processing unit (5) which is communicatively connected at least to the control unit (3) of the device for modulation (2) and the detection system (4) and is designed to determine a distance (El) to a leak, characterized in that the profiles of the modulated pressure and volume flow signal recorded by means of the detection system (4) are compared and, upon detection of a time difference (Atl) between defined signal components of the pressure signal and the volume flow signal, a distance of a leak to this location (xl) is derived from this time difference (Atl).

16. Computer-aided processing unit (6) which is connected to at least one device (1) according to claim 15 and is designed to carry out the method according to one of claims 1 to 14.

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