WO2024213216A1

WO2024213216A1 - System and method for water hammer detection

Info

Publication number: WO2024213216A1
Application number: PCT/DK2024/050086
Authority: WO
Inventors: Eva Kühne
Original assignee: Ewa Sensors Aps
Priority date: 2023-04-12
Filing date: 2024-04-09
Publication date: 2024-10-17
Also published as: DK202300317A1; DK181714B1

Abstract

A method for monitoring water hammer (10) in an environment (20) comprising at least one pump (4) having an electrical induction motor (8) is disclosed. The at least one pump (4) is in fluid communication with a number of pipes (12, 12') and configured to pump a media (18), wherein the method comprises the step of detecting: a) the synchronous speed (co g) of the magnetic field of the motor (8) and b) the rotational speed (co M) of the motor (8). The method comprises the following steps: - for a predefined time period, on the basis of the detected synchronous speed (co g(t)) of the magnetic field of the motor (8) and the rotational speed (co M(0) °f the motor (8) calculating the slip speed (S(t)) of the motor (8) as function of time (t), wherein the slip speed (S(t)) is defined as the difference between the synchronous speed (co g(0) of the magnetic field of the motor (8) and the rotational speed (co M(0) of the motor (8): (2) S(t) = (co g(t) - co M(1))/KI g determining the alternating portion (A i (t)) of the slip speed (S(t)); analysing the alternating portion (A i (t)) of the slip speed (S(t)) and concluding that water hammer (10) is present in one of the pipes (12, 12') if: a) the alternating portion (A i(t), A 2(0, A a(t)) of the slip speed (S(t)) comprises three spaced apart positive peaks (P i, P 3, P 5), wherein the time (t 1) between the first positive peak (P 1) and the second positive peak (P 3) is larger than the time (t 2) between the second positive peak (P 3) and the third positive peak (P 5) and b) the first positive peak (P 1) is larger than the second positive peak (P 3) and the second positive peak (P 3) is larger than the third positive peak (P 5).

Description

System and Method for Water Hammer Detection

Field of invention

The present invention relates to a method for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor, wherein the at least one pump is in fluid communication with a number of pipes and configured to pump a media. The present invention also relates to a water hammer detection system for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor, wherein the at least one pump is in fluid communication with a number of pipes and configured to pump a media.

Prior art

Water hammer is a pressure surge or wave, caused when a fluid in motion is forced to stop or change direction suddenly - a momentum change. This phenomenon commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.

This pressure wave can cause major problems, from noise and vibration to pipe rupture or collapse.

In electrical induction motors the slip speed is the difference between an electrical induction motor's synchronous and asynchronous speed e.g. measured as revolutions per minute (RPM). The synchronous speed is the speed of the revolution of the magnetic field in the stator winding of the motor. The asynchronous speed is the rotating speed of the motor shaft.

Typically, the slip speed S is defined as the difference between the rotational speed of the motor ω_M and the synchronous speed ω_B of the magnetic fields of the motor: This can be defined as:

(1) S = (ω_B - ω_M) When the rotor is not turning the slip speed S is 0 RPM. Full-load slip speed, however, is typically in the rage between 30-60 RPM.

The prior art methods and systems for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor are rather complex and expensive. Moreover, the prior art solutions are not capable of distinguishing between water hammer and vibrations that are not related to water hammer. Accordingly, there is a need for a method and a system which reduces or even eliminates the above mentioned disadvantages of the prior art.

US 20170248142 Al discloses a method for detecting faults or operational parameters in a pump assembly by use of a handheld communication device is described. The pump assembly includes an electric motor and a pump, wherein the pump assembly or electric motor has at least one rotating shaft The method comprises the steps of: a) contactless measuring a sound signal emanating from the pump assembly by use of a microphone connected to or implemented in the handheld communication device, b) processing the measured sound signal, and c) recognising one or more sound emanating condition including any possible faults by way of the processed sound signal. It would be desirable to have an alternative solution that is simpler and cheaper.

US 20200182684 Al discloses a system for continuously monitoring at least one machine including a plurality of magnetic sensors synchronously sensing magnetic fields emitted by at least one machine. The plurality of magnetic sensors are sensing the magnetic fields along a corresponding plurality of channels and outputting magnetic field emission signals corresponding to the magnetic fields. A signal analyser is receiving at least a portion of the magnetic field emission signals and performing analysis of the magnetic field emission signals. The signal analyser is providing an output based on the analysis, wherein the output includes at least an indication of a condition of the at least one machine. A control module is receiving the indication of the condition and initiating at least one of a repair event on the at least one machine. An adjustment to a maintenance schedule of the at least one machine and an adjustment to an operating parameter of the at least one machine based on the indication. It would be desirable to have an alternative solution that is simpler and cheaper.

