US1788873A - Insulating bushing and electrostatic potential transformer - Google Patents

Description

G. E. .JANsSoN 1,788,873

`INSULATINCT BUSHING AND ELECTROSTATIC POTENTIAL TRANSFORMER Jan. 13, 1931.

`Filed Jan. 2o. 1928 lll 20 ZZ Patented Jan. 13, y1931 UNITED STATES cus'rav n. Jansson, or woLLAs'roN, nassacnrrsm'rs, nssIoNoa To connir une# Parrain' OFFICE j TBIGALMANUFACT'UBING CORPORATION, OF SOUTH BOSTON, MASSACHUSETTS, A

coaroaa'rron or 'ua'ssacnusn'rrs msunarnro RUSHING AND anamnesi-Anc ro'raN'rIaL 'rnansroam Application med :tummy` ao, 192s. 4serial no. 248,237.

4 This invention relates to high tensioninsulating bushings and electrostaticV potential transformers associated therewith.A Y

` It is oftendesirable to derive small 5 amounts of power from a high tension alternating current line for the pur ose of operatin instruments to indicate t e voltage of the ine, for synchronizing uses and the like.

The use, of high tension electromagnetic 1e transformers for this purpose is undeslrable because of the high cost ofthe transformers since Athey must be insulated against full line potential and must have a prlmary winding which will withstand full line otential. Consequently, it has been ro ose down the potential of the line y the use of condensers which are connected in series with the instrument and across the line. The condensers allow .a small but suiciently large current to. ass, and the current, through, and the potential at, the terminal of the insulator also been `proposed to use an insulator, as a string of suspension insulators as the capacif tance, the lnsulator thus performing the double function of supplying suicient en` ergy for operating the instrument and also for insulating the instrument from the line potential.v y l It is an object of the present invention to provide a high tension insulating bushing such as used with oil filled switches, transformers,` and the like with means Vwhereby a small amount of energy can be derived from the line connected with the bushing conductor for the operation of instruments and the like. v

A further object of the invention is the to step Figs. 2- and 3 are sectional details of modiyfied bushing constructions, wherein the condenser plate'is protected against flash-over within the bushing.

Fig. 4 is adiagrammatic View of the elec- ,trical circuit of the insulatorand its capacity element. ,A As here shown the oil filled bushing embodying the invention comprises upper and lower porcelain shells v'10 and 12 respectively" which are secured-in alignment 4an are cementedv to yattaching collars 14 and 16 respectively, which collars are 'clamped together switch or transformer or, it may be, the

wall of a building.` A conductor 22 extends axially through the bushing'and has a tera high tension line and a terminal `26 at its lower end for connection with electrical apparatus or with the movable member of an electric switch, not shown.

A plurality of insulating tubes 28, 30 and 32 are disposed in spaced concentric relation about said conductor 23 and the ybushino` includinv the space between said tubes is `filled with ,011. The bushing so far described is of more or less usualconstruction.

In accordance with this invention,-I provide a condenser element in the form, preferably, of a metal tube 34 which is interposed between the insulating tube 32 and the shells 10l and 12. Said metal tube may be secured 'either to the insulating tube 32 or to the lower shell 12, or, as here shown, to both of them by bodies of cement 36 and 38 respectively. An insulating ,bushing 40 is hxed iny an oil tight manner in the attaching collar 16 and has a conductor 42 therein which extends through the bushing 40 into the inte'-y rior of the shell 12 and is connected electrically with the condenser tube 34 by ak lead 44. Said conductor 42 is extended through the bushing and has a terminal 46 to `which a circuit leadl can be connected. The condenser tube 34 is electrically insulated both from the high tension conductor 23 and from l. vminal 24 at its upper end for connection with follows invariation the line potential. It has the ground and thus is caused to assume a potential the valve of which depends upon its distance from the high tension conductor, or its position between said conductor and the collars 14 and 16, which are at ground potential, and also upon the dielectric capacity of the insulating material between said tube and the high tension conductor. The potential of the condenser tube can thus be measured by connecting a volt meter between the terminal 46 and the ground and, since the potential of the condenser plate varies in proportion to variations of potential of the conductor 22, the volt meter, if properly calibrated, wil-l read in terms of line voltage.

