Title of Invention	PROCESS FOR PRODUCING MICA-CONTAINING INSULATING TAPES FOR WINDINGS.
Abstract	There is disclosed a process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, said process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such as herein described, on a fiber-containing mica film, which in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber-containing mica film which has been sprinkled with said powder enamel, being cemented to a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture.

Title of Invention

PROCESS FOR PRODUCING MICA-CONTAINING INSULATING TAPES FOR WINDINGS.

Abstract

There is disclosed a process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, said process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such as herein described, on a fiber-containing mica film, which in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber-containing mica film which has been sprinkled with said powder enamel, being cemented to a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture.

Full Text	PROCESS FOR PRODUCING MICA-CONTAINING INSULATING TAPES FOR WINDINGS This invention relates to a process for producing mica containing insulating tapes for winding elements of rotating high voltage electrical machinery which after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, and their use in the main insulation of rotating high voltage electrical machines. Prior Art To insulate winding elements in rotating high voltage electrical machines the impregnation technique based on vacuum pressure impregnation has become very popular in recent years, In doing so, the winding elements for construction engineering reasons are made either as preformed coils or conduct and scolds preferably performed bars. The winding elements are provided with mica-containing mail solution and are further tired in a vacuum pressure impregnation process. Here operator apreferably low-visco solvent-free resin systems, are used as the impregnation resins. At this point they impregnate in a vacuum and under pressure the mica-containing main insulation formed from several winding layers so that cavities which can cause partial discharges between the winding layers are completely filled so that after curing of the impregnation resin an electrically and mechanically stable insulating sleeve is formed. The winding layers of the main insulation are formed by mica-containing insulating tapes. They are produced such that a mica film is cemented to a porous carrier material using a binder. This porous mica-containing insulating tape is designed to absorb the aforementioned impregnation resin under a vacuum and pressure to the greatest possible extent. Mainly in generator construction in recent years has the demand grown for mica-containing insulating tapes which are to have not only good workability on modern winding machines, but also satisfactory impregnation capacity since due to the increasing size and power of generators likewise high insulating wall thicknesses have become necessary. Known insulating tapes can only partially meet this requirement since they act rather as barrier due to their physical and chemical composition relative to the penetrating impregnation resin so that at longer impregnation times the impregnation depth, i.e. the number of impregnated winding layers, is insufficient for high insulating wall thicknesse. Description of the Invention The object of this invention is therefore to devise a mica-containing insulating tape of the initially mentioned type which in addition to very good winding properties on modern automatic winding machines also exhibits much improved impregnation behavior during vacuum pressure impregnation. In addition, this mica-containing insulating tape should be easy to produce and stable in storage. The present invention provides a process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, said process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such as herein described, on a fiber-containing mica film, which in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber-containing mica film which has been sprinkled with said powder enamel, being cemented to a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture. The epoxy resin mixture which is used in the form of a powder enamel may be selected from the group consisting of bisphenol-A epoxy resins, phenol-novolac epoxy resins and mixtures thereof. Preferably the carrier material consists of a glass fabric, a formed fabric or a plastic film. Introducing fibers into the mica film makes the latter more porous so that its capillary action is increased relative to the impregnation resin during vacuum pressure impregnation. The resulting advantages are shorter impregnation times and impregnation with more highly viscous resins to be able to impregnate also very high insulating wall thicknesses entirely with impregnation resin. It must be noted that a proportion of fiber less than 3% by weight does not contribute to improvement of the impregnation capacity; and a proportion of fiber exceeding 50% by weight even reduces the dielectric strength of the mica-containing insulating tape. In a preferred embodiment of the invention, organic and/or inorganic fibers in the fiber- containing mica film have an average diameter of 0.1 to 20 microns and preferably an average length of 0.5 to 10 mm. Furthermore, the organic fibers may be selected from the group consisting of aromatic polyamides and aromatic polyesters such as polyethylene terephthalate and the inorganic fibers may be selected from the group consisting of E-glass, S-glass, silicon glass and aluminium. According to another version of the process of the invention, the fiber-confining mica film has a curing accelerator, preferably zinc naphthenate, which acts on the solvent-free synthetic resin. In addition, the powdered enabel system can also give curing agent, preferably an aminic curing agent on the basis of