It is an object of the invention to provide an alternative to the than the prior art solutions by providing a simpler and cheaper system and method for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor.

It is also an object to the invention to provide a system and a method that is capable of distinguishing between water hammer and vibrations that are not related to water hammer.

Summary of the invention

The object of the present invention can be achieved by a method as defined in claim 1 and by a system as defined in claim 9. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

The method according to the invention is a method for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor, wherein the at least one pump is in fluid communication with a number of pipes and configured to pump a media, wherein the method comprises the step of detecting: a) the synchronous speed ω_B of the magnetic field of the motor and b) the rotational speed ω_M of the motor, wherein the method comprises the following steps: - for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor calculating the slip speed S(t) of the motor as function of time, wherein the slip speed S(t) is defined as the difference between the synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor: (2) S(t) = ω_B(t) - ω_M(t) determining an alternating portion A₁(t) of the slip speed S(t); analysing the alternating portion A₁(t) of the slip speed S(t) and concluding that water hammer is present in one of the pipes if: a) the alternating portion A₁(t) of the slip speed S(t) comprises three spaced apart positive peaks (P₁, P₃, P5), wherein the time (ti) between the first positive peak P₁ and the second positive peak P₃ is larger than the time (t₂) between the second positive peak P₃ and the third positive peak P₅ and b) the first positive peak P₁ is larger than the second positive peak P₃ and the second positive peak P₃ is larger than the third positive peak P₅.

Hereby, it is possible to provide a simpler and cheaper method than the prior art solutions. It is also possible to provide a method that is capable of distinguishing between water hammer and vibrations that are not related to water hammer.

In an embodiment, the method comprises: a) determining if the alternating portion A₁ is repeated or not and b) if the alternating portion A₁(t) is repeated it is concluded that water hamming is occurring.

In an embodiment, the method determines if the alternating portion A₁ is repeated within a predefined time from a previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.01-10 times the duration of the previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.02-5 times the duration of the previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.2-3 times the duration of the previous alternating portion A₁.

The method is suitable for detecting water hammer in an environment comprising at least one pump having an electrical induction motor. The method is suitable for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor.

At least one pump is in fluid communication with a number of pipes and configured to pump a media. The pump would typicall be connected to an inlet pipe that delivers the media to be pumped. The pump would typically be connected to an outlet pipe receiving media that is pressurised by the pump.

The method comprises the step of detecting the synchronous speed ω_B of the magnetic field of the motor. In an embodiment, this step is carried out by applying a non-invasively installed detection unit. In an embodiment, the detection unit comprises a sensor configured to detect a magnetic field.

The method comprises the step of detecting the rotational speed ω_M of the motor. In an embodiment, this step is carried out by applying a non- invasively installed detection unit. In an embodiment, the detection unit comprises a sensor configured to detect vibrations. In this embodiment, the system is configured to determine the rotational speed ω_M of the motor on the basis of detected vibration data.

The method comprises the step of, for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor calculating the slip speed S(t) of the motor as function of time.

The slip speed S(t) is defined as the difference between the synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor:

(2) S(t) = ω_B(t) - ω_M(t)

The method comprises the step of, for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor determining the alternating portion A₁(t) of the slip speed S(t).

The method comprises the step of analysing an alternating portion A₁(t) of the slip speed S(t) and concluding that water hammer is present in one of the pipes if: a) the alternating portion A₁(t) of the slip speed S(t) comprises three spaced apart positive peaks P₁, P₃, P5, wherein the time ti between the first positive peak P₁ and the second positive peak P₃ is larger than the time t₂ between the second positive peak P₃ and the third positive peak P₅ and b) the first positive peak P₁ is larger than the second positive peak P₃ and the second positive peak P₃ is larger than the third positive peak P₅.

The peaks can be detected by using any suitable peak detection technique. In an embodiment, the peak detection technique applies the fact that the first derivative of a peak has a downward-going zero- crossing at the peak maximum. To avoid false zero-crossing due to the noise, it is possible to: a) first smooth the first derivative of the signal, before looking for downward-going zero-crossings, and b) take only those zero crossings whose slope exceeds a certain predetermined minimum (slope threshold) at a point where the original signal exceeds a certain minimum (amplitude threshold).

By adjusting the smooth width, slope threshold, and amplitude threshold, it is possible to detect only the desired peaks and ignore peaks that are too small, too wide, or too narrow.

