JP7780751B2 - Submersible pump monitoring system and submersible pump monitoring method - Google Patents

Description

Patent Act Article 30, Paragraph 2 applied. Presented in the proceedings and poster at the 16th IEEE International Conference on Nano/Micro Engineered & Molecular Systems on April 25, 2021.

The present invention relates to a system and method for determining and monitoring the condition of shaft seal oil in submersible pumps used in fields such as sewage treatment and civil engineering.

As shown in Figure 13, a conventional submersible pump 1P comprises a pump chamber 5 that houses an impeller 2 and has an inlet 3 and a discharge port 4, a motor base 6 connected to the casing 5a that forms the pump chamber 5, a motor chamber 7 formed by the motor base 6 and a motor frame 7a connected to it, a stator 8 fixed within the motor chamber 7, a rotor 10 equipped with a motor shaft 9, a seal housing 11 that closes a recess 6a formed in the lower part of the motor base 6, and a shaft seal device (mechanical seal) 12 attached to the motor shaft 9 within the recess 6a of the motor base 6 that is closed by the seal housing 11. The recess 6a is closed by the seal housing 11 to form an oil chamber 13, which is filled with seal oil L and the seal device 12 is immersed in the seal oil L.

The shaft seal device 12 is a consumable part and must be replaced periodically, but if the shaft seal device 12 deteriorates before the periodic replacement, it can lead to failure of the submersible pump.

The most common failure in this type of submersible pump is caused by deterioration of the shaft seal device 12, which allows water or fine particles such as metal powder or mud to get into the oil chamber 13.

Conventionally, an electrode 14 is inserted into the shaft seal oil L, which is essentially an insulator, and the electrical resistance (insulation resistance) between the electrode 14 and earth (the grounded motor frame 7a) is measured to detect a decrease in insulation resistance due to water contamination of the shaft seal oil. A threshold is set, and when the insulation resistance value falls below a set value (e.g., 0.1 MΩ), it is determined that a malfunction has occurred due to water entering the shaft seal oil L (see Patent Documents 1 and 2, etc.).

However, water intrusion detection methods that measure the insulation resistance value of the seal oil alone cannot clearly distinguish between water and metal powder such as iron powder mixed into the seal oil, nor can they detect fine mud particles in the seal oil. Therefore, the inventors previously proposed a submersible pump monitoring system that uses an oil sensor equipped with a light-emitting element that irradiates light onto the seal oil and a light-receiving element that detects the intensity of light that passes through the seal oil from the light-emitting element, and detects changes in the intensity of the received light to detect the inclusion of fine metal powder, mud, or other particles in the seal oil (Patent Document 3).

Japanese Patent Application Laid-Open No. 2002-310091 Japanese Unexamined Patent Publication No. 54-1083 Japanese Patent Application Laid-Open No. 2019-203799

However, in the above-mentioned conventional monitoring systems, the received light intensity can change even when the moisture content increases, making it difficult to determine whether the change in received light intensity is due to moisture or an increase in foreign matter such as iron powder.

The primary objective of the present invention is to provide a submersible pump monitoring system and a submersible pump monitoring method that can determine whether there is an increase in water content or an increase in fine particles such as iron powder or mud in the seal oil of a submersible pump's seal device.

To achieve the above objective, one aspect of the present invention provides a submersible pump monitoring system that includes a light-emitting unit that irradiates light onto the shaft seal oil of a submersible pump, a light-receiving unit that detects the light from the light-emitting unit through the shaft seal oil, and a determination unit that determines whether the change in intensity of the light received by the light-receiving unit follows an exponential function or a power function, thereby determining whether water or non-transparent fine particles are mixed into the shaft seal oil.

Another aspect of the present invention is a method for monitoring a submersible pump, which includes the steps of irradiating light from a light-emitting unit onto the shaft seal oil of a submersible pump, detecting the light from the light-emitting unit through the shaft seal oil, and determining whether the change in intensity of the detected light follows an exponential function or a power function, thereby determining whether water or non-transparent fine particles have been mixed into the shaft seal oil.

It is preferable that the light-emitting unit emits red light.

According to the present invention, by determining whether the change in the intensity of light received by the light receiving element follows an exponential function or a power function, it is possible to distinguish whether the moisture content of the shaft seal oil is increasing or whether there is an increase in particles other than moisture.

