CA1049338A - Increasing the dielectric strength in metal electrodes - Google Patents
Increasing the dielectric strength in metal electrodesInfo
- Publication number
- CA1049338A CA1049338A CA202,879A CA202879A CA1049338A CA 1049338 A CA1049338 A CA 1049338A CA 202879 A CA202879 A CA 202879A CA 1049338 A CA1049338 A CA 1049338A
- Authority
- CA
- Canada
- Prior art keywords
- portions
- layer
- increasing
- resin
- liquid
- 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
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/28—Coils; Windings; Conductive connections
- H01F27/32—Insulating of coils, windings, or parts thereof
- H01F27/324—Insulation between coil and core, between different winding sections, around the coil; Other insulation structures
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B17/00—Insulators or insulating bodies characterised by their form
- H01B17/56—Insulating bodies
- H01B17/62—Insulating-layers or insulating-films on metal bodies
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F27/00—Details of transformers or inductances, in general
- H01F27/34—Special means for preventing or reducing unwanted electric or magnetic effects, e.g. no-load losses, reactive currents, harmonics, oscillations, leakage fields
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F41/00—Apparatus or processes specially adapted for manufacturing or assembling magnets, inductances or transformers; Apparatus or processes specially adapted for manufacturing materials characterised by their magnetic properties
- H01F41/005—Impregnating or encapsulating
Abstract
ABSTRACT OF THE DISCLOSURE :
For increasing the dielectric strength in metal electrodes, particularly in parts of the electrodes around which there prevail inhomogeneous electrical fields with uncon-trollable electrical field strength, a layer of resin with a dielectric constant which is high in comparison with the dielec-tric constant of transformer oil is applied to the electrode by means of electrostatic spraying.
For increasing the dielectric strength in metal electrodes, particularly in parts of the electrodes around which there prevail inhomogeneous electrical fields with uncon-trollable electrical field strength, a layer of resin with a dielectric constant which is high in comparison with the dielec-tric constant of transformer oil is applied to the electrode by means of electrostatic spraying.
Description
The present in~ention relates to a method for increasing the dielectric ~trength in metallic electrodes, and in particular in parts of the electrodes around which there prevail inhomogeneous electric fields with uncontrollable electric field strength. The term "electrodes" must here be taken in its broad sense, and in this context it comprises construction parts for electric machines and apparatus which have high voltage to earth or otherlive parts or earth-connected parts which are located in the vicinity of live parts As e~amples of what is meant may be mentioned the iron core with relevant parts, splash ring~ for live parts and the like.
In the manufacturé of, for example, iron cor~s for transformers, the sheets will display small irregularities in the cut edges. Even such construction parts as press beams, lifting devices and the like cannot be.made absolutely, 3mooth, and even after a normal gri~ding there will be irregularities which, in normal cases, are of no significance. However, if a conductor with high ~oltage passes in the vicinity of an carthed object displaying such insignificant irregul~rities o on the surface, the electric field between the conductor and the earth~d object will be affected very strongly quite close to the .
.: -: ~ .
,;" ~ . ' ' ~. . , ~, .,,, . : . . ..
.. ~ ,.. ...
. ~ . , :. . ..
..
irregularities, and the insulating material just outside even an almost microscopic elevation will be exposed to a considerably increased field strength with a resultant risk of glow discharge appearing there. Such a seemingly insignificant partial dischar-ge can easily increase and will eventually give rise to a flash-over in the liquid insulating agent between the earthed object and the live conductor.
Tests have shown that, if the parts between which the electric field occurs are coated with a thin layer of a resin, the dielectric constant of which is higher and preferably consi-derably higher than the dielectric constant of the liquid insulat-ing agent, the said phenomenom with partial discharges at the metal surfaces will practically disappear. In this connection it is important to ensure that the layer is thin and that it co-vers the irregularities present on the surfaces only. Further it is important that the surface of the applied resin has no sharp corners and edges.
; According to the present invention, the problem of a-voiding partial discharge in an electrical apparatus which com-prises first and second members formed of conductive material with an insulating liquid therebetween, one of said members being a live member, one of the members having a surface exposed to the insulating liquid, said surface having portions which are exposed to a considerably greater field strength that other portions of the surface when a high voltage exists in such live element has been solved by providing a layer on such surface of a resin with a dielectric constant which is high in comparison with the dielec-tric constant of thc insulating liquid, said laycr being substan-tially thicker at such portions exposed to the greater field strength than at such other portions .
