Insulation system, insulant, and insulation material for producing the insulation system

Abstract

Various embodiments include an insulation material for an electrical rotating machine comprising: a curable matrix material; a curing agent; and a filler embedded in the matrix material. The filler comprises electrically conductive doped metal oxide particles.

Claims

1. An insulation material for an electrical rotating machine, the material comprising: a curable matrix material; a curing agent operable to set the curable matrix material; and a filler embedded in the matrix material; wherein the filler comprises electrically conductive n-doped metal oxide particles including at least one metal oxide in binary and tertiary mixed phase; and wherein the particles are doped with at least two elements selected from the group consisting of: fluorine, chlorine, phosphorus, and sulfur.

2. The insulation material as claimed in claim 1, wherein a concentration of the particles in the filler exceeds a respective percolation threshold.

3. The insulation material as claimed in claim 1, wherein the particles have an aspect ratio of 10 or higher.

4. The insulation material as claimed in claim 1, further comprising a second filler comprising electrically conductive doped metal oxide particles embedded in the curable matrix material.

5. The insulation material as claimed in claim 1, further comprising a second filler comprising electrically conductive doped metal oxide particles embedded in the curable matrix material; wherein the particles of the second filler have a different form in comparison to particles of the first filler.

6. The insulation material as claimed in claim 1, wherein the particles comprise spheres.

7. The insulation material as claimed in claim 1, further comprising a second filler comprising electrically conductive doped metal oxide particles embedded in the curable matrix material; wherein the particles of the second filler have different dimensions in comparison to particles of the first filler.

8. The insulation material as claimed in claim 1, wherein the particles have a nanoscale dimension.

9. The insulation material as claimed in claim 1, wherein the particles have a microscale dimension.

10. The insulation material as claimed in claim 1, wherein the particles comprise solid material.

11. An insulation system comprising: a main insulation; an outer corona shielding; and an overhang corona shielding; wherein the outer corona shielding includes an insulation material for an electrical rotating machine, the insulation material comprising: a cured matrix material; and a filler embedded in the matrix material; wherein the filler comprises electrically conductive n-doped metal oxide particles including at least one metal oxide in binary and tertiary mixed phase; wherein the particles are doped with at least two elements selected from the group consisting of: fluorine, chlorine, phosphorus, and sulfur.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a drawing showing a schematic of tin oxide particles having high-resistance depletion boundary layers.

(2) FIG. 2 shows the formation energies of defects in tin oxide particles.

(3) FIG. 3 shows a measuring system for testing use.

(4) FIG. 4 shows two specimens from FIG. 3 in comparison.

(5) FIG. 5 shows the measurement of the resistance over that region of the left-hand specimen from FIG. 4 that is stressed by partial discharges.

DETAILED DESCRIPTION OF THE DRAWINGS

(6) The teachings of the present disclosure include various insulation materials for an electrical rotating machine, comprising a curable matrix material and a curing agent with filler embedded therein, the filler having at least one particle fraction of metal oxide particles which through doping are conductive, insulants which are produced by curing the insulating material, and/or insulation systems which comprises such an insulant.

(7) In some embodiments, the at least one filler fraction with the metal-oxidic particles which are electrically conductive through doping is present in the insulation material at a concentration which exceeds the percolation threshold.

(8) In some embodiments, as outer corona shielding, overhang corona shielding and/or internal potential control, the insulation system contains a layer of an insulant which is producible by curing by virtue of the insulation material with the curable matrix material, the curing agent and the at least one filler fraction.

(9) In some embodiments, there is an insulation system present which comprises an insulant that is obtainable by curing of an insulation material according to the invention and that, as outer corona shielding OCS, overhang corona shielding OvCS and/or internal potential control, has a layer having a resistance in the kiloohm to megaohm range, as the square resistance of a layer of this kind having a thickness of several 100 μm.

(10) In some embodiments, as outer corona shielding and/or as internal potential control in the insulation system, there is a layer present of an insulant which is producible by curing by virtue of the insulation material with the curable matrix, the curing agent and the at least one filler fraction, this layer having a square resistance of 1 to 100 kohms at a layer thickness of around 100 to 400 μm.

(11) In some embodiments, the insulation system comprises a main insulation, an internal potential control, IPC, an outer corona shielding, OCS, and an overhang corona shielding, OvCS, it being possible to set an electrical resistance in a range from 10.sup.4 ohms to 10.sup.12 by adjusting the filler fraction(s) in the polymeric matrix of the insulant. The resistance can be set through the choice of the metal oxide, the doping of the metal oxide, in terms both of the doping element and of the concentration, and also by the layer thickness of the insulant, and also by any combinations of the aforesaid possibilities for variation.

