Disc-Type Insulator With a Cast-in Electrode and Process for Its Manufacture

The invention relates to a disc-type insulator with a cast-in electrode, which is designed to be used in enclosed high-voltage equipment. The cast-in electrode, which is convex-cambered towards the disc axis, extends along at least a portion of the periphery of the disc-type insulator, and is connected to contact electrodes which are located on the surface of the disc-type insulator, the connection being capable of conducting electricity.

Disc-type insulators are employed to retain a conductor, or a plurality of conductors, in the gas-filled interior of the enclosure, and, customarily, also for hermetically sealing of various portions of the enclosure. The cast-in electrode, which is connected to the enclosure via the contact electrodes in a manner such that electricity can be conducted, functions to prevent the occurrence of intense electrical fields at the anchorage point of the disc-type insulator in the enclosure. Corona discharges, which are otherwise impossible to prevent at a reasonable cost, which occur because of the unavoidable contact between conducting material and non-conducting materials possessing different dielectric constants (enclosure, disc-type insulator, insulating gas) are avoided by smoothing out the electric fields.

A disc-type insulator is described in U.S. Pat. No. 3,652,778. This disc-type insulator possesses a cast-in electrode which is designed as a continuous ring and which is connected to contact electrodes, by means of straight contact tongues, in a manner such that the connection conducts electricity. These contact electrodes serve at the same time as cast-in sleeves which carry threads.

In the case of a disc-type insulator, particularly one having a comparatively large diameter, it has been found that cast-in electrodes of the abovementioned design can easily be damaged and, in particular, distorted as a result of the shrinkage which occurs during the curing of the the disc-type insulating material after it has been cast, or as a result of thermal stressing during operation. Moreover, the contact tongues can be torn away, which can lead to the cast-in electrode becoming functionally unserviceable and, in consequence, to corona discharges and even to insulation breakdowns, or the insulator can break away from the cast-in electrode over a portion of the periphery.

It is an object of the invention to remedy the abovementioned disadvantages. As characterised in the claims, the invention achieves the object of providing a disc-type insulator with a cast-in electrode, in which the electrode and, likewise, the contact tongues exhibit so much flexibility, particularly in the radial direction, that they adjust themselves to the changes in the dimensions of the disc-type insulator during shrinkage. The electrode maintains its flexibility when under thermal stresses during operation, to an extent such that both the stresses at the interfaces between the insulator material and the electrode, and the pull acting on the contact tongues remain safely below critical values and thus damage is reliably prevented to any portion of the disc-type insulator. A simple and economical process for the manufacture of a disc-type insulator according to the invention is additionally specified.

The advantages of the invention reside, above all, in the fact that the occurrence of dangerous mechanical stresses in the disc-type insulator is prevented and, with this, the danger of the disc-type insulator being damaged as a result of stresses of this nature is effectively countered. This is achieved, in part, by dividing the electrodes into a plurality of segments.

However, the division of the cast-in electrode into a plurality of electrode segments also entails the advantage that the latter are easier to install, being, in particular, less sensitive to assembly tolerances, are cheaper to manufacture, and require less room during transportation and storage. They also render it possible to attach a cast-in electrode only over portions of the periphery, as in the case of, for example, enclosed 3-phase installations.

Moreover, the division of the cast-in electrode into segments enables the disc-type insulator to be manufactured by means of a simple process, irrespective of the casting process which is employed. In particular, the electrode segments can be fixed inside the casting mould before the casting operation by fastening them to the casting mould by means of the contact electrodes which are connected to them. Because the electrode segments and the contact tongues are flexible, it is also possible to carry out the operation of curing the disc-type insulator without first having to release this fastening.

Below the invention is explained in more detail by reference to drawings which illustrate merely one possible embodiment, and in which:

FIG. 1 shows a plan view of a disc-type insulator according to the invention, possessing a metal mounting ring, the cast-in electrode being exposed over a portion of the periphery,

FIG. 2 shows an enlarged view of a section along line II--II in FIG. 1, portions of the enclosure which adjoin the disc-type insulator being also indicated,

FIG. 3 shows a joint between two electrode segments, by depicting a section through the mid-plane of the mounting ring and of the cast-in electrode, and

FIG. 4 shows a section through a joint of the type shown in FIG. 3, along the line IV--IV.

The figures illustrate a disc-type insulator 2 which is surrounded by a metal mounting ring 1. This disc-type insulator 2 is configured basically as a disc-shaped or conical body, made, for example, of epoxy resin containing an inorganic filler. The body contains a convex-cambered cast-in electrode 3 which is connected to contact electrodes 4a, 4b, via contact tongues 5a, 5b, in a manner such that the connection conducts electricity. The contact electrodes 4a, 4b bear against the mounting ring 1. In the center, the disc-type insulator 2 contains a metal inner fitting 6, which can be surrounded by a second cast-in electrode (not shown). In addition, the disc-type insulator 2 possesses, on each side, a peripheral groove 7a, 7b for a sealing ring 8a, 8b, which is located, on each side, between the disc-type insulator 1 and an adjoining portion 9a, 9b of the enclosure when the disc-type insulator is in the installed condition (FIG. 2).

According to the invention, the cast-in electrode 3 is subdivided into a plurality of electrode segments 10. The contact tongues 5a, 5b, which connect them to the contact electrodes 4a, 4b, are bent, preferably into an "S" shape. In a manner which is particularly advantageous with regard to mechanical strength and simplicity of manufacture, each electrode segment 10 possesses a contact tongue 5a, 5b at each end, which is formed by prolongations (lengthening) of the electrode segment 10, which are bent over towards the edge surface 11 of the disc-type insulator 2. The contact electrodes 4a, 4b bear against the edge surface 11 of the disc-type insulator 2 and, in turn, are formed by prolongations of the contact tongues 5a, 5b. Contact electrodes 4b, 4a which are connected to the oppsitely-located ends of electrode segments 10 which follow one another in the peripheral direction are, in each case, superimposed and are jointly fastened to the mounting ring, for instance by means of a screw 12. This means of fastening very secure and, at the same time, can be effected with only a small expenditure of labor. In order to increase the flexibility of the electrode, the contact tongues 5a, 5b can also, if required, be designed to be narrower than the electrode segments 10. The most suitable material for the electrode segments 10, the contact tongues 5a, 5b, and the contact electrodes 4a, 4b is sheet aluminum, which can be provided with perforations in order to save material and weight, and also to increase its flexibility. A better bond between the electrode segments 10 and the insulating material which surrounds them is also obtained.

During the manufacture of the disc-type insulator according to the invention, the electrode segments 10 can be fixed inside the casting mould in simple manner, prior to the casting operation, by fastening them to the casting mould by means of contact electrodes 4a, 4b to which they are connected. The high flexibility of the electrode segments 10, and of the contact tongues 5a, 5b, which enables the disc-type insulator 2 to cure without this fastening being released, enables a disc-type insulator according to the invention to be manufactured in the above manner, with a mounting ring 1, even when the ring forms a portion of the casting mould and the contact electrodes 4a, 4b are fastened to it in the manner described above.

It is possible to manufacture each electrode segment together with the contact tongues and contact electrodes connected thereto, in a simple and inexpensive manner, by bending a single continuous metal part.