In a preferred embodiment of this invention, the resin is applied by electrostatic spraying.
~ -2-v~A~
Electrostatic spray painting as such is ~/ell-known, but so far it has not been known to employ this method for strengthen-ing the capacity of the electrodes to endure strong electrical fields in electrical apparatus. The method according to the in-vention makes use of the tendency of the applied material to ac-cumulate mostly where the electrical field strength is highest, which is where the strongest insulation is required.
In the accompanying drawings, Figure 1 shows a sharp corner in metallic construction part coated with an insulating agent according to the in-:; .,,,, , ~ , ; ' ' '~' ' ,' ' . , ' ~ .
iO49338 ~ention. Figure 2 ~hows a vertical section through a toroidalsplash ring on the line II-II of Figure 3. Figure 3 is a view from above of the splaqh ring according to Figure 2. Figure 4 shows an enlarged cros~-section of the area IV in ~igure 2.
Figure 5 shows a time-temperature curve for the application of a coating according to the invention.
Figure 1 show~ a sharp corner in a metallic construc-tion part 1 in an electrical apparatus. Thi~ may be, for example, the iron core in a transformer. When cutting trans-former sheet, burks will always appear and these will havea particular importance at the corners of the construction, with a resultant risk of glow phenomena. To avoid glow dis-charge and to strengthen~electric ~trength, an insulating layer 2 i8 applîed by means of electrostatic spraying of a powdered re~in or a resinous solution. Because of the increa~-ed field strength at the corner 3, an extra thick coating will appear there. This means that a coating is obtained, the thickness of which is related to the risk of flash-over between the construction part and a live conductor in the vicinity thereof.
Figure 2 shows a vertical section through a toroidal splash ring 4, which is placed on that end of a transformer bushing which is located in the oil in a transformer tank.
The lower end of the bushing is indicated at 5. The spla~h ring i3 supported by the bushing by means of stays 6. Figure 3 show3 the spla~h ring from above. Such splash rings are manufac-tured of a thin material, and the field ~trength will thus be high along the edges 7 with a subsequent risk of glow discharge.
Figure 4 ~hows a ~ection through the edge 7 on an enlarged ~0 ~cale, after the splash ring has been treated according to the invention. The figure ~hows that the said edge i~ coated with a layer 8 of insulating material so that the otherwise sharp edge has a considerably increased radiu~ of curvature. ~he ri~k of glow di3charge and flash-over at the edge i8 thu~
con~iderably reduced.
The treatment with resin according to the invention cau~es all sharp edge~ to acqulre a smooth curvature with a definable radius. This decreases the field strength and re~uces the risk of glow discharge and flash-over.
In order that the powder may ~tick and be evenly distributed~the object to be sprayed i~ preheated to a tempera-ture e~ceeding the melting point of the powder. ~igure 5shows the time - temperature curve during the process of coating an object. ~he straight part 10 indicates the temperature of the ob~ect before the start of the spraying. At 11 the object is removed from the heating furnace and the spraying comQences.
While the spraying is going on, the temperature decreases, which i~ marked by the downward curve part 12. At 13 the spraying is finished and the applied resin must be cured and this curing can be performed under a continuing temperature drop in the object according to one of the curve parts 14 or 15. It is also possible to place the object in a furnace 90 that the curing continues at constant temperature, as shown by the curve part 16. In any event it mu~t be ensured that the temperature does not rise after the spraying has been finished.
In the foregoing it has been assumed that the spray-ing is carried out with resin in the form of powder, but it is also po~sible to spray with solutions of powdered resin.
In the manufacturé of, for example, iron cor~s for transformers, the sheets will display small irregularities in the cut edges. Even such construction parts as press beams, lifting devices and the like cannot be.made absolutely, 3mooth, and even after a normal gri~ding there will be irregularities which, in normal cases, are of no significance. However, if a conductor with high ~oltage passes in the vicinity of an carthed object displaying such insignificant irregul~rities o on the surface, the electric field between the conductor and the earth~d object will be affected very strongly quite close to the .
.: -: ~ .
,;" ~ . ' ' ~. . , ~, .,,, . : . . ..
.. ~ ,.. ...
