Abstract:
A cooling gas ventilation circuit for an endwinding of a rotary machine having a rotor and a plurality of coils seated in radial slots provided in the rotor, the coils each comprising a plurality of radially stacked turns, the turns having radial passages therein, the coils extending beyond a pole face of the rotor to form an endwinding; a substantially cylindrical baffle ring covering radially innermost turns of the plurality of coils in the endwinding, the baffle ring having a plurality of holes therein aligned with the radial passages; and wherein the radial passages communicate with cavities between the coils in the endwinding.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to the rotor windings of a dynamo-electric machine, and particularly, to endwinding ventilation schemes for machines with concentric rotor windings. 
     The rotors in large gas cooled dynamo-electric machines have a rotor body which is typically made from a machined high strength solid iron forging. Axially extending radial slots are machined into the outer periphery of the rotor body at specific circumferential locations to accommodate the rotor winding. The rotor winding in this type of machine typically consists of a number of complete coils, each having many field turns of copper conductors. The coils are seated in the radial slots in a concentric pattern with, for example, two such concentric patterns in a two-pole rotor. The coils are supported in the rotor body slots against centrifugal forces by metallic wedges which bear against machined dovetail surfaces in each slot. The regions of the rotor winding coils which extend beyond the ends (or pole faces) of the main rotor body are called “endwindings” and are supported against centrifugal forces by high strength steel retaining rings. The inboard end of each retaining ring is typically shrunk onto a machined surface at the end of the rotor body. The outboard end of each retaining ring is typically shrunk onto a circular shaped steel member called a centering ring. A section of the rotor shaft forging which is located underneath the rotor endwindings is referred to as the spindle. 
     Thus, the rotor winding can be separated into two major regions, the rotor body region within the radial slots in the rotor, and the rotor endwinding region that extends beyond the pole face, radially spaced from the rotor spindle. This invention relates primarily to ventilation schemes for the rotor endwinding region. 
     In order to reduce costs and machine size, rotating machine manufacturers are continuously seeking methods of obtaining more power output from a given volume of machine. Rotor winding thermal limitations are a major obstacle toward achieving this goal. Accordingly, more effective rotor winding cooling schemes facilitate the manufacturer&#39;s ability to achieve the desired higher power output. 
     Several rotor endwinding cooling approaches have been used in the past. Most of these approaches utilize longitudinally grooved copper windings where cooling gas enters the field turns from an open cavity via inlet ports at the sides of the turns, and then flows longitudinally along the grooves to discharge locations which are typically either chimneys in the rotor body or discrete baffled discharge zones under and around the endwinding. The gas in these baffled zones is typically discharged either to the air gap (i.e., the gap between the rotor and stator) via machine slots in the pole face, or to the area outside of the centering ring via openings in the centering ring. Some schemes utilize discharges through radial holes in the retaining rings. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention provides a new direct gas cooled rotor endwinding ventilation scheme for machines with concentric rotor windings. A typical application is for round rotor turbine driven generators. 
     The present invention utilizes a non-metallic baffle ring on each end of the machine, completely covering the radially inner surfaces of the respective rotor endwindings and segregating the rotor body ventilation regions of the windings from the rotor endwinding ventilation regions of the windings. Since the endwindings at opposite ends of the rotor are identical, only one will be described herein. 
     Carefully located radial holes are formed in the baffle ring that allow the entrance of cooling gas through the baffle ring to the rotor endwinding. Cooling gas flows radially through the holes in the baffle ring to corresponding in-line radial vent holes or ducts forming radial passages in the copper field turns of the rotor endwinding coils. A selected number (or all) of these turns have lateral exit ports machined therein. In one embodiment of the invention, the lateral exit ports extend from the radial passage to the outer edge of the turn on one or both sides of the turn. The rotor&#39;s pumping head drives the flow of gas through the cooling paths. Cooling gas thus flows through the radial passages and lateral ports and exits into longitudinal cavities formed between the coils on one or both sides of the coil of interest. 
     In another embodiment, some or all of the field turns have longitudinal grooves that originate at the radial passages in the turns. These grooves run along the turns (for uniform or different lengths) and terminate at lateral exit ports machined in the turns from the longitudinal grooves to the outer edge of the turns on one or both sides of the turns. Cooling gas can thus flow through the radial passages in the field turns, then longitudinally along the grooves to the lateral exit ports where it discharges into the longitudinal cavities formed between the coils (on one or both sides of the coils). 
