US2887729A - Method of embedding electrical high voltage apparatus - Google Patents

Description

May 26, 1959 A. IMHOF 2,387,729

METHOD OF EMBEDDING ELECTRICAL HIGH VOLTAGE APPARATUS Filed June 15. 1954 rag-.2,

United States Patent METHOD OF EMBEDDING ELECTRICAL HIGH VOLTAGE APPARATUS Alfred Imhof, Zurich, Switzerland Application June 15, 1954, Serial No. 436,866

Claims priority, application Switzerland June 18, 1953 2 Claims. (Cl. 18-59) The present invention relates to high voltage apparatus and to a method for manufacturing same.

It is an object of the present invention to avoid the drawbacks and deficiencies of high voltage apparatus, particularly if the same have insulating parts consisting of a casting resin.

It is another object of the present invention to avoid the internal mechanical stresses due to contractions during the hardening, contractions and extensions occurring at changing temperatures, and/ or faulty casting.

It is a further object of the present invention to avoid the drawbacks due to inaccessibility of embedded parts.

It is still another object of the present invention to avoid the drawbacks due to the necessity of the repair or replacement of entire apparatuses in case of defects during the operation or the testing of the apparatus.

According to the present invention, these difliculties and deficiencies are avoided in a simple manner by manufacturing the entire insulating parts of high voltage ap paratuses and the like from parts, preferably consisting of casting resin, which may be assembled like bricks, and filling the joints remaining between the insulating structural parts with an easily deformable insulating material having high-class dielectric properties.

For such easily deformable materials are suitable materials being liquid at normal temperature, ointments, paste-like materials, mixtures of such materials with mineral or organic powders, easily deformable solids, particularly in shape of flexible foils wetted by liquid or pasty materials, rubber-like materials, also in combination with solvents rendering the surface thereof soft and sticky, porous materials impregnated with liquid dielectries, gases and mixtures thereof having a high dielectric strength such as compressed air, compressed nitrogen, compressed carbon dioxide, gaseous halogens, etc.

The subdivision of the entire insulation into individual insulating parts may be arbitrary or governed, for instance, by the nature and form of the part to be embedded, for instance a metal, or by the mechanical, electric, and dielectric requirements, etc. Apparatuses of any size may be insulated according to the present invention.

Particular advantages of the invention reside in the fact that the joints are easily formed when the insulating parts are manufactured by casting; for instance, the joints may be formed in a very simple manner by arranging separating Walls in advance and removing the same after the casting so that even complicated joints can be achieved without a finishing operation.

If the joints are narrow and if liquid dielectrics are only used as impregnating materials of porous foils or as Wetting agents of flexible solid dielectrics, the quantity of the liquid dielectric is relatively small, thus reducing the danger of fire and rendering feasible the use of, for instance, expensive liquid materials which have more valuable properties such as of being not easily inflammable,

2,887,729 Patented May 26, 1959 of being incombustible, or of a widely uniform viscosity over a large range of temperatures, a small surface tension particularly coupled with the property of a good wettening, a vary high electric strength, a low loss factor, a high chemical stability, slow soot formation, etc.

Materials having all these and further advantageous properties are, for instance, silicon oils, certain fluoroethers, certain fluoro-t-amines, chloro-phenyl-indane, chloro-diphenyls. The halogen compounds mentioned hereinabove have, i.e., the particular advantages of incombustibility, partly also non-sootability, high electric strength, compatibility with the solid insulating materials used according to the invention, good wettability, high heat and cold resistance.

Silicon oils are furthermore advantageous because the viscosity thereof remains the same within wide limits of temperature; also those are usable, which for instance remain liquid from -60 C. to 200 C. Furthermore, they are Water-repellant. Also very viscous silicon oils are to be taken into consideration since they render easy anty sealing and have particularly good dielectric propfil 16S. Fluoro-t-amines and fluoro-ethers are advantageous if it is a question of a very low dielectric constant, somewhat smaller than 2, Whereas the ehloro-diphenyls have a particularly high dielectric constant and are relatively inexpensive.

instead of chloro-diphenyls, the chloro-phenyl-indanes with properties very similar to those of the chloro-diphenyls are advantageous and are distinguished from the latter by the greater chemical stability thereof, particularly at higher temperatures.

Fluoro-ethers, fluoro-t-amines, and fluoro-indanes are moreover very stable under changes of temperatures, have a very good wettability, and a high dielectric strength. In this respect they are superior to, for instance, mineral oils; but particularly they are entirely incombustible.

As insulating materials for the solid structural elements are particularly suitable the casting resins and among these particularly the embedding resins hardening from the direct initial materials thereof by a poly-reaction such as a polymerization or poly-addition without the splitting off of volatile components. These materials adapt themselves so Well during and after casting to the metal parts under voltage or the metallic or insulating covers, etc. that small joint spaces result.

Preferably the joints are designed in such manner that the electric field lines are normal or at least approximately normal to the joints.

In order to seal the joints, the latter may be packed by a foil of solid material which is wetted on both sides with a liquid insulating material. The liquid may be prevented from flowing out of the joints by utilizing for sealing purposes, for instance the marginal portions of the material filling the joints. A desired complete filling of the joint by the liquid may be obtained particularly by a reduction of the width of the joints after the filling operation. In certain cases, the packing of the joint consists preferably of a porous foil, the marginal portions of which are preferably non-porous. The porous portion is filled with a dielectric liquid, the marginal portions serving as a sealing means.

