US1728522A - Insulator for high-voltage systems - Google Patents

Description

Sapin l?, w29. F. G. BAUM INSULATOR FOR HIGH VOLTAGE SYSTEMS Filed Aug. 19. 1921 y I N VEN TOR.

Patented Sept. 17, 1929- UNITED STATES PATENT7 OFFICE FRANK Gr. BAUM, OF SAN FRANCISCO, CALIFORNIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC AND MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA INSULATOR FOR HIGH-VOLTAGE SYSTEMS Application filed August 19, 1921. Serial No. 493,613.

This invention relates to insulating supports for transmission lines carrying high voltages. These supports now generally consist of a series of porcelain discs Which are fastened together in a string by metallic parts. The cap and pin and the link types are most commonly used. Vhen the type of insulator used for high voltage lines was changed from the pin type to the disc type, it

10 was assumed that the addition of more voltage to the line merely required the addition of more units or discs in order to provide the necessary insulation, but it was found that the result-s were not at all in proportion to the number of units or discs in the string. Upon an investigation of the cause it was found that the voltage tended to pile up on the insulator units or discs adjacent the line Wire instead of being evenly distributed over the entire string. With a great fall in voltage over any insulator unit, particularly those units adjoining the high potential wire, the likelihood of serious damage to an insulator unit from flash-over currents.v

following abnormal increases in voltage,such as those due to lightning or other causes, is very much increased. The insulator units which are commonly formed of glass or porcelain, are refractory and thus easily inured by the heavy currentl following a flashover or puncture by the breaking down of' the dielectric strength of the insulator with the abnormal increase of voltage. .The piling up of the excess voltage on the insulator units adjacent the line wire breaks down the air at the metal fittings where it is highly stressed with the result that the air is broken down serially from one unit to another by transferring the high electric stress from 40 one to another in the string. Tests upon insulator strings haveshown the volrtage distribution among the separate units to be very uneven, the maximum being from ve to ten times the minimum. This causes uneven stress and a Wide variation in the leakage resistance over the surface of the insulators under outdoor conditions. It hasbeen found that with a string having dirty surfaces, the wetting and drying out of the string due to Weather changes causes a variation in the potential distribution of the string, the distribution improving with the increase of moisture. Ttwill therefore be seen that if the voltage stresses could be more uniformly distributed over the units of the insulator string' or column, the length of the string or column could be increased to permit of the use of almost any desired voltage on the Wire, 'or the equivalent or effective length of any string or column could be increased.

Tn the present constructions the capacity currents through the several units determine the distribution of voltage, but the capacity currents from the metal parts to ground and from line to metal parts have thel greatest influence. These currents are extremely small and since they cannot be varied Widely, some other means of controlling the voltage distrif bution is necessary.

An object of the invention is to provide an lnsulator construction in which the distribution of voltage over the separate units will be as nearly uniform as possible and this uniform distribution maintained for all conditions in practice. A further object is to provide an insulator construction which is simple,` durable, efficient and inexpensive, and which can be used without any changes in the .methods of suspension noT commonly used. Further objects and advantages will be apparent from the following description of embodiments of the invention and the novel features of the invention will be particularly pointed out in claims.

In the practical application of the invention T propose to provide on the insulator surfacea definite high resistance conducting or current leakage path between the metal parts of each unit, with the leakage current through this path large enough to control the voltage distribution over the insulator string under all conditions. That is, the leakage current over the combined resistance of a series of units would uniformly distribute the fall of potential over the string and while it would be larger than the capacity currents over the string the total amount of power lost in this manner` would be little .more than that lost in present construction-s. For further details of the manner of application of the invention to practice, reference may be had to the accompanying desc-ription of two embodiments of the invention.

In the accompanying drawing:

l Fig. 1 is a plan of an insulator unit which is constructed in -accordance with the in vention.

Fig. 2-- is a section of the same taken substantially along theline 2 2 of Fig. 1.

Fig. 3 is a plan of a slightly modified embodiment of an insulator unit.

Fig. 4 is a side elevation of a plurality of insulators, 'such as that Shown in Fig. 3, in the relation thereof to a transmission line and a supporting tower.

