US1947085A - Electrical apparatus - Google Patents

Description

INVENTORS alr/es F afm 2mes 7'.' orf G 5. #Wj ATTORNEY Filed sept. 22, 1951 Feb. 13, 1934-.,

WITNESSES Patented Feb. 13, 1934 PATENT OFFICE 1,947,085 ELECTRICAL APPARATUS Charles F. Hill, Edgewood, and James T. Goff, Wilkinsburg, Pa., assignors to Westinghouse Electric and Manufacturing Company, a

ration of Pennsylvania como' Application September 22, 1931 Serial N0.. 564,280

6 Claims.

This invention relates to electrical apparatus in which the active parts are subject to heating and which is required to be insulated from the walls of a surrounding tank or container.

The present invention is more particularly directed to a construction of electrical apparatus, such as transformers, in which novel means is employed for insulating and cooling the apparatus.

It is common practice to immerse electrical apparatus, such as transformers, in an insulating and cooling oil. There are, however, limitations to the use of oil as an insulating and cooling material, because of the fire hazards that accompany its use and because of the necessity of in specting the transformer from time to time to insure that the oil is maintained at the proper level in the tank, and retains its normal insulating characteristics. Under certain conditions of operation of transformers employing insulating oil, explosive hydrocarbon gases or hydrogen or a mixture thereof, may bev given off from the transformer oil which may unite with the oxygen of the air and form an explosive gaseous mixture. Such a mixture is especially dangerous whenvthe transformer is located in an enclosure such as the room of a building.

It is an object of our invention to provide a new material for insulating electrical apparatus, such as transformers, that will reduce fire hazards and be substantially explosion proof.

It is a further object of our invention to provide such an insulating material that possesses sufficiently high dielectric strength and high heat conductivity.

It is another object of our invention to provide an insulating material for surrounding the apparatus that is permanent in character and does not require frequent servicingy in order to maintain the desired quality andy quantity of insulating material within the tank containing the apparatus.

In accomplishing the purpose of our invention, we dispense with the usual insulating mineral oil and substitute, therefore,.an\inorganic granular or powdered material having high dielectric strength and high heat conductivity and impregnate this material with an insulating and heat J conducting material having a binding action. This material may be a polymerized vegetable oil, such as perilla, linseed oil, or tung oil, or a fusible salt, such as boric acid, potassium nitrate, or sodium nitrate, or it may be a gum or synthetic resin that solidines in a non-porous condition, that is, without giving oir moisture, such as halowax.

We prefer, however, to employ a polymerized vegetable oil, and particularly, jelled tung oil.

'I'he single figure of the drawing is a side elevation partially in section, illustrating a transformer organized in accordance with our invention.

Referring to the drawing, a tank 1 is employed which contains the transformer or other electrical apparatus, and, as illustrated, comprises a core 2 upon which is wound a primary winding 65 3 and a secondary winding 4. The primary winding is connected by means of conductors 5 and 6 to the terminals '7 and 8, and the secondary winding 4 is connected by means of conductors 9 and l0 to the terminals 11 and 12. About the core and coils of the transformer, the electric insulating material 13. is placed and by means of this material the heat generated in the core and coils of the transformer is conducted to the tank wall.

The refractory powdered or granular material, together with the bonding material, may be placed in the tank in one of several ways. Tha two materials may be mixed and then molded in place in the tank, heat being applied during the molding operation, or the granular material may ilrst be placed within the tank and the impregnating material forced through the spaces between the particles of the granular material and heat afterwards applied to solidify the impregnating material. Another method of applying the insulating material to the transformer is to pour first the bonding fluid into the tank and then heat the granular material and pour this material in a heated condition into the bonding fluid. The bonding fluid and granular material may be mixed by thoroughly stirring the two materials together and then placing this mixture in the tank and heating it to between 150 C. and 200 C. for about five hours to produce the bonding action.

