Abstract:
A turbine generator utilizing a passive high pressure fluid source such as a natural gas well head. The generator includes a core and lead wires encapsulated in a dielectric medium to isolate current-bearing components from the motivating fluid, thereby preventing carbon bridging and reducing the explosion hazard when the motivating fluid is a hydrocarbon. The turbine generator includes a rotor that utilizes the full length as an impingement surface for imparting momentum to the rotor, thereby maintaining a compact design that reduces the overall footprint of the turbine generator. Fluid exits the generator via horizontal passages that penetrate the lower extremities of the turbine generator, preventing the buildup of condensation in the unit.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Patent Application No. 60/795,743, filed 27 Apr. 2006, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to turbines and generators and, more particularly, to turbines with integrated generators. 
       BACKGROUND OF THE INVENTION 
       [0003]    Turbine generators that exploit passive pressurized sources such as natural gas well heads have found utility in low power applications (100 watts or less). An example of such a generator is disclosed in U.S. Pat. No. 5,118,961 to Gamel and owned by S&amp;W Holdings, Inc., the assignee of the present patent application. The reliability of these units has resulted in a wider variety of applications by relevant consumers, and attendant demands for higher power output. 
         [0004]    A challenge with increased power output is the requirement for higher voltage levels. Devices that rely on the spatial separation of electrical connections to provide electrical isolation between the winding terminations may require a larger footprint to accomplish the required isolation. Units that service the petrochemical industry are often powered by high pressure hydrocarbon gases. Increased potential between electrical connections may result in arcing, creating an explosion hazard. Even where an explosion does not result, such arcing may lead to a build up of carbon deposits on the exposed connections that may eventually bridge between the connections, causing the unit to short out and incur structural damage. 
         [0005]    One approach to increasing the power is to increase the size of the various components. Exemplary is U.S. Patent Application Publication No. 2005/0217259 by Turchetta, which discloses an in-line natural gas turbine that utilizes bevel gears to transmit the rotational power to a generator outside a pipeline. However, in spatially constrained areas (e.g. off shore drilling platforms), the footprint of such an approach may be prohibitive. 
         [0006]    Increased power output generally requires a higher mass flow rate through a given unit, which leads to an increase in the amount of condensate that forms and accumulates in the unit. Existing units have been known to become flooded with accumulated condensation to the point of becoming inoperable. 
         [0007]    Another issue in certain applications, independent of power level, is the effect of corrosive gases. Natural gas wells, for example, are known to contain hydrogen sulfide (H 2 S), also referred to as “sour gas.” The sour gas has a highly corrosive effect on metals commonly used in electric generators. Another common component indigenous to natural gas wells is water vapor, which is also corrosive and can cause operational problems when condensing out as a liquid. 
         [0008]    Certain technologies utilize pressurized liquids to prevent hazardous gasses from entering unwanted portions of an assembly, such as disclosed in U.S. Pat. No. 5,334,004 to Lefevre et al. Where isolation from electrical machinery is desired, such an approach may require an isolation chamber distinct from the compartment housing the electrical machinery, as the use of liquids may be precluded for reasons of electrical isolation. The need for an isolation chamber will generally add to the required footprint of the generator. 
         [0009]    What is needed is a gas turbine generator capable of utilizing a hydrocarbon medium without posing an explosion or carbon forming hazard, is resistive to the corrosive components that may be indigenous to the pressure source, and eliminates the potential of condensation flooding while maintaining a small footprint. 
       SUMMARY OF THE INVENTION 
       [0010]    The various embodiments of the disclosed invention provide an arrangement that prevents arcing between adjacent lead connections, thereby minimizing the explosion hazard and eliminating carbon bridging between connections. Various units have also been made more compact relative to existing designs, to provide more electrical generation capacity within a smaller footprint. For example, the present disclosure may produce a natural gas turbine that produces 500 Watts while occupying only a 250-mm×250-mm plan view footprint. The problem of condensation buildup is also mitigated. 
         [0011]    In one embodiment, the turbine generator has a core assembly that includes windings with terminations connected to lead wires. The core assembly is encapsulated in a dielectric potting or casting which hermetically seals the windings, the winding terminations, and at least a portion of the lead wires leading to the connection with the terminations. The lead wires, either individually or as a group, may also be contained within a dielectric shroud such as shrink fit tubing that terminates on one end within the dielectric casting and on the other end within a packing in a sealed container. By this approach, all current-bearing components are isolated from the flow stream. Certain embodiments of the invention have found favor in an industrial context, earning Factory Mutual (FM) approval for use with natural gas. 
         [0012]    The turbine generator has a rotor that is motivated by a high pressure fluid such as natural gas that is directed tangentially to impinge on the outer perimeter of the rotor. A design is disclosed wherein the full axial length of the rotor is utilized as the impingement surface, thereby increasing the power imparted to the rotor over a minimum length, thereby maintaining a small overall footprint for the turbine generator. 
         [0013]    The fluid enters the turbine generator via inlet passages and exits the unit via outlet passages. The outlet passages are configured to penetrate the interior of the turbine generator at a substantially horizontal angle and at the bottom of the cavities that house the components of the turbine generator, thus enabling the cavities to drain and reducing build up of condensation within the cavities. 
         [0014]    In another embodiment, a natural gas turbine generator includes a housing that defines an interior chamber in fluid communication with an inlet and an outlet for passage of a gas therethrough, the gas including a hydrocarbon. A rotor is operatively coupled within the interior chamber, the rotor including an impingement surface and cooperating with the interior chamber to form an annular passageway about the impingement surface. The rotor is rotationally driven when the gas passes through the annular passageway. An electric generator including a core assembly is operatively coupled with at least one magnetic element, the core assembly being stationary relative to the housing and hermetically sealed within a dielectric casting for isolating the core assembly from the gas. The at least one magnetic element is secured to the rotor for rotation with respect to the core assembly. 
         [0015]    Another embodiment may further include a framework portion having a first axial length, the framework portion including an impingement surface having a second axial length, the second axial length being is greater than one-half of the first axial length. 