. ~ . , :. . ..
..
irregularities, and the insulating material just outside even an almost microscopic elevation will be exposed to a considerably increased field strength with a resultant risk of glow discharge appearing there. Such a seemingly insignificant partial dischar-ge can easily increase and will eventually give rise to a flash-over in the liquid insulating agent between the earthed object and the live conductor.
Tests have shown that, if the parts between which the electric field occurs are coated with a thin layer of a resin, the dielectric constant of which is higher and preferably consi-derably higher than the dielectric constant of the liquid insulat-ing agent, the said phenomenom with partial discharges at the metal surfaces will practically disappear. In this connection it is important to ensure that the layer is thin and that it co-vers the irregularities present on the surfaces only. Further it is important that the surface of the applied resin has no sharp corners and edges.
; According to the present invention, the problem of a-voiding partial discharge in an electrical apparatus which com-prises first and second members formed of conductive material with an insulating liquid therebetween, one of said members being a live member, one of the members having a surface exposed to the insulating liquid, said surface having portions which are exposed to a considerably greater field strength that other portions of the surface when a high voltage exists in such live element has been solved by providing a layer on such surface of a resin with a dielectric constant which is high in comparison with the dielec-tric constant of thc insulating liquid, said laycr being substan-tially thicker at such portions exposed to the greater field strength than at such other portions .
In a preferred embodiment of this invention, the resin is applied by electrostatic spraying.
~ -2-v~A~
Electrostatic spray painting as such is ~/ell-known, but so far it has not been known to employ this method for strengthen-ing the capacity of the electrodes to endure strong electrical fields in electrical apparatus. The method according to the in-vention makes use of the tendency of the applied material to ac-cumulate mostly where the electrical field strength is highest, which is where the strongest insulation is required.
In the accompanying drawings, Figure 1 shows a sharp corner in metallic construction part coated with an insulating agent according to the in-:; .,,,, , ~ , ; ' ' '~' ' ,' ' . , ' ~ .
iO49338 ~ention. Figure 2 ~hows a vertical section through a toroidalsplash ring on the line II-II of Figure 3. Figure 3 is a view from above of the splaqh ring according to Figure 2. Figure 4 shows an enlarged cros~-section of the area IV in ~igure 2.
Figure 5 shows a time-temperature curve for the application of a coating according to the invention.
Figure 1 show~ a sharp corner in a metallic construc-tion part 1 in an electrical apparatus. Thi~ may be, for example, the iron core in a transformer. When cutting trans-former sheet, burks will always appear and these will havea particular importance at the corners of the construction, with a resultant risk of glow phenomena. To avoid glow dis-charge and to strengthen~electric ~trength, an insulating layer 2 i8 applîed by means of electrostatic spraying of a powdered re~in or a resinous solution. Because of the increa~-ed field strength at the corner 3, an extra thick coating will appear there. This means that a coating is obtained, the thickness of which is related to the risk of flash-over between the construction part and a live conductor in the vicinity thereof.
Figure 2 shows a vertical section through a toroidal splash ring 4, which is placed on that end of a transformer bushing which is located in the oil in a transformer tank.
The lower end of the bushing is indicated at 5. The spla~h ring i3 supported by the bushing by means of stays 6. Figure 3 show3 the spla~h ring from above. Such splash rings are manufac-tured of a thin material, and the field ~trength will thus be high along the edges 7 with a subsequent risk of glow discharge.
Figure 4 ~hows a ~ection through the edge 7 on an enlarged ~0 ~cale, after the splash ring has been treated according to the invention. The figure ~hows that the said edge i~ coated with a layer 8 of insulating material so that the otherwise sharp edge has a considerably increased radiu~ of curvature. ~he ri~k of glow di3charge and flash-over at the edge i8 thu~
con~iderably reduced.
The treatment with resin according to the invention cau~es all sharp edge~ to acqulre a smooth curvature with a definable radius. This decreases the field strength and re~uces the risk of glow discharge and flash-over.
In order that the powder may ~tick and be evenly distributed~the object to be sprayed i~ preheated to a tempera-ture e~ceeding the melting point of the powder. ~igure 5shows the time - temperature curve during the process of coating an object. ~he straight part 10 indicates the temperature of the ob~ect before the start of the spraying. At 11 the object is removed from the heating furnace and the spraying comQences.
