U.S. patent application number 09/226292 was filed with the patent office on 2002-04-25 for composite electrical insulation with contacting layer and method of making the same.
Invention is credited to MILLER, MARK LEE.
Application Number | 20020047442 09/226292 |
Document ID | / |
Family ID | 22848327 |
Filed Date | 2002-04-25 |
United States Patent
Application |
20020047442 |
Kind Code |
A1 |
MILLER, MARK LEE |
April 25, 2002 |
COMPOSITE ELECTRICAL INSULATION WITH CONTACTING LAYER AND METHOD OF
MAKING THE SAME
Abstract
An insulating material (10) and method of forming the same
having an electrically insulating substrate (12) and a contacting
layer (14) bonded to the substrate, the contacting layer having a
predetermined coefficient of friction. The substrate may be an
epoxy saturated fiberglass, and the contacting layer may be a
polyester material such as PEN. The thickness of the insulating
material is easily controlled without sanding and the contacting
layer provides a surface with low coefficient of friction for use
between adjacent layers of copper in the windings of an electrical
generator.
Inventors: |
MILLER, MARK LEE; (OVIEDO,
FL) |
Correspondence
Address: |
SIEMENS WESTINGHOUSE POWER CORPORATION
SIEMENS CORPORATION
INTELLECTUAL PROPERTY DEPARTMENT
186 WOOD AVENUE SOUTH
ISELIN
NJ
08830
|
Family ID: |
22848327 |
Appl. No.: |
09/226292 |
Filed: |
January 7, 1999 |
Current U.S.
Class: |
310/179 |
Current CPC
Class: |
H02K 3/34 20130101 |
Class at
Publication: |
310/179 |
International
Class: |
H02K 001/00 |
Claims
I claim as my invention:
1. An insulating material comprising: an electrically insulating
substrate; and a contacting layer disposed on said substrate;
wherein said contacting layer provides a top surface having a
predetermined coefficient of friction.
2. The insulating material of claim 1, wherein said coefficient of
friction of said top surface is in the range of 0.2-0.25.
3. The insulating material of claim 1, wherein said contacting
layer comprises aramid paper.
4. The insulating material of claim 1, wherein said contacting
layer comprises a polyester.
5. The insulating material of claim 1, wherein said contacting
layer comprises PEN.
6. The insulating material of claim 5, wherein said contacting
layer has a nominal thickness of 0.001-0.002 inches.
7. The insulating material of claim 1, wherein said coefficient of
friction of said top surface is less than that of a bottom surface
of said substrate.
8. The insulating material of claim 1, wherein said substrate
further comprises: a woven glass fabric; and a thermosetting
polymer resin saturating said woven glass fabric.
9. The insulating material of claim 8, wherein said thermosetting
polymer resin further comprises: an upper resin layer located on a
first side of said woven glass fabric and between said woven glass
fabric and said contacting layer; and a lower resin layer located
on a second side of said woven glass fabric opposed said first
side.
10. The insulating material of claim 9, wherein said upper resin
layer has a thickness of no more than 0.002 inches, and said lower
resin layer has a thickness of no more than 0.002 inches.
11. The insulating material of claim 9, wherein said upper resin
layer has a thickness of no more than 0.001 inches, and said lower
resin layer has a thickness of no more than 0.001 inches.
12. The insulating material of claim 8, wherein said woven glass
fabric comprises eight harness weave having a nominal thickness of
0.009 inches.
13. The insulating material of claim 1, further comprising a layer
of adhesive disposed between said substrate and said contacting
layer.
14. A method of manufacturing an insulating material comprising the
steps of: providing an electrically insulating substrate; and
disposing a contacting layer on said substrate to provide a top
surface having a predetermined coefficient of friction.
15. The method of claim 14, further comprising the step of bonding
said substrate and said contacting layer with a layer of
adhesive.
16. The method of claim 14, wherein the step of providing an
electrically insulating substrate further comprises the steps of:
providing a woven glass fabric; and saturating said woven glass
fabric with a thermosetting polymer resin.
17. The method of claim 16, wherein the step of saturating further
comprises the steps of: providing an upper resin layer located on a
first side of said woven glass fabric and between said woven glass
fabric and said contacting layer; and providing a lower resin layer
located on a second side of said woven glass fabric opposed said
first side.
18. The method of claim 17, further comprising the steps of:
controlling the thickness of said upper resin layer to no more than
a first predetermined upper limit; and controlling the thickness of
said lower resin layer to no more than a second predetermined upper
limit.
19 The method of claim 18, wherein said first and said second
predetermined upper limits are each 0.002 inches.
20. The method of claim 18, wherein said first and said second
predetermined upper limits are each 0.001 inches.
Description
FIELD OF THE INVENTION
[0001] This invention relates generally to the field of electrical
insulation. The invention relates more particularly to the field of
composite electrical insulation for use between the layers of
copper that form the windings of an electrical generator rotor.