In an embodiment, the method comprises the step of determining the mean value of the slip speed S(t), wherein the alternating portion A₁(t) of the slip speed S(t) is determined by subtracting the mean value of the slip speed S(t) from the slip speed S(t).

In an embodiment, the method comprises the step of applying a detection unit that is attached to the motor of the pump, wherein the detection unit is configured to measure the magnetic field of a stator of the motor and hereby determine the synchronous speed ω_B of the magnetic field of the motor.

In an embodiment, the method comprises the step of applying a detection unit that is attached to the motor of the pump, wherein the detection unit is configured to detect vibrations and hereby determine the rotational speed ω_M of the motor.

In an embodiment, the detection unit that is detachably attached to the motor of the pump.

In an embodiment, the detection unit is attached to the motor of the pump by using mechanical fastening structures including bolts, a hose clamp, or a mounting bracket.

In an embodiment, the motor comprises a motor shaft, wherein the detection unit is configured to, on the basis of the vibrations detected by the detection unit, determine the rotational speed ω_M of the motor shaft. Determination of the rotational speed ω_M of the motor shaft may be carried out by using prior art technique disclosed in US 11009520 B2 or in the article "A Method for Estimation of Motor Rotational Speed from STFT Spectrogram at a Non-stationary Conditions" IFAC-PapersOnLine Volume 51, Issue 6, 2018, Pages 283-288.

In an embodiment, the method comprises the step of determining that a foreign body is in the pumped media if: a) the alternating portion A₁(t), A₂(t), A₃(t) comprises a U-shaped peak having a peak level that is larger than three times the average of the alternating portion A₁(t), A₂(t), A₃(t) outside the U-shaped peak.

In an embodiment, the area below a single U-shaped positive peak having a duration t₃ is more than 10 times the area below any adjacent signal for a time corresponding to two times the duration t₃.

In an embodiment, the method comprises the step of determining that gravel is in the pumped media (18) if the variance of the alternating portion A₁(t), A₂(t), A₃(t) is larger than three times the average of the alternating portion A₁(t), A₂(t), A₃(t).

In an embodiment, the detection unit comprises a communication module configured to wirelessly transmit detected data.

In an embodiment, the detection unit comprises a housing, wherein an accelerometer and a coil assembly is provided in the housing.

In an embodiment, coil assembly is configured to determine the amplitude of the magnetic field of the motor. In an embodiment, coil assembly is configured to determine the direction of the magnetic field of the motor.

In an embodiment, coil assembly is configured to determine the direction of the magnetic field in two dimensions.

In an embodiment, coil assembly is configured to determine the direction of the magnetic field in three dimensions.

In an embodiment, a communication module is provided in the housing. The water hammer detection system for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor, wherein the at least one pump is in fluid communication with a number of pipes and configured to pump a media, wherein the system comprises a detection unit arranged and configured for detecting: a) the synchronous speed ω_B of the magnetic field of the motor and b) the rotational speed ω_M of the motor, wherein the system is configured to: for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor calculate the slip speed S(t) of the motor as function of time t, wherein the slip speed S(t) is defined as the difference between the synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor:

(2) S(t) = ω_B(t) - ω_M(t) determine the alternating portion A₁(t) of the slip speed S(t); analyse the alternating portion A₁(t) of the slip speed S(t) and concluding that water hammer is present in one of the pipes if: a) the alternating portion A₁(t) of the slip speed S(t) comprises three spaced apart positive peaks P₁, P3, P5, wherein the time ti between the first positive peak P₁ and the second positive peak P₃ is larger than the and the time t₂ between the second positive peak P₃ and the third positive peak P₅ and b) the first positive peak P₁ is larger than the second positive peak P₃ and the second positive peak P₃ is larger than the third positive peak P₅.

Hereby, it is possible to provide a simpler and cheaper system than the prior art solutions. It is also possible to provide a system that is capable of distinguishing between water hammer and vibrations that are not related to water hammer.

In an embodiment, the system is configured to: a) determine if the alternating portion A₁ is repeated or not and b) if the alternating portion A₁(t) is repeated it is concluded that water hamming is occurring.

In an embodiment, the system is configured to determine if the alternating portion A₁ is repeated within a predefined time from a previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.01-10 times the duration of the previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.02- 5 times the duration of the previous alternating portion A₁. In an embodiment, the predefined time is in the range 0.2-3 times the duration of the previous alternating portion A₁.

The system is suitable of detecting water hammer in an environment comprising at least one pump having an electrical induction motor. The system is suitable for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor.

The system according to the invention is a water hammer detection system for monitoring water hammer in an environment comprising at least one pump having an electrical induction motor, wherein the at least one pump is in fluid communication with a number of pipes and configured to pump a media.