         [0016]    In another embodiment, the rotor includes a shaft portion having a standoff portion that separates two end portions, the end portions being operatively coupled with bearings. The standoff portion may have a length substantially equal to the axial length of the framework. 
         [0017]    In yet another embodiment, the interior chamber defines a lower extremity. The outlet passage extends from the lower extremity in an orientation for draining condensation from said interior chamber. 
         [0018]    In still another embodiment, a turbine generator for generating electricity that is powered by a flow of gas therethrough includes a housing that defines an interior chamber in fluid communication with an inlet and an outlet for passage of the gas therethrough. The gas may contain a hydrocarbon. A rotor is operatively coupled within the interior chamber, the rotor including a continuous impingement surface and cooperating with the interior chamber to form an annular passageway bounded on an inner perimeter by the continuous impingement surface. The rotor is rotationally driven when the natural gas passes tangentially through the annular passageway. The embodiment includes an assembly of armature plates having an inner radial portion and an outer radial portion, and at least one winding interlaced with the outer radial portion of the assembly of armature plates. The at least one winding has a plurality of terminations. A plurality of leads, each having a proximal portion and a distal portion, one each of the plurality of lead wires, is electrically connected to one of the plurality of terminations at the proximal portion. A dielectric casting encases the outer radial portion, the at least one winding and the proximal portions of the plurality of lead wires and hermetically seals the at least one winding and the proximal portions from contact with the natural gas. 
         [0019]    In another embodiment, an orifice passes through the inner radial portion of the assembly of armature plates and has a front end located on the front face of the assembly of armature plates. The dielectric casting encases the front end of the orifice. 
         [0020]    Another embodiment of the invention includes a housing that defines an interior chamber in fluid communication with an inlet and an outlet for passage of a fluid therethrough, the interior chamber having a lower extremity, the outlet passage extending from the lower extremity in an orientation for draining condensation from the interior chamber. A rotor is operatively coupled within the housing and has a continuous impingement surface. A flow restricting device is disposed between the inlet and the continuous impingement surface of the rotor, the flow restricting device directing the fluid onto the continuous impingement surface and causing the rotor to rotate about an axis. An electric generator is mounted within the interior chamber and includes a core assembly and a magnetic element. The core assembly is stationary relative the housing, and the magnetic element is secured to the rotor and rotates proximate the core assembly. The embodiment also includes means for isolating the core assembly from the fluid. 
         [0021]    An electrical generating system is also disclosed that includes a turbine generator in fluid communication with a pressurized gas source, the pressurized gas source producing a gas flow, the gas flow including a natural gas. The turbine generator includes a stationary core assembly operatively coupled with a magnetic element that rotates relative to the stationary core assembly to produce electricity. The core assembly includes current-bearing components that are encapsulated within a dielectric casting that hermetically seals the current-bearing components from the gas flow. A throttling device may be disposed between said pressurized gas source and the turbine generator, the throttling device imposing a reduced pressure in the gas flow entering the turbine generator. A pre-heating system may be disposed between the pressurized gas source and the rotor for transferring heat to said gas flow. 
         [0022]    In another embodiment of the invention, a method of using a natural gas turbine includes selecting a turbine generator that has a plurality of electrical outputs and an interior chamber in fluid communication with an inlet and an outlet. The interior chamber contains a stationary core assembly operatively coupled with at least one magnetic element mounted on a rotor rotatable relative to the stationary core assembly for producing electricity at the plurality of electrical outputs. The rotor in this embodiment has a continuous impingement surface. The core assembly has current-bearing components that include a plurality of windings and being at least partially encapsulated within a dielectric casting that hermetically seals the current-bearing components. The method further entails connecting the plurality of electrical outputs to an electrical load and connecting a gas supply line to the inlet, the gas supply line being in fluid communication with a pressurized gas source, the pressurized gas source including a natural gas composition. A gas return line is connected to the outlet, and a gas flow is enabled from the pressurized gas source to flow through the turbine generator, the gas impinging the continuous impingement surface and causing the rotor to rotate the at least one magnetic element relative to the core assembly and produce electricity at the plurality of electrical outputs. The method may further include operating a switch between the electrical output and the electrical load, the switch being switchable between at least a load position and a no-load position. The switch is repeatedly cycled between the load position and the no-load position according to a periodic cycle to increase the average rotational speed of the rotor. 
