US2933553A - High-tension insulator - Google Patents

Description

April 19, 1960 M ZUHLKE 2,933,553

HIGH-TENSION INSULATOR 3 Sheets-Sheet 1 Filed July 30, 1957 WITNESSES aux/$441? 4%. amp.

INVENTOR Marcellus Z'L'lhlke ATTORNEY April 19, 1960 Filed July 30, 1957 Fig.l0.

3 Sheets-Sheet 2 April 19, 1960 M. ZUHLKE HIGH-TENSION INSULATOR 3 Sheets-Sheet 5 Filed July 30, 1957 Fig. I3.

United States PatenfO HIGH-TENSION IN SULATOR Marcellus Ziihlke, Berlin, Germany, assignor to Siemens- Schuckertwerke Aktiengesellschaft, Erlangen, Germany, a corporation of Germany Application July 30, 1957, Serial No. 675,075 Claims priority, application Germany August 4, 1956 7 Claims. (Cl. 174-211) The invention relates to insulators, insulating bushings, insulating housings and insulator arrangements, generally, which are used for high voltages and subjected to conditions favorable to the formation of foreign layers thereon. Foreign layers result from the deposition of particles of foreign matter from the ambient atmosphere, such as dust, flue ash, salt, soot, etc., as well as water. Thus, under conditions of high atmospheric humidity, such foreign layers will act as electrolytic conductors and reduce the flashover voltage of the insulator. All attempts to increase the flashover voltage of the insulator under conditions favorable to the formation of foreign layers heretofore had for their object a voltage distribution as even as possible over the length of the insulator or arrangement of insulators, respectively. Thus, the drop of the flashover voltage has been attributed so far only to the voltage distortion caused by the layer of foreign matter. The invention is based upon a different conception of the nature of a surface flashover.

The flashover on an insulator carrying a layer of foreign matter is caused by primary discharges receiving current through the conductive layer of foreign matter. The flashover will occur when these primary discharges reach a high current density. In this case, the current flow is no longer evenly distributed over the surface with regard to current density, but it contracts along separate paths and, in critical cases, along one single path forming a firing bridge. This contraction of the current flow is a consequence of the negative temperature coefficient of the resistance of the foreign layer. w The invention is based on the knowledge that the value Patented Apr. 19, 1960 solid layers and form a crust thereon. By causing the longitudinal separating strips to have a higher temperature, said strips will remain dry and, therefore, non-conducting.

The invention will now be described with reference to the drawings in which Figures 1 and 2 illustrate the phenomena leading to a flashover in a smooth, cylindrical insulator of the usual type; Figures 3 and 4 show means preventing a flashover in said cylindrical insulator; and Figures 5 to 13 illustrate, by way of example, various forms of insulators according to the invention, partly shown schematically in sectional views.

In Figures 1 and 2, reference numeral 1 designates the insulator, and 2 designates the layer of foreign matter. The initial creep current is indicated by broken lines 4'. When there occurs a glow discharge 3, the creep currents 4 will converge at 3' and 3". As soon as the current density is high enough, a flashover will occur between the electrodes 5 and 6 of the insulator.

Figures 3 and 4 show a side elevation and a cross-section of an insulator which is provided with longitudinal separating strips in the form of ribs or ledges 7 to 10. The foreign layers adhering to the insulator surface between said longitudinal separating strips are indicated at 11 to 14. In view of the fact that the ribs or ledges representing said longitudinal separating strips afford the particles of foreign matter from the atmosphere less opportunity to adhere thereto than the insulator surface portions therebetween, said ledges function as points of interruption for the creep currents.

For the sake of illustration, said ledges are shown in Figure 4 without foreign layers thereon. In case of a glow of the flashover voltage can be increased by limiting the current density of the primary discharges, particularly the current strength of the glow discharge. According to the invention, the current density of the discharges can be limited by dividing the foreign layer on the surface carrying the leakage, or creep, current into a plurality of narrow strips. Then each primary discharge will receive only a fraction of the current flowing over the entire width of the foreign layer, so that only glow discharges may occur which have a low initiating power insufficient to effect a complete flashover.

Said foreign layer may be divided into a plurality of narrow strips in various ways within the scope of the invention. Thus, for example, the surface may be subdivided by longitudinal strips having but little adhesive strength in regard of the particles of foreign matter from the ambient atmosphere. In order to reduce said adhesive strength, the insulator may be provided with a special surface configuration, such as longitudinal ribs, particularly edged ribs. No foreign layer, or only one of low conductivity, will form on said edges, and, therefore, the latter represent points of interruption preventing the current carried by the foreign layer from crossing over.

Another method of dividing the surface into longitudinal strips may reside in the provision of longitudinal separating strips of glaze having foreign-matter-repellent properties so that dust will not settle on said glaze in discharge 16, said creep currents 4- will again converge at 16' and 16", but this involves only those creep currents 4 and 4" which are carried by the portion 11 of the foreign layer lying between the ledges 7 and 8, whereas the creep currents from the adjacent portions 12 and 14 of the foreign layer will be kept away from said glow discharge 16. Thus, the current density in the glow discharge is reduced.

According to a further feature of the invention, it is advantageous to provide as many longitudinal separating strips or longitudinal ribs, respectively, as possible and, consequently, to divide the foreign layer into a maximum number of separate portions so as to reduce the current density more and more. In case of an extremely fine subdivision of said insulator surface, there may develop no glow discharges at all but only a great number of parallel streak discharges, or glow threads, which have a small current density.

