US1742628A - High-tension insulator - Google Patents

Description

' Jan. 7, `1930.

s.` BARFOED 1,742,628

HIGH TENS ION INSULATOR Filed May 11. 1927 Fig/.1. E

JNVENTOR. i6'

BY HLM' ,nuxaal TTORNEYS.

Patented 7,' i i l narrans'raras anf/Fran 'lfforr'llCE;A

avana Eamonn, or aan rmorsco, cantonale inea-Tannen* msuna'roa,

application mea my 11, ma?. sel-151m. 190,500.

This invention relates to insulatorsY and particularlyi that kindemployed for high tension electric` transmission lines. These insulators may be either what is known as the suspension type orthe pin type. Y

To safely insu ate high tension transmission lines in districts where fog and dust conditions alternately prevail for long periods, serious difficulties have been encountered.

Fo, dew, mist and light rain,'in combination 4with dirt and dust render insulator surfaces of the usual shape conducting to a degree lWhere it becomes, at times, difficult to keep-a transmission line in operation.

When a series of the suspension type msulators of the common disc shape were used, it did not hel matters to any appreciable extent by mere y adding further u nits to the string, nor did it im rove conditions to enlarge rthe diameter o the units of either the suspension type or the pin type.

By adding further units to a suspension strin of insulators, the electrical potential distribution amongst the units composing the string is rendered worse than before and the strin tends to fail by cascading around the hi h y stressed umts unless the potential distri ution is a ain corrected by exterior an-v tennaes and evices, such as grading` rings, etc.,.which for most lines would be pro ibitlve in cost. Further, the string length has thereby 'become so great that ground clearances to the supporting tower or pole is reduced to the danger point, and if again brought to a proper value, the tower or pole mustV be made much stronger, will Weigh more', and the cost of construction correspondingly increased.

By increasing the diameter of either type 4 leakage distance for the moisture and dirt conditions as above described, a. point is very qulckly reached where increased diameter v.

actually means increased leakage. This is demonstrated as follows Assume a plane cir- 'unit diameter, then renden-its surface partially conducting tothe electric current by moisture and dust, and then apply an electric potential to electrodes in the center on 5 either side of the disc. Now consider a secof insulator, in order to provide increased cular solid disc of insulating material and ofA tor of the disc of unit center-angle and lobserve' that the leakage current fndsin its path a ,s conductor cross-sectio1-1 of ever increasing value towards the edge of the The ability, per unit length,of the partially conducting surface to absorb thek impressed potential is, therefore, reduced in direct'proportion to the lengths of the radius as the ed e of the disc is ap reached. y now making t e diameter of the two units instead of one unit, the ability of this extra length of leakage path to absorb electric potential is still further reduced, and if this process is continued the condition of short circuit is approached renderin the increased surface of n o value as an 1n' slilator. This method of providing leakage distance has, therefore, resulted in complete failure.

The present invention is based on the discove that leakage of the electric current may e greatly 'reduced if the exposed area or insulating surface upon which dust and moisture can collect is reduced to a minimum by reduction of diameter ofthe insulating body, combined with increased axial length of the insulating body and protection of the exposed insulatin surface by corrugations or skirts of small iameter and of a definite shape and prescribed spacing and disposition. It was discovered that to increase the leaka e path by merely introducing skirts on the bo y of the insulator or building the insulator up of a number of shells or skirts -is beneficial in an economical manner for the dirt and moisture ceondltions only, when the shells or skirts are disposed with relation to each other and to the main body of the insulator in a denite' manner., The manner in which this maximum insulating value of the skirts or shells is obtained ,is by so spacing them and giving them such form that for the dust and moisture conditions a balance is obtained between the value of the sparking distance through the air between the rims of the skirts and the leakage distance along the surface of the insulator from rim to rim of skirts. It has in this manner been possible to produce insulators which have an insulating value when moist and dirty which is only 20% less than the insulating value of the same insulators` @i i matices when pertectly dry and' clean. To obtain dais result tile air space between the skirts assume a shape which in crosssection in a radial plane shows the rims of theskirts are closer together than the roots, and depending upon the conditions to be net, lsuch for instance as, proximity to cement plants, railroad yards, also in arid, dusty countries and in combination with moisture in the form of dew, tog, salt iogs, mist or light rain, the relation between the distance or air gap from edge to edge of rims oi the skirts and the leakage distance along the surface of the insulator from edge to edge of rims may vary.