In an embodiment, the media is a water containing media. In an embodiment, the media is water.

The system comprises a detection unit arranged and configured for detecting: a) the synchronous speed ω_B of the magnetic field of the motor and b) the rotational speed ω_M of the motor.

In an embodiment, the detection unit comprises a vibration sensor.

In an embodiment, the detection unit comprises a magnetic field sensor.

The system is configured to: for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor calculate the slip speed S(t) of the motor as function of time t, wherein the slip speed S(t) is defined as the difference between the synchronous speed ω_B(t) of the magnetic field of the motor and the rotational speed ω_M(t) of the motor:

(2) S(t) = ω_B(t) - ω_M(t)

The system is configured to determine the alternating portion A₁(t) of the slip speed S(t).

The system is configured to analyse the alternating portion A₁(t) of the slip speed S(t) and concluding that water hammer is present in one of the pipes if: a) the alternating portion A₁(t) of the slip speed S(t) comprises three spaced apart positive peaks P₁, P₃, P5, wherein the time ti between the first positive peak P₁ and the second positive peak P₃ is larger than the time t₂ between the second positive peak P₃ and the third positive peak P₅ i and b) the first positive peak P₁ is larger than the second positive peak P₃ and the second positive peak P₃ is larger than the third positive peak P₅.

In an embodiment, the system is configured to determine the mean value of the slip speed S(t), wherein the alternating portion A₁(t) of the slip speed S(t) is determined by subtracting the mean value of the slip speed S(t) from the slip speed S(t).

In an embodiment, the detection unit is attached to the motor of the pump, wherein the detection unit is configured to measure the magnetic field of a stator of the motor and hereby determine the synchronous speed ω_B of the magnetic field of the motor.

In an embodiment, the detection unit is attached to the motor of the pump, wherein the detection unit is configured to detect vibrations and hereby determine the rotational speed ω_M of the motor.

In an embodiment, the detection unit is detachably attached to the motor of the pump.

In an embodiment, the motor comprises a motor shaft, wherein the wherein the detection unit is configured to, on the basis of the detected vibrations determine the rotational speed ω_M of the motor shaft.

In an embodiment, the system is configured to determine that a foreign body is in the pumped media if: a) the alternating portion A₁(t), A₂(t), A₃(t) comprises a U-shaped peak having a peak level that is larger than three times the average of the alternating portion A₁(t), A₂(t), A₃(t) outside the U-shaped peak.

In an embodiment, the system is configured to determine that gravel is in the pumped media if the variance of the alternating portion (A₁(t), A₂(t), A₃(t)) is larger than three times the average of the alternating portion (A₁(t), A₂(t), A₃(t)).

In an embodiment, coil assembly is configured to determine the amplitude of the magnetic field of the motor.

In an embodiment, coil assembly is configured to determine the direction of the magnetic field of the motor.

In an embodiment, coil assembly comprises two coils arranged and configured to determine the direction of the magnetic field of the motor.

In an embodiment, coil assembly comprises three coils arranged and configured to determine the direction of the magnetic field of the motor.

In an embodiment, a communication module is provided in the housing.

In an embodiment, the detection unit comprises a tachometer arranged and configured to measure the rotation speed of the shaft of the motor. In an embodiment, a tachometer is arranged in the housing. By using the tachometer, which is also known as a revolution-counter or RPM gauge, it is possible to measure the rotation speed of the shaft of the motor.

In an embodiment, at least one Hall effect sensor is arranged in the housing. Hereby, it is possible to detect the presence and magnitude of the magnetic field of the motor.

Description of the Drawings

The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

Fig. 1 shows a schematic view of a system according to the invention;

Fig. 2 shows two curves depicting the synchronous speed ω_B of the magnetic fields of the motor and the rotational speed ω_M of the motor as function of time t;

Fig. 3A shows the alternating portion A₁(t) of the slip speed S(t) as function of time t in a situation, in which water hammer is occurring;

Fig. 3B shows the alternating portion A₂(t) of the slip speed S(t) as function of time t in a situation, in which a foreign body is in the media being pumped by the pump;

Fig. 3C shows the alternating portion A₃(t) of the slip speed S(t) as function of time t in a situation, in which gravel is in the pumped media;

Fig. 4 shows a flowchart illustrating the steps of a method according to the invention;

Fig. 5A shows a pipe 12 with no flowing media due to a closed valve;

Fig. 5B shows the pipe 12 shown in Fig. 5A, in a configuration in which the media is flowing through the open valve;

Fig. 5C shows the pipe 12 shown in Fig. 5B, in a configuration in which water hammer occurs when the valve is being closed;

Fig. 6 shows a system according to the invention;

Fig. 7A shows a detection unit according to the invention and

Fig. 7B shows another detection unit according to the invention.