         [0023]    Another method according to the present invention includes operating a plurality of switches, one each in line with one of the plurality of windings, each of the plurality of switches being switchable between one of the plurality of the electrical outputs and a plurality of resistive elements. Each of the plurality of resistive elements are operatively coupled between two of the plurality of windings, wherein switching the plurality of switches to the plurality of resistive elements causes dynamic braking of the turbine generator. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0024]      FIGS. 1   a  and  1   b  are perspective views of a turbine generator in an embodiment of the invention; 
           [0025]      FIG. 2  is a front elevation view of the turbine generator of  FIG. 1   a  with the front housing portion and the rotor removed for clarity; 
           [0026]      FIG. 3  is an exploded view of the turbine generator of  FIG. 1   a;    
           [0027]      FIG. 4  is a perspective view of the rotor of  FIG. 3 ; 
           [0028]      FIG. 5  is a sectional view of the turbine generator of  FIG. 1   a  along the datum indicated in  FIG. 2 ; 
           [0029]      FIG. 6  is a plan view of an assembly of armature plates in an embodiment of the invention; 
           [0030]      FIG. 7  is a sectional view of the assembly of armature plates of  FIG. 6 ; 
           [0031]      FIG. 8  is a sectional view of a turbine generator in an embodiment of the invention; 
           [0032]      FIG. 8   a  is a sectional view of the rotor of  FIG. 8  in isolation; 
           [0033]      FIG. 9   a  is a sectional view of a nozzle arrangement for directing a jet onto the impingement surface at a substantially tangential angle of incidence; 
           [0034]      FIG. 9   b  is an enlarged partial sectional view of the rotor and nozzle ring of  FIGS. 5 and 8 ; 
           [0035]      FIG. 9   c  is an enlarged partial cut-away view of the rotor of  FIG. 9   b;    
           [0036]      FIG. 10  is a perspective view of a core assembly secured to a back housing portion in an embodiment of the invention; 
           [0037]      FIG. 11  is an enlarged partial view of the core assembly of  FIG. 10  with a cut-away view of the plate assembly within; 
           [0038]      FIG. 12  is an enlarged partial view of the core assembly of  FIG. 10  in the vicinity of an encased front end of an orifice for feeding through wire terminations; 
           [0039]      FIG. 13  is a schematic of a turbine generator system in an embodiment of the invention; 
           [0040]      FIG. 14  is a cut-away view of a turbine generator depicting the use of heating elements in a plenum of the turbine generator in an embodiment of the invention; 
           [0041]      FIG. 15  is a sectional view of a turbine generator with a control board mounted therein in an embodiment of the invention; 
           [0042]      FIG. 16  is a partial sectional view of a turbine generator with a control board that is convectively cooled in an embodiment of the invention; 
           [0043]      FIG. 16   a  is a sectional view of the control board of  FIG. 16  having finned elements for convective heat transfer in an embodiment of the invention; 
           [0044]      FIG. 17  is a partial sectional view of a turbine generator with a control board that is conductively cooled in an embodiment of the invention; 
           [0045]      FIG. 18  is a perspective view of a front housing of a turbine generator in an embodiment of the invention; and 
           [0046]      FIG. 19  is an electrical schematic of an operating circuit in accordance with an embodiment of the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0047]    Referring to the  FIGS. 1 through 7 , a turbine generator  10  including a housing  12  with an inlet passage  14  and a pair of fluid outlet passages  16  is depicted in an embodiment of the invention. In this embodiment, a rotor  18  having a continuous impingement surface  20  and a magnetic element  22  attached to the rotor  18  is disposed in the housing  12 . The rotor  18  may be configured to substantially surround a core assembly  24 . The continuous impingement surface  20  may be characterized by a roughened or structured surface such as a saw-tooth profile. A flow restricting device  26  such as a nozzle ring may be fixed in the housing  12  about the rotor  18 . 
         [0048]    The housing  12  may include a front housing portion  28  and a back housing portion  30  separated by a spacer ring  32  that combine to form an interior chamber  33  in fluid communication with the inlet passage  14  and the outlet passages  16 . The front housing portion  28  includes a flange  34  in which one of the fluid outlet passages  16  may be formed. The flange  34  may also include a recess  36  for receiving an o-ring  38  and side portion of the flow restricting device  26 . 
         [0049]    The spacer ring  32  has front and back faces  40  and  42  for bearing against the front and back housing portions  28  and  30 , respectively. An o-ring gland  41  for housing an o-ring  43  may be formed on the front face. The spacer ring  32  may further include the inlet passage  14  formed therein and an interior perimeter  44 . A plenum or intake manifold  45  may be formed by the separation between the interior perimeter  44  and the outer peripheral surface  27  of the flow restricting device  26 . A pressure regulating device (not depicted) that reduces the pressure of the incoming fluid without reducing the mass flow through the turbine generator  10  may be placed upstream of the inlet passage  14 . 
         [0050]    The front housing portion  28  may further include an annular shaped cavity  46  that defines part of the interior chamber  33 . A rotor mount  48  may be formed about a central axis  49 . The rotor mount  48  in this embodiment includes a pedestal portion  50  and a collar portion  52  extending from the pedestal portion  50 . The collar portion  52  extends in a substantially horizontal direction from the pedestal portion  50  when the gas turbine generator  10  is in an upright (i.e. operating) position. A rotor bearing  54  is contained within the collar portion  52 . 
         [0051]    The back housing portion  30  may include an annular shaped cavity  56  about the core assembly  24  that defines a portion of the interior chamber  33  and a concentric mount  58  for the rotor  18 . The concentric mount  58  in this embodiment includes a rotor bearing  60  and a shoulder  62  with threaded screw taps  64 . The core assembly  24  is secured to the concentric mount  58  with socket head cap screws  66 . 
         [0052]    In the  FIGS. 1 through 7  embodiment, the back housing portion  30  also includes a partition  68  and an annular wall portion  70  extending from the partition  68 . The partition  68  may include the other outlet passage  16  extending from the cavity  56  to the exterior of housing  12  and a pair of annular recesses  74 ,  76  in which respective o-rings  78  and  80  are disposed. A front face  82  runs parallel to the back face  42  of the spacer ring  32 . The annular recess  76  fixedly and sealingly receives a side portion of the flow restricting device  26 , thereby exerting a compression force on o-ring  80 . The annular wall portion  70  defines a large cavity or compartment  84  that may house electronic appurtenances such as buck converters, RS  485  interfaces, and assorted instrumentation. 
         [0053]    The housing  12  may be held together by bolts  88  that pass through the front housing portion  28  and spacer ring  32  and threadably engage tapped bores  89  on the front face  82  of the partition  68  of the back housing portion  30 . The housing  12  is supported by a foot structure  90  fastened to the bottom of the back housing portion  30 . The passages  14  and  16  may be partially threaded with standard pipe threads. 
         [0054]    The flow restricting device  26  may take the form of a nozzle ring that includes a plurality of apertures or jet orifices  92  for directing fluid onto the center of the continuous impingement surface  20 . Typically, between fourteen and eighteen jet orifices  92  are uniformly distributed about the outer peripheral surface  27  of the nozzle ring. The number of jet orifices  92  may be changed to accommodate space and optimize torsion requirements. The structure and function of the nozzle ring and its interaction with the continuous impingement surface  20  is further described in U.S. Pat. No. 5,118,961, the disclosure of which is hereby incorporated by reference other than any express definitions of terms specifically defined therein. 
