Insulating material for rotating machines

Abstract

An insulating material and its method of use of insulating material for rotating machines such as motors and generators. The insulating material includes a resin embedded with a filler that is not based only on a monomodal nanoparticle size particle distribution. Radiation erodes the material and is conductive to the formation of in situ protective layers on the body to be insulated.

Claims

1. A coil winding comprising a winding coated with a cured insulating material of a curable formulation comprising: a resin, and a nanoparticulate filler embedded in the resin, wherein the nanoparticulate filler is present in at least bimodal size distribution according to a distribution curve having a full distribution width at half maximum, as characterized by transmission electron microscopy, of greater than 1.5 d.sub.max, wherein the nanoparticulate filler is configured to absorb energy in the form of partial discharges provided by the coil winding to build at least locally sintered parts.

2. The coil winding as claimed in claim 1, wherein the filler is present with an average diameter of from 1 to 500 nm.

3. The coil winding as claimed in claim 1, wherein the filler is present in an amount of 1 to 80 wt % of the formulation.

4. The coil winding as claimed in claim 1, wherein the resin is polymerizable thermally and/or by UV light.

5. The coil winding as claimed in claim 4, wherein the filler is present on the basis of a metal oxide and/or semimetal oxide.

6. The coil winding of claim 4, wherein the resin is an epoxy resin.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagrammatic embodiment of the passivation coat by degradation of the polymeric matrix on a body surface coated with insulating material.

(2) FIG. 2 shows the relationship between the erosion depth and the filler content.

(3) FIG. 3 shows the particle size distribution according to one exemplary embodiment of the invention.

(4) FIG. 4 shows a further particle size distribution of an exemplary embodiment of the invention.

DESCRIPTION OF AN EMBODIMENT

(5) In FIG. 1 it is seen that the model of the passivation coat goes through a number of stages until a protective coat is formed. In the initial processes, the pure polymer between the nanoparticles is eroded, leading to concentration of the nanoparticles. A further absorption of energy in the form of partial discharges results in a local sintering operation on the part of the nanoparticles. Because of this mechanism, a ceramic layer is formed which protects the uneroded nanoparticulate polymer beneath from further erosion.

(6) It has been possible to show that the use of at least two different kinds and/or sizes of nanoparticles, differing significantly in their particle diameters, leads to nanocomposites which have a particularly pronounced erosion resistance. A bimodal distribution is already of advantage here; in other embodiments, multimodal particle fractions are preferred.

(7) This can be understood schematically in the above-simplified representation of FIG. 1 and of FIG. 2 for the formation of passivation coats. Under the influence of partial discharges, there is agglomeration of the nanoparticles through chemical or physical processes, ending in a passivating protective coat. The combination of at least two different sized nanoparticles reinforces this process, since, under the influence of TE, the nanoparticles with relatively low diameter and correspondingly enlarged active surface area support the agglomeration or local sintering processes, and therefore lead more quickly to the development of an erosion-resistant coat. This has the advantage that the concentration of nanoparticles with a small diameter can be kept low, this being valuable both economically and from a chemical standpoint, since it allows more effective control over properties such as viscosity, reactivity, and storage stability at the same time the positive properties, such as high specific surface area and smaller nanoparticles, for example, can be exploited.

(8) In accordance with the invention, nanoparticles are dispersed in a resin, as for example an epoxy resin, which comprises a distribution curve having a full width at half maximum of not less than 1.5 d.sub.max. According to one embodiment of the invention, therefore, the minimum half width at full maximum for the distribution curve is 1.55 d.sub.max, more particularly 1.6 d.sub.max, or even higher values.

(9) This describes a particle distribution which encompasses not only one size of nanoparticles, but instead a plurality of particle size fractions.

(10) According to one advantageous embodiment of the invention, the nanoparticles are dispersed monodispersely in the filler.

(11) According to a further advantageous embodiment of the invention, the nanoparticles in the filler are based on a metal oxide, a semimetal oxide, and especially preferably on silicon dioxide and/or aluminum oxide.

(12) According to a further advantageous embodiment of the invention, the polymeric matrix in which the filler is dispersed is an epoxy resin, as for example a diglycidyl ether based on bisphenols, such as bisphenol A and/or bisphenol F, for example.

(13) According to one embodiment of the invention, the resin further comprises a hardener, as for example an acid anhydride hardener such as methyltetraphthalic anhydride and/or methylhexahydrophthalic anhydride.

(14) According to a further advantageous embodiment of the invention, the resin further comprises an accelerator, as for example an amine derivative and/or a naphthenate.

(15) According to a further advantageous embodiment of the invention, the filler comprises nanoparticle fractions having particle diameters in the range from 1 to 200 nm, more particularly from 1 to 150 nm, and very preferably in the range from 1 to 80 nm.

(16) According to one advantageous embodiment of the invention, the filler is present with an average diameter D.sub.50 of 1 to 500 nm, preferably of 1 to 300, especially preferably of 1 to 100 nm.

(17) According to a further advantageous embodiment of the invention, the filler is present in the insulating material in an amount of 1 to 80 wt %, more particularly 1 to 60 wt %, and very preferably in the range from 1 to 50 wt % of the overall formulation.

(18) The use of a particle fraction having a distribution curve with a full width at half maximum of more than 1.5 d.sub.max produces substantial advantages not only in the selection and manufacture of the nanocomposites but also in the quality assurance of the composites. The particle dispersions are prepared preferably by sol-gel operations. To establish the desired particle size distribution, it is also possible to employ a combination of different particle dispersions. The particle size is characterized according to the prior art, preferably a manual or automatic evaluation of the particle diameter on the basis of micrographs from transmission electron microscopy, TEM for short.

(19) FIG. 3 shows by way of example a particle size distribution of one working example of the invention. The particle system shown for the filler is reproduced graphically, through a representation of the percentage fraction of the respective powder fraction in intervals of 1 nm against the particle diameter. The particle mixture exhibits its d.sub.max, in other words the peak in the distribution curve that has the greatest fraction relative to the corresponding particle size, at 9 nm. The full width at half maximum of the distribution curve is given by the width of the distribution curve in nm at half height relative to d.sub.max. In this particle composition, the full width at half maximum of the distribution curve is found to be 1.6 d.sub.max.

(20) FIG. 4, lastly, shows a comparable representation to that of FIG. 3, albeit of a different working example of the invention, in which a system is shown that comprises aluminum oxide particles and silicon dioxide particles. The size distribution set out in FIG. 4 shows a local d.sub.max at 9 nm. On this basis, the distribution curve has a full width at half maximum of 1.7 d.sub.max.

(21) The invention discloses for the first time an insulating material with a filler which is based not only on a monomodal nanoparticle size distribution. As a result, the formation of coats on the element to be insulated that provide protection in situ is greatly favored.