CA1130402A - Shear resisting cable with transposed strands and method of its manufacture - Google Patents
Shear resisting cable with transposed strands and method of its manufactureInfo
- Publication number
- CA1130402A CA1130402A CA332,260A CA332260A CA1130402A CA 1130402 A CA1130402 A CA 1130402A CA 332260 A CA332260 A CA 332260A CA 1130402 A CA1130402 A CA 1130402A
- Authority
- CA
- Canada
- Prior art keywords
- cable
- strands
- temperature
- transposed
- adhesive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Landscapes
- Insulating Of Coils (AREA)
Abstract
5D-5574 SHEAR RESISTING CABLE WITH TRANSPOSED STRANDS AND METHOD OF ITS MANUFACTURE A heat shrinkable polymeric material is wrapped around a plurality of adhesive coated wire strands placed together in a transposed configuration prior to heating the strands to cause the adhesive to melt and cure. The shrink initiation temperature of the polymeric material is selected to exceed the temperature at which the adhesive melts while preceeding the temperature at which the latent catalyst initiates the cure cycle. The shrinking of the polymeric wrapping causes the transposed cable strands to become compacted and substantially increases the surface area of the strands in contact with the adhesive material.
Description
113~Z
SHEAR RESISTING CABLE WITH TRANSPOSED
STRANDS AND METHOD OF ITS MANUFACTURE
Back round of the Invention __ g Transposed cables are used in high power transformers for reducing the circulating currents that otherwise occur between electrical conductors in close proximity and in a side by side relationship. In order to cause the strands to adhere to each other for the purpose of resisting short circuit forces, which tend to cause the strands to separate, a layer of adhesive material is applied to each individual strand. Since the actual contact area held by the adhesive material represents approximately 10 percent of the available contact surface, added strand material is generally provided to insure resistance to the shear forces. The added strand material adds to the overall transformer cost since expen-sive copper alloys are required for good electrical conducti-vity, and further, since added transformer volume and dielec-tric coolants are required to contain the added copper material.
The purpose of this invention is to provide methods and materials for compacting the individual transposed cable strands in order to provide for greater adhesive contact between the individual strands so that less strand material can be employed.
Summary of the Invention The invention comprises the addition of a heat shrinkable polymeric layer wrapped around a cable of adhesively coated ~g 113(~40Z
transposed strands prior to heating the cable to melt the adhesive. The heat shrinking properties of the polymeric material are selected to lie between the temperature at -which the adhesive melts and the temperature at which adhesive cure is initiated. The shrinking of the polymeric material while the adhesive is in a liquid condition causes a substantial increase in the contact area between the individual cable strands.
Brief Description of the Drawings FIGURE 1 is a side perspective view of a transposed cable for use with the method and ma~erials of the inven-tion;
FIGURE 2 is a top perspective view of a few layers of ' transposed cables around a winding cylinder for use within a power transformer;
FIGURE 3 is a cross section view of an adhesive coated i cable strand for use within the cable of FIGURE l;
FIGURE 4 is a cross section view of a transposed cable containing an insulating paper wrapping;
FIGURE 5 is an enlarged cross section view of the transposed cable of FIGURE 4 including a wrapping of a polymeric material;
FIGURE 6 is a top perspective view of the cable depicted , in FIGURE 5;
FIGURE 7 is a top perspective view of the winding of FIGURE 2 including a wrapping of polymeric material around the cable layers; and
SHEAR RESISTING CABLE WITH TRANSPOSED
STRANDS AND METHOD OF ITS MANUFACTURE
Back round of the Invention __ g Transposed cables are used in high power transformers for reducing the circulating currents that otherwise occur between electrical conductors in close proximity and in a side by side relationship. In order to cause the strands to adhere to each other for the purpose of resisting short circuit forces, which tend to cause the strands to separate, a layer of adhesive material is applied to each individual strand. Since the actual contact area held by the adhesive material represents approximately 10 percent of the available contact surface, added strand material is generally provided to insure resistance to the shear forces. The added strand material adds to the overall transformer cost since expen-sive copper alloys are required for good electrical conducti-vity, and further, since added transformer volume and dielec-tric coolants are required to contain the added copper material.
The purpose of this invention is to provide methods and materials for compacting the individual transposed cable strands in order to provide for greater adhesive contact between the individual strands so that less strand material can be employed.
Summary of the Invention The invention comprises the addition of a heat shrinkable polymeric layer wrapped around a cable of adhesively coated ~g 113(~40Z
transposed strands prior to heating the cable to melt the adhesive. The heat shrinking properties of the polymeric material are selected to lie between the temperature at -which the adhesive melts and the temperature at which adhesive cure is initiated. The shrinking of the polymeric material while the adhesive is in a liquid condition causes a substantial increase in the contact area between the individual cable strands.