         [0055]    The rotor  18  ( FIG. 4 ) may include a cylindrical side wall  94  having an axial length  96  that extends axially from the perimeter of a base portion  98 , wherein the side wall  94  and base portion  98  define a receptacle or framework portion  100  that substantially covers or surrounds the core assembly  24 . The base portion  98  may be disc-shaped as depicted, or of other structure suitable for supporting the side wall  94  such as a hub-and-spoke arrangement. In the depiction of  FIG. 4 , the framework portion  100  is further characterized as having an interior perimeter surface  102  and a base surface  104 . 
         [0056]    In one embodiment, the perimeter portion  106  of the rotor  18  is recessed to provide gaps  108  between the perimeter portion  106  and the front and back portions  28  and  30  of the housing  12 . The rotor  18  further includes a rotor shaft  109  having a standoff portion  111  that separates end portions  110 ,  112  that mount within bearings  60 ,  54 , respectively. The rotor shaft  109  may be integrally formed with the rotor  18 . 
         [0057]    The axial length  96  of the continuous impingement surface  20  may extend over a majority of an overall length  97  of the framework portion  100 . The rotor of  FIG. 8   a , for example, depicts the axial length  96  of the continuous impingement surface  20  as almost equal to the overall length  97  of the framework portion  100 ; the length  96  is shorter than the overall entire length  97  only by the amount of the recess at the perimeter portion  106 . Hence, in this configuration, the length  96  of the continuous impingement surface  20  is over 90% of the overall length  97  of the framework portion  100 . 
         [0058]    The interior perimeter surface  102  defines a recess  114  extending radially into the cylindrical side wall  94 . The magnetic element  22  may be comprised of eight rare earth magnets disposed in pairs equally spaced at 45° from each other. Each of the magnet pairs may abut each other and have an inner peripheral surface  116  that is substantially flush with the non-recessed portion of the interior perimeter surface  102 . 
         [0059]    In certain embodiments, the core assembly  24  includes an armature plate assembly  118  comprising a plurality of laminated steel armature plates  120  ( FIG. 6 ) configured for mounting on concentric mount  58  of back housing portion  30  via the cap screws  66 . A trio of windings  122  (one for each phase of a 3-phase generator) is interlaced with an outer radial portion  124  of the armature plate assembly  118 . Further details of the armature plates  120  and the configuration of the windings  122  are presented in U.S. Pat. No. 5,118,961. 
         [0060]    The armature plate assembly  118  is characterized as having an inner radial portion  126  in addition to the outer radial portion  124  that includes a plurality of poles  125  extending radially outward and an armature interface  127  on the tangential face of the outer radial portion  124 . The individual plates  120  of the armature plate assembly  118  may be angularly offset with respect to the neighboring plates to provide a trapezoidal shape  129  on the armature interface  127  of the armature plate assembly  118  (best depicted in  FIG. 11 ). 
         [0061]    In one embodiment, the inner radial portion  126  is further characterized as having a front face  128  and a back face  130 . The back face  130  of the armature plate assembly  118  rests against the shoulder  62  of the concentric mount  58 . An orifice  132  passes through the inner radial portion  126 , the orifice  132  having a front end  134  that faces the framework portion  100  of the rotor  18  and a back end  136  adjacent the shoulder  62  of the concentric mount  58 . The orifice  132  is aligned with a wire way passage  138  passing between the shoulder  62  and the compartment  84  of the back housing portion  30 . 
         [0062]    The windings  122  may have terminations  140  that are located within the framework portion  100  of the rotor  18 , in close proximity to the front end  134  of the orifice  132 . A set of three phase leads  142  having a proximal portion  143  and a distal portion  145  are connected to the terminations  140  at the ends of the proximal portion  143 . The distal portion  145  is routed through the orifice  132 , the wire way passage  138  and a sealed connector  146  attached to the back end  136  of the wire way passage  138 . A neutral lead  144  may also be similarly routed and connected. The leads  142 ,  144  may be shrouded in a sleeve  147  such as a shrink fit tube, either individually or as a group. The sleeve  147  extends from the packing gland of the connector  146 , through the wire way passage  138  and into the orifice  132 . 
         [0063]    Referring to  FIG. 8 , the terminations  140  depend from the windings  122  into the annular cavity  56 , with the wire way passage  138  being in substantial alignment with the terminations in another embodiment of the invention. The leads  142 ,  144  traverse the annular cavity  56  between the terminations  140  and the wire way passage  138 . Again, the leads  142 ,  144  may be wrapped with sleeve  147  extending from the terminations  140  through the wire way  138  and through the packing gland of the connector  146 . The configuration of the wiring in  FIG. 8  negates the need for an orifice  132  passing through the armature plate assembly  118 . 
         [0064]    The embodiment of  FIG. 8  also depicts a rotor shaft  109   a  as having a standoff portion  111  that is substantially equal to the overall length  97  of the framework portion  100  of the rotor  18 . The standoff portion  111  of the rotor shaft  109   a  is characterized by a length L that is longer than the comparable portion of the rotor shaft  109  of  FIG. 5 . To accommodate the longer length L, the bearing  60  may be recessed within the concentric mount  58 , such that the shoulder  62  extends beyond the end portion  112  of the rotor shaft  109   a.    
         [0065]    Functionally, the extended length L of the rotor shaft  109   a  may enhance the dynamic balance of the rotor  18 , particularly at higher rotational speeds. The working fluid  149  may be directed through the flow restricting device  26  to impinge on the axial center of the continuous impingement surface  20  of the rotor  18 . Referring to  FIG. 8   a , forces are generated on the rotor having a radial component directed F R  inward toward the central axis  49 . Any moments supported by the rotor shaft  109   a  will cause unequal loading between the bearings  54  and  60 , which can manifest itself as a vibration, particularly at high rotational speeds. Also, if the radial forces F R  are not uniform, the shaft may experience a net load in a direction orthogonal to the central axis  49 . 
         [0066]    The extended length L of the rotor shaft  109   a  enables the radial force components F R  to intersect substantially coincident with the center  109   b  of the rotor shaft  109   a , thereby reducing the moment supported by the rotor shaft  109   a  and promoting the uniform loading of the bearings  54  and  60 . The configuration may provide dynamic stability across a range of rotational speeds. 
