U.S. patent number 3,720,897 [Application Number 05/170,005] was granted by the patent office on 1973-03-13 for electrical inductive apparatus.
This patent grant is currently assigned to Westinghouse Electric Corporation. Invention is credited to Landis E. Feather, Louis Morris.
United States Patent |
3,720,897 |
Feather , et al. |
March 13, 1973 |
ELECTRICAL INDUCTIVE APPARATUS
Abstract
An arrangement for supporting a winding tube of a power
transformer. The winding tube is supported and held in position by
a supporting structure constructed of rigid plastic foam. Spaces or
openings in the supporting structure, which are created by suitably
shaped members, permit the liquid dielectric of the transformer to
flow through the supporting structure to cool adjacent structures.
The suitably shaped members are inserted between the winding tube
and its supporting member before the plastic foam is placed
therein, thereby defining the shape of the spaces or openings in
the supporting structure.
Inventors: |
Feather; Landis E. (Sharon,
PA), Morris; Louis (Campbell, OH) |
Assignee: |
Westinghouse Electric
Corporation (Pittsburgh, PA)
|
Family
ID: |
22618133 |
Appl.
No.: |
05/170,005 |
Filed: |
August 9, 1971 |
Current U.S.
Class: |
336/60;
336/198 |
Current CPC
Class: |
H01F
27/306 (20130101) |
Current International
Class: |
H01F
27/30 (20060101); H01f 027/08 () |
Field of
Search: |
;336/60,205,55,198,208
;310/65 ;174/143,15C |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
512,761 |
|
Feb 1939 |
|
GB |
|
233,608 |
|
Nov 1959 |
|
AU |
|
1,074,801 |
|
Jul 1967 |
|
GB |
|
Primary Examiner: Kozma; Thomas J.
Claims
We claim as our invention:
1. A transformer comprising a winding tube having a winding
disposed thereon, a mounting member for said winding tube, a
supporting structure constructed of a rigid plastic foam disposed
between said winding tube and said mounting member, said supporting
structure having openings therethrough for providing channels
through which liquid dielectric may flow.
2. The transformer of claim 1 wherein the mounting member comprises
a leg of a magnetic core.
3. The transformer of claim 1 wherein the mounting member comprises
solid insulating material wrapped around a winding structure.
4. The transformer of claim 1 wherein the rigid plastic foam is
selected from the group consisting of epoxides, phenolics and
silicones.
5. The transformer of claim 1 wherein the rigid plastic foam from
which the supporting structure is constructed comprises rigid
polyurethane foam.
6. The transformer of claim 1 wherein the openings in the
supporting structure are cylindrically shaped.
7. The transformer of claim 6 wherein the openings in the
supporting structure are defined by hollow cylindrical tubes.
8. The transformer of claim 6 wherein the cylindrically shaped
openings are substantially equally spaced at the same radial
distance through the supporting structure.
9. The transformer of claim 6 wherein the cylindrically shaped
openings are positioned throughout the supporting structure in a
radially staggered pattern.
10. The transformer of claim 1 wherein the openings in the
supporting structure are formed by a corrugated boundary of the
supporting structure.
11. The transformer of claim 10 wherein the corrugated boundary is
defined by a boundary layer constructed of insulating material.
12. The transformer of claim 11 wherein the insulating material
from which the boundary layer is constructed comprises paper
board.
13. The transformer of claim 11 wherein a spacer is positioned
between said mounting member and said boundary layer.
14. The transformer of claim 13 wherein the spacer and the boundary
layer are constructed of similar materials.
15. The transformer of claim 13 wherein the spacer is constructed
of a material which dissolves in the liquid dielectric of the
transformer.
16. The transformer of claim 13 wherein said spacer is constructed
of polyethylene film.
17. The transformer of claim 13 wherein said spacer is constructed
of paper.
18. The transformer of claim 13 wherein said spacer is constructed
of fibrous mat.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates, in general, to electrical inductive
apparatus and, more specifically, to insulating and supporting
means for the windings of core-form transformers.