Brief Description of the Drawings FIGURE 1 is a side perspective view of a transposed cable for use with the method and ma~erials of the inven-tion;
FIGURE 2 is a top perspective view of a few layers of ' transposed cables around a winding cylinder for use within a power transformer;
FIGURE 3 is a cross section view of an adhesive coated i cable strand for use within the cable of FIGURE l;
FIGURE 4 is a cross section view of a transposed cable containing an insulating paper wrapping;
FIGURE 5 is an enlarged cross section view of the transposed cable of FIGURE 4 including a wrapping of a polymeric material;
FIGURE 6 is a top perspective view of the cable depicted , in FIGURE 5;
FIGURE 7 is a top perspective view of the winding of FIGURE 2 including a wrapping of polymeric material around the cable layers; and
-2-., . .
. .
~13~40Z
FIGURE 8 is a top perspective view in partial section of a transformer containing windings of transposed cable accordi~g to the invention.
Description of the Preferred Embodiment FIGURE 1 contains a transposed cable 10 of the type wherein a plurality of wire strands are interposed in a transposed configuration for the purpose of reducing magnetic transaction between the individual strands. The configuration of FIGURE 1 for example shows one strand lla transposed relative to an adjoining strand llb in an over-lapping trans-j posed arrangement. In forming a transformer winding a plurality of transposed cables 10 are arranged around a winding cylinder 12, as shown in FIGURE 2, to complete a transformer winding 9. As discussed earlier one of the problems involved in using transposed cables within trans-former windings is the tendency of the individual strands to ~ become separated under the intense shear forces to which the
. .
~13~40Z
FIGURE 8 is a top perspective view in partial section of a transformer containing windings of transposed cable accordi~g to the invention.
Description of the Preferred Embodiment FIGURE 1 contains a transposed cable 10 of the type wherein a plurality of wire strands are interposed in a transposed configuration for the purpose of reducing magnetic transaction between the individual strands. The configuration of FIGURE 1 for example shows one strand lla transposed relative to an adjoining strand llb in an over-lapping trans-j posed arrangement. In forming a transformer winding a plurality of transposed cables 10 are arranged around a winding cylinder 12, as shown in FIGURE 2, to complete a transformer winding 9. As discussed earlier one of the problems involved in using transposed cables within trans-former windings is the tendency of the individual strands to ~ become separated under the intense shear forces to which the
3 cables become subjected under transformer short circuit conditions. FIGURE 3 shows an individual cable strand 11 containing a layer of insulating enamel 13 which is applied to the strand in order to electrically insulate the individual strands within the cable. An adhesive layer 14 is applied - over the insulating enamel 13 in order to cause the individual strands to adhere to each other and to substantially increase the cable resistance to separation under the aforementioned shear force effects. A completed cable configuration 10 is shown in FIGURE 4 wherein a plurality of individual strands 11 .
~13(~40Z
containing the adhesive coating 14 are wrapped with an - outer layer o insulating papex 16 to provide insulation between the cable and other internal elements within a transformer casing.
When transformer windings are caused to fail under repeated subjection to short circuit shear forces the separated cable strands are found to adhere to each other at only scattered portions along the adjacent strand sur-face. It was discovered therefore that some means must be provided during the adhesive melting operation to force the individual strands into intimate contact in order to assure that the melted~ adhesive intermixes between the individual strands in its melted state and remains in intimate contact while the adhesive undergoes a thermosetting chemical reaction.
One means for providing compaction to the transposed cable during the adhesive melting operation is shown in ~-- F GU~ 5 and consists in the application of a layer of ` m~ r film 15 around transposed cable 10 containing the usual adhesive coated strands 11. The mylar material is selected to have a shrink initiation temperature of approximately 90C when the adhesive material comprises an epoxy having a melt temperature of approximately 70C. The mylar shrinks therefore while the epoxy is liquid and forces the individual strands into a tight compact arrangement and holds the individual strands in the tight configuration while the epoxy adhesive reacts. The epoxy material comprising the
~13(~40Z
containing the adhesive coating 14 are wrapped with an - outer layer o insulating papex 16 to provide insulation between the cable and other internal elements within a transformer casing.
When transformer windings are caused to fail under repeated subjection to short circuit shear forces the separated cable strands are found to adhere to each other at only scattered portions along the adjacent strand sur-face. It was discovered therefore that some means must be provided during the adhesive melting operation to force the individual strands into intimate contact in order to assure that the melted~ adhesive intermixes between the individual strands in its melted state and remains in intimate contact while the adhesive undergoes a thermosetting chemical reaction.
