U.S. patent number 3,789,337 [Application Number 05/209,466] was granted by the patent office on 1974-01-29 for insulation structure for electrical apparatus.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Harry R. Sheppard.
United States Patent |
3,789,337 |
Sheppard |
January 29, 1974 |
INSULATION STRUCTURE FOR ELECTRICAL APPARATUS
Abstract
Insulation structure having filler members which keep the
overall insulation structure tight when heated. The filler members
are located within the insulation structure at various places and
in sufficient quantities, with the shortest dimension of the filler
member oriented in the direction in which expansion is desired. As
the insulation structure is heated, the shortest dimension of the
filler member increases to tighten the insulation structure. The
filler member is constructed from a material which tends to reduce
its surface area when heated without changing its volume.
Inventors: |
Sheppard; Harry R. (Sharon,
PA) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22778861 |
Appl.
No.: |
05/209,466 |
Filed: |
December 17, 1971 |
Current U.S.
Class: |
336/60; 336/57;
336/206; 174/116; 336/196; 336/210 |
Current CPC
Class: |
H01F
27/303 (20130101) |
Current International
Class: |
H01F
27/30 (20060101); H01f 027/08 () |
Field of
Search: |
;336/196,198,206,94,57,100,60,210 ;174/13R,116 ;317/258 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goldberg; E. A.
Attorney, Agent or Firm: A. T. Stratton et al.
Claims
I claim as my invention:
1. Electrical apparatus comprising electrical conductors separated
by an insulation structure, said insulation structure including an
insulating member and a plurality of spaced filler members which
expand when heated to compress said insulation structure, said
insulating and filler members being constructed of different
materials, and each said filler members being prestretched in a
direction along at least one of its dimensions.
2. The electrical apparatus of claim 1 wherein a first dimension of
a filler member tends to increase in size when heated and at least
one of the other two dimensions tends to decrease in size when
heated, said first dimension being oriented in a direction in which
compressive forces tighten the insulation structure.
3. The electrical apparatus of claim 1 wherein a filler member is
constructed of a material which has a tendency to decrease its
surface area, when heated, without substantially changing its
volume.
4. The electrical apparatus of claim 1 wherein a filler member is
constructed of a material selected from the group of materials
consisting of polytetrafluorethylene, polyvinyl chloride,
polyvinylidene chloride, polyvinylidene fluoride, polyethylene,
polypropylene, isotatic polystyrene, polyphenylene oxide,
polycarbonate, nylon, and silicone rubber.
5. The electrical apparatus of claim 1 wherein the insulating
member includes a cellulosic material.
6. The electrical apparatus of claim 1 wherein the first dimension
of a filler member is not greater than its other two dimensions
before being heated.
7. The electrical apparatus of claim 6 wherein the electrical
conductors are formed into a hollow winding and disposed around a
leg of a magnetic core of a transformer to form a core-winding
structure, and wherein the insulation structure physically
separates the electrical conductors from each other and from the
magnetic core.
8. The electrical apparatus of claim 7 wherein a filler member has
its first dimension oriented in a radial direction of the winding
structure.
9. The electrical apparatus of claim 8 wherein a filler member is
disposed between the electrical conductors of the winding
structure.
10. The electrical apparatus of claim 8 wherein a filler member is
disposed between the winding structure and the magnetic core
leg.
11. The electrical apparatus of claim 8 wherein the winding
structure comprises concentric windings and a filler member is
disposed between concentric windings of the winding structure.
12. The electrical apparatus of claim 7 wherein a filler member has
its first dimension oriented in the axial direction of the winding
structure.
13. The electrical apparatus of claim 12 wherein the winding
structure comprises a plurality of stacked coil disk windings and a
filler member is disposed between coil disks of the winding
structure.
14. The electrical apparatus of claim 12 wherein a pressure ring is
disposed adjacent said winding structure and a filler member is
disposed between the winding structure and the pressure ring.
15. The electrical apparatus of claim 7 wherein a filler member is
wrapped around the insulation of the electrical conductors.
16. Electrical inductive apparatus comprising a laminated magnetic
core, an insulated winding structure disposed in inductive
relationship with said magnetic core, an insulation structure, end
frame means for holding the laminations of said magnetic core
together, a prestretched filler member disposed between said end
frame means and said magnetic core, said filler member having a
first dimension which tends to increase in size when heated, said
first dimension of said filler member being not greater than its
other two dimensions before being heated, said first dimension
being oriented in the direction which is perpendicular to the
adjacent faces of said magnetic core and said end frame means.
17. The electrical inductive apparatus of claim 16 wherein the
filler member is constructed of a material which has a tendency to
decrease its surface area, when heated, without substantially
changing its volume.
