US1997688A - Insulator - Google Patents

Description

April 6,1935. M. H. HUNT ETAL 1,997,688

7 INSULATOR Filed Oct. 6, 1933 WITNESSES: INVENTOR5.

g 6eo/?EM&rr-ow an a Mar-aa e b. f/unfj RNEY Patented Apr. 16, 1935 UNITED STATES PATENT OFFICE INSULATOR Application October 6, 1933, Serial No. 692,446

10 Claims.

Our invention relates to electrical insulators and particularly to means for reducing electrostatic discharges thereon.

The present application isa continuation in part of our copending application, Serial No.

548,588, filed July 3, 1931.

An object of our invention is to prevent radio interference and to overcome other objectionable results normally caused by electrostatic discharges between the electrodes, or terminals, and the dielectric bodies of insulators.

Another object of our invention is tofacilitate the coating of dielectric bodies with conducting and semi-conducting materials, such as metals and the oxides thereof.

Another object of our invention is to provide an insulator that shall be simple and durable in construction, economical to manufacture and effective in its operation.

In high-voltage transmission-line practice, electrostatic discharges occur between the metal and the dielectric parts of insulators, as between the metal cap or pin and the porcelain body of an insulator of one type, and between the tiewire or cable and the dielectric body of an insulator of another type. These discharges cause interference with radio reception.

To overcome this objection, various means have been suggested to modify the surface resistance of the insulators, usually by providing a conducting coating thereon, but porcelain, the most extensively useddielectric material, renders the provision of a simple, economical and permanent metal or conducting coating very difllcult. It has also been suggested the porcelain be coated with metallic glaze, an electrolytically-deposited film, a solder coat, a sprayed coat over a smooth or roughened surface, carbon particles rubbed into the porcelain, and various other expedients.

While each of the prior suggestions may be made to operate more or less successfully, the questions of cost and durability have not been solved in a satisfactory manner.

Our objective is the provision of a permanent and effective coating for a porcelain insulator that shall be reduced to substantially the minimum of cost and manufacturing difilculty or, in effect, become almost as simple in application as the usual silicate glaze and which shall be substantially as permanent as the silicate glaze coat and of substantial strength. In this aspect, it is notonly as good for preventing radio interference as any suggestion of which we are aware,

' in a uniform layer and be self-supporting, while but it more nearly approaches metallic glaze in tensile strength or adherence to the porcelain than any other coating of which we are aware.

Figure 1, of the accompanying drawing, is a view, in elevation, of the top unit of a multi-part 5 insulator of the pin type, showing diagrammatically how the unit may be spray-coated before firing,

Figs. 2 and 3 are similar views of the unit at successive stages of production, and

Fig. 4 is a view, partly in section, of a complete insulator embodying our invention.

Referring to Fig. 1, the insulator, which is a preferred embodiment of the invention but illustrative of only one of several embodiments, comprises a body portion 2, a petticoat or'surfacecreepage flange 4, a head portion including a tie-wire groove 6, a bead or flange 8 and a portion I0 through which extends a cable-receiving groove or channel at right angles to the structure, as viewed in the drawing.

As illustrated in Fig. 1, the insulator is in a state just previous to firing and, being of porcelain, is of a subst ntially light bufi or cream color before being oated, as by dipping or by the use of a spray gun I2. In the condition indicated, the insulator is of a relatively hard, chalky consistency having a smooth surface. Being a solid of revolution, a preferred method of coating it is to rotate the insulator, while operating the spray gun, to ensure an evenly distributed coat.

A preferred spraying material, indicated as having been partially deposited on the insulator of Fig. 1 at the top thereof, is of a light-slate gray color and comprises water, copper oxide and a quantity of inert filler material, such as calcined zinc oxide, red oxide of iron, china. clay, and the like. i

The fluid composition may comprise one or more of the inert materials, in proportions of from ten to eighty per cent of the solids. The inert materials are provided to give body or viscosity to the resulting mixture, so that it will be deposited 45 drying, and not run, by gravity, to form overlaps, waves or beads.

A preferred coating liquid comprises, as its solid constituents, forty to fifty per cent copper oxide and sixty to fifty per cent zinc oxide, with enough water to allow the liquid to wet the porcelain and be firmly attached thereto.

