Abstract:
An electrical machine is described that has a ceramic material as insulation around the winding wire. In some embodiments, the ceramic material is hexagonal boron nitride (HVR), aluminum oxide, aluminum nitride, or beryllium oxide. The ceramic material may be rolled, brush, sprayed, or dipped onto the wire using a binder-less or binder-containing solution. The whole wire may be coated, or just parts that are particularly subject to abrasion of the conductor and/or electrical contact with other conductive materials.

Description:
FIELD 
       [0001]    The present invention relates to dynamo-electric machines. More specifically, the present invention relates to dynamo-electric machines having particular insulation on their windings. 
       BACKGROUND OF THE DISCLOSURE 
       [0002]    Rotating electrical machines use the relative motion between a rotating component (“rotor”) and a static component (“stator”) to convert between electrical and mechanical energy. One of these components is typically made of metal, while the other is typically a magnet, and at least one of them typically has a wire wrapped around it. 
         [0003]    One type of electrical machine, an electric motor, converts electrical energy to mechanical energy. Electric motors typically operate using the interaction between magnetic fields and current-carrying conductors to generate rotational force. The two main parts of a generator can be thought of in either mechanical or electrical terms. In mechanical terms, the “rotor” is the rotating part of an electrical machine, while the “stator” is the stationary part. In electrical terms, the “armature” is the power-producing component of an electrical machine, and the “field” is the magnetic field component. The armature can be on either the rotor or the stator. Electromagnets or permanent magnets mounted on either the rotor or the stator provide the magnetic field. 
         [0004]    As illustrated in  FIG. 1 , the current-carrying conductor(s)  110  that make the “windings” of the armature are conventionally coated with one or more layers  115  of enamel, wrapped tapes, or epoxy to electrically insulate them from neighboring portions of the conductor  110  and other adjacent conductive components in the system, such as stator body  105 . For example, a tape impregnated with polyimide, glass, mica, fluorinated ethylene propylene, or a blend thereof may be wrapped around a wire along its length, then the wire is wound around one of the motor&#39;s major components. In this example, the tape keeps electrical current from passing directly between adjacent windings and between the winding wire and the machine component (e.g., stator). 
         [0005]    In some designs, the insulator  115  is not strong enough to withstand friction with the machine component  105  around which is wound. Therefore, to protect the insulator  115 , the “slots”  120  that guide placement of the windings include additional material (a “slot liner”)  125  that protects the insulation-wrapped conductor  110  that is laid in the slot  120 . For example, the slot liners  125  may be made from fiber or rag-polyester as described in US Published 
         [0006]    There is thus a need for improved electric machines and better insulators for the conductors used in their windings. 
       SUMMARY 
       [0007]    In various embodiments, an electric machine includes a stator and a rotor, at least one of which has windings of a conductor covered with a ceramic material, such as hexagonal boron nitride (HBR), aluminum oxide, aluminum nitride, or beryllium oxide. In some embodiments, a powder form of the ceramic is dissolved in water or another solvent, then is applied to the conductor by rolling, brushing, dipping, or spraying. In some implementations, the windings are around the stator, while in others, the windings are around the rotor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a cross-sectional schematic diagram of a prior art stator and some of its windings. 
           [0009]      FIG. 2  is a cross-sectional schematic diagram of a machine embodying a first design according to the present disclosure. 
           [0010]      FIG. 3  is a cross-sectional schematic diagram of a machine embodying a second design according to the present disclosure. 
           [0011]      FIG. 4  is a flowchart of acts in a method of producing the product shown in  FIG. 2 . 
       
    
    
