US2300910A - Transformer - Google Patents

Description

Nov. 3, 1 942;

G. CAMILLI TRANSFORMER Filed Sept. 10, 1940 m m I p I p u a 1 n n Inventbr: Guglielmo Ca b9 )6 illi,

His Attorney Patented Nov. 3, 1942 TRANSFORMER Guglielmo Camilli, Pittsfleld, Mass., assignor to General Electric Company, a corporation of New York Application September 10, 1940, Serial No. 356,179

12 Claims.

My invention relates to transformers, and although not limited thereto, it has particular application to instrument current and potential transformers.

It has been the practice to manufacture instrument transformers, such as current transformers, with crepe paper around the high voltage winding for insulating'that winding from the low voltage winding, the transformer being encased in a porcelain shell or other suitable container. The transformer is vacuum treated and dried to remove all moisture and is impregnated with any suitable insulating fluid, such as oil. The porcelain shell is then hermetically sealed. Should the porcelain, however, be broken in service, the oil will drain oil? and the high voltage winding will be exposed to the atmosphere so that it will absorb moisture, and the transformer must be returned to the factory for complete retreatment. Besides the inconvenience in returning the transformer to the factory, the retreatment of insulation which has been wet with either oil or any other fluid which is used to impregnate the insulation, is a considerable problem. It appears that the moisture particles, which reach the insulation, are surrounded by a film of insulating fluid which is very difficult to break off for the releasing of the moisture. In view of this difliculty of removing moisture from a winding which has already been treated with oil it is usually easier to remove all insulation from the winding and rewind with fresh insulation and then go through the procedure of vacuum treating the winding and impregnating with the insulating fluid.

In order, therefore, to simplify the procedure of reconditioning the transformer following the breakage of the porcelain or the enclosing container, the solid porous insulation has been surrounded with a fluid impervious covering, such as cellulose acetate, so that once the insulation is impregnated, breakage of the porcelain will not drain the liquid therefrom. Electrical apparatus provided with a fluid impervious covering is described and claimed in a copending application, Serial No. 288,000, filed August 2, 1939, and issued to me on September 29, 1942, as Patent 2,297,605, and which is assigned to the same assignee as this present invention. However, with the fluid impervious bag or covering surrounding the high voltage winding for preventing the insulating fluid from leaving the solid porous insulation once it has been impregnated, there is the problem of efficiently and quickly removing all moisture from the insulation after it has been 55 covered by the fluid impervious covering and before it is impregnated with the insulating fluid. A It is, therefore, an object of my invention to provide an improved structure for transformers of the above-mentioned type.

It is another object of my invention to provide an arrangement through which the solid porous insulation of a transformer may be impregnated with a fluid in an improved and eflicient manner.

It is a further object of my invention to provide a structure for transformers which will facilitate the vacuum treating and drying operation thereof.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing, Fig. 1 is a sectional side elevation of a current transformer which is provided with an embodiment of my invention; Fig. 2 is a side elevation in partial section of the insulated high voltage winding of the transformer illustrated in Fig. 1 Fig. 3 is a side elevation in partial section of the insulated high voltage transformer winding illustrated in Figs. 1 and 2 provided with a modification of my invention, and Fig. 4 is an end elevation taken along the lines 4-4 of Fig. 3.

In the arrangements illustrated in the drawing, I have provided a tube between the high voltage winding and the surrounding insulation of any suitable electrical apparatus, such as a transformer. This tube has one end which extends to that point of the winding most remote from the leads, and another end which may be connected to a source of insulating fluid. Thus, after the drying operation the high voltage wind-' ing, which has porous insulation surrounding it and a fluid impervious covering surrounding the insulation may have the insulating fluid introduc'ed first into that part of the space within the fluid impervious covering most remote from the leads, or the lowermost portion of the winding. In this manner the insulating fluid may be introduced so that it will displace, or push to the top any remaining moisture or air which may be within the space surrounded by the fluid impervious covering. Furthermore, in order to facilitate the drying operation of the high voltage winding, I may also provide spacers between the fluid impervious covering and the solid porous insulation so that the moisture may be withdrawn from the paper through the space formed between the insulation and the covering. The flliing tube may also be employed in this arrangement, if desired.

