US1729691A - Insulator - Google Patents

Description

Patented Oct. 1, .1929

UNITED STATES PATENT OFFICE HAROLD B. SMITH, OF WORCESTER, MASSACHUSETTS, ASSIGNOR TO WESTINGHCUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA msuna'ron Application filed May 10, 1922. Serial No. 559,743.

My invention relates to insulators and particularly to insulators for supporting high voltage conductors.

One object of my invention is to provide a high-voltage insulator that shall have a relatively higher wet to dry arc-over voltage ratio than heretofore attained and a wet areover voltage comparable with dry arc-over voltages heretofore customary.

Anotherobject of my invention is to so remove the drippings of precipitated moisture, such as rain or snow, from the arc-over zone in the more intense dielectric field directly between the terminals of an insulator as to largely eliminate the drippings as factors in the determination of the wet arc-over voltage value at which the insulator will break down and to thus increase wet arc-over voltages for given spacing between terminals.

A further object of my invention is to provide a high-voltage insulator that shall be simple and durable in construction, economical to manufacture and effective in its operation.

Whilemy invention is applicable to highvoltage insulators of various forms, it is par ticularly adapted for employment with an insulator of the type set forth in my copending application,'Serial No. 548,818, filed April 1, 1922, and assigned to the Westinghouse Eleotrio and Manufacturing Company, for a more thorough understanding of which reference may be had.

Heretofore. to the best of my knowledge, all outdoor insulators and similar devices have been subjected to flashover at very greatly n.- duced voltage values under wet conditions as compared with dry conditions. This is true, even'whore the upper unit is snaped to constitute a rain shed. l'iecause the drippings from rain or snow in a field of high potential gradieut cause localized concentration of the stresses in the dielectric field starting thewet and dry conditions and to increase the wet arc-over voltages as compared with those heretofore secure In practicing my invention, I provide a weather protective member that is constructed of such material and shapeas to not unduly attract the electrostatic lines of force from a given or controlled path or field between the special metallic or other terminals of'an insulator and that is also of such shape and relation to the insulator as to remove the drip pings a sufficientdistance from the positions of high-potential gradient in the field as to avoid causing an excessively localized concentration of the electrostatic stresses.

In the above mentioned manner, the arc over voltage values are maintained more nearly equal under both wet and dry conditions.

Figure 1 of the accompanying drawing is a side View, partially in elevation and partially in section, of an insulator embed, my invention, and

Fig. 2 is a similar view of a modified form thereof.

Referring to Fig. 1, an insulator for which my invention is adapted may comprise, in general, an elongated insulating member upper and lower terminal members 2 and respectively, and upper and lower electr c static flux distributing members 4 and 5, re spectively.

The insulating member 1, preferably of relatively small diameter, may be a rod or tube of wood, molded fibre or any other suit i able insulating material having ends of sub stantially frusto-conical shape, or otherwise suitably formed. for the reception of metal members 8 that may be attached thereto, as by swaging. The members (3 may be provided with scrcw-threadml studs 7 for attachn'icnt lo the terminal members i and 3.

The upper electrostatic flux-distributingand-directing member-'4, shown in Fig. l of inverted howl-shape, may be provided with a portion 8 of inverted cup-slums, having a central recess for positioning it over the up per stud 7. and be held in position between the member 0 and the terminal member 2. The

member 1 is provided with a rounded lower edge 9 of relatively great radius.

The lower electrostatic stress-distributingand-directing member 5 is formed as an annulus having toroidal surfaces 10 of relatively great radius and a central opening 11 of larger diameter than the insulating member 1. A bracket 12, having a collar 14 secured to the lower member 6 and rounded arms extending between the collar l l and the member 5, is provided to hold the latter in position.

