US1708038A - Low-loss insulator - Google Patents

Description

- Aprfl 9, 1929. L. T. WILSON LOW LOSS INSULATOR Filed Dec. 24, 1925 INVENTOR JZMZSOIW A TTORNE Y Patented Apr. 9, 1929.

) UNITED STATESPATENT OFFICE.

LEON T. WILSON, OF EAST ORANGE, NEW JERSEY, ASSIGNOR TO AMERICAN TELE- PHONE AND TELEGRAPH'COMPANY, A CORPORATION. OF NEW YORK.

LOW-LOSS INSULATOR.

Application filed December 24, 1925. Serial No. 77,584.

This invention relates to insulators, and more particularly to insulators having a low v leakage loss.

Heretofore it has been proposed to produce insulators having low leakage losses by forming the insulators of glass or other dielectric material having very low loss angles. As is fully explained in application Serial No.

40,933, filed July 1, 1925, by H. A. Aifel and .the insulator and the dielectric hysteresis decreases as the loss angle of the dielectric increases. Therefore, if a dielectric material having a low loss angle is used in making up the insulator, the attenuation due to the action of the insulator will be correspondingly decreased.

In general, dielectric materials available for insulator construction tend to be somewhat fragile if their composition is such as to produce a very low effective loss angle.

Those materials having the desired low loss angle which have not been readily breakable are more expensive than the flint glasses which have heretofore been employed for ordinary telephone insulators. It is, therefore,

desirable that some type of insulator be available which may be constructed of flint or other cheap glass and will at the same time have a relatively low leakageloss. This result is accomplished in accordance with the present invention by so shaping the insulator that the groove in which the conductor is carried is formed on the outer periphery of a flange which is of a diameter relatively large as compared with the diameter of the pin upon which the insulator is supported, the

flange being so formed that an air-space will be interposed between the groove and the surface of the pin. As is well known, air considered as a dielectric has a loss angle which very'closely approaches zero. Also, its dielectric constant is virtually unity as compared with a value several times as greatfor air. Therefore, the air which constitutes a part of the dielectric material between the two effective plates of the condenser formed -bythe conductor attached to the groove and the supporting pin, reduces the leakage loss due to the condenser action of the insulator, first, because the loss in the air dielectric is negligible, and second, because the'capacity of the condenser is reduced.

This reduction in capacity is important in another respect. An essential factor producing leakage loss is the so-called crossarm effect. This loss is proportional to PR, where R is the resistance of the crossarm and I is the current flowing through the crossarm. Since decrease in capacity of the insulator decreases the current flowing through the crossarm, the crossarm effect is relatively greatly reduced for. a'small reduction in the current, being proportional to the square of the current.

The invention may now be more fully understoo'd from the following detailed descriptionwhen read in connection with the accompanying drawing, the figure of which illustrates the preferred embodiment thereof.

As is well understood, the attenuation resulting from the action of an insulator is largely due to dielectric hysteresis loss inherent in the condenser action of the insulator. The line wire and tie-wire connected in the outer groove of the insulator constitute one plate of a condenser, the area of which becomes enlarged when the outersurface of the insulator is wet. The pin upon which the insulator is mounted is sometimes of wood and sometimes of metal. Even when a. wooden pin is used, the wood is to some extent a conductor, and is always a conductor to a considerable extent when it iswet. Therefore, the pin forms the second plate of a condenser and between these two plates intervenes the dielectric material of the insulator itself. m

Now, dielectric hysteresis loss is a function of the capacity of the'insulator, and if the capacity is reduced, the hysteresis loss, and hence the attenuation, will be correspondingly reduced. It has been fully pointed out in an application, Serial No. 40,934, filed July 1, 1925, by H. A. Afi'el and E. I. Green, that where the insulatoris cylindrical in form so that its outer surface when wet forms anouter cylindrical plate concentric with the inner cylindrical surface of the pin, the capacity of the insulator may be materially decreased by making the outer diameter of the insulator large as compared with the diameter of the This result is accomplished in accordance 11c with the present invention by constructing the insulator, whose main body is indicated at A in the figure of the drawing, with an outwardly extending flange B at its top, so that the diameter of the flange will be large as compared with the diameter of the opening C for accommodating the supporting pin. The flange may be provided with the usual groove D for accommodating the transmission conductor and the tie-wire. By arranging this groove in a flange instead of a cylindrical insulatorhaving extremely thick walls, a considerable saving of material is eflected. Inasmuch as the decrease in hysteresis loss resulting from increasing the diameter of the groove for. accommodating the tie-wire is necessarily limited for mechanical reasons, it is proposed in accordance with the present invention to combine this structure with the novel feature of an air-gap interposed between the outer groove and thepin. Accordingly, the flange is provided with a deep groove E extending upwardly from its lower surface, this groove extending well above the upper side of the conductor supporting groove D. The groove E not only interposes an air-gap between the outer conductor and the pin, but it forms along dry path between the outer conductor and the skirt F of the insulator for practically preventing direct current leakage due to moisture particularly in wet weather. i

