Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-12-02
2001-04-17
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S256000, C310S256000, C310S260000, C310S270000
Reexamination Certificate
active
06218759
ABSTRACT:
TECHNICAL FIELD
The present invention relates to dynamoelectric machines and, more particularly, to an end support for applying radial outward forces to armature windings cantilevered axially outboard of the stator core slot dovetails.
BACKGROUND OF THE INVENTION
Dynamoelectric machines typically employ a stator core comprised of stacked laminations of magnetic material forming a generally annular assembly. An array of axially extending circumferentially spaced slots are formed through the radial inner surface of the annular assembly and armature windings are disposed in the slots. A rotor is coaxially arranged within the stator core and contains field windings typically excited from an external source to produce a magnetic field rotating at the same speed as the rotor. With the foregoing arrangement, it will be appreciated that electrical output is generated from the armature windings.
In typical stator core arrangements, the armature windings are maintained in the axially extending stator core slots by wedges axially disposed in dovetail grooves along or near the radial inner ends of the stator core. The wedges impose radial forces on the armature windings for resisting magnetic and electrically induced radial forces on the windings. In order to prevent excessive heat build-up in the ends of the stator core during operation, it is common practice to taper the ends of the stator core in a radially outer direction. This outward taper intersects the dovetails in the stator slots such that the armature windings extend from the ends of the slots to comprise the end turns without radial structural support.
More particularly, the armature windings of generators operate under continuous strain of electromagnetic forces that must be completely contained to prevent high voltage armature winding insulation damage. Insulation damage is also exacerbated by relative movement of the elements, e.g., the armature windings and stator core. For example, the core end geometry which reduces core heating also leaves the armature windings extending from the stator core unsupported at the ends of the slots. Seal oil leakage, if present, also reduces restraining friction forces applied by side ripple springs. It is also possible that static residual forces exerted by the end windings may displace the armature windings off the core slot bottom, either initially or over time in service, allowing radially outwardly directed electromagnetic forces to initiate armature winding vibration. Radial clearance may also develop over a long period of service due to aging of materials. Once clearance is developed and vibration begins, damage to armature winding insulation can accelerate quickly, particularly in the presence of oil contamination, to a point where electrical failure can occur.
A similar problem exists with respect to P-bar excitation systems, for example, disclosed in U.S. Pat. No. 4,584,497 of common assignee herewith. The P-bar windings extending from the radially innermost dovetail of the dual dovetail system disclosed in that patent are cantilevered and provided with a beam support between the radially inner dovetail and yokes supported on end space blocks of the stator core. In that arrangement, the beam is supported at opposite ends by the radially inner dovetail and the yoke to provide structural support for the P-bar windings and the underlying armature bars within that length. That patent is concerned only with P-bar windings and beam supports therefor. It has been found, however, desirable to not only provide support for the armature windings but also to provide outward radial biasing forces on the armature windings which are unsupported outboard of the stator core dovetails.
BRIEF SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a non-metallic ring affixed to the metallic support structure at each end of the stator core. The ring, in conjunction with end wedge sub-assemblies and dovetails on the stator core, apply radially outward forces on the armature windings at the end of the stator core which project from the end of the stator core where wedge pressure in the stator core is lost or reduced because of the core end geometry. Particularly, the support structure includes a ring formed of high strength glass fiber-filled resin which is secured to the end of the stator core. The ring has a plurality of circumferentially spaced radially outwardly opening recesses in axial spaced alignment with the axial slots in the stator core. The ring is secured to space blocks which support the stator core end. An end wedge assembly, including an end wedge having surfaces complementary to the dovetail surfaces of the stator core slot, is in part received in the end portion of each stator core slot. The opposite end of the wedge sub-assembly is received in a recess of the ring. Each end wedge sub-assembly spans the end of the stator core slot and the ring and radially underlies the armature windings extending from the stator core slot through the stator core support at the end of the dynamoelectric machine. The undersurface of the end wedge is tapered. A slide having a complementary tapered surface overlies the tapered surface of the end wedge. Radially outwardly of the slide there is provided a ripple spring and a filler strip lying intermediate the end wedge and the extended armature windings. By inserting the ripple spring and insulating filler strip, as well as the end wedge, through the recesses of the ring and radially inwardly of the armature windings and then inserting the tapered slide, it would be appreciated that the wedge sub-assembly can be locked in place while simultaneously applying a radial outward force to the armature windings.
In a preferred embodiment according to the present invention, there is provided apparatus for applying a radial outward force on armature windings extending from stator core slots at an end of a generator stator core, the stator core slots extending axially and having dovetails extending within the slots, the stator core end tapering radially outwardly toward one end and outwardly of the dovetails comprising a support ring at one stator end and lying on a common axis with the stator core, a core end support for securing the ring and the stator core to one another, end wedges at least in part having corresponding surfaces at one end for engaging in the dovetails at end portions of the stator slots, tapered radially outwardly facing surfaces and opposite end portions for engaging the ring at circumferential locations thereabout and slides having tapered radially inwardly facing surfaces engageable with the tapered faces of the end wedges and receivable radially outwardly of the end wedges for maintaining radially outward forces on the armature windings extending from the stator core slots.
In a further preferred embodiment according to the present invention, there is provided a generator stator comprising a stator core having a plurality of radially inwardly opening stator slots spaced circumferentially one from the other about the core and opening through one end thereof, a plurality of armature windings extending in the slots and projecting from the slots at one end of the generator stator core, the stator core slots extending axially and having dovetails extending within the slots, one stator core end tapering radially outwardly of the dovetails, a support ring at one stator end and lying on a common axis with the stator core, a plurality of core end supports for securing the ring and the stator core to one another, end wedges at least in part having corresponding surfaces at one end for engaging in the dovetails at end portions of the stator slots, tapered radially outwardly facing surfaces and opposite end portions for engaging the ring at circumferential locations thereabout and slides having tapered radially inwardly facing surfaces engageable with the tapered faces of the end wedges and receivable radially outwardly of the end wedges for maintaining radially outward forces on the armature windings which are unsupported
Blakelock Thomas R.
Butman, Jr. Thomas R.
Iversen Alan M.
General Electric Co.
Lam Thanh
Nixon & Vanderhye
Ramirez Nestor
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