Fig. 2 shows the still unfired insulator, with the parts 4, 6, 8 and I!) covered with the slategray coating material and the part 2 of its natural 55 kiln firing is not exactly known but, in any event,

the resultant structure is a usual porcelain insulator, with an oxide coating on it which, when reduced to metal, requires several thousand pounds tension per square inch to dislodge it.

Particles of the porcelain, the copper oxide and the inert filler become thoroughly mixed and vitrified together in a homogeneous solid mass to a substantial depth in the insulator surface, with particles of the oxide constituting an outer stratum of substantial thickness and so homogeneously united as to provide a continuous, fluidimpervious film.

After firing, the black copper oxide coating may be developed,'or reduced, by means of a suitable oxidizing agent, to a metallic copper coating, or the reduction may be restricted to a desired area of the oxide glaze. One method of accomplishing such reduction is to place the insulator in an acid bath including nascent hydrogen caused by the addition of powdered zinc; the

' operation being facilitated by rotating the insulator and rubbing the surface, as by a brush.

During this operation, which is exceedingly simple, the bright copper layer appears quickly and the insulator is finished.

Ordinarily, where the shed is covered entirely withsilicate glaze,electrostatic discharges occurin the intense electrostatic field between the tiewire or cable and the insulator surface to cause radio interference. This, discharge is reduced or eliminated entirely by the metal coat in accordance with its texture, shape and thickness, depending upon the voltage employed; it being feasible to grade and alter the coat in various ways; as by cutting out regular areas of it, by electroplating it, by soldering to it, by oxidizing it, by exposing it to the weather and by other means.

One method of grading the resistance of the coating is to only partially develop the metal from the oxide. This effect can be produced by applying a paste comprising powdered zinc andstrong sodium hydroxide. After remaining on the insulator a certain'length of time, the paste may be washed off; the copper being developed only where the surface was coated, or only partially developed, depending upon the strength of the paste and the length of time it is allowed to remain on the oxide.

Referring to Fig. 4, the insulator shown is of the multi-shed type, for supporting electrical apparatus, such as switchgear, comprising nested porcelain elements 24 and 20, each having laterally extended creepage surfaces. The upper ele- ,ment 24 is provided with a head portion for receiving a metallic cap 21 which is provided with suitable means, such as threaded sockets 22, for cooperating with the apparatus to be supported. The lower element 28 is provided with a recess having disposed therein a metallic threaded thimble 29 for receiving a correspondingly threaded head of a supporting pin.

The upper surface of the element 24 is initially entirely covered by the copper oxide glaze material and the under surface is covered with a silicate glaze material. The unit is then fired to vitrify the glaze materials, resulting in a copper oxide glaze 30 and a usual silicate glaze 32; the two glazes meeting at a line 34. A selected portion 35 of the oxide glaze, asdefined by the lines 36 and' 38 is then covered with a reduclnfl paste, as above described, to completely or partially reduce the oxide, as desired; Similarly the lower element 26 is fired and subjected to a reducing reaction producing asilicate glaze 40, an oxide glaze 42, and a chemically reduced oxide glaze 44; the latter extending up into the pin hole. The two elements are then cemented together, preferably with a body 46 of resilient material therebetween, and the reduced oxide glaze portions 35 and are covered or tinned by a layer of solder," or similar material, to prevent reoxidation and abrasion thereof.

The cap 21 and. thimble 29 are then cemented in position with.=the peripheral edges thereof in electrical contact with the tinned surface of the reduced glaze areas 35 and ,respectively, although in some cases it is suificient-if the reduced glaze is in contact with the cement-between the metallic fitting on the heat and pinhole portions. Electrostatic discharge between these metallic fittings and the porcelain is thereby prevented. The thimble 29 may, in accordance with usual practice, be a separate preformed sheet metal punching, or it may be die-castin position in the pin hole.

In developing the surfaces 35 and 44, the reduction may be quite accurately controlled, as to the area covered, but a minute semi-reduced edge or stratum will occur between the reduced conducting surface -and the adjacent resistive oxideglaze surface. Such semi-reduced edge, or stratum is desirable however, in that it effectively damps any discharge between the two surfaces.

