JPS59163812A - Transformer with corona shielding means - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to electrical induction equipment, and more particularly to a transformer having corona shielding means for shielding the edges of the coil windings of the induction equipment.

Corona is an ionization phenomenon that results from the ejection of electrons from the surface of an electrical conductor at a high potential. This phenomenon depends on the curvature of the conductor surface, with maximum electron emission occurring from the pointed tip when the electric field strength is high enough to cause dielectric breakdown of the surrounding air. Such dielectric breakdown is caused by −
・It is not desirable for 4 yen because it is a seed and deteriorates the surrounding electrical insulation.

Typically, when a discharge occurs, a current pulse is generated, which causes power loss and radio interference.

The transformer core usually consists of laminates or thin sheets of electrical steel. Although such cores exhibit optimal magnetic properties, many of the edges of the stack exhibit the deleterious effect of creating voltage stress concentrations.

Furthermore, many conventional coils are constructed from epoxy spools, so that the winding of the coil is done in four separate sections. One of the inherent disadvantages of such a configuration is that a regular winding pattern is not obtained, ie the windings are seven trands. Another drawback is that no high voltage shielding means are provided.

It is an object of the present invention to provide a transformer that overcomes the drawbacks of the prior art.

According to the invention, a transformer includes a phase winding arranged in inductive relationship with a magnetic core having at least one leg portion, said phase winding having a low voltage and a high voltage coil on said core. , the coils are concentrically wound on the leg portions of the core, each coil having inner and outer layers wound between its edges, the edges of the outer coil corresponding to the inner coil. a plurality of layers of electrically insulating material indented inward from the edges and disposed between the low voltage and high voltage coils; and at least one electrically conductive, non-magnetic material disposed within the layer of electrically insulating material. a first corona shielding means formed by a layer, a second corona shielding means formed by at least one layer of electrically conductive, non-magnetic material disposed around said outer coil, and surrounding said core. So resilient (r
semiconducting tape which provides a ground plane and increases the voltage gradient between the high voltage winding and ground.

An advantage of the device of the present invention is that it eliminates localized electrical failures by using avalanche effects to rapidly increase the fault current and quickly blow out the associated fuses, avoiding gas generation and the explosion that normally accompanies it. That's true.

Electrical inductive devices, such as transformers, have electrical windings disposed in inductive relationship with a magnetic core.

The magnetic core is formed from a metal laminate, such as grain-oriented silicon steel, with at least one opening for winding an electrical winding, and the laminate is designed to form a complete magnetic circuit. has been done. The edges of the magnetic core facing the windings are usually formed by shearing the laminates and therefore contain many sharp edges, which form a pointed electrode and cause a corona discharge or radiation. . The corona significantly erodes and degrades the solid insulation on adjacent windings, resulting in premature breakdown.

Embodiments of the present invention will be described in detail below with reference to accompanying drawings.

Referring to FIGS. 1 and 2, transformer 10 includes first and second magnetic core portions in a juxtaposed relationship. Each magnetic core section consists of a plurality of magnetic laminates stacked together in a conventional manner.

Each laminate has an opening 16 for winding the winding 20.22.
．． The arrangement is such that a complete magnetic circuit is formed around 18. Although the illustrated transformer 10 is a single-phase transformer having two high-voltage coils for use between lines, it may also be used as one high-voltage coil for use between lines and ground.

The winding assembly shown in FIG. 3 according to the present invention includes a low voltage coil 24, an insulating layer 26, a corona shielding means 28, and a high voltage winding 2.
0.22, and an outer corona shielding means 30.32.

Additionally, each core portion 12.14 is coated with an insulating material 34.36 as shown in FIG. Core 12.
14 are formed by stacking thin sheets stamped from raw materials, they have many sharp edges that cause voltage stress concentration, and are therefore more difficult to use than butyl-stamped semiconductive tapes. The core is wrapped with an insulating coating 34,36 consisting of: A smooth and resilient ground plane is thus obtained and the voltage gradient between the energized and grounded components is increased.

