GB2085667A - Submersible electric motors - Google Patents

Abstract

A submersible electric motor unit or motor/pump unit includes an isolating and pressure-equalising device which comprises tubular members 10, 11, 12 located one within another to form coaxial closed spaces in one of which a diaphragm or piston 17 separates fluid liable to be contaminating from a barrier fluid and in another of which a diaphragm 18 or piston separates the barrier fluid from a clean controlled fluid used in the motor. The said closed spaces may be annular spaces formed one within another by three coaxial tubular members as shown or may be annular spaces located one above another (fig. 2 not shown), each being formed between two coaxial tubular members. An inner axial tubular member or members may serve as hollow shaft for transmitting a drive from motor to pump and/or to afford a central bore for the passage of a wire-line tool. The interior of an innermost passage may be closable by a valve when the unit is in operation. <IMAGE>

Description

SPECIFICATION Submersible electric motors This invention concerns improvements relating to submersible electric motors, particularly such motors for driving pumps or combined with such pumps as a submersible unit or assembly. Submersible assemblies comprising a pump driven by an electric motor have a wide application in the extraction of fluids, water or oil inter alia, from bore holes and wells, commonly from considerable depths.

In such assemblies, the drive shaft to the pump commonly passesthrough a mechanical seal which separates the motor from the pump. The motor is filled with a controlled, clean, fluid which serves to lubricate bearings and/or assist with heat tra nsfer or the like. It is importantthatthisclean fluid should not become contaminated, for instance from the pumped fluid.

During operation ofthe motor, considerable temperature changes may occur in the controlled fluid in the motor and tend to cause changes of volume of that fluid due to its thermal expansion properties. Especially in deeperwells, the effect of such changes may be aggravated by ambient pressure and temperature conditions of the fluid at pump depth, particularlydifferencesfrom ambientwork- shop conditions prevailing or assumed when the motor unit was initially filled in a workshop.

It is an object of the present invention to provide a submersible motor which not only satisfies the requirements of isolating the controlled clean fluid against contamination, but also affords means for accommodating volume changes and for equalising pressures between the well or bore hole fluid and the controlled fluid.

According to the invention, with the above object in view, a submersible electric motor unit contains or comprises tubular members located one within another to form closed annular spaces in one of which a piston or diaphragm separates fluid liableto be contaminating from a barrier fluid and in the other of which a diaphragm or piston separates the same barrier fluid from a controlled clean fluid used in the motor unit. In such a unit, the last-named fluid is triply isolated from contaminating fluid, for example well water or oil to be pumped by a pump driven by the motor. The integrity of the controlled fluid can thereby be positively ensured.Volume changes of the last-named fluid can be simply accommodated and equalisation between internal fluid pressure in the motor and external fluid pressure, particularly the aforesaid water or oil pressure, can be achieved.

In one embodiment of the invention, three tubular members can be compactly accommodated in a short length which does not unacceptably increase the length of the unit. Conveniently, the aforesaid one space is the inner of two concentric annular spaces and the separation is by an annular piston slidable therein and the other is an outer concentric annular space in which the separation is by an annular flexible diaphragm which extends between, at one end, the tube bounding the annular space on the one side and, atthe other end, the tube bounding that space on the other side.

An innermost axial tubular member or members mayform a hollowshaftfortransmitting a drivefrom motorto pump. Advantageously this innermost tubular member or members may form a passage for a wire-line tool for actuating or manipulating a device or devices below the pump without the necessity for the removal of the same.

The unit will operate in a vertical or horizontal position or at any other angle.

Preferred forms of embodiment of the invention will now be more fully described, by way of example, with reference to the accompanying diagrammatic drawings, in which: Fig. 1 is an axial section through part of one form of submersible motor/pump unit in accordance with the invention.

Figs. 2a and 2b are half axial sections through part of another form of unit having provision for the use of a wire-line tool system for actuating a device or devices below the unit, the top of Fig. 2b being continuous with the bottom of Fig. 2a, and Figs. 3a and 3b are like sections through a third form of unit generally similarto that of Figs. 2a and 2b, but illustrating additional components.

