US1643565A - High-tension insulator - Google Patents

Description

A. SIMON Sept. 27, 1927. 1543565 uien TENSION INSULATOR Filed July 10, 1925 Patented Sept. 27, 1927. 4

UNITED STATES arnxannnn smon, or MUNICH, GERMANY.

HIGH-TENSION INSULQTOR.

Application filed July 10, 1925, Serial No. 42,695, and in Germany October 12, 1922.

The high tension insulators used at present do not utilize the insulating capacity of the material to the best advantage; and, moreover, have certain other defects which im- 5 pair their dependability. At certain points or portions on the insulator, static fields of high intensity are liable to be formed, either normally or after exposure to'moisture, so that the air surrounding the said insulator is subjected locally to excessive stress. This stress may increase until glow or brush discharges occur which may lead to regular discharges. These latter discharges occur far below the potential for which the insulator is rated, and may cause the insulator to break down because of local development of heat.

These defects are known, and endeavours have been made to overcome them by giving the insulator body a special shape, or arti-' ficially influencing the electric field. Examples of insulators of this kind are, for instance, the bell insulator and the metalshielded insulator. These devices are, however, merely modifications of standard types, involving no radically new principle.

The present invention has for its primary object eliminating the aforesaid defects in insulators by diminishing the intensity of .the field existing between the electrodes, and by providing for a continuous distribution of that part of the fiel-d' between the electrodes which lies within the insulator. If the intensity of the electric fieldis 11111- 3 form, the potential gradient is uniform also.

The reduction of the intensity of the field' is attained by increasing the distance between the electrodes, this being eifected by providing an umbrella shaped insulating body surrounding an axially .disposed electrode, with a convexly curved metallic cap covering said insulating body and being so arranged as to contact the rim thereof, and as to include a 1gap. with said body, which increases from t e rim of said captoward the central axis of said body and is filled with an insulating medium, preferably with a aseous medium. In this way, a consider ab e distance between the inner electrode and the cap forming the second electrode may be obtained without the necessit of using very thick insulating parts whic are difiicult to manufacture in good qualities. The

cap provides for the protection from rain and affords a high mechanicalstrength. The provision of a uniform eld distribution, and of a corresponding fall of potential between the electrodes is'attained by giving the insulator and electrodes a particular shape, the chief features in these respects being that the electrodes, that is to say the bracket and the metallic cap, used sometimes to support a conductor, are so shaped and arranged with respect to each other and'the interposed insulator that abrupt changes of shape between adjacent parts are avoided, and that the shortest distances from any given or selected point of the cap to the other electrode are proportioned in accordance with the dielectric constant of the in- 'sulating means traversed by the respective lines of such distances.

Where the lines of distance extend through two different dielectrics, as porcelain and air, the calculation of these'distance lines must be based upon the corresponding mean or average values of the individual dielectric coefficients. If, for instance, a given distance line L extends through the length L, within a medium with the coeflicient E and through the length L within a medium with the coeificient E the mean value EM in question is, according to well known prinv ciples,- i

. L2 XEI+LIXEZ it being L'=L,+L,. According to the invention, the parts are so shaped that the ratio LzEM is substantially. equal for all distance lines which extend within the insulator. 7

An embodiment of the invention designed according to the principles set forth in the preceding paragraphs is shown by way of example in the accompanying drawing, in

' which Fig. 1 shows an elevation partly in section of a pin-type insulator;

Fig. '2 shows the invention applied to a suspended insulaton 7 Referring to Fig. 1, the umbrella shaped insulator body 2; is formed of any appro-' priate insulating material and. is provided with a bore to receive a pin a which may be made of metal. .A. metallic cap h is shaped to engage the insulator body at s and overhangs the body by a considerable distance as shown at t. The conducting wire I) is not attached directly to the insulator body, but is attached to the cap it, forming an electrical connection therewith. The function of the cap it is to protect the insulator body from rain and by virtue of its conducting properties to distribute the area of high potential rather than allowing it to remain concentrated at the conductor 7;. The inner surface of the bore is coated in a known manner with a conducting layer f forming the inner electrode from which the electric field lines extend to the cap forming the outer electrode. As will be noted in the drawing, the upper surface of the insulator body is slightly convex, while the top of the metallic cap is more convex, so that the thicknessof the gap between the two elements increases from the rim to the axis of the insulator. suitable insulating medium, preferably with air.

