US2776332A - Self-cleaning outdoor high-tension insulators - Google Patents

Description

Jan. 1, 1957 van R0 2,776,332

SELF-CLEANING OUTDOOR HIGH-TENSION INSULATORS Filed June 25, 1952 2 Sheets-Sheet 1 Jan. 1, 1957 H- VON CRON SELFCLEANIN QU'IDOOR HIGH-TENSION INSULATORS Filed June 25, 1952 2 Sheets-Sheet. 2

[Ml entan- W Wv 011; 6"

to Siemens-Schucltertwerke Aktiengeselischat't, Berlin- Siernensstadt, Germany, a corporation of Germany Application June 25, 1952, Serial No. 295,523

6 Claims. (Cl. 174-411) My invention relates to outdoor high-tension insulators for electric transmission or distribution purposes and is described hereinafter with reference to the drawings, in which:

Fig. 1 shows, partially in section, a high-tension overhead-line insulator of the known rain-shedding bell type;

Fig. 2 is a view partly in section of a rod-shaped insulator the angle being exaggerated and, in fact, being substantially zero in the preferred form of the invention, as shown in Figs. 3a, 4 and 5;

Figs. 3a, 3b, and show respective cross-sectional modifications applicable to insulators according to the invention; and

Figs. 4 and 5 are respective views of two other insulators according to the invention.

Outdoor insulators for high-tension lines are either of the rain-shedding or of the self-cleaning type. The rain-shedding insulators are now being given an almost exclusive preference. The rain sheds or petticoats of these insulators have such a shape and spread that a zone under each shed is kept dry from rain. In the rain, the voltage across the insulator terminals is divided into a major portion across the dry zones, and a fractional portion across the wet insulator parts. Such insulators have the disadvantage that coats of dirt collecting upon the dry surface zones may in time become thick enough to appreciably reduce the flashover voltage of the insulator when a moisture film precipitates due to fog or dew. This is because the moisture on the dirt coating dissolves conductive constituents of the dirt and thus greatly increases the conductivity of the moisture film. The resulting reduction in fiashover voltage makes it necessary to clean the insulators more frequently as the danger of dirt precipitation increases.

As an example of such an insulator, Fig. 1 shows a pin-type insulator with three sheds or petticoats. When installed, the insulator body 1 of porcelain is supported on a metal pin 2,. The voltage is effective between the pin 2 and the line mounted at 3 or supported by the top notch or a top cap (not shown) of the insulator. The relatively large petticoats of the insulator keep three surface zones dry from rain, these zones being schematically shown at ab, c-d and e in time, thick coats of dirt may accumulate in these zones.

So far, vertical outdoor insulators of the self-cleaning type have found only rare application for high-tension lines. These self-cleaning insulators have been used as strings of insulator units, each unit having a metalcapped insulator disc joined with the adjacent unit by a link pin. In the rain, the underside of each disc is rinsed by the water so that the entire insulator surface Patented Jan. 1, 1957 is washed clean. However, the distance between the discs of such an insulator string must be relatively large so that only a relatively small number of discs can be accommodated on any given length (total fiashover distance) between the line electrode and the grounded electrode. Hence, the fiashover voltage is unfavorably small. it is an object of my invention to provide a high-tension outdoor insulator of the self-cleaning type for installation in a vertical or approximately vertical position, which, when covered by a coherent moisture film due to fog or dew, has a much higher fiashover voltage than heretofore attainable with insulators of this type.

Another, ancillary object of my invention is to devise a self-cleaning insulator which, for any given axial length, permits providing a larger number of insulating disc-like projections thus greatly increasing the leakage distances.

Still another object of my invention is to make certain that even in heavy rain storms the leakage current along the insulator cannot assume excessive values due to water dripping from the disc edges, or due to the formation of thick layers or streams of water especially on the lower part of the insulator surface.

An object of my invention is also to give the selfcleaning insulator such a design that any coherent film of moisture formed during a rainfall is thereafter rapidly heated and thereby disrupted simultaneously at a large number of places.

According to a feature of my invention, a self-cleaning outdoor insulator to be mounted in a vertical or approximately vertical position, has an insulating trunk portion integral with disc-type projections which surround the trunk portion in form of a helix and which are rinsable by the rain water not only on the upper side but also on the underside of each helical turn. Thus, any accumulation of dirt is washed Ofi in a manner comparable to the self-cleaning of the above-mentioned known insulators. However, while the known insulators, if the rain impinges laterally as is generally the case, are cleaned mainly on the windward side, the helical turns of the disc-like projections in an insulator according to the invention distribute the rain water also over the leeward side, thus securing a more uniform cleaning of the entire insulator surface.