1 is a central vertical cross-sectional view showing an embodiment of a submersible pump used in the present invention. 2 is a circuit diagram illustrating an embodiment of a measurement circuit for the submersible pump of FIG. 1. FIG. FIG. 2 is an enlarged cross-sectional view showing a part of FIG. 1 . FIG. 1 is a schematic diagram showing a simulation test device. 10 is a graph showing the relationship between the amount of increased iron powder in the shaft sealing oil and the intensity of received light. 10 is a graph showing the relationship between the amount of increased iron powder in the shaft sealing oil and the intensity of received light. 10 is a graph showing the relationship between the amount of increased iron powder in the shaft sealing oil and the intensity of received light. 10 is a graph showing the relationship between the amount of moisture increase in the shaft sealing oil and the intensity of received light. 10 is a graph showing the relationship between the amount of moisture increase in the shaft sealing oil and the intensity of received light. 10 is a graph showing the relationship between the amount of moisture increase in the shaft sealing oil and the intensity of received light. 1 is a flowchart showing a determination process in the submersible pump monitoring system according to the present invention. 1 is a system showing one embodiment of a submersible pump monitoring system according to the present invention. FIG. 1 is a central vertical cross-sectional view showing a conventional submersible pump.

One embodiment of a submersible pump monitoring system according to the present invention will be described below with reference to Figures 1 to 12. Note that the same or similar components are designated by the same reference numerals throughout all figures and examples, including those of the prior art.

Figure 1 is a longitudinal cross-sectional view showing one embodiment of a submersible pump equipped with a submersible pump monitoring system according to the present invention. Referring to Figure 1, the submersible pump 1 comprises a motor chamber 7 that houses a rotor 10 and a stator 8, a pump chamber 5 that has an inlet 3 and a discharge port 4 and houses an impeller 2, an oil chamber 13 that is located between the motor chamber 7 and the pump chamber 5, a motor shaft 9 that is connected to the rotor 10 and extends from the motor chamber 7 through the oil chamber 13 into the pump chamber 5, and a shaft seal device 12 that seals the motor shaft 9 within the oil chamber 13.

Shaft seal oil L is sealed within the oil chamber 13. The submersible pump 1 is equipped with a light-emitting unit 15 that irradiates light onto the shaft seal oil L, and a light-receiving unit 16 that is positioned to receive the light emitted from the light-emitting unit 15 through the shaft seal oil L. The light-receiving unit 16 receives the light emitted from the light-emitting unit 15 and outputs a signal corresponding to the intensity of the received light.

The light-emitting unit 15 is composed of a light-emitting diode. Instead of a light-emitting diode, other light-emitting elements such as laser diodes can be used for the light-emitting unit 15. The light-receiving unit 16 is composed of a photodiode. A photodetector such as a phototransistor can also be used for the light-receiving unit 16.

The light received by the light receiving unit 16 is output as a current corresponding to the intensity of the received light. Figure 2 shows the measurement circuit 17 that measures the output of the light receiving unit 16. The intensity of the light received by the light receiving unit 16 is measured by measuring the voltage across resistor R2 with a voltmeter V. The measurement data from the voltmeter V is recorded in a data logger D.

Referring to Figure 3, the light-emitting unit 15 is attached to a first support 18 that is suspended within the oil chamber 13. The light-emitting unit 15 is not limited to the first support 18 shown in the figure, and can be disposed within the oil chamber 13 by any suitable means.

The light-emitting unit 15 can also be placed outside the oil chamber 13. In this case, a transparent window (not shown) can be provided in part of the wall surface that constitutes the oil chamber 13, and the light-emitting unit 15 can be placed outside the oil chamber 13 so that light enters the oil chamber 13 through the transparent window.

Referring to Figure 3, the light receiving unit 16 is attached to a second support 19 that is suspended from the oil chamber 13. The second support 19 is disposed parallel to and spaced apart from the first support 18. The light receiving unit 16 is not limited to the second support 19 shown in the figure, and can be disposed within the oil chamber 13 by any suitable means.

Furthermore, like the light-emitting unit 15, the light-receiving unit 16 can also be placed outside the oil chamber 13. In this case, a transmission window (not shown) can be provided in part of the wall surface that constitutes the oil chamber 13, and the light-receiving unit 16 can be placed outside the oil chamber 13 so that it receives light emitted from the oil chamber 13 through the transmission window.