         [0067]    Referring to  FIG. 9   a , each of the orifices  92  may be configured with a larger aperture portion  92   a  having a concave end and a smaller diameter aperture portion  92   b . An axis  93  of each of the orifices  92  may be substantially tangential to the continuous impingement surface  20  of the rotor  18 . 
         [0068]    Referring to  FIGS. 9   b  and  9   c , an enlarged view of the fluid flow about the cylindrical sidewall  94  of the rotor  18  is presented in an embodiment of the invention. As fluid pressure builds in the plenum  45 , the working fluid  149  flows through the jet orifices  92  to tangentially impinge the continuous impingement surface  20  to rotationally drive the rotor  18 . The working fluid  149  exiting the jet orifices  92  fan out over the continuous impingement surface  20  through the gaps  108  into cavities  46 ,  56  ( FIG. 9   b ) and is conveyed by pressure out of the housing  12  through fluid outlets  16 . 
         [0069]    The continuous impingement surface  20  subtends the diverging angle of the fanning jet until the fluid pours over the edge of the continuous impingement surface  20  and into gaps  108 . A wider continuous impingement surface  20  (i.e. greater axial length  96 ) may extract more momentum extracted out of the fluid because the working fluid  149  is in contact with continuous impingement surface  20  over a longer tangential track ( FIG. 9   c ). 
         [0070]    Accordingly, a majority of the overall length  97  of the framework portion  100  of the rotor  18  may be utilized as an impingement surface to increase the area and length over which angular momentum is imparted on the rotor  18  for the given axial length  96 . The axial length  96  may exceed 90% of the overall length  97  in some embodiments. Integration of the continuous impingement surface  20  and the interior perimeter surface  102  on a common cylindrical side wall  94  provides further compactness and economization of space. 
         [0071]    The continuous impingement surface  20  may include a roughened or structured surface. Impingement surfaces  20  that include a structured surface may possess a higher degree of aerodynamic drag than a machine finished surface, which also can extract more momentum out of the working fluid  149 . For example, the continuous impingement surface  20  may have a saw-tooth profile as depicted in  FIG. 9   a  across the entire axial length  96 . The structure may have a peak-to-valley dimension greater than 0.17-mm. A representative and non-limiting range for the peak-to-valley dimension of the saw-tooth profile is 0.5- to 1.0-mm. An increased transfer of momentum may result in a greater rotational velocity of and/or more rotational power to the rotor  18 . Other structured surfaces include knurled surfaces, hobbed or herring bone, and may have typically the same peak-to-valley dimensions. 
         [0072]    The continuous impingement surface  20  may be characterized by a roughness parameter. A representative and non-limiting value for the surface roughness is a root-mean-square (RMS) value of 0.1-mm or greater. Accordingly, the continuous impingement surface  20  may roughened by other structural means, such as by sandblasting. 
         [0073]    Referring to  FIGS. 10 through 12  and again to  FIGS. 5 and 8 , the core assembly  24  is depicted as being hermetically sealed in an embodiment of the invention. The outer radial portion  123 , windings  122 , terminations  140  and the portion of the leads  142 ,  144  that extend between the terminations  140  and the front end  134  of the orifice  132  are encased in a dielectric potting or dielectric casting  148 . The dielectric casting  148  also floods the orifice  132  during the potting process, encasing the leads  142 ,  144  and an end of the sleeve  147  located within. The other end of the sleeve  147  is sealed against the leads  142 ,  144  by the packing gland of the connector  146 . The dielectric casting  148  may be of any suitable potting having appropriate dielectric, thermal and mechanical characteristics. An example is an epoxy such as Epoxylite 230 manufactured by Altana Electrical Insulation of St. Louis Mo. Other candidates for the casting material  148  include electrical resins such as Scotchcast Electrical Resin 251 and general purpose electronic impregnation materials. Some applications may require dielectric castings suitable for elevated temperatures, for example to 200° C. Silicone-based materials may also be appropriate in some applications. 
         [0074]    The housing  12 , including the housing portions  28 ,  30  and spacer ring  32 , as well as the foot structure  90 , are typically formed of a stainless steel. Alternative materials include aluminum and plated 8620 steel. The rotor  18  is also typically formed of a stainless steel, although aluminum may be used. The nozzle ring  26  is typically fabricated from a stainless steel or anodized aluminum. The various o-rings  38 ,  43 ,  78  and  80  provide a gas tight seal between respective mating components. 
         [0075]    In operation, a working fluid  149  such as natural gas, passes through the inlet passage  14  and through nozzle ring  26 , impinging on the continuous impingement surface  20  to drive the rotor  18  and magnetic element  16  about the core assembly  24 . As the rotor  18  is driven by the impinging fluid on the continuous impingement surface  20 , the magnetic element  22  spins about core assembly  24  to generate electricity in a brushless fashion. Approximately 500 watts of alternating current power may be generated. Both the  FIG. 5  and  FIG. 8  embodiments are motivated in this manner. 
         [0076]    The standard pipe threads in the passages  14  and  16  enable the coupling of supply and return lines to the turbine generator  10 . Fluid flowing through the inlet passage  14  impinge on the outer peripheral surface  27  of the nozzle ring  26 , circulates tangentially through the plenum  45  and over the jet orifices  92 . 
         [0077]    The implementation of a pressure regulating device upstream of inlet passage  14  (discussed above but not depicted) may increase the aerodynamic drag of the fluid against the continuous impingement surface  20 , thereby transferring more momentum from the fluid to the rotor  18 . The density ρ of an ideal gas is generally proportional to the pressure P of the gas. For a given mass flow rate mdot of the gas through a passage having a flow cross-section AC, the corresponding velocity U of the gas through the passage is derived from the relationship 
         [0000]        m dot=ρ· U·A   C    
         [0078]    Thus, a reduction in the pressure P generally causes a proportional increase in the velocity U for a fixed mdot and A C . The drag force D exerted on a surface is proportional to the density ρ and the square of the velocity U of the gas, that is: 
         [0000]      D∝ρ·U 2    
         [0000]    The tradeoff between the reduced density ρ and the increased velocity U caused by a reduction of the upstream pressure may result in an increase in the drag force D, which in turn imparts more momentum from the gas to the rotor  18 . An increase in the drag force D results in a more powerful rotation of the rotor  18  and a higher rotational speed. Therefore, where head losses permit, regulation of the pressure to the inlet to a lower pressure without an attendant reduction in mass flow rate should result in enhanced performance of the turbine generator  10 . 
