US1701334A - Transformer - Google Patents

Description

Feb. 5, 1929. 1,701,334

' K. K. PAL UEFF TRANSFORMER Fig.1.-

Fig.2.

Inventor Konstantin KFaluef'f, WW

His/Attorney.

'it ma 1,701,334 PATENT OFFICE.

KONSTANTIN K.

TAL'UEFE'OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

TRANSFORMER.

Application filed April 18, 1928. Serial No. 271,044.

My invention "relates to transformers and more particularly to the insulation of high voltage transformer windings. The electrical losses in transformers appear as heat which must be dissipated rapidly enough to prevent excessive temperatures. Suitable ducts are therefore usually provided through which cooling currents of some cooling and insulating fluid such as air or oil may flow. The windings must be effectively insulated and supported and for this purpose some suitable solid insulating material having the necessary rigidity and mechanical strength is used. .These requirements often necessitate the use of two kinds of insulation, such as a solid and a fluid, arranged in series between the high and low voltage windings.

Where the high voltage winding and the low volta e winding of a transformer are separated %y two kinds of insulation arranged in series, the total voltage between the two windings will be distributed between the two insulating mediums in direct proportion to their thicknesses and in inverse proportion to their permitivities or specific inductive capacities. If the two series arranged insulating mediums are air and impregnated pa er of a type commonly used in transformers, t en be shown that the voltage gradient in the a1r will be approximately four times as great as that in the paper insulation. The dielectric strength of the air, however, is much lower than that of the paper. Now, if the total voltage is such that the air is subjected to its maximum safe stress, then the paper insulation may be subjected to only about one tenth of the maximum voltage stress which it could safely withstand. The paper insulation would, therefore, not be used economically. If the two insulating mediums are impregnated paper and a type of insulatin oil in which transformers are often immerse then the paper insulation could be subjected to only about one quarter of its maximum safe voltage stress without causing the oil insulation to break down and again the paper insulation would not be used economieally. In order to prevent a breakdown of the fluid insulation in either of these cases, a much greater thickness of the solid insulation is required than that which would otherwise be necessary for it to withstand its own volta e.

The thermal and mechanical characteristics of many transformers, particularly of those of the larger sizes, make necessary the use of both solid and fluid insulation arranged in series between the two windings and for the reasons already explained an excessive amount of solid insulation has been used in order to prevent breakdown of the fluid insulation. The distance between the windings required for the insulation has thus often been greater than desirable because the leakage reactance of a transformer is proportional to the distance between its windings. The general object of the invention is to provide an improved construction and arrangement whereby both solid and fluid insulation may be used economically and efiiciently between high and low voltage transformer windings so that the windings may be placed reasonably close together and a low reactance secured.

The invention will be better understood from the following description taken in connection with the accompanying drawing in which Fig. 1 shows an encased oil immersed transformer having windings of the concentric type insulated from each other in accordance with the invention, the figure being partly in section to reveal the construction more clearly, and Fig. 2 shows a transformer, partly in section, having interleaved windings insulated from each other in accordance with the invention.

The transformer shown in Fig. 1 includes a magnetic core 10 with a high voltage winding 11 and a low voltage winding 12 arranged concentrically with respect toeach other and about the winding leg 13 of the core and the high voltage winding 11 surrounding both the low voltage winding and the winding leg of the core. The low voltage winding 12 is insulated from the winding leg 13 by an interposed insulating cylinder 14.

The high and low voltage windings are separated by a cylindrical space containing a solid insulating cylinder 15 next to the high voltage winding and a duct 16 filled with an insulating fluid next to the low voltage winding. The transformer is immersed-in an insulating'liquid such as oil in a casing 17 so that this liquid or fluid may circulate through the duct 16 and along the surface of the low voltage winding 12 to carry away heat and prevent excessive temperature in this winding. Solid and fluid insulations having different permitivities are thus arranged 1n series between the two windings and for reasons already explained the thickness of the solid insulation and therefore the spacing of the windings and the reactance of the transformer must be much greater than that required by the voltage across the solid insulation unless there is some provision to prevent breakdown of the fluid insulation.

A layer or cylinder 18 of conductive material is carried by the insulating cylinder 15 and is preferably embedded in it between its inner and outer surfaces. The conductive layer 18 is maintained at a low voltage not diflering greatly from that of the low voltage winding 12, a convenient way of maintaining this low voltage being by a connection 19 between the conductive layer 18 and the core 10 of the transformer which is usually grounded. This conductive layer 18 will obviously protect the fluid insulation in the duct 16 from all effects of the high voltage of the winding 11.

The thicknesses of solid insulation on the opposite sides of the conductive layer 18 will of course depend upon the voltages of the two windings 11 and 12 and upon the dielectric strength of the insulation. The space between the high voltage winding 11 and the conductive layer 18 is completelyfilled with solid insulation which need therefore be only thick enough towithstand the voltage across it and need not be depended upon at all to prevent breakdown of the fluid insulation in the duct 16. The presence of the conductive layer 18 thus permits a considerably smaller quantity of insulation to be used so that the windings may be considerably closer together and this results in a considerably reduced reactance.

Generally, if the duct 16 is thick enough for a satisfactory flow of cooling fluid, this fluid alone may provide suflicient insulation between the low voltage winding 12 and the conductive layer 18. It is usually preferable, however, that there be some solid insulation to protect the inner surface of the conductive layer. In any event, the thickness of this solid insulation, if used at all, may be small .because the voltage of the winding 12 is low.

A transformer of the interleaved winding type is shown in Fig. 2, the high and low voltage windings being insulated from each otherin accordance with the invention. The high voltage winding includes two groups of winding turns 20 instead of a single group as shown in Fig. 1. These high voltage groups of turns 20 are interposed between two spaced low voltage groups of turns 21. Each group of low voltage turns 21 is separated from the adjacent group of high voltage turns 20 by an annular space containing a. duct 22 next 'to the low voltage turns for an insulating fluid such as air or oil and a solid annular insulating ring 23 next to the high voltage turns. Each solid insulating'ring 23 carries a conductive layer 24, preferably embedded in the ring,

to prevent breakdown of the fluid insulation in the duct 22 by the high voltage of the adjacent group of winding turns 20, each conductive layer 24 also permitting efficient use of the solid insulation between it and the adjacent high voltage group of winding turns so that the high and low voltage turns may be reasonably close together and the reactance reasonably low.

The invention has been explained by describing and illustrating diiferent specific forms thereof and it will be obvious that various other modifications may be made without departing from the scope of the invention as defined in the appended claims.

What I claim as-new and desire to secure by Letters Patent of the United States is:

1. A transformer including spaced high and low voltage groups of turns, the spacebetween said groups of turns containing two layers of insulation having different permitivities and arranged in series between said groups of turns, and a low voltage conductive layer carried by said insulating layer nearest said high voltage turns.

2. A transformer including spaced high and low voltage groups of turns, the space between said groups of turns containing two layers of insulation having different per- 1 mitivities and arranged in series between said tween said groups of turns containing a layer of fluid insulation next to said low voltage turns'and a layer of solid insulation next to said high voltage turns, and a low voltage conductive layer carried by said solid insulation and spaced from said high voltage turns.

5. A transformer including spaced high and 'low voltage groups of turns, the space between said groups of turns containing a layer offluid insulation next to said low voltage turns and a layer of solid insulation next tosaid high voltage turns, said solid insulation having greater permitivity than that of said fluid insulation, and a low voltage conductive layer carried by said solid insulation and spaced from said high voltage turns.

In witness whereof, I have hereunto set my hand this 13th day of April 1928.

KONSTANTIN K. PALUEFF.

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