Detailed description of the invention

Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a system 2 of the present invention is illustrated in Fig. 1.

Fig. 1 illustrates a water hammer detection system 2 for monitoring water hammer in an environment 20. The environment 20 comprises at a pump 4 having an electrical induction motor 8. The pump 4 is in fluid communication with an inlet pipe 12' and an outlet pipe 12. The pump 4 is arranged and configured to pump a media. The media will typically be a liquid, preferably a water-containing liquid. In an embodiment, the pump 4 is arranged and configured to pump sewage water.

The system 2 comprises a detection unit 24 arranged and configured to detect: a) the synchronous speed ω_B(t) of the magnetic field of the motor 8 and b) the rotational speed ω_M(t) of the motor 8.

The system 2 is configured to for a predefined time period, on the basis of the detected synchronous speed ω_B(t) of the magnetic field of the motor 8 and the rotational speed ω_M(t) of the motor 8 calculate the slip speed S(t) of the motor 8 as function of time (t).

The slip speed S(t) is defined as the difference between the synchronous speed ω_B(t) of the magnetic field of the motor 8 and the rotational speed ω_M(t) of the motor 8. Accordingly, the slip speed can be defined by the following equation S(t) :

(2) S(t) = ω_B(t) - ω_M(t)

The detection unit 24 is configured to determine the alternating portion A₁(t) of the slip speed S (t) by calculating the mean value of the slip speed S(t) by using of a filter 16.

Fig. 1 illustrates that the slip speed S(t) of the motor 8 as S as function of time (t) can be split into two components:

- A mean value C and

- An alternating A₁(t).

Fig. 2 illustrates a first curve depicting the synchronous speed ω_B (frequency F) of the magnetic fields of the motor as function of time t. Fig. 2 also illustrates a second curve depicting the rotational speed ω_M (frequency F) of the motor as function of time t. The mean value C of the slip speed (the difference between the synchronous speed ω_B of the magnetic fields of the motor and the rotational speed ω_M of the motor is indicated.

Fig. 3A illustrates the alternating portion A₁(t) of the slip speed S(t) as function of time t in a situation, in which water hammer is occurring.

A first condition is fulfilled since: a) the alternating portion A₁(t) of the slip speed S(t) comprises three spaced apart positive peaks P₁, P₃, P5, wherein P₁ > P₃ > P5 b) the time ti between the first positive peak P₁ and the second positive peak P₃ is larger than the time t₃ between the second positive peak P₃ and the third positive peak P₅.

Since these two conditions are fulfilled, the system and method according to the invention will conclude that water hammer is present. However, for ensuring that the water hammer is present is determined if the signature of the alternating portion A₁(t) is repeated. Since this is the case, it can be concluded that water hammer is present.

It can be seen that the water hammer signature is repeated. In an embodiment, the method takes advantage of this by requiring repetition of the signature as a criterion when it should be determined that water hammer is present.

Fig. 3B illustrates the alternating portion A₂(t) of the slip speed S(t) as function of time t in a situation, in which a foreign body is in the media being pumped by the pump. The alternating portion A₂(t) contains a U- shaped positive peak having a peak level L₄that is larger than three times the RMS of the alternating portion A₂(t) outside the U-shaped peak.

The U-shaped positive peak has a duration t₃. The area below a single U-shaped positive peak is more than 10 times the area below any adjacent signal for a time corresponding to two times the duration t₃.

Fig. 3C illustrates the alternating portion A₃(t) of the slip speed S(t) as function of time t in a situation, in which gravel is in the pumped media. The variance of the alternating portion A₃(t) is larger than three times the RMS of the alternating portion A₃(t). The alternating portion A₃(t) contains a series of peaks having peak levels L₆, L₇, L₈ that are larger than the amplitude Lg of the remaining portion of the alternating portion A₃(t).

Fig. 4 illustrates a flowchart illustrating the steps of a method according to the invention. The first step the synchronous speed ω_B(t) of the magnetic field of the motor 8 and the rotational speed ω_M(t) of the motor 8 is provided. In the next step the slip speed S(t) of the motor 8 as function of time t is calculated by using the formula:

(2) S(t) = ω_B(t) - ω_M(t)

In the next step, the alternating portion A₁(t) of the slip speed S(t) is determined and analyses.