a secondary and/ or aromatic amine in substituted or unsubstituted form whereby the epoxy resin mixture is comprised of a bisphenol-A epoxy resin and a phenol-novolac construction and ratio of 1:2. According to the present process the epoxy resin mixture which is used in the form of a powder enamel has preferably a softening point exceeding 85°C. The invention furthermore relates to use of a mica-containing insulating tape which was produced according to the aforementioned process versions as the main insulation in rotating high voltage electrical machines, the mica-containing insulating tape being wound in several layers around a winding element and then impregnated under a vacuum and pressure with a solvent-free synthetic resin. The epoxy resin may be in the form of a bisphenol-A epoxy resin, a phenol-novolac epoxy resin or a mixture thereof. These resins are characterized by the fact that they exhibit a softening point > 85°C. Further the epoxy resin is preferably used in a mixture with an aminic curing agent selected on the basis of a secondary aliphatic and/or aromatic amine in substituted or unsubstituted form. Furthermore, in the aforementioned vacuum pressure impregnation preferably solvent-free synthetic resins such as for example epoxy acid anhydride mixtures based on bisphenol-A or bisphenol-F are used. Epoxy resin acid anhydride system structure and 60-70oC to have viscosity low enough for the impregnation process Mica containing Insulating tapes which have been produced according to the process as claimed the information can however satisfactorily impregnated at a much higher resin viscosin and therefore especially well suited for impregnation with resins which can only be heated to roughly 30°C and therefore have a mostly very high impregnation viscosity, for example polyester resins with styrene or vinyl alcohol as the monomer. One embodiment of the invention The invention will now be described in detail using the embodiments and the diagrams prepared using the embodiments as shown in Figures 1 and 2, of the accompanying drawings which show diagrams. Example 1 A fiber-confining mica film with a weight of 160 g/m2 consisting of a mixture of uncalcined muscovite or phlogopite and 5% by weight alkali-free E-glass short fibers which have a diameter of on average 8 microns and a fiber length of roughly 3 mm is impregnated with a solution of zinc naphthenate in methylethyl ketone and the solvent is evaporated. The fiber- containing mica film which has been preimpregnated with roughly 4 g/m2 naphthenate is sprinkled with a powdered epoxy resin mixture with a softening point > 85°C and by means of a heatable calender under pressure and the action of heat is cemented to the carrier material. To achieve especially satisfactory impregnation values during vacuum pressure impregnation a curing agent, preferably an aminic curing agent, can be added to the epoxy resin mixture. The following can be used as the term and condition. a) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 2 g/m2 of a flexibly cross-linking acrylic resin and then is temperature-treated in an oven at 100°C to cure the acrylic resin; or b) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 0.5 g/m2 zinc naphthenate; or. c) a polyester formed fabric with a mass per unit area of 20 g/m2, or d) a polyester film with a mass per unit area of 42 g/m2. Example 2 A fiber -containing mica film with a weight of 160 g/m2 consisting of a mixture of uncalcined muscovite or phlogopite and 5% by weight alkali-free E-glass short fibers which have a diameter of on average 8 microns and a fiber length of roughly 3 mm is preimpregnated with a solution of an epoxy resin mixture in methylethyl ketone After the solvent is evaporated, roughly 4 g/m2 epoxy resin remain in the fiber-containing mica film. This measure prevents detachment of the mica flakes during subsequent processing so that the fiber-containing mica film is more resistant to medicine. The mica film which has been promoted and this is sprinkled with bordered epoxy resin mixture with a softening point >85o.C. The fiber-containing mica film which has been sprinkled in this way is then cemented to the carrier material by means of a heatable calender under pressure and the action of heat. The following can be used as the carrier material: a) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 2 g/m2 of a flexibly cross-linking acrylic resin which is temperature treated in an oven at 100°C for curing, or b) a polyester formed fabric with a mass per unit area of 20 g/m2, or c) a polyester film with a mass per unit area of 42 g/m2. The advantages of a mica-containing insulating tape produced using the process as claimed in the invention can be represented very effectively using the number of impregnated layers during vacuum pressure impregnation compared to known mica-containing insulating tapes. For this reason profile rods are wound with 20 layers each of the mica-containing insulating tape half-overlapped, the end faces of the insulation are sealed with resin and the model rods which have been produced a winding element in the form of a conductor rod are imbredmated with a silvent-free epoxy acid anhydride impregnation resin at 60°C for three hours. After curing, the model rods are cut crosswise to be able to measure the nation depth. In this way a mica-containing insulating tape produced using the process as described and as shown in Example 1 (sample A) or a known mica-containing insulating tape with a comparable structure, but without adding fibers (sample B), are used. The results are shown in the diagrams in Figures 1 and 2 of the accompanying drawings. The diagram in Figure 1 shows that when using the mica-containing insulating tape A which has been produced in accordance with the present invention, the insulation thickness, i. e. the thickness of the 20 layers, is impregnated overall. But, in known insulating tapes B, without adding