2. Description of the Prior Art
The construction of core-form transformers takes into consideration
certain aspects of the electrical and mechanical performance of the
transformer. The metallic laminations which form the magnetic core
of the transformer must be mechanically held together for proper
operation of the transformer. The most common method presently used
includes the use of bolts which are inserted through holes in the
laminations. While this provides sufficient mechanical strength,
the electrical performance of the transformer suffers due to the
core losses caused by the holes in the laminations.
It is also a requirement in power transformers that the magnetic
core be cooled as effectively as possible. This is accomplished in
liquid cooled power transformers by circulating the liquid
dielectric, which is usually mineral insulating oil, along the
surfaces of the core. This makes it necessary to provide a space or
channel between the core and the winding positioned thereon to
allow the flow of oil adjacent to the core. Since the innermost
winding is subjected to inward forces during short circuits which
tend to collapse the winding, there must be a compromise between
rigid supporting members and cooling channels adjacent to the
core.
Generally, the innermost winding is first wound on a rigid
insulating tube, then the tube and the winding assembly is slipped
over the magnetic core. The tube is blocked to the core by
inserting spacer sticks or rods between the core and the tube. This
arrangement is undesirable for several reasons. The winding tube
must be sufficiently thick to provide adequate mechanical support
between spacer rod support points. As a result, the winding tube
must be thicker than required by electrical considerations. It also
positions the winding farther from the core than is electrically
required.
The use of spacer rods also results in inadequately supported
winding tubes. Due to variations in core width, spacer diameter,
and winding tube size, some spacers may not completely fill the gap
between the core and the tube, thus, the winding tube may be
subjected to additional flexural stresses under short circuit
conditions. To permit assembly when tolerances tend to reduce the
gap, the tube is normally fitted loosely, which adds to the
possibility of mechanical deformation of the winding tube. The
spacer rod arrangement is very time consuming to assemble and there
is a substantial possibility of damage to the tube when the rods
are driven between the tube and the core.
Therefore, it is desirable and it is an object of this invention,
to provide an economical, efficient, and satisfactory arrangement
for supporting the windings of a power transformer.
SUMMARY OF THE INVENTION
The invention disclosed herein provides a new and useful
arrangement for supporting a winding tube of a power transformer
which may be economically constructed and which performs
efficiently. Suitably shaped spacing members are inserted in the
region between the winding tube and the structure from which it is
supported, such as the magnetic core. Plastic foam is then placed
into the region and allowed to solidify, thus forming a supporting
structure. The spaces provided by the spacing members allow the
liquid dielectric of the transformer to flow through the supporting
structure and conduct heat away from adjacent structures.
This arrangement permits the use of a winding tube having a smaller
wall thickness than permitted by prior art arrangements since the
winding tube is supported continuously around its circumference.
Since the plastic foam conforms to the size and shape of the
winding tube, all areas of the winding tube are sufficiently
supported. Because of the ability of the foam to compensate for
manufacturing tolerances, the winding tube is always solidly
supported. Additionally, since the winding tube does not have to be
oversized to allow for tolerances, the winding thereon is
consistently closer to the magnetic core when the arrangement
taught by this invention is used. The fact that the supporting
structure surrounds the magnetic core, and provides securing means
therefor, allows modification of the conventional bolt arrangement
for holding the laminations together. The elimination of some or
all of the lamination bolts improves the efficiency of the
transformer.
BRIEF DESCRIPTION OF THE DRAWINGS
Further advantages and usages of this invention will become more
apparent when considered in view of the following detailed
description and drawings, in which:
FIG. 1 is an elevational view of a core-form transformer
constructed according to the teachings of this invention;
FIG. 2 is a cross-sectional view of the winding structure taken
along the line II--II of FIG. 1 and constructed according to the
teachings of an embodiment of this invention;
FIG. 3 is a cross-sectional view of a winding structure constructed
according to the teachings of another embodiment of this
invention;
FIG. 4 is a partial cross-sectional view of a winding structure
illustrating an embodiment of this invention wherein the windings
are separated by a supporting structure;
FIG. 5 is an enlarged partial cross-sectional view illustrating a
supporting structure arrangement which is located between the
windings and constructed according to the teachings of an
embodiment of this invention; and
FIG. 6 is an enlarged partial cross-sectional view illustrating a
supporting structure arrangement which is located between the
windings and constructed according to the teachings of another
embodiment of this invention.
