AU2021107164B4

AU2021107164B4 - Power and control of a submersible pump

Info

Publication number: AU2021107164B4
Application number: AU2021107164A
Authority: AU
Inventors: Mark Vincent Keogh; Anthony Carl Reid
Original assignee: LAA Industries Pty Ltd
Current assignee: LAA Industries Pty Ltd
Priority date: 2016-08-16
Filing date: 2021-08-25
Publication date: 2022-03-31
Anticipated expiration: 2025-08-05
Also published as: AU2023214334A1; AU2017210650C1; AU2021203584A1; AU2017210650A1; AU2019203740A1; AU2020103197B4; AU2021107164A4; AU2017210650B2; AU2020103197A4

Abstract

A power and control system for a dewatering submersible pump includes a generator assembly, an automatic voltage regulator (AVR), an engine control unit, a system controller, a circuit breaker, human machine interface (HMI), and a network interface. The generator assembly comprises an engine coupled to an alternator. The power and control system is electrically connected to at least one motor, which powers a submersible pump for dewatering. The motor or motors can be started and controlled by the generator assembly of the power and control system.

Description

AUSTRALIA

Patents Act 1990

COMPLETE SPECIFICATION

Invention title:

"POWER AND CONTROL OF A SUBMERSIBLE PUMP"

Applicant:

LAA INDUSTRIES PTY LTD

Associated provisional applications:

The following statement is a full description of the invention, including the best method of performing it known to me:

"POWER AND CONTROL OF A SUBMERSIBLE PUMP"

Field of the Invention

[0001] The present invention relates to submersible pumps used in dewatering applications, such as within the Australian mining industry. In particular, it relates to the powering of such pumps when mains power supply is not available.

Background to the Invention

[0002] Mining operations frequently occur below the local water table. In such operations, it is necessary to remove local ground water by an operation known as dewatering. Dewatering is achieved by drilling a bore; locating a submersible pump within the bore; and operating the pump to remove water from the vicinity of the pump.

[0003] In practice, dewatering is achieved by the drilling of a number of bores around the perimeter of an area to be mined, and operating a submersible pump in each bore. A typical arrangement will see bores of depths up to 100m, and diameters in the order of 250 to 400mm. Such bores are typically spaced tens of metres apart. This is known as a "deep well" system of dewatering.

[0004] Submersible pumps used in dewatering are typically driven by an electrically powered motor. In a typical installation the motor may be in the between 7.5kW and 500kW in power, running at between 30Hz and 60Hz.

[0005] Where mains power is not available, the electrical power for the motor must be generated on the surface. This is typically achieved by use of a generator having an internal combustion engine which drives an alternator.

[0006] In a traditional installation, electrical power and voltage produced by the generator is supplied to an electrical control unit which includes a combination of transformers, variable speed drives, soft starters such as star delta starters, direct-on-line starters, and wound-rotor motors. The electrical control unit, in turn, provides electrical power to the pump motor. Such an electrical control unit may weight up to four tonne, and cost up to $300,000.

[0007] In order to maintain the motor condition the pump must be operated within a range of interdependent parameters. For a given pump speed, such as 40Hz, the pump curve for that pump will show the flow rate of the pump for a given pressure head (assuming pure water). In a dewatering operation the pressure head, a desired flow rate and the quality of water (including the specific gravity) are subject to change. Such changes can be accommodated by a change in the pump speed, within safe pump operating limits. This is typically achieved by the use of a variable speed drive within the electrical control unit.

[0008] The present invention seeks to avoid the use of a variable speed drive by instead providing direct control of the generator. In a preferred embodiment, this may eliminate the need for a separate electrical control unit.

[0009] For the avoidance of doubt, the term 'dewatering' as used herein is defined as the removal of groundwater from a bored well in order to lower the level of the local water table; that is, the level of the local water table within a region having a diameter at least ten times that of the well. Those skilled in the art will appreciate that an individual well may create a cone of depression or drawdown in an aquifer which may extend for up to several hundred metres or even further.