Figure 5 shows a cross-section of a form of an insulator 17 whose surface is divided by many longitudinal separating strips 18 into a great number of narrow, longitudinal strips 19 carrying layers of foreign matter. This kind of surface split may be used on all types of outdoor and indoor insulators. Figures 6 and 7 schematically show, partly in longitudinal and cross-section, a rod insulator having a cap 20, a shaft 21, shields or water sheds 22, and longitudinal separating strips, e.g'. longitudinal ribs 23. In principle, an insulator chain may consist of members of similar design, for example, of cap insulators of the type shown in Figure 8. This figure is a cross-sectional view of a cap type insulator comprising an insulator body 24 provided with longitudinal separating strips, e.g. longitudinal ribs 25, a cap 26, and a connector 27.

It is not necessary to make the longitudinal ribs very high, as indicated at 28 in Fig. 9, since ribs forming small shoulders 29 will suflice. It is important only that there are edges, since such configuration of the insulator surface Will prevent foreign matter from depositing upon said edges and, consequently, from forming a continuous foreign layer.

Figures and 11 show an embodiment of the invention in which the periphery of the insulator is divided into many longitudinal sections. Such a multiple split is obtained by providing'an insulator which consists for example, of eightseparate sectional insulators, e.g. insulator'rods 30 and 30. These insulator rods have their upper and lower ends each secured to rings 31 and. 32, and each individual insulator rod offers a narrow path to creep currents. As indicated in the drawings 'with reference to the insulator rods 30,'the surfaces of these rods may, in addition, be divided by longitudinal separating strips, e.g. longitudinal ribs 33, into longitudinal strips 34 each covered with a layer of foreign matter. In connection with this arrangement it is important that the individual insulator rods be freely accessible'to the cleansingforces of rain and wind.

.Theinsulating housing shown in Figures 12 and '13 has a hollow generally cylindrical'body "3,5 of molded resin. It is provided with an integral'base 36 "for attaching to a suitable support. The exterior surface of the body is of a fluted configuration having a plurality of longitudinally extending ridges, 37 and valleys 38 thereon. The edges of the ridges 37 are relatively narrow, thereby being less susceptible to the accumulation of foreign matter thereon than the surface areas of the'valleys 38 between the ridges. In this manner a continuous layer of foreign matter is prevented from forming on the exterior surface of .the insulator,

. According tothe invention, the dividing of said surface into narrow longitudinal areas by means oflongitudinal separatingstrips may also be accomplished ina different manner than by means of longitudinal ribs. Thus, for example, instead of-using longitudinal ribs, the insulator surface may be provided with strips of glaze unfavorable to the deposition of foreign layers. .At the same time, such strips of glaze are also water-repellent. Such glazing may consist, for example, .of silicones or similar .substances.

The insulators proper. may be made of any of the materials heretofore used in the production of insulators, such as molded resin, synthetic plastic material, ceramics,g'lass, pressed glass, and the like. Molded resin and pressed glass are particularly suitable since these materials lend themselves easily to the process of forming longitudinal ribs. This is done simply by arranging the adjoining edges of the individual parts formingthe mold so'that' the longitudinal ribs will automatically appear during the molding or pressingprocess.

According to the invention it is likewise possible to combine the separate means for preventing a passage or the creep currents from one strip of foreign layer to an adjacent one. For example, the shoulders, or ledges, may be coated with substances which are unfavorable to the deposition of layers of foreign matter, and/or tend to effect an increase in temperature.

' I claim as my invention:

1. An electrical insulatorcomposed ofinsulatingmaterial, the extegior surface of said insulator being divided into a phi "ality of areas by means of longitudinally extending separating strips, said separating strips being formed on the insulator surface by equally spaced longitudinal ribs, each one of said ribs having a single narrow edge which is less susceptible to the accumulation of 'foreign matter thereon than the surface areasbetween said edges.

2. An electrical insulator comprising a generally cylindrical body composed of insulating material, the exterior surface of said body having a plurality of longitudinally extending equally spaced ribs thereon, and each one of said ribs having a single narrow edge which is less-susceptible to the accumulation of foreign matter thereon than the surface areas between said edges.

3. A high-tension insulator comprising a generally cylindrical' body composed of insulating material, substantially'the entire exterior surface of said body having a plurality of longitudinally extending'ridges and valleys thereon, and each one of said ridges having a single sharp edge which is narrower than the width of said valleys between the ridges.

4. A high-tension insulator comprising a generally cylindrical body composed of insulating material, substantially the entire exterior surface of said body having a plurality of longitudinally extending ridges and valleys thereon, and each one of said ridges terminating in a single narrow edge which is less susceptible to the accumulation of foreign matter thereon than the surface areas of the. valleys between said ridges. I

5. An insulating housing comprising a hollow generally cylindrical body composed of insulating material, the exterior surface of said body having a plurality of integrally formed longitudinally extending equally spaced ridges thereon, said ridges extending along substantially the entire length of the cylindrical body, and each one of said ridges terminating in a single narrow edge which is less susceptible to the accumulation of foreign matter thereon than the surface areas between said edges.

'6. An insulating housing. comprising a hollow generally cylindrical body composed of insulating material, substantially the entire exterior surface of said'body being of a fluted configuration having a plurality of longitudinally extending ridges and valleys thereon, and each one of .said ridges terminating in a single edge which is narrower than the width of said valleys between the ridges.

7. An electrical insulator having an exterior surface which is divided into a plurality of relatively narrow areas by .means of longitudinally extending equally spaced separating strips, said separating strips consisting of a glazing materialwhich is more repellent'to foreign matter than .the. material in the surface areas between said separating :strips.

References Cited in the file of this patent UNITED STATES PATENTS 1,493,262 Hammond ;"May 6, 1924 2,056,813 Vroorn'an Oct. 6, 1936 12,576,723 Perrins Nov. 27, -1

FOREIGN PATENTS 4,450 .Great Britain 1,882

214,170 Great Britain Apr. 17, 1924 w. st.

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