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 laminated magnetic core 10 of a tranformer constructed
according to the teachings of this invention. The magnetic core 10
includes legs 12, 14 and 16 which have positioned thereon the
winding structures 18, 20 and 22, respectively. The magnetic core
10 is constructed of layers of metallic laminations, with the width
of the laminations varied to provide the pattern of a cruciform
magnetic core. The winding structures 18, 20 and 22 are rigidly
attached to their respective core legs by the arrangement
hereinafter described in detail.
FIG. 2 is a cross-sectional view of the winding structure 22 taken
along the line II--II of FIG. 1. The winding structure 22 includes
an outer winding 24 and an inner winding 26. The windings are
separated by the vertical spacers 28 which allow the liquid
dielectric, which is not illustrated, to flow vertically between
the windings 24 and 26. The vertical spacers 30 are positioned
between the inner winding 26 and the winding tube 32 for a similar
reason.
The winding tube 32 is supported from the magnetic core 16 by the
supporting structure 34. The magnetic core 16 provides a mounting
member for the winding tube 32. The inner boundary of the
supporting structure 34 has a corrugated shape which provides
channels through which the liquid dielectric may flow. The
corrugated boundary of the supporting structure 34 is shown in more
detail in the enlarged portion of FIG. 2. A boundary layer 36
defines the inner boundary of the supporting structure 34. The
boundary layer 36 is constructed of a corrugated material which is
faced on one side by the face member or spacer 38. The corrugated
material of the boundary layer 36 comprises any suitable material,
such as paper board. The face member 38 may be constructed of a
similar material or it may be constructed of a material, such as
polyethylene film, which will dissolve when exposed to the hot
liquid dielectric of the transformer. This permits the dielectric
to directly contact the magnetic core 16. The face member 38 should
be thin for minimum resistance to heat transfer, while the boundary
layer 36 should be reasonably stiff in order to prevent collapse of
the corrugations during assembly. A paper material having a
thickness of from 7 to 15 mils would be suitable composition for
the boundary layer 36 material. The corrugations may be of coarse
texture, such as the industry standard A fluting which is
approximately 1/4 inch high. A synthetic film or fibrous mat could
also be used for the face member 38.
The supporting structure 34 is constructed of a suitable solid
insulating material, such as rigid plastic foam. A polyurethane
foam having a density of from 6 to 10 lbs. per cubic foot should be
adequate for most applications, however, foams with densities
between 2 and 30 lbs. per cubic foot could also be used depending
on the strength required. Rigid plastic foams comprising epoxides,
phenolics or silicones could also be used.
Constructing the structure illustrated in FIG. 2 may be
accomplished by several different methods. One convenient method is
to attach the single-faced corrugated structure, comprising the
boundary layer 36 and the face member or spacer 38, to the magnetic
core 16 with a suitable adhesive. The adhesive is placed between
the magnetic core 16 and the face member or spacer 38 and, since
the boundary layer 36 is attached to the face member 38, the
boundary 36 generally follows the contour of the magnetic core 16.
The winding tube 32 is positioned around the magnetic core 16 and
the bottom opening therebetween is blocked off. The plastic foam,
in liquid form, is then injected into the region between the
magnetic core 16 and the winding tube 32. The foam flows into the
corrugations of the boundary layer 36 to provide radially extending
ridges 40 which secure the supporting structure 34 to the magnetic
core 16 when the foam expands and solidifies. The spaces 42, from
which the foam has been restricted by the boundary layer 36,
provide the cooling channels through which the liquid dielectric of
the transformer may flow.