The cap and the body are in fact so designed that the ratio between the dielectric soeflicient along a distance line extending from any point on the capto the pin a, and such distance line is a constant for all such distance lines which lie within the insulator. For instance, along the distance line 2' extending through a layer of air and a thicker layer of porcelain, the dielectrical coefiicient has a different value from that measured along the line 2' extending through a thinner layer of porcelain and a thicker layer of air, the lengths of both these lines having the same ratio as the respective dielectrical coeflicients.

The insulator body is provided with an annular flange (1 designed to reinforce the body against breakage, and to protect the body against rain. In some cases it may be deslrableto employ several flanges like 03. The body is also provided with a skirt e to prevent surface discharges. The skirt 6 serves a urpose similar to that of flange d and may e duplicated according to the cond1t1ons for which the insulator is designed.

It will be seen that the apparatus of the present invention prevents the concentration of electrostatic charges which might cause discharges over the surface-as a result of ionization of the adjacent air.

A suflicientl uniform field distribution also arises w en the individual distances measured at neighbouring places show only gradually increasing deviations from the values of ratio of the dielectric constant. There is also to be considered the circumstance that the singly measured distances do not coincide accurately with the path or course of the lines of. force as these are subjected to refraction at the boundary surface of two dielectrics i, i i and i, are distance The gap is filled with any lines which are in the same proportion td the dielectrical coefficient measured along those lines. The line 2' is a broken line representing the course of a field line subjected to refraction.

In regard to the known metal-shielded insulators m invention resembles them in re spect of using the metallic cap for artificlally influencing the electric field, but it is also employed for other and quite different pur- .ished. A substantial uniformity of the field distribution is not attained. In contradistinction thereto a considerably better uniformity and reduction of the electric field is attained by means of a particular shape of the metallic roof, in combination with a particular shape of the insulating body.

An essential feature as regards the efl'ect obtained by this improved insulator resides also in the ,feature that in the case of a change of the difference of potential existing between the electrodes the field existing between them is varied, it is true, as regards its strength, but not as regards its extensional distribution.

The insulator illustrated in Fig. 1 may be used also as a suspended insulator in that the metal cap of one insulator is connected in any suitable manner with the bracket or the equivalent therefor of the adjacent insulator, and so on. Theelectric properties of the insulator are not materially changed thereby.

The modification shown by Fig. 2 is an insulator of the suspended type comprising an umbrella shaped insulatingbody la, the

thickness of which decreases from the center to the rim. The upper surface may be truly conical or slightly curved so as to form an arched body which has a downwardly directed rim 7" as its base. By this construction the arched insulating body acts like an arched bridge which is supported. by its bases. A central draw-bolt 'LQ con-i stituting the inner' electrode, extends through the body is; its upper portion is conical, terminating in a flange, and is covered with a layer 1 of insulating material such as rubber. The insulator is is provided with a central aperture or internal bore to receive the draw-bolt or member ,w. A lower insulatin skirtn'r fits snugly,a ainst the member is, being held in posltion y an internally threaded clamp m, an annular metallic member at being interposed between clamp m and member an.

A metallic cap it constituting the second Hill electrode covers or fits over the entire insulator and supports-the insulator body It by engaging the rim thereof. In this manner the cap maintains the insulating body in position even if the said body is broken because the broken parts act as members of an arch and are held in place by the basesor inthe present construction by the rim 1'.

The suspension means comprises the usual knob o and the loop p. The joints between the cap it, the body In and the skirt a; are filled, prior to assembly, with insulating cement of any suitable composition.