18. The electrical inductive apparatus of claim 16 wherein the
filler member is constructed of a material selected from the group
of materials consisting of polytetrafluorethylene, polyvinyl
chloride, polyvinylidene chloride, polyvinylidene fluoride,
polyethylene, polypropylene, isotatic polystyrene, polyphenylene
oxide, polycarbonate, nylon, and silicone rubber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, in general, to electrical apparatus and,
more specifically, to electrical apparatus insulation
structures.
2. Description of the Prior Art
Insulation structures for electrical apparatus physically separate
the electrical conductors to prevent current transfer between
adjacent electrical conductors and other conducting members of the
apparatus. The arrangement and composition of insulation structures
depends largely upon the type and rating of the electrical
apparatus. In nearly all types of electrical apparatus, the
insulation structure must support the electrical conductors and/or
the windings they form. Insufficient support may result in damage
to the electrical apparatus and possible failure.
In electro-mechanical apparatus, such as motors and generators, the
insulation structures are usually associated with the winding
structures of the rotor and stator. In electrical inductive
apparatus, such as power transformers, the insulation structures
are usually associated with the winding structures which are
positioned around the magnetic core. In all cases, good mechanical
integrity of the insulation structure is desirable for proper
apparatus performance and reliability.
The need for mechanically tight insulation structures is
particularly desirable in power transformers where conductor
movement may be caused by excessive forces, such as encountered
when the transformer is subjected to a short-circuit load. Although
the need is great, the ability to produce tight insulation
structures in transformers is complicated by the insulation
materials normally used.
In nearly all high power transformers, cellulosic materials
comprise the largest amount of the insulation structure. Kraft
paper, crepe paper, Nomex, wood, and press-board are some of the
more generally used materials. Since cellulosic materials are
hydroscopic, they are normally assembled into the insulation
structure while containing a certain amount of water. In subsequent
processing, water is removed to enhance the electrical insulating
characteristics of the cellulosic materials. Unfortunately, when
the moisture is removed from the cellulosic materials, they tend to
shrink and the entire insulation structure becomes loose.
A loose insulation structure not only permits movement of the
conductors during short circuit conditions, but also permits
movement due to thermal cycling and shipment vibrations. Therefore,
various methods have been employed to reduce the effects of
insulation shrinkage in transformers. A present method involves the
precompression of the insulating material at specified loads,
together with subsequent tightening of the structure to produce a
rigid winding structure. While this method is adequate, the time
and labor involved therein is considerable.
Therefore, it is desirable, and it is an object of this invention,
to provide an insulation structure for electrical apparatus which
does not become loose when heated to remove the moisture contained
in the insulating material.
SUMMARY OF THE INVENTION
There is disclosed herein new and useful electrical insulation
apparatus which permits the heating of the insulating materials
without a loosening of the insulation structure. Filler members are
inserted in the insulation structure at various locations and in
sufficient quantities. The filler members are constructed of a
material which has a tendency to reduce its surface area when
heated without any substantial change in its volume. As a
consequence thereof, the smallest dimension of the filler material
tends to increase when heated. The filler members are positioned in
the insulation structure with the dimension which is not greater
than its other two dimensions oriented in the direction in which
expansion is desired. As the cellulosic insulation shrinks with the
application of heat, the filler member enlarges in a direction
which prevents the insulation structure from becoming loose. If the
other materials of the insulation structure do not shrink as much
as the filler member expands, compressive forces are developed
which may be used to brace the insulation structures to each other.
The ratio of filler material to insulation can be adjusted so that
the filler material expansion always exceeds the insulation
shrinkage.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and uses of this invention will become more
apparent when considered in view of the following detailed
description and drawings, in which:
FIG. 1 is a view of a three-phase power transformer constructed
according to the teachings of this invention;
FIG. 2 is a partial top view of a transformer illustrating an
insulation structure constructed according to the teachings of this
invention;
FIG. 2A is a view of a vertical spacing member constructed
according to the teachings of this invention;
FIG. 3 is a sectional elevational view taken along the line
III--III of FIG. 1;
FIG. 4 is a partial elevational view of a disk-type transformer
constructed according to the teachings of this invention;
FIG. 5 is a sectional view of a disk-type transformer constructed
according to the teachings of this invention; and
FIG. 5A is an enlarged view of a portion of the transformer shown
in FIG. 5 .
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Throughout the following description, similar reference characters
refer to similar members in all figures of the drawings.