This section explains the relationship between the light receiving intensity of the light receiving unit 16 and the moisture or iron particles in the shaft sealing oil, based on tests using a simulation test device.

Figure 4 shows the schematic configuration of the simulation test device 20. The measurement circuit is the same as that shown in Figure 2, with a voltage VCC of 5 V, resistor R1 of 1 kΩ, and resistor R2 of 10 kΩ. The test conditions are as follows:

Light-emitting unit 15: Light-emitting diode manufactured by OptoSupply, model number OS5RKA3131A, center wavelength 624 nm
Light receiving unit 16: Photodiode manufactured by Hamamatsu Photonics Co., Ltd., model number S7183, sensitivity wavelength range 300 to 1000 nm
Distance between the light-emitting unit 15 and the light-receiving unit 16: 6 cm
The light emitting unit 15 and the light receiving unit 16 are fixed to supports 22 and 23, respectively, which are installed in a container 21 filled with shaft sealing oil L.

First, iron powder was mixed into 1.8 L of shaft sealing oil filled in container 21, increasing the amount from 0 g to 0.6 g in 0.1 g increments, and then from 0.6 g to 1 g in 0.2 g increments. The agitator 24 was set to 2000 rpm and the voltage at the light receiving section was measured while stirring. This measurement was also performed when 0 ml, 10 ml, and 20 ml of water were mixed in.

The measurement results are shown in Figures 5 to 7. Figure 5 shows 0 ml of water, Figure 6 shows 10 ml of water, and Figure 7 shows 20 ml of water. The graphs in Figures 5 to 7 plot the output of the light receiving unit 16 and display the approximate curves. The approximate curves in Figures 5 to 7 are all approximated by exponential functions.

When the light from the light-emitting element 15 hits the iron powder, it is reflected and scattered, resulting in the light reaching the light-receiving element 16 being attenuated and the output (voltage) decreasing. Furthermore, this phenomenon occurs more frequently as the amount of iron powder mixed in increases, which is thought to be the reason for the test results above. According to Beer-Lambert's law, the following equation holds true:

Here, I is the intensity of light after incidence, I ₀ is the intensity of light before incidence, α is the absorption coefficient, x is the distance of the medium, ε is the molar absorption coefficient, and c is the molar concentration.

The amount of iron powder mixed in the shaft sealing oil can be estimated from the approximate curves in Figures 5 to 7 by measuring the output (voltage) of the light receiving unit 16 with the measurement circuit 17. The approximate curve in Figure 5 can be expressed by the following equation 2 when the amount of water is 0 g.

Here, y is the voltage (V) and x is the amount of iron powder (g). Transforming this equation 2 gives the following equation 3:

By measuring the output (voltage) of the light-emitting unit 15 and using Equation 3, the amount of mixed iron powder can be estimated.

Next, using the above-mentioned simulation equipment, 1.8 L of shaft sealing oil was placed in container 21 and mixed with 5 ml, 10 ml, 20 ml, 30 ml, 40 ml, and 80 ml of water. The agitator 24 was set to a rotation speed of 2000 rpm and the voltage on voltmeter V was measured while stirring. Figures 8 to 10 show the results of this measurement when 0 g, 0.1 g, and 0.5 g of iron powder were mixed in. Figure 8 shows the case when 0 g of iron was mixed in, Figure 9 shows the case when 0.1 g of iron was mixed in, and Figure 10 shows the case when 0.5 g of iron was mixed in.

The graphs in Figures 8 to 10 show a tendency for voltage to decrease as the moisture content increases. The amount of moisture in the shaft seal oil is difficult to distinguish visually, but there is a clear difference in the voltage of the received light. In other words, by measuring the output (voltage) of the light-receiving unit (photodiode), it is possible to determine the amount of moisture contained in the shaft seal oil. This is thought to be due to the fact that water and shaft seal oil do not mix completely and to the absorption spectrum. Furthermore, because water has the property of easily absorbing red light, it is thought that the agitated water absorbs the light from the red LED, causing the voltage to decrease. The graphs in Figures 8 to 10 are all approximated by a power function.