For instance, in case ol ordinary dust and fog the relation would be one to four, and for salt tog, one to live, etc. Y

The invention is shown by way of illustration with accompanying drawings in which:

tion through one of the insulators.

. Fig. 2 shows a string or assembly ofjnsu-v laters and' aconductor suspended therefrom.

Fig. 3 is a diagrammatic view illustrating the fallacy of increasing the diameter of disc type insulators.

Fig. 4 is a side elevation partially in section, showing a pin typle insulator.

Referring to t e drawings indetail, apd particularly Fi 1 and Fig. 2, A indicates the cross-.arm o a transmission line tower or pole of suitable construction; B the conductor carrying the high? tension current and C a string of insulators from which the conductor is suspended. The type of insulator employed is that illustrated in Fig. 1. It consists of a head portion 2 and a petticoat or skirt ortion 3. This skirt portion is slightly are or bell-shaped and its exterior surface is provided Withasuitable number of superposed interspacedy annular flanges or petticoats. These petticoats are of substantially equal diameter and an exterior corrugated cylindrical surface is the apparent result.

The head member 2 is hollow to receive anwhich encloses the head 2 of the insulator and is secured thereto -by a cementitious material 8, or the like. The connections between the head members 2a and the anchor bolts 5 are referably pivotal, as indicated at 9, and a exible string of insulators is obtained;

The method' of anchoring the bolts 5, the head members 2* and the manner of attaching the link 7 is of no importance and maybe changed `to suit varying conditions. The manner of formin the annular petticoats 4 on the exterior sur ace, the spacin employed between the annular flanges and t e proportional area and 'length obtained is, however, 0f great importance and forms the subject matter of the present application. fis previcusly stated, the invention is based on the discovery that leakage losses in a transmission linge may be materially reduced ii the exposed area or insulating surfaces upon which dust and fog can collect is reduced and the length ot the'leakage path increased.

To clearly illustrate and describe this feature, reference will be made to Fig. 3. lthis illustration the inner circle 10 represents a plan view of the type of insulator illustrated in Fig. 1 and the circle indicated at 11 represents a elan View of a disc type of insulator which as been increased in diameter. By dividin these circles into a segment, as illustrated y the lines l2 and 13, it will -be noted that the triangle indicated at 14 repren sents defined and total area upon which dust and fog may collect and that the remainder of the triangle, indicated at 15, represents the increased:q area upon which dust and fog may collect, if the diameter of an insulator is increased.

Itis well known that the resistance to the flow of an electric current depends upon the cross-sectional area of the conductor. If this the area yis increased, the resistance is materially reduced. Again, it is well known that the length of the conductor also increases or decreases resistance.

By referring to Fig. V3 it will be supposed that dust and moisture has collected on the surface of the insulator to about a thickness of one-thirty-second of an inch. If this is thecase, the cross-sectional area. of the dust at the base of the triangle 14, and indicated at 14, will represent a much'smaller area than a cross-section taken atA the base of the triangle f15, 'such as indicated at 15". Hence, the amount of material collected on the area 14 will fafford a much greater resistance to the flow 'of current than the material collected on the area 15, as the cross-sectional areas presented are small in one instance and comparatively large in the kother instance, and thus by progressively increasing the di ameter of the discs the annular surface for each unit increase in diameter will beless and less able to sustain its share of the im ressed potential, and when eventually the diameter of the discs are made ve large, this leaka e value per unit length of ea-kage path will e so low that short circuit conditions per unit length will be approached, resulting in an uneconomical deposition of the insulating material.

By constructing the insulator, as shown in Fig. l, the diameter of the annularilanges or petticoats 4 are maintained as small as posl sible, thereby presenting small surfaces for the collection of dust andl fog, with a consequent reduction in cross-sectional leakage area and by elongating the insulator as by providing the skirt portion 3 and additional 'is decreased, the resistance increases and if annular flanges 4 the length of the leakage path is materially increased without increasing the cross-sectional area of the leakage path, hence ideal insulating conditions are obtained.

