Abstract:
A cooling gas ventilation circuit is provided 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 comprise a plurality of radially stacked turns, the coils extending beyond a pole face of the rotor to form an endwinding with longitudinal cavities between the coils. A substantially cylindrical baffle ring covers the radially innermost turns of the plurality of coils in the endwinding, and has a plurality of holes therein aligned with at least one of the longitudinal cavities between the coils.

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 or circuits 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. The holes are located so as to communicate with the longitudinal inlet cavities between certain of the coils in the endwinding region. As a result, cooling gas flows radially through the holes in the baffle ring and into longitudinal inlet cavities. It is to be noted that for any given coil of interest, a longitudinal inlet cavity is located on only one side of that coil in the rotor endwinding. 
     A certain number of the copper field turns of the coil of interest have longitudinal grooves machined along the length of the turns. The grooves are of various lengths and can be of different sizes, i.e., cross sections. At the beginning or upstream end of each groove, a lateral groove inlet port is machined in the turn between the groove and the side of the turn adjacent the longitudinal inlet cavity. At the downstream end of the groove, a lateral groove exit port is machined in the turn from the groove to the outer edge of the turn on the opposite side of the turn. Cooling gas can thus flow from the longitudinal inlet cavity into the copper turns via the groove inlet ports, then through the longitudinal grooves and finally through the lateral groove exit ports where the gas discharges into a longitudinal outlet cavity on the opposite side of the coil of interest. 
     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 windings 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 example is to design bypass 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 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. 
     Accordingly, in its broader aspects, the 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 coils extending beyond a pole face of the rotor to form an endwinding with longitudinal cavities between the coils; 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 at least one of the longitudinal cavities between the coils. 
    
    
     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 through one of the coils in the rotor endwinding shown in FIG. 2; 
     FIGS. 4 and 5 are partial plan views, partially sectioned, of rotor endwinding turns illustrating alternative arrangements for bypassing flow around or through spacer blocks; 
     FIG. 6 is a partial plan view of an endwinding turn illustrating multiple side-by-side flow paths; 
     FIG. 7 is a partial plan view of an endwinding turn illustrating staggered flow paths in vertically stacked turns; 
     FIG. 8 is a partial side section through several turns in a coil, illustrating a ventilation flow path in accordance with an alternative embodiment of the invention; 
     FIG. 9 is a partial plan view illustrating a counterflow ventilation scheme in vertically stacked turns; 
     FIG. 10 is a partial radial section through a modified end of a machine rotor; 
     FIG. 11 is a top plan view, partially sectioned, of a two pole rotor incorporating the endwinding ventilation scheme of FIG. 10; and 
     FIG. 12 is a simplified end view of the rotor endwinding shown in FIGS. 10 and 11, but also illustrating the lower half of the rotor. 
    
