US1895396A - Joint for high tension electric cables - Google Patents

Description

Jan. 24, 1933. w, PFANNKUCH 1,895,396

JOINT FOR HIGH TENSION ELECTRIC CABLES Filed Oct. 14. 1929 k \\\\\\\l\ \\Y\\ Inventor": Wilhelm Pfannkuch,

His Attorney Patented Jan. 24, 1933 UNITED STATES PATENT OFFICE WILHE'LM PFAN'NKUCH, OICOPENICK-WENDENSCHLOSS, GERMANY, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK JOINT B H IGH TENSION ELECTRIC CABLES Application fled October 14,1929, Serial No. 399,485, and in Germany March 15, 1929.

ends of adjacent-lengths to receive a connec tor or sleeve which-1s soldered or otherwise secured to said ends. Insulation is removed from the conductor ends either by what is known as penciling or steplby step, the net elfect being to taper the insulation with a long taper from the connector to the full diameter of the insulation. Subsequently, the connector and the tapered ends of the insulation are wrapped with strips of paper or equivalent material to a diameter substantially larger than that of the factory wound insulation.

The penciling method is not very favorable because of the difficulty in winding the insulation properly over the smooth conical surfaces. On the other hand, the step-wise re.- duction has the disadvantage that it is only possible to attain favorable results when the number of steps is relatively great, which again is objectionable because of the lack of simplicity and because of the increased cost. Furthermore, if the number of steps is restricted and each step of necessity made cor respondingly great, intermediate spaces, gaps or voids "are formed or occur at the shoulders of thesteps and which extend radially. If

these voids are not perfectly filled with ini pregnating fluid when the joint is being made,

they later give rise to intense ionization when the cable is in operation, which leads to a rapiddestruction of the joint as a whole.

My invention has for its object to overcome the objections above noted, and to provide in high tension electrical apparatus having I bodies of separately applied insulation means for preventing glowing and arcing at the joints between the bodies. More specifically,

my invention has for its object the provision in a cable joint of the step type of means for preventing injurious electrical effects at the steps where the factory wound insulation makes a sudden and substantial change of diameter.

For a consideration of what I believe to be novel and my invention, attention is directed to the accompanying description, and the claims appended thereto.

In the drawing which is illustrative of my invention, Fig. 1 'is a longitudinal section. ofto' a high tension cable joint, and Fig. 2 is a slight modification thereof.

3 indicates a stranded conductor which may be hollow or solid as desired. The ends of the two adjacent lengths are united by a metal connector 4 of sleeve formation, said parts being soldered or otherwise united to form a good electrical and mechanical union. 5 indicates the insulationon the conductor and is composed of rather narrowstrips or ribbons of paper wound layer by layer thereon with overlapping joints. This is done by any suitable machine. The paper is impregnated with oil or a suitable compound, usuall after the cable is completed. Outside the msulation is an enclosing sheath 6 made of lead or equivalent material to prevent the 'entrance of air and moisture and the escape of the impregnating material.

In order to properly insulate the joint, the factory wound insulation on each cable end is removed in such manner as to form relatively large steps. The invention is not limited to any definite number of steps since this will depend largely upon the potential at which the cable is designed to operate, and upon the thickness of insulation. As a general proposition, however, it may be stated that thenumber of steps is relatively small. With a prior construction, for example, of which I' have knowledge it is customary to provide as many as eighteen steps on each of the adjacent ends of a 132 KV cable, or