These and other features and advantages of my invention will be apparent from, and will be referred to in, the following description of the embodiments of insulators according to the invention shown in Figs. 2 to 5.

The insulator according to Fig. 2 has a trunk portion 10 and a disc-like projecting structure formed of an integral body of ceramic material such as porcelain. The projecting structure consists of two helical turns 11 and 12 extending around and along the trunk portion. The trunk portion may be tubular as illustrated, or it may be given a solid design. In either case, the trunk has a uniform cross-section throughout its length. The terminal electrodes 13 and 14 of the insulator are sunken into the ends of the trunk portion to minimize the electric field strength at the edge of each electrode thus avoiding excessive discharges as well as an electrostatic precipitation of dust. The pitch angle of the helical projection is designated by or. The axial cross section of each individual turn of the projecting helix structure has its top side inclined relative to the horizontal by an angle 5. The corresponding underside of the cross section is inclined an angle 7 relative to the horizontal. The angles 5 and are hereinafter briefly referred to as the radial inclinations of the projecting surface, in contrast to the tangential inclination or pitch angle a. The inclination a of the helix and the radial inclinations 8 and 'y of the contour are such that, in the rain, the entire surface of the insulator, i. e. also the undersides of the projections are rinsed by a substantially uniform veil of water. At the undersides, this veil need only be just sufficient for eliminating any accumulated dirt or at least dissolving its soluble constituents. The rain water caught by the helical projections therefore divides itself into two portions. One portion flows vertically over the helix edges in a quantity depending upon the radial inclinations and forms a more or less pronounced veil of water running downwardly along the insulator. The other, larger portion of the rain water collecting upon the insulator surface flows downwardly along the upper surfaces of the projections along the helical path formed thereby.

As mentioned, the individual insulator discs in the known self-cleaning insulators for high-tension lines must have a large axial spacing from each other. This is because all of the rain water collected upon the insulator must flow downwardly over the disc edges and thence tends to form thick rings and large drops of water at these edges. In contrast, the disc-like projections formed by the helical turns in an insulator according to the invention may be given a narrow spacing from one another. This is possible because as mentioned, a large portion of the collected rain water is immediately drained from the insulator along the helical path so that only a small residual portion of water can flow over the edges and over the underside of the disc-like projections. By thus providing a very large number of projections or discs along a given axial length or fiashover distance, the leakage distances are greatly increased. This is especially advantageous in humid weather resulting in the formation of a coherent film of condensed moisture. The small leakage current passing through the film has a heating effect which is a maximum at the surface points of the insulator trunk between the successive helix turns. Since there is a large number of such places, the electric discharge that may occur at these places due to the heating and disruption of the film are numerous and occur locally within narrow limits. Under these conditions the electric discharges resulting from the disruption of the moisture film consume a relatively high voltage per unit of length. As a result, the leakage current is very strongly reduced so that a fiashover along the entire arcing distance between the terminal electrodes of the insulator is safely prevented.

During rain storms, the stream of water draining oif along the helical path has a very large length compared with the axial length of the insulator. Consequently, any leakage current that may then be flowing remains relatively small and can be interrupted without difficulty when the rain ceases. As mentioned above, the direct leakage path, on which the water runs vertically downward over the edges of the helical turns, is likewise relatively long. The formation of thick-layered runs of water in the longitudinal direction of the insulator that may directly connect one electrode with the other is prevented not only because a large portion of the water drains off along the helix, but also because all water particles are given a tangential component of motion so that they can nowhere follow the strictly vertical direction of gravity.

When the rain ceases, preliminary discharges occur at the peripheral edges of the helical projections because the film of rain Water is thinnest and hence evaporates first at these places. The portion of water which drains along the helical path forms a shunt resistor to all these locations of initial disiuption, and thus effects a substantially uniform voltage distribution over these locations. This prevents any of the individual discharges from growing into a fiashover between the terminal electrodes.

As mentioned, the helical projecting structure in the embodiment of Fig. 2 is designed as a double-turn helix. This has the advantage that a large number of individual turns or projections can be accommodated within a given arcing distance, while giving the pitch angle a a satisfactorily large magnitude to impart to the run-off water a correspondingly increased acceleration in the tangential direction. For the same reasons, more than two helical turns may be provided although, as apparent from Fig. 4, the helical projection may also be given a single-turn design.