         [0079]    The use of anodized aluminum for a nozzle ring  26  provides a surface that is softer than a stainless steel rotor  18 , thus minimizing damage to the continuous impingement surface  20  of the rotor in the event that the rotor  18  contacts the nozzle ring  26  during operation. 
         [0080]    The extension of the collar portion  52  helps prevent moisture from entering the rotor bearing  54 . If the rotor bearing  54  were mounted flush with the pedestal portion  50 , condensation forming on the face of the pedestal portion  50  could run down and into the rotor bearing  54 . The extension provided by the collar portion  52  causes accumulated condensation on the face of the pedestal portion  50  to flow around the collar portion  52 , preventing the condensation from entering the rotor bearing  54 . 
         [0081]    The dielectric casting  148 , in combination with the sleeve  147 , hermetically seals all current-bearing components that would otherwise come in contact with the flowing fluid. In particular, the connections between the terminations  140  and the leads  142 ,  144 , which may otherwise be in direct contact with the flowing gas, are well isolated by the disclosed potting scheme. The isolation provided by the dielectric casting  148  prevents arcing between the connections and the accompanying damage and reliability problems that arcing poses. Embodiments utilizing the dielectric casting  148  eliminate the formation of carbon build up on the leads due to arcing, and are also deemed explosion proof for natural gas or other hydrocarbon gas applications. 
         [0082]    The sleeve  147 , whether applied to individual leads  142 ,  144  or to the group, is sealed on one end by the potting material  148  and on the other by the packing gland in the connector  146 . Accordingly, it is possible to affect the isolation of the leads  142 ,  144  from fluid of the turbine generator  10  by other means that encase the wire, such as a rubber or silicone dip that coats the wires along an equivalent portion. 
         [0083]    The trapezoidal shape  129  of the armature interface  127  of  FIG. 9  promotes smooth revolution of the rotor  18  at low rotational rates. For generators utilizing magnetic elements  22  and armature interfaces  127  that are rectangular in shape, the rotor  18  may jump from one equilibrium position to another as the magnetic elements  22  cross between segments of the armature interface  127 . This phenomenon, known as “cogging,” is mitigated by the trapezoidal shape  129  because the trapezoid provides a bridging between the armature interface  127  and the discrete, rectangularly-shaped magnetic elements  22 . 
         [0084]    Referring to  FIG. 13 , a generator system  150  including the turbine generator  10  and a gas pre-heater  152  is depicted in an embodiment of the invention. The generator system  150  may further include a gas supply line  154 , a gas return line  156  and a throttling device  158  located between the gas supply line  154  and a pressurized gas source  160 . In the embodiment depicted, the pre-heater  152  may apply energy to a heated segment  162  of the gas supply line  154  for transfer to an incoming gas stream  163 . In other embodiments, the pre-heater  152  may be mounted within the gas supply line  154  to impart energy directly to the incoming gas stream  163 . Hence, energy delivered to the heated segment  162  may be applied externally and transferred through the walls of the gas supply line  154 , or applied internally, within the boundaries of the gas supply line  154 . 
         [0085]    The energy source for the pre-heater  152  may comprise any of several heat sources, including but not limited to a heating element such as heat tape operatively coupled to the heated segment  162 , or a heat exchanger operatively coupled to the heated segment  162  which draws heat from an ancillary process. Other mechanisms that can be utilized to introduce energy into the incoming gas stream  163  include a slip stream used to introduce a hot gas into the incoming gas stream. A controlled vitiation process wherein a fraction of the incoming gas is combusted may also be implemented to add heat. Furthermore, several heat source mechanisms may be combined to provide the pre-heating function at various times, depending on availability. 
         [0086]    In practice, the throttling device  158  may be utilized to reduce the pressure of the pressurized gas source  160  upstream of the turbine generator  10 . The throttling process may cause expansion of the gas across the throttling device  158 , reducing the temperature of the gas. The reduced temperature of the gas limits the expansion of the gas as it enters the turbine generator. The density ρ of the gas increases, but as previously discussed, the increased density ρ will proportionately reduce the velocity U of the gas as it flows across the rotor  18  resulting in a net loss to the drag force D that motivates the rotor  18 . 
         [0087]    A similar reduction in temperature may also occur as the gas passes through the nozzle ring  26 . Depending on the magnitude of the combined step down in pressure, the temperature reduction may be enough to degrade the performance of the generator system  150  to a level that does not meet specification. 
         [0088]    The pre-heater  152  may restore at least partially the temperature of the gas and bring the generator system  150  to within performance specifications. The power or energy imparted by the pre-heater  152  may be a predetermined value, or adjustable to enable trimming, such as in a feedback control scheme. 
         [0089]    The skilled artisan will recognize that the energy addition may be made anywhere upstream of the turbine generator  10  and, aside from non-adiabatic losses, still counter the temperature losses associated with the expansion across the throttling device  158 . 
         [0090]    Referring to  FIG. 14 , an alternative heating arrangement  162  for providing the pre-heating function internal to the natural gas turbine  10  is depicted in an embodiment of the invention. A plurality of passages  163  may be formed in the partition  68  to penetrate the plenum  45 . Each of the passages may be capped on the end opposite the plenum  45  with a feedthrough  164  such as a compression fitting. Only one such passage  163  and feedthrough  164  is depicted in  FIG. 14  and is discussed herein. A heating element  165  such as a cartridge heater may be fed through the feedthrough  164  and passage  163  so that a distal end  166  extends into the plenum  45 . The heating element  165  may comprise a heated portion  167  near the distal end  165 , an unheated portion  168  adjacent the partition  68 , and lead wires  169  that may be terminated within the compartment  84 . 
