US1585359A - Insulator - Google Patents

Description

May i8 1926.

A. O, AUSTIN I'NSULATOR Original Fled Dec. 5, 1920 Patented May 155, 19225.

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rarest or-lirica@ ARTHUR o. Austria, or Basisstation, caro, nssreuoar trnsnn nssrennnn'rs, 'ro 'man ome saAss COMPANY, or iuansrrnnn, orare, a coaroanfrron or 'new JnnsnY.

INSULATOBJ.

Original` application led December 6, 1920, Serial No. 428,438. Divided. and this application tiled ,December 4, 1924.

This invention relates to electrical insulators, and especially to insulators for high voltages, and has for its object improved distribution of electrostatic flux and the provision of insulators Which shall be of improved construction and operation.

The invention is exemplified in the combination and arrangement of parte sho-wn in the accompanying drawings and described in the following specification, and it is more particularly pointed out in the appended claims.

This is a division of application, Serial No. 428,438, filed December 6, 1920, Patent No. 1,521,743, dated January 6, 1925.

Tn the drawing, the ligure is a vertical sectional vieu1 of an insulator embodying one form of the present invention.

In high tension insulators where tivo conductors of different potentials are separated from one another by an insulating member, it is Well known that an electrostatic field is present in which the lines of force extend through the insulator and the surrounding medium from one of the conductors to the other, Other conditions being equal these v lines of force are most closely concentrated at the portions of the insulated conductors Which are nearest to one another.V The lines of force also concentrate at-restricted pro.- jections or points formed upon the conductors. Y

lVhen insulators or dielectrics are Worked at highr pressures or potentials the resulting high electrostatic density may set up a stress of such magnitude that yit Will damage the dielectric. This stress may be set up around a conductor imbedded in a solid dielectric or around a conducting surface which operates in a medium, such as air, oil, Wax, or other medium. W hen the conducting surface operates in air, corona or brush discharge may occur at a fairly loiv voltage, particularly Where the conductor has a sharp edge or point. if corona or brush discharge occurs at normal frequency, say 60 cycles, and an electrical stress at high frequency is impressed on the electrodes, the current Will be increased in the streamer or brush discharge. Since the resistance of the streamer drops oli very rap idly with an increase in the current it is Where the frequency is high the Serial No. 753,734.

urrent may be very materially increased. This increase in current lowers the resistance in the streamer permitting the streamer tofioiv out further from the electrode. This increase in distance increases the capacitance of the streamer and permits more current to flow. The increased current in turn still further lowers the resistance in the streamer so that it extends still further. ll] here a persistent Wave at high frequency is applied, such as in Wireless Work, a comparatively small voltage -will cause the streamer to build out several feet once it is Started. This streamer may arc to ground Vor absorb considerable energy or damage any insulator which may be near the surface which discharges.

ln Wireless Work Where a high frequency generator is used, or .the equivalent, the point of brush discharge from `a conducting surfacek limits the voltage Which may be used. 1f this discharging sul face is covered by a dielectric having greater strength than the air, it Will be possible to operate at a higher voltage or stress, siuce a streamer, which Will grow to serious proportions, is prevented. lt Will be seen thatl Where this is the condition and a strong dielectric is used to cover the surface which has greatest tendency to discharge, a higher opera-ting voltage may be used.

1f a conducting surface has a tendency to discharge, the bringing of another surface charged with the same potential near will screen the first surface or reduce part of the concentration of stress. The added surfaces forms a parallel path or circuit for the electrostatic flux and hence reduces the amount of flux emanating from the original surface. Where the screening surface is insulated it may be placed in a stronger field Without danger of diseharg ing. This vWill permit it to be so placed that it Will Greatly reduce the concentration of flux from some uninsulated surface. This insulated screen or shield may be effectively used to set up a better electrical gradient in the insulator or surrounding medium and permits operation at a higher potential Withouty setting up streamers on the metal parts of an insulator or a charged surface with which itis used@ @the abete is applicable to high teascn lines tor there is Otten a strong tendency for the line to arc to ground at the insulator. This tendency to arc is greatly aggravated by surges on the system produced by resonant arcing to ground, switching surge, poor wave torni or electrical discharge, suoli as lightning. Any condition such as those named above that produces a high voltage wave or series ot waves .in the line will, ot course, increase the tendency to arcing at the time of increased voltage. rlhe starting up or slowing down ot a generator excited and connected to a parallel circuit may set up a resonant condition'and cause arcing of insulators from streamers which develop in the manner described.