In order to secure the above-described results, the underside of each helical turn must slope continuously downward from the edge of the turn to the upper side of the next lower turn. The radial inclination "y of the underside of each projection should be at least 20, and preferably about 30. With such an inclination, the water runs in an approximately uniform layer thickness along the undersides of the projections toward the trunk portion of the insulator.

The upper contour line of the axial cross section of each projection should not be given, at most, more than a slight angle of inclination 5 relative to the horizontal. In the preferred form this angle is made zero so that the upper contour of each individual projection or turn cross section has a horizontal direction. This is highly desirable because the amount of water accelerated along the helical path is subjected to centrifugal force which urges a small portion of the water radially toward the edge of the helical projection. Thence, the water flows in a thin coherent layer over the underside of the projection, this layer clinging closely to the insulator due to the strong adhesive action exerted by the insulator surface upon such a thin film of water. Hence, this small amount of water suflices to clean the insulator from accumulated dust also at the places not directly impinged upon by the rain.

The radial spread distance of the disc-like projections from the trunk portion (smallest exterior diameter) of the insulator is preferably made about equal to the vertical spacing of respective points on the periphery of two adjacent individual projections. Tests have shown that such a dimensioning results in an insulator design of optimum qualties.

Since the quantity of the helically draining water increases from the top toward the foot of the insulator, the upper contour line of the projections may be given a concave shape in the lower part of the insulator. In this manner, the quantity of the portion of water flowing over the edges downwardly along the direct leakage path of the insulator can readily be kept from assuming excessive magnitudes.

Figs. 3a, 3b and 3c show different profiles suitable for thus modifying the ratio of the helical run-0E to the over-edge portions of water in the lower part of the insulator. In the upper portion of the helical turns in an insulator designed, for instance, in accordance with Fig. 2, the upper contour line of the turn cross section is substantially horizontal as shown at 11a in Fig. 3a. The turn portions in the middle part of the insulator have a slightly concave contour line as shown at 11b in Fig. 3b. In the turn-portions near the bottom of the insulator the corresponding contour line is more strongly concave as shown at in Fig. 30.

Since the helical path of the water is considerably longer than the vertical path, the electrical resistance of the helical current passage is so high that only a small electric current can flow along the turns of the helix. Such a small current can readily be interrupted and stays below the magnitude at which a fiashover may be ignited. The helical water path may be made longer by giving the trunk portion a larger diameter or providing a singleturn helix. Due to the fact that, when the rain ceases,

the water flowing downwardly over the shortest leakage distance evaporates first at the helical edges because of the slight thickness of the water layer at these places, the current flow along the vertical leakage distance is first interrupted at the helical edges and at very many individual places. Thereafter the helically flowing residual current is also interrupted as the water drains ofi.

In dewy weather, fog or drizzle, the thin film of moisture first evaporates at the points of the trunk between the turns of the helical projections, and glow discharges may occur at these places over individual discharge distances of a very small length. Due to the high voltage consumption of these series discharges, the leakage current cannot reach a detrimental value, and a complete flashover from electrode to electrode is prevented.

For promoting the simultaneous disruption of the moisture film at many dispersed places, a helical heating conductor may be provided on or between the turns of the projecting structure so as to helically surround the trunk portion of the insulator. The heating conductor may consist of a strip-shaped surface glaze of electrically resistive or semi-conductive properties. Such a glazed strip may be provided, for instance, along the peripheral edge of the projections or on the trunk portion between the projecting turns.

The insulators illustrated in Figs. 4 and 5 embody the above-mentioned features. The trunk portion of the insulator shown in Fig. 4 is integral with a projecting structure 11 which forms a single-turn helix. As can be readily seen, the trunk has a uniform cross-section throughout its length. The axial ends of the insulator are recessed to receive respective portions of the terminal electrodes 13 and 14. A helical heating conductor is disposed on the edge of the projecting structure 11 and consists of a semiconductive glaze of small width. The ends of the glazed strip are conductively joined with the respective terminal electrodes 13 and 14 so that the glazed conductor 15 is traversed by a slight current when the insulator is under voltage. By virtue of the illustrated insulator design, the peripheral edge of the helical projection can be brought up to a locally raised temperature by means of a very small heating current flowing through the conductor 15, this being possible because the mass and heat capacity of the edge portion is small in comparison with the mass of the insulator trunk portion. The heating efiect of the conductor 15 aids materially in rupturing the moisture film at very many places along the extended helical course of the projecting edge.