The halves of the units of Figs. 2a, 2b and 3a, 3b are symmetrical with respectto the central axis C of the respective unit.

In the embodiment shown in Fig. 1 of the drawing, components of the motor/pump unit and components of an isolating and pressure-equalising device are shown inside a unit housing 1 within a well lining 2 forthe case in which the motor indicated generally by 3, is located above the pump (not shown). Below an imaginary line A-A, within a casing 3', are the motor 3, which may be of conventional design and of which only part is shown, a journal bearing 4 and thrust bearing 5, a filter 6, seals and the pump (not shown), which may also be of conventional design.

Above the line B-B is a space 7, hereinafter referred to, which accommodates fuse, cable-gland and like components (not shown), and a discharge cone 9 for the pumped fluid. Between the lines A-A and B-B, the unit comprises three concentric tubes 10, 11, 12 having a cap 13 at one end and caps 14, 15 at the other end. The outer tube 10 forms part, functionally, of a common casing which also comprises the motor casing 3'. On the outside, the casing 3' and tube 10 are in contact with the pumped well fluid in the annular space between them and the casing 1. The end cap 13 is screwed into the tube 10 on the one hand and into the motor casing 3' on the other hand. The innertubes 11 and 12 are located in the cap 13 and retained by the caps 14, 15. The cap 14 is screwed into the cap 15 and these caps are locked in position axially by a retaining ring 16 which encloses the space 7. As illustrated, locking is to be effected by turning the tube 10, which has a flange 10a overlapping the ring 16. Alternatively, the ring 16 could be designed to be screwed into the tube10. All of the tubes and caps are sealed against each other with the assistance of 'O' rings, whose positions are indicated, or other sealing devices.

An annular piston 17 is a precision sliding fit in the annular space between the tubes 11 and 12. A non metallic piston is illustrated, but a metal piston provided with piston rings could alternatively be employed. An annular elastic diaphragm 18 is disposed in the space between the tubes 10 and 11 with one end edge anchored between the tube 11 and end cap 15 and the other adhered to a flange of the end cap 13 extending into the end of the tube 10. The diaphragm 18 thus positively divides the space between the tubes 10, 11 into inner and outer annular chambers 19,20. The chamber 19 communicates by way of passage 21, plugged at 21a, with an annular chamber 22, bounded by the piston 17, atthe lower end of the space between the tubes 11 and 12.A passage 23 connects the annular chamber 24 on the other side of the piston 17 to the annular space, between the tube 10 and housing 1,through which the pumped fluid passes. A passage 25 connects the space 20 outside the diaphragm 18 to the end space 7.

A vent passage 26 serves for initial filling of the system on manufacture of the unit and is then plugged.

The region comprising the chambers 19 and 22 contains a barrier fluid of high specific gravity. During operation of the unit, the chamber 24 contains pumped, that is contaminated, fluid. The region comprising the chamber 20, the space within the inner tube 12 and the space 7 is filled with controlled motor fluid, for example light mineral oil, which is also contained in the interior of the motor 3 within the casing 3'.

The manner of operation is as follows: when the temperature of the motor rises during operation, the controlled motor fluid will expand, crossing the line A-A and passing up through the interior 27 of the tube 12 into the space 7 and thence down the passage 25 into the chamber 20. The diaphragm 18 is displaced to accommodate the extra volume, thereby displacing or further displacing barrier fluid from the chamber 19 through the passage 21. As a result, the annular piston 17 moves upwardly in the chamber 24 so as to accommodate the barrier fluid entering the chamber 22. Fluid in the chamber 24 is displaced through the passage 23 into the space between the tube 10 and housing 1.When the temperature falls, the reverse effects will occur.At all times, the controlled motor fluid is effectively isolated by the annular piston 17, the barrier fluid and the diaphragm 18 from fluid which can become contaminated by pumped well fluid, i.e. by fluid in the annular chamber 24. The barrier fluid is isolated from both of the other fluids.

As neither the diaphragm 18 not the piston 17 is a fixed barrier, effective pressure equalisation between the pumped fluid and the controlled motor fluid is ensured.