In the next step is determined if the alternating portion A₁(t) of the slip speed S(t) comprises several spaced apart positive peaks P₁, P3, P5, wherein the time ti, t₂ between adjacent positive peaks P₁, P3, P5 fulfills that ti > t₂. If this condition is not fulfilled, the first method will start over from the initial step. If, on the other hand, this condition is fulfilled, the method will continue to the next step, in which it is determined if the part of the level L2 of the first of said positive peaks P₁ is at least three times as large as the level Li of the part of the alternating portion A₁(t) of the slip speed S(t) that contains none of said positive peaks P₁, P3, Ps. If this condition is not fulfilled, the first method will start over from the initial step. If, on the other hand, this condition is fulfilled, it is concluded that a pressure shockwave is present: Accordingly, the conditions for water hamming are present. In order to ensure that water hamming is occurring it is, however, determined if the alternating portion A₁(t) is repeated or not. If the alternating portion A₁(t) is repeated (like shown in and explained with reference to Fig. 3A) it can be concluded that water hamming is occurring.

Fig. 5A illustrates a pipe 12 with no flowing media 18 because the valve 14 is closed.

Fig. 5B illustrates the pipe 12 shown in Fig. 5A, in a configuration in which the media 18 is flowing through the open valve 14. The direction of the media 18 is indicated with arrows.

Fig. 5C illustrates the pipe 12 shown in Fig. 5B, in a configuration in which water hammer 10 occurs when the valve 14 is being closed.

Fig. 6 illustrates a system 2 according to the invention. The system 2 comprises a rotatory machine 4 that is mechanically connected to a floor 34. The rotatory machine is a pump 4 comprises a motor 8 provided with a motor shaft 22. The motor 8 is arranged and configured to rotate a pump shaft 15 of a pump that is driven by the motor 8.

The pump shaft 15 is connected to the motor 8 via a coupling 11.

The system 2 comprises a detection unit 24 placed on the motor 8 of the first rotatory machine 4. The detection unit 24 is configured to be attached to and hereby detect vibration data 28 of the rotatory machine 4.

The system 2 comprises a processing unit 32 configured to receive and process said data 28. The processing unit 32 may be contained in a webbased server accessible via the Internet 30. In an embodiment, the processing unit 32 is integrated in the detection unit 24. In an embodiment, the processing unit 32 is integrated in an external device (e.g. a laptop computer or a tablet that is communicatively connected to the detection unit 24).

The rotatory machine 4 is mechanically connected to the floor 34 via a base member 20 placed on the floor 34.

The system 2 is designed for monitoring water hammer in an environment comprising the rotary machine 4 formed as a pump.

The pump housing 17 is connected to and receives a media to be pumped via an inlet pipe 12'. The pump housing 17 is connected to and pumps the media out through an outlet pipe 12.

It is important to underline that the pump 4 may be different from the ones shown in Fig. 1. In an embodiment, the rotatory machine(s) are pumps, wherein the motor and the pump are joint (built together or integrated). In an embodiment, the rotatory machine(s) are pumps, wherein the motor of the pump is fixed the pump housing of the pump.

The detection unit 24 may be attached to any suitable structure of the motor 8. The attachment may be established by using any suitable mechanical fastening structures including bolts, a hose clamp, or a mounting bracket.

Fig. 7A illustrates a detection unit 24 according to the invention. The detection unit 24 comprises a housing 40 configured to be attached to a motor of a pump. The detection unit 24 comprises a battery 42 for providing electrical power to the detection unit 24. The detection unit 24 comprises a printed circuit board 44 provided with a communication module 36. The communication module 36 is configured to communicate wirelessly with an external device (e.g. via a local network). In an embodiment, the detection unit 24 comprises a modem configured for sending digital data wirelessly. In an embodiment, detection unit 24 comprises a Bluetooth radio module with built-in antenna.

The detection unit 24 comprises an accelerometer 38 arranged and configured to detect vibrations of the detection unit 24. Accordingly, when the detection unit 24 is attached to a motor, the accelerometer 38 ci capable of detecting the vibrations of the motor. In an embodiment, the accelerometer 38 is a multi-axis accelerometer configured to detect both the magnitude and the direction of the proper acceleration, as a vector quantity. In an embodiment, the accelerometer 38 is a two-axis accelerometer. In an embodiment, the accelerometer 38 is a three-axis accelerometer. In an embodiment, the accelerometer 38 is a single-axis accelerometer 38.

In an embodiment, the accelerometer 38 is a micromachined microelectromechanical systems (MEMS).

In an embodiment, the detection unit 24 comprises a control unit. In an embodiment, the control unit comprises a processing unit.

The detection unit 24 comprises a coil assembly 60 arranged and configured to detect the magnetic field of a motor to which the detection device is attached. In an embodiment, the coil assembly 60 comprise one or more coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor. In an embodiment, the coil assembly 60 comprise two coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor. In an embodiment, the coil assembly 60 comprise three coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor.

