Abstract:
The invention concerns an AC electric motor ( 1 ) comprising a stator magnetic circuit including a first part ( 2 ) whereon are mounted electrical windings ( 7  and  8 ) and a second recessed part ( 10 ) wherein is mounted a rotor ( 14 ). The invention is characterized in that the first part ( 2 ) of the stator magnetic circuit and the electrical windings ( 7  and  8 ) are mounted inside a stator chamber ( 20 ) with sealed wall, the second part ( 10 ) of the stator magnetic circuit, the cylindrical rotor ( 14 ) being located outside said chamber. The invention is applicable in the oil industry for pumping fluids in bottom holes producing hydrocarbons in liquid, gas or polyphase form and in chemical and nuclear industries for pumping dangerous or chemically harmful fluids.

Description:
This application is the national phase under 35 U.S.C. § 371 of PCT International Application No. PCT/FR00/02410 which has an International filing date of Aug. 31, 2000, which designated the United States of America. 
    
    
     The present invention relates to an alternating-current motor intended to drive a pump or a compressor. 
     It is particularly suitable for the production of pumping units which are immersed in a liquid. 
     It finds its application especially in the oil industry for pumping fluids at the bottom of production wells for hydrocarbons in liquid, gaseous or multi-phase form. 
     BACKGROUND OF THE INVENTION 
     The electric motors which are most widely used are single-phase or multi-phase asynchronous alternating-current motors. Their structure is described in TECHNIQUES DE L&#39;INGENIEUR (ENGINEERING TECHNOLOGY), a treatise on electrical engineering, Volume D 3 II Chapter D 3 490 Asynchronous motors—choice and related problems. 
     According to this document, asynchronous alternating-current motors essentially include a stator and a rotor. 
     The stator consists of coiled windings of conducting wires distributed within a yoke ring forming a framework and housed within a magnetic circuit supported by this yoke ring. This magnetic circuit is formed by stacks of laminations in the form of circular crowns into which slots are cut parallel to the axis of the yoke ring and in which the conducting wires of the coiled windings are housed. 
     Within the crown-shaped magnetic circuit formed by the stack of laminations is placed the cylindrical-shaped rotor which includes a rotational shaft supported by a support bearing which is integral with the yoke ring of the stator. 
     The most widespread type of rotor is the squirrel cage rotor, the circuit of which consists of conducting bars regularly spaced between two metal crown rings forming the extremities. 
     This squirrel cage is inserted within a magnetic circuit consisting of disks stacked on the rotational shaft. 
     With this type of motor, since the distances between the windings of the stator are very short, they cannot be supplied with very high voltages and the installation of insulators is an intricate matter. 
     The same problem is posed for the insulation of the windings with respect to the laminations of the stator circuit. 
     For certain applications, for example for raising water from a water table or hydrocarbons laid down at the bottom of a well, the shaft of the motor is coupled to a pump and the motor-plus-pump assembly is immersed in the fluid to be pumped. 
     In this case, the space between the rotor and the stator is filled with liquid, which further accentuates the problems of electrical insulation set out above. 
     One known solution consists in separating the motor from the pump, but requires the use of a dynamic sealing device mounted on the shaft of the motor. Such sealing devices are delicate and unreliable. They are poorly adapted to the long-term service required for those installations to which access is difficult, expensive or even dangerous. 
     SUMMARY OF THE INVENTION 
     The precise object of the present invention is to remedy these drawbacks, and especially to provide an alternating-current electric motor the windings of which can withstand a high voltage and which are easy to produce by virtue of the large distances which separate the windings from each other and the windings from the stator magnetic circuit. 
     This electric motor is particularly suitable for forming a submerged electric-pump unit. 
     To this end, the present invention proposes an alternating-current electric motor including a stator magnetic circuit comprising a first part on which electrical windings are mounted and a second, hollow, part within which is mounted a cylindrical rotor equipped with a rotational shaft supported by at least two bearings, which motor is characterized in that it further includes a stator chamber with a leaktight wall, at least a part of which is produced from a non-magnetic insulating material, within which are mounted the first part of the stator magnetic circuit and the electrical windings, the second part of the stator magnetic circuit, the cylindrical rotor and the support bearings lying outside the said chamber and being arranged in such a way that the stator magnetic circuit passes through the wall of the said chamber in the part produced from non-magnetic insulating material. 
     According to another characteristic of the motor of the invention, with the shaft of the rotor of the said motor being linked mechanically to the shaft of the rotor of a pump, the second part of the stator magnetic circuit, the rotor of the said motor, the support bearings and the rotor of the pump are enclosed in a rotor chamber with a leaktight wall equipped with an inlet and with an outlet for a fluid to be pumped. 