fibers, only roughly two thirds of the insulation thickness are impregnated; this necessarily results in cavities between the individual layers which lead to partial discharges and thus to failure of the insulating system. In another test, profile rods are wound with 10 layers each of mica-containing insulating tape half-overlapped, the end faces of the insulation are sealed with resin so that model rods which simulate a winding element in the form of a conductor bar are produced. Mica- containing insulating tapes can be which has been produced as shown in Example 1 of the process of the invention insulating tape as in the prior art (sample B), but without the fiber adope. Then the cured model rods which have been provided with sample A or stable B are subjected to a thermal aging cycle, one cycle meaning the heating of the rods 55oC over 16 hours and subsequent cooling to room temperature. After each cycle the loss tangent value (tan d) is measured as a function of the voltage. The resulting maximum increase (tan d max) reproduces the optical and mechanical state of the insulation after each cycle. Higher increase values mean earlier "rising" of the insulation which subsequently leads to electrical breakdown and thus to failure of the insulation. In the diagram shown in Figure 2 the number of thermal aging cycles is plotted against the maximum loss tangent increase (tan d max in %). This indicates that the mica-containing insulating tape without the addition of fibers (sample B) after a few aging cycles has a higher maximum loss tangent increase than sample A which is shown for comparison and which was produced using the process of the invention; this also makes it possible to draw conclusions about very rapid delamination of the insulation. Commercial applicability Fiber-containing and mica-containing Mutating tapes as are produced in with the present invention, when used in form of winding elements such as conductor rods, show extremely satisfactory long-term several thermal and an extremely low tendency to delamination. 1. Process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery comprising the steps of: sprinkling an epoxy resin mixture in the form of a powder enamel such as herein described on a fiber-containing mica film which in addition to fine mica is comprised also of organic and/or inorganic fibers in the amount of 3 to 50 %, the side of the fiber-containing mica film which has been sprinkled with said powder enamel being cemented to a carier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture, winding said produced mica containing insulating tape onto windings of rotating, high voltage electrical machines, being impression a vacuum and porsure Vwith a solvent-free synthetic resin; followed by couring thereof under the action of heated 2. Process as claimed in claim 1, wherein the carrier material consists of a glass fabric, a formed fabric or a plastic film. 3. Process as claimed in claim 1 or 2, wherein the organic and/or inorganic fibers in the fiber-confining mica film have an average diameter of 0.1 to 20 microns. 4. Process as claimed in any one of claims 1 to 3, wherein the organic and/or inorganic fibers in the fiber-confining mica film have an average length of 0.5 to 10 mm. WE CLAIMS: 1. Process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, said process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such as herein described, on a fiber-containing mica film, which in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber- containing mica film which has been sprinkled with said powder enamel, being cemented to a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture. 2. Process as claimed in claim 1, wherein the carrier material consists of a glass fabric, a formed fabric or a plastic film. 3. Process as claimed in claim 1 or 2, wherein the organic and/or inorganic fibers in the fiber-confining mica film have an average diameter of 0.1 to 20 microns. 4. Process as claimed in any one of claims 1 to 3, wherein the organic and/or inorganic fibers in the fiber-confining mica film have an average length of 0.5 to 10 mm. 5 Process as claimed in any one of claims 1 to 4, wherein the organic fibers are selected from the group consisting of aromatic polyamides and aromatic polyesters such as polyethylene terephthalate. 6 Process as claimed in any one of claims 1 to 5, wherein the inorganic fibers are selected from the group consisting of E-glass, S-glass, silicon glass and aluminium 7. Process as claimed in any one of claims 1 to 6, wherein the fiber-containing mica film has curing accelerator, preferably zinc naphthenate, which acts on the solvent-free synthetic resin 8 Process as claimed in any one rein the powder enabel system also contains a curing agent, preferably an arrobic curing agent on the basis of aliphatic and/or aromatic amine in substituted substituted form whereby the resin mixture is comprised of a bisphenol-A epoxy resin and a phenol-novolac epoxy resin in the ratio of 1 2 9 Process as claimed in any one of claims 1 to 8, wherein the epoxy resin mixture which is used in the form of a powder enamel system has a softening point of > 85°C 10. Process as claimed in any one of claims 1 to 9, wherein the solvent free synthetic resin consists of a mixture comprised of one or more epoxy resin(s), preferably based on bisphenol-A or bisphenol-F epoxy resins, and an acid-anhydride hardener There is disclosed a process for producing mica-containing insulating tapes for windings of rotating high voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured under the action of heat, said process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such as herein described, on a fiber-containing mica film, which in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber-containing mica film which has been sprinkled with said powder enamel, being cemented to a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy resin mixture.

