Patent Application
20060026818
The present invention relates to apparatus and methods for removing wedges overlying the windings of a stator core in an electrical machine and particularly relates to apparatus and methods for cutting the wedges longitudinally parallel to the slots to facilitate removal of the wedges and refurbishment of the machine.
In electrical machines such as generators, the stator core has a slot wedging system for retaining the windings in the core. The windings are arranged in circumferentially spaced, longitudinally extending slots, which, along radially inward ends of the slots have dovetail or tapered surfaces. A plurality of wedges typically extend along the length of each circumferentially spaced slot to retain the windings in the slot. The radial outer sides of the wedges are tapered and tapered slides underlie the wedges, forcing the wedges radially inwardly against the dovetail slots. In recent electrical machine construction, ripple springs underlie the slides or wedges and bias the wedges in a radial inward direction. The ripple springs can apply as much as 3500 pounds force to the wedges.
It is common practice to rewedge or rewind the stator core during refurbishment, thus necessitating the removal of the wedges. The wedges are typically removed by sawing them in half in a longitudinal direction. In the past, where ripple springs have not been used, handsaws were used to split the wedges and remove them from the stator core. When biasing the wedges using ripple springs, however, the ripple springs cause the wedge halves to move toward one another as the cut is being made. That is, the action of the ripple spring causes the wedges to bind the cutting blade, causing slippage and tool and core damage as well as generating a potential for injury to the operator. Efforts to remove wedges biased by ripple springs have resulted in labor-intensive, tedious, slow and expensive processes, typically using hand-chisels. Accordingly, there is a need for apparatus and methods for safely, inexpensively and expeditiously removing wedges from a stator core.
In a preferred embodiment according to the present invention, there is provided a method of removing wedges in axially extending slots in a stator core of an electrical machine wherein springs in the stator core bias the wedges radially inwardly, comprising the steps of (a) disposing a frame carrying a carriage in the stator core, (b) providing cutter heads on the carriage diametrically opposite one another, (c) engaging the heads against diametrically opposed wedges of the stator core, (d) applying a force to the wedges through the heads in a direction against the bias of the springs; and (e) cutting the wedges in a direction generally parallel to an axis of the stator core.
In a further preferred embodiment according to the present invention, there is provided a method for removing wedges in axially extending slots of a stator core of an electrical machine, comprising the steps of (a) disposing a frame within the core extending between diametrically opposite wall portions of the stator core, (b) providing a carriage carrying a cutter head, the carriage being carried by the frame for pivotal movement about the axis of the stator core to position the cutter head carried thereby adjacent a wedge in a first slot of the stator core, (c) displacing the cutter head in an axial direction to cut a plurality of the wedges longitudinally in the slot to enable removal of the wedges and (d) pivoting the carriage about the axis to locate the cutter head adjacent a wedge in another slot circumferentially spaced from the first slot.
In a further preferred embodiment according to the present invention, there is provided apparatus for cutting wedges in axially extending slots in a stator core of an electrical generator, comprising a frame receivable within the stator core, a carriage carried by the frame for axial movement along the stator core and relative to the frame, diametrically opposed heads carried by the carriage and a cutter carried by each of the heads for cutting the diametrically opposed wedges as the carriage and heads move axially relative to the stator core.
Referring now to the drawings, particularly to
A wedge removal assembly is illustrated in
It will be appreciated that the frame 30 is disposed longitudinally within the stator core with elements 36 and 38 extending diametrically within the core. Upon actuation of the hydraulic ram 39, the pads 40 are engaged against the wedges 16 in diametrically opposed slots.
The frame 30 mounts a carriage assembly generally designated 50 on a linear drive assembly generally designated 52. The linear movement assembly 52 includes a drive box 54 and an idler box 56 at opposite ends and adjacent opposite ends of the frame. The drive box 54 and idler box 56 are pivotally carried by bearings mounted on the end stanchions 36, 38 of the frame 30. Preferably, the linear drive assembly 52 is mounted for rotation about the stator core axis. Four rails or bars 58 extend between the drive and idler boxes 54 and 56, respectively, and the carriage 50 is slidably mounted on the bars or rails 58 for axial sliding movement along the bars or rails between opposite ends of the linear drive assembly 52.
Referring to
Carriage 50 mounts a pair of diametrically opposed cutter heads generally designated 70 as best illustrated in
Referring to
To utilize the wedge removal system hereof, the frame 30 is disposed longitudinally within the stator core 10 with the pads 40 aligned with diametrically opposite wedges of diametrically opposed stator core slots. The hydraulic cylinders or rams 39 in each of the stanchions 36, 38 are actuated to engage the diametrically opposed wedges 16 and secure the frame within the stator core. It will be appreciated that the frame 30 extends a limited length within the stator core and is repositioned longitudinally upon successful completion of cutting the wedges at the location of the wedge removal assembly to further longitudinal positions to complete the cutting of the wedges in each of the slots.
With the frame 30 fixed within the stator core, the linear drive assembly 52 including the carriage assembly 50 and heads 70 are rotated into a position aligning the heads 70 with diametrically opposed wedges in slots circumferentially spaced from the slots having wedges engaged by the frame pads 40. For example, as illustrated in
With the saw blades engaged and cutting the wedges, the linear drive assembly 52 is actuated to draw the carriage 50 and consequently the heads and saw blades 76 longitudinally along the wedges of the slots whereby the wedges are cut. It will be appreciated that by maintaining the wedges under radial outward pressure with the ripple springs compressed, the saw blades are able to cut through the wedges without the wedges binding the saw blades as would be the case if the ripple springs were not compressed. When each saw blade reaches the end of its travel, the air cylinder 86 is actuated to withdraw the saw blade from the last wedge cut. Additionally, the cylinder 78 is actuated to displace the heads 70 in radially inward directions out of engagement with the cut wedges. The carriage 50 is then displaced longitudinally to its start position along the linear drive assembly by driving the chains 66 in a reverse direction. With the heads spaced radially inwardly of the wedges, the linear drive assembly 52 is manually rotated about its axis to align the heads 70 with the next circumferentially adjacent slots and wedges. Upon alignment, the cylinder 78 is actuated to displace the heads 70 radially outwardly to engage and apply sufficient forces to the wedges to compress the ripple springs. The previously described process is repeated by engaging the saws with the wedges and displacing the carriage 50 along the drive assembly to cut the wedges. It will be appreciated that the heads 70 and saw blades are then withdrawn from the cut wedges and the linear drive assembly displaces the carriage back to the start position for rotation into a further circumferential position to cut wedges of further circumferentially spaced slots.
Upon completion of the cutting operations for all circumferentially spaced slots except for the slots mounting the frame 32, the hydraulic rams 39 at opposite ends of the frame 32 can be retracted to release the frame from the stator core. The frame is then rotated to engage diametrically opposed adjacent slots which have been cut. The operation is then repeated with the cutting heads 70 aligned with the remaining two diametrically opposed uncut wedges of diametrically opposed slots. Once these slots have been cut, the wedge removal operation for that length or section of the stator core is complete. The frame is then removed from that portion of the stator core and advanced longitudinally to another section of the stator core to repeat the foregoing described process to cut the wedges of the slots in the next core section.
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