         [0091]    In operation, the working fluid  149  enters the inlet  14  and courses through the plenum  45  before passing through the nozzle ring  26 . Heat is transferred to the working fluid  149  as it passes over the heated portion  167  of the heating element  165 , thereby raising the temperature and providing the pre-heating function prior to passage through the nozzle ring  26 . The feedthrough  164  provides a gas-tight seal about the passage  163  and the heating element  165 , thereby preserving the integrity and explosion-proof rating criteria of the compartment  84 . 
         [0092]    The unheated portion  168 , which resides in the passage  163 , may be tailored for a substantially lower watt density than the heated portion  167 . One reason for including an unheated portion  168  is because the unheated portion  168  of the heater  165  is in a region of stagnant flow, and may not be adequately cooled if the unheated portion  168  were subject to the same watt density as the heated portion  167 . An untailored heating element (i.e. one with a uniform watt density across its entire length) may fail because of overheating of the portion within the passage  163 , or the untailored heating element may have to be operated at a reduced capacity to prevent such failure, thereby delivering inadequate heat to the working fluid Another reason to configure the heating element  165  with an unheated portion  168  is to limit unnecessary heating of the partition  68  and preserve the cooling capabilities that the partition  68  provides, which is described below. 
         [0093]    Referring to  FIGS. 15 through 17 , various embodiments of a turbine generator  170  are depicted as including a control board  172 . The control board  172  may include heat-generating components  173  for operations such as switching or power relay or other control and monitoring functions, including but not limited to buck converters, silicon-controlled rectifiers (SCRs), RS  485  interfaces, and assorted instrumentation to control or condition the electrical output and/or operation of the turbine generator  170 . 
         [0094]    In the embodiments of  FIG. 15 , the control board  172  is mounted on a back surface  174  of the partition  68  of the back housing portion  30 , within compartment  84 , using fasteners  176  and spacers  178 . The spacers  178  may provide a gap  180 . The gap  180  may be bridged between selected heat-generating components  173  and the back surface  174  with heat conducting bridges  181  comprising a heat conducting medium such as aluminum or copper. The heat conducting bridges may be formed on a single plate that is coupled to the back surface  174 , with varying thickness to accommodate varying heights of the heat-generating components relative to the control board  172 . Individual heat conducting bridges  181  attached to individual heat generating components  173  may also be used. A heat conductive paste  183  may be disposed between the heat conducting bridges  181  and the back surface  174  and heat-generating components  173 , respectively. 
         [0095]    In other embodiments, the gap  180  that may be left open ( FIG. 16 ) or may be filled with an interstitial material  182  ( FIG. 17 ). The interstitial material  182  may be in the form of a bonding or cement that provides intimate contact with both the control board  172  and the back surface  174 . The interstitial material  182  may possess dielectric properties as appropriate to prevent shorting between the heat-generating components  173  or other components of the control board  172 , as well as electrical isolation between these components and the back surface  174 . In certain embodiments, the open gap  180  may include a finned structure  185  coupled to the board  172  ( FIG. 16   a ). 
         [0096]    A cover or lid  184  may be placed over the back housing to form a enclosure  186  with compartment  84 . A seal  188  such as a gasket or o-ring may be secured between the lid  184  and the back housing portion  30  to form a substantially air tight enclosure  186 . 
         [0097]    In operation, a byproduct of the control board  172  may be a substantial amount of heat generation within the various heat-generating components  173 . Certain embodiments of the present invention provide a synergistic way to cool the heat-generating components  173 . As discussed above, gas entering the turbine generator  170  undergoes an expansion, potentially at the nozzle ring  26  as well as upstream such as with throttling device  158  ( FIG. 13 ). The gas is in intimate contact with the partition  68  as it courses through the annular cavity  56  and the outlet passages  16 , and may cause the partition  68  to operate at a temperature significantly below ambient temperatures. 
         [0098]    The partition  68  may thereby act to cool the heat-generating components  173 , via conductive coupling ( FIGS. 15 and 17 ) or convective coupling ( FIGS. 16 and 16   a ) to the back surface  174  of the partition  68 . The heat conductive paste  183 , when utilized, enhances the conductive heat transfer by reducing the contact resistance between the heat conducting bridges  181  and the back surface  174  and heat-generating components  173 , respectively (e.g.  FIG. 15 ). 
         [0099]    In  FIG. 16 , a natural convection loop  187  may be established and driven between the cool back surface  174  and the opposing face of the warmer control board  172 . When utilized, the finned structure  185  ( FIG. 16   a ) enhances the effect of convective cooling by increasing the effective heat transfer area. Fins may also be formed or disposed on the back surface  174  (not depicted) to further enhance the heat exchange between the heat-generating components  173  and the partition  68 . 
         [0100]    Radiative heat transfer to the back surface  174  of the partition  68  is also generally present, and may be enhanced by providing a coating of high emissivity on either the back surface  174  or the surfaces adjacent the back surface  174  (e.g. the heat emitting components  173  of  FIG. 15  or the control board  172  of  FIG. 16 , or the finned structure  185  of  FIG. 16   a ) to further enhance the cooling of the heat emitting components  173 . The finned structure  185 , as well as any fins formed or disposed on the back surface  174 , may further enhance the radiative coupling by increasing the apparent emissivity of the radiative surface. 
         [0101]    In certain embodiments of  FIG. 17 , the interstitial material  182  may provide sufficient bonding between the control board  172  and the back surface  174  of the partition  68  to forego the use of fasteners. The dielectric requirements of the interstitial material  182  may manifest a lower thermal conductivity than the highly conductive materials available for the heat conducting bridges  181 , the combination of a larger surface area and a smaller dimension for the gap  180  may still provide sufficient cooling of the heat conducting components  173 . 