(12) In some embodiments, the insulation system comprises the insulant and an insulating tape, in the form of a wrapping tape, for example.

(13) In some embodiments, the at least one particle fraction of doped metal oxide has an aspect ratio of 10 or higher, and so is present in platelet form.

(14) In some embodiments, the insulation material has a plurality of particle fractions, which are embedded in the curable matrix material.

(15) In some embodiments, there are a plurality of particle fractions having different forms.

(16) In some embodiments, there is at least one particle fraction present having platelet-shaped particles.

(17) In some embodiments, there is at least one particle fraction present having globular particles.

(18) In some embodiments, there is at least one particle fraction present having rodlet-shaped particles.

(19) In some embodiments, at least one particle fraction is present in the form of short fibers.

(20) In some embodiments, there are at least two particle fractions present, one with platelet-shaped particles and one with globular particles.

(21) In some embodiments, there are at least two particle fractions of the same form present.

(22) In some embodiments, there are at least two particle fractions present having different dimensions.

(23) In some embodiments, there is at least one particle fraction present which has particles with at least one nanoscale dimension.

(24) In some embodiments, there is at least one particle fraction present which has particles with at least one microscale dimension.

(25) In some embodiments, the particles have n-doping.

(26) In some embodiments, the particles are solid.

(27) In some embodiments, the particles are porous.

(28) In some embodiments, the particles are hollow.

(29) In some embodiments, the platelet-shaped particles have one nanoscale and two microscale dimensions. “Nanoscale” in the present disclosure means that at least one particle fraction has a dimension in the nanometer range, for example below 500 nm, preferably below 300 nm and very preferably below 100 nm.

(30) In some embodiments, the metal-oxidic material of which the particles of the at least one doped filler fraction are made is selected from the group of the following metal oxides, glasses and ceramics: metal oxides in binary and tertiary mixed phase, especially tin oxide, zinc oxide, zinc stannate, titanium oxide, lead oxide, silicon carbide, chromium oxide, aluminum oxide, any desired mixtures thereof, and/or further metal oxides or mixed metal oxides that are suitable for doping. The metal oxides stated above may be doped using, for example, the following elements, and also any desired mixtures of these elements: antimony, fluorine, chlorine, tungsten, molybdenum, iron, phosphorus, sulfur, nickel, alone or in any desired combinations. The concentration of the doping may be in the range from 5 to 30 mol %, more particularly from 10 to 20 mol %.

(31) For use as a filler in the outer corona shielding it is possible as a result to realize, for example, small square resistances in the range from 10.sup.3 to 10.sup.5, more particularly in the region of 10.sup.4, ohms. Suitable material for the filler particles are all n-conducting semiconductors which can be produced as particles, can be embedded in the form of a composite insulant into a curable matrix, and can then be processed in thin layers. For example, the n-conducting filler particles may also be present in coated form. In some embodiments, under an oxidizing atmosphere, the filler particles are to form a notable superficial depletion boundary layer, and which by doping achieve a useful resistance range of an OCS, i.e., for example, in the range from 10.sup.2 to 10.sup.7 ohms.

(32) In some embodiments, metal-oxidic filler particles, if appropriately produced and given n-conducting doping, are suitable as electron donors as a result of manifestation at depletion boundary layers with oxygen vacancies. In the case of partial discharges, these depletion boundary layers widen into lower layers and so give rise locally to a high-resistance region, in which the partial discharges are taken down simply by way of the potential. Accordingly, the electrical resistance of the percolated particle network increases with the oxygen vacancies in the insulant to such a degree that the properties of an overhang corona shielding are locally present and therefore the electrical field which can trigger a partial discharge is controlled resistively. Accordingly, defects present in the layer undergo self-passivation. Under the same loading, conventional OCS layers with carbon particles in insulants are completely destroyed.

(33) Under an oxidizing atmosphere and at high temperature, the surface boundary layer of a metal oxide, as elucidated in FIGS. 1 and 2 with reference to tin oxide as an example, forms oxygen vacancies which act as electron donors and are here used with preference. In operation, therefore, an OCS produced therewith has—locally—a resistance structure which—comparable to the principle of the overhang corona shielding—effects resistive control of the electrical field, with the local field intensity and hence the local partial discharge activity decreasing over time for a voltage which remains the same.

(34) Accordingly, an existing defect, through the n-conducting material that is present, automatically builds—so to speak—its own high-resistance layer providing resistive control, as a result of the self-oxidizing depletion boundary layers, and, consequently, the partial discharge activity in the defect subsides or disappears entirely. Hence a self-regulating layer is formed.