     According to another characteristic of the motor of the invention, the leaktight wall of the stator chamber includes a device for compensating for the pressure difference between the inside and the outside of the said chamber. 
     According to another characteristic of the motor of the invention, the stator electrical windings include at least one connection for drawing electrical energy. 
     According to another characteristic of the motor of the invention, the stator magnetic circuit includes a supplementary electrical winding for drawing electrical energy. 
     According to another characteristic, the motor of the invention further includes an inlet tapping and an outlet tapping which are mounted on the wall of the stator chamber for connecting an external device for cooling a fluid filling the stator chamber. 
     According to a final characteristic, the motor of the invention further includes a jacket produced from a non-magnetic insulating material which encases the first part of the stator magnetic circuit, connected in leaktight fashion to the part produced from non-magnetic insulating material of the wall of the chamber in order to render the said chamber leaktight. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other characteristics and advantages of the invention will become apparent on reading the description which follows, given by way of example and by reference to the attached drawings, in which: 
     FIG. 1 is a view in longitudinal section of an electric motor according to a first embodiment of the invention, 
     FIG. 2 is a side view of a part of an electric motor according to the first embodiment of the invention, 
     FIG. 3 is a perspective view of a part of an electric motor according to the first embodiment of the invention, 
     FIG. 4 is a view in longitudinal section of an electric motor according to a second embodiment of the invention, 
     FIG. 5 is a view in longitudinal section of an electric motor according to a third embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 represents a view in longitudinal section of a first embodiment of the motor  1  of the invention which includes a laminated stator magnetic circuit which comprises: 
     a first part  2  consisting of three core segments  3 ,  4  and  5 , of which only the segments  3  and  4  are visible in FIG. 1, spaced in this instance by 120° and forming a yoke  6  at one of their ends. 
     a second part  10 , consisting of three core segments  11 ,  12  and  13  which extend the three segments  3 ,  4  and  5 , of which only  11  and  12  are visible in FIG.  1  and the ends of which form a cylindrical. hollow. 
     On each of the core segments  3 ,  4  and  5  are mounted electrical windings  7 ,  8  and  9  of which only  7  and  8  are visible in FIG.  1 . 
     The three segments  3 ,  4  and  5  of the stator magnetic circuit and the electrical windings which they support are placed in a fixed cylindrical casing  19 , closed in leaktight fashion at one end by a back plate  21  and, at the opposite end, by a closure plate  22 . 
     This plate  22  is produced from an insulating and non-magnetic material so as not to constitute a short-circuit turn around the stator magnetic circuit, nor a magnetic shunt of the same circuit. 
     The casing  19  and the plate  22  form a leaktight stator chamber  20 . The casing  19  includes a leaktight cable bush for a stator-winding power-supply cable to pass through. The plate  22  includes leaktight bushes  18  for the passage respectively of the three cores of the stator magnetic circuit consisting of the segments  3 ,  4 ,  5 ,  11 ,  12  and  13 . 
     The laminations which constitute the cores of the stator circuit are assembled in leaktight fashion in the region of their passage through the plate  22 , for example by means of a thin layer of flexible insulating material arranged between two adjacent laminations. 
     The yoke  6  of the stator magnetic circuit  2  is held by the support  26 . 
     The casing  19  is also equipped with an inlet tapping  23  and with an outlet tapping  24  for connecting an external device for cooling an insulating fluid filling the stator chamber  20 , not represented in FIG.  1 . 
     In the hollow situated at the end of the second part  10  of the stator magnetic circuit  2  is mounted a laminated rotor  14  which includes a rotational shaft  15  which rests on the fixed bearings  16  and  17  linked mechanically by fixing pieces  41  and  42  to the second part  10  of the stator circuit so as to ensure centering of the rotor and of the stator. The fixing pieces  41  and  42  are produced from insulating and non-magnetic material so as not to form a short-circuit turn around the segments of stator cores and not to magnetically short-circuit the stator magnetic circuit. 
     FIG. 2 represents a partial side view of the motor, which shows the relative positions of the stator magnetic circuit comprising the core segments  3 ,  4 ,  5  which are linked by the yoke  6 , the core segments  11 ,  12  and  13 , the windings  7 ,  8 ,  9  mounted on the core segments  3 ,  4 ,  5  and the rotor  14  with its shaft  15 . 