Summary of the Invention

[0010] According to one aspect of the present invention there is provided a power and control system arranged for powering a dewatering submersible pump, the system including: a generator comprising an engine and an alternator, the engine having an Engine Control Unit (ECU), the alternator having an automatic voltage regulator (AVR), the generator supplying electrical power to the pump, the electrical power having a frequency determined by the speed of the engine and a voltage determined by the AVR; at least one sensor arranged to provide information regarding pump operation and/or surrounding conditions including information about at least one measured parameter of pump operation and/or surrounding conditions; and a system controller, the system controller being arranged to receive information from the sensor, the system controller being arranged to receive information regarding a desired setpoint for the parameter measured by the sensor; wherein the system controller controls the ECU based on a comparison between the received information from the sensor and the desired setpoint to govern the speed of the engine, and the system controller controls the AVR based on the received information to govern the voltage of the electrical power supplied to the pump so as to maintain the parameter at the desired setpoint.

[0011] According to a second aspect of the present invention there is provided a power and control system when used for powering a dewatering submersible pump, the system including: a generator comprising an engine and an alternator, the engine having an Engine Control Unit (ECU), the alternator having an automatic voltage regulator (AVR), the generator supplying electrical power to the pump, the electrical power having a frequency determined by the speed of the engine and a voltage determined by the AVR; at least one sensor arranged to provide information regarding pump operation and/or surrounding conditions; and a system controller, the system controller being arranged to receive information from the sensor, wherein the system controller controls the ECU based on the received information to govern the speed of the engine, and the system controller controls the AVR based on the received information to govern the voltage of the electrical power supplied to the pump.

[0012] As will be well understood by those skilled in the art, an AVR provides an excitation voltage to the alternator in order to regulate an output voltage of the alternator, such that a desired, quantified output voltage is obtained. The excitation voltage is arranged to vary in response to a comparison of measured output voltage of the alternator and a desired output voltage indicated by the system controller.

[0013] As will be well understood by those skilled in the art, an ECU operates by regulating the volume of fuel delivered by fuel injectors into the engine.

[0014] The sensor may be arranged to monitor the operation of a motor controlling the pump; to monitor the operation of the pump; to monitor the condition of fluid within a system connected to the pump; or to monitor external conditions.

[0015] Ina preferred embodiment, the power and control system has sensors available to it arranged to provide information about at least three parameters of pump operation and/or surrounding conditions: a borehole water level; a fluid flow rate of the pump output; and a pump outlet pressure. The system preferably includes means to select one of these three parameters at the option of a user to be the information received by the system controller in order to control the ECU and the AVR.

[0016] Alternatively, the power and control system may have sensors available to it arranged to provide information about one or two of the three parameters of pump operation and/or supporting conditions being borehole water level, fluid flow rate of the pump output, and pump outlet pressure.

[0017] It is preferred that fluid flow rate of the pump outlet is measured by at least one sensor is arranged to measure a fluid flow rate within a pipe connected to an outlet of the pump.

[0018] It is preferred that pump outlet pressure is measured by at least one sensor is arranged to measure fluid pressure within a pipe connected to an outlet of the pump.

[0019] Preferably, the system controller is arranged to compare the received information to an input setpoint, and to control the AVR and the ECU in response to deviation of the received information from the setpoint.

[0020] The setpoint may be one of the set of: desired water level in a bore; desired fluid flow rate of the pump output; and desired pump outlet pressure.

[0021] According to a third aspect of the present invention there is provided a method of controlling a dewatering submersible pump to achieve a steady state condition maintaining an operating or surrounding condition at a desired setpoint, the desired setpoint being one of set comprising borehole water level, fluid flow rate, and output fluid pressure, the pump including an electric motor, the electric motor being powered by electrical power provided by a generator, the generator having an engine and an alternator, the generator outputting electrical power to the electric motor, the electrical power having a frequency and a voltage, the method including: monitoring an operating or surrounding condition using at least one sensor; using a system controller to receive information from the at least one sensor; using the system controller to control an ECU to in turn control an output frequency of the generator in response to the received information; using the system control to control an AVR to in turn control an output voltage of the generator in response to the received information; and using the controlled electrical power to operate the electric motor and pump so as to maintain the operating or surrounding condition at the desired setpoint.

