US1978122A - Grounding terminal - Google Patents

Description

A. E. ANDERSON GROUNDING TERMINAL Filed July 9, 1951 Oct. 23, 1934.

Patented Oct. 23, 1934 UNITED STATES PATENT OFFICE 7 Claims.

l frequently used around the individual component cables making up the usual formof high tension cable, in such 'a manner as to minimize the formation of corona discharge and the accompanying deterioration in the rubber insulation at the ends l of the cable.

With this object in view and such others as may hereinafter appear, the invention consists in the grounding terminal' for the conducting Asheathing or wire mesh of high tension cables and in the l various structures, arrangements and combinations of parts hereinafter described and particularly defined in the claims at the end of this specication.

In the drawing illustrating the preferred embodiment of the invention,

Fig. 1 is a front elevation of the grounding terminal; Fig. 2 is a longitudinal section taken on the line 2-2ofFlg.l;and so Fig. 3 is a sectional view taken on the line 3 31 of Fig. 2.

-Experience has shown that insulated cable, and particularly the rubber insulated cable employed as high tension cable tends to deteriorate rapidly adjacent the ends of the cable at which connection is made to a connector. 'I'he deterioration and-disintegration of the rubber insulation, as is well known, is due to the action of corona discharge'in the air space adjacentthe rubber. The corona discharge in the air space adjacent to tie rubber produces two simultaneous effects. The air is changed to ozone '(03) and oxides of nitrogen all of which are very active chemical compounds. They attack and disintegrate all but the most stable of organic materials, as is well known. Rubber is very susceptible to their chemical action, particularly that of the ozone. Under the high-voltage stress the molecules of air are dissociated into positive charges and negative charges (electrons). Under the influence of the electric field the positive charges move at high velocity 4toward the electrode which at the instant happens to be negative: the negative charges likewise move toward the electrode4 which at the instant happens to be positive. When one electrode is negative the positive charges move toward it at high velocity but are 'stopped by colliding with the surface of the rubber. The surface of the rubber is thus literally subjected to a terric bombardment of heavy positive ions which not only perforate the 6o surface but develop heat as well. Now the chemically active molecules of ozone and oxides of nitro# gen are driven into the rubber and come into intimate contact with the molecules of the rubber. This accelerates the chemical destruction of the a5 rubber and the effect is cumulative, for the cracks which develop in the surface make the rubber even more susceptible to further bombardment and further chemical action results.

'I'his same action has occurred with portable 70 rubber cables laid upon the ground, particularly between the portion of the outside surface that is nearest the ground. 1f no grounded mesh is present between the conductors of the cable and the ground there is an electrical potential between the conductors and the ground. The

-conductors and the ground form a composite condenser with the rubber and the air in series.

vCorona discharge forms between the cable and the ground attacking the outside surface of the so rubber sheathing.

In accordance with the present invention th formation of corona discharge is eliminated by the grounding of the conducting sheathing around the insulation of the individual conductors. In practice during manufacture, the individual cables of a high tension cable are frequently provided with wire mesh wound tightly about the individual cables, and thereafter the outside belt of rubber is squeezed tightly about 9. the wire mesh so that the rubber is forced in between the meshes so that intimate contact is made everywhere`l with the rubber, thus eliminating practically alli-the air. However, when the outside protective belt of rubber was cut back and the sheathing removed from the ends of the individual cables to expose the conductors for making a splice or other connection, such as connection to a high tension connector, the wire mesh about the individual conductors l tended to become loose. This has permitted a layer of air to be formed between the meshand the surfaces of the individual cables, and as high potential exists between the conductors of this mesh, corona would form in this space and m. attack the rubber. The present grounding terminal eliminates the formation of such corona discharge. It isfurthermore well-known that corona forms most readily at sharp edges and points, and accordingly the corona discharge l fio would be most intense at the edge or end of the.

preferred construction herein shown as comprising the metal conductor 20 surrounded' by the usual rubber insulation 22 protected by a copper wire mesh 24, and all of the cables 12,' 14, 16 are encased within an outer protective insulated casing 25, exactly as in the` construction of commercial forms of such cables designed for use in connection with three phase high tension current. In order to connect the individual metal cables '20 to the plugs of a high voltage' connector, such as a high voltage connector of the plug and socket type, the outer casing 25 inserted into the heads 26 of the plugs 28 of a highvoltage connector and soldered thereto.

