US1563946A - High-tension terminal - Google Patents

Description

Dec. 1, 1925- R- w. ATKINSON HIGH TENSION TERMINAL Filed Feb. 19, 1923 2 Sheets-Sheet l FIELI.

IIIIIIIIII-lllllllll'llllllllllll 6 6 if m@ Dec. 1, 19251 R. W ATKINSON HIGHl TENSION TERMINAL 2 Sheets-Sheet 2 1^/ MEN TOR WT/VIESSES- l aM 7 f ff Patented Dec. 1, 1925.

UNITED STATES PATENT OFFICE.

RALPH W. ATKINSON, OF PERTH AMBOY, NEW JERSEY, ASSIGNOR TO STANDARD UNDERGROUND CABLE COMPANY. OF PITTSBURGH, PENNSYLVANIA, A CORPORA- TION 0F PENNSYLVANIA.

'HIGH-TENSION TERMINAL.

Application filed February 19, 1923. Serial No. 619,795.

T0 all whom it may concern.:

Be it known that I, RALPH W. ATKINSON, residing at Perth Amboy, in the county of Middlesex and State of New Jersey, a citizen of the United States, have invented or discovered certain new and useful Improvements in High-Tension Terminals, of which improvements the following is a specification.

My invention relates to improvements in that element in electrical installation known as a terminal,-a structure wherein electrical union is made between the conductor of an electrical cable and an aerial wire or other bare conductor.

The invention is illustrated in the accompanying drawings. Fig. I is a view in vertical section of a terminal structure built for experimentalwork but embodying my invention, and illustrating the invention in somewhat diagrammatic manner. Fig. II is a similar view of the same essential structure, having added to it, certain supplementary structural features of electrical value, as will presently be explained. Figs. III, IV, and V are views in vertical section, illustratin the essential feature of the invention deve o ed in forms and with adaptations for eld service.

The cable incased in its lead sheath is indicated at l; 2 indicates the cable insulation, exposed where the sheath has been cut away; and 3 indicates the cable conductor. 4: is the conductor, between which and the cable conductor electrical union is to be made, as indicated at 5, Fig. I. It is this union, and the proximate parts of the cable and conductor which are enclosed and protected by the -terminal structure.l

Essentially and typically, a terminal structure consists if a casing filled with insulation, surrounding and enclosing the joint. The insulating material contained within the casing and immediately enveloping the joint is ordinarily a heavy liquid, or a substance having the slow fluidity of pitch.

When dealing with high voltages a weak point appears in the typical terminal structure; there is danger of electro-static discharge between ca le conductor and cable sheath, over the surface of the unsheathed expanse of cable insulation, where the cable insulation proper and the body of insulating substance which fills the terminal meet surface to surface. Referring -to Fig. I of the drawings there is danger of break-down between points a, and b longitudinally over the outer surface of insulation 2. The average value of this stress for reasonable terminal dimensions would (if it were uniformly distributed over the interval) ybe within entirely satisfactory limits, but the stress is far from uniform, and there is a very great concentration in intensity at the point Z1. As the voltage is increased on a cable, this concentration of stress results in discharges beginning at b and carried over the surface of the insulation, resulting, at still higher voltages, either in liashover (failure between the points a and b) or inldestruction to the insulation by the discharges and failure by puncture of the insulation between a and b, and near b. My invention is found in a structure in which the concentration of stress is reduced, so that the stress at b is no longer dangerously high. I surround the cable at the point b, that is to say, at the end of the cut-away sheath, with a shield of 'conducting material, coaxially arranged with respect to the cable, encircling the point of maximum stress indicated above, and extending longitudinally of the structure but in its extent receding from the cable structure, in a direction from point b, Fig. I, toward point ai I unite this shield electrically with the sheath of the cable, and preferably I fill the interval between the surface of. the otherwise exposed cable insulation and the inner surface o the shield with such dielectric material as that indicated above. The presence of such a shield so proportioned and arranged accomplishes the end desired; and, when it comes tohigh-tension service, notably increases the 'serviceability of the structure, and contributes to the solution of the roblem of conveyance of current under igh-tension. It becomes possible, for example, to carry electric power at a potential of 110,000 volts, and that as a practical matter, has not hitherto been achieved.

Incidentally, I achieve improvements of the nature and character which presently I shall explain.