In the drawing, the numeral 1() designates an insulator which may be a simple bar, or which may be et any cross-sectional shape, which working conditions require. To one end of the insulator 10 is secured a cap 11 provided with a supporting ring 12 and connected to the end out' the insulator by cement 18. The cap 11 is provided with a number ot arms 14. extending toward the opposite end ot the insulator and arranged to carry a shield ot insulating material 15. rThe shield 15 is turned back ardly at 16 providing a rearwardly extending 'told 17, and the surface ot the insulator within the backwardly turned portion is plated with a coat ing ot conducting material, as indicated at 1S. The plating 18 extends backwardly along the shield 15 and is electrically connected with the arms 111 and the cap 11 by a winding of metal wire 19 interposed between the shield 15 and the arms 14 for securing the shield in place within the arms. It will thus be seen that the plating 18 is electrically connected with the conductor se cured to the end of the insulator', and that the foremost portion of the plating 18 being` the nearest to the opposite conductor will constitute the source `from which the greatest number ot electrostatic lines ot force will emanate toward the conductor at. the opposite end oi the insulator. lt will be apparent that these lines oi' force must pass through the dielectric material ot which the shield 15 is composed, and since this material is ot greater dielectric strength than the surrounding medium, the shield 15 will olt'er an effective resistance to any tendency to tlashover along the lines ot force of the concentrated electrostatic tield. The plating 18 also provides an extended smoothly curved surface so that there are no points to cause a concentration ot the electrostatic fiux. It is sometin'ies desirable to provide a lilling of conducting material between the front. edge of the end cap 11. and insulator 10, as shown at 20. This will protect the cement 13 'from any leakage currents between the cap and the surface of the insulator.

The end of the insulator is provided with a longitudinally extending opening 21 into which a pin 22 connected with the cup 11 projects. The pin 22 may be secured to the interior oit the opening 2l, by cement 2?, t

'form a supplemental interior connection hetween the cap and th'e insulator. fthe end ot the pin 22 constitutes a radiating point Vl'or the electrostatic flux, which like the plating 18 is surrounded by an insulating medium o l' greater dielectric strength than that ot the atmosphere. rlhe inner sui-'tace ot the opening 21 may be plated with a metallic coating 24 similar to the coating 18, and this. coating should extend over the rounded surilace at the inner end ot the opeiiing where it forms electrical contact with the end ot the pin 9.2. The coating may also extend to the end ot the insulator so that it lorn'is contact with the end ot the cap 11.

The opposite end of the insulator ma),VY be provided with a duplicate ot the attachuieiit described, or it may be equipped, shown, with a simple cap 26 and an internal pin 27, similar to the pin 22.

lt is not essential to beneficial operation ot the invention that the coating 1S be. in electrical contact with the arms lit since streamers will bridge the space between the arms 11i and coating 18 even when there is considerable gap. 1t the. coatingl 15% be omitted the line oit force emanating trom the members 1d are intercepted by the member 15 and, in some cases, discharge streamers Atroni these arms will form, in el'tect, a conductor coating for the cavity within the member 153.

l claim 1- 1. An insulator comprising` an clon,` bar of dielectric material, fittings secured to said bar at opposite ends thereo't, and an electrostatic screen supported upon one of said iittings, said screen compr cup-shaped plate oi' dielectric material surrounding said elongated bar` said plate being bent backwardly at. its edges to overlie the extremities oi the fitting to which said plate is secured. i

