Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-09
2001-06-26
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S260000, C310S270000
Reexamination Certificate
active
06252318
ABSTRACT:
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'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'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
General Electric Co.
Nixon & Vanderhye
Waks Joseph
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