Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-11-22
2001-12-18
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100
Reexamination Certificate
active
06331745
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to generator stators and, more specifically, to a wedge and slide system used at the ends of the stator core. The wedge and slide system is adjustable to permit in situ radial correction for radial pressure and dimension losses which occur over time.
Electric utility companies require large turbine-generators to operate reliably for long periods of time, for example, thirty years or more. Normal, steady-state electromagnetic forces acting on the armature winding are capable of causing armature bar vibration within a much shorter period than the expected generator lifetime. Armature bar vibration can occur if radial clearances are present within the stator core slot. Bar vibration can result in armature bar insulation abrasion. The abrasion can become severe if maintenance actions are not taken to retighten the slot support system and arrest the vibration. Typically, a prolonged maintenance outage is required to retighten the slot support system and eliminate radial clearances within the slot.
The electrical windings at opposite axial ends of the stator core slots may be particularly susceptible to accelerated abrasion due to: 1) pre-existing or rapidly-evolving radial clearances, 2) the effects of excessive or continuous oil contamination, 3) the effects of end winding electromagnetic forces, and 4) abnormally-high electromagnetic design forces on the slot portion of the winding. It is therefore important to provide an in situ means for eliminating radial clearances that develop in this location in order to prevent unscheduled or prolonged service outages.
In an attempt to address these problems, a stepped wedge and slide arrangement is proposed in U.S. Pat. No. 4,149,101 but for the purpose of preventing axial displacement of wedges within the core slot. A stepped bracing arrangement is proposed in U.S. Pat. No. 3,842,303 but in the context of an end winding support fit-up device between the coil end arms.
BRIEF SUMMARY OF THE INVENTION
The present invention seeks to provide a stepped dovetail wedge and slide system which permits re-tightening of generator stator end-of-slot wedges (or simply, end wedges), restoring the required radial force on the winding bars in a location where loosening is most likely to occur. Significantly, the re-tightening process can be carried out without removal or replacement of parts, and without removal of the generator field. The invention also increases the long-term durability and reliability of the end wedges by making design and materials improvements, and hence contributes to a decrease in the frequency of generator inspection outages.
Accordingly, the present invention relates to a dovetail wedge and slide combination that can be used at the ends of the stator core, and that has matching inclined surfaces that are stepped to permit in situ radial correction for any radial pressure and dimension losses which occur over time, and to prevent axial regression of the slide after adjustment. The invention is preferably applied to large turbine generator stators that have relatively high electromagnetic forces during normal operation and, in some cases, have exhibited the development of radial clearance in the windings at the ends of the core and subsequent end wedge loosening.
More specifically, the invention provides an adjustable version of a restraining device commonly referred to as a “stator slot wedge” that has the primary purpose of supplying a radial force to the armature winding (stator bars) to prevent it from vibrating under the influence of electromagnetic forces experienced continuously during normal operation, and which can become much more severe under conditions caused by misoperation or system faults. There are several features which, in combination, yield a unique support device, the main feature of which is adjustable tightening of the wedges in place, while also increasing the radial force on the stator bar.
In accordance with one embodiment of the invention, matching stepped contact planes are machined on the sloped surfaces of the slide and dovetail wedge components. In the initially installed condition, the slide is driven tight to provide the required radial force on the bars, but with the capacity to be driven an additional distance in the axial direction, as needed at later dates, to eliminate radial clearances and to restore radial wedge force.
In the preferred arrangement, the stepped surface is machined on the sloped side of a slide component, made from a high strength laminate. The wedge is formed by laminating a slide component to a flat slidable dovetail piece made from a non-abrasive laminate. The non-abrasive portion of the wedge is the only part of the wedge-slide system in contact with the iron thus eliminating core wear.
In another variation, the wedge component can be composed of a high strength laminate, which may be abrasive, but to which non-abrasive strips or pads have been bonded on any surface in contact with the core.
A further enhancement of the invention is achieved by designing the end wedge to incorporate a device which can be used to tighten the next axially inboard wedge. This involves drilling through the end wedge in an axial direction to allow insertion of a movable part such as a hard, non-metallic dowel which can be positioned to contact the outboard end of the next adjacent slide. The outboard end of the dowel can then be driven inwardly if needed at the same time the end slide is adjusted. The thickness of the end wedge may be increased if necessary to accommodate the dowel pin without sacrificing radial strength. The sloped surfaces of the next adjacent inboard wedge and slide are also stepped (as in the case of the end wedge and slide) to permit adjustable tightening and to prevent axial regression of the slide after adjustment. This arrangement allows radial load adjustment over a greater axial length and compensates for any loosening of the inboard wedge caused by re-tightening the end wedge.
Accordingly, in its broader aspects, the present invention relates to a generator stator including a magnetic core having a plurality of axially extending radial slots arranged about the periphery thereof with stator windings in each radial slot; at least one adjustable assembly in an axially outermost end of each radial slot, arranged to restrain the windings in the radial slot, the adjustable assembly comprising mating wedge and slide components which interface along stepped matching surfaces which lie at an acute angle to a center axis of the magnetic core.
REFERENCES:
patent: 3391294 (1968-07-01), Moxie
patent: 3624432 (1971-11-01), Merz
patent: 3842303 (1974-10-01), Simmonds et al.
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patent: 4584497 (1986-04-01), Butman, Jr. et al.
patent: 4607183 (1986-08-01), Rieber et al.
patent: 4633574 (1987-01-01), Bath et al.
Blakelock Thomas R.
Butman, Jr. Thomas R.
Iversen Alan M.
General Electric Company
Nixon & Vanderhye P. C.
Waks Joseph
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