     In both embodiments, vent holes or slots are machined in the steel teeth at the end of the rotor body. Thus, cooling gas discharged from the coil can now flow via the longitudinal cavities through the tooth vent slots and discharge into the machine&#39;s air gap. In addition, one or more of the coils may have turns with longitudinal grooves extending into the rotor body to permit an alternative gas discharge circuit where the cooling gas exits via radial chimneys in the windings themselves, along and within the rotor body. 
     Any inter-coil spacer blocks in the longitudinal cavities (used to maintain adjacent coils in predetermined spaced relationship) that are obstructing cooling flow can be provided with vent passages that allow the cooling gas to flow through the spacer blocks. Another alternative is to bypass the spacer blocks via internal grooves machined along the field turns to suitable exit ports on the far side of the spacer block. Other bypass schemes may be devised as well. One such example is to design by-pass passages into the baffle ring design. 
     In still another variation, to further increase the cooling gas discharge area in the endwinding, the baffle ring may be modified to provide an additional axial gas flow passage to distribute gas to slots machined in the rotor pole faces or to radial holes in the centering ring via the longitudinal cavity in the center of the coils. In other words, additional holes in the baffle ring are aligned with the space at the center of a group of concentrically arranged coils, and one or more discharge slots are provided in the pole face, opening into the longitudinal cavity and discharging into the air gap. Axially extending baffle plates are used to channel cooling gas axially into the area of the modified baffle ring holes so that gas flowing radially inwardly from the longitudinal cavities through the discharge holes in the sleeve-like baffle ring, flows axially between the baffle plates and discharges into the pole face discharge slots or into the discharge holes in the centering ring, or both. 
     With the radial/lateral rotor endwinding ventilation schemes in accordance with this invention, many new ventilation arrangements are possible, such as using multiple side-by-side ducts, multiple staggered ducts, and diagonal flow passages, which then also opens up the possibility for counterflow schemes that reduce and provide more uniform rotor endwinding temperatures. The cooling schemes disclosed herein also make full use of the space on each side of the coil of interest as ventilating gas flowpaths, and for convection cooling of the outer surfaces of the field turns of the coils. 
     With the rotor endwinding ventilation schemes in accordance with the invention, several advantages may be realized: 
     a) Improved ventilation via direct gas cooling in which hot spot and average winding temperatures are reduced; 
     b) More uniform temperatures throughout the endwinding; 
     c) Ability to provide many short length cooling passages in direct contact with the copper field turns, thereby limiting cooling gas temperature rise; 
     d) Ability to devise many ventilation patterns including counterflow ventilation schemes; 
     e) Relatively simple manufacturing complexity compared to other schemes; and 
     f) Reduced machine volume for a given output rating. 
     In its broadest aspects, therefore, the present invention relates to a cooling gas ventilation circuit for an endwinding of a rotary machine having a rotor, and a plurality of coils seated in radial slots provided in the rotor, the coils each comprising a plurality of radially stacked turns, the turns having radial passages therein, the coils extending beyond a pole face of the rotor to form an endwinding; a substantially cylindrical baffle ring covering radially innermost turns of the plurality of coils in the endwinding, the baffle ring having a plurality of holes therein aligned with the radial passages; and wherein the radial passages communicate with cavities between the coils in the endwinding. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial radial section of one end of a machine rotor; 
     FIG. 2 is a partial top plan view, partially sectioned, of the coils of a rotor endwinding at one end of the rotor; 
     FIG. 3 is a partial side section taken along the line  3 — 3  of FIG. 2; 
     FIG. 4 is a partial plan view of an endwinding turn in accordance with an alternative embodiment of the invention, showing multiple rows of radial ducts in line; 
     FIG. 5 is a partial plan view of an endwinding turn in accordance with still another alternative embodiment of the invention, showing multiple rows of radial ducts in line; 
     FIGS. 6 and 7 are partial plan views, partially sectioned, of rotor endwinding turns illustrating alternative arrangements for bypassing flow around spacer blocks; 
     FIG. 8 shows still another alternative similar to FIGS. 6 and 7 but wherein coolant flow passes through the spacer block; 