    
     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 pole face  23  of 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 region from the rotor body ventilation region 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. 
     With reference also to FIGS. 2 and 3, the baffle ring has oblong holes  40  machined or molded into the ring at specifically identified locations. The purpose of these holes is to feed the cooling gas which flows axially between the inside diameter of the baffle ring  32  and the rotor spindle  24  into longitudinal inlet cavities located between certain coils ( 16  and  18 ) in the rotor endwinding region. In the exemplary embodiment, only one inlet cavity  44  is shown, between adjacent sides of coils  16 ,  18 . Cavities  42  and  46  on the opposite sides of coils  16  and  18  are referred to as discharge cavities as further explained below. 
     A certain number of the turns  21  (determined by specific application) in the coil of interest (in this case, coil  16  or  18 ) have longitudinal grooves  48  machined in them of various lengths and sizes. The lengths and sizes (i.e., cross sectional areas of the grooves) can be selected to insure that cooling gas flow distribution is adequate for effective cooling of each turn in the section of the winding of interest. One end of each longitudinal groove is connected to the longitudinal inlet cavity  44  on one side of the turn  16  and  18  via a lateral inlet port  50  machined in the turn so that cooling gas can flow from the longitudinal inlet cavity  44  on one side of the turns of coils  16  and  18  into and along the longitudinal grooves  48  within the turns. At the opposite end of the longitudinal grooves, a lateral exit port  52  is machined in the turns extending from the grooves  48  to the outer edge of the respective turn on the opposite sides of the turns. Cooling gas can thus flow through the longitudinal inlet cavity  44  into the copper turns of coils  16  and  18  via the inlet ports  50  and then flow longitudinally along the grooves  48 , then through the lateral exit ports  52  and discharge into discharge cavity  42  formed on the opposite side of coil  16  and discharge cavity  46  on the opposite side of coil  18 . The number of turns  21  formed with the above described flow paths and the number of flow paths per turn are variable depending on cooling requirements. 
     Vent slots or holes  54  are machined in the rotor body teeth (those portions of the rotor between the radial slots) to allow the cooling gas to flow from the longitudinal discharge cavities  42  and  46  into the slots or holes  54  in the rotor teeth to the air gap of the machine. As previously noted, the air gap is the annular space between the machine&#39;s stator and rotor. 
     The lateral inlet ports  50  nearest the rotor body can be used to feed the cooling gas into short grooves  56  machined along the copper turns of coils  16  and  18  which discharge into radial or generally radial chimneys  58  which exit into the machine air gap, thus cooling the winding&#39;s transition section from the endwinding region to the rotor body region. Note that cooling gas which does not flow through the baffle ring holes  40 , will flow into sub-lots  57  in the rotor body and, in one possible rotor body ventilation scheme, will discharge through radial chimneys (not shown) in the rotor body. Also note that groove  56  and chimney  58  do not communicate with the sub-slot  57 . 
     When the machine is running at rated speed, the pumping head of the machine&#39;s rotor drives cooling gas flow through the passages. With reference to FIG. 4, any obstacle which is in the cooling gas flow path (specifically the longitudinal cavities  42 ,  44  and  46  between the turns  21  of coils  16  and  18 ), such as a rotor endwinding spacer block  60 , can be bypassed via grooves  62  machined along the copper turn from inlet ports  64  to suitable exit ports  66  on the far side of the obstacle. Alternatively, one or more holes  68  can be formed in the spacer  70  itself to allow the gas to flow through the obstacle (see FIG.  5 ). Another possibility is to use spacer block bypass schemes via bypass pockets in the baffle ring design. 
     The invention is not limited to single groove configurations as described above. Rather, multiple groove configurations are also contemplated. In FIG. 6, the one or more turns  72  within a coil may include side-by-side grooves  74 ,  76  with corresponding inlets  78 ,  80 , and outlets  82 ,  84  may be used to increase the cooling capacity. In the above arrangement, the inlets and outlets may be combined separately, so that a single large inlet feeds two parallel grooves while a single large outlet discharges gas from those individual grooves. 
     With reference to FIG. 7, for any pair of vertically stacked turns, the grooves may be staggered. Thus, in the upper surface of turn  88 , a groove  90  is formed with an inlet  92  and an outlet  94 . The bottom surface of that same turn may be formed with a groove  96  having an inlet  98  and an outlet  100 , in axially staggered relationship. Rather than have a pair of grooves in the upper and lower surface of the same turn, however, it will be appreciated that the staggered grooves may be provided in adjacent or in vertically spaced turns. 
     It is also within the scope of this invention to introduce radial ducts at various locations within the turns to interconnect grooves and thus form longitudinal/radial ventilation passages. Many combinations of these various longitudinal and radial ventilation passage schemes are possible if, for example, different radial ducts or passages feed the longitudinal grooves (of various lengths) in the areas with exit ports out the sides of the turns, or out the sides of other radial passages, as illustrated for example in FIG.  8 . Specifically, cooling gas from baffle ring holes  102  enters a longitudinal inlet cavity on the near side of a coil  104 . Some of the gas will enter a lateral port  106  in turn  108  and travel along a longitudinal groove  110  which has an exit port  112  communicating with a radial passage  114  machined into the stack of turns of coil  104 . Other longitudinal grooves  116 ,  118  in turns  120 ,  122  communicate with the radial passage  114  with additional outlets  124 ,  126  on opposite sides of the coil  104  communicating with a discharge cavity (not shown) on the far side of the coil. The longitudinal grooves can be machined on either side of the various turns, and for multiple conductor-per-turn windings, the grooves can be machined on the overlapping surfaces of the mating conductors. 
     Counterflow ventilation schemes in which, for a given region of the coil, cooling gas flows in separate passages in opposite directions with opposite inlet and exit locations are also contemplated. Such an arrangement is shown in FIG. 9 where cooling gas flows in opposite directions in two adjacent stacked turns. In the upper turn  128 , cooling gas will flow into inlet  130 , through a longitudinal groove  132  and out the outlet port  134  on the opposite side of the turn. At the same time, cooling gas will enter an inlet port  136  in the underlying turn, travel along a groove (not visible in Figure ) in an opposite direction, and exit the outlet port  138  on the opposite side of the coil. A similar arrangement may be achieved with staggered lateral inlet and exit ports. Counterflow schemes have not been done in rotor end windings prior to this invention, and the advantage of counterflow is that both lower and more uniform temperatures can be achieved in the rotor endwinding as compared to non-counterflow schemes. 
     With reference now to FIGS. 10-12, a ventilation scheme is illustrated for applications where additional cooling gas discharge area may be required in the rotor endwinding region. Here, the baffle ring  140  is modified to include additional holes  142  opening into an axial cavity or passage  144  in the center of the concentric coil arrangement. The center cavity is further defined by radial plates  146 ,  148  between the baffle ring  140  and the spindle  150  and extending axially between the rotor body or pole face  152  and a semi-annular end cover  154  (FIG. 10) located radially between the spindle  150  and the centering ring  156 . As will be appreciated from FIGS. 10 and 11, the holes  142  in the baffle ring  140  are located to open into the spaces between the coils  158 ,  160 ,  162  and  164 , and between the plates  146 ,  148 . 
     In this arrangement, cooling gas exiting the ports in the turns of the coils passes through the radial holes  142  in a radially inward direction from the spaces or cavities between the coils into the axial passage defined by plates  146 ,  148  below the baffle ring  140 . The cooling gas can then flow axially in either direction, and can be discharged either into the air gap via vent slots  166 ,  168  machined into the pole face  152 , or into the outside diameter of the centering ring  156  via discharge holes  170 , 172  forming radial (or generally radial) chimneys in the centering ring. Note that FIG. 14 illustrates the position of additional baffle plates  174 , 176  and vent slots  178 ,  180  for the opposite endwinding in a two pole rotor. The schemes can be used for machines with more than two poles by adding additional radial plates for each pole. 
     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 ventilation schemes in accordance with the invention can be used on any machine with a concentric wound field winding of suitable turn dimensions with square cornered and/or C-shaped corner construction. This can most readily be applied to two-pole and four-pole round rotor turbine driven generators. The ventilation schemes described herein can be applied to machines with either forward or reverse flow ventilation arrangements. The cooling of the rotor body itself can be achieved by an compatible method such as radial cooling (or axial/radial cooling) by means of cooling gas fed from sub-slots 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. 
     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.