.a total of thirty-six. As illustrated, there are'three steps, that is to say, the first from the conductor to part 7, thesecond from art 7 to 8, and the third from part 8 to 9, w ich latter has the full diameter of the cable insulation. At each step a shoulder is formed, and the annular facial surface is, according to my invention, provided with an annular metallic covering 10. Without this covering there would be small gaps between the factory wound insulation and theedges of the tape or second body of insulation which is subsequently applied to the joint. These gaps would extend in the direction of the electric field about the conductor or at a slight angle thereto Stated in another way, there are two bodies of insulation both of which are wrapped around the conductors in concentric layers with the edges of the layersof the second body in abutting relation with those of the first at each step, and interposed between these abutting edges are annular elements which form short circuiting devices. It

is important that these coverings be annular since otherwise there would be a high concentration of stresses at any joint therein. Where the pressure or potential differences between the ste s is for any reason not very eat semi-con ucting material may be used or the coverings instead of metal. These coverings, whether. of one kind or the other, are advantageously made of thin soft material which can readily be formed to the required shape. either prior to or after being mounted in position. The coverings, for the purpose of illustration, have been exa gerated in size and especially in thickness. ach covering is provided with cylindricaTor flanged portions 11 which fit snugly over the 'adacent parts of different diameters and which are united by a ring-like portion 12 that abuts the cut end of the factory wound insulation. These metallic coverings or coatings are independent of each other, in other words, are isolated one from the other, and are not connected to ground and consequently each assumes an intermediate potential due to capacity conditions. Each of these coverings forms a metallic short circuiting device between the part or portion of smaller diameter and the part or portion of larger diameter of the cable. The absolute strength of the insulating layerat each of these points or regions is somewhat decreased by reason of the covering, but this is'compensated for by correspondinglyincreasing the amount of insulation which is applied over the joint. These metal coverings revent all glowi or arcing at the face sur ace of the steps, an

- on that account even if a small void at such step should exist, and which is not filled by the impregnating compound, it will no longer have an appreciable destructive action.

After the steps have been formed in the factory wound insulation and the coverings applied to each step or shoulder, the joint is taped with impregnated paper tape 13 or e uivalent material so as to completely fill all 0? the spaces and assemble about the joint the necessary amount of insulation. This will include what may be termed the normal amount of insulation plus that amount which may be necessary to compensate for the presence of the conducting or semi-conducting coverings 10. Surroundin the joint is a casing or enclosure 14 which is suitably united at its ends to the sheaths 6 of the adjacent cable lengths.

In Fig. 2 is shown a slight modification of the invention, wherein the coverings 10 are applied to the ends only of the steps instead of having cylindrical parts or flanges which embrace the adjacent cylindrical surfaces of the parts of the cable. In effect they form rings which fit over the smaller parts and at their peripheries are flush with the surface of the next larger part. These also may be made of some thin and relatively soft material so as to occupy a small space and snuglyfit the insulation.

The invention is not only advantageous for cable joints of the character hereinbefore referred to, but also for other constructions where it is im ortant to prevent the .disadvantageous in uence of layers or of gaps in the insulating material, which extend in the direction of the electric field about a conductor or at a slight angle to the same within the insulating covering.

Looking at the matter from one point of view, a conductor is provided which carries current of high potential and which is enclosed in a casing of much lower potential, usually that of the earth, and between the two is a body of insulation composed of two parts, one of which is applied initially in the manufacture and is machine wound, and the other applied subsequently and which, no matter how it is applied, is distinctly separate from the first, and to prevent glowing at the edges or the joints between the two insulations a metallic element is interposed,

, What I claim as new and desire to secure by Letters Patent of the United States, is:

1. In a cable joint, the combination of a where their edges are in abutting relation.

2. The combination of a current carrying conductor, a casing therefor and separate bodies of insulation which are wrapped around the conductor in layers, one of said bodies. being cut away to form steps, with conducting elements located at the steps where the edges of the two bodies are adja-,

cent, each of said elements comprising-a portion located "between said edges and other ortions which overlie the insulation at the ottom and top of the step.

3. In a joint for high tension cables, the combination of a pair of conductors, each 5 of which has a body of factory-wound insulation' thereon, the diameter of which is reduced step-by-step toward the ends, a connector for uniting the ends, a short circuiting device located at each step, said devices being 10 electrically independent of each other, a second body of insulation which is wound over the connector, devices and a portion of the factory-wound insulation, and a metallic enclosure for the joint and cable. In witness whereof, I have hereunto set my hand this 30th day of September, 1929.

W'ILHELM PFANNKUCH.

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