Abstract:
A technique is provided for constructing a submersible motor. The submersible motor has a stator positioned within a housing. Windings are arranged through the stator with end coils on opposite ends of the stator. The winding end coils are supported by a support structure that prevents the end coils from collapsing inwardly.

Description:
BACKGROUND 
       [0001]    Submersible motors are used in a wide variety of well related applications. For example, submersible motors are utilized in electric submersible pumping systems employed to produce fluids, such as hydrocarbon based fluids. The electric submersible pumping systems also can be used to deliver fluid downhole or to transfer fluid to other locations. The submersible motor generally is a long cylindrical motor sized to fit within a wellbore and designed to drive a centrifugal pump. 
         [0002]    Because submersible motors operate in a submerged environment, conventional submersible motor stators have been insulated with a varnish material. However, with recent modifications made to the magnet wire, and impregnating the stator and windings with varnish is a relatively expensive procedure. Additionally, the varnish can degrade over time and cause a variety of problems, including contamination of the motor oil and cause bearing failures. The varnish also can limit certain operational parameters of the submersible motor. As a result, attempts have been made to construct submersible motors without varnish. Other insulating materials, including epoxies, have been used to cover the windings and end coils associated with the stator of the submersible motor. However, these approaches have proved inadequate in providing support for the winding end coils to prevent them from collapsing into the stator bore, particularly with larger submersible motors. 
       SUMMARY 
       [0003]    In general, the present invention provides a system and method for constructing a submersible motor. A stator is positioned within a housing, and stator windings are arranged with an end coil on an end of the stator. The winding end coil is supported by a support structure that prevents the end coil from collapsing inwardly and causing failure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Certain embodiments of the invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
           [0005]      FIG. 1  is a front elevation view of a well system having a submersible motor in a wellbore, according to an embodiment of the present invention; 
           [0006]      FIG. 2  is a partial cross-section of the submersible motor illustrated in the well system of  FIG. 1 , according to an embodiment of the present invention; 
           [0007]      FIG. 3  is a front view of one embodiment of a support structure for use in the submersible motor, according to an embodiment of the present invention; and 
           [0008]      FIG. 4  is a top view of the support structure illustrated in  FIG. 3 , according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    In the following description, numerous details are set forth to provide an understanding of the present invention. However, it will be understood by those of ordinary skill in the art that the present invention may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible. 
         [0010]    The present invention generally relates to a well system that utilizes a submersible motor. For example, a submersible motor may be used in an electric submersible pumping system to produce or otherwise move desired well fluids. The technique improves the run life of submersible motors and facilitates the use of both larger motors and motors constructed without varnish to isolate the stator and windings of the motor. In some applications, for example, motors are constructed without varnish to reduce cycle time and cost. However, removing the varnish also removes some of the support for the winding end coils. 
         [0011]    In the present system and methodology, the end coils of the stator windings are supported by an insert. The insert prevents the winding end coils from moving and collapsing into the stator bore due to its own weight, thus avoiding failure or detrimental operation of the submersible motor. By way of specific example, the insert may comprise a conical structure positioned on the radially inward side of the end coils to prevent detrimental movement and collapse of the end coils in a radially inward direction toward the stator bore. 
         [0012]    Referring generally to  FIG. 1 , one example of a well system  30  utilizing a submersible motor  32  is illustrated according to an embodiment of the present invention. In this embodiment, well system  30  comprises an electric submersible pumping system  34 . The electric submersible pumping system  34  may comprise a variety of components depending on the particular application or environment in which it is used. In many applications, electric submersible pumping system  34  comprises at least a submersible pump  36 , submersible motor  32 , and a motor protector  38  positioned between submersible pump  36  and submersible motor  32 . 
         [0013]    In the embodiment illustrated, electric submersible pumping system  34  is designed for deployment in a well  40  within a geological formation  42  containing desirable production fluids, such as hydrocarbon based fluids. A wellbore  44  typically is drilled into formation  42  and, at least in some applications, is lined with a wellbore casing  46 . The wellbore casing  46  is perforated to form a plurality of openings (perforations)  48  through which production fluids can flow from formation  42  into wellbore  44 . In other applications, the submersible pumping system  34  can be used to deliver treatment fluids downhole and out through perforations  48  into the surrounding reservoir. 
         [0014]    The electric submersible pumping system  34  may be deployed into wellbore  44  with a suitable conveyance system  50  that can be constructed in a variety of forms and configurations depending on the application. For example, conveyance system  50  may comprise a tubing  52 , such as production tubing or coiled tubing. The conveyance system  50  is connected to submersible pump  36  or to another appropriate component of electric submersible pumping system  34  by a connector  54 . In the embodiment illustrated, a power cable  56  is routed downhole along conveyance system  50  and electric submersible pumping system  34  to submersible motor  32 . The power cable  56  provides electrical power to submersible motor  32  so the submersible motor can, in turn, power submersible pump  36 . In operation, submersible pump  36  draws well fluid into the electric submersible pumping system  34  via a pump intake  58  and pumps the fluid to a collection location through, for example, tubing  52 . By way of example, submersible motor  32  may comprise a three-phase, induction motor in which stator windings provide the motor field. The submersible motor may be constructed with/without varnish, and the stator windings have end coils that are uniquely supported with a support structure, as described in greater detail below. 