Other arrangements may be used to provide spaces in the supporting
core 34 for dielectric flow. FIG. 3 illustrates an arrangement
whereby hollow cylindrical tubes 44 are placed adjacent to the
magnetic core 16 prior to the injection of the supporting structure
34 material into the region between the magnetic core 16 and the
winding tube 32. The tubes 44 may be constructed of a suitable
material, such as paper board, and left in position after the foam
becomes rigid. The tubes 44 may be suitably constructed so that
they can be removed after the foam becomes rigid. By using
cylindrical tubes 44, spaces are created in the supporting
structure 34 which permit the flow of dielectric therethrough to
adequately cool the magnetic core 16. The diameter of the tubes may
be varied to increase or decrease the cooling channel area,
provided that a sufficient amount of the supporting structure 34
contacts the magnetic core 16 to adequately support the winding
tube 32.
Due to the closed-cell gas-filled nature of the plastic foam
material, corona may develop in the supporting structure 34 if the
stress between the magnetic core 16 and the inner winding 26 is
large enough. Corona discharges in the supporting structure 34 may
be prevented by providing a grounded shield between the magnetic
core 16 and the inner winding 26. Such a shield would be provided
by the conductive coating 35 which is applied to the inner portion
of the winding tube 32, with a suitable lead attached to the
coating 35 and to a point at ground potential. Other shielding
arrangements may be used to prevent corona discharges in the
supporting structure 34.
The teachings of this invention may also be applied to the other
regions of a transformer which require supporting means. In
three-winding transformers, the middle winding tends to collapse
under short circuit conditions. FIG. 4 illustrates an embodiment of
this invention wherein a third winding 45 is positioned around the
winding 24 with vertical spacers 47 therebetween. The winding 24 is
supported from the winding 26 by the supporting structure 46
instead of using vertical spacers 28 as shown in FIGS. 2 and 3. The
winding tube 50 and the insulating member 52 define the outer and
inner boundaries, respectively, of the supporting structure 46. The
insulating member 52, which provides a mounting member for the
winding tube 50, may comprise the solid insulating material which
is wrapped around the outside of the winding structure 26. The
cylindrical tubes 48 are positioned in the supporting structure 46
to provide spaces for the flow of the liquid dielectric. The
composition of the tubes 48 may be similar to the composition of
the tubes 44 shown in FIG. 2. The placement of the tubes, and the
diameter thereof, is dependent upon the desired mechanical and
thermal properties of the supporting structure 46. The tubes 48
shown in FIG. 4 are substantially equally spaced at the same radial
distance throughout the supporting structure 46. Although not
illustrated, additional channel space area may be obtained by
making the outside diameter of the tube 48 substantially equal to
the width of the supporting structure 46, that is, the radial
distance between the insulating member 52 and the winding tube
50.
The tubes 48 may be radially staggered throughout the supporting
structure 46, as shown in FIG. 5, in order to place the liquid
dielectric channel spaces adjacent to the surfaces which require
cooling. The arrangement shown in FIG. 5 uses the corrugated
members 54 and 56 to provide the spaces in the supporting structure
46. Although FIG. 5 illustrates liquid dielectric spaces adjacent
to the winding tube 50 and to the insulating member 52, it is
within the teachings of this invention that liquid dielectric
spaces may be provided at either the inner or outer boundary only.
The boundary layers 54 and 56 may be constructed of a material
similar to that used to construct the boundary layer 36 illustrated
in FIG. 2. It is also within the contemplation of this invention
that face members may be attached to the corrugated boundary layers
54 and 56 to aid in the application of the boundary layer to the
winding tube 50 and to the insulating member 52.
There has been disclosed a new and useful arrangement for
supporting a winding tube of a power transformer. The winding tube
is secured in position by a supporting structure which has spaces
therein to provide channels for the flow of liquid dielectric
therethrough. Since numerous changes may be made in the above
described 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.
* * * * *