         [0102]    By virtue of such cooling mechanisms being provided by the expanded gas in contact with the partition  68 , the compartment  84  may still be maintained as the enclosure  186  without encountering excessive temperatures therein. The capability of maintaining the enclosure  186  enables the gas turbine generator  170  to retain certain safety ratings, such as a Class 1, Division 1 or Division 2 certification from Underwriters Laboratories or equivalent. 
         [0103]    Referring to  FIG. 18 , the front housing portion  28  is depicted in an embodiment of the invention. When the gas turbine  10  is in an upright (i.e. operational) position, the central axis  49  of the gas turbine  10  is in a horizontal orientation, thereby defining a lower extremity  85  for each of the annular cavities  46  and  56 , respectively. The outlet passages  16  are formed along axes  87  that are substantially horizontal when the gas turbine generator  10  is in an upright position, as depicted in  FIG. 19 . The outlet passages  16  penetrate the annular cavities  46  and  56  near their respective lower extremities  85 . 
         [0104]    Functionally, the orientation of the outlet passages  16  enable active purging of condensates from the gas turbine  10 . Another potential consequence of the expansion of the working fluid  149  (discussed above) is the formation of condensation as the working fluid  149  cools. The location and horizontal orientation of the outlet passages  16  enable condensation to be cleared from the unit as a matter of course. Condensation that flows to the lower extremities  85  is propelled out of the annular cavities  46  and  56  and through the passages by the flowing gas. Even where flow rates or pressure differentials are marginal, the configuration enables condensate to drain hydrostatically out of the outlet passages  16 . 
         [0105]    Referring to  FIG. 19 , an electrical schematic of an operating circuit  200  of a turbine generator is depicted in an embodiment of the invention. A trio of windings  202   a ,  202   b  and  202   c  contained within the core assembly  24  are connected in a 3-phase wye configuration and terminating at a plurality of electrical outputs  204 . The operating circuit  200  is depicted as powering a load  206 . The load  206  may be any device that can operate off the power provided by the turbine generator, with or without attendant conditioning circuitry. Examples include a battery, a lamp, a video camera or a three-phase motor. 
         [0106]    The operating circuit  200  may include a multi-pole switch  208  that alternates between a load position (depicted) and a no-load position. The multi-pole switch  208  may be cycled between the load and the no-load position. 
         [0107]    Functionally, cycling multi-pole switch  208  between the load and no-load positions may increase the average speed of the rotor  18 . When current is flowing through the windings (i.e. multi-pole switch  208  is in the load position), the rotor  18  experiences a torque load or resistance to rotational movement due to the electromotive force that is generated. When current is absent (i.e. the multi-pole switch  208  is in the no-load position), the rotor  18  rotates more freely in the absence of the electromotive force. Switching multi-pole switch  208  between the load and no-load positions cyclically allows the rotor  18  to speed up during the off cycle and gather additional angular momentum which in turn produces more electromotive force during initial stages of the on cycle immediately following the off cycle. The on/off duty of the cycle may be tailored to produce a desired average operating speed of the turbine generator  10 . A range of on-duty cycles from 70% to 95% is exemplary, but not limiting. For example, the on/off duty cycle may comprise approximately 60-sec. of on duty and approximately 10-sec. of off duty. 
         [0108]    The operating circuit  200  may also include a resistive load  210 , depicted by the resistive elements  210   a ,  210   b  and  210   c  configured in a delta configuration. The windings  202   a - 202   c  may be connected to the resistive load  210  through a multi-pole switch  212  that switches current away from the load  206  to the resistive elements  210   a - 210   c.    
         [0109]    Functionally, switching to the resistive load  210  may be tailored to increase the torque load experienced by the rotor  18 , thereby causing the resistive load  210  to function as a dynamic brake. The torque load is a function of the current generated, which in turn is a function of the rotational speed of the rotor; hence the functional description “dynamic brake.” The resistive load  210  may be tailored to optimize the braking torque load. 
         [0110]    Alternatively, the multi-pole switch  212  may be directed to a shorting bridge (not depicted). The shorting bridge may be affected by replacing resistive elements  210   a  and  210   b  with an electrical short and leaving the connections to resistive element  210   c  open. 
         [0111]    In yet another alternative, the multi-pole switch  212  may divert current to a battery for charging (not depicted). The load imposed by the battery may also affect dynamic braking. 
         [0112]    In either configuration (resistive load  210  or a short bridge or charging battery), current through the windings may increase compared to normal loads, thereby increasing the joule heating effect in the windings. Certain embodiments can tolerate this effect by virtue of the core  24  being immersed in the cooling flow of the working fluid  149 . Accordingly, the resistive elements  210   a - 210   c  or shorting bridge elements may be encased within the dielectric casting  148  to provide cooling of these elements. Alternatively, the resistive elements  210   a - 210   c  or shorting bridge elements may be contained within the enclosure  186  and coupled to the back surface  174  of the partition  68  for the transfer of heat in a manner similar to that described in connection with  FIGS. 15 through 17 . 
         [0113]    The invention may be embodied in other specific and unmentioned forms, apparent to the skilled artisan, without departing from the spirit or essential attributes thereof, and it is therefore asserted that the foregoing embodiments are in all respects illustrative and not to be construed as limiting. 
         [0114]    References to relative terms such as upper and lower, front and back, left and right, or the like, are intended for convenience of description and are not contemplated to limit the present invention, or its components, to any specific orientation. All dimensions depicted in the figures may vary with a potential design and the intended use of a specific embodiment of this invention without departing from the scope thereof. 
         [0115]    Each of the additional figures and methods disclosed herein may be used separately, or in conjunction with other features and methods, to provide improved systems and methods for making and using the same. Therefore, combinations of features and methods disclosed herein may not be necessary to practice the invention in its broadest sense and are instead disclosed merely to particularly describe representative and preferred embodiments of the instant invention. 
         [0116]    For purposes of interpreting the claims for the present invention, it is expressly intended that the provisions of Section 112, sixth paragraph of 35 U.S.C. are not to be invoked unless the specific terms “means for” or “step for” are recited in a claim.