     FIG. 9 is a partial side section through a stack of turns in the endwinding portion of a coil illustrating a diagonal ventilation pattern achieved by offsetting radial ducts in the turns; 
     FIG. 10 is a partial side section through a stack of turns in the endwinding portion of a coil illustrating a diagonal/counterflow scheme; 
     FIG. 11 is a partial plan view of a turn in the stack shown in FIG. 10; 
     FIG. 12 is a partial radial section through a modified end of a machine rotor; 
     FIG. 13 is a top plan view, partially sectioned, of a two-pole rotor incorporating the endwinding ventilation scheme of FIG. 12; and 
     FIG. 14 is a simplified end view of the rotor endwinding shown in FIGS. 12 and 13, but also illustrating the lower half of the rotor; 
     FIG. 15 is a partial top plan view, partially sectioned, of the coils of a rotor endwinding at one end of a rotor in accordance with a second exemplary embodiment of the invention; 
     FIG. 16 is a partial side section taken along the line  16 — 16  of FIG. 15; 
     FIG. 17 is a partial plan view, partially sectioned, of rotor endwinding turns illustrating a bypass flow arrangement around a spacer block consistent with the second embodiment of the invention; 
     FIG. 18 is a partial plan view, partially sectioned, of rotor endwinding turns illustrating an alternative bypass flow arrangement consistent with the second exemplary embodiment of the invention; 
     FIG. 19 is a partial plan view illustrating multiple rows of radial passages in an endwinding turn consistent with the second embodiment of the invention; 
     FIG. 20 is a partial plan view of a turn illustrating staggered rows of radial passages consistent with the second exemplary embodiment of the invention; 
     FIG. 21 is a partial side section through a stack of turns in an endwinding in accordance with the second embodiment of the invention, but with the length of the grooves formed within the individual turns having varying lengths; 
     FIG. 22 is a partial plan view of a turn illustrating a counterflow scheme consistent with the second exemplary embodiment of the invention; 
     FIG. 23 is a partial plan view of a stack of turns illustrating counterflow paths in opposite directions on alternate turns; and 
     FIG. 24 is a partial plan view of a turn consistent with a second exemplary embodiment of the invention, but wherein a pair of longitudinal grooves extend from a single radial passage. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, one end of a rotor body  10  is illustrated with a rotor endwinding  12  extending beyond one end of the rotor body. The rotor endwinding includes the end region of a number of complete coils  14 ,  16 ,  18  and  20  in a concentric, generally rectangular configuration. For a two pole rotor, two such concentric sets of coils are arranged on opposite sides of the rotor. The invention is applicable, however, to other rotor configurations as well. Each coil includes many field turns  21  of copper conductors in a stacked configuration. This invention can be applied to windings where the individual turns are made up of multiple layers of conductors as well as just single conductors. These coils are nested within the radial slots  22  machined into the outer periphery of the rotor body, with the endwindings extending axially beyond the rotor body at both ends of the machine in conventional fashion. A spindle portion  24  of the rotor extends in an axial direction, radially inward of the endwinding. The coils  14 ,  16 ,  18  and  20  are supported in the slots  22  of the rotor body against centrifugal forces by metallic wedges (not shown) which bear against machined dovetail surfaces (not shown) in each rotor coil slot. The endwinding is supported against centrifugal forces by a high strength, annular steel retaining ring  26 . The inboard end of each retaining ring is shrunk onto a machined surface  28  of the rotor body, while the outboard end of the retaining ring  26  is shrunk onto a circular shaped steel member or centering ring  30 . The rotor winding is electrically insulated from the rotor body and retaining ring via appropriate ground insulation. In addition, the turns which make up the coils of the rotor winding are electrically insulated against each other via appropriate turn-to-turn insulation. For the sake of simplicity, the insulation is not shown in the drawings. Note also that in FIG. 2, one half of the endwinding  12  is shown in simplified form. Spacer blocks that are normally present in the endwinding to separate the coils  14 ,  16 ,  18  and  20  have been eliminated for clarity. 
     A cylindrical sleeve-like baffle ring  32  is installed underneath the concentric rotor endwinding  12  to separate the endwinding ventilation section from the rotor body ventilation section of the rotor. The rotor endwinding is thus completely enclosed by the rotor body  10 , the retaining ring  26 , the centering ring  30 , and the baffle ring  32 . The baffle ring  32  is preferably constructed of non-metallic material and may be a full 360° ring, or may be formed as several arcuate segments with overlapping joints. 