I shall describe first my laboratory structure, shown in Fig. I. A succession of coaxially arranged cylinders of rigid insulating material, 6, 7, 8 (the particular number is not essential) surrounds the joint, from beyond point b below to beyond point 5 above. The structure is arranged vertically, as indicated in the drawing.` A lower head 9 closes the lower ends of the cylinders, and constitutes with the cylinders a container for such liquid insulation as has been indicated. This lower head 9 of the casing is structurally united with the cable sheath. Metal cylinders 11, 12, 13, are carried by the cylinders 6, 7, 8. These metal cylinders may take the form of foil wrappings upon the outer surfaces of the cylinders of insulation, but of course the structure in this respect may be varied, within the intelligent operations of anelectrical engineer. These metal cylinders are in electrical connection with the sheath 1 of the cable, and, to this end the head 9 may be formed of metal, if convenient, and united electrically with cable sheath on the one hand, and with the metal cylinders l1, 12, 13 on the other. These metal cylinders 11, 12, 13 extend from below point b upwardly to different lengths; the innermost, 11, is shortest, extending upwardly beyond point b a relatively short distance; the succeeding outer cylinders, 12 and 13, are successively longer, extending each further upward, beyond the preceding inner cylinder. The vertically standing structure finally is filled with suitable insulation, ordinarily liquid, at least liquid when introduced, indicated at C.

To give specific dimensions, the structure is about three feet high; the outermostl cylinder is'11 inches in diameter, and its wall is one eighth of an inch thick; the cylinders 6 and 7 are respectively seven and nine inches in diameter. The walls of the innermost cylinder are shown to be thicker, and are, specifically one quarter of an inch thick. The upper. edges of the meta- l cylinders 11, 12, 13 are aligned with point b, and a surface extending from the circumference in which point Z) lies and subtending the tips` of the sleeves, is a conical surface and extends at an angle of 20"-3()O to the axial line of the cable. I do not intend to limit Inyself to these dimensions; I give them by way of example, merely.

Fig. II shows identically Vthe structure of Fig. I, already described, with this added feature: The upper end of the outermost metallic layer 13 is overlain with an insulating covering, conveniently a wrapping 14 of varnished cloth. This layer of insulation extends for an appreciable distance from the upper end of cylinder 13 downward. Upon this insulating layer is applied another sleeve of conducting material, conveniently a layer 15 of foil, and this layer of foil is in electrical continuity with the otherwise uncovered lower portion of sleeve 13,-that is to say, with the cable sheath 1. The foil layer 15 in turn is covered entirely with an envelope of insulation, conveniently a wrapping 16 of varnished cloth.

Itwill be particularly remarked that the upper edge of cylinder 15 is more remote from the upper end of the structure as a whole, than is the upper edge of the otherwise exposed outermost conducting cylinder 13. There is at the upper edge of cylinder 13 (Fig. I) a concentration ofstress, similar to that which, but for the terminal structure, would occur at b. This concentration of stress is less in amount than that which Ywould occur at b, but still may be of sutiicient. magnitude to require special attention. The enveloping ofthe upper portion of the outermost cylinder 13 with insulation and then the laylng on of the cylinder 15 properly y insulated, connected below with. the sheath but more remote at its upper edgeY from the lead 4, has the effect of 'diminishing this concentration of stress and thus of diminishing the danger of breakdown externally of the terminal. In short, by providing such a structure as cylinder 15, connected and insulated as explained, the

` initial idea of a widening screen, afforded by the successive cylinders 11, 12, 13, may be carried to the extent otherwise most desirable, and then any appreciable danger of discharge over the outer surface of the terminal may be guarded against by the provision of such a structure as the cylinder 15, proportioned, connected and insulated as described.

Turning from the laboratory structure of Figs. I and II, to the service structure of Fig. III, these features only need be noted, in order to gain full understanding: (1) the head 9 of Fig. I and the metal cylinders 11, 12, '13, are here modified, so far as concerns manufacturing operations, and in Fig. III `reappear as a'metallic bell 9 with upstanding ianges 11, 12, adapted to be united to the cable sheath in familiar manner, as indicated at 10, and adapted to receive and carry the'cylinders 6, 7 continued use, the insulating envelope 14 of Fig. II, here reappears as a porcelain cylinder, similarly designated 14. If for outdoor service, this outermost porcelain cylinder 14 may be superficially petticoatcd in 1 well-known manner, to prevent leakage. (3) Referring again to Fig. I, for testing purposes no closure of the structure above is needed, and none is shown. But it is manifest that for continued service the structure should be capped over, and, accordingly it will be understood that with ,the structure of Fig. III, an upper capor head will be provided, covering cylinder 14 above, and united upon the edge of cylinder 14, and

(2) Intended for 1 'cap is indicated at 17.

through this cap or head the aerial lead 4 will be centrally introduced. The penetration of the aerial through this cap will be a tight joint, and similarl the union of the cap upon cylinder 14 will be tight. Since the expanse of cylinder 14 separates this cap from the bell 9, the cap itself may be formed of any desired material, even metal. Such a (4) The c linder 15 of Fig. -II here reappears, modifie in shape; it here consistsof a'sheet-metal Static shield. This shield 15 is a modified arrangement for accomplishing the 'prevention of undesired electrostatic discharge lover lthe surface of the terminal. It will beunderstood, in view of what already has been saidin connection with Fig. II, that this static shield might lack the flaring feature shown and closely overlie the base of cylinder 14 and extend upwardly to greater or less, degree, as found advantageous.