The insulator illustrated in Fig. 5 is equipped with two helical projecting structures 11 and 12 and, in this respect, is similar to the above-described insulator of Fig. 2. Connected with the terminal electrodes 13 and 14 are two heating conductors 16 and 17 which extend helically around the trunk portion between the adjacent turns of the double-turn helix, following the smallest exterior diameter of the insulator body.

Insulators according to the invention may be used or designed as suspension insulators, as supporting insulators in open air stations, as lead-in insulators and entrance bushings for outdoor installation, as arc chambers of out-door power breakers, as terminal bushings for topconnected outdoor breakers, as an enclosure of overvoltage protectors or measuring transformers, as an insulating bushing for bushing-type current transformers, and other outdoor purposes requiring an insulating structure to be mounted in a vertical or approximately vertical position.

I claim:

1. An outdoor insulator of the self-cleaning type for vertical or approximately vertical mounting, comprising an elongated rod-shaped trunk portion and a projecting structure both of insulating material and integral with each other, said structure having helical turns around and along said trunk portion, each turn having a vertical cross section whose upper edge is substantially horizontal and whose underside edge has a continuously downward slope from the periphery down to the upper side of the next lower turn, and heating conductor means of helical shape joined with the insulator and forming a helix coaxial with said trunk portion.

2. An outdoor insulator of the self-cleaning type for vertical or approximately vertical mounting, comprising an elongated rod-shaped trunk portion and a projecting structure both of insulating material and integral with each other, said structure having helical turns around and along said trunk portion, each turn having a vertical cross section whose underside edge has a continuously downward slope from the periphery down to the upper side of the next lower turn, two conductive terminals mounted on the respective axial ends of said trunk portion, and heating resistor means electrically connected between said terminals and forming a helix coaxial with said trunk portion.

3. An outdoor insulator of the self-cleaning type for vertical or approximately vertical mounting, comprising an elongated rod-shaped trunk portion and a projecting structure both of insulating material and integral with each other, said structure having helical turns around and along said trunk portion, each turn having a vertical cross section whose upper edge is substantially horizontal and whose underside edge has a continuously downward slope from the periphery down to the upper side of the next lower turn, two conductive terminals mounted on the respective axial ends of said trunk portion, and heating resistor means electrically connected between said terminals and extending along the peripheral edge of said helical projecting structure.

4. An outdoor insulator of the self-cleaning type for substantially vertical mounting, comprising an elongated trunk portion having a uniform cross-section throughout its length and a projecting structure, both of insulating material and integral with each other, said structure having plural helical turns around and along said trunk portion, each turn having a cross-section whose underside has a continuously downward slope from the periphery down to the upward side of the next lower turn, and heating conductor means of helical shape joined with the insulator and forming a helix coaxial with, and following the smallest exterior diameter of, the trunk portion.

5. An outdoor insulator of the self-cleaning type for vertical or approximately vertical mounting, comprising an elongated circular trunk portion having a uniform cross-section throughout its length, and a projecting structure, said trunk portion and said structure being both of insulating material and integral with each other, said structure having helical turns around and along said trunk portion, each turn having a vertical cross section whose upper edge is substantially horizontal and whose underside edge has a continuously downward slope from the periphery down to the upper side of the next lower turn, so that, when the insulator is mounted and exposed to rain, the upper sides as well as the undersides of said helical turns are rinsed by rain water, said trunk portion and said projecting structure consisting of a ceramic body, said insulator having an electrically semiconductive surface glaze forming a helical and coaxial heater strip along the insulator.

6. An outdoor insulator of the rain self-cleaning type for vertical or approximately vertical mounting, comprising an elongated trunk portion having a projecting structure, said trunk portion and said structure being both of insulating material and integral with each other, said structure comprising a helix coiled around and along said trunk portion providing a helical ledge forming a path for rain water, the ledge providing a vertical cross section whose upper edge is substantially horizontal whereby a small portion of the water is urged radially outward by centrifugal force, the underside of each turn having a continuously downward slope from the periphery down to the upper side of the next lower turn, so

that, when the insulator is mounted and exposed to rain, the underside of said helix is rinsed by said small portion of rain water, said upper horizontal cross-sectional edge of the ledge being in the upper portion of the insulator, the middle portion and the lowermost portion having upper surfaces which are concave viewed downwardly, the lowermost portion having a more greatly concave surface than the middle portion, to modify the ratio of the water run-01f along the helical path to the run-off over the edge of the helical ledge.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Switzerland Dec. 31, 1907

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