As a specic example of our invention, we pro-- pose to use quartz sand or quartz gravel as the inorganic granular material, either in a powdered or granular form, but a number of other materials, such as zirconium oxide, clay, alundum, carborundum or andralusite may be used. One or more of the above named materials may be employed for `the insulating filler. Quartz sand or gravel is, however, preferred, because it has the highest heat conductivity and best dielectric characteristics of any materials tested, is easi- 1y obtained and can be found in quantity with smooth rounded edges which is of value in producing a. mixture of high dielectric strength.

The bonding material or binder is added to the inorganic insulating material in order to ll the spaces between the particles and thereby improve the heat conductivity and the electrical insulating characteristics of the quartz sand or similar material. To obtain the highest dielectric strength of the mixture, the bonding material used to fill the voids of the granular material should approach as near as possible the specific inductive capacity of the granular material. It

is, however, also desirable that the insulation shall be mechanically strong and conduct heat readily from the transformer. With these several objectives in mind, it has been found that both organic and inorganic bonding materials are satisfactory, such materials as jelled Chinawood oil or tung oil, sulphur boric acid, halowax or lead borate are found to be satisfactory.

The dielectric strength of the jelled tung oil and quartz sand is approximately one-half that of the tung oil itself, because of the great dierence in specific inductive capacity of the tung oil and quartz. The actual dielectric strength of the quartz is greater than that of the oil. In order to improve the dielectric strength of the tung oil and sand combination, it may be desirable to employ an insulating compound formed of three materials. We have found that the dielectric strength of the resultant material is increased by using a rather coarse gravel and adding a fusible salt, such as boric acid, thereto heating the two materials together to the fusing point of the salt and stirring to thoroughly wet the gravel with the fused salt. This hot mixture is then poured into place in the transformer tank, thus allowing the fused salt to seal the joints or points of contact between the particles of gravel as it cools. This material is then impregnated with tung oil, which is jelled by heating. Bakelite varnish may be used in place of the boric acid to wet the gravel and bond it at the contact points between adjacent pebbles.

The tung oil seals the mass against moisture. A gum coating may be added over the top of the mixture to aid in sealing it against moisture if desired.

Boric acid powder and sand or gravel may be mixed dry and poured into place in the tank, afterwards being heated to fuse the boric acid to allow the fused salt to seal the joints between the particles of sand or gravel, and the mixture afterwards impregnated with tung oil and jelled by further heating.

Since many modifications in the materials and methods of processing them may be employed other than those described without departing from the spirit of our invention, we do not wish to be limited other than by the scope of the appended claims.

We claim as our invention:

1. In combination, a tank, electrical apparatus contained therein, and heat conducting and insulating material disposed between said apparatus and said tank comprising a mixture of quartz sand and an impregnating jelled vegetable oil.

2. An insulating material for electrical apparatus including a pulverulent granular solid insulating material mixed with a solidifying binder of jelled vegetable oil.

3. In combination, a container, electrical apparatus contained therein, and an insulating substance lling the space between said apparatus and the Walls of said container comprising a granular ller and a jelled vegetable oil binder.

4. In combination, a tank, electrical apparatus contained therein, heat conducting and electric insulating material embedding said apparatus and substantially filling the space between the apparatus and said tank, said material comprising a pulverulent inorganic filler and a binder comprising a polymerized vegetable oil binder.

5. An insulating material for electrical apparatus comprising a granular inorganic filler and a fusible salt fused and mixed with the filler to seal the points of contact between the particles thereof, and an impregnating binder of jelled vegetable oil.

6. The process of making. an insulating materal comprising heating a mixture of a rather coarse quartz granules and a fusible salt to the fusing point of the salt and stirring to thoroughly wet the granules with the fused salt and seal the points of contact between the particles, impregnating the resulting mixture with a binder including a drying vegetable oil, and then applying heat to solidify the mass.

CHARLES F. HILL. JAMES T. GOFF.

Images