BACKGROUND OF THE INVENTION
[0002] Electrical power generators are known in the art to contain
rotor windings that are constructed of layers of copper rotor
conductors. Multiple layers of copper are stacked radially in
channels formed on the generator rotor. Layers of insulating
material are installed between the individual layers of copper to
provide both electrical insulation and a slip surface for
accommodating differential movement between adjacent copper winding
layers. The stack of copper and insulating layers is pre-loaded and
mechanically constrained by a wedge device to minimize the movement
of the layers and to restrain the stack as it undergoes centrifugal
and electromagnetic forces during the operation of the
generator.
[0003] A prior art insulating material for this application is a
step-laminated epoxy glass NEMA grade G-11 composite material
formed from multiple layers of prepreg that are pressed together
under high pressure and temperature to form a roll format laminated
material. This material is known to provide adequate compression
creep resistance during centrifugal force loading and a surface
that does not cause abrasion of the adjacent copper layer during
turning gear operation. However, in order to achieve the required
tolerance for overall thickness of this prior art laminated
material, it is necessary to sand one side surface of the material
before its use in an electrical generator. Sanding provides the
required thickness control while the unsanded side provides an
acceptable coefficient of friction for contact with the adjacent
copper layer. The sanded side of the material is then coated with
adhesive and affixed to a first layer of copper while the unsanded
side is allowed to slip against the adjoining layer of copper. Step
laminating has slow process cycle times, and the sanding step adds
further time and expense to the manufacturing process, thus making
the prior art step-laminated epoxy glass composite product
expensive. Further, the step laminating process requires expensive
tooling, thereby limiting the number of suppliers willing to invest
in the required production facilities.
SUMMARY
[0004] Accordingly, it is an object of this invention to provide an
electrical insulating material for insulating between the layers of
copper windings of an electrical generator that provides
performance characteristics similar to prior art insulating
material but that is less expensive to manufacture than prior art
insulating material. Further, it is an object of this invention to
provide a method for manufacturing an electrical insulating
material for insulating between the layers of copper windings of an
electrical generator that uses standard, inexpensive processing
equipment.
[0005] In order to achieve these and other objects of this
invention, an insulating material according to one aspect of this
invention includes an electrically insulating substrate and a
contacting layer disposed on the substrate; wherein the contacting
layer provides a surface having a predetermined coefficient of
friction. A method of manufacturing an insulating material
according to another aspect of this invention includes the steps of
providing an electrically insulating substrate, and disposing a
contacting layer having a predetermined coefficient of friction on
the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 illustrates a cross-sectional view of composite
insulating material in accordance with this invention installed
between adjacent windings of an electrical generator rotor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0007] An electrical insulating material for use in the windings of
an electrical generator should be formed in roll format and should
have the electrical insulating properties predetermined by the
generator design. The insulating material should also exhibit a
predetermined small amount of mechanical creep when subjected to
the high compression forces created during the operation of the
electrical generator. Creep in this context means a reduction in
the thickness of the insulating material over time. A reduction in
the thickness of the insulating material will cause a reduction in
the pre-load applied to the winding stack, thereby allowing
relative movement between the layers of the winding. Some movement
between the layers is unavoidable and is, in fact, desirable to a
limited extent to relieve thermal stresses. This limited movement
is provided in some generator designs by allowing some slippage
between the insulating layer and the adjoining copper winding.
However, significant loosening of the stack due to excessive creep
of the insulating material will result in fretting of the copper
material. This is particularly a problem when the generator is
rotated slowly on its turning gear, because during such periods of
slow rotation there is no centrifugal force to help restrain the
layers of the stack. Movement of the windings may cause fretting of
the copper windings, thereby creating copper dust. It is known that
such copper dust serves to reduce the dielectric properties of the
insulating material, and it has been known to cause shorting
failures in electrical generators.
[0008] An insulating material 10 according to this invention is
illustrated in FIG. 1. The insulating material 10 includes an
electrically insulating substrate layer 12 and a contacting layer
14. The substrate layer 12 may include a woven glass fabric 16
saturated with a thermosetting polymer resin 18. The contacting
layer 14 is disposed on a surface of the substrate layer 12 and is
chosen to be a material that will provide predetermined abrasion
and friction properties. When used as an insulating material for an
electrical generator, the bottom surface 19 of the insulating
material 10 opposed to the contacting layer 14 is bonded to a first
layer of copper winding material 20 by a bonding layer 22. The
bonding layer may be a dry adhesive such as nitrile rubber. A
second layer of copper winding material 24 is then placed over the
insulating material 10 with no bonding therebetween. The contacting
layer 14 acts as a slip surface with a predetermined coefficient of
friction on its top surface 21 to provide for relative movement
between the first and second layers of copper winding material 20,
24. The desired coefficient of friction is the same as, or somewhat
less than, that of the unsanded epoxy resin surface of the prior
art material formed in a high pressure and temperature press.