[0022] The ECU and AVR are preferably operated to maintain pump speed within a recommended range. This may be between 30Hz and 50Hz or 60Hz.

Brief Description of the Drawings

[0023] It will be convenient to further describe the invention with reference to preferred embodiments of the present invention. Other embodiments are possible, and consequently the particularity of the following discussion is not to be understood as superseding the generality of the preceding description of the invention. In the drawings:

[0024] Figure 1 is a schematic view of a power and control system for a submersible pump in accordance with the present invention;

[0025] Figure 2 is a flow diagram for the control system of Figure 1; and

[0026] Figure 3 is an illustrative pump curve diagram as used in the control system of Figure 1.

Detailed Description of Preferred Embodiments

[0027] Referring to the Figures, there is shown a water bore 10 into which a submersible pump 12 has been lowered. The submersible pump 12 is powered by an electrical motor 14. A primary power cable 16 provides electrical power to the motor 14. A discharge pipe 18 carries water from the pump12 to the surface.

[0028] When used in typical Australian hard rock mining operations the submersible pump 12 may be directly inserted into the water bore 10. In granular soils or weaker rock it may be necessary to locate the submersible pump 12 within a perforated well screen packed with a filter medium. In either case, it will be appreciated that ground water can readily flow laterally from a surrounding aquifer into an intake of the submersible pump 12.

[0029] A power and control unit 20 is located on the surface. The power and control unit 20 includes outer casing 22 which houses a generator 24 comprising an internal combustion engine 26 and an alternator 28. The generator 24 supplies electrical power to the primary power cable 16.

[0030] The power and control unit 20 includes a controller 30.

[0031] The controller 30 is arranged to manage an electronic Engine Control Unit (ECU) 32 and an Automatic Voltage Regulator (AVR) 34.

[0032] The AVR 34 regulates the voltage supplied via the primary power cable 16 to the motor 14. It achieves this by applying an excitation voltage to the alternator 28, and varying the excitation voltage in response to measured output of the alternator 28. The arrangement is such that the controller 30 provides an indication of desired output voltage to the AVR 34, and the AVR 34 constantly manages the excitation voltage in order to achieve the desired output voltage by means of a feedback loop.

[0033] The ECU 32 controls the speed and power of the engine 26, primarily through control of electronic fuel injectors. The controller 30 provides the ECU with a desired speed (i.e. frequency) and load for operation of the alternator 28 under the relevant conditions. The ECU 32 acts to maintain efficiency of the engine 26 through changing conditions. The ECU 32 actively controls the volume of fuel delivered per engine stroke by the fuel injectors to provide the required engine speed and torque. The ECU 32 is able to meet any desired speed within a continuous operating range; that is, the frequency is essentially infinitely variable.

[0034] A circuit breaker 36 is located electrically between the generator 24 and the primary power cable 16.

[0035] The controller 30 is connected to a plurality of sensors. A first sensor is located within the bore 10, and extends down to the pump 12. The first sensor 40 is arranged to detect and monitor the level of ground water within the bore 10.

[0036] The discharge pipe 18 is fluidly connected to a discharge main 42. A second sensor 44 is mounted on the discharge main 42. The second sensor is a flow meter, arranged to detect the flow rate of water passing through the discharge main 42.

[0037] Two third sensors 46 are mounted at spaced locations along the discharge main 42. The third sensors 46 are pressure sensors, arranged to detect pressure within the discharge main 42.

[0038] A temperature sensor (not shown) is attached to the motor 14.

[0039] Operation of the controller 30 may be done directly via a human machine interface (HMI) 48, or may be done remotely via a network interface , arranged to communicate with an electronic network 52 and to be operated from a remote control centre 54.

[0040] Figure 3 shows a typical pump curve diagram for a submersible pump 12. The pump 12 has a maximum operating speed of 50Hz, and a minimum operating speed of 30Hz. At a given speed the pump curve 60 shows the relationship between head pressure generated and flow rate.

