CA1212435A - Electrical transformer having corona shielding means - Google Patents
Electrical transformer having corona shielding meansInfo
- Publication number
- CA1212435A CA1212435A CA000447954A CA447954A CA1212435A CA 1212435 A CA1212435 A CA 1212435A CA 000447954 A CA000447954 A CA 000447954A CA 447954 A CA447954 A CA 447954A CA 1212435 A CA1212435 A CA 1212435A
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- Prior art keywords
- layer
- coil
- layers
- edges
- electrical transformer
- 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.)
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Abstract
ABSTRACT OF THE DISCLOSURE
An electrical transformer of the shell type characterized by a phase winding disposed in inductive relation with a magnetic core with a low voltage coil around the core leg and a high voltage coil wound concen-trically about the low voltage coil. Corona shielding is disposed between the coils as well as around the outer high voltage coil. The outer coil employs special winding whereby the combination of the winding and shielding provides better controlled voltage stresses and directly reduces internal failures.
An electrical transformer of the shell type characterized by a phase winding disposed in inductive relation with a magnetic core with a low voltage coil around the core leg and a high voltage coil wound concen-trically about the low voltage coil. Corona shielding is disposed between the coils as well as around the outer high voltage coil. The outer coil employs special winding whereby the combination of the winding and shielding provides better controlled voltage stresses and directly reduces internal failures.
Description
ELECTRICAL TRANSFORMER HAVING
CORONA SHIELDING MEANS
BACKGROUND OF THY INVENTION
Field of the Invention:
_ This invention relates generally to electrical inductive apparatus and, more particularly, to trays-former having corona shielding means for shielding edges of coil windings of electrical inductive apparatus.
Description of the Prior Art:
Corona is an ionization phenomena and occurs as a result of an emission of electrons from the surface of lo electrical conductors at high potentials, and is dependent upon the curvature of a conductor surface with most ems-sons occurring from sharp points when the electric field strength is high enough to cause a breakdown of the sun-rounding air. Such a breakdown is a discharge of current and is particularly undesirable due to its deteriorative effect upon surrounding electrical insulation. The disk charges commonly cause current pulses which, in turn, result in power losses and radio interference.
A transformer core normally consists of famine-lions or thin sheets of electrical steel. Though such adore provides optimum magnetic properties, the many edges of the laminations have the detrimental effect of product in voltage stress concentrations.
Moreover, many prior coils were constructed of an epoxy spool which provided for winding the coil in four r I 3 discrete sections. One inherent problem with such a con-struction was the lack of an orderly Jinxing pat-tern, i.e., random winding. Another problem was the absence of any high-voltage shielding.
SUMMARY O THE INVENTION
It has been found in accordance with this invent lion that the foregoing problems may be overcome by pro-voiding an electrical transformer comprising a phase wind-in disposed in inductive relation with a magnetic core having at least one leg portion; the phase winding having low-voltage and high-voltage coils on the core; the coils being concentrically wound on and around the core leg portion; each core having inner and outer layers wound between opposite edges; the outer coil having opposite edges indented within corresponding edges of the inner coil; a plurality of layers of electrically insulating material between the low- and high-voltage coils; a first corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed within the layers of electrically insulating material; a second corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed around the outer coil; and a semi-conductive tape enclosing the core so as to provide a resilient ground plane and tug enhance voltage radiant between high-voltage winding and ground.
The advantage of the device of this invention is the elimination of sectionalized electrical failure by using an avalanche effect and rapidly increasing the fault current to thereby open an associated fuse quickly and 0 avoiding gas generation and its usual explosive effect.
GRIEF DESCRIPTION OF TOE DRAWINGS
figure 1 is a perspective view of electrical inductive apparatus;
Fig 2 is a vertical sectional view, taken on I the inn II-II of Fig. 1, and showing in broken line a surrounding envelope of a thermosetting resin;
Fig. 3 is a vertical sectional view, taken on the line III-III of Fig. 2;
Fig. 4 is an enlarged sectional view of a port lion of the high-voltage winding shown in Fig. 3;
Fig. 5 is a circuit diagram;
Fig. 6 is a graph of applied voltage vs. number of layers of insulation for an unshielded coil; and Fig. 7 is a graph of applied voltage vs. number of layers of insulation for a shielded coil structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Electrical inductive apparatus, such as trays-former, include electrical windings disposed in inductive relation with a magnetic core. The magnetic core includes at least one opening for receiving electrical windings, lo and is formed of a plurality of stacks of metallic famine-lions, such as grain oriented silicon steel, with the stacks being arranged to form a complete magnetic circuit.