Full Text

PROCESS FOR PRODUCING MICA-CONTAINING INSULATING TAPES
FOR WINDINGS
This invention relates to a process for producing mica containing insulating tapes for
winding elements of rotating high voltage electrical machinery which after winding under a
vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured
under the action of heat, and their use in the main insulation of rotating high voltage electrical
machines.
Prior Art
To insulate winding elements in rotating high voltage electrical machines the impregnation
technique based on vacuum pressure impregnation has become very popular in recent
years, In doing so, the winding elements for construction engineering reasons are made
either as preformed coils or conduct and scolds preferably performed bars. The winding elements
are provided with mica-containing mail solution and are further tired in a vacuum
pressure impregnation process. Here operator apreferably low-visco solvent-free resin
systems, are used as the impregnation resins.
At this point they impregnate in a vacuum and under pressure the mica-containing main
insulation formed from several winding layers so that cavities which can cause partial
discharges between the winding layers are completely filled so that after curing of the
impregnation resin an electrically and mechanically stable insulating sleeve is formed. The
winding layers of the main insulation are formed by mica-containing insulating tapes. They
are produced such that a mica film is cemented to a porous carrier material using a binder.
This porous mica-containing insulating tape is designed to absorb the aforementioned
impregnation resin under a vacuum and pressure to the greatest possible extent.
Mainly in generator construction in recent years has the demand grown for mica-containing
insulating tapes which are to have not only good workability on modern winding machines,
but also satisfactory impregnation capacity since due to the increasing size and power of
generators likewise high insulating wall thicknesses have become necessary.
Known insulating tapes can only partially meet this requirement since they act rather as
barrier due to their physical and chemical composition relative to the penetrating
impregnation resin so that at longer impregnation times the impregnation depth, i.e. the
number of impregnated winding layers, is insufficient for high insulating wall thicknesse.
Description of the Invention
The object of this invention is therefore to devise a mica-containing insulating tape of the
initially mentioned type which in addition to very good winding properties on modern
automatic winding machines also exhibits much improved impregnation behavior during
vacuum pressure impregnation. In addition, this mica-containing insulating tape should be
easy to produce and stable in storage.
The present invention provides a process for producing mica-containing insulating tapes for
windings of rotating high voltage electrical machinery, said tapes, after winding under a
vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured
under the action of heat, said process comprising sprinkling an epoxy resin mixture in the
form of a powder enamel, such as herein described, on a fiber-containing mica film, which
in addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to
50%, the side of the fiber-containing mica film which has been sprinkled with said powder
enamel, being cemented to a carrier material, such as herein described, under the pressure
of at least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the
epoxy resin mixture.
The epoxy resin mixture which is used in the form of a powder enamel may be selected from
the group consisting of bisphenol-A epoxy resins, phenol-novolac epoxy resins and mixtures
thereof.
Preferably the carrier material consists of a glass fabric, a formed fabric or a plastic film.
Introducing fibers into the mica film makes the latter more porous so that its capillary action is
increased relative to the impregnation resin during vacuum pressure impregnation. The
resulting advantages are shorter impregnation times and impregnation with more highly
viscous resins to be able to impregnate also very high insulating wall thicknesses entirely
with impregnation resin.
It must be noted that a proportion of fiber less than 3% by weight does not contribute to
improvement of the impregnation capacity; and a proportion of fiber exceeding 50% by
weight even reduces the dielectric strength of the mica-containing insulating tape.
In a preferred embodiment of the invention, organic and/or inorganic fibers in the fiber-
containing mica film have an average diameter of 0.1 to 20 microns and preferably an
average length of 0.5 to 10 mm.
