US1715889A - Insulator - Google Patents

Description

A. O. AUSTIN June 4, 1929.

INSULATOR Original Filed Dec. 6, 1920 in m f/YVE/vra Md (0. M

Patented June 4, 1929.

UNITED STATES PATENT OFFICE.

ARTHUR O. AUSTIN, OF BARBERTON, OHIO, ASSIG-NOR, BY MESNE ASSIGNMENTSyTO THE OHIO BRASS COMPANY, OF MANSFIELD, OHIO, A CORPORATION 01 NEW JERSEY.

INSULA'IOR.

Original application illed December 6, 1920, Serial No. 428,488. Divided and this application filed 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 provi- 5 sion of insulators which shall be of improved construction and operation;

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

This is a divisionof application, Serial No. 428,438, filed Dec. 6, 1920.

In the drawing, the figure is an elevation of one end of an insulator partly in section showing one form of the invention.

In high tension insulators where two 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 lines of force are most closely concentrated at the portions of the insulated conductors which are nearest to one another. The lines of force also concentrate at restricted projections or points formed upon the con notors.

When insulators or dielectrics are worked at high pressures or potentials the resulting high electrostatic density may set up a stress of such magnitude that it will damage the dielectric. This stress may be set up around a conductor imbedded in a solid die ectric or around a conducting surface which operates in a medium, such as air, oil, wax, or other medium. When the conducting surface operates in air, corona or brush discharge may occur at a fairly low 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 imressed on the electrodes, the current will be increased in the streamer or brush discharge. Since the resistance of the streamer drops ofl very rapidly with an increase in the cur- Serial No. 753,795.

rent it is seen that where the frequency is high the current may be very materially increased. This increase in current lowers the resistance in the streamer permitting the streamer to flow 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. Where a persistent wave at high frequency is applied, such as in wireless work, a comparatively small voltage will cause the streamer tobuild out several feet once it is started. This streamer may arc to ground or absorb considerable energy or damage any insulator which may be near the surface which discharges.

In wireless work where a high frequency generator is used, or the equivalent, the point of brush discharge from a conducting surface limits the voltage which may be used. If this discharging surface is covered by a dielectric having greater strength than the air, it will be possible to operate at a higher voltage or stress, since a streamer, which will grow to serious proportions, is prevented. It will be seen that where this is the condition and a strong dielectric is used to cover the surface which has greatest tendency to discharge, a higher operating voltage may be used.

If 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. Ihe added surface 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 discharging. This will 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 mediam and permits operation at a higher potential without setting up streamers on the metal parts of an insulator or a charge surface with which it is'used.

The above is applicable to high tension lines for there is often a strong tendency for the line to are to ground at the insulator. This tendency to are is greatly aggravated by surges on the system produced by resonant arcing ground, switching surge, poor wave or electrical discharge, such as lightning. Any condition such as those named above that produces a high voltage wave or series of waves in the line will, of course, increase the tendency to arcing at the time of increased voltage. The starting up or slowing down of 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 form of the invention shown in the drawing, an insulator 29 is provided with an end cap 30 and a series of external flux distributing members 31. These members comprise supports 32 which carry the distributing members 31. The members 31 are composed ofdielectric material having a central opening 33 internally coated with a metallic covering 34 from which the lines of force emanate. The coat-ing 34 may be brought into direct contact with the support 32, or for high potential work the cement will afford sufiicient conductivity between the two parts. It will be apparent that the covering 34 is surrounded with the insulating material of the member 31, so that any tendency to dischar e along the lines of force emanata ing from t e covering 34 is prevented by the insulating material. tion of the shield or flux rod relieves the terminal portion of the insulatin member for the flux rod of dangerous surface charging currents because of the resistance it offers to such currents and permits operation at high voltages. Where a construction of this kind is used a bug, raindrop or other projection is not so likely to cause a burr or are to form on the insulator shield as would be the case if the surface of the shield were of conducting material. This is due to the fact that the insulation limits the surface currents. This is particularly important in radio insulators used on a persistent wave.

The flux control members may be provided with ribs 35 added to the members 31 to break up the surface into small sections and limit the charging current in case streamers start. The ribs keep down the charging current in the small streamers by cutting the surface up into small sections. Where streamers start the resistance decreases and the length of the streamers increase as the current increases. Limiting the current in any streamer is then of particular advantage.

The external insula I claim 1. An insulator comprising a bar of dielectric material, a supporting cap secured to one end thereof, metal pins mounted on said cap and spaced about the periphery thereof and extending therefrom in the direction of the length of said bar and inclined outwardly from said bar, and members of dielectric material having internal openings therein secured to the extremities of said pins, said openings having the inner surfaces thereof provided with a coating of conducting material and having the ends of said openings away from said pins closed to form a completecovering of dielectric material for the conductors consisting of said pins and coatmgs.

2. An insulator comprising a bar of dielectric material, a cap secured to said bar, pins pro ecting outwardly from said cap and in the direction of the length of said bar, hollow dielectric members supported on the ends of said pins, said members having the inner surface thereof coveredwith a coating of conducting material and having the ends thereof away from said pins enlarged to provide increased insulation at the ends of said memers.

3. An insulator comprising a bar of dielectric material, a cap fixed at one end of said bar, pins projecting outwardly from said cap in the direction of the length of said bar, tubular dielectric members having open ends mounted on said pins and having the ends thereof opposite said pins enlarged and closed, and conducting material within said tubular dielectric members connected with said pins.

4. An insulator comprising an elongated bar of dielectric material, a cap secured to one end of said bar, a plurality of pins projecting outwardly at an angle away from said cap and forwardly in the direction of said bar, and hollow members of dielectric material eachhaving one end open and mounted on'said pins and having its opposite end closed and enlarged, conductingmaterial disposed within said members and electrically connected with said pins, and ribs formed on the outer surfaces of said members to divide said surfaces into sections.

5. In combination,-an insulator bar, a cap secured to one end of said bar and a plurality of flux screens mounted on said cap and disposed about said bar in spaced relation to one another, each screen comprising a conductor member extending from said cap outwardly and along said bar, and a covering of dielectric material disposed over the end of each of said conductor members.

6. In combination, an elongated bar of dielectric material, a fitting secured to one end of said bar, and 'a flux screen comprising a plurality of conductor members secured to said fitting and extending outwardly therelfrom and along said bar, hollow dielectric members having open ends disposed over the ends of said conductor members respectively and having the ends extending away from said conductor members, closed, conducting material within said hollow dielectric mem-

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