Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1999-06-30
2001-08-14
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S043000
Reexamination Certificate
active
06274961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the technical field of rotating electric machines. It refers to an elastic insulating material element for wedging a winding, in particular the stator winding, of an electric machine in the slots provided for this purpose in a laminated body.
Such an insulating material element is known, for example, from the publication U.S. Pat. No. 3,949,255 or U.S. Pat. No. 4,200,816.
2. Description of Background
Elastic insulating material elements are employed, in particular in the stators of rotating electric machines, for elastic fastening (wedging) of the stator winding in the slots of the laminated body. The stator windings are, as a rule, insulated conductor bundles of rectangular cross section which are inserted with slight play into slots of the stator body. In order to ensure a firm fit of the winding in the slot, the wedging must withstand stresses due to the intrinsic mass of the winding and to electromagnetic forces occurring during operation and in the event of a short circuit, in such a way that it does not become possible for the winding to be loosened and to vibrate.
Conventional slot wedges, in particular for relatively small machine units, consist of an insulating material which is worked or machined in the form of a prism. As a rule, glass-fiber reinforced epoxy resin is used as insulating material (see, for example, U.S. Pat. No. 4,200,818). With the aid of a plastically elastic intermediate layer (fleece, felt), these wedges are adhesively bonded axially into the slots of the toothed tips of the lamination stack and partly, in an impregnating process, to the winding and the lamination body. Another conventional wedge design is based on the action of double wedges. Two flat wedges located one above the other are pushed into the wedge slots, the prestressing force being built up by one flat wedge being driven axially (see, for example, U.S. Pat. No. 3,949,255).
A disadvantage of both forms of wedge is that the wedge design is inherently rigid and inflexible. The prestressing force is undefined. Thermal expansions of the slot packing result, due to rigid wedging, in an enormous increase in the pressure forces exerted on the slot packing, and this may lead to a pronounced settling of the slot packing, with the resulting undesirable loosening of the winding.
Wedging with the aid of plastic corrugated springs (U.S. Pat. No. 3,949,255) eliminates the disadvantage of inelastic wedging. For this purpose, elastic corrugated springs are inserted between a rigid wedge and a winding (or between two rigid wedges). The necessary prestressing force is achieved by the defined compression of the corrugated spring. Shrinkage of the slot packing due to settling processes is compensated by the respringing of the corrugated spring. Use of elastic wedges is another solution for achieving elastic wedging. By means of appropriately thin wedges or centrally cut-out wedges (convex/concave wedges), the flexibility of the wedges is increased and the prestressing forces are reduced. With this solution, too, settling processes in the slot packing can be compensated to some extent.
In both elastic wedging methods, maintaining the minimum prestressing force permanently is ensured only when the elastic plastic elements also preserve their elastic properties completely. It is known, however, that all reinforced plastics tend to yield or creep under constant bending stress and, in particular, increased temperatures. As complicated tests have shown, considerable yield is already to be expected at normal operating temperatures, even when fiber reinforced plastics with heat-resistant binders are used. In the event of operating faults in which temperatures are increased even further for a short time, yield of this kind may become critical, so that there is the possibility of loosening of the winding.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel insulating material element for the wedging of windings, in which element yield/creep of the insulating material or the effects of yield/creep of the insulating material on the elastic behavior of the wedging can be reliably avoided.
In an insulating material element of the type initially mentioned, the object is achieved in that the insulating material element has a striplike metal spring core which is surrounded on all sides by a casing made of an insulating material. The essence of the invention is that the insulating material body is no longer used as the elastic element, but, instead, the metal spring core embedded therein. In this case, the insulating material is functionally necessary only for the electric insulation of the metal spring core and, if appropriate, additionally for shaping the corresponding structural part. By contrast, its contribution to the mechanical behavior of the structural part must, at most, still be marginal. The metal spring core, which preferably consists of a nonmagnetic resilient metal, in particular of a high-grade steel, and has a thickness of a few millimeters, preferably between 2 and 3 mm, exhibits virtually no yield behavior even at relatively high temperatures.
A first preferred embodiment of the insulating material element according to the invention is defined in that the metal spring core has means by which eddy currents induced in said metal spring core are limited. This prevents strong eddy currents, along with the corresponding thermal effects in the elements, from being excited as a result of the high airgap induction in the machine. A preferred development of this embodiment is distinguished in that the means for limiting induced eddy currents comprise slitlike incisions which, arranged so as to be distributed in the longitudinal direction of the metal spring core, project into the interior of said metal spring core, in each case starting from the longitudinal edges of the latter. The metal spring core is subdivided into individual sectors by the provision of the incisions. This ensures that possible loops, in which eddy currents can flow, are limited to electrically and thermally uncritical geometric dimensions. The slitting is, at the same time, to be arranged in such a way that the mechanical spring action of the metal spring core remains optimal. This may be achieved, for example, in that the incisions project into the interior of the metal spring core alternately from the opposite longitudinal edges of the latter, and in that the incisions starting from the different longitudinal edges overlap in the interior of the metal spring core.
The casing of the insulating material element according to the invention preferably consists of a fiber reinforced plastic, in particular a high-temperature thermoset or high-temperature thermoplastic. This ensures that the settling of the casing material or embedding material under compressive stress is negligibly small.
In order to avoid delamination due to shear stresses, according to a further preferred embodiment additional means are provided for improving the mechanical connection between the metal spring core and the casing. For this purpose, on the one hand, it may be considered to pretreat the metal spring core with an adhesion promoter; on the other hand, as an additional means for improving the mechanical connection, the metal spring core may be provided with bores arranged in a distributed manner. In addition to good adhesive bonding, however, the incisions (slits) in the metal spring core, which are provided on account of the eddy currents, also ensure a uniform introduction of force because of the resulting positive connection with the embedding material.
The insulating material element according to the invention may selectively be designed both as a slot wedge and as a corrugated spring and be used solely as a slot wedge or as a corrugated spring or in a combination of a slot wedge and corrugated spring.
If the element is designed as a slot wedge, it may preferably have a concave cross-sectional profile on the underside and a convex cross-s
Baumann Thomas
Joho Reinhard
Oesterheld Jorg
ABB Research Ltd.
Burns Doane Swecker & Mathis L.L.P.
Perez Guillermo
Ramirez Nestor
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