Furthermore, the organic fibers may be selected from the group consisting of aromatic
polyamides and aromatic polyesters such as polyethylene terephthalate and the inorganic
fibers may be selected from the group consisting of E-glass, S-glass, silicon glass and
aluminium.
According to another version of the process of the invention, the fiber-confining mica film has
a curing accelerator, preferably zinc naphthenate, which acts on the solvent-free synthetic
resin.
In addition, the powdered enabel system can also give curing agent, preferably an
aminic curing agent on the basis of a secondary and/ or aromatic amine in
substituted or unsubstituted form whereby the epoxy resin mixture is comprised of a
bisphenol-A epoxy resin and a phenol-novolac construction and ratio of 1:2.
According to the present process the epoxy resin mixture which is used in the form of a
powder enamel has preferably a softening point exceeding 85°C.
The invention furthermore relates to use of a mica-containing insulating tape which was
produced according to the aforementioned process versions as the main insulation in rotating
high voltage electrical machines, the mica-containing insulating tape being wound in several
layers around a winding element and then impregnated under a vacuum and pressure with a
solvent-free synthetic resin.
The epoxy resin may be in the form of a bisphenol-A epoxy resin, a phenol-novolac epoxy
resin or a mixture thereof. These resins are characterized by the fact that they exhibit a
softening point > 85°C. Further the epoxy resin is preferably used in a mixture with an aminic
curing agent selected on the basis of a secondary aliphatic and/or aromatic amine in
substituted or unsubstituted form.
Furthermore, in the aforementioned vacuum pressure impregnation preferably solvent-free
synthetic resins such as for example epoxy acid anhydride mixtures based on bisphenol-A or
bisphenol-F are used.
Epoxy resin acid anhydride system structure and 60-70oC to have viscosity low
enough for the impregnation process Mica containing Insulating tapes which have been
produced according to the process as claimed the information can however satisfactorily
impregnated at a much higher resin viscosin and therefore especially well suited for
impregnation with resins which can only be heated to roughly 30°C and therefore have a
mostly very high impregnation viscosity, for example polyester resins with styrene or vinyl
alcohol as the monomer.
One embodiment of the invention
The invention will now be described in detail using the embodiments and the diagrams
prepared using the embodiments as shown in Figures 1 and 2, of the accompanying
drawings which show diagrams.
Example 1
A fiber-confining mica film with a weight of 160 g/m2 consisting of a mixture of uncalcined
muscovite or phlogopite and 5% by weight alkali-free E-glass short fibers which have a
diameter of on average 8 microns and a fiber length of roughly 3 mm is impregnated with a
solution of zinc naphthenate in methylethyl ketone and the solvent is evaporated. The fiber-
containing mica film which has been preimpregnated with roughly 4 g/m2 naphthenate is
sprinkled with a powdered epoxy resin mixture with a softening point > 85°C and by means
of a heatable calender under pressure and the action of heat is cemented to the carrier
material. To achieve especially satisfactory impregnation values during vacuum pressure
impregnation a curing agent, preferably an aminic curing agent, can be added to the epoxy
resin mixture.
The following can be used as the term and condition.
a) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 2 g/m2 of a flexibly
cross-linking acrylic resin and then is temperature-treated in an oven at 100°C to cure the
acrylic resin; or
b) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 0.5 g/m2 zinc
naphthenate; or.
c) a polyester formed fabric with a mass per unit area of 20 g/m2, or
d) a polyester film with a mass per unit area of 42 g/m2.
Example 2
A fiber -containing mica film with a weight of 160 g/m2 consisting of a mixture of uncalcined
muscovite or phlogopite and 5% by weight alkali-free E-glass short fibers which have a
diameter of on average 8 microns and a fiber length of roughly 3 mm is preimpregnated with
a solution of an epoxy resin mixture in methylethyl ketone After the solvent is evaporated,
roughly 4 g/m2 epoxy resin remain in the fiber-containing mica film. This measure prevents
detachment of the mica flakes during subsequent processing so that the fiber-containing
mica film is more resistant to medicine.
The mica film which has been promoted and this is sprinkled with bordered
epoxy resin mixture with a softening point >85o.C. The fiber-containing mica film which has