In accordancewith the present invention, the

.deterioration, which has heretofore accompanied the connection ofthe ends of a high tension cable of the character described to a high voltage connector by reason of the decomposition of the rubber insulation under the influence of the corona Vdischarge which has been formed adjacent the surface of the rubber or insulation, is prevented or eliminated by a ground terminal having provision for connection to the wire mesh of each individual or ycomponent cable, and which also has provision for connection to the ground.` When the ends f the individual cables forming the high tensio cable are fanned out or spread apart preparatory to connection to a high tension connector, a tendency exists for the wire mesh to become loosened and for air pockets between it. and the insulation to be formed. The present grounding terminal is preferably designed to squeeze the mesh into flrm contact with the rubber and to eliminate such air pockets and the accompanying corona discharge. Previously it has been the practice to carry the ends of the cables out through end bells filled with insulating compound to thereby eliminate air. For portable connectors it is impracticable to use end bells and the present grounding connection finds particular use in connection with portable high tension connectors.

In the preferred embodiment of the invention the present grounding terminal comprises a copper plate provided with a plurality of openings or holes 42 therein through which the individual cables making up the high tensioncable may be extended after the outer protective layer 25 of' rubber .has been cut away as described; The holes 42 are preferably spacedv apart and arranged with respect to one another so as to space the cables from one another in a manner such as to facilitate the introduction of the ends of the cables into the high voltage connector at the proper place. The ground terminal 40 is preferably provided with split sleeves 44 formed in,-

tegrally therewith to be capable of being tightly pressed against the Wire mesh 24 upon the individual cables and is preferably soldered thereto so as to make an eiiicient electrical connectionl v therewith. In soldering the sleeves to .the wire mesh, care should be taken, however, not to overheat the rubber or to disturb the close-fitting relation of the wire mesh 24 upon the rubber of the individual cables, and particularly care should be taken that the wire mesh adheres to the rubber of theca'ble in such close-fitting relation as to preclude the existence of an air .pocket or space under the wire mesh and betweenit and the rubber. The terminal ground is also preferably providedl with ahollow boss into which one end of a flexible copper grounding lead 52 may be soldered, and the boss is preferably cast centrally on the front side of the plate in a position such as is illustrated, to permit the grounding lead 52 to be extended into and soldered to the plug 54 of the ground connection of the high tension connector. As herein shown the copper terminal plate is :preferably shaped -to form a cen- 'trai portion 'I0 and peripheral portions 72 angularly inclined with respect to the central portion 70 and` in which .the cable holes are formed, so that in use the individual cables may be properly spaced for connection to the ihigh voltage connector. I

In addition to its utility in connection with high tension cables constructed with wire sheathing or mesh around the individual cables, the present grounding terminal is also useful in connection with the prevention of corona discharge with lead ooveredcables in which no wire mesh is utilized. In such an instance I prefer to Wind metal sheathing, such as tinfoil, iirmly or tightly against the individual cables, and the present grounding terminal may be used to ground such metal sheathing vIn addition to its utility in connection with grounding the individual wire meshes of yeach cable, the present grounding terminal, it will be observed, enables the circuit of the ground -wie meshes to vbe made continuous throughout the several lengths of the portable cable system in that the circuitmay be completed through each high .tension connector to the wire meshes of the next length of cable, and the center contact or lead 52 is in the illustrated grounding terminal 125 connected to the ground connection of the high tension connector, as above described. The present grounding terminal is simple in construction, may be manufactured at a minimum expense, and by its use a ground connection may be made in such manner as to minimize the formation of air pockets between the wire mesh and Ithe rubber or insulation of any of the cables and as a result the deterioration of the f insulation by the effects of corona discharge may beeliminated, thus prolonging the life of th cable and increasing the utility thereof. j

In the event-that ashort circuit should occur between conductors of opposite polarity within the cable for any reason, as for example because 140 of the breakingl down of the insulation, the use of the present grounding terminal offers a maxi.- mum protection to the operator by providing a positive and ready ground for the short circuit.