         [0015]    Referring generally to  FIG. 2 , one embodiment of submersible motor  32  is illustrated. In this embodiment, submersible motor  32  comprises an outer housing  60 , such as a tubular housing. A stator  62 , having a stator bore  64 , is positioned within the housing  60  such that the stator bore  64  is generally aligned with housing  60  in an axial direction. As illustrated by dashed lines, a rotor  66  is rotatably positioned within stator bore  64  and coupled to a drive shaft  68 . During operation, the rotating rotor  66  causes drive shaft  68  to rotate, and this rotation is used to drive submersible pump  36 . 
         [0016]    By way of example, stator  62  is formed with a plurality of laminations  70 , such as steel laminations. The stack of steel laminations may be insulated by suitable insulating laminations  72  disposed at opposed axial ends of the lamination stack. In many applications, the laminations are perforated in a manner that creates generally axial slots to receive insulated wire conductors  74  that form the motor windings  76 . At axial ends of the lamination stack, the insulated wire conductors  74  of the windings  76  are looped into end turns  77  that form winding end coils  78 . The end turns  77  enable the insulated wire conductors  74  to be directed back through the lamination stack via axial slots according to a desired winding pattern. The insulated wire conductors  74  that form end coils  78  can be grouped together with each group secured by a suitable wrap  80  or other type of covering. Electrical power can be supplied to winding  76  via appropriate lead wires  82 . If submersible motor  32  is a three-phase motor, the end coils  78  comprise end turns  77  for all three phases. 
         [0017]    The end coils  78  are supported by a support structure  84  that limits or prevents radial collapse of the end coils by preventing undesirable movement of the end turns  77 . Generally support structure  84  comprises an insert  86 , and typically a pair of inserts  86 , that are inserted at a radially inward position relative to the end coils  78 , as illustrated in  FIG. 2 . The inserts  86  prevent the end coils  78  from collapsing toward stator bore  64  which otherwise could result in motor damage or failure of the motor. The support structure  84  also is designed to accommodate the insertion of rotor  66  and a drive shaft  68  while protecting the end turns  77  from being damaged by the rotor  66  and drive shaft  68  during assembly and disassembly of submersible motor  32 . 
         [0018]    In the embodiment illustrated, inserts  86  are preformed inserts constructed from a stiff, high temperature, insulation material. The inserts  86  may be secured in position by an appropriate adhesive material  88 , such as glue or epoxy. The end coils  78  also can be infused or covered with the adhesive material  88 , e.g. glue or epoxy, to further enhance the mechanical stability of the end coils. In some applications, the end coils  78  can be further supported by appropriate structures, such as coil forming blocks or wedges  90 . 
         [0019]    With added reference to  FIGS. 3 and 4 , one embodiment of support structure  84  utilizes inserts  86  that are conical structures  92  sized to fit within the end coils  78  at each end of stator  62 . As illustrated in the front view of  FIG. 3  and the top view of  FIG. 4 , each conical structure  92  comprises smaller end  94  of reduced diameter relative to a larger end  96 . The smaller diameter end  94  is positioned adjacent the stack of laminations  70  such that the conical structure increases in diameter at increasing distances from the lamination stack. An opening  98  extends axially through the conical structure  92  and increases in diameter moving from smaller diameter end  94  to larger diameter end  96 . This conical structure maintains end coils  78  at a position that does not interfere with the stator bore  64  while enabling easy insertion and removal of rotor  66 . 
         [0020]    The shape, size, material and configuration of support structure  84  and inserts  86  can be adjusted according to the environment and the type/size of submersible motor  32 . If a conical structure  92  is utilized, the diameter and length of the conical structure can vary from one application to another or even within the same submersible motor  32 . In  FIG. 2 , for example, the upper insert  86  is illustrated as a cone that can either have a long sidewall, as illustrated on the left, or a short sidewall, as illustrated on the right. Numerous other adaptations of the preformed insert can be made as required for a given submersible motor design or application. 
         [0021]    The embodiments described above provide examples of submersible motors and support structures that can be used to improve the run life of a variety of well systems. It should be noted, however, that the support structures can be used to prevent the radially inward collapse of end coils in many types of motors and in a wide variety of well related applications. Additionally, the material used to create the support structure, the number of support structure components used in an individual motor, and the configuration of those components can be adjusted as needed for a given application. Though multiple end coils  78  are noted most often, one or more end coils are contemplated. Also, though end coils  78  and associated parts and description and most often contemplated with respect to both ends of a motor/stator device, it is contemplated that separate features are equally applicable to only one end thereof. 
         [0022]    Accordingly, although only a few embodiments of the present invention have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this invention. Such modifications are intended to be included within the scope of this invention as defined in the claims.