Fig. 7B illustrates another detection unit according to the invention. The detection unit 24 comprises a housing 40 configured to be attached to a rotatory machine such as a pump or motor. The detection unit 24 comprises a power supply 46 connected to a power cable 48 protruding from the housing 40.

The detection unit 24 comprises a printed circuit board 44 provided with a communication module 36. The communication module 36 is connected to an external device by using a data cable 52. The data cable 52 may be electronically connected to a control box of rotatory machine (e.g. a pump). In an embodiment, the detection unit 24 comprises no communication module but is electrically connected to an external communication module (e.g. built into an external device such as a control box of a pump or a motor).

The detection unit 24 comprises an accelerometer 38 corresponding to the one shown and explained with reference to Fig. 7A. In an embodiment, the detection unit 24 comprises a control unit. In an embodiment, the control unit comprises a processing unit. The detection unit 24 comprises a coil assembly 60 arranged and configured to detect the magnetic field of a motor to which the detection device is attached. In an embodiment, the coil assembly 60 comprise one or more coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor. In an embodiment, the coil assembly 60 comprise two coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor. In an embodiment, the coil assembly 60 comprise three coils arranged and configured to detect the direction and magnitude of the magnetic field of the motor.

List of reference numerals

2 System

4 Pump

6 Motor shaft

8 Motor

10 Water hammer

11 Coupling

12, 12' Pipe

14 Valve

15 Pump shaft

16 Filter

17 Pump housing

18 Pumped media (e.g. water)

20 Environment

21 Base member

22 Motor shaft

24 Detection unit

28 Data (e.g. sent as wireless signals)

30 Internet

32 Processing unit

36 Communication module

38 Accelerometer

40 Housing

42 Battery

44 Printed circuit board

46 Power supply

48 Power cable

52 Data cable

60 Coil assembly

5 Slip speed ω_B Synchronous speed of the magnetic fields of the motor ω_M Rotational speed of the motor (the asynchronous speed) ω_B (t) Synchronous speed of the magnetic fields of the motor as function of time ω_M (t) Rotational speed of the motor as function of time t Time t₁ Time

F Frequency (e.g. revolutions per minute, RPM)

C Mean value

L₁, L₂ Level

L₃, U Level

L₅, L₆ Level

L₇, L₈ Level A₁(t) Alternating part of the slip speed as function of time

A₂(t) Alternating part of the slip speed as function of time

A₃(t) Alternating part of the slip speed as function of time t₂ Duration P₁ Peak

P₃ Peak

P5 Peak

Claims

1. Method for monitoring water hammer (10) in an environment (20) comprising at least one pump (4) having an electrical induction motor (8), wherein the at least one pump (4) is in fluid communication with a number of pipes (12, 12') and configured to pump a media (18), wherein the method comprises the step of detecting: a) the synchronous speed (ω_B) of the magnetic field of the motor (8) and b) the rotational speed (ω_M) of the motor (8), wherein the method comprises the following steps:

- for a predefined time period, on the basis of the detected synchronous speed (ω_B(t)) of the magnetic field of the motor (8) and the rotational speed (ω_M(t)) of the motor (8) calculating the slip speed (S(t)) of the motor (8) as function of time (t), wherein the slip speed (S(t)) is defined as the difference between the synchronous speed (ω_B(t)) of the magnetic field of the motor (8) and the rotational speed ( ω_M(t)) of the motor (8):

(2) S(t) = ω_B(t) - ω_M(t), characterised in that the method comprising: determining an alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)); analysing the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) and concluding that water hammer (10) is present in one of the pipes (12, 12') if: a) the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) comprises three spaced apart positive peaks (P₁, P₃, P5), wherein the time (ti) between the first positive peak (P₁) and the second positive peak (P₃) is larger than the time (t₂) between the second positive peak (P₂) and the third positive peak (P₅) and b) the first positive peak (P₁) is larger than the second positive peak (P₃) and the second positive peak (P₃) is larger than the third positive peak (P₅).

2. Method according to claim 1, wherein the method comprises the step of determining the mean value (C) of the slip speed (S(t)), wherein the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) is determined by subtracting the mean value (C) of the slip speed (S(t)) from the slip speed (S(t)).

3. Method according to claim 1 or 2, wherein the method comprises the step of applying a detection unit (24) that is attached to the motor (4) of the pump (8), wherein the detection unit (24) is configured to: a) measure the magnetic field of a stator of the motor (8) and hereby determine the synchronous speed (ω_B) of the magnetic field of the motor (8) and b) detect vibrations and hereby determine the rotational speed (ω_M) of the motor (8).