[0041] The present invention operates on the understanding that pump speed, flow rate, and pressure head together provide an interrelated three dimensional operation range for the pump 12.

[0042] Operation of the power and control system will now be described.

Start-up procedure

[0043] The circuit breaker 36 is closed prior to start-up.

[0044] The controller 30 sends a 'start-up' signal to the ECU 32 and to the engine 26. A starter motor (not shown) acts to start the engine 26, and bring it to idle. At this time the drive shaft of the engine 26 will turn a rotor of the alternator 28, however the AVR 34 will not supply an excitation voltage to the alternator 28.

[0045] When the engine 26 is idling correctly (typically about 10 seconds after starting) the controller 30 sends "soft-start" signal to the AVR The AVR 34 provides an excitation voltage to the alternator 28, causing the voltage supplied by the alternator 28 to the motor 14 to 'ramp' linearly from zero to

270V over a period of about 2 seconds. During this time the motor 14 accelerates from rest to a speed of about 33Hz. The controller 30 then sends signal to the AVR 34 indicating a desired output voltage (typically 415V). The AVR 34 adjusts its excitation voltage accordingly, as the motor accelerates up to its final required pump speed (which could be about 50Hz). The ECU 32 acts concurrently to bring the engine 26 to its required pump speed (which could be about 1500RPM). It will be appreciated that the generator 24 could be producing up to 415V at about 50Hz.

[0046] It will be appreciated that references to pump speed assume a two pole motor 14, and are discounting any slip. Actual pump revolutions for a nominal 50Hz speed are likely to be in the order of 2900rpm.

[0047] Once the motor 14 is operating at its correct speed and the pump 12 has begun pumping water via the discharge pipe 18 to the transport pipe 42, an appropriate mode of operation can be selected. The present invention proposes three alternative set-point control modes: water-level maintenance mode; constant flow rate mode; and constant pressure mode. It will be appreciated that other modes of control (such as manual control) may also be available to a user.

Water-level maintenance mode

[0048] In this mode the key sensor is the first sensor 40, measuring the level of water in the bore 10. The level of ground water in a cone drawdown surrounding a bore 10 can be calculated using the baseline aquifer level, the porosity of the surrounding medium, the distance from the bore, and the level within the bore. As such, maintaining an appropriate level within the bore 10 provides certainty that the water level in the surrounding area will be below the required level. This appropriate level is input into the controller 30 as a setpoint. In practice, a perimeter of an dewatering area is established by a plurality of bores 10, each of which may have associated controllers 30 controlling a constant level of water at each bore.

[0049] In water-level maintenance mode, the pump 12 is operated at its full speed (e.g. 50Hz) to achieve maximum possible flow rate until the water level in the bore reaches the setpoint. Once the setpoint has been reached, the controller 30 operates a feedback loop between the engine speed governed by the ECU 32 (operated in conjunction with excitation voltage of the AVR 34) and the measured water level of the first sensor 40 until a steady state is reached maintaining the required bore water level. It will be appreciated that the steady state must be within the system capacity (including within safe pump speeds and system pressures) otherwise an alarm will activate and the pump 12 will be shut down. In a preferred embodiment, the feedback loop employs Proportional Integral Derivative (PID) control.

[0050] The controller 30 will continue to operate the feedback loop in the event that there is a change in surrounding conditions.

Constant flow rate mode

[0051] In this mode the key sensor is the second sensor 44, measuring the flow rate through the transport pipe 42. Water being extracted from the bore can be used in many applications, some of which (for instance, use as process water within ore processing operations) require a constant flow rate of water. This flow rate is input into the controller 30 as a set point.

[0052] Inconstant flow rate mode, the controller 30 operates a feedback loop between the engine speed governed by the ECU 32 (operated in conjunction with excitation voltage of the AVR 34) and the measured water flow past the second sensor 44 until a steady state is reached. In a preferred embodiment, the feedback loop employs PID control. It will be appreciated that the steady state must be within the system capacity (including within safe pump speeds and systems pressures temps) otherwise an alarm will activate and the pump 12 will be shut down.

