Spline retaining ring

Details Spline retaining ring Spline retaining ring

2000-04-17

2001-09-04

Mullins, Burton S. (Department: 2834)

Electrical generator or motor structure

Dynamoelectric

Rotary

C310S052000, C310S059000, C310S261100

Reexamination Certificate

active

06285110

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to retaining rings used to contain centrifugal forces experienced by field winding end turns in a generator.
During normal operation, heat is produced in a generator due to the copper, iron, windage, load or other losses. A ventilation/cooling system is used to remove such generated heat sufficiently to insure the reliable operation of the generator. The objective of the ventilation/cooling system is to achieve relative uniform temperature distribution in the generator with low power consumption. However, due to the complexity of the generator geometry and heat generation, hot spots may exist in certain locations. For air or hydrogen cooled generators, the ventilation flow field at the gap entrance between the generator stator and retaining ring has drawn special attention, since it can result in large ventilating windage loss.
Retaining rings are typically mounted around the end portion of the rotor to enclose the field winding end turns of the generator. In conventional practice, these retaining rings are designed to have a substantially cylindrical shape, with a flat outer profile. This conventional retaining ring design can, however, result in a large pressure drop across the stator-rotor gap entrance and high drag force against the cooling flow, thus leading to a lower generator cooling efficiency. More specifically, conventional retaining rings with flat outer profiles form part of a flow bottleneck at the cooling flow entrance to the gap between the stator core and the rotor. In addition, the interface of the retaining ring nose and the rotor core forms a backward facing step. As cooling gas passes the stator-rotor gap entrance, it generates a large flow recirculation at the retaining ring nose. This results in a large pressure drop at the gap entrance.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to the design of a retaining ring with a spline profile near its nose, to thereby improve the axial cooling flow fluidity and enhance generating cooling capability. By altering the outer profile of the ring, at that end of the ring projecting into the gap between the stator core and rotor, it has been found that approximately 60% of the pressure drop across the stator-rotor gap entrance can be eliminated. As a result, the overall generator efficiency may increase by about 0.01%.
More specifically, by incorporating an aerodynamically smooth spline shape in the radially outer surface of the ring, at the axially inboard portion thereof, in combination with a rounded nose, the effective flow area of the gap is increased while the drag force against the axial cooling flow is decreased. In order to minimize the impact of the spline on the retaining ring strength, the reduction of the retaining ring thickness at its nose is small, and the spline length is only about 17% of the total length of the retaining ring. In the exemplary embodiment, the spline shape is described by a function of a cubic curve where three constants may be adjusted to provide the desired curvature.
Accordingly, in its broader aspects, the present invention relates to a retaining ring for a rotor assembly, the retaining ring adapted to constrain field winding end turns in a rotor body, the retaining ring comprising axially inner and outer ends and radially inner and outer surfaces, the radially outer surface at the axially inboard end having an aerodynamically smooth spline shape defined by compound radii that merge into a rounded nose portion.
In another aspect, the invention relates to a rotor assembly including a rotor body having at least one field winding seated therein with end turns of the field winding extending beyond the rotor body, and an annular retaining ring fixed to the rotor body and adapted to constrain the end turns against centrifugal forces, the retaining ring comprising axially inboard and outboard ends and radially inner and outer surfaces, the radially outer surface at the axially inboard end having an aerodynamically smooth spline shape defined by compound radii that merges into a rounded nose portion.
In still another aspect, the invention relates to a retaining ring for a rotor assembly, the retaining ring adapted to constrain field winding end turns of a plurality of field windings arranged in a rotor body, the retaining ring comprising axially inboard and outboard ends and radially inner and outer surfaces, the radially outer surface at the axially inboard end having an aerodynamically smooth spline shape defined by compound radii that merge into a rounded nose portion; wherein the aerodynamically smooth spline shape extends about 17% of a length dimension of the retaining ring, measured from the rounded nose portion; and wherein the aerodynamically smooth spline shape is described by a function of the cubic curve
y
=
x
a
+
bx
+
cx
2
where a, b, and c are constants; and further wherein a is in a range of less than or equal to 5 and greater than or equal to 0.2; b is in a range of less than or equal to 2.5 and greater than or equal to 1.5; and c is in a range of less than or equal to 0 and greater than or equal to −0.005.


REFERENCES:
patent: 3324324 (1967-06-01), Richardson et al.
patent: 4547688 (1985-10-01), Hammer et al.
patent: 5113114 (1992-05-01), Shih et al.
patent: 5174011 (1992-12-01), Weigelt
patent: 5358432 (1994-10-01), Shih et al.
patent: 5861698 (1999-01-01), Murphy
patent: 1141021 (1962-12-01), None

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