Referring now to the drawings, and FIG. 1 in particular, there is
shown a power transformer having a laminated magnetic core 10 and
winding structures 12, 14 and 16. An end frame having a top support
18, a bottom support 20, and side braces 22 and 24, is positioned
around the magnetic core 10. The insulating barriers 26 are located
between adjacent winding structures and between the winding
structures 12 and 16 and the side braces 22 and 24,
respectively.
Each winding structure includes a plurality of turns of an
electrical conductor with insulation disposed between adjacent
turns. Normal practice is for each winding structure to include at
least a high voltage or primary winding and a low voltage or
secondary winding. The lead groups 28, 30 and 32 provide means for
connecting the winding structures 12, 14 and 16, respectively, to
other components of the transformer, such as bushings mounted on
the transformer casing. The insulation structure of the winding
structure is shown in detail in FIG. 2.
FIG. 2 is a partial top view of the transformer shown in FIG. 1
illustrating the detail of the insulation structure with the lead
groups eliminated from the figure in the interest of clarity. The
winding is formed by a plurality of turns or turn groups 34 which
are disposed concentrically around the magnetic core leg. Each turn
group 34 may include one or more insulation conductors of the strap
or sheet type. Various turn groups 34 may be interconnected to form
separate windings, such as a high voltage winding and a low voltage
winding. Cellulosic insulation covers the conductors and/or turn
groups 34.
The turn groups 34 are separated by vertical spacing members 36
which provide channels for the flow of the fluid coolant of the
transformer. The vertical spacing members 36 include a material
which increases its dimension in the radial direction. In the
embodiment shown, each vertical spacing member comprises a bracing
member 38 and a filler member 40. The bracing member 38 is
constructed of a conventional material, such as pressboard. The
filler member 40 is constructed of a material which increases its
dimension in the radial direction when heated.
The filler member 40 has a configuration which permits the desired
increase in the radial direction, More exactly, the dimension in
the radial direction is not greater than the other two dimensions
of the filler member before being heated.
FIG. 2A illustrates a vertical spacing member 36 removed from the
insulation structure of FIG. 2. The radial dimension of the filler
member 40 is designated r, the axial dimension is designated a, and
the tangential dimension is designated t. Proper performance of the
filler member may also be realized when the radial r and the
tangential t dimensions are equal to each other and each is less
than the axial a dimension. If sufficient bracing can be achieved
and if the required dimensions of the filler member can be
maintained, it is within the scope of this invention that the
bracing member 38 may be eliminated.
The filer member 40 is constructed of a material which tends to
decrease its surface area when heated, without substantially
decreasing its volume. This produces the effect of decreasing the
longest dimension and increasing the shorter dimensions, or
shortest dimension, depending upon the original configuration.
Suitable materials include the thermoplastics of "teflon" or
polytetrafluoroethylene, polyvinyl chloride, polyvinylidene
chloride, polyvinyl fluoride, polyethylene, polypropylene, isotatic
polystyrene, polyphenylene oxide, polycarbonate, and nylon.
Thermosetting materials, such as silicone rubber, may also be
used.
When the insulation structure is heated to remove the moisture from
the cellulosic insulation, the cellulosic insulation shrinks.
However, the filler member increases in its size in the radial
direction and keeps the insulation structure tight. The materials
disclosed will continue to increase their size in the radial
direction throughout the life of the transformer, thus providing a
tight insulation structure for as long as it is desirable. An
expanding member 42, constructed and dimensioned as disclosed
above, may be placed between the insulation structure and the wedge
block 44. The expanding member 42 also increases its demension in
the radial direction to tighten the insulation structure.
The expanding materials disclosed herein are prepared by
prestretching the material along one or two of its dimensions.
Since the volume remains constant, one dimension must decrease in
size during the prestretching operation. Consequently, the
dimension which decreases in size during the prestretching
operation is the dimension which increases in size when heated.
A sectional view of the transformer shown in FIG. 1 and taken along
the line III--III is illustrated in FIG. 3. The laminations of the
magnetic core 10 are secured by the top support 18 and by the
bottom support 20 of the end frame. The top support 18 includes the
overlapping portions 46 and 48 which are pressed together and
welded to hold the laminations. Insulating members are usually
placed between the support portions and the magnetic core to
provide an air gap between these members for reducing flux in the
end frame structure, to reduce the effects of irregularities in the
end frame portions, and for other reasons. As shown in FIG. 3, the
insulating members include the spacing members 50 and the filler
members 52. The filler members 52 are constructed and dimensioned
similar to the filler members already described. They may be in the
form of strips, sheets, or other configurations. The dimension
which is oriented in the direction which is perpendicular to the
adjacent faces of the magnetic core and the end frame portions is
not greater than either of its other two dimensions. The filler
members 52 are constructed of similar materials as described
concerning the filler members 40.