[0053] The controller 30 will continue to operate the feedback loop in the event that there is a change in surrounding conditions.

[0054] Figure 3 shows usage of the pump curve diagram in constant flow rate mode. As head pressure changes from 230m to 90m (for instance, different valves are opened or closed downstream, or in response to changes in bore water level), the pump speed is changed from 50Hz to 35Hz while maintaining a flow rate of 301/s.

Constant pressure mode

[0055] In this mode the key sensors are the third sensors 46, measuring the pressure in the transport pipe 42. Water being extracted from the bore 10 can be used in many applications, some of which (for instance, dust suppression and tank filling via a pressure valve) may require a constant water pressure. This pressure is input into the controller 30 as a set point.

[0056] Inconstant pressure mode, the controller 30 operates a feedback loop between the engine speed governed by the ECU 32 (operated in conjunction with excitation voltage of the AVR 34) and the measured water pressure at the third sensors 46 until a steady state is reached. In a preferred embodiment, the feedback loop employs PID control. It will be appreciated that the steady state must be within the system capacity (including within safe pump speeds) otherwise an alarm will activate and the pump 12 will be shut down.

[0057] The controller 30 will continue to operate the feedback loop in the event that there is a change in surrounding conditions.

System operating safeguards

[0058] The controller 30 includes a plurality of thresholds within which the system must operate, including current draw, pump speed, system pressure, bore water level, motor temperature, and minimum flow rate. The controller is arranged to activate an alarm and, if necessary, shut down the system should any of the thresholds be breached. These thresholds will typically apply in all operating modes discussed above.

[0059] Typical thresholds include a motor speed of 30Hz to 50Hz or 60Hz, a bore water level sufficiently above the pump 12, and a motor temperature below 65 0C or 70 0C. Thresholds such as minimum flow rate are specific to particular pump/motor combinations.

[0060] In order to provide sufficient electrical power, in a preferred embodiment the generator 24 is sized to be able to provide power in the order of 125% to 333% of the kW rating of the motor 14. The engine 26 may have a minimum operating threshold, such as a 30% load, below which the controller 30 may shut down the system.

[0061] It will be appreciated that the system controller 30 is preferably a microprocessor and/or microcontroller based system programmed with appropriate algorithms to generate the feedback loops as discussed above.

[0062] The instructions provided by the controller 30 to the ECU 32 and AVR 34 may be control signals (e.g. a reference voltage, an analogue signal, a digital signal etc.) and/or logical instructions (e.g. machine code, packetized data, etc.).

[0063] The HMI 48 is a physical interface electronically coupled to the controller 30. The HMI 48 includes output means, such as a display, speaker and/or printer; and input means, such as a keypad, keyboard, touch screen, touch pad and the like. The HMI 48 provides the ability to control the system controller 30 locally, that is, by a user physically located in the vicinity of the power and control unit 20.

[0064] The network interface 50 provides network access to and from the system controller 30. In a preferred embodiment, the network interface 50 is a cellular modem compatible with 3G/4G, LTE, EDGE, HSPA, CDMA or other mobile communications protocol. The network interface 50 may additionally or alternatively be a wi-fi, ethernet, cable, ADSL/DSL and/or Bluetooth T M interface. The network interface 50 connects the controller 30 to the network

52, which may be the Internet or other LAN or WAN, and thereby to the remote control centre 54.

[0065] The remote control centre 54 is and/or includes a device (e.g. computer, laptop, smartphone, tablet, etc.) operable to generate and transmit instructions to the system controller 30.

[0066] It will be appreciated that the methods described above essentially allow the power and control unit 20 to provide the function of a variable speed drive (VSD), thereby removing the need for a dedicated VSD and hence the additional capital and operating expenditures associated with having a VSD coupled to a fixed speed generator.