Variation from the above-described arrangement would be possible: thus an annular piston could be substituted for the diaphragm 18 and/or a diaphragm for the piston 17. The functions of the inner and outer annular spaces between the tubes 10 and 11 ontheonehandandll and 12 on the other hand could be interchanged. In the present example, the motor is above the pump and the isolation provision is at the end of the motor remote from the pump.

However, the motor could be located belowthe pump and the isolation provision could b? located at the end of the motortowardsthe pump. If required, the central passage 27 bounded by the tube 12 could be utilised for an additional function such as the accommodation of a drive shaft.

To suit different volume-change requirements, the dimensions and length-diameter ratios of the tubes 10,11,12 may be varied, the length in particular being increased to accommodate larger volumechange requirements.

In the embodiment illustrated in Figs. 2a and 2b, the whole unit, or more specifically the whole motor, including stator, rotor and bearings, and the isolating and pressure-equalising device is in an annular cavity 30 bounded on the outside by an axially extending unit casing 31 exposed to well fluid in the space between it and the well wall or lining 32. The portion of this annular cavity 30 which encloses the motor (not shown) is bounded on the inside by a hollow motor shaft 33 whose bore 33a is also exposed to the well fluid. The lower end of the space 30 is sealed by an annular plug 34, with wear surface at 34a, and a mechanical seal 35. The pressure on the well-fluid side of the seal 35 is communicated through a passage 36, connecting the space 33a inside the shaft 33 to the space outside the casing 31.

She plug 34 is pierced by bore 37, not communicating with the passage 36, which affords communication between the motor space 30, which contains controlled clean motor fluid, and a passage 57 hereinafter referred to.

The isolating and pressure-equalising device, located within the casing 31, comprises a cylindrical annular space 38 bounded on the inside and outside by stationary tubes 39,40,41, capped by the plug 34, and closed below by an annular plug 42. In conjunction with a cap 43 and retaining ring 44, the plugs 34, 42 serve to locate the device symmetrically about the central axis C. The annular space 38 is divided by an annular intermediate plug 45 into upper and lower parts. The parts 34,42,43 and 45 are provided, as indicated, with '0' rings 48 or like sealing means to prevent leakage past them.

The upper part of the annular space 38 is divided by a sliding annular piston 49 into two chambers 50a, SOb. The lower part of the said space is divided by a diaphragm 51 of elastomeric material into two chambers 52a, 52b. The positions of the pistons and diaphragm may be interchanged or two pistons or two diaphragms may be employed. The chambers 50b and 52a which are in communication through a passage 54 in the plug 45, are filled with barrier fluid of high specific gravity. The chamber 50a eventually becomes filled with well liquid entering via the passage 36 and a passage 55 and past the wear surface 34a. The chamber 52b, which is in communication with the motor cavity 30 via a passage 56 in the plug 42 and the passages 57 and 37, contains controlled clean motor fluid. A further passage 58 is provided in the plug 42 for venting the chambers 50a, 52b during initial filling, after which it is plugged.

The cap 43 seals the lower end of the device against well fluid. A region 59 below the cap may be utilised to contain other components, if required in a particular case, for example anti-recirculation valves. Also the cap 43 may be extended to accommo date supply-cable glands.

The manner of operation of the device is as follows: On increase of temperature in the region 30 of the motor and resultant increase in volume of the controlled fluid, controlled fluid will expand through the passages 37, 57 and 56 into the chamber 52b, thereby displacing the diaphragm 51. Barrier fluid is displaced from the chamber 52a into the chamber 50b, causing the piston 49 to be moved upwardly and well fluid in the chamber 50a to be expelled into the well through the passages 55,36. On contraction of the controlled fluid, the reverse action will occur.

Because there is no rigid barrierto pressure transmission between the well fluid in the chamber 50a and the controlled fluid in the chamber 52b, pressure equilibrium is ensured. The internal pressure in the motor is maintained equal to the well pressure. Positive separation between the well fluid and controlled fluid is obtained by virtue of the multi-stage isolation provided, so that contamination of the latter fluid is avoided and its integrity assured. These effects will be obtained irrespective of whether the device is disposed vertically, as illustrated, or horizontally or at some other angle.