A similar arrangement may be used for the bottom support 20 of the
magnetic core. The support portions 54 and 56 enclose the magnetic
core 10 with the spring members 58 and the filler members 60
therebetween. Construction and operation of the filler members 60
is similar to that described in connection with the support 18.
The winding structure 16 is axially supported from the yoke
portions of the magnetic core 10. Insulating members 62 and filler
members 64 are located between the ends of the winding structure 16
and the yoke portions of the magnetic core 10. The filler members
64 expand in the axial direction when heated to tighten the widing
structure 16 in the axial direction. Similar filler members may be
positioned between the winding structure 16 and brace members
connected to the top and bottom supports.
The elevational view of the winding structure 16 shown in FIG. 3
illustrates a modification of the winding structure shown in FIG.
2. Instead of having filler members 40 included in each layer of
vertical spacers, as in FIG. 2, FIG. 3 illustrates an embodiment
wherein filler members 40 are positioned at only one layer in the
winding structure. The number of layers requiring filler members
depends on the size of the filler member, the amount of cellulosic
insulation shrinkage, and on other factors. Although shown as a
continuous strip from one end of the winding structure 16 to its
other end, a plurality of shorter strips may be used without
departing from the teachings of this invention. Additionally, the
filler members 40 may be disposed by winding a suitably dimensioned
strip around the winding structure between its conductor turn
groups in a concentric or spiral pattern.
Application of this invention to a transformer having disk-type
coil sections is illustrated in FIG. 4. Disk coil sections 66 are
concentrically positioned around the leg of the magnetic core 68 of
the transformer. Each coil section 66 contains one or more
insulated electrical conductors which are interconnected to the
other coil sections by a suitable means. The coil sections 66 are
separated from the magnetic core 68 by the insulating region 70
which comprises the insulation 72 and the filler member 74.
The filler member 74 may be in the form of axial strips, concentric
sheets, spirally wound strips, or in other forms. Regardless of the
form, the radial dimension of the filler member 74 is not greater
than its other two dimensions. With the filler member constructed
from a material similar to those herebefore mentioned, heating of
the transformer will produce an expansion of the filler member 74
in the radial direction. Thus, any shrinkage of the other
insulating materials is counteracted by the filler member 74 and
the insulation structure remains tight.
Axial tightening of the insulation structure is accomplished by the
filler members 76 which are positioned between the pressure ring 78
and the winding structure, and between the coil disks 66 of the
winding structure. Radial spacers 80, which separate the coil disks
66, are usually constructed of pressboard material. They may be
replaced completely by filler members, such as the filler members
76, or the filler members 76 may, as shown, be placed adjacent to
only a few of the radial spacers 80. The number of locations of
filler members 76 depends on the size, type and rating of the
insulation and filler member materials, and upon other factors. As
in the other embodiments described, the dimension of the filler
member 76 in the axial direction must not be greater than either of
its other two dimensions. The insulating material which is wrapped
around the conductors of the coil disks 66 may include a layer of
material acting as a filler member. With this arrangement,
tightening in both the axial and radial directions will result when
the filler member expands.
In high power, concentrically wound transformers, it is often the
case that the high and low voltage windings are wound separately on
separate winding cylinders and then slipped over each other during
the assembly operation. FIG. 5 illustrates an embodiment of this
invention used in securing the winding cylinders. The low voltage
winding 82 is disposed around the magnetic core leg 84. The high
voltage winding 86 is disposed concentrically with the low voltage
winding 82, with spacing members 88 placed therebetween to provide
coolant convection channels 89. FIG. 5A shows the winding cylinder
90 of the low voltage winding 86 braced to the insulation structure
92 around the low voltage winding 82 by the spacing member 88. The
spacing member 88, as illustrated, includes a bracing member 94 and
a filler member 96. It is within the contemplation of this
invention that the spacing member 88 may comprise only a filler
member. As hereinbefore disclosed, the dimensions and material of
the filler member may be such as to exhibit a tendency to increase
its radial dimension when heated. This tightens the insulation
structure and, as applicable to other embodiments of this
invention, if the other insulation members have a smaller
dimensional change than the filler members, a force is exerted by
the filler member which tends to hold the structures together.
There has been disclosed a new and useful arrangement for improving
the insulation structures of electrical apparatus. Since numerous
changes may be made in the abovedescribed apparatus and different
embodiments of the invention may be made without departing from the
spirit thereof, it is intended that all of the matter contained in
the foregoing description, or shown in the accompanying drawings,
shall be interpreted as illustrative rather than limiting.
* * * * *