     The baffle ring  32  may be captured in grooves  34  and  36  machined in the end of the rotor body  10  and the centering ring  30 , but other assembly and mounting techniques may be employed. For example, the baffle ring  32  could be supported by a plurality of spokes (four preferred) radially extending between the spindle  24  and the baffle ring  32  at 90° intervals, or by any other suitable means as would be appreciated by one of ordinary skill in the art. 
     The baffle ring  32  has oblong holes  40  (FIG. 1) machined or molded therein at specific locations. The purpose of these holes is to feed cooling gas which flows axially between the inside diameter of the baffle ring  32  and the rotor spindle  24  into specifically positioned radial passages  42  in the field turns of the rotor endwinding coils, best seen in FIGS. 2 and 3. Passages  42  are formed by punching or machining vertically aligned holes or ducts into the copper turns  21 . In this first exemplary embodiment of the invention, gas exit ports or grooves  44 ,  46  are machined on each lateral side of the radial passages  42  in some or all of the turns to allow cooling gas to exit from the radial passages  42  into longitudinal cavities or grooves  48 ,  49  and  50  between the coils  14  and  16 ,  16  and  18 , and  18  and  20 , respectively. 
     Curved vent slots  52  (FIGS. 1 and 2) are machined in the rotor body “teeth” (the solid portions between the radial slots  22  at the radial edge of the rotor body, also referred to herein as the pole face  23 ). This allows the cooling gas to flow from the longitudinal cavities  48 ,  49  and  50  between the coils into the slots  52  in the rotor body and then into the annular air gap between the machine&#39;s stator (not shown) and the rotor body  10 . It will be appreciated that the curved vent slots  52  may be replaced by combinations of axially and radially extending holes. Some or all of the turns in coils  14 ,  16 ,  18  and  20  may also have longitudinal grooves  53  extending from the radial holes  42  closest to the pole face to radial chimneys  55  formed in the turns within the rotor body  10 . 
     Returning to FIG. 1, in one possible cooling scheme, some of the cooling gas flows axially within a sub-slot  57  in the rotor body that, in turn, communicates with additional radial chimneys (not shown) formed in the coils at axially spaced locations along the rotor body. Note that chimney  55  does not connect with the sub-slot  57 , but the chimneys axially inboard of chimney  55  do connect to the sub-slot  57 . Chimney  55  communicates only with the grooves  53  in the field turns of the coils, i.e., with the endwinding ventilation scheme. 
     The flow of cooling gas into the vent slots or holes  52 , grooves  53  and chimneys  55  results in the cooling of the transition section between the endwinding  12  and the rotor body  10 . It should be appreciated that the cooling of the rotor body itself can be achieved by any compatible method such as radial cooling (or axial/radial cooling) via cooling gas fed from sub-slots (such as sub-slot  57 ) machined under the main coil slots in the rotor body, or any gap pickup body cooling scheme where cooling gas enters and discharges from the machine&#39;s air gap. 
     An additional benefit of the above described ventilation scheme is that cooling gas which flows in the longitudinal passages or cavities  48 ,  49  and  50  between the coils  14 ,  16 ,  18  and  20  will also help cool by convection the outer exposed surfaces of the turns  21  which make up the coils. 
     When the machine is running at rated speed, the pumping head of the machine&#39;s rotor drives the cooling gas flow through the passages. The cooling gas flow distribution within the radial passages  42  can be controlled via sizing of the holes  40 , sizing of the punched holes in the turns which form the radial passages  42 , sizing of the lateral exit ports  44  and  46 , and the radial/axial alignment of the turns to insure that each turn in the section of the rotor endwinding of interest is ventilated properly. Multiple radial passage configurations are also possible. For example, two or more side-by-side radial passages can be employed in one or more of the coils, with appropriate modification to the baffle ring  32 . In FIG. 4, side-by-side radial passages  58 ,  60  are located at axially spaced locations along the length of the coil turns (one indicated at  62 ). Lateral ducts or grooves  64  extend from passages  58  to one side of the turns, while lateral ducts or grooves  66  extend from passages  60  on the other side of the turns. FIG. 5 illustrates a similar arrangement but where the radial passages  68 ,  70  are staggered or offset in the axial direction. 