The edges of the magnetic core which face the windings normally include many sharp edges as a result of prior shearing of the laminations from stock, which edges form sharp electrodes that are a possible source of corona discharge or streamers. Corona may seriously erode and degrade the solid insulation on the adjacent windings, accelerating the breakdown process.
A transformer generally indicated at lo (Figs.
l, I) includes first and second magnetic core sections 12, 14 disposed in side-by-side relation. Each magnetic core section includes a plurality of stacks of. superposed magnetic laminations in the conventional manner. The stacks are disposed to form complete magnetic circuits about a plurality of openings 16, 18 for receiving elect tribal windings 20, 22. Although the transformer 10 is disclosed and described as a single-phase electrical transformer having two high-voltage coils for line-to-line applications, it is understood that the transformer may comprise one high-voltage coil for line Toronado applique-lions.
I
In accordance with this invention a winding assembly (Fig. 3) includes a low-voltage coil I insular -lion layers 26, a corona shield 28, the high voltage windings 20, 22, and outer corona shields 30, 32. In addition, each of the core sections 12, 14 is covered with an insulative coating 34, 36, respectively (Fig. 2).
Inasmuch as the cores 12, 14 are comprised of stacks of laminating thin sheets that are stamped from electrical steel stock, they have a detrimental effect of many sharp edges which result in voltage stress concentrations for which reason the cores are wrapped with insulative coat-ins 34, 36 which are comprised of a butyl-backed semi-conductive tape. Thus, a smooth and resilient ground plane is provided to enhance the voltage gradient between live and grounded components.
The low-voltage coil 24 is comprised of at least -two layers of wire which is spirally wound with each layer being a continuation of an adjacent layer. Leads or cables 38, 40 (Fig. 3) extend from the coil 24 in a con-ventional manner. The wire comprising the coil may have either round or rectangular cross section, the latter being preferred for a more even low-voltage ground plane.
The insulation layers 26 are wound around the low-voltage coil 24 and more directly upon a layer or coating 42 of dielectric material such as one layer of a polyester composite. Opposite sides 44, 46 are coextensive with opposite sides of the low-voltage coil 24. The spirally - wound insulating layers 26, preferably polyester film, ~-~. include opposite sides which are indented to provide a margin between said sides and the opposite sides 44, 46 of the layer 42, thereby avoiding breakdown of a medium over an intervenirlg solid insulating surface which is known as creep age breakdown.
A second layer 48 of insulating arterial similar to the layer or coating 42 is applied around the outer surface of the spirally wound insulating layer 26. The insulative layer 48 includes similar opposite side port ~99~
lions 50 which extend beyond opposite sides of the insulating layers 26 but within the extensions of the sides 44, 46 of the layer 42. 'the opposite edges of the layer 48 are indented to eliminate internal electrical tracking.
Like the layer 42, the layer 48 is comprised of a polyp ester composite and is disposed between the slayer 26 and the corona shield 28.
The shield 28 is a cylindrical or sleeve-like member around the outer surface of the layer 48 and prey-drably has similar edges 52 which are indented within the side portions 50 of the layer 48. The shield 28 is metal-fig and is composed of either copper or aluminum and preferably the latter. Opposite ends of the shield 28 are connected to the midpoint of high voltage golfs 20 and 22 lo as shown in Fig. 5.
The layer 54 of semi-conductive material, such as crepe tape, is wound around the outer surface of the shield 28. The layer 54 covers the shield completely from edge to edge to grade off any sharp edges in the shield.
Parts 24, 26, 28, 42, 48 and 54 are collectively indicated at 55 in Fig. 2.
The high-voltage windings 20, 22 are wound around the outer surface of the semi-conductive layer 54 and spaced from each other as shown in Fig. 3. Each winding 20, 22 is comprised of uniformly wound layers of a metal wire having a high coefficient of electrical conduct tivity, such as copper, for many multiple turns per layer.
For example, 200 turns per layer may be provided with a No. 29 gauge wire (0.113 inch) for, say, thirty layers.