- It will be clear from the construction above described that a part of the dielectric intervening between the outer surface of the pin and the plate formed by the transmission conductor and tie-wire is composed of air. Air has a loss angle very closely approaching zero, and as is full explained in the application of Aflel and reen, Serial No. 40,933, the dielectric hysteresis is reduced as the loss angle decreases an becomes zero when the loss angle is zero. If we consider the insulator as a condenser, its characteristics may be thought of as a capacity due to the efiective plates on the inner and outer surfaces of the insulator and an effective conductance due to the dielectric hysteresis. The insulator then becomes equivalent to a capacity shunted by a conductance. As iswell known, if such a combination is bridged across a pair of conductors, the transmission through the condenser merely produces a change in phase and the actual attenuation loss'is due to-the leakage through the conductance. If the conductance is eliminated, there will be merely a change in. phase as the alternating current is propagated along the conductors without any actual transfer of energy from conductor to conductor. .In orther words, the current flowing through the insulator will be a wattless current if there is no conductance component or dielectric hysteresis present. It

thus becomes apparent that the interpositionof the air dielectric in the groove E between moaoae the wire mounted on the insulator and the supporting pin very materially reduces the dielectric hysteresis and this, coupled with the decrease in capacity due to the mounting of the wire upon the flange B of large diameter, results in an insulator which, though constructed of ordinary flint glass, will nevertheless be practically as 'eflicient as an insulator constructed of some special glass having a very low loss angle. v

It will be noted that the groove E is near the top of the insulator and hence a considerable distance above the crossarm. This reduces the possibility of the dry path (the surface within the groove) being rendered less effective due to splashing from the crossarm. Also, since the groove E is located close to the wire groove 1), the wet surface conductively connected to the wire is reduced. Consequently, the variation of capacity, due to change in area of the outer condenser plate with variation of weather conditions, is reduced.

In the abovedescription the invention is set forth as an improvement of such nature as to enable the insulator to be made of cheap glass, thus constituting a substitute for an insulator of ordinary form constructed of glass having a low loss angle. It will nevertheless be obvious that the insulator of the present invention may beconstructed of glass having a low loss angle, where the additional expense of the glass is not an important consideration, thus obtaining the advantage of reduction of loss due both to the improved form of the insulator and to the inherent characteristics of the glass itself.

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention as defined in the appended claims.

What is claimed is:

1. An insulator having a flange extending outwardly therefrom, a groove in said flange for carrying a line conductor and tie-wire, an interior bore within the insulator whereby it may be mounted on a supporting pin, said groove being located well below the top of said support pin and the diameter of said groove being more than twice the diameter of said internal bore, and a groove extending upwardly into said flange from the under side thereof to a point a sufiicient distance above the external groove so that an air-s ace will intervene between the said externa groove and the entire'surface of the supporting pin.

2. An insulator comprising a body of dielectric material having an. internal bore whereby it may be mounted upon a supportlng pin, a flange extending outwardly and downwardly from near the top of said insulator to provide an air-space between said flange and said body, an external groove around the periphery of said flange for accommodating a line conductor and tieswire, the diameter of said groove being more than twice the diameter of the internal bore of the insulator, and said groove being so located upon the outer surface of said flange that the air in the space between the inner side of the flange and the main body of the insulator will comprise a part of the dielectric path intervening between the conducting material mounted in the external groove and each element of the surface of the supporting pin.

3. An insulator having a flange extending outwardly therefrom, a groove in said flange or carrying a line conductor and a tie-wire, an inter or bore within the insulator whereby cember, 1925.

it may be mounted upon a supporting pin,

said 'groove'being located well below the top of sald supporting pin and the diameter of said groove being more than twice the diameter of said internal bore, tending "upwardly into said flange from the underside thereof to a pointwell above the external groove and approximately as high as said interior bore so that an air-space will intervene between the'said external groove and the supportin pin. In testimony w ereof, I have signed my name to this specification this 23rd day of De- LEON T. WILSON.

and a groove ex-

Images