Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-10-28
2001-04-17
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S214000, C310S215000
Reexamination Certificate
active
06218756
ABSTRACT:
FIELD OF THE INVENTION
This invention is related to the power generation industry and, more particularly, to the field of power generators.
BACKGROUND OF THE INVENTION
In the power generation industry, as well understood by those skilled in the art, a power generator has a generator rotor and a generator stator. The generator rotor includes several rotor slots. The rotor slots conventionally have a plurality of electrically-conductive rotor wedges which hold the slot contents, e.g., coils, slot filler, within the slots. The slot contents should remain tight to prevent relative motion of the copper windings during slow roll operations which could result in wear of the windings and conductive particle creation, e.g., copper dusting. A tight slot contents also ensures the provision of adequate contact pressure on a damper system of the rotor, e.g., a wedge and rotor tooth, at low speeds to conduct currents generated with static start operation. The tightening of the slot contents is even further problematic between rotor slot wedges.
A conventional method for tightening the slot is to use a brute force technique which can be labor intensive. In this conventional method, all of the slots are gauged along the length. Slot fillers are then sanded to fit, and wedges are driven into the slot with a large hydraulic ram. The filler thickness under a given wedge is chosen by trial and error. If the filler is sanded too thin, the slot will be loose. If the filler is too thick, galling can occur when the wedge is driven into the slot. Tolerances between “too thin” and “too thick” can be too great and cause problems for the rotor. This method also allows the slot to loosen as the machine ages and insulation components creep with time.
Systems, such as shown in U.S. Pat. No. 5,430,340 by Shih et al. titled “Harmonic Current Path Spring Device Between Retaining Ring And Rotor Wedge Of A Dynamoelectric Generator,” have been developed which use a spring below rotor slot wedges to bias the wedges against overlapping retaining rings. Such systems, however, fail to adequately address some of the above described problems and particularly the problem with loose contents between wedges.
Other systems have been developed, such as shown in U.S. Pat. No. 5,550,417 by Morrison et al. titled “Amortisseur Winding Arrangement, In A Rotor For Electrical, Rotating Equipment,” which attempt to solve the problem of loose slot contents between wedges by physically and electrically connecting the wedges. Such a system uses arcuate linking members or inserts which are spring loaded to assist in retaining the wedges. The physical connection of the wedges and the custom forming of the wedges, however, are often not desirable.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention advantageously provides a method of tightening a generator rotor slot and an associated apparatus which does not require the physical connection of slot wedges or the custom forming of a wedge interface. The present invention also advantageously provides a method of tightening a generator rotor slot which uses slot filler members to assist in the tightening of or maintaining the tightness of the contents of the rotor slot. The present invention further advantageously provides a method and apparatus for tightening a generator rotor slot which effectively accommodates creep of components in time.
More particularly, a method for tightening slot wedges of a generator rotor is provided which preferably includes the steps of positioning an electrically-conductive slot tightening member within a recess formed in at least one slot filler member positioned within a rotor slot and positioning at least two end portions of electrically-conductive slot wedges to overlie the recess and abuttingly contact at least portions of the slot tightening member so that an electrically-conductive path is provided from one of the at least two end portions of the slot wedges, through the slot tightening member, and to another one of the at least two end portions of the slot wedges.
Another method of tightening a rotor slot preferably includes forming a recess in at least one slot filler member, positioning the at least one slot filler member within a rotor slot, positioning an electrically-conductive slot tightening member within the recess formed in at least one slot filler member, and positioning at least two end portions of electrically-conductive slot wedges to overlie the recess so that an electrically-conductive path is provided from one of the at least two end portions of the slot wedges, through the slot tightening member, and to another one of the at least two end portions of the slot wedges.
The present invention additionally provides a rotor slot tightening apparatus which preferably includes at least one slot filler member for positioning within a rotor slot. The at least one slot filler member has a recess formed therein. An electrically-conductive slot tightening member is positioned within the recess, and at least two electrically-conductive slot wedges are positioned so that respective end portions thereof overlie the recess so that an electrically-conductive path is provided from one of the respective end portions of the slot wedges, through the slot tightening member, and to another one of the respective end portions of the slot wedges.
By forming recesses in slot filler members, the present invention takes advantage of the existing material conventionally used in maintaining or tightening a rotor slot without the necessity of developing extensive physically connecting members or other extensive arrangements which can be costly to tool or manufacture, especially where low quantities are concerned. This can also greatly reduce manufacturing time and costs associated therewith. The insulating channel positioned within the recess advantageously provides a barrier or buffer from the electrically conductive path formed from the slot wedges and the slot tightening member to enhance protection of the slot contents.
REFERENCES:
patent: 3976901 (1976-08-01), Liptak et al.
patent: 4369389 (1983-01-01), Lambrecht
patent: 4387316 (1983-06-01), Katsekas
patent: 4469971 (1984-09-01), Moore
patent: 4633116 (1986-12-01), Derderian
Gardner William C.
Paris Calvin L.
Rico Raul R.
Nguyen Tran
Siemens Westinghouse Power Corporation
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