Each layer is spirally and helically wound upon a precede in layer and is a continuation thereof in a conventional manner. Between each layer insulation is provided (Fig.
4) in the form of layers 56 of insulative material, such as friction-coated polyester film to prevent wire slippage during winding of each consecutive layer. Thus, kinesic-live layers 58 of wire winding are insulated by the layers 56.
Several outer layers of each winding 20, 22 comprise only one turn 60 per layer with insulative layers 56 there between. The outer one-turn-per-layer structure improves the voltage surges and impulse strength of the overall transformer structure.
The corona shield 30 which is comprised of a strip of metal such as aluminum and cased in polyester film is wound around the outer single turn layer 60 and is connected at one end to the end of the single turn 60 and at the other end to a large diameter bus wire 62, thereby providing a uniform high-voltage plane-to-ground and good mechanical connection with the coil.
A conductive layer 64 surrounds each outer corona shield 30 and is preferably comprised of a semi-conductive tape to grade off any non-uniformity in the shield construction. The insulative layers 26, 54, 56 are layers of a resinous film, such as polyester film without fibers. On the other hand, the layers 42, 48 are fibrous composites for hi-lo insulation. Also, layers 54 and 60 are fibrous composites, semi-conductive in nature.
Inasmuch as the core sections 12, 14 are come prosed of stacks of laminated steel having a thickness of approximately 11 miss, there may be sharp edges that are detrimental to providing a uniform ground plane which results in voltage stress concentrations. For that reason the butyl-backed semi-conductive tape 34, 36 is wrapped around the cores. This construction provides a smooth and resilient round plane as well as enhancing voltage grad-tent between the high-voltage windings and ground. More-over, the buty].-backed semi conductive tape 34, 36 allows mechanically for differentiation in coefficients of expand soon between the core and an outer epoxy encapsulant 56.
Finally, in order to control inter-turn and inter-la~er voltage stresses during impulse surges, start and finish shields are incorporated within the windings.
Without the shields the voltage distribution would be non linear with most of the voltage being across the first few turns of the first layer such as shown in Fig. 6. To produce a uniform response and eliminate the voltage concentrations across the layers, the impressed outage must be uniformly graded radially from line to ground and constrained axially to be parallel with the windincJ
layers. This is accomplished by positioning concentric-cylindrical shields at the start and finish of the wind-ins. As a result a substantially uniform radial voltage gradient (Fig. 7) is produced because the field is con-trolled between two cylinders and approximates the grad-tent between the parallel plates. Moreover, equipoten-trials (voltage) are constrained in an axial direction lobe parallel with the major portion of each layer so that little voltage appears between turns and the normal inter-turn insulation is adequate.
By using the outer shields 30, 32 as turns on the windings 20, 22 a back EM created by an ungrounded (floating) turn is eliminated. The shield itself is comprised of a polyester-aluminum-polyester laminate thereby providing insulation and stress control. Terminal lion of each shield 30, 32 is accomplished with a self-piercing crimp which insures a mechanical as well as - electrical connection.
In conclusion, toe shielded layer winding is characterized by an excellent surge response, and an insulated structure which is well suited to withstand the directional stresses developed during both steady-state and transient conditions. The electrostatic fields pro-duped are such that the winding is always stressed in the direction of its maximum strength, normally to the round plane of the core.
CORONA SHIELDING MEANS
BACKGROUND OF THY INVENTION
Field of the Invention:
_ This invention relates generally to electrical inductive apparatus and, more particularly, to trays-former having corona shielding means for shielding edges of coil windings of electrical inductive apparatus.
Description of the Prior Art:
Corona is an ionization phenomena and occurs as a result of an emission of electrons from the surface of lo electrical conductors at high potentials, and is dependent upon the curvature of a conductor surface with most ems-sons occurring from sharp points when the electric field strength is high enough to cause a breakdown of the sun-rounding air. Such a breakdown is a discharge of current and is particularly undesirable due to its deteriorative effect upon surrounding electrical insulation. The disk charges commonly cause current pulses which, in turn, result in power losses and radio interference.
A transformer core normally consists of famine-lions or thin sheets of electrical steel. Though such adore provides optimum magnetic properties, the many edges of the laminations have the detrimental effect of product in voltage stress concentrations.