The shape of the cap is designed as follows: The radial distanceline 2', between the rim of the umbrella shaped insulating body is and the inner electrode 10, is calculated according to well known principles in such a manner that a puncture of the insulator along this radial distance line extending within the insulatin material cannot occur. The dielectric coe cient of this material may bee. The axial dstance line 2', between the top of the cap and the inner electrode w measured along the axis is given by the equation:

wherein e, is the mean dielectric coefficient of the media filling the space between the inner electrode and the cap h. The height and the diameter of the cap being .determined, the profile of the cap is so designed that the gap included between the cap and the insulating body. increase continuously from said rim toward the center of the body. It is obvious that, due to the above given calculation, the field intensity along the line 2' must equal the intensity along the line 2',. By the gradual curvature of the cap profile, however, a uniform field distribution is also attained in the insulator sections between these lines. e

In order to eliminate the overturning moment exerted upon the insulator body, shown in Fig. 1, by the pull of the conducting wire, the wire may, if desired, be passed through two eyes disposed in diametrical relation to each other upon the cap, the conducting wire being secured as usual to the binding post which is provided at the center of the cap. An advantage of the foregoing structure lies in the fact that the entire insulator body may, if desired, be manufactured in one piece. The dielectric strength of the insulator is then not appreciably lessened by local defects in the material, since the stress to which the insulator is subjected'is considerably less for a given voltage than with the known devices. For the same reason, cheaper and more easily worked materials such as earthen ware, stone ware, glass and the like nay be employed.

I claim:

1. In a high tension electrical insulator, the combination comprising an. umbrella shaped insulating body having an internai bore for the reception of an electrode, an electrode in said bore, a convexly curved metallic cap, constituting a second electrode,

so superimposed upon said bodyas to include a gap withsaid body, and an insulating medium in said gap, the said insulating body and the said cap being so shaped and arranged with respect to each other that the shortest distance lines drawn from given points on said cap to the surface of the first named electrode and extending within the insulator are approximately proportional to the average dielectric coefficients measured along said lines.

2. In a high tension electrical insulator, the combination comprising an umbrella shaped insulating part having an axial bore, an electrode arranged within said bore, a cap of conducting material forming the other electrode and being so shaped and arranged as to contact the rim of said part and to include a gap therewith which con tinuously increases from said rim toward the axis of said body. the said cap being spaced from the first named electrode b a definite distance in axial direction, an a gaseous insulating medium withinsaid gap, the ratio of said distance to the radal distance between the rim of said part and said electrode being substantially equal to the ratio of the average dielectric coefiicients' measured along the respective lines of said distances.

3. In a high tension suspended electrical insulator, the combination comprising an umbrella shaped insulating body traversed by an internal bore, a'central draw-bolt posi-- tioned in said internalbore constituting one electrode and being arranged so as to transmit the load forces to the upper surface of said insulating body, a convexly curved metallic cap fitted over said insulating ,body so as to include a gap therewith and to engage and support the rim of said body, and an insulating medium in said gap, the said insulating body and the said cap being so shaped and arranged with respect to each other that the shortest distance lines drawn from given points on said cap to the surface of the. first named electrode and extending within the insulator are approximately proportional to the average dielectric coetficient's measured along said lines.

4.'In a high tension suspended electrical insulator, the combination "comprising an umbrella shaped insulating body having an arched cross-section and traversed by an internal bore, a central draw-bolt positioned in said internal bore constituting one electrode and being arranged so as to transmit the load forces to the top of the said arched insulating body, a convexly curved metallic cap fitted over said insulating body so as to include a gap therewith and to engage the rim of said arched body, thereby supporting the base of the same and maintaining it in position even if broken, and an insulating medium in said gap, the said insulating body and the said cap being so shaped and arranged with respect to each other that the 10 shortest distance lines drawn from given points on said cap to the surface of the first named electrode and extending within the insulator are ap roximatel proportional to the average die ectric coe 01 along said lines.

In testimony where? I afiixmy signature.

' ALE ANDER SIMON.

ents measured 15 r

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