[0009] The insulating material 10 can be manufactured by using
common coating processes known in the art without the use of a high
pressure and temperature press. The substrate 12 is formed by first
selecting an industrial fiber glass fabric 16 which will provide
the desired thickness and density as dictated by the insulation
system design. It is preferable to select a high glass content
fabric 16 in order to minimize the mechanical compression creep
that will occur under the high centrifugal forces typically
experienced in an electrical generator rotor. A plain weave with
medium to high weight per unit area may be selected. Other fabric
weaves may be selected such as five or eight harness satin weave.
In one embodiment the fabric 16 used complies with specification
ASTM-D-578, style 7781, as published by the American Society for
Testing and Materials. This material is an eight harness (8H) satin
weave and has a nominal thickness of 0.009 inches (0.229 mm).
[0010] The glass fabric 16 selected for the substrate 12 is
saturated with a thermosetting polymer resin 18 and then cured. In
order to minimize the susceptibility of the insulating material to
creep, a high cross-linking thermosetting epoxy may be used as
resin 18. Furthermore, to minimize creep, the thickness of the
upper resin layer 26 located above the glass fabric 16 and that of
the lower resin 28 layer located below the glass fabric 16 should
be minimized. A predetermined upper limit for the thickness of
these layers should be selected to ensure that the glass fabric 16
is entirely enveloped by the resin 18, while at the same time
minimizing the thickness of non-reinforced resin upper and lower
layers 26, 28. For the embodiment discussed above with style 7781
fabric 16, an epoxy resin 18 may be applied with upper and lower
resin layer thicknesses 26, 28 of no more than 0.002 inches (0.50
mm) each, and preferably with thicknesses of no more than 0.001
inches (0.025 mm) each. The resin 18 may then be cured at a
temperature of 280-350 degree F. (125-160 degrees C.) for
approximately one-half to one hour.
[0011] A contacting layer 14 is then applied to the substrate layer
12. The contacting layer 14 may be applied to the substrate layer
12 before the step of curing the thermosetting resin 18, thereby
bonding the contacting layer 14 directly to the substrate layer 12
by means of the upper resin layer 26. Alternatively, a layer of
adhesive 30 may be applied to the bottom surface of the contacting
layer 14 prior to it being applied to the substrate 12 after the
substrate resin 18 has been cured. The adhesive 30 may be urethane
rubber based product and it may be applied to a thickness of
approximately 0.0005-0.0010 inches (0.013-0.025 mm). The contacting
layer 14 with adhesive 30 is applied to the substrate layer 12 by
nip rolling or other process known in the art, then cured at an
appropriate temperature, for example 280-350 degrees F (125-160
degrees C.).
[0012] A contacting layer 14 material is incorporated as part of
the insulating material 10 to provide the desired coefficient of
friction and resistance to abrasion of the adjoining layer of
copper winding material 24. The thickness of the substrate 12
depends only upon the thickness of the selected glass fabric 16 and
the thickness of the applied upper and lower resin layers 26, 28,
and it is, therefore, easily controlled. Similarly, the thickness
of the contacting layer 14 and layer of adhesive 30 is easily
controlled. Therefore, sanding is not necessary to control the
thickness of the insulating material 10 of this invention.
[0013] Unlike the surface of the prior art step-laminated composite
material that is controlled to be relatively smooth by the surface
of the press, the top surface of the substrate 12 as it exists
after the curing step is too rough for use as generator winding
insulation. Controlling the type and amount of resin 18, the type
of substrate glass 16, and the curing process variables may control
the properties of the as-cured substrate layer 12. The applicant
has found that such controls are adequate for controlling the
surface 19 of the substrate 12 that is bonded to the copper winding
material 20. However, to obtain the desired surface properties for
the surface of the insulating material which will abrade against
the adjacent copper winding material 24, the applicant has found
that it is necessary to use a contacting layer 14 to provide a
coefficient of friction that is less than that of the substrate
layer 12.
[0014] The coefficient of friction of the top surface 21 of the
contacting layer 14 may be, by way of example, in the range of
0.2-0.25. The sliding properties of the contacting layer 14 may be
selected to be similar to those of the unsanded top surface of
thermosetting epoxy of the prior art insulating material. The
material of the contacting layer 14 may be a plastic film, paper,
treated felt, or coated glass fabric. In one embodiment the
contacting layer 14 is aramid paper. In another embodiment the
contacting layer 14 is a polyester material such as polyethylene
naphalate (PEN) with a nominal thickness of 0.001-0.002 inches
(0.025-0.050 mm).
[0015] Other aspects, objects and advantages of this invention may
be obtained by studying the Figure, the disclosure, and the
appended claims.
* * * * *