Moreover, many prior coils were constructed of an epoxy spool which provided for winding the coil in four r I 3 discrete sections. One inherent problem with such a con-struction was the lack of an orderly Jinxing pat-tern, i.e., random winding. Another problem was the absence of any high-voltage shielding.
SUMMARY O THE INVENTION
It has been found in accordance with this invent lion that the foregoing problems may be overcome by pro-voiding an electrical transformer comprising a phase wind-in disposed in inductive relation with a magnetic core having at least one leg portion; the phase winding having low-voltage and high-voltage coils on the core; the coils being concentrically wound on and around the core leg portion; each core having inner and outer layers wound between opposite edges; the outer coil having opposite edges indented within corresponding edges of the inner coil; a plurality of layers of electrically insulating material between the low- and high-voltage coils; a first corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed within the layers of electrically insulating material; a second corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed around the outer coil; and a semi-conductive tape enclosing the core so as to provide a resilient ground plane and tug enhance voltage radiant between high-voltage winding and ground.
The advantage of the device of this invention is the elimination of sectionalized electrical failure by using an avalanche effect and rapidly increasing the fault current to thereby open an associated fuse quickly and 0 avoiding gas generation and its usual explosive effect.
GRIEF DESCRIPTION OF TOE DRAWINGS
figure 1 is a perspective view of electrical inductive apparatus;
Fig 2 is a vertical sectional view, taken on I the inn II-II of Fig. 1, and showing in broken line a surrounding envelope of a thermosetting resin;
Fig. 3 is a vertical sectional view, taken on the line III-III of Fig. 2;
Fig. 4 is an enlarged sectional view of a port lion of the high-voltage winding shown in Fig. 3;
Fig. 5 is a circuit diagram;
Fig. 6 is a graph of applied voltage vs. number of layers of insulation for an unshielded coil; and Fig. 7 is a graph of applied voltage vs. number of layers of insulation for a shielded coil structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Electrical inductive apparatus, such as trays-former, include electrical windings disposed in inductive relation with a magnetic core. The magnetic core includes at least one opening for receiving electrical windings, lo and is formed of a plurality of stacks of metallic famine-lions, such as grain oriented silicon steel, with the stacks being arranged to form a complete magnetic circuit.
The edges of the magnetic core which face the windings normally include many sharp edges as a result of prior shearing of the laminations from stock, which edges form sharp electrodes that are a possible source of corona discharge or streamers. Corona may seriously erode and degrade the solid insulation on the adjacent windings, accelerating the breakdown process.
A transformer generally indicated at lo (Figs.
l, I) includes first and second magnetic core sections 12, 14 disposed in side-by-side relation. Each magnetic core section includes a plurality of stacks of. superposed magnetic laminations in the conventional manner. The stacks are disposed to form complete magnetic circuits about a plurality of openings 16, 18 for receiving elect tribal windings 20, 22. Although the transformer 10 is disclosed and described as a single-phase electrical transformer having two high-voltage coils for line-to-line applications, it is understood that the transformer may comprise one high-voltage coil for line Toronado applique-lions.
I
In accordance with this invention a winding assembly (Fig. 3) includes a low-voltage coil I insular -lion layers 26, a corona shield 28, the high voltage windings 20, 22, and outer corona shields 30, 32. In addition, each of the core sections 12, 14 is covered with an insulative coating 34, 36, respectively (Fig. 2).
Inasmuch as the cores 12, 14 are comprised of stacks of laminating thin sheets that are stamped from electrical steel stock, they have a detrimental effect of many sharp edges which result in voltage stress concentrations for which reason the cores are wrapped with insulative coat-ins 34, 36 which are comprised of a butyl-backed semi-conductive tape. Thus, a smooth and resilient ground plane is provided to enhance the voltage gradient between live and grounded components.
The low-voltage coil 24 is comprised of at least -two layers of wire which is spirally wound with each layer being a continuation of an adjacent layer. Leads or cables 38, 40 (Fig. 3) extend from the coil 24 in a con-ventional manner. The wire comprising the coil may have either round or rectangular cross section, the latter being preferred for a more even low-voltage ground plane.