One means for providing compaction to the transposed cable during the adhesive melting operation is shown in ~-- F GU~ 5 and consists in the application of a layer of ` m~ r film 15 around transposed cable 10 containing the usual adhesive coated strands 11. The mylar material is selected to have a shrink initiation temperature of approximately 90C when the adhesive material comprises an epoxy having a melt temperature of approximately 70C. The mylar shrinks therefore while the epoxy is liquid and forces the individual strands into a tight compact arrangement and holds the individual strands in the tight configuration while the epoxy adhesive reacts. The epoxy material comprising the
4--113~4~ 5D5574 adhesive cures and holds the lndividual strands tenaciously , ,'`1 against opposing shear forces when the Mylar wrapped cables are subject to short circuit tests. The Mylar material, which is a heat shrinkable polyester film, is selected for convenience of application since it is currently available in both sheet and tape form. It is to be clearly understood that other heat shrinkable polymeric materials can also be employed providing that the material is durable enough to hold the cables during the adhesive melting and thermosetting operations. The polyesters that are satisfactory for the purposes of the invention are thermoplastic synthetic resins not usually containing fatty acids or drying oils. Other thermoplastic heat shrinkable materials can be employed providing that the temperatures at which the thermoplastic materials shrink are selected lower than the adhesive cure temperature but higher than the adhesive melt point. The method for applying the Mylar film 15 of FIGURE 5 is shown in FIGURE 6 wherein the individual strands 11 formed in a transposed configuration are wrapped with a continuous winding layer of Mylar 15 wherein the strands are not completely covered. The gaps between the individual wraps of the Mylar film are necessary for outgassing during transformer drying and the subsequent impregnation with transformer oil. The occurrence of free gas at the surface can cause undesirably low corona excitation voltages during transformer test and operation. It is within the scope of the instant invention to employ heat shrinkable porous or micro-perforated heat 113~C~2 shrinkable tapes whereby the sub~strate materials can readily become outgassed and oil impregnated through the polymeric material thereby allowing ~he use of the polymeric as primary insulation. Multiple wraps of the polymeric heat shrinkable material will result in further compaction with a resultant increase in bond area. It is further within the scope of the instant invention to use the wrapping of the heat~shrinkable film as a substitute for the paper insulation shown for example in FIGURES 4 and 6 commonly employed with transposed cables. The excellent insulating properties of the polymeric film provides a function similar to the insulating papèr while compacting and holding the individual strands in a tight intimate and close-knit configuration.
FIGURE 7 shows a winding 9 comprising a plurality of layers of transposed cable 10 further including a wrapping of heat shrinkable film 15 around the individual layers 8.
The wrapping of polymeric material 15 around the individual winding layers 8 in combination with the aforementioned winding of polymeric material around the transposed cable used within winding 9 provides a tighter more compact winding substantially increasing the overall shear resistance proper-ties of the winding.
The substantial increases in shear resistance observed by the use of heat shrinkable polymeric films around trans-posed cable configurations reduces the amount of metalrequired for use within the cable strands and further reduces the interior volume of the transformer and the transformer .
ll3a40z overall weight. The decrease, fo:r example, in the amount of wire employed in the transformer windings further decreases the quantity of dielectric oil used for cooling and insulating the transformer 17 of FIGURE 8 of the type consisting of a metallic casing 18 and having a plurality of windings 9 con-centrically arranged around the core 19. When transposed cables having the configuration depicted in FIGURE 6 are used within the windings 9 of transformer 17,the windings are reduced in diameter to such an extent that the trans-former casing 18 is correspondingly reduced and the volumeof oil contained therein is reduced accordingly.
Although the described methods and materials for providing transposed cable configurations according to the invention have application within power transformer this is by way of example only. ~he transposed cable of the invention finds application wherever conductor bundles having high flexural strength properties may be required.
FIGURE 7 shows a winding 9 comprising a plurality of layers of transposed cable 10 further including a wrapping of heat shrinkable film 15 around the individual layers 8.
The wrapping of polymeric material 15 around the individual winding layers 8 in combination with the aforementioned winding of polymeric material around the transposed cable used within winding 9 provides a tighter more compact winding substantially increasing the overall shear resistance proper-ties of the winding.