In case of a cooling of the apparatus or apparatuses, for instance for drawing off the heat generated by the copper losses, or dielectric or other losses, the joints may be connected with one another and the preferably liquid filling material subjected to a circulation, for instance by recooling the same in a cooling device The apparatuses or groups of the same having a bricklike structure may be cast in one piece and in one form.

The spaces of the joints are formed thereby as to position and form preferably by walls arranged in the molding form preferably consisting of a material which does not adhere to the resin such as polyethylene or polytetrafluoro-ethylene, so that they may be removed with great ease after a hardening of the resin. However, the walls may consist instead of a material such as metal sheet which is provided with a suitable cover or coating, for in stance of silicone fat.

Preferably also active parts of the apparatus are protected against adhering to the resin bodies, for instance by coating the parts with a material preventing any adhesion, or by covering the parts with a foil which either prevents the adhesion by its own nature or does this after being covered with a varnish or coating.

In cases when the apparatus should be provided with a metallic cover it is advisable to use the metal cover itself as a casting mold. The required joints between the walls of the casing and the resin body are automatically formed by the contraction of the resin, particularly if the walls of the casing are provided on the inner side thereof with a coat preventing any adhesion.

Other objects and advantages of the present invention will become clear from the following detailed description thereof with reference to the accompanying drawings showing, by way of example, some embodiments of the present invention. In the drawings:

Fig. 1 is a sectional elevation of a voltage transformer with insulating parts according to one embodiment of the present invention;

Fig. 2 is a sectional elevation of a modified embodiment of the voltage transformer shown in Fig. 1;

Fig. 3 is a sectional elevation of a current transformer according to the present invention; and .Fig. 4 is a sectional elevation of the embodiment shown in Fig. 3 taken at right angles thereto.

Referring now to the drawings and first to Fig. 1, a voltage transformer, one terminal of which is grounded, compi'isesa primary winding 1 enclosing the secondary wind ing 2 which in turn is wound on the magnetic iron core 3. Between the windings 1 and 2 an insulating tube or pipe 4 is arranged which together with the solid insulating parts mentioned hereinafter consists partly of porcelain, ceramics, or casting resin. The primary winding 1 and part of the insulating pipe 4 are enclosed by the insulating structural members 5 and 6 in a casing-like manner. Between these parts joints 7 are arranged which are filled by a liquid insulating material. The conductor 8 serving as a high voltage lead-in is closely surrounded by an insulating member 20 serving as a lead-in insulation. The ends of the pipe 4 are closely connected with the insulatinglparts 5 and 6, for instance by a cement consisting of synthetic resin, or in case of the application of ceramics or glass by a metal solder.

The voltage transformer shown in Fig. 2 differs from that shown in Fig. 1 by a metal casing 9 containing the solid insulating members 5 and 6.

Referring now to Figs. 3 and 4 showing a current transformer, a primary winding 10, is enclosed by a metallic mantle 11 continued by a stem 12 serving as a guiding means for the leads (not shown) of the primary Winding 10. The transformer is arranged in an insulating body 13 consisting of casting resin and provided at its upper side with a funnel-shaped continuation 14. A condenser lead-in 15 is arranged to dip with the lower end thereof into the continuation 14 and is separated from the same by a conical joint 16 filled with an insulating liquid. On its upper side, the joint 16 is sealed by means of a ring washer 17. An iron core 18 is arranged within the central cross sectional part 21 and carries the secondary winding 19 of the transformer. If desired, the condenser lead-in may be protected by ceramic or porcelain screens (not shown) against rain and moisture, if the apparatus is intended for outdoor use.

Having now particularly described the invention and the advantages and uses thereof in connection with voltage and current transformers, it will be understood that it may be applied if desired, to other types of apparatus such as dry rectifiers, enclosed bus bar systems, or any combination of the same, and that the invention is not to be limited to the details herein disclosed, otherwise than set forth in the appended claims.

I claim:

1. A method of enclosing a high voltage apparatus in an electric insulation consisting of individual rigid insulating blocks forming joint spaces between each other, said method comprising the steps of placing a high voltage apparatus into a mold, arranging removable partitions at the spaces defining the joints of the insulation, casting a polymerizable resinous material in said mold, setting said resinous material into blocks separated by said partitions, removing said partitions, and filling the spaces previously occupied by said partitions with a readily deformable insulating material.

2. A method as claimed in claim 1, comp-rising coating a metal mold forming the enclosure of the apparatus with a coating preventing the sticking of the casting material, and casting the resinous material into said coated metal mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,888,613 Apple Nov. 22, 1932 2,068,940 Wiseman Ian. 26, 1937 2,094,287 Zimmerman et al Sept. 28, 1937 2,112,241 Hyde Mar. 29, 1938 2,216,010 Hobart Sept. 24, 1940 2,262,831 Burleson Nov. 18, 1941 2,402,366 Camilli June 18, 1946 2,489,891 Hull Nov. 29, 1949 FOREIGN PATENTS 679,220 Germany Aug. 1, 1939 473,119 Italy July 12, 1952 OTHER REFERENCES Publication, Silicone Rubber Emerges as a Dielectric Material, Electrical Manufacturing, June 1950, pages 101-103, 200, 202. (Page 101 relied on.) (Copy in Scientific Library and Div. 69 174-1107.)

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