US3538470A

US3538470A - High tension electrical inductive apparatus

Info

Publication number: US3538470A
Application number: US806075A
Authority: US
Inventors: Bernard Crugnola
Original assignee: Alstom Savoisienne SA
Current assignee: Alstom Savoisienne SA
Priority date: 1968-03-12
Filing date: 1969-03-11
Publication date: 1970-11-03
Anticipated expiration: 1987-11-03
Also published as: FR1586642A; NL6903852A; DE1911682A1; BE729274A

Description

United States Patent 3,538,470 HIGH TENSION ELECTRICAL INDUCTIVE APPARATUS Bernard Crugnola, Tresserve, France, assignor to Alsthom Savoisienne, Saint Ouen, France, a corporation of France Filed Mar. 11, 1969, Ser. No. 806,075 Claims priority, application France, Mar. 12, 1968, 2 805 Int. (:1. limit 15/04, 15/14 US. Cl. 33669 6 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to high tension electrical inductive apparatus, and more particularly to extra high tension transformers and improvements in the effectiveness of insulation between the transformer windings and transformer housing.

It is known to provide sufficient space between metallic housings, and the windings of electrical apparatus to provide a potential gradient of the electrical field which is compatible with the insulating effectiveness of the insulation material in the space, and further to provide for sufiicient separation so that the stray magnetic field does not cause excessive stray losses. In concentric windings, equal potential lines are not perpendicular to the axis of the concentric windings at the ends thereof; in other words, the equipotential lines will not be parallel to the metallic masses at the ends of the axis but rather will present a different distribution.

It is an object ofthe present invention to provide a high tension electrical apparatus in which the efiectiveness of insulating materials is improved.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, concentric windings are surrounded, at the outside, by cylinders formed of metallic armatures so arranged as to form an electrostatic image of the windings themselves, the image being arranged and located with respect to an imaginary cylinder having an axis congruent with the axis of the concentric winding, and a diameter slightly larger than the external diameter of the largest winding. The term electrostatic image as used in this specification may be defined as an arrangement of location of such metallic armatures, or metal sheets such that the capacity between the armatures will, itself, cause a potential gradient distribution in that space outside of the winding, which is symmetrical, and a mirror image of the potential gradient distribution between the layers of the winding itself.

The invention will be described by way of example with reference to the accompanying drawings, wherein:

FIG. 1 is a cross sectional view through half of a toroidal-type winding, arranged in accordance with the prior art, and illustrating equally potential lines;

FIG. 2 is a view similar to FIG. 1, in which metallic armatures are placed in accordance with the present invention, also showing the resulting equipotential lines.

The basis for the present invention can best be understood by referring to FIG. 1, in which a cross-section, in highly schematic form, along a radial plane of the outer end of an electrical apparatus shown. A group of concentric layers of windings, C C C only half of which are shown, must be considered to be wound in a toroid in a plane perpendicular to the figure. A metal shield, for example, terminating in a rounded loop A will be substantially at the potential of the outside turn of layer C The distribution of equal potential lines will then be as shown by the dashed lines in FIG. 1. This distribution is determined by surrounding metallic masses, in which the magnetic core is indicated by M the outer housing by M and a metallic mass which may be an adjacent column, or a vertical wall of the apparatus itself indicated by M M is assumed to be grounded.