Referring to the drawing, and particularly to Fig. l, I have illustrated a current trans-former having a casing or porcelain shell Iii, an insulated high voltage winding ii, and a low voltage-winding l2 which links the high voltage wind ng. The high voltage winding is provided with leads I! and I! which may extend through the casing where terminals l5 and I. are provided so that the high voltage winding may be suitably connected to an electrical line. The low voltage winding i2 is provided with leadsi1 and I8 which extend through the base of the casing Ill where terminals ll and 20 are providedin order that the low voltage winding may be suitably connected to the desired instrument or other suitable equipment. Referring to Fig. 2 the high voltage winding Ii is provided with any suitable number of winding turns 2|, which are connected to the leads II and I. In order to insulate the high voltage winding from the low voltage winding suitable insulation 22 is placed around the high voltage winding turns 2| and around a suflicient portion of the leads II and il so as to keep the creepage path between the uninsulated portion and ground to a safe length; that is, so that the voltage drop along the path will not be greater than a safe value, such as volts per mil. This insulation may be of any suitable type, such as wrappings of crepe paper'which may be applied to a suitable thickness. Thus the insulating covering substantially closes the winding and is contiguous with outer surfaces of turns of the winding which, as will be seen in Fig. 2 restricts passages through which gaseous impurities may be withdrawn from interstices between the winding turns. when taping the leads, each may be insulated a sufficient amount as to withstand the voltage drop between them and then both may be taped together for a sufllcient length. In order to prevent any air or moisture from coming in contact with the solid porous insulation 22 once it has been impregnated with a suitable insulatin fluid, a fluid impervious covering 2| is provided around and relatively closely fltting the insulation which surrounds the winding turns 2i and the leads II and II, and this covering may be of any suitable type. such as cellulose acetate. The covering is so applied as to leaNe a small portion of the insulation uncovered, such as the uppermost portion. as is illustrated in Fig. 2. A protective covering 24 of any suitable type, such as cotton tape, may be applied around the fluid impervious covering for protecting it from abrasion.

In transformers built according to the above mentioned application, after the insulated high voltage winding has been surrounded with a fluid impervious bag or covering, and after it has been treated to remove moisture from the insulation.

insulating fluid is introduced into the space inside this fluid impervious covering. However, even after the winding has had the conventional treatments there may remain traces of moisture, and although a vacuum process has been employed traces of air may also remain in the insulation. Any air or mositure pockets in the impregnated insulation are, of course, undesirable. Therefore, in accordance with the present invention in order to be able to introduce the insulating fluid from a suitable portion, such as the lowermost portion of the high voltage winding so that'impurities,

such as any traces of air or moisture therein will be forced upwardly or displaced -by the introduced fluid during the filling operation, I provide a tube 25 of any suitable material within the fluid impervious covering 23. As the insulation has a portion near the upper and adapted to communicate outside the covering, the impurities may be forced out this passage. This tube may be positioned at any desirable place, such as between the winding turns and the insulation. Thus if paper insulation is used, it may be wrapped around the turns and tube. However, of course, some insulation may be placed between the turns and leads and the tube. One end or the exhaust end of the tube extends to the most remote point from the leads or, to that portion of the insulated winding which is the lowest part, and the other end or intake end may extend through a suitable hole 28 in the casing so that it may be connected to a suitable source of insulating fluid, which is diagrammatically indicated by a vessel 21 in Fig. 1, In order to further facilitate the impregnation, and, if desired, for use during the vacuum drying process, a vacuum pump (not shown) may be connected through the pipe 28 to the space within the casing or porcelain shell l0.

After the transformer winding has been assembled as illustrated in Fig. 1, it may receive any suitable process, such as a vacuum treatment, in order to remove air and moisture from the insulation. The insulating liquid such as oil, or its equivalent, or any other suitable fluid, may then be introduced through the tube 25 from the source 21. This fluid will be introduced into the space within the fluid impervious covering at its lowermost portion and any traces of air or moisture which may be within the covering will be pushed above the fluid as the quantity of fluid within the covering is increased. When the insulation and the interstices between the winding turns in the space within the fluid impervious covering are completely saturated the space around the covering and inside the casing ll may also be completely fllled with the fluid in any suitable manner. such as through the port Illa. Before this is done the pipe 28 and that part of the pipe 25 extending outside the casin may be removed, and the remaining parts may be plugged so that after the casing I0 is fllled it may be hermetically sealed. The transformer is then ready for use.

I have illustrated in Fig. 3 an improved arrangement for facilitating the drying operation of a transformer having a fluid impervious covering around the insulation which includes any suitable number of spa'cers 20 of suitable insulating material, such as pressed board which are placed between the insulation 22 and the fluid impervious covering 23 and extend substantially to the uncovered or upper portion of the insulation. These spacers may be of any suitable shape and. as illustrated in Fig. 3, they are tapered, the smaller portion being near the bottom of the high voltage winding. The spacers 29 are inserted only in the outside periphery cf the high voltage winding. as will be seen in the end elevation of Fig. 4, so that the high voltage winding will dry from the inside out. It will, of course. be apparent that the spacers may be applied on the inside periphery only or, if desired, they may be suitably spaced all the way around the periphery. The fllling tube 25 may also be employed in this modification. Thus the air and moisture may be withdrawn through the spaces formed between the spacers. The spacers also, if desired, may be placed between the insulation and the winding turns.