The insulation layers 26 are wound around the low-voltage coil 24 and more directly upon a layer or coating 42 of dielectric material such as one layer of a polyester composite. Opposite sides 44, 46 are coextensive with opposite sides of the low-voltage coil 24. The spirally - wound insulating layers 26, preferably polyester film, ~-~. include opposite sides which are indented to provide a margin between said sides and the opposite sides 44, 46 of the layer 42, thereby avoiding breakdown of a medium over an intervenirlg solid insulating surface which is known as creep age breakdown.
A second layer 48 of insulating arterial similar to the layer or coating 42 is applied around the outer surface of the spirally wound insulating layer 26. The insulative layer 48 includes similar opposite side port ~99~
lions 50 which extend beyond opposite sides of the insulating layers 26 but within the extensions of the sides 44, 46 of the layer 42. 'the opposite edges of the layer 48 are indented to eliminate internal electrical tracking.
Like the layer 42, the layer 48 is comprised of a polyp ester composite and is disposed between the slayer 26 and the corona shield 28.
The shield 28 is a cylindrical or sleeve-like member around the outer surface of the layer 48 and prey-drably has similar edges 52 which are indented within the side portions 50 of the layer 48. The shield 28 is metal-fig and is composed of either copper or aluminum and preferably the latter. Opposite ends of the shield 28 are connected to the midpoint of high voltage golfs 20 and 22 lo as shown in Fig. 5.
The layer 54 of semi-conductive material, such as crepe tape, is wound around the outer surface of the shield 28. The layer 54 covers the shield completely from edge to edge to grade off any sharp edges in the shield.
Parts 24, 26, 28, 42, 48 and 54 are collectively indicated at 55 in Fig. 2.
The high-voltage windings 20, 22 are wound around the outer surface of the semi-conductive layer 54 and spaced from each other as shown in Fig. 3. Each winding 20, 22 is comprised of uniformly wound layers of a metal wire having a high coefficient of electrical conduct tivity, such as copper, for many multiple turns per layer.
For example, 200 turns per layer may be provided with a No. 29 gauge wire (0.113 inch) for, say, thirty layers.
Each layer is spirally and helically wound upon a precede in layer and is a continuation thereof in a conventional manner. Between each layer insulation is provided (Fig.
4) in the form of layers 56 of insulative material, such as friction-coated polyester film to prevent wire slippage during winding of each consecutive layer. Thus, kinesic-live layers 58 of wire winding are insulated by the layers 56.
Several outer layers of each winding 20, 22 comprise only one turn 60 per layer with insulative layers 56 there between. The outer one-turn-per-layer structure improves the voltage surges and impulse strength of the overall transformer structure.
The corona shield 30 which is comprised of a strip of metal such as aluminum and cased in polyester film is wound around the outer single turn layer 60 and is connected at one end to the end of the single turn 60 and at the other end to a large diameter bus wire 62, thereby providing a uniform high-voltage plane-to-ground and good mechanical connection with the coil.
A conductive layer 64 surrounds each outer corona shield 30 and is preferably comprised of a semi-conductive tape to grade off any non-uniformity in the shield construction. The insulative layers 26, 54, 56 are layers of a resinous film, such as polyester film without fibers. On the other hand, the layers 42, 48 are fibrous composites for hi-lo insulation. Also, layers 54 and 60 are fibrous composites, semi-conductive in nature.
Inasmuch as the core sections 12, 14 are come prosed of stacks of laminated steel having a thickness of approximately 11 miss, there may be sharp edges that are detrimental to providing a uniform ground plane which results in voltage stress concentrations. For that reason the butyl-backed semi-conductive tape 34, 36 is wrapped around the cores. This construction provides a smooth and resilient round plane as well as enhancing voltage grad-tent between the high-voltage windings and ground. More-over, the buty].-backed semi conductive tape 34, 36 allows mechanically for differentiation in coefficients of expand soon between the core and an outer epoxy encapsulant 56.
Finally, in order to control inter-turn and inter-la~er voltage stresses during impulse surges, start and finish shields are incorporated within the windings.
