Patent Application
20170174867
The present disclosure relates to an epoxy resin formulation, a support to surround an end winding of a stator or a rotor of an electric machine made from such an epoxy resin formulation, to a method to fabricate an epoxy resin formulation, and to the use of an epoxy resin formulation as a support for an end winding of a stator or rotor of an electric machine.
The electric machine is a synchronous generator to be connected to a gas or steam turbine, commonly referred to as turbogenerator. In particular the concerned turbogenerator is a short circuit generator to provide high power for a very limited time in laboratory tests.
Short circuit generators are electric machines which operate generally in qualified laboratories to provide the necessary power during qualification tests of components like insulators, switchgears, terminal boxes, etc. The end windings of a stator of the electric machine are heavily stressed by the huge electromagnetic force induced during the short circuit. The end windings are the parts of the electric winding or coils which are not housed in the slots of the stator but lying outside. Due to the forces in short circuit generators the end windings must be held in position with specific fixing means. These fixing means are sometimes designed as supports made from a resin which enclose and mechanically hold the end windings. The end windings are embedded in the support. These supports are named resin baskets in the art. The supports have the further function to avoid heavy partial discharges during high voltage acceptance tests. Thus, such supports also serve as insulators. The supports have generally a weight of 2 tons and a diameter of 2 meter for a specific application. With long term operation and wide ambient temperature ranges down to −20° C. to −30° C., a problem with the support material may arise. In the material cracks occur which weaken the structure and can induce damages to the generators leading to failures.
It is an object of the invention to enhance the reliability of a support for an end winding of a stator of an electric machine. It is a further object of the invention to provide a material with a high mechanical and electrical reliability. This object is solved with the features of a support to surround end windings, the use of a support, a method to fabricate an epoxy resin formulation as described herein, and an epoxy resin formulation.
Further characteristics and advantages will be more apparent from the description of a non-exclusive embodiment of the epoxy resin formulation and the support to surround an end winding of a stator of an electric machine, illustrated by way of non-limiting example in the accompanying drawing, in which:
With reference to
The support 1 is made from an epoxy resin formulation which comprises the compounds of at least an epoxy resin of the type of bisphenol A or F, at least a hardener of type diamine, e.g. polyoxypropylendiam or polyoxypropylenetriamine, and at least an inorganic filler, in an example silica, in a further example aluminium oxide. Further, the inorganic filler in the epoxy resin formulation has different particle sizes. In a further example the inorganic filler has an amount of the epoxy resin formulation between 40 and 80 parts per weight. In an example the support 1 comprises at least one catalyst. The epoxy resin formulation is fabricated with common methods. Moreover, a specific mixing and casting process contains the steps of mixing the compounds with a temperature between 15° C. and 35° C., casting the material with a temperature between 15° C. and 35° C., and postcuring the material for several hours, e.g. four to six hours, with a temperature between 60° C. and 100° C. The support 1 is reinforced with several layers of glass fabric embedded into the support 1 itself. The glass fabric embedded into the support 1 creates an additional mechanical stability and reduces the internal stresses due to the different thermal expansion coefficients of the various components within the end winding basket. Some glass fabric layers can be properly shaped and arranged in a form of a pipe network, ensuring an improved resin flow during the impregnation process down to any remote place of the end winding basket volume which needs to be properly filled in. With this aim it is generally envisaged to perform the resin casting after vacuum has been established in the whole end winding basket.
In an embodiment, the invention furthermore covers the disclosed material as such, the epoxy resin formulation comprising the compounds of at least an epoxy resin of the type of bisphenol A or F, at least a hardener of type diamine, e.g. polyoxypropylendiam or polyoxypropylenetriamine, and with or without an aliphatic diamine having benzene ring e.g. Xylylenediamine, and at least an inorganic filler. The specific examples and the fabrication method of the epoxy resin formulation are the same as described above. The epoxy resin formulation can be used in a variety of industrial applications in which high mechanical and/or electrical requirements dominate together with large ambient temperature variations, like bushings, capacitors, electric transformers, electric generators and motors with compact stator end winding designs.
While the invention has been described in detail with reference to exemplary embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention. The foregoing description of the embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 15200983.3 | Dec 2015 | EP | regional |
| 16156128.7 | Feb 2016 | EP | regional |
