Abstract:
A modular electric motor. The modular motor includes a plurality of mechanically and electrically coupleable stator sections and mechanically coupleable housing sections. At least one stator section has conductors extending longitudinally therethrough for generating a magnetic field to impart rotative motion in a rotor. A given motor may be assembled to a variety of desired lengths by mechanically and electrically coupling the appropriate number of motor sections. This facilitates construction of a desired horsepower motor for a given application.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electric motors, and particularly to a modular stator assembly that facilitates motor construction. 
     BACKGROUND OF THE INVENTION 
     Submersible electric motors are used in submersible pumping systems to lift wellbore fluids from depths of up to several thousand feet. A conventional motor used to provide the equivalent pumping power on the surface cannot be used in a wellbore because the diameter of such a motor would be too wide to fit into the wellbore. Therefore, as compared to short, thick surface motors, the stators of submersible electric motors are relatively thin and extremely elongated. 
     Elongating the stator allows the motor to produce the required torque to drive a pump by developing magnetic force over a stator of a much larger length. Thus, if long enough a motor that produces a relatively smaller torque per foot can produce a sufficient total torque. Depending on the horsepower required of the motor, electric submersible pumping system motors can utilize stator assemblies thirty feet long or more. Preparation of the stator windings requires long, thin polished rods that serve as needles for pulling the insulated, conductor wires through a lengthy assembly of stator laminations. This conventional process is a comparatively slow and expensive process for manufacturing such motors. Additionally, repair or rebuilding of such motors often requires complete destruction or tear down of the motor with little component repair value due to the unitary stator assembly. 
     It would be advantageous to have a modular stator that could be used to construct motors, such as motors utilized in electric submersible pumping systems. Benefits of such a modular construction would include reduced cost and assembly time, reduced repair time and reduced motor component inventory. 
     SUMMARY OF THE INVENTION 
     The present invention features an electric motor with a modular stator. The modular stator comprises a plurality of stator sections and a rotor disposed within the stator sections. The stator sections are mechanically and electrically coupleable to form a stator of a desired length. According to additional aspects of the invention, a submersible pumping system is provided that utilizes an electric motor with a modular stator assembly. 
     According to another aspect of the invention, a method is provided for facilitating the assembly of an electric motor. The method includes manufacturing a plurality of stator sections wherein each stator section is mechanically and electrically coupleable to another stator section. The stator sections include a top stator section electrically coupleable to a source of electric power, a middle stator section with conductors extending longitudinally therethrough, and a bottom section with conductors. When coupled, the stator sections complete a conductive loop through the stator sections to the source of electric power. 
     The method includes determining the desired motor length for a given application and assembling a top section, a bottom section, and an appropriate number of middle sections to form a stator of the desired length. The method further includes assembling the stator sections and disposing a rotor within the stator sections. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a front elevational view of a submersible pumping system that utilizes a submersible electric motor, according to a preferred embodiment of the present invention; 
     FIG. 2 is a cross-sectional view of a submersible electric motor, according to a preferred embodiment of the present invention; 
     FIG. 3 is a top view of a stator lamination, according to a preferred embodiment of the present invention; 
     FIG. 4 is a top view of conductors extending through longitudinal openings in a stator lamination, according to a preferred embodiment of the present invention; 
     FIG. 5 is a top view of a portion of a female insulated block and female terminations for conductors extending through an opening in a stator lamination, according to a preferred embodiment of the present invention; 
     FIG. 6 is a top view of a portion of a male insulated block and male terminations for conductors extending through an opening in a stator lamination, according to a preferred embodiment of the present invention; 
     FIG. 7 is a top view of a modular stator section having a female end, according to a preferred embodiment of the present invention; 
     FIG. 8 is a top view of a modular stator section having a male end, according to a preferred embodiment of the present invention; 
     FIG. 9 is a cross-sectional view of two modular stator sections prior to coupling; 
     FIG. 10 is a cross-sectional view of two modular stator sections coupled together; 
     FIG. 11 is an alternative embodiment of an electric motor illustrating a coupling device to combine two middle stator sections together; and 
     FIG. 12 is an alternative embodiment of an electric motor featuring two middle stator sections coupled together. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring generally to FIG. 1, a submersible pumping system  20  is shown that utilizes a modular electric motor  22 , according to a preferred embodiment of the present invention. The submersible pumping system  20  may be comprised of a variety of components depending on the particular application or environment in which it is used. However, submersible pumping system  20  typically includes a submersible motor, such as modular electric motor  22 , to drive a submersible pump  24 . Fluid is drawn into the submersible pump  24  through a pump intake  26 . Typically, a motor protector  28  is connected between submersible pump  24  and electric motor  22  to isolate well fluid from internal motor oil within motor  22 . A coupler  30  is used to connect the submersible pumping system to a deployment system  32 , such as production tubing, cable or coil tubing. A multi-conductor cable  34  supplies three-phase alternating current (AC) electrical power from the surface to motor  22 . 