Without the shields the voltage distribution would be non linear with most of the voltage being across the first few turns of the first layer such as shown in Fig. 6. To produce a uniform response and eliminate the voltage concentrations across the layers, the impressed outage must be uniformly graded radially from line to ground and constrained axially to be parallel with the windincJ
layers. This is accomplished by positioning concentric-cylindrical shields at the start and finish of the wind-ins. As a result a substantially uniform radial voltage gradient (Fig. 7) is produced because the field is con-trolled between two cylinders and approximates the grad-tent between the parallel plates. Moreover, equipoten-trials (voltage) are constrained in an axial direction lobe parallel with the major portion of each layer so that little voltage appears between turns and the normal inter-turn insulation is adequate.
By using the outer shields 30, 32 as turns on the windings 20, 22 a back EM created by an ungrounded (floating) turn is eliminated. The shield itself is comprised of a polyester-aluminum-polyester laminate thereby providing insulation and stress control. Terminal lion of each shield 30, 32 is accomplished with a self-piercing crimp which insures a mechanical as well as - electrical connection.
In conclusion, toe shielded layer winding is characterized by an excellent surge response, and an insulated structure which is well suited to withstand the directional stresses developed during both steady-state and transient conditions. The electrostatic fields pro-duped are such that the winding is always stressed in the direction of its maximum strength, normally to the round plane of the core.
Claims (6)
1. An electrical transformer comprising:
(a) a phase winding disposed in inductive relation with a magnetic core having at least one leg portion;
(b) the phase winding having low voltage and high voltage Coils on the core;
(c) the coils being concentrically wound on and around the core leg portion;
(d) the outer coil having opposite edges indented within corresponding edges of the inner coil;
(e) a plurality of layers of electrically insulat-in material between the low and high voltage coils;
(f) a first corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed outside the layers of electrically insulating material;
(g) a second corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed around the outer coil; and (h) the outer layers of the high voltage coil comprising only one coil turn per layer and said one coil turn being within the second corona shield;
whereby sectionalized electrical failure is eliminated by using an avalanche effect to rapidly increase the fault current and avoid gas generation on a sectionalized fault.
(a) a phase winding disposed in inductive relation with a magnetic core having at least one leg portion;
(b) the phase winding having low voltage and high voltage Coils on the core;
(c) the coils being concentrically wound on and around the core leg portion;
(d) the outer coil having opposite edges indented within corresponding edges of the inner coil;
(e) a plurality of layers of electrically insulat-in material between the low and high voltage coils;
(f) a first corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed outside the layers of electrically insulating material;
(g) a second corona shield formed of at least one layer of electrically conductive, non-magnetic material disposed around the outer coil; and (h) the outer layers of the high voltage coil comprising only one coil turn per layer and said one coil turn being within the second corona shield;
whereby sectionalized electrical failure is eliminated by using an avalanche effect to rapidly increase the fault current and avoid gas generation on a sectionalized fault.
2. The electrical transformer of claim 1 in which the layers of insulating material include opposite edges indented within corresponding edges of the inner low voltage coil.
3. The electrical transformer of claim 2 in which the layers of insulating material include at least one first layer adjacent the inner coil, and said one layer having op-posite edges coextensive with corresponding edges of the inner coil.
4. The electrical transformer of claim 3 in which the layers of insulating material include at least one second layer spaced from and between said first layer and said first corona shield, and said second layer having opposite edges that are indented inwardly of corresponding edges of said first layer.
5. The electrical transformer of claim 4 in which the outer high voltage coil comprises two spaced coil portions for three-phase systems.
6. The electrical transformer of claim 5 in which each outer high voltage portion comprises a plurality of layers of a wound conductor, a stratum of electrical insulation between each layer of conductor, and each stratum having oppo-site edges extending beyond corresponding edges of the stacked layers.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US46953283A | 1983-02-24 | 1983-02-24 | |
| US469,532 | 1983-02-24 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1212435A true CA1212435A (en) | 1986-10-07 |
Family
ID=23864142
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000447954A Expired CA1212435A (en) | 1983-02-24 | 1984-02-21 | Electrical transformer having corona shielding means |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS59163812A (en) |
| CA (1) | CA1212435A (en) |
| ZA (1) | ZA841155B (en) |
-
1984
- 1984-02-16 ZA ZA841155A patent/ZA841155B/en unknown
- 1984-02-21 CA CA000447954A patent/CA1212435A/en not_active Expired
- 1984-02-24 JP JP3508184A patent/JPS59163812A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| JPS59163812A (en) | 1984-09-14 |
| ZA841155B (en) | 1984-09-26 |
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