Example

[0067] An embodiment of the present invention was used for dewatering in a bore drilled to receive a 305mm diameter casing. The static water level was m below ground level. A 110kW SP160-10-AA submersible pump was lowered into the bore at a depth of 183m below ground level. The power and control unit used employed a 250 KVA variable speed generator.

[0068] The controller was set to provide electrical power from the variable speed generator at frequency of between 30Hz and 50Hz.

[0069] The system was operated in water level maintenance mode, with a water level setpoint of 155m below ground level, a dynamic head of 165m and flow rate of 25 litres/sec. The system was operated at speed (50Hz) until the water level setpoint was reached.

[0070] In order to maintain this level, the speed of the engine (controlled via the ECU) was set using PID control based on a level sensor within the bore. The PID settings employed were: P=1.86; 1=0.18; D=0.02. Ultimately, this resulted in a steady state where the speed of the engine resulted in a pump frequency of 42Hz.

[0071] The AVR was set to maintain a (three phase) voltage of V= 7.7f +30. In the steady state, the AVR supplied a voltage of 353V

[0072] The controller was equipped with alternative settings for a constant flow rate mode and for constant pressure mode.

[0073] For constant flow rate mode the speed of the engine (controlled via the ECU) was set using PID control based on fluid flow in the discharge main. The PID settings employed were: P=2; 1=0.02; D=0.11.

[0074] For constant pressure mode the speed of the engine (controlled via the ECU) was set using PID control based on fluid pressure in the discharge main. The PID settings employed were: P=2;1=0.02; D=0.11.

[0075] Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention. For instance, in some circumstances it may be preferable to include a transformer located electrically between the alternator 28 and the motor 14. It will be noted that Figure 2 indicates that the generator 24 may power a plurality of motors 14. It will also be appreciated that further sensors may be employed, for instance measuring operating temperatures, currents and voltages, and/or operating speeds.

Claims

Claims 1. A power and control system arranged for powering a dewatering submersible pump, the system including: a generator comprising an engine and an alternator, the engine having an Engine Control Unit (ECU), the alternator having an automatic voltage regulator (AVR), the generator supplying electrical power to the pump, the electrical power having a frequency determined by the speed of the engine and a voltage determined by the AVR; at least one sensor arranged to provide information regarding pump operation and/or surrounding conditions including information about at least one measured parameter of pump operation and/or surrounding conditions; and a system controller, the system controller being arranged to receive information from the sensor, the system controller being arranged to receive information regarding a desired setpoint for the parameter measured by the sensor; wherein the system controller controls the ECU based on a comparison between the received information from the sensor and the desired setpoint to govern the speed of the engine, and the system controller controls the AVR based on the received information to govern the voltage of the electrical power supplied to the pump so as to maintain the parameter at the desired setpoint.
2. A power and control system as claimed in claim 1, wherein the power and control system has sensors available to it arranged to provide information about at least three parameters of pump operation and/or surrounding conditions: a borehole water level; a fluid flow rate of the pump output; and a pump outlet pressure.
3. A power and control system as claimed in claim 2, wherein the power and control system includes means to select one of the parameters at the option of a user to be the information received by the system controller in order to control the ECU.
4. A power and control system as claimed in any preceding claim, wherein the system controller is arranged to compare the received information to an input setpoint, and to control the AVR and the ECU in response to deviation of the received information from the setpoint.
5. A method of controlling a dewatering submersible pump to achieve a steady state condition maintaining an operating or surrounding condition at a desired setpoint, the desired setpoint being one of set comprising borehole water level, fluid flow rate, and output fluid pressure, the pump including an electric motor, the electric motor being powered by electrical power provided by a generator, the generator having an engine and an alternator, the generator outputting electrical power to the electric motor, the electrical power having a frequency and a voltage, the method including: monitoring an operating or surrounding condition using at least one sensor; using a system controller to receive information from the at least one sensor; using the system controller to control an ECU to in turn control an output frequency of the generator in response to the received information; using the system control to control an AVR to in turn control an output voltage of the generator in response to the received information; and using the controlled electrical power to operate the electric motor and pump so as to maintain the operating or surrounding condition at the desired setpoint.