The equipotential lines, shown in broken form, of the electrical field which will arise during operation clearly show that they are not at all instances parallel to the mass M but rather strongly inclined with respect thereto. Insulating material, and left off from the drawing for the purpose of clarity, located between the windings and the housing wall M will thus be traversed by an electrical gradient which will have horizontal and vertical components (with respect to FIG. 1). Such insulating material is thus electrically unevenly loaded. Insulating material frequently has its highest insulating effectiveness, that is resistance to breakdown, transverse to its major surface. Thus, most effective resistance to flashover is transverse to the surface M Inclination of the electrical field will provide a vector component which is not trans verse, but parallel to surface M FIG. 2 illustrates the solution to the problem, the windings C to C being identical to those shown in FIG. 1, and the internal magnetic circuit M as well as the housing or otherwise shown metallic outer part M M also being identical. In accordance with the invention, metallic equipotential armatures A A A are located in the housing to surround the winding layers C C C from the outside, and so disposed that they will be an electrostatic image of the windings. The image is taken with respect to an imaginary cylinder, formed by the layers C C C the axis of the cylinder being congruent with the axis of the windings. The cylinder itself which, of course, is imaginary is indicated by the broken line B in FIG. 2. It will be seen that the windings have axial terminations which are staggered; similarly, and as a mirror image, the axial termination of the armature A A are likewise staggered. The radial distances between succesive armatures A A A as well as the axial lengths thereof are so calculated that the magnetic field will be as close to the ideal distribution as possible, so that the insulating material, located between the layers of the windings as well as between the armature elements will be loaded as much as possible in a transverse direction. This result is achieved when the equipotential lines, in the plane of FIG. 2, are parallel to as large an extent as possible to the housing wall M and to housing wall M respectively. The radial distances between armatures A A A are thus s'o arranged that, due to the capacitative distribution of voltage, each of the armatures will be at an average potential corresponding to the layers of the windings C C C and the length of the armatures A A A will then also be equal to the length of the corresponding layers C C C of the windings.

The metallic armatures A A .A are preferably made of magnetic material of high permeability, with sufiicient cross-section so that the material wil not saturate magnetically due to stray magnetic fluxes. This is particularly important in connection with extra high voltage, high power transformers.

The electrical field distribution can further be improved by combining auxiliary armatures B B B with the armature elements A A A The auxiliary elements B B B are arranged radially and axially between the outer ends of the winding layers C C C and housing M Armatures B B B are carried at the potential of the outside turn of the next adjacent winding layer C C C by interconnections, which are not shown in the drawings.

By providing a structure in which the equipotential lines of the electrostatic shield are essentialy parallel to the metallic parts of the apparatus, so that the insulation will be loaded transversely thereto, the distances between the electrical windings and the metallic housings may be reduced, without simultaneously increasing losses due to stray magnetic fields in the metallic elements which surround the windings, and in particular Within the generally substantial vertical wall of the housing surrounding the transformer.

I claim:

1. Electrical high tension inductive apparatus having concentric layer of windings (C C C said windings having a common circle of concentricity;

insulating material surrounding the windings,

and a housing located outside of said insulating material, comprising a plurality of radially spaced, concentric metallic armatures (A A A equal in number to the number of winding layers, said armatures being concentric with said windings (C C C and being located outside of the circle of concentricity of said windings and positioned in said housing at diameters, with respect to the center of said circle of concentricity, to form an electrostatic image of the windings with respect to an imaginary cylinder (E) having its axis at the center of the circle of concentricity, said cylinder having a greater diameter than said circle of concentricity.

2. Apparatus according to claim 1 wherein said metallic armatures consist of magnetic material having high permeability and of suflieient cross-section to operate in unsaturated state during operation of the apparatus.

3. Apparatus according to claim 1 wherein the layers of said windings are cylindrical and have progressively different axial length.

4. Apparatus according to claim 3 wherein said metallic armature comprises cylindrical sheet metal elements symmetrically located with respect to said windings and forming mirror images thereof With'the length thereof matching the length of said layer-s of windings.

5. Apparatus according to claim 3 including metal inserts located transverse to the axis of said windings at the ends thereof and forming magnetic guides for magnetic flux from said layers of windings to said sheet metal element.

6. Apparatus according to claim 1 wherein said metallic armatures are equal in length to their corresponding winding layers.

References Cited FOREIGN PATENTS 53,188 5/1967 Germany.

THOMAS J. KOZMA, Primary Examiner U.S. Cl. X.R. 336-84