With the construction describedit should be apparent that the electrical resistance of the insulator coated may be graded between terminals as desired. The-highly reduced oxide glaze adjacent the high-tension terminal will be metallic, or substantially so, the minute semi-reduced stratum between the metallic area and the oxide glaze area will be of greater resistance, and the resistance of the oxide glaze and silicate glaze areas are successively greater.

Quite obviously, the same treatment may be given to an insulator of the suspension type, or various other types of insulators wherein the effect of corona discharge is undesirable.

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

We claim as our mvention:

1. In an insulator comprising a porcelain body portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of said flange, a coating for the insulator comprising a fired silicate glaze covering a substantial area of the insulator and a chemically reduced metallic-oxide glaze covering an area adjacent to the silicate glaze, said glaze coatings meeting in edge-to-edge relation with a stratum of partially reduced oxide glaze therebetweenz. I

2. In an insulator comprising a porcelain body portion having laterally extending creepage flange. and: upper i and lower terminal portions on opposite sides of said flange, a graded electrical resistance coating for the insulator comprising an area surrounding the upper terminal portion covered by a .vitrified metallic-oxide glaze a portion of the area of which adjacent the terminal has been chemically reduced, and a silicate glaze coating beyond the area covered by i said metalic-oxide glaze, said glazed coatings meeting in intimate abutting relation.

3. In an insulator comprising a porcelain bod portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of said flange, a graded portions on opposite sides of said flange, a graded electrical resistance coating for the insulator comprising an area surrounding said terminal portions covered by a fired metallic oxide glaze a portion of the area ofwhich adjacent the terminals has beende-oxidized and metallic fittings cemented to said terminal portions, and a fired silicate glaze covering the remaining portion of .the insulator; said silicate glaze, oxide glaze and chemically de-oxidized area of the latter constituting a smooth continuous coating of substantially constant thickness.

5. In an insulator comprising a porcelain body portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of said flange, a graded .electrical resistance coating for the insulator comprising an area surrounding said terminal portions covered by a 'fired metallic oxide glaze a portion of the area of which adjacent the terminals has been de-oxidized and metallic fittings cemented to said terminal portions, and a fired silicate glaze covering the remaining portion of the insulator; said silicate glaze, oxide glaze and chemically de-oxidized area of thelatter constituting a smooth continuous coating of substantially constant thickness, and a protective coating of conducting material covering said chemically reduced area.

6. In an insulator, a protective coating therefor comprising a vitrified glaze consisting of from 40% to 50% copper oxide and from 50% to 40% zinc oxide, and an adjacent portion compris-v ing said vitrified glaze which has been chemically reduced to a predetermined amount.

7. In an insulator comprising a vitreous body portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of the flange, a coating for the insulator, comprising a metallic layer adjacent to and surrounding the upper terminal portion, an adjacent vitrified metallic-oxide layer covering a circumferential area beyond said metallic layer and a vitrified silicate-glaze area beyond said metallic-oxide layer, said metallic, metallic-oxide and silicate glaze areas being substantially in edge-to-edge relation to constitute a graded electrical resistance coating between said terminal portions.

8. In an insulator comprising a porcelain body portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of said flange, a coating for the insulator comprising a fired silicate glaze covering a substantial area of the insulator and a metallic-oxide glaze covering an area adjacent to the silicate glaze, said glaze coatings meeting in edge-to-edge relation, and a metallic coating adjacent to and surrounding said upper terminal portion and in substantially edge-toedge relation with said metallic-oxide coating.

9. In an insulator comprising a body portion having an annular laterally extending creepage flange and upper and lower terminal portions on opposite sides of said flange, a coating for the insulator comprising a fired silicate glazecovering a substantial-area of the insulator and a metallic-oxide glaze covering an area adjacent to the silicate glaze, said glaze coatings meeting in edge-to-edge relation, and a metallic coating adjacent to and surrounding one of said terminal portions and in substantially edge-to-edge relation with said metallic-oxide glaze.

10. In an insulator comprising a body of vitreous material having an annular laterally extending creepage flange and upper and lower terminal portions on oppositesides of said flange, a coating for the insulator including a vitrified metallic-oxide glaze covering a substantial area of the insulator and a metallic coating adjacent to and surrounding one of said terminal portions and in substantially edge-to-edge relation with said metallic-oxide coating.

MARSDEN H. HUNT. GEORGEM. BARROW.

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