Whilel the preferred embodiment of the invention has been herein illustrated and described, it will be understood that the invention may be embodied-'in other forms within the scope of the 4 following claims. m 150 Having thus described the invention what is claimed is:-

1. The combination with a cable having a plurality of insulated component conductors provided with conducting coverings under tension and in intimate contact with the insulation on said conductors to avoid air gaps between the conductive coverings and said insul-ation, of a terminal member having openings through which the individual conductors are extended to space them apart and provided with gripping means to engage the conducting coverings on one side of grounding terminal comprising a metal rplate provided with openings through which the component conductors are extended and provided with sleeves surrounding and gripping the conductive coverings of said component conductors to hold them on one side of said member under tension and in intimate contact with the insulation of said conductors, said plate being provided with a grounding lead for a ground connection.

3. A ground terminal comprising a terminal member provided with a plurality of openings through which are extended the individual conductors of a high tension cable having on the insulation of saidrconductors conducting sleeves capable of being placed under tension to `eiect intimate contact with said insulation, mechanical gripping means projecting from said terminal memberin line with the openings therein for gripping the conducting sleeves and holding the latter on one side of the terminal member under tension, said terminal member having means for making a ground connection for the said gripping members and the conducting sleeves held under tensionthereby.

4. A ground terminal comprising a terminal plate provided with a plurality of openings for the passage through them of a plurality of insulated conductors. having sleeves of wire mesh under tension and in intimate contact with the insulation on said conductors, clamping sleeves projecting from said plate for surrounding and gripping the sleeves of Wire mesh and holding them under tension and in intimate contact with the insulation on said conductors, and a grounding lead secured to the terminal plate for making the ground connection.

5. 'Ihe combination with a cable vhaving a plurality of insulated component conductors provided with sleeves of wire mesh under tension and in intimate contact with the insulation on said conductors to avoid air gaps between the said sleeves and said insulation, of a member cooperating with the individual conductors are provided with means to space them apart and having means for gripping the sleeves of wire mesh to hold them under tension and in intimate contact with the insulation of said conductors, and to connect said sleeves electrically, and means for grounding said sleeves.

6. The combination with a. cable having a plurality of insulated component conductors provided with conducting coverings under tension and in intimate contact with the insulation on said conductors to avoid air gaps between the con- 105 ductive coverings and said insulation, of a grounding terminal comprising a metal plate mounted upon said component conductors and provided with split sleeves mechanically gripping the conductive coverings and soldered thereto.

7. A ground terminal comprising a terminal plate provided with a plurality of openings for the passage through them of a plurality of insulated conductors having sleeves of wire mesh under tension and in intimate contact with the insula- 115 tion on said conductors, clamping sleeves having ilngers projecting from said plate in relatively close proximity to one another for gripping the sleeves of wire mesh, and a hollow boss projecting from said plate for connection with a ground- 120 ing lead.

.ALF E. ANDERSON.

CERTIFICATE or CORRECTION.

Patent No. l', 978,122. v

October 23, 1934.

ALF E. ANDERSON.

It is hereby certified that error-.appears in the printed specification of the above numbered patent requiring correction as follows: Page 3, line 94, claim 5, for "are" read and; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the lfatent Office.

Signed and sealed this 8th day of January, A. D. 1935 (ser) `Lesl ie Frazer Act ing Conmissioncr of. Patente.l

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