From the above test results, if the output of the light-receiving unit 16 decreases according to a power function, it can be determined that there is an increase in moisture in the shaft seal oil. On the other hand, if the output of the light-receiving unit 16 decreases according to an exponential function, it can be determined that there is an increase in foreign matter (fine particles) such as iron powder in the shaft seal oil L that reflects and scatters light without allowing it to pass through. Note that moisture includes freshwater and seawater. Fine particles other than water that do not allow light to pass through (non-transparent) include metal powder such as iron powder, as well as mud particles.

The above judgment is performed by the judgment unit 25 (Figure 2). The judgment unit 25 can be equipped with a CPU, memory, timer circuit, etc. (not shown), and receives measurement data of the received light intensity (voltage signal) measured by the measurement circuit 17 from the data logger D, and uses the measurement data in an application (analysis software) stored in memory to perform calculations in the CPU to determine whether the amount of moisture in the shaft seal oil L has increased or whether the amount of foreign matter such as iron has increased.

Figure 11 is a flowchart showing the judgment process in the judgment unit 25. In step S1, the judgment unit 25 reads and stores the voltage output V1 of the measurement circuit 17 at a predetermined time interval t. In step S2, the judgment unit 25 judges whether the output V1 has dropped to a predetermined threshold value. In step S3, when the output V1 falls below the predetermined threshold value, the judgment unit 25 calculates and generates an approximation function using the least squares method or the like. In step S4, the generated approximation function is used to determine whether the approximation function is an exponential function or a power function, thereby determining whether there is an increase in moisture in the shaft seal oil or an increase in foreign matter (fine particles) other than moisture, such as iron powder. The judgment results can be displayed on a monitor.

If it is determined that there is an increase in fine particles (solids) such as iron powder in the seal oil, it is highly likely that the condition of the shaft seal device (mechanical seal) is deteriorating, so by removing the submersible pump from the water and inspecting it early, it is possible to determine whether maintenance should be performed before the shaft seal device fails. On the other hand, if it is determined that there is an increase in water rather than iron powder, there is no need to inspect it immediately, but if there is a large amount of water, there is a risk of water entering the motor room, so a certain threshold can be set and the submersible pump can be inspected when the amount of water exceeds that threshold.

In one embodiment of the submersible pump monitoring system, the submersible pump 1 is equipped with a wireless communication module 26 (Figure 1) that transmits the signal output of the light receiving unit 16. The wireless communication module 26 can be installed inside the motor room 7 as shown in Figure 1, or, although not shown, can be connected via a wire to an external device outside the submersible pump 1, such as a power control device 27 (Figure 12) that controls the submersible pump 1. If the wireless communication module 26 is installed inside the motor room 7, a cable can be pulled out from the submersible pump 1 and connected to an external antenna (not shown).

Measurement data from the measurement circuit 17 of the light receiving unit 16 is stored in a data logger, wirelessly transmitted by the wireless communication module 26, and, as shown in FIG. 12, sent via a gateway 28, a mobile communication base station 29, and a network line 30 to a server 31, where it can be stored. The measurement data stored in the server 31 is read into a personal computer 32 connected via a line such as the Internet, and analyzed by software installed on the personal computer 32, making it possible to determine whether there has been an increase in moisture in the shaft sealing oil or an increase in non-transparent fine particles other than moisture, such as iron.

The present invention should not be construed as being limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

REFERENCE SIGNS LIST 1 Submersible pump 5 Pump chamber 7 Motor chamber 12 Shaft seal device 13 Oil chamber 15 Light-emitting unit 16 Light-receiving unit 25 Determination unit

Claims (4)

a light-emitting unit that irradiates light onto the shaft seal oil of the submersible pump;
a light receiving unit configured to detect light from the light emitting unit through the shaft sealing oil;
a determining unit that determines whether the change in intensity of the light received by the light receiving unit follows an exponential function or a power function, thereby determining whether water or non-transparent fine particles are mixed in the shaft sealing oil;
A submersible pump monitoring system comprising: The submersible pump monitoring system of claim 1, wherein the light-emitting unit emits red light. A step of irradiating light from a light emitting unit onto shaft sealing oil of the submersible pump;
detecting light from the light emitting unit through the shaft sealing oil;
determining whether the change in the detected light intensity follows an exponential function or a power function, thereby determining whether water or non-transparent fine particles are mixed in the shaft sealing oil;
A method for monitoring a submersible pump, comprising: The submersible pump monitoring method of claim 3, wherein the light-emitting unit emits red light.