While the spraying is going on, the temperature decreases, which i~ marked by the downward curve part 12. At 13 the spraying is finished and the applied resin must be cured and this curing can be performed under a continuing temperature drop in the object according to one of the curve parts 14 or 15. It is also possible to place the object in a furnace 90 that the curing continues at constant temperature, as shown by the curve part 16. In any event it mu~t be ensured that the temperature does not rise after the spraying has been finished.
In the foregoing it has been assumed that the spray-ing is carried out with resin in the form of powder, but it is also po~sible to spray with solutions of powdered resin.
Claims (3)
1. In an electrical apparatus, which contains an insu-lating liquid, said apparatus having members formed of conductive material with portions of said members in contact with the liquid, said portions being exposed to inhomogeneous electric fields with uncontrollable electric field strengths, said portions being pro-vided with a layer of a resin with a dielectric constant which is high in comparison with the dielectric constant of said liquid, said layer being substantially thicker at such portions exposed to a greater field strength than at such other portions.
2. Apparatus as claimed in claim 1, in which said layer is produced by electrostatic spraying.
3. Apparatus as claimed in claim 1, in which said ap-paratus is a transformer.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7308658A SE382715B (en) | 1973-06-20 | 1973-06-20 | PROCEDURE FOR INCREASING THE ELECTRICAL FLASH RESISTANCE OF METALLIC ELECTRODES. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1049338A true CA1049338A (en) | 1979-02-27 |
Family
ID=20317824
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA202,879A Expired CA1049338A (en) | 1973-06-20 | 1974-06-19 | Increasing the dielectric strength in metal electrodes |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US3911384A (en) |
| BR (1) | BR7405004A (en) |
| CA (1) | CA1049338A (en) |
| DE (1) | DE2427474B2 (en) |
| NO (1) | NO134885C (en) |
| SE (1) | SE382715B (en) |
| ZA (1) | ZA743884B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4320437A (en) * | 1980-06-23 | 1982-03-16 | General Electric Company | Capacitor with edge coated electrode |
| DE4030806A1 (en) * | 1990-09-28 | 1992-04-02 | Siemens Ag | METHOD FOR INCREASING THE VOLTAGE RESISTANCE AND IMPROVING THE CROSS-CURRENT BEHAVIOR OF INSULATION CIRCUITS AND APPLICATION OF THIS METHOD TO VACUUM SWITCHES |
| SE507383C2 (en) * | 1996-11-22 | 1998-05-25 | Abb Research Ltd | Field control electrode |
| CN104634898B (en) * | 2013-11-08 | 2016-10-12 | 中国石油天然气股份有限公司 | Test method and the device of transformer oil aerogenesis trend is evaluated under electric heating mixing field |
| US10449648B2 (en) | 2016-08-04 | 2019-10-22 | Robert Bosch Tool Corporation | Transferring rotation torque through isolator for table saw |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2730461A (en) * | 1953-02-19 | 1956-01-10 | Ransburg Electro Coating Corp | Electrostatic coating method |
| US3265998A (en) * | 1964-04-14 | 1966-08-09 | Charles W Park | Compact high voltage transformer having more uniform equipotential line spacing |
-
1973
- 1973-06-20 SE SE7308658A patent/SE382715B/en unknown
-
1974
- 1974-06-07 DE DE2427474A patent/DE2427474B2/en not_active Withdrawn
- 1974-06-17 NO NO742180A patent/NO134885C/no unknown
- 1974-06-18 ZA ZA00743884A patent/ZA743884B/en unknown
- 1974-06-19 CA CA202,879A patent/CA1049338A/en not_active Expired
- 1974-06-19 US US480929A patent/US3911384A/en not_active Expired - Lifetime
- 1974-06-19 BR BR5004/74A patent/BR7405004A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR7405004A (en) | 1976-02-24 |
| NO742180L (en) | 1975-01-13 |
| ZA743884B (en) | 1975-06-25 |
| DE2427474B2 (en) | 1979-07-19 |
| NO134885B (en) | 1976-09-20 |
| SE382715B (en) | 1976-02-09 |
| SE7308658L (en) | 1974-12-23 |
| NO134885C (en) | 1976-12-29 |
| US3911384A (en) | 1975-10-07 |
| DE2427474A1 (en) | 1975-01-23 |
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