The low voltage coil 24 consists of at least two layers of helically wound wire, each layer being a continuation of an adjacent layer, and in FIG.
extends from coil 24 in a conventional manner. The cross section of the wire constituting the coil may be circular or rectangular, but the latter is preferred in order to obtain a more uniform low voltage ground plane. Insulating layer 26 is wrapped directly around low voltage coil 24 onto dielectric material layer 42, such as a layer of polyester composite. Its edges 44 , 46 are interleaved with the corresponding edges of the low voltage coil 24 .

A second layer 48 of an insulating material similar to layer 42 is provided around the outer surface of the helically wound insulating layer 26. The edges 50 of the insulating layer 48 extend beyond the edges of the insulating layer 26, but are inboard of the extensions of the sides 44, 46 of the layer 42. The corresponding edge of layer 48 is connected to internal electrical trough 4.
They are indented to eliminate "acking".

Like layer 42, layer 48 is formed from a polyester composite and is disposed between layer 26 and corona shielding means 28.

The shielding means 2B is a cylindrical or sleeve-like member disposed around the outer surface of the layer 48, preferably with its like side 52 indented inwardly than the side 50 of the layer 48. The shielding means 28 is made of metal and is formed of copper or aluminum, the latter being preferred.

Both ends of the shielding means 28 are connected to the midpoint of the high voltage coils 20 and 22 as shown in FIG.

A layer 54 of semiconductive material, such as crepe tape, is wrapped around the outer surface of the shielding means 28, and the layer 54 is wrapped around both sides of the shielding means so that no sharp edges of the shielding means are exposed. Cover between the edges.

High voltage windings 20.22 are wound around the outer surface of semiconducting layer 54 in spaced relation to each other as shown in Figure S3. Each winding 20,22 consists of a layer of highly conductive metal wire, such as copper, evenly wound in each layer. for example,
No. 29 diameter 0.287cI11 (0,113 inches)
For example, 3 wires are wound 200 times in each layer.
It may be configured in 0 layers. Each layer is spirally wound around the previous layer -1- and is continuous with the previous layer in the usual manner. An insulator in the form of a layer of insulating material 56, such as a polyester film coated with a friction material, is provided between each layer to prevent the wire from slipping as the @ wire is wound one after the other. Thus, each successive layer 58 of the winding is insulated by layer 56.

The several layers of the outer part of each winding 20,22 consist of only one turn of the coil 60 for each layer, with an insulating layer provided between them.

By providing a single turn of coil for each layer of such outer portion, the voltage surge characteristics and impulse strength of the overall transformer structure are improved.

A corona shielding means 30 consisting of a piece of metal such as aluminum and wrapped in a polyester film has an outer single-wound layer 60.
and is connected at one end to the end of its single turn 60 and at the other end to the large diameter pass wire 60 to provide a uniform connection between the high voltage surface and ground and a good mechanical connection with the coil. Make it.

A conductive layer 64 covers each outer corona shielding means 3° and is preferably comprised of a semiconductive tape to eliminate non-uniformities in the shielding structure. Insulating layer 26.54.5
6 is a layer of resin film such as polyester film without fibers. On the other hand, layers 42.48 are at high voltage -
It is a resin composite for low voltage insulation. In addition, the layer 54
and 60 are resin composites and are semiconductive.

The core portions 12.14 are made of laminated steel plates approximately 11 mils thick and have sharp edges that can adversely affect the formation of a uniform ground plane and result in voltage stress concentrations. Therefore, the core is wrapped around the core with semiconductive tape 34, 36 lined with gutil. This configuration not only provides a smooth and resilient ground surface, but also increases the voltage gradient between the high voltage winding and ground. In addition, the butyl-backed semiconductive tape 34,362 serves to mechanically accommodate differences in expansion coefficients between the core and the outer epoxy encapsulant.