been sprinkled in this way is then cemented to the carrier material by means of a heatable
calender under pressure and the action of heat.
The following can be used as the carrier material:
a) a glass fabric with a mass per unit area of 23 g/m2 which is coated with 2 g/m2 of a
flexibly cross-linking acrylic resin which is temperature treated in an oven at 100°C for curing,
or
b) a polyester formed fabric with a mass per unit area of 20 g/m2, or
c) a polyester film with a mass per unit area of 42 g/m2.
The advantages of a mica-containing insulating tape produced using the process as claimed
in the invention can be represented very effectively using the number of impregnated layers
during vacuum pressure impregnation compared to known mica-containing insulating tapes.
For this reason profile rods are wound with 20 layers each of the mica-containing insulating
tape half-overlapped, the end faces of the insulation are sealed with resin and the model
rods which have been produced a winding element in the
form of a conductor rod are imbredmated with a silvent-free epoxy acid anhydride
impregnation resin at 60°C for three hours.
After curing, the model rods are cut crosswise to be able to measure the nation depth.
In this way a mica-containing insulating tape produced using the process as described and
as shown in Example 1 (sample A) or a known mica-containing insulating tape with a
comparable structure, but without adding fibers (sample B), are used.
The results are shown in the diagrams in Figures 1 and 2 of the accompanying drawings.
The diagram in Figure 1 shows that when using the mica-containing insulating tape A which
has been produced in accordance with the present invention, the insulation thickness, i. e.
the thickness of the 20 layers, is impregnated overall. But, in known insulating tapes B,
without adding fibers, only roughly two thirds of the insulation thickness are impregnated;
this necessarily results in cavities between the individual layers which lead to partial
discharges and thus to failure of the insulating system.
In another test, profile rods are wound with 10 layers each of mica-containing insulating tape
half-overlapped, the end faces of the insulation are sealed with resin so that model rods
which simulate a winding element in the form of a conductor bar are produced. Mica-
containing insulating tapes can be which has been produced as shown in
Example 1 of the process of the invention insulating tape as in the
prior art (sample B), but without the fiber adope.
Then the cured model rods which have been provided with sample A or stable B are
subjected to a thermal aging cycle, one cycle meaning the heating of the rods 55oC over
16 hours and subsequent cooling to room temperature. After each cycle the loss tangent
value (tan d) is measured as a function of the voltage. The resulting maximum increase
(tan d max) reproduces the optical and mechanical state of the insulation after each cycle.
Higher increase values mean earlier "rising" of the insulation which subsequently leads to
electrical breakdown and thus to failure of the insulation.
In the diagram shown in Figure 2 the number of thermal aging cycles is plotted against the
maximum loss tangent increase (tan d max in %).
This indicates that the mica-containing insulating tape without the addition of fibers (sample
B) after a few aging cycles has a higher maximum loss tangent increase than sample A
which is shown for comparison and which was produced using the process of the invention;
this also makes it possible to draw conclusions about very rapid delamination of the
insulation.
Commercial applicability
Fiber-containing and mica-containing Mutating tapes as are produced in with
the present invention, when used in form of winding elements such as conductor rods,
show extremely satisfactory long-term several thermal and
an extremely low tendency to delamination.
1. Process for producing mica-containing insulating tapes for windings of rotating high
voltage electrical machinery comprising the steps of:
sprinkling an epoxy resin mixture in the form of a powder enamel such as herein
described on a fiber-containing mica film which in addition to fine mica is comprised also of
organic and/or inorganic fibers in the amount of 3 to 50 %, the side of the fiber-containing
mica film which has been sprinkled with said powder enamel being cemented to a carier
material, such as herein described, under the pressure of at least 0.2 N/mm2 and at an
elevated temperature higher than the softening point of the epoxy resin mixture,
winding said produced mica containing insulating tape onto windings of rotating, high
voltage electrical machines, being impression a vacuum and porsure