     With reference to FIG. 9, a diagonal flow passage is formed by offsetting the holes  72  in each successive radial turn  74 , the lowermost (or radially innermost) hole  72  communicating with the oblong hole  76  in the baffle ring  78 . Lateral ducts or grooves  80  extend to the edges of the turns as in FIG.  2 . 
     Counterflow ventilation schemes are also contemplated. For example, in a given region of the coil, cooling gas can flow in separate passages in opposite directions with opposite inlet and exit locations. A side-by-side staggered radial duct arrangement as illustrated in FIG. 5 may be used to establish such a counterflow scheme. Thus, with reference to FIGS. 10 and 11, axially offset holes  82  in the stacked turns communicating with baffle ring hole  84  on the near side of turns  86  will establish a left-to-right diagonal flow pattern as viewed in FIG.  10 . An oppositely staggered array of holes  88  on the opposite or far side of the turns  86  (see FIG. 11) communicating with baffle ring hole  89  will establish a second diagonal passage to thereby provide a counterflow path from right-to-left as also viewed in FIG.  10 . This configuration provides lower and more uniform temperatures in the rotor endwinding as compared to non-counterflow schemes. 
     With reference now to FIG. 6, any obstacle in the cooling gas flow path, such as a rotor endwinding spacer blocks  90 ,  92  between adjacent endwinding coils (one shown at  94 ) can be bypassed via one or more grooves  96  machined along one or more adjacent field turns from the radial passage  98  to suitable exit ports  100 ,  102  on the far side of the spacer block, either at the next radial duct  104  (FIG. 6) or via separate exit ports  106 ,  108  adjacent the next radial duct  110  (FIG.  7 ). Alternatively, a hole  112  can be formed in the spacer block  114  to allow the gas to flow through it, as shown in FIG.  8 . Another possibility is to utilize spacer block bypass schemes via bypass pockets in the baffle ring design. 
     With reference now to FIGS. 12-14, a ventilation scheme is illustrated for applications where additional cooling gas discharge area may be required in the rotor endwinding region. An arrangement for two-pole machines is shown, but the concept can be extended to machines with more than two poles. Here, the baffle ring  116  is modified to include additional holes  118  opening into a longitudinal cavity  120  or passage in the center of the concentric coil arrangement. The center cavity is further defined by radial plates  122 ,  124  between the baffle ring  116  and the spindle  126  and extending axially between the rotor body or pole face  128  and a semi-annular end cover  130  (FIG. 12) located radially between the spindle  126  and the centering ring  132 . As will be appreciated from FIGS. 12 and 13, the holes  118  in the baffle ring  116  are located to open into the spaces between the coils  134 ,  136 ,  138 ,  140  and  141 , and between the plates  122 ,  124 . 
     In this arrangement, cooling gas exiting the ports in the turns of the coils passes through the radial holes  118  in a radially inward direction from the spaces or cavities between the coils into the axial passage defined by plates  122 ,  124  below the baffle ring  116 . The cooling gas can then flow axially in either direction, and can be discharged either into the air gap via vent slots  142 ,  144  machined into the pole face  128 , or into the outside diameter of the centering ring  132  via discharge holes  146 ,  148  forming radial chimneys in the centering ring. Note that FIG. 14 illustrates the position of additional baffle plates  150 ,  152  for the opposite endwinding in a two pole rotor. 
     The centering ring discharge and pole face slot discharge scheme can be used independently or together, and can be combined with the ventilation schemes previously described to create as much discharge area as practical. The pole face discharge should work well for forward-flow and reverse-flow ventilated machines, while the centering ring discharge works best with forward-flow ventilated machines. The schemes can be used for machines with more than two poles by adding additional radial plates for each pole. 