     Submersible pumping system  20  is designed for deployment in a wellbore  36  containing desirable production fluids, such as petroleum. In a typical application, wellbore  36  is drilled and lined with a wellbore casing  38 . Holes  40  in the wellbore casing  38  allow production fluids to enter wellbore  36 . Submersible pumping system  20  is deployed within wellbore  112  to a desired location in order to pump the production fluids. Instead of a unitary stator, that may be thirty feet long or more, the illustrated electric motor  22  utilizes modular stator sections, including, for example, a top stator section  42 , a bottom stator section  44 , and two middle stator sections  46 . Electricity flowing through the middle stator sections  46  produces a rotating magnetic field that causes rotation of a rotor within electric motor  22 . The rotor is drivingly coupled through motor protector  28  and pump intake  26  to submersible pump  24 . 
     Although two middle stator sections  46  are illustrated, the exact number of middle stator sections  46  in a given submersible electric motor  22  can vary depending on the system requirements. During assembly, the modular stator sections are partially assembled, the rotor is placed inside the partially assembled modular stator, and then assembly is completed. In the event of repair or servicing, the modular stator sections can be disassembled and uncoupled as necessary. For example, if a particular stator section requires replacement, the surrounding components can be uncoupled, e.g. unplugged, and a replacement stator section inserted. This modular concept greatly simplifies the assembly, servicing, repair, and stocking of replacement stator components for electric motor  22 . 
     Referring generally to FIG. 2, a cross-sectional view is shown of submersible electric motor  22 . Electric power from multi-conductor cable  34  is coupled through an outer housing  47  of stator section  42  to an electrical connector  48  of the stator section  42 . Conductors  50  in cable  34  are coupled to a female connector  52  in top stator section  42 . Conductors  54  in middle stator section  46  are coupled to a male electrical connector  56 . When top stator section  42  is mated to middle stator section  46 , conductors  50  in top stator section  42  are electrically coupled to conductors  54  in the first middle stator section  46 . In this view, for clarity, only two conductors  54  are shown extending through each middle stator section  46 . Typically, there are multiple conductors for each single conductor shown here. Furthermore, as will be more fully discussed in the following paragraphs, there are multiple groups of these multiple conductors oriented around a central axis. 
     Conductors  54  of middle stator section  46  extend longitudinally through middle stator section  46  to another female connector  52 . This female connector is designed to engage the male connector  56  of the second middle stator section  46 . Similarly, conductors  54  extend through the second middle stator section  46  to another female connector  52 . Bottom stator section  44  also has a male connector  56 , disposed within an outer housing  57 , and conductors  58  of bottom stator section  44  are coupled to male connector  56 . When bottom stator section  44  is mated to the second middle stator section  46 , conductors  58  of bottom stator section  44  electrically couple each conductor  54  of middle stator section  46  with a corresponding conductor  54  disposed through the middle stator section  46  at a different location. 
     In the illustrated embodiment, each middle stator section  46  is formed with male connector  56  at one end and female connector  52  at the other end. This allows a plurality of middle stator sections  46  to be coupled together end-to-end. Additionally, top stator sect on  42  is configured with a female connector  52  and bottom stator section  44  is configured with a male connector  56 . Note that the selection of whether a top or bottom stator section is to be male or female is entirely arbitrary, as long as the selection is consistent so that the modular stator sections can be assembled together. 
     When the modular stator sections are joined, the conductors in the top, middle and bottom stator sections are electrically coupled to a source of electrical power on the surface. Electricity flowing through conductors  54  in middle stator sections  46  produces a rotating magnetic field that causes a rotor  60  within the modular stator to rotate about an axis  61 . Rotor  60  is coupled to and rotates a shaft  62  which, in turn, rotates pump  24 . Bearings  63  are used to support rotor  60 . The magnetic field that causes rotation of rotor  60  is prompted by a plurality of metallic laminations  64  that are stacked together and held in place within an outer housing  65  by snap rings  66 , as in conventional stator construction. 
     As best illustrated in FIG. 3, each metallic lamination  64  has a central opening  67 . As laminations  64  are stacked to form a middle stator section  46 , central openings  67  form an interior passage or opening  68  that extends through the middle stator section  46  in which rotor  60  is disposed. Laminations  64  also have a plurality of openings  70  that are radially outlying from the central opening  67 . As laminations  64  are stacked, openings  70  are aligned to create longitudinal slots  72 . Typically, multiple conductors  54  are inserted through each of the longitudinal slots  72 . The lamination stacks are disposed within outer housing  65 . 