Vwith a solvent-free synthetic resin; followed by couring thereof under the action of heated
2. Process as claimed in claim 1, wherein the carrier material consists of a glass fabric, a
formed fabric or a plastic film.
3. Process as claimed in claim 1 or 2, wherein the organic and/or inorganic fibers in the
fiber-confining mica film have an average diameter of 0.1 to 20 microns.
4. Process as claimed in any one of claims 1 to 3, wherein the organic and/or inorganic
fibers in the fiber-confining mica film have an average length of 0.5 to 10 mm.
WE CLAIMS:
1. Process for producing mica-containing insulating tapes for windings of rotating high
voltage electrical machinery, said tapes, after winding under a vacuum and pressure can be
impregnated with a solvent-free synthetic resin and then cured under the action of heat, said
process comprising sprinkling an epoxy resin mixture in the form of a powder enamel, such
as herein described, on a fiber-containing mica film, which in addition to fine mica is
comprised also of organic/inorganic fibers in the amount of 3 to 50%, the side of the fiber-
containing mica film which has been sprinkled with said powder enamel, being cemented to
a carrier material, such as herein described, under the pressure of at least 0.2 N/mm2 and at
an elevated temperature higher than the softening point of the epoxy resin mixture.
2. Process as claimed in claim 1, wherein the carrier material consists of a glass fabric, a
formed fabric or a plastic film.
3. Process as claimed in claim 1 or 2, wherein the organic and/or inorganic fibers in the
fiber-confining mica film have an average diameter of 0.1 to 20 microns.
4. Process as claimed in any one of claims 1 to 3, wherein the organic and/or inorganic
fibers in the fiber-confining mica film have an average length of 0.5 to 10 mm.
5 Process as claimed in any one of claims 1 to 4, wherein the organic fibers are
selected from the group consisting of aromatic polyamides and aromatic polyesters such as
polyethylene terephthalate.
6 Process as claimed in any one of claims 1 to 5, wherein the inorganic fibers are
selected from the group consisting of E-glass, S-glass, silicon glass and aluminium
7. Process as claimed in any one of claims 1 to 6, wherein the fiber-containing mica film
has curing accelerator, preferably zinc naphthenate, which acts on the solvent-free synthetic
resin
8 Process as claimed in any one rein the powder enabel system
also contains a curing agent, preferably an arrobic curing agent on the basis of
aliphatic and/or aromatic amine in substituted substituted form whereby the resin
mixture is comprised of a bisphenol-A epoxy resin and a phenol-novolac epoxy resin in the
ratio of 1 2
9 Process as claimed in any one of claims 1 to 8, wherein the epoxy resin mixture which
is used in the form of a powder enamel system has a softening point of > 85°C
10. Process as claimed in any one of claims 1 to 9, wherein the solvent free synthetic
resin consists of a mixture comprised of one or more epoxy resin(s), preferably based on
bisphenol-A or bisphenol-F epoxy resins, and an acid-anhydride hardener
There is disclosed a process for producing mica-containing insulating tapes for
windings of rotating high voltage electrical machinery, said tapes, after winding under a
vacuum and pressure can be impregnated with a solvent-free synthetic resin and then cured
under the action of heat, said process comprising sprinkling an epoxy resin mixture in the
form of a powder enamel, such as herein described, on a fiber-containing mica film, which in
addition to fine mica is comprised also of organic/inorganic fibers in the amount of 3 to 50%,
the side of the fiber-containing mica film which has been sprinkled with said powder enamel,
being cemented to a carrier material, such as herein described, under the pressure of at
least 0.2 N/mm2 and at an elevated temperature higher than the softening point of the epoxy
resin mixture.

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Patent Number

225221

Indian Patent Application Number

IN/PCT/2000/00084/KOL

PG Journal Number

45/2008

Publication Date

07-Nov-2008

Grant Date

05-Nov-2008

Date of Filing

16-Jun-2000

Name of Patentee

ISOVOLTA - OSTERREICHISCHE ISOLIERSTOFFWERKE AKTIENGESELLSCHAFT.

Applicant Address

INDUSTRIEZENTRUM NO-SUD, ISOVOLTASTRASSE 3/OBJECT 1, A-2355, WIENER NEUDORF

Inventors:

#	Inventor's Name	Inventor's Address
1	GSELLMANN HELMUT	OBERE TEICHSTRASSE 25A, A-8010 GRAZ

PCT International Classification Number

H01B 3/04, H02K 3/30

PCT International Application Number

PCT/EP1999/07669

PCT International Filing date

1999-10-13

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	98890304.3	1998-10-16	EUROPEAN UNION