     DESCRIPTION 
       [0012]    For the purpose of promoting an understanding of the principles of the present invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will, nevertheless, be understood that no limitation of the scope of the invention is thereby intended; any alterations and further modifications of the described or illustrated embodiments, and any further applications of the principles of the invention as illustrated therein are contemplated as would normally occur to one skilled in the art to which the invention relates. 
         [0013]    Generally, one form of the disclosed system is an electric machine. The wire(s) that form the windings of the electrical machine are coated with a ceramic insulator, providing a hard, insulating, heat-conductive layer around the conductor and improving heat transfer, durability, and performance. 
         [0014]    Turning to  FIG. 2 , electrical machine  200  comprises stator  210  around rotor  220 . Stator  210  has a substantially circular inner diameter  212  and an outer diameter  214 . Breaks along inner diameter  212  open into slots  216 , through which one or more winding wires  230  go. Each wire  230  has a coating  235  of a ceramic material that has been applied using any of the techniques described herein or that will occur to those skilled in the art. 
         [0015]    Those skilled in the art will appreciate that, while three cross-sections of conductors  230  are shown in slot  216 , other numbers of windings and/or conductors  230  are used in other embodiments. Likewise, other slot counts and spacing are used in different designs without departing from this invention. Because the conductors  230  are covered with ceramic insulator  235 , they avoid electrical connection with each other and with the (typically conductive and grounded) interior of slot  216 . Further, because of the hardness of ceramic insulator  235 , the interior of slot  216  does not need a slot liner to protect the insulator  235  from wear. Finally, in many embodiments, the thermal conduction properties of insulators  235  help remove heat from conductors  230 . 
         [0016]    Another electrical machine is shown as machine  300  in  FIG. 3 . In machine  300 , component  310  is separated from complementary component  320  by air gap  330 . Conductors  340  have ceramic coating  345  and rest along surface  350 . Again, ceramic coating  345  protects conductors  340  from physical damage by their contact with component  310  and facilitates transfer of heat (generated by ohmic losses) away from conductors  340 . 
         [0017]    A variety of ceramic materials are suitable for use in the disclosed system. Those with breakdown temperatures adequate to withstand the temperatures typically generated in the given design, dielectric strength sufficient to insulate the conductors from each other and the machine component, and thermal conductivity sufficient for appropriate cooling in the given design will do. In some embodiments, the ceramic material is hexagonal boron nitride (HBR), aluminum oxide, aluminum nitride, or beryllium oxide. HBR, for example, is harder than steel, so that slot liners are not needed to protect the wire from damage by the machine component. HBR has a dielectric strength of about 35 kV/mm, so a 0.2-0.3 coating would yield 7-10 kV of insulation. HBR has thermal conductivity similar to steel, so heat generated in the wire easily passes through the ceramic to the machine component (stator or rotor) or other heat sink, as will occur those skilled in the art. 
         [0018]    A flowchart illustrating the process of making and the electric machine according to the present disclosure is shown in  FIG. 4 . Process  400  begins by coating ( 410 ) a wire with ceramic material. In some embodiments, coating step  410  comprises rolling, brushing, dipping, or spraying the wire with a solution of the ceramic material in powder form with water (or another solvent) and optionally a binder. 
         [0019]    As an example, water-based and solvent-based systems are available from Momentive Performance Materials of Columbus, Ohio, USA, that apply boron nitride (BN) powder. These application systems may use one or more organic binders, one or more inorganic binders, or no binder at all. Each approach has its advantages and disadvantages, as will occur to those skilled in the art:
       Binder-less coatings used in such systems are more chemically pure than some other coatings, but include nothing that tends to adhere the coating to the substrate.   Organically bound coatings use an organically based cross-linked binder system. When they dry, they handle well, but the binder is stable only up to about 300° C.   Inorganically bound coatings retain their surface integrity even when used at relatively high temperatures, but sometimes require high-temperature curing.
 
A variety of such coating systems, binder types, and other variations are available, and one or more of those options might be chosen or specified as a function of the electrical machine design and/or context. For high-temperature machine applications, for example, inorganic binders would be preferred.
       
 
         [0023]    In some embodiments, the ceramic coating is applied with a concentration of about 10-40% ceramic with the remainder being solvent and binder. The solvent in some embodiments is water, while in others the solvent is an inorganic compound. The binder in some embodiments is alumina, bentonite, or titanium oxide. The coating is applied to a thickness adequate to serve the dielectric demands of the design, such as a thickness of 0.1-0.3 mm for boron nitride having a dielectric strength of about 30 kV/mm. 
         [0024]    After the wire is coated ( 410 ), it is wound ( 420 ) around the component of the electrical machine. The number and pattern of windings may vary widely from one embodiment to the next depending on the design and purpose of each machine, as will occur to those skilled in the art Likewise, the wire is formed before coating in some embodiments, while in others, the wire is coated before it is formed. The component is then installed or assembled ( 430 ) in the machine. 
         [0025]    All publications, prior applications, and other documents cited herein are hereby incorporated by reference in their entirety as if each had been individually incorporated by reference and fully set forth. While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.