US2029140A - Bushing for transformer casings - Google Patents

Description

Jan. 28, 1936. D, TREANOR BUSHING FOR TRANSFORMER CASINGS Filed Nov. 1, 1934 m w =2 3mm N Ut e w vd WW d Ey b Patented Jan. 28, 1936 PATENT OFFICE BUSHING FOR TRANSFORMER CASINGS Edward D. Treanor, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Application November 1, 1934,- Serial No. 750,993

3 Claims.

My invention relates to bushings for transformer casings. Metal casings for transformers, particularly of the distribution type, are often provided with overhanging pockets in the side walls, the leads from the transformer windings being brought out of the casings through the insulating bushings extendingthrough these pockets and with the outer ends of the bushings extending downwardly from the pockets and adjacent the side walls of the casings. The general object of the invention is to provide an improved construction and arrangement of bushings of this type which shall be compact and mechanically well protected from breakage and 5 which will offer eifective protection to the transformer from excessive voltages on circuits con nected thereto through the bushings.

the following description taken in connection with the accompanying drawing in which Fig. 1 is a side view of a metal-encased transformer with a bushing arranged in accordance with the invention, part of the transformer casing broken away to show details; Fig. 2 is an enlarged sectional view of the bushing with a small adjacent section of the transformer casing; and Fig. 3 is a. view of the outer end of the bushing.

Like reference characters indicate similar parts in the different figures of the drawing. The transformer l0 shown in the drawing is immersed in an insulating liquid H in a metal casing 12 having an outwardly projecting side pocket 13. An insulating bushing l4, which may be formed of porcelain, is secured through an opening in the bottom of the pocket l3 by a clamp I 5, a gasket l6 being provided to seal the joint between the edge of the opening in the pocket l3 and a shoulder on the bushing I4. The upper end of the bushing I4 is curved inwardly through the pocket l3 and. into the interior of the casing l2. A lead I! from a winding of the transformer It! extends through the bushing to an outside terminal l8 sealed through the outer end of the bushing and provided with a clamp 19 to permit a conductor 20 of an external circuit to be secured to the terminal.

The metal casing l2 may be and usually is at ground potential and the terminal l8, which is often at rather a high potential, must be sulficlently spaced from the casing to prevent an are between these two parts. It is desirable, however, that the outer end of the bushing l4 and terminal "3 be as close as possible to the adjacent side wall of the casing l2 in order to require no unnecessary floor space and also to be The invention will be better understood from mechanically protected as much as possible by the overhanging pocket l3. To secure these advantages the outer end of the bushing I4 is provided with an integral flange or wall 2| projecting between the terminal I8 and an adjacent side 5 wall of the casing I2. This flange increases considerably the breakdown distance between the terminal and the casing and permits the terminal I 8, and therefore the outer end of the bushing, to be positioned close to the casing and under the 10 pocket l3 so as to require minimum floor space and secure maximum mechanical protection from the overhanging pocket.

A metal electrode 22 is secured to the terminal [8 and projects away from the casing l2 through 15 an opening 23 in the side of the flange 2i opposite the casing. The outer end of the electrode 22 may be curved upwardly toward the adjacentouter portion of the pocket [3. The external lead 20 may also pass from the terminal I8 20 through the opening 23 in the flange 2|.

The outer end of the bushing M with the terminal [8 projects below the level of the insulating liquid in the casing I2 andif an arc should occur between the terminal l8 and the adjacent side 25 wall of the casing I2 a hole might be burned in the casing wall with serious results. Considerable liquid would escape and this liquid is usually highly inflammable and especially so when at the operating temperature of the transformer. 30 The are very probably would ignite the escaping liquid and a serious fire would result. The outer end of. the electrode 22 should consequently be spaced suificiently near the outer part of the pocket l3 to provide a preferential breakdown 35 path for any are due to excessive voltage of the I terminal l8 such as might result from lightning or other surge reaching the terminal by way of the external circuit conductor 20. The outer portion of the pocket I3 is above the level of the liquid in the casing l2 so that if a hole is burned in the pocket I3 by an are, no liquid can escape.

It is desirable of course that the voltage necessary to start an are between the electrode 22 and the pocket l3 be less than that which might cause 45 damage to the transformer l0 and its windings so that the transformer is protected from electrical disturbances in the externalcircuit to which it is connected.

The invention and its-advantages have been 5i explained by describing and illustrating a preferred form thereof but it will be obvious that changes may be made without departing from the spirit of. the invention and the scope of the appended claims. 55

1. A transformer casing having an overhangingside pocket, an insulating bushing secured through the bottom of said pocket, a transformer terminal secured in the outer end of said bushing, said bushing having an integral flange extending between said terminal and the adjacent wall of the casing and having an opening in its side opposite the casing, and an electrode secured to the terminal and extending through said flange opening with its outer end spaced from the outer part of said pocket to provide a discharge gap.

' 2. A transformer casing having an overhanging side pocket, an insulating bushing secured through the bottom of said pocket, a transformer terminal secured in the outer end of said bushing, an electrode secured to the terminal with its outer end spaced from the outer part of said pocket to provide a discharge gap, and an insu-= lating liquid in said casing with its level between that of said terminal and said outer part of the pocket.

3. A transformer casing having an overhanging side pocket, an insulating bushing secured through the bottom of said pocket, a transformer terminal secured in the outer end of said bushing, said bushing having an integral flange extending between said terminal and the adjacent wall of the casing and having an opening in its side opposite the casing, an electrode secured to the terminal and extending through said flange opening with its outer end spaced from the outer part of said pocket to provide a discharge gap, and an insulating liquid in said casing with its level between that of said terminal and said outer part of the pocket.

EDWARD D; TREANOR.

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