It will be apparent that, electrically considered, these concentric cylinders 11, 12', 13 of metal, of graded length successively from the innermost outward, 'are in their conjoint effect merely a stepped Haring screen, flaring yon the 20-30 surface from edge b already alluded to, Fig. I, and in Fig. IV I indicate a yflaring screen in which the steps which characterize the structure of Figs. I-III have been infinitely multiplied, that is to say the stepped feature hasbeen eliminated,l and in place is the continuously flaring conical screen 9. Otherwise, the structure is essenti-ally that of Figs. I-III, and requiresno further particular description. The extension 15 of Fig. IIIis noty present, and p manifestly it vneed not be. yThe figure is diagrammatic, and particularly so in the mounting of the outer porcelain cylinder 14 Y upon the screen 9.

Fig. V shows the structure of Fig. IV with the feature which distinguishes Fig. II from Fig. I. Already I have explained how the flaring cone-shaped screen 9 of Fig. IV is electrically ,the equivalent of the stepped cylinders 11, 12, 13 of Fig. I. The reversely iared cone-shaped shield 15 of Fig. V, madel of metal and electrically continuous with shield 9 is similarl the electrical equivalent of, and achieves t e described' functions of the cylinder 15 of Fig. II.

With the particular construction of Fig. V in view, it manifestly becomes Ipossible to cause the outermost cylinder which as has been indicated will lordinarily be a weathertight casing of porcelain, to extend at its lower edge beyond the lower edge of the screen 15, and so aii'ord the well-known effect of a petticoat.

Again, it should be remarked in connection with Fig. V also, that it is diagrammatic, particularly in the structure o f shield 15, its union with shield 9, and WithV cylinder 14.

ythe first problem, is the problem of taking careof radialstresses in the insulating comound with which the terminal structure is illed. This compound, as already I have indicated, is ordinarily a massive liquid, or at least a substance capable of being applied in liquid condition. t The structure I have described, including concentrically arranged cylinders of rigid material submerged in the lilling substance, reenforces lthe dielectric properties of the whole, and strengthens the whole, to resist to far greater, and to a practically suflcient degree, all tendency to breakdown and penetrationby electrostatic discharge. The cylinders 6,V 7, 8 are barriers to electrostatic discharge. A third problem is the elimination of the danger of superficial discharge over the outer surface of the terminal. It is overcome and corrected by the provision of the device 15 in its various modications and arrangements sufficiently described.

I claim as my invention: l

1. A terminal structure for an electrical cable including at one end a screen of conducting material surrounding the cable end, electrically Vunited with the cable sheath, and flaring from the sheath longitudinally of the cable and in direction toward the exosed end, a second shield of conducting material electrically united with the cable sheath and arranged peripherally of vthe screen first named and terminating at a point more remote from the exposed end of the conductor than the first screen, and a t casing of insulating material. Y

2. A terminal structure for an electrical cable consisting of av screen of conductin material surrounding the cable end, and electrically united with the cable sheath, and flarin from the sheath longitudinally of the cab e and in direction toward its exposed end, a plurality of cylinders of rigid insulating material of different diameter, concentrically 'surrounding' the cable end and contacting with said screen', and a body of insulation filling the spaces between the said cylinders in the `assembled structure.

3. A terminal structure for an electrical 4cable including a plurality of cylindersqof conducting material, unequal in diameter, coaxially surrounding the cut-away end of the sheath of a cable, all of said cylinders united electrically with the cable sheath but otherwise insulated one from another, and each outer cylinder extendin further toward the bared end of the ca le conductor vthan the nextinner cylinder.

length.

5. A terminal structure for an electrical cable including at one end a screen of conducting material surrounding the cable end, i

electric-ally united with the cable sheath and Haring from the sheath toward the exposed end of the conductor, a second shield also 10 electrically united with the cable sheath surroundin the screen first named and flaring to a wi er periphery, and a casing of insulating material.

In testimony whereof I have hereunto set l5 my hand.,

RALPH W. ATKINSON.

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