It will be seen therefore. that I have provided an improved arrangement for introducing an insulating fluid into a transformer, or any other suitable electrical apparatus, within the space surrounded 'by a fluid impervious covering. Thus, the insulating fluid may be, introduced at the lowermost portion of the winding in order that any traces of air and moisture may be displaced as the space within the covering is filled with the fluid. I have also provided an improved arrangement for facilitating the drying Operation when a fluid impervious covering is employed. Thus. any suitable number of spacers may be'placed between the fluid impervious covering and the contiguous insulation in order to provide a path through which the air and moisture may be removed. I

Modifications of the particular arrangements which I have disclosed embodying my invention will occur to those skilled in the art, so I do not desire my invention to be limited to the particular arrangements set forth and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope-of my invention.

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

1. la transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding and relatively closely fitting said insulation, said insulation having a portion near the upper end of said winding adapted to communicate outside said as covering, and a tube havingan exhaust and within said covering for fllling the space within said covering with an insulating fluid from said exhaust end so that impurities may be displaced by said fluid during the filling operation.

2. A transformer including a winding, a terminal lead extending from said winding, solid porous insulation surrounding said winding and lead, a fluid impervious covering surrounding and relatively closely fitting said insulation, said insulation having a portion near the upper end of said winding adapted to communicate outside said covering, and a tube within said covering and extending from said lead to that portion of the winding most remote from. said lead for n11- ing the space within said covering. with an insulat ing fluid from said remote portion so that impurities may be displaced by said fluid during the fllling operation.

3. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding and relatively closely fitting said insulation, said insulation having a portion near the upper end of said winding adapted to communicate outside said covering, and a tube between said winding and said insulation and having an exhaust end within said covering for filling the space within said covering with an insulating fluid from said exhaust end so that impurities may be displaced by said fluid during the fllling operation.

4. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding and relatively closely fltting said insulation, said insulation having a portion near the upper end of said winding adapted to communicate outside said covering, and a tube within said overing and having one end terminating inside said covering and the other end projecting outside thereof 75 forfilling hemcewithinsaidcoveringwithan insulating fluid from that portion of said space surrounding said inner end of said tube so that impurities may be displaced by said fluid during the filling operatiom 5; A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding and relatively closely fitting said insulation, said insulation having a portion near the upper end of said windingadapted to communicate outside said covering, a casing surrounding said covering, and

a tube having an exhaust end within said covering for filling the space within said covering with an insulating fluid from said exhaust end so that impurities may be displaced by said fluid during the filling operation.

6. A transformer including a winding, solid porous insulationsurrounding said winding, a

fluid impervious covering surrounding and relatively closely fitting said insulation, said insulation having a portion near the upper end of said winding adapted to communicate outside said covering, a casing surrounding said covering so that said transformer may be surrounded with an insulating fluid, and a tube within said casing and having one end'terminating inside said covering and the other end projecting outside said casing for filling the space within said covering with an insulating fiuid from said one end so that impurities may be displaced by said fluid during the filling operation.

7. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding said insulation, a casing surrounding said covering so that said transformer may be surrounded with an insulating fluid, means for connecting a vacuum pump to said casing so that the pressure therein may be reduced when said transformer is filled with an insulating fluid, and a tube within said covering and having one and terminating inside said covering and the other end projecting outside said casing for filling the space within said covering with an insulating fiuid.

8. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding said insulation and leaving a portion near the upper end of said winding uncovered, and spacers within said covering and extending substantially to said uncovered portion for facilitating the drying of said insulation during a treating step.

9. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding said insulation and leaving a portion near the upper end of said winding uncovered. and spacers between said covering and said insulation and extending substantially to said uncovered portion for facilitating the dryingof said insulation during a treating step.

10. A transformer including a winding. a solid porous insulation surrounding said winding, a

fluid impervious covering surrounding said insulation and leaving a portion near the upper end of said winding uncovered, and spaicers between said covering and said insulation and extending substantially to said uncovered portion for facilitating the drying of said insulation during a treating step, and a tube having an exhaust end within said covering for filling the space within said covering with an insulating fluidfrom said exhaust end so that impurities may be displaced by said fluid during the filling operation ii. A transformer including a winding, solid porous insulation surrounding said winding, a fluid impervious covering surrounding said insulation and leaving a portion near the upper end of said winding uncovered, and spacers between said covering and said insulation and extendin substantially to said uncovered portion for facilitating the drying of said insulation during a treating step. and a tube between said winding and said insulation having an exhaust end within said covering for filling the space within said covering with an insulating fluid from said xhaust end so that impurities may be displaced by said fluid during said filling operation.

12. An electric apparatus including a winding having a plurality of turns, an insulating covering substantially enclosing said winding and contiguous with outer surfaces of turns 01 said winding thereby restricting passages through which gaseous impurities may -be withdrawn from the interstices between said winding turns, and tube means within said insulating covering adapted to communicate outside said insulating covering and with an exhaust end adjacent the approximate lowermost portion of said winding through which an insulating fluid may be introduced into the winding structure.

GUGLIELMO OAMILLI.

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