(35) FIG. 1 in this regard shows a schematic of tin oxide particles having high-resistance depletion boundary layers. The figure shows a potential barrier 10 of the interface between two tin oxide particles 12 at which there is mutual repulsion by electrons 13 from the two tin oxide particle depletion boundary layers 11.

(36) FIG. 2 shows the formation energies of defects in tin oxide particles. The formation energy of oxygen vacancies for tin oxide particles is located, as can be seen, in the region +/−0 eV and accordingly, in this material, oxygen vacancies can form under a reducing atmosphere and disappear again under an oxidizing atmosphere.

(37) FIG. 3 shows a measuring system for testing use. The property tested was the electrical exposure under partial discharges of the kind occurring in the operation of an insulation system with main insulation, potential control internally, outer corona shielding and overhang corona shielding. The specimen tested comprised an insulant which can be used as outer corona shielding. The figure shows the plate electrode 1, on which the specimen 2 lies, followed by the rod electrode 5, of stainless steel, for example, and by a cover 4 and an annular support 3. The partial discharge is represented by the arrow 6.

(38) FIG. 4 then shows two specimens 2 from FIG. 3 in comparison: on the left, after testing, an insulant incorporating teachings of the present disclosure, a bedding matrix and therein at least one filler particle fraction which consists of a doped metal oxide, virtually undamaged, and on the right, a comparative specimen with conventional carbon black/graphite-filled insulant, which has suffered complete destruction locally.

(39) It can be seen that in the tests in which partial discharges were triggered with a bar electrode on test coatings over a number of hours, an insulant whose electrical conductivity is generated by the doped metal oxide particles of the invention exhibits a significantly higher resistance toward partial discharges. Hence under the same particle discharge exposure conditions, at the time at which the carbon black/graphite-filled conventional insulants already have a complete hole, having thus been locally “eaten up” entirely, the specimen composed of the insulant incorporating teachings of the present disclosure shows virtually no traces of erosion.

(40) In the case of a destroyed site in the insulation system of a generator, as shown on the right in FIG. 4, therefore, a conventional outer corona shield would undergo successive dissolution, and the defect would grow with increasing rapidity, accompanied by stress to and destruction of the main insulation as a result of increasing field intensities and hence partial discharge activities. The left-hand specimen with the comparative layer incorporating teachings of the present disclosure, in the example an insulant filled with doped tin oxide, on the other hand, exhibits not only the erosion resistance but also a significantly increased resistance profile, as can be seen in FIG. 5.

(41) FIG. 5 shows the measurement of the resistance over that region of the left-hand specimen from FIG. 4 that is stressed by partial discharges, and, as expected, a shift in resistance was observed from the “normal” OCS resistance range, of around 10.sup.4 ohms, to the resistance range of the OvCS, of around 10.sup.9 ohms. This effect is attributable to the surface boundary layers—in this regard, compare FIG. 1—and to their oxidation through the local energy of the partial discharges and the presence of an oxidizing atmosphere, as shown in FIG. 2. The result in the case of the left-hand specimen, locally, is an OvCS resistance structure whereby the electrical field is resistively controlled and hence the local field intensity and, accordingly, the local partial discharge activity go down over time for the same voltage.

(42) Accordingly, an existing defect, through the n-conducting material that is present, automatically “builds”—so to speak—its own high-resistance layer providing resistive control, as a result of the self-oxidizing depletion boundary layers, and, consequently, the partial discharge activity in the defect subsides or disappears entirely. Hence a self-regulating insulant for an outer corona shield is formed. FIG. 5 shows the measured shift in resistance over the partial discharge-stressed site of the outer corona shielding test layer incorporating teachings of the present disclosure, with doped tin oxide particles as a filler fraction in the insulant.

(43) Here, for the first time, an insulation material for an insulation system is presented in which filler particles embedded in a polymeric matrix are used for the OCS which in principle are n-doped metal oxides which on the one hand in the composite material, above the percolation threshold, have a square resistance of 1 to 1000 kohms and on the other hand at the same time, as a result of local electrical discharges at the defects, cause a local rise in the OCS resistance under an oxygen-containing atmosphere by up to 7 decades, so that the locally increased resistance region functions like a locally resistive-capacitive field control—comparable with an overhang corona shield OvCS. As a result of the stress which occurs as a result of partial discharges, the electrochemical properties of the particles are altered such that they automatically develop into an OCS layer. In the present context, therefore, it is possible to refer to a system as “self-healing” or self-“passivating”, and this significantly lengthens the lifetime of the insulation systems of electrically rotating machines.