Finally, starting and finishing shielding means are incorporated within the windings to suppress voltage stress between the windings and between the layers during impulse surges. Without these shielding means, the voltage distribution would be non-linear with most of the voltage being applied to the first few turns of the first layer as shown in FIG. In order to produce a uniform response and eliminate voltage concentrations across these layers, the applied voltage must vary uniformly in the radial direction from line to ground and be parallel to the layers of the winding in the axial direction. This is achieved by arranging cylindrical shielding means concentrically at the start and finish portions of the winding. As a result, the electric field is suppressed between these two cylindrical members and approximates the gradient between parallel plates, resulting in a substantially uniform radial voltage gradient (FIG. 7). Furthermore, equipotential lines are formed in the axial direction parallel to the main part of each layer, so that little voltage appears between each turn, and normal turn insulation is sufficient.

Outer shielding member 30.32 as a winding on winding 20.22
By using 1, the back electromotive force caused by ungrounded (floating) winding parts is eliminated. The shielding member itself is made of a polyester-aluminum-polyester laminate for insulation and stress control. The terminal connections of each shielding member 30, 32 are made with self-piercing crimps, which ensure a reliable mechanical as well as electrical connection.

This shielded winding is characterized by a good surge response and an insulated structure, which is well suited to withstand the directional stresses occurring both in steady state and transient conditions. It is something. The electrostatic field generated is such that the winding is always stressed in the direction of its maximum field strength, which direction is perpendicular to the core earth.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an electrical induction device. FIG. 2 is a vertical cross-sectional view along line II--II of FIG. 1, with the thermosetting resin envelope shown in dotted lines. FIG. 3 is a vertical cross-sectional view taken along line m--m in FIG. FIG. 4 is an enlarged sectional view of a portion of the high voltage winding shown in FIG. 3. FIG. 5 is a circuit diagram. FIG. 6 is a graph showing applied voltage versus number of insulator layers for a coil without shielding means. FIG. 7 is a graph showing applied voltage versus number of insulator layers for a shielded coil structure. 10...Transformer 5 12.14...Magnetic core 20.22...High voltage coil 24...Low voltage coil 28...First corona shielding means 30...Second corona shielding means 58...End edge 60 of outer coil...Single turn coil portion 6 79 -80- +2345 1 1234! j

Claims (1)

Claims: 1. A phase winding is disposed in inductive relationship with a magnetic core having at least one leg portion, said phase winding having low voltage and high voltage coils wound on said core; The coil is wound concentrically on the leg portion of the core, the ends of the outer coil are indented more inwardly than the corresponding ends of the inner coil, and the outer coil is further indented between the low voltage and high voltage coils. a first corona shielding means formed by a plurality of layers of electrically insulating material and at least one layer of electrically conductive, non-magnetic material disposed outside the layer of electrically insulating material; and a first corona shielding means disposed about the outer coil. The shielding means is formed from at least one layer of conductive, non-magnetic material, and thus uses the avalanche effect to rapidly increase the fault current and prevent gas generation due to localized faults. A transformer that is characterized by eliminating common failures. 2. The transformer according to item 1, wherein both edges of the insulating material layer are indented from corresponding edges of the inner low voltage coil. 3. the layer of insulating material includes at least one first layer adjacent to the inner coil;
3. The transformer according to claim 1 or 2, wherein both edges of the layer extend in a continuous manner with corresponding edges of the inner coil. 4. The layer of insulating material includes at least one second layer spaced apart from the first layer and between the first layer and the first corona shielding means; 4. A transformer according to claim 3, wherein both edges of the layers are indented inwardly from corresponding edges of the first layer. 5. 5. A transformer according to claim 1 or 4, characterized in that the outer high voltage coil comprises two separate coil sections for use in a three-phase system. 6. Each of the outer high-voltage coils is comprised of a plurality of layers of wound conductors and a layer of electrically insulating material between each conductor layer, with both edges of each insulating layer being further forward than the corresponding edges of the conductor layer. 6. The transformer according to claim 5, wherein the transformer is elongated. 7. Said item 1.4 or 6, characterized in that said core is wrapped with semiconductive tape to provide a resilient ground plane and increase the voltage gradient between the high voltage winding and ground.
Transformer mentioned in section.