4. Method according to claim 3, wherein the motor (4) comprises a motor shaft (6), wherein the detection unit (24) is configured to, on the basis of the detected vibrations determine the rotational speed (ω_M) of the motor shaft (6).

5. Method according to one of the preceding claims, wherein the method comprises the step of determining that a foreign body is in the pumped media (18) if: a) the alternating portion (A₁(t), A₂(t), A₃(t)) comprises a U-shaped peak having a peak level (L4) that is larger than three times the average of the alternating portion (A₁(t), A₂(t), A₃(t)) outside the U- shaped peak.

6. Method according to one of the preceding claims, wherein the method comprises the step of determining that gravel is in the pumped media (18) if the variance of the alternating portion (A₁(t), A₂(t), A₃(t)) is larger than three times the average of the alternating portion (A₁(t), A₂(t), A₃(t)).

7. Method according to one of the preceding claims, wherein the detection unit (24) comprises a communication module (36) configured to wirelessly transmit detected data (28).

8. Method according to one of the preceding claims, wherein the detection unit (24) comprises a housing (40), wherein an accelerometer (38) and a coil assembly (60) is provided in the housing (40).

9. A water hammer detection system (2) for monitoring water hammer (10) in an environment (20) comprising at least one pump (4) having an electrical induction motor (8), wherein the at least one pump (4) is in fluid communication with a number of pipes (12, 12') and configured to pump a media (18), wherein the system (2) comprises a detection unit (24) arranged and configured for detecting: a) the synchronous speed (ω_B) of the magnetic field of the motor (8) and b) the rotational speed (ω_M) of the motor (8), wherein the system (2) is configured to: for a predefined time period, on the basis of the detected synchronous speed (ω_B(t)) of the magnetic field of the motor (8) and the rotational speed (ω_M(t)) of the motor (8) calculate the slip speed (S(t)) of the motor (8) as function of time (t), wherein the slip speed (S(t)) is defined as the difference between the synchronous speed (ω_B(t)) of the magnetic field of the motor (8) and the rotational speed (ω_M(t)) of the motor (8):

(2) S(t) = ω_B(t) - ω_M(t), characterised in that the system (2) is configured to: determine an alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)); analyse the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) and concluding that water hammer (10) is present in one of the pipes (12, 12') if: a) the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) comprises three spaced apart positive peaks (P₁, P₃, Ps), wherein the time (ti) between the first positive peak (P₁) and the second positive peak (P₃) is larger than the time (t₂) between the second positive peak (P₃) and the second positive peak (P₅) and b) the first positive peak (P₁) is larger than the second peak (P₃) and the second positive peak (P₃) is larger than the third peak (P₅).

10. System (2) according to claim 9, wherein the system is configured to determine the mean value (C) of the slip speed (S(t)), wherein the alternating portion (A₁(t), A₂(t), A₃(t)) of the slip speed (S(t)) is determined by subtracting the mean value (C) of the slip speed (S(t)) from the slip speed (S(t)).

11. System (2) according to claim 9 or 10, wherein the detection unit (24) that is attached to the motor (4) of the pump (8), wherein the detection unit (24) is configured to: a) measure the magnetic field of a stator of the motor (8) and hereby determine the synchronous speed (ω_B) of the magnetic field of the motor (8) and b) detect vibrations and hereby determine the rotational speed (ω_M) of the motor (8).

12. System (2) according to claim 11, wherein the motor (4) comprises a motor shaft (6), wherein the wherein the detection unit (24) is configured to, on the basis of the detected vibrations determine the rotational speed (ω_M) of the motor shaft (6).

13. System (2) according to one of the preceding claims 9-12, wherein the system (2) is configured to determine that a foreign body is in the pumped media (18) if: a) the alternating portion (A₁(t), A₂(t), A₃(t)) comprises a U-shaped peak having a peak level (L4) that is larger than three times the average of the alternating portion (A₁(t), A₂(t), A₃(t)) outside the U- shaped peak.

14. System (2) according to one of the preceding claims 9-13, wherein the system (2) is configured to determine that gravel is in the pumped media (18) if the variance of the alternating portion (A₁(t), A₂(t), A₃(t)) is larger than three times the average of the alternating portion (A₁(t), A₂(t), A₃(t)).

15. System (2) according to one of the claims 9-14, wherein the detection unit (24) comprises a communication module (36) configured to wirelessly transmit detected data (28).

16. System (2) according to one of the claims 9-15, wherein the detection unit (24) comprises a housing (40), wherein an accelerometer (38) and a coil assembly (60) is provided in the housing (40).