The substantial increases in shear resistance observed by the use of heat shrinkable polymeric films around trans-posed cable configurations reduces the amount of metalrequired for use within the cable strands and further reduces the interior volume of the transformer and the transformer .
ll3a40z overall weight. The decrease, fo:r example, in the amount of wire employed in the transformer windings further decreases the quantity of dielectric oil used for cooling and insulating the transformer 17 of FIGURE 8 of the type consisting of a metallic casing 18 and having a plurality of windings 9 con-centrically arranged around the core 19. When transposed cables having the configuration depicted in FIGURE 6 are used within the windings 9 of transformer 17,the windings are reduced in diameter to such an extent that the trans-former casing 18 is correspondingly reduced and the volumeof oil contained therein is reduced accordingly.
Although the described methods and materials for providing transposed cable configurations according to the invention have application within power transformer this is by way of example only. ~he transposed cable of the invention finds application wherever conductor bundles having high flexural strength properties may be required.
Claims (11)
1. A shear resisting cable for use in forming trans-former windings comprising:
a plurality of rectilinear metal strands arranged adjacent each other in a transposed configuration;
a layer of insulating enamel on the surface of the metal strands;
a layer of adhesive material having a predetermined melting temperature on the insulating enamel for holding the individual strands together in opposition to a shearing force;
and a layer of heat shrinkable tape having a shrink initiation temperature higher than the adhesive material wrapped around the outer surface of the transposed cable in a gapped configuration for compacting the cable strands and for increasing the shear resistance of the cable, said gapped configuration providing for the outgassing of said cable and for the impregnation of said cable with transformer oil.
a plurality of rectilinear metal strands arranged adjacent each other in a transposed configuration;
a layer of insulating enamel on the surface of the metal strands;
a layer of adhesive material having a predetermined melting temperature on the insulating enamel for holding the individual strands together in opposition to a shearing force;
and a layer of heat shrinkable tape having a shrink initiation temperature higher than the adhesive material wrapped around the outer surface of the transposed cable in a gapped configuration for compacting the cable strands and for increasing the shear resistance of the cable, said gapped configuration providing for the outgassing of said cable and for the impregnation of said cable with transformer oil.
2. The cable of claim 1 wherein the heat shrinkable tape comprises a thermoplastic polyester resin.
3. The cable of claim 1 wherein the adhesive comprises an epoxy compound.
4. The cable of claim 1 wherein said shrink initiation temperature comprises approximately 90°C and said melting temperature comprises approximately 70°C.
5. A method for compacting strands in transposed cables for use within transformers comprising the steps of:
providing a plurality of adhesive coated insulated wire strands in close proximity with each other in a transposed cable configuration;
wrapping a layer of heat shrinkable polymeric material around said cable in a gapped configuration to contain said strands in close proximity with each other and to allow for the egress of gaseous material and the impregnation of insulating oil through said gaps;
arranging said wrapped transposed cable around a winding cylinder to form a transformer winding;
evacuating said transformer winding;
heating said transformer winding to a first temperature to cause said adhesive to melt; and heating said transformer winding to a second temperature to cause said polymeric material to shrink and to compact said strands.
providing a plurality of adhesive coated insulated wire strands in close proximity with each other in a transposed cable configuration;
wrapping a layer of heat shrinkable polymeric material around said cable in a gapped configuration to contain said strands in close proximity with each other and to allow for the egress of gaseous material and the impregnation of insulating oil through said gaps;
arranging said wrapped transposed cable around a winding cylinder to form a transformer winding;
evacuating said transformer winding;
heating said transformer winding to a first temperature to cause said adhesive to melt; and heating said transformer winding to a second temperature to cause said polymeric material to shrink and to compact said strands.
6. The method of claim 5 including the step of heating said transformer winding to a third temperature to cause said adhesive material to become cured.
7. The method of claim 6 wherein said second temperature is lower than said third temperature and higher than said first temperature.
8. The method of claim 5 wherein said polymeric material comprises a thermoplastic polyester.
9. The method of claim 5 wherein said polymeric material contains a plurality of microperferations for providing further egress means for said gaseous material.
10. The method of claim 5 wherein said first temperature comprises at least 70°C. and wherein said second temperature comprises at least 90°C.
11. The method of claim 10 wherein said third temperature comprises at least 100°C.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA332,260A CA1130402A (en) | 1979-07-20 | 1979-07-20 | Shear resisting cable with transposed strands and method of its manufacture |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA332,260A CA1130402A (en) | 1979-07-20 | 1979-07-20 | Shear resisting cable with transposed strands and method of its manufacture |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130402A true CA1130402A (en) | 1982-08-24 |
Family
ID=4114746
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA332,260A Expired CA1130402A (en) | 1979-07-20 | 1979-07-20 | Shear resisting cable with transposed strands and method of its manufacture |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1130402A (en) |
-
1979
- 1979-07-20 CA CA332,260A patent/CA1130402A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |