Metal working – Means to assemble or disassemble – Puller or pusher means – contained force multiplying operator
Reexamination Certificate
2001-02-08
2001-12-11
Watson, Robert C. (Department: 3723)
Metal working
Means to assemble or disassemble
Puller or pusher means, contained force multiplying operator
Reexamination Certificate
active
06327762
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to generator stators and, more specifically, to a wedge and slide system that can be used internally of the end wedge and permits 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 within the ends of the stator core slots may become susceptible to accelerated abrasion due to: 1) pre-existing or rapidly-evolving radial clearances, 2) the effects of excessive or continuous oil contamination, and 3) 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 at least some of 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.
A stepped dovetail wedge and slide system which permits retightening of the generator stator end slot wedges so as- to restore the required radial force on the winding bars is disclosed in copending application Ser. No. 09/453,776 filed Nov. 22, 1999, now U.S. Pat. No. 6,294,855 and entitled “Adjustable Generator Stator Slot Wedge System”).
BRIEF SUMMARY OF THE INVENTION
This invention provides an improved mechanism for tightening generator stator internal slot wedges (wedges which are inboard of the end wedges), and restoring the required radial force on the winding bars in a location where loosening can occur. It also allows the tightening process to be carried without the removal of the generator field.
The invention also increases the long term durability and reliability of the internal wedges by making design and materials improvements which also contribute to decreasing the outage frequency for generator inspections and down time.
In an exemplary embodiment of the invention, an adjustable version of the restraining device commonly referred to as a stator slot wedge is provided. The principal purpose of the stator slot wedge is to supply a radial force to the armature winding (stator bars) to prevent it from vibrating under the influence of electromagnetic forces which act continuously during normal operation and which can become much more severe under conditions caused by misoperation or system faults.
The invention has several features which in combination yield the unique support device, the main feature of which is adjustable tightening of internal wedges in place, i.e., without removal of the generator field. The individual design features include: (1) an oblong slot in the wedge component that provides access for a tightening tool; (2) rounded holes in the slide component that serve as an insert location for a tool designed to provide proper tightening; and (3) stepped internal wedges and slides, otherwise similar to the end wedges and slides in the above identified co-pending application, that prevent reverse axial movement or loosening.
In the exemplary embodiment, wedge and slide components are provided that are similar to those disclosed, in copending application Ser. No. 09/453,776, now U.S. Pat. No. 6,294,855 identified above. In accordance with this invention, an elongated or oblong slot is formed in the wedge component that provides access to the stepped surface on the underlying slide component. In addition, a series of round holes are provided in the slide component in generally aligned relationship with the slot, to allow the head of an adjustment tool to be inserted through the slot and into one of the holes on the slide component. By appropriately locating and then pushing the tool inwardly, the slide component is moved inwardly in a ratcheting type action, to tighten the internal slot wedge/slide assembly and thereby restore the required radial force on the winding bars.
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 windings in each radial slot; at least one adjustable assembly axially inboard of an outermost end assembly in 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, the wedge component having an elongated slot therein providing access to the slide component.
In another aspect, the invention relates to a generator stator including a magnetic core having a plurality of axially extending radial slots arranged about the periphery thereof with windings in each radial slot; at least one adjustable assembly axially inboard of an outermost end assembly in 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, the wedge component having an elongated slot therein providing access to the slide component; wherein a second adjustable assembly is located axially inboard of the at least one adjustable assembly, the second adjustable assembly comprising a second wedge component and a second slide component having interengaging stepped surfaces, the second wedge component having an elongated slot therein providing access to the stepped surface in the slide.
In still another aspect, the invention relates to a tool for use in adjusting an axially inboard wedge and slide assembly in a generator stator slot wedge system, the tool comprising an elongated handle, a tool head comprising an elongated handle, a tool head pivotally secured to the handle, and a stub formed on a remote end of the tool head, the stub having a substantially cylindrical shape.
Other objects and advantages of the subject invention will become apprent from the detailed description which follows.
REFERENCES:
patent: 1320126 (1919-10-01), Dudley
patent: 2316635 (1943-04-01), Staak
patent: 2990486 (1961-06-01), Willyoung
patent: 3139550 (1964-06-01), Geer
patent: 3842303 (1974-10-01), Simmonds et al.
patent: 4149101 (1979-04-01), Lesokhin et al.
patent: 4184091 (1980-01-01), Khutoretsky et al.
patent: 5701650 (1997-12-01), LaFleur et al.
General Electric Company
Nixon & Vanderhye P.C.
Watson Robert C.
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