In the embodiment illustratedin Figs. 1 and 2 an insulator disc of the cap and pin type has a body portion 1 of suitable insulating material, such as glass or porcelain. The cap 2 which is secured in a well known manner, such as by cement, to a boss 3 upon the under face to the central portion of the disc where it contacts with the metal connecting pin, the convolutions upon the under face being preferably directly beneath the convolutions in the upper face. This groove is filled with a suitable resistance material 7, such as carborundum, graphite or the like, and is held against displacement from the groove in anysuitable manner, such as by a protective coating 8 applied to the surface of Y the unit.

In Fig. 3 a slightly diferent arrangement of the resistance path is provided, the groove 6a extending from the central portion in contact with the metallic cap, radially and outwardly to the periphery, then over the peripheral edge .and inwardly across the under face to the central portion where it contacts with the connecting pin. The groove may also obviously have other shapes andv paths dependent upon individual conditions and selections.

Vhen the insulator body 1 is of porcelain it may be made up into the desired shape and size and dipped in glaze in the usual manner. but before firing, a band or groove is cut out of the glaze, or out ofthe glaze and porcelain, having the desired path, after which the unit would be fired. After this firing the grooves are filled with the resistance material 7, such as the carborundum or graphite, and the unit is 'again glazed and those skilled in the art within the the groove. These steps may be varied to some extent or some of them eliminated in some instances.

While I find it advisable to have the resistance path upon the under face disposed directly under theresistance path upon the upper face, good results may b'e obtained nevertheless when the paths are not so arranged, providing that the paths extend across the surfaces of the disc between the connections. The proportions of the paths, their disposition on each unit and the selection of the resistance material may be varied in accordance with variations in the regular voltage and other operating conditions.

In Fig. 4, a plurality of insulators, such as that shown in Fig. 3, are connected in series relation between a grounded supporting tower 10 and a transmission-line conductor 12 in a usual and well known manner. However, since the resistance material 7, on each of the insulator units, extends from the cap to the pin thereof, this arrangement provides a continuous and unbroken path for leakage current between the conductor 12 and the grounded support 10.

I. have illustrated and described the invention as applied to line insulators in order to explain the nature of the invention but this is intended for the purpose of explanation only and by the use of the term insulator7 I mean not only linev wire insulators but other. insulating devices for use with high voltages such as, for example, the bushings for transformers, over which'it 1s also desirable vto prevent variation of potential. It will also be understood that this inventlon is applicable to a single unit or a series of units.

It will be obvious that various changes 1n 'the details and arrangements herein described and illustrated may' beU made by prmclple and sco-pe of the invention. Iclaim:

1. Means for supporting and insulating a current conductor from a grounded support comprising a series of insulator units interposed therebetween and connected therewlth, each unit having an insulating surface and a high-resistance surface of conducting material forming a continuous and unbroken local path along said insulating surface for leakage current between' the conductor and the grounded support, the width of said path being relatively small in comparison to the diameter of the insulator.

2. A high-voltage insulator including an insulating body member and means for grading the voltage distribution in predetermined mannerover the insulator embodying a strip of resistance substance of negligible Watt consumption extending, and energized in response to the difference of potential between the insulator terminals and constituting a local path for leakage current on the surface of said body member, the total outer surface area of the strip being ap reciably lessthan the total surface area of tlie insulating body between the terminals.

3. A high-voltage insulator including an insulating body member and means for grading the Voltage distribution in predetermined manner over the insulator embodying a strip of resistance substance of negligible watt consumption extending, and energized in re- Sponse to the difference of ftential, between the insulator'terminals and constituting a local path for leakage current on the surface of said body member, said strip extending windingly across said surface.

4. A high-voltage insulator including an insulating body member and means for grading the voltage distribution in predetermined manner over the insulator embodying a strip of resistance substance of negligible watt consumption extending, and energized in response to the difference of potential, between the insulator terminals 4and constituting a local path for leakage current on the surface lofsaid body member, said strip being of substantially sheet construction having its sides conforming to the surface of the body member and of appreciably less total outer surface area than the total sur face area of said insulating body member between the terminals.-

In witness whereof I hereunto subscribe my signature.

FRANK G. BAUM.

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