The bore 33a, suitably with a nominal diameter of 5 cm, of the hollow shaft 33 which extends through the motor/pump assembly and its continuation by the tube 39 through the isolating and pressureequalising device allow of the passage of a wire-line system for activating devices located below the aforesaid device or be low the pump (not shown).

In the unit illustrated in Figs. 3a and 3b, the general arrangement of the isolating and pressureequalising device is similar to that described with reference to Figs. 2a and 2b and the same reference numerals have been used for similar components.

However, Fig. 3a also shows the disposition of the motor, namely the stator 60, mounted in the stationary casing 31, and a rotor 61, mounted on the hollow shaft 33, of a conventional A.C. induction motor, which may be of either the wet-wound or canned type. The shaft is mounted in the casing 31 by an upper journal bearing 62, whose housing with cap 62a also accommodates an upper mechanical seal 63, and by a lower bearing assembly comprising a journal bearing 64, a thrust disc 65 and thrust bearing 66 supported from the casing 31 by a housing 67 which accommodates a lower mechanical seal 68.

The motor cavity 30 containing uncontaminated fluid is thus sealed below the thrust-bearing surfaces on 65,66 by the seal 68 in its housing 67, which are supported by a retaining plug 69.

At its upper end 70, the motor shaft 33 is splined for coupling to the hollow shaft (not shown) of a pump unit, which may be of a conventional type.

Alternatively the shaft 33 may be extended upwardly to carry directly the rotational assembly of the pump, additional bearings being provided as required.

Either the suction or delivery flow of the pump is arranged to be directed overthe outside of the motor casing 31 to serve as coolant for the motor 60, 61. As illustrated, the pump will be located above the motor, but it could be arranged below it.

The isolating and pressure equalising device itself is substantially identical in its action with that described with reference to Figs. 2a and 2b. The passage 55 for the entry of well fluid into the region 50a and its expulsion therefrom is provided in the retaining plug 69.

The bore within the hollow pump shaft (not shown), the motor shaft 33 and tube 39 affords a continuous passage 33a for a wire-line tool. For closing the lower end of the passage 33a during normal pump operation a valve 71, as shown of clam-shell type, is movable, through-linkage, by a remotely controlled actuator72, between the projected, closed, position shown and a retracted position within a cavity 73 formed in an extension 74 of the lower plug 43 and by a retaining cap 75.

The main power supply enters by way of a gland 76 in the cap 75, whence leads are passed upwardly through a duct 77, the passage 57 and ducts through the parts 67 and 64 and through intermediate spaces to the stator 60 of the motor.

Claims (9)

1. A submersible electric motor unit or motor/pump unit including an isolating and pressure-equalising device which comprises tubular members located one within another to form coaxial closed spaces in one of which a diaphragm or piston separates fluid liable to be contaminating from a barrier fluid and in another of which a diaphragm or piston separates the barrier fluid from a clean controlled fluid used in the motor.

2. A unit according to claim 1, wherein the said closed spaces are annular spaces formed one within another by three coaxial tubular members.

3. A unit according to claim 2, wherein the said one space is the inner of two annular spaces, in which the separation is by an annular sliding piston, and the other is an outer annular space in which the separation is by a flexible diaphragm.

4. A unit according to claim 1, wherein the said closed spaces are annular spaces located one above another, each being formed between two coaxial tubular members.

5. A unit according to claim 1,2 or 3, wherein an inner axial tubular member or members serves as hollow shaft for transmitting a drive from motor to pump.

6. A unit according to any one of claims 1 to 5, wherein an innermost axial tubular member or members afford a central bore for the passage of a wire-line tool.

7. A unit according to any one of claims 1 to 6, wherein the interior of an innermost passage formed by the said tubular member is closable by a valve when the unit is in operation.

8. A unit according to claim 1 and substantially as hereinbefore described with reference to Fig. 1 of the accompanying drawings.

9. A unit according to claim 1 and substantially as hereinbefore described with reference to Figs. 2a and 2b or Figs. 3a and 3b of the accompanying drawings.