A conductor 15, which the insulator is adapted to support, maybe covered by a conducting sheath or jacket 16 of relatively great length and diameter to avoid the concentration of electrostatic flux on the conductor adjacent to the insulator and be secured to the latter by a clamp 17 As set forth in the above-mentioned c0- pending application, the members 4 and 5 may be variously constructed so long as they are conducting on certain of the surfaces thereof in a manner to direct the electrostatic flux field substantially as indicated by the dotted lines. The field is thus directed to be of shortest distance along a line 18 and to be so gradually decreased toward the center of the insulator as to constitute a substantially hollow tubular field through which the insulating member extends.

As pointed out in my co-pending application, the above-described arrangement prevents the impingement of arcs against the insulating member 1 and so simultaneously definitely directs and widely distributes the flux as to increase the arc-over voltage value of the insulator to a point not hitherto attained in insulators of similar weight and dimensions.

It has been found that, under wet conditions, the accumulation of water drops on the upper unit of an insulator, such as on the edge 9, causes localized concentration of the electrostatic field, with the resultant flashover at values much below the dry arcing voltage value of the insulator.

To correct the above fault, I propose the removal of the dripping portion or edge of an insulator from the arc-over zone in the flux field. This has been accomplished by providing a protective shed or hood 19 over and aroundthe member 4. This has been attempted before but always in such a manner as to permit the water to drip in or near the arcing path and in a field of high potential gradient. The provision of means for placing the terminal under the protective hood avoids this condition.

In this instance, the hood 19 comprises an inverted bowl of a material which may have higher resistance than the member a and is shaped and related to the flux field to have, over a ortion of its surface, all points substantial 1 coincident or nearly coincident,

with an equipotential surface. Being out of the main electrostatic flux path and having less attraction for the electrostatic lines, the

water drops, at the lower edge of the hood 19, are in a field of lower potential gradient and do not so greatly tend to locally concentrate the field. Thus, when fiashover occurs, it will occur under desirable conditions between the members 4: and 5 irrespective of the weather.

As shown in Fig. 2, in which corresponding parts are designated by corresponding reference characters, the upper electrostatic flux distributing and directing member 4a is similar to the lower member 5.

It will be understood that various modifications as to the size and shape of the members 4 and 5 as well as various combinations of the members may be efl'ected within the spirit and scope of t e invention.

In accordance with my invention, a, sim is compact insulator of more nearly equal e ectiveness under wet and dry conditions is obtained, that also increases the wet flashover voltage values materially above wet flashover voltage values heretofore attained.

While I have shown and described particular forms of my invention, changes may be made therein without departing from the spirit and scope thereof, as set forth in the appended claims.

I claim as my invention:

1. An insulator comprising an elongated insulating member, an uppstr terminal mem her having a. conducting su antially toroidal surface of relatively great area surrounding the insulating member in widely radiallyspaced relation thereto at a position downwardly removed from the upper end thereof, said surface mer ing at its inner portion into a conducting sur ace of inverted substantially bowl shape, said upper terminal member also having a water-dnp portion disposed laterally-outwardly beyond said toroidal surface, and a lower terminal member having a conducting substantially toroidal surface of relatively great area surrounding the insulating member in radially-spaced relation thereto, the space surrounding the insulating member between that member and the lower toroidal a of the upper terminal member.-

2. A high-voltage insulator comprising an elongated insulating member and upper and lower terminal members therefor having substantially toroidal conducting surfaces of relatively great area disposed about the insulating member in laterally spaced relation thereto to widely distribute the electrostatic flux over said surfaces and to prevent the concentration of the electrostatic field at the ends of the insulating member and to direct the electrostatic field to conform to a uniform substantially cylindrical zone having a Weakened longitudinal central portion through Which the insulatin member extends, said upper terminal mem er having a water-dri portion disposed laterally outwardly beyon its toroidal surface, the spaces surrounding the insulating member between the latter and each toroidal surface and for relatively great distances longitudinally beyond the toroidal surfaces away from each other being open to prevent interference with the electrostatic field as directed by said toroidal surfaces with respect to each other.

. In testimony whereof, I have hereunto subscribed my name this 18th day of April 1922.

16 HAROLD B. SMITH.

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