     Turning now to FIGS. 15-24, a second embodiment of the invention is illustrated where a certain number of turns in each of the coils have longitudinal grooves of any desired lengths that originate at the radial passages in the field turns. Specifically, and with reference to FIGS. 15 and 16, a baffle ring  156  is again formed with oblong holes  158  which are radially aligned with radial passages  160  that are established by holes formed in the various turns of one or more of the coils  162 ,  164 ,  166  and  168 . In the figure, the uppermost surface of selected (or all) turns  170  is formed with a longitudinal groove  172  which communicates at one end with each radial passage  160 . The longitudinal grooves  172  can be machined in either side of the turn and, for multiple conductor-per-turn windings, the grooves can be machined on the overlapping surfaces of mating conductors. The opposite end of the groove  172  communicates with lateral exit ports  174 ,  176  machined in the turn and extending from the longitudinal groove  172  to the outer edges of the turn, on both sides of the turn. Cooling gas can now flow through the grooves  172  and discharge through the lateral exit ports  174 ,  176  into the longitudinal cavities or spaces  178 ,  180 ,  182  and  184  formed between the coils on both sides of the coil of interest. It will be appreciated, however, that exit ports on only one side of the turn is also within the scope of the invention. As in the previously described embodiment, vent slots  186  (or holes) are machined in the rotor body to allow the cooling gas to flow from the longitudinal cavities  178 ,  180 ,  182  and  184  between the coils into the slots  186  and then into the air gap of the machine. As also apparent from FIG.  15 , longitudinal grooves  188  can also be formed in the turns at locations close to the pole face of the rotor, with the grooves extending axially to radial discharge holes or chimneys  190  formed within the turns seated within the rotor slots. 
     FIGS. 17 and 18 illustrate additional bypass arrangements for spacer blocks. In FIG. 17, a longitudinal groove  192  is formed in the turns on either side of a spacer block  194  with lateral exit ports  196 ,  198  located on the far side of the spacer block. This allows cooling gas from radial passages  200  to bypass block  194  before entering the space  201  between the coils, downstream of the block. FIG. 18 illustrates an alternative arrangement where the lateral exit ports  202 ,  204  are located upstream of the spacer block, but the spacer block itself is formed with a through passage  206  to allow free flow of the cooling gas. Another possibility is to utilize spacer block bypass schemes via bypass pockets in the baffle ring design. 
     Multiple radial duct/groove configurations are also possible with this second embodiment of the invention, as illustrated in FIGS. 19 and 20. In the former, side-by-side longitudinally extending grooves  208  are paired with radial passages  210 , with lateral exit ports  212  at opposite ends of the longitudinal grooves. This pattern can be repeated along the length of the turns as necessary to provide the desired cooling. FIG. 20 illustrates a staggered arrangement where radial passages  214  and longitudinal grooves  216  have single outlet exit ports  218  on one side of the turn, while a staggered array of radial passages  220 , longitudinal grooves  222  and exit ports  224  extend along the opposite side of the turn. 
     It is also possible to provide a diagonal exit port array as illustrated in FIG.  21 . In this figure, the oblong hole  226  in baffle plate  228  communicates with a radial passage  230  formed by holes in the stacked turns  232 . Longitudinal grooves  234  extend from the radial passage  230  to exit ports (indicated schematically at  236 ). Note that the axial extent of the longitudinal grooves in successive turns increases to create a staggered discharge configuration through the stack of turns. It should be appreciated that other than diagonal exit port arrays are possible by simply varying the groove lengths within the conductors. In this way, all the turns can be effectively ventilated. 
     Counterflow schemes may be employed with this embodiment as well, and examples are illustrated in FIGS. 22 and 23. In FIG. 22, staggered radial passages feed longitudinal grooves  242 ,  246  and exit ports  248 ,  250  in which the cooling gas flow is in opposite directions. A similar arrangement may be implemented with side-by-side radial passages. Another example is shown in FIG. 23 in which axially spaced radial passages  251 ,  252  supply cooling gas to longitudinal grooves in alternate turns. Thus, the longitudinal groove  254  in the top turn is fed with cooling gas from the first radial passage  251 , and the cooling gas flows from left to right. The longitudinal groove in the lower or bottom turn is fed with cooling gas from the second radial duct  252 , and the cooling gas flows from right to left. Another possibility is to feed a pair of grooves  258 ,  260  from a single radial passage  262  as shown in FIG.  24 . 
     It should also be pointed out that the mechanism by which cooling gas discharge areas can be increased as described in connection with FIGS. 12-14 may also be combined with the ventilation schemes described above in connection with FIGS. 15-24. 
     The above described ventilation schemes can be employed on any machine with a concentric wound field winding of suitable turn dimensions with square corner and/or C-shaped corner construction, and can most readily be applied to two pole and four pole round rotor turbine driven generators. The cooling gas can be any suitable gas but is most typically air or hydrogen. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.