The amount of current which will flow through the circuit including the condenser element 34 is a function of the area of the element; and sufficient current to operate volt meters, synchronizing instruments and the .like can be derived from the condenser element without making said element unduly large and without materially decreasing the dielectric strength of the bushing.

In the modified construction illustrated in Fig. 2, the collars 14a and 16a, corresponding with the collars 1 4 and 16 of Fig. 1, are connected by and are integral with a metal shell 48 of substantial length that has the attaching flange 20a located at the upper end thereof. The shell is exposed to the interior of the bushing. A condenser tube 34a is located within the bushing close to and spaced and insulated from Said shell 48, and a terminal 50 thereof is taken out of the shell through an insulating bushing 52 located beneath the attaching flange 20a. The function of the condenser tube is as described in connection with Fig. 1. Annular rings 54 are connected electrically with the shell 48, which is at ground potential, and overlie and are spaced from the upper and lower ends of the condenser tube 34a and are located between said tube and the high .tension conductor of the bushing and thus serve to protect the condenser tube from a flashover arc, and especially one due to a puncture of the dielectric more or less radially from the high tension conductor, the arc striking one or the other of said rings, rather than the tube.

In the modification illustrated in Fig. 3 the metal ground shell 48a, corresponding with thef shell 48 of Fig. -2, is integral with the lower collar 16a buti's separate from the upper collar 14a, and is connected detachably therewith by bolts passed through flanges 56 and 58 of said upper collar'and shell respectively. The 'condenser tube 34a is located within the bushing at and spaced from the shell 48a and the terminal 46 thereof is brought out through the bushing 40, which is located above the supporting flange 20a of v the shell 48a. In this modification the collars 14a and 16a have inwardly extendedl - flanges 60 and 62 which are spaced from and radially inward beyond said project into the oil space of the high tension bushing especially above and below the upper and lower ends of and beyond the condenser tube so that the tube, in effect, occupies a recess in the grounded shell 48 and is protected against internal flash over by said flanges 60 and 62.

In Fig. 4 a diagrammatic representation of the electric circuits of the condenser elements is illustrated. In this figure, the condenser element is connected through the primary winding 64 of a step up transformer to ground and the instrument 66 is connected with the high voltage secondary winding 68 of thel transformer. If desired, other well-known forms of voltage or current-amplifying apparatus can be substituted for the transformer in a manner unnecessary to illustrate. The intrument circuit is grounded by the conductor 7() as a precautionary measure.

I claim:

l. Aninsulating bushing comprising an outer shell, an inner high tension conductor, an insulated condenser plate located within said shell and between it and said conductor and having a terminal thereof extended through said shell, and a grounded metal flash-over protective member overlying the end of said condenser plate and projecting radially inward beyond said condenser plate toward said high tension conductor and providing a shorter breakdown path between ground and said conductor than between said conductor and said condenser plate.

2. An insulating bushing comprising an outer shell, an inner high tension conductor, an insulated condenser plate located within said shell and between it and said conductor and having ay terminal thereof extended y through said shell, and grounded metal flash-over protective members located respectively at and overlying the top and bot'- tom of said condenser plate and projecting late toward said high tension conductor an providing a shorter breakdown path between round and said conductor than between said conductor and said condenser plate.

3. An insulating bushing having a ground tube having upper and lower vrearwardly directed Walls provided with inturned ends providing an internal recess, insulating shells carriedby said ground tube at the ends thereof, a high tension conductor extended through said vshells and tube, and an insulated condenser plate located in said internal recess with the inturned ends'of said walls located between it and said high tension conductor and having an insulated terminal thereof extended through said ground tube.

In tesimony whereof, I have signed my name to this specification.

- GUSTAV -EQJIANSSON.

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