     Modular stator sections may be mechanically coupled together in a variety of ways. In the illustrated embodiment (see FIGS. 2,  9  and  10 ), mechanical coupling is provided by plug connectors  52 ,  56 , and by threaded collar assemblies mounted to the external housings  47 ,  57  and  65 . The modular stator sections  42 ,  44  and  46  are configured with either a male threaded end  74  or a female threaded collar  76  formed as part of or mounted to the corresponding outer housing  47 ,  57  or  65 . A seal  78 , such an O-ring, a crush ring, or a metal-to-metal seal maintains a fluid seal between the inside of motor  22  and wellbore  36 . A passageway  80  allows motor oil to pass from one modular stator section to another. A passageway  82  in top stator section  42  allows motor oil to expand into or contract from the motor protector  28  as the temperature of the oil rises and falls during operation. 
     Referring generally to FIG. 4, a cross-sectional view is shown of a metallic lamination  64  with a plurality of conductors  54  wound through each axial opening  70 . However, as described above, FIGS. 2,  9  and  10  only illustrate one conductor  54  disposed through each axial opening  70  for clarity. 
     Referring generally to FIGS. 5 and 6, each group of conductors disposed through each axial opening  70  is terminated in an insulated block in the connectors. Male connector  54  has a male insulated block  84  (FIG.  6 ), while female connector  52  has a female insulated block  86  (FIG.  5 ). The insulated blocks insulate the conductors, e.g. bare copper wires, from one another. The insulated blocks may be readily formed from a moldable polymeric material. Exemplary insulating materials include polyetheretherketone (PEEK), kapton, and mylar. 
     In the illustrated embodiment, the plurality of conductive strands, disposed through each axial opening  70 , are terminated in the insulated blocks with a single electrical termination. This reduces the overall number of electrical terminations that must be completed between modular motor modules. However, each conductor could have its own individual termination. Conductors that are terminated at a male insulated block  84  are terminated with a male termination  88  while the conductors terminated in a female insulated block  86  are terminated with a female termination  90 . Each male termination  88  is disposed within a raised portion  96  of each male insulated block  84 , while each female termination  90  is disposed in a recess  98  in each female insulated block  86 . When two modular motor sections are abutted, the raised portion  96  of the male insulated block  84  is inserted into the recess  98  in the female insulated block  86 . This causes the male terminations  88  to be guided and inserted into the female terminations  90 . 
     Referring generally to FIG. 7, a female end of a middle stator section  46  is illustrated. This female end includes female connector  52  having an opening  99 , through which the rotor  60  passes. Female connector  52  is surrounded by threaded collar  76 , having internal threads  101 . In FIG. 8, an end view of the male end of a middle motor section  46  is illustrated. Male connector  56  is surrounded by threaded end  74 , having external threads  103 . Connector  56  also includes a central opening  105 . 
     Referring generally to FIGS. 9 and 10, cross-sectional views are shown illustrating the process of joining two middle stator sections  46 . In FIG. 9, the two middle stator sections  46  have not yet been joined. The threaded female collar  76  is moveable along a slot  100  in the outer housing, e.g. housing  65 , of the stator section. Typically, collar  76  includes a ring  105  captured in slot  100  such that collar is rotatably retained to the appropriate outer housing. 
     Initially, the threaded female collar  76  is pulled away from the end of the modular stator section  46  on which it is mounted. With the ends exposed, the two modular stator sections  46  are axially aligned and brought together. In the illustrated embodiments, the insulated blocks and terminations are aligned with the key  92  and keyway  94  system. Once aligned, the two sections are brought together. Electrical coupling is accomplished by forcing the two stator sections together so that the male terminations  88  of one middle stator section  46  are inserted into the female terminations  90  of the next adjacent middle stator section  46 . Once terminations  88  and  90  are joined, threaded collar  76  is tightened over threaded end  74 , as illustrated in FIG.  10 . This ensures a secure mechanical and electrical coupling of the components. Top stator section  42  and bottom stator section  44  may be joined to the appropriate ends of middle stator sections  46  in a similar fashion. 
     An alternate embodiment of the present invention is illustrated in FIGS. 11 and 12. In this embodiment, a separate coupler  102  is used to couple two middle stator sections  104 . The separate coupling device  102  may be configured to electrically and mechanically connect stator sections  104 . For example, each coupler  102  can include a plurality of receptacles, and each of the stator sections can include a plurality of conductive tips configured for insertion into the plurality of receptacles. Alternatively, the coupling device  102  may be configured such that the middle stator sections  104  are mechanically coupled by device  102  but electrically coupled directly to each other, rather than through the coupler  102 . 
     It will be understood that the foregoing description is of a preferred embodiment of this invention, and that the invention is not limited to the specific forms shown. For example, a variety of different configurations can be can be used to electrically and mechanically couple individual stator sections to one another. A variety of component shapes and sizes may be utilized. Furthermore, different motor styles and types may benefit from the modular construction described above. Other components may be used to couple the modular stator sections. For example, the conductors may be terminated with male terminations and joined together by a female-to-female connectors inserted between the two modular stator sections. Indeed, various plug configurations and coupling structures can be used to combine components. Also, the subject motor may be utilized in a variety of systems and environments. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the appended claims.