     FIG. 3 represents a partial view in perspective of the motor, on which appear the stator magnetic circuit  2  comprising the core segments  3 ,  4 ,  5  linked by the yoke  6 , the core segments  11 ,  12  and  13 , the rotor  14  with its shaft  15 , the electrical winding  7  mounted on the core segment  3  and the plate  22  equipped with a leaktight bush  18  for the passage of the segment  11 . 
     FIG. 3 further includes a supplementary electrical winding  50  mounted on core segment  3  next to electrical winding  7 . As is known to those skilled in the art, such a supplementary electrical winding forms an electrical transformer together with the stator magnetic circuit and electrical winding  7 . The supplementary winding acts as a secondary winding of the transformer and accordingly is capable of delivering an electrical voltage when winding  7  is supplied with an alternating electrical voltage. 
     According to a second embodiment represented diagrammatically in longitudinal section in FIG. 4, the motor  1  of the invention has its axis vertical and includes a stator magnetic circuit  2 , electrical windings  7 ,  8 , a casing  19 , a plate  22  and a rotor  14  as described for the first embodiment and arranged in the same way. 
     According to this second embodiment, the motor  1  further includes: 
     a pump impeller  32  equipped with a shaft  27  linked to the end of the shaft  15  of the rotor  14  and equipped at its lower end with an axial abutment  33 , 
     a bellows  40  for compensating for the pressure difference between the two faces of the plate  22 , 
     an extension  28  of the casing  19  fitted with an end plate  36 , which forms a rotor chamber  30  which encloses the second part  10  of the stator magnetic circuit, the rotor  14  and the impeller  32  of the pump, 
     an electrical connection  38  for drawing electrical energy which passes through the casing  21  via a leaktight cable bush  37 . 
     The shafts  15  and  27  are supported by bearings  16 ,  17  and  31 , the bearings  16  and  17  being linked mechanically to the stator magnetic circuit by means of fixing pieces  41  and  42  as in the first embodiment, the bearing  31  and the abutment  33  being integral with the extension  28  of the casing  19 . 
     The extension  28  of the casing  19  includes an inlet  34  and an outlet  35  for the liquid put into circulation by the impeller  32  driven by the rotor  14  of the motor. 
     In order to make the motor operate according to this second embodiment, immersed at the very great depth in a liquid, that is to say under very high static pressure, the stator chamber  20  is filled with a liquid. 
     By virtue of the bellows  40 , the pressures between the stator chamber  20  and the rotor chamber  30  balance out, and thus the problems relating to the pressure difference between these two chambers disappear. 
     According to a third embodiment represented diagrammatically in longitudinal section in FIG. 5, the motor  1  of the invention has its axis vertical and includes a stator magnetic circuit  2 , electrical windings  7 ,  8 , a casing  19 , a plate  22  and a rotor  14  as described for the first embodiment and arranged in the same way. 
     According to this third embodiment, the leaktight bushes referenced  18  in FIG. 1 are replaced by a jacket referenced  43  in FIG.  5 . 
     This jacket  43 , produced from an insulating and non-magnetic material, encases the first part  2  of the stator magnetic circuit and is connected in leaktight fashion by a weld  44  to the part  22  of the wall of the stator chamber  20 . 
     By virtue of this jacket, the leaktightness of the stator chamber  20  is ensured and the stator magnetic circuit is under the pressure conditions of the rotor chamber  13 , which eliminates the problem of leaktightness of the passage through the part  22  of the wall of the rotor chamber  30  by the laminations of the stator magnetic circuit, and especially leaktightness between the laminations which may be difficult to achieve. 
     By virtue of the shape of the stator windings and of their mounting on the magnetic core segments, their electrical insulation is not limited by the size of the slots as in conventional motors, and, that being so, they can be supplied with voltages substantially higher than those of conventional motors, which avoids the use of a transformer in proximity to the motor when the latter is very far from its electrical power-supply source. 
     The electric motor of the invention also exhibits the advantage of including only static sealing devices which do not present the drawbacks of dynamic sealing devices, which confers on it great reliability, indispensable for numerous applications in which the motor is difficult of access, for example at the bottom of an offshore oil production well or in a dangerous area, as is the case in the nuclear industry and certain chemical industries where hazardous products are manufactured. 
     The electrical windings mounted in the leaktight chamber  20  are completely isolated from the surrounding medium and pumped fluid, which renders them insensitive to mechanical and chemical attack relating to the nature of the pumped fluids and of the surrounding medium. 
     The motor of the invention is particularly suitable for pumping hydrocarbons in multi-phase form at the bottom of offshore production wells at very great depth.