Another importantfeature of the present invention is the spacing maintained between the annular iianges or petticoats 4 and the shape of the annular channels 4a formed between the same. It was discovered that to increase the leakage path by merely introducing skirts or petticoats on the body 3 of the insulator or buildin the insulator up of a number of shells is bene cial in an economical manner or the dirt and moisture conditions only when the shells or skirts are disposed with relation to each other and to the main body of the insulator in a definite manner. The manner in which this maximum insulating value ofthese skirts or shells is obtained is by so spacing them and giving them such form that for the dust and moisture conditions, a balance is obtained between the value of the sparking distance through the air between the rims ofv the skirts and the leakage distance along the surface of the insulator from rim to rim of the skirts. It has, in this manner, been possible to produce insulators which have an insulating value when moist and dirty, which is only 20% less than the insulating value of the same insulators when perfectly dry. To obtain this result, the air space indicated at 4" between the skirts asL suming a shape which in cross-section in a radial plane shows the rims of the skirts are closer together than the bases, this distance depending upon 'the conditions to be met, Such for instance, as proximity to cement plants, railroad yards; also in arid, dusty countries and in combination with moisture in the form of dew, fog, salt fog, mist or light rain. {The relation between the distance or air gxp from ed e to edge of rims of the skirts and a leakage istance along the surface of the insulator from edge to ed e of rims may var For instance, in case o ordinary dust an fo the relation would be approximately one to our, and for salt fog, one to tive.

From the fore the skirt 3 is so s aped as to be provided with an inner protected surface 3l on which little or no dirt and moisture will collect and that 'the outer surface is to a large extent protected by the petticoats 4, which are so formed and arranged as to obtain proper air space between the superposed petticoats and at the same time provide a protection for the exterior surface of the skirt 3 to reduce the amount of dust and moisture collected. Briel the spacing between the petticoats 4 is snc that leakage resistance over the surface when covered with dirt and fog is substantially equal tothe air resistance formed vertically between the superposed petticoats as indicated at 4", thusA producing a. balance oing it should be noted that design of economic proportions. That is, with a given quantityy of insulating material shaped and proportioned as here described,

eilicient insulating qualities or conditions are obtained with a minimum of insulating material, this being also important as a material weight reduction is obtained and cost of manufacturing is reduced. The type of insulagor employed is not limited to suspension insu ators but may also be employed where pin type insulators are required, as shown in Fig/i. Only one section, such as indicated at is employed where comparatively low voltages are encountered but one or more shells such as indicated at E may be added when higher voltages are encountered. The pin type of insulator, whether constructed in one or two sections, is identical in construction to the suspension ty e illustrated in Fig. 1 and' a detailed description thereof is accordingly thought unnecessary. Sulice it to say that the interior of the head 2" may be threaded to receive the upper threaded end of the supporting pin. This is, of course, an old feature and forms no part of the present invention.

While certain features of the present invention are more or less specifically described and indicated, I wish it understood that various changes may be resorted to within the sco e of the appended claims; similarly, that the materials and finish of the several parts employed may be such as the manufacturer may dictate or varying conditions or uses may demand.

Having thus described my invention, what I claim and desire to secure by Letters Patent 1. insulator of the character described having a body portion, anda plurality of annular interspaced superposed flanges formed on the exterior surface thereof, the spacing between said flanges being such that t e air gap resistance between the anges shall be substantially equal to the leakage pathbetween the flanges when their surfaces are 'covered with dust and moisture.

2. A suspension insulator of the character described, aving an elongated body rtion open at the lower end and closed at t e top, and a plurality of annular interspaced su erposed flanges formed on the exterior surace of the'body portion, the exterior' diameter of said flanges being substantially ual and presenting a substantially cylindrical corrugatedexterior surface, said anges having a spacin which is greatest adjacent their base and less tween the lperi heral edges the said spacing being such t at t e air gap resistance between the adjacent peripheral edges shall be substantially equal to the leakage path formed between the flanges when their surfaces are covered with dust or moisture.

SVEND BARFOED.

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