2. An insulator comprising an elongated bar of dielectric material, littings secured to the opposite ends oi" said bar, one o1l said fittings having fingers termed thereon extending in the general direction oic the length ot said bar, and an electrostatic screen comprising a plate o15 dielectric material supported by said lingers and surrounding said bar, the edge oit said plate extending away from said lingers being bent backwardly to intercept lines of force emanating trom said lingers. Y

3. An insulator comprising au elongated bar of dielectric material, a htting sedui'ed to one end ot said bar, and a dielectric screen carried by said fitting and surround inel said bar, said screen comprising a plate of dielectric material having the edges there of disposed away from said fitting .lient outl` wardly and backwardly toform a recess separated :trom said bar by said plate, and a coating of conducting material on the inner 'tace of said recess, said tting having supporting means thereon tor said screen disposed outside of the inner portion of said plate.

4. An insulator comprising an elongated dielectric bar, a cap secured to one end of said bar, a conductor connected with said cap and extending into an internal opening in the end of said bar, an external liux screen supported by said cap and surrounding said bar, said screen comprising a plate of dielectric material having the edge thereof disposed away from said cap bent outwardly and bacliwardly, and a coating of conducting material on the edge ot said plate adjacent said cap, said coating being electrically connected with said cap and supporting means on said cap extending outside ot the inner portion ot said plate.

5. An insulator comprising an elongated member of dielectric material, a cap secured to one end oit said member and having attaching means formed thereon and spaced from said dielectric member, a plate of dielectric material connected with said attaching means and interposed between said attaching means and said dielectric member, said plate extendingbeyond said attaching means in the direction of the length of said dielectric member, the extremity or" said plate being bent outwardly and backf wardly towards said attaching means, and a covering of conducting material electrically connected with said attaching means and disposedv on the surface of said plate included in the recess formed by the bend therein.

6. An insulator comprising` a bar of dielectric material, caps secured to the opposite ends of said bar, internal electrostatic flux distributing members secured to said caps and disposed within openings'in the opposite ends ot' said bar, and an external flux screen secured to one of said caps and surrounding said bar, said external screen comprising a plate of dielectric material having the edge thereof away from its supporting` cap bent outwardly and backwardly and having a coating of conducting material disposed on the surface ot said plate included in the recess formed by said bend, said cap having supporting means thereon disposed outside of the inner portion oit said plate.

7, The combination with an insulator having a fitting at one end thereof, of a dielectric screen comprising a ring ot dielectric material, U-shaped in cross section, surrounding said insulator and having the opening ot' the t! directed towards said iitting, and conducting means extending `rom said itting to the outside oi' the inner leg of the U formed by said screen.

8. The combination with an insulator having a ittingsecured to one end thereof, of a flux screen comprising a dielectric ring, U-shaped in cross section, surrounding said insulator' and providing spaced petticoats having their edges directed toward said fitting, and supports Ltor said screen e);- tending from said litting to the outer suriace of the inner petticoat.

9. rilhe combination with an insulator having a fitting secured to one end thereof, of a flux screen comprising a dielectric ring, ll-shaped in cross section, surroundinev said insulator, and providing spaced petticoats having their edges directed towards said fitting, and a support for said screen eX- tendinn' trom said iitting to the outer surface or the inner petticoat, said inner petticoat being longer than the outer petticoat.

1G. rlhe combination with an insulator having a vfitting secured to one end thereof, oi a flux screen comprising a dielectric ring, U-shaped in cross section, su yrounding said insulator and providing spaced petticoats having their edges directed toward said titting, a support Jfor said screen extending from said dielectric member to the outer` surface of the inner petticoat, and a coating of conducting material disposed on the surface oit said screen within the space between said petticoats.

In testimony whereof I have signed my name to this specification on this 29th day of Nov. A. D, 1924.

ARTHUR O. AUSTIN.

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