US1976608A - Electrical apparatus - Google Patents

Description

Oct. 9, 1934. J 31 FORD 1,976,608

ELECTRI CAL APPARATUS Filed May 3, 1933 WITNESSES: INVENTOR James G. Ford.

ATTO R N EY Patented Oct. 9,

UNITED STATES .nmo'rmcar. mana'ros James G. Ford," Forest Hills, "Pa, assignmto Westinghouse Electric G; Manufacturing Coinpany, East Pittsburgh, Pa., 9. corporation of Pennsylvania Application May 3,1933, Serial no. 869,193 9 Claims. (01. 175-361) My invention relates to oil-immersed electrical apparatus and moreparticularly to such apparatus in which provision is made for preventing a deposition of oxidation products, such as sludge,

upon the apparatus, or the formation of acids in the insulating oil.

It has been recognized as desirable to provide a gas cushion irithe space above the oil of oilinsulated electrical apparatus, such as transformers and reactors, and to maintain a chemically inert gas, that is, *a gas devoid of oxygen, in the cushioning space 'in order to prevent'or reduce the formation of acids that attack the insulating material, and cause the formation of solid matter which may be deposited upon the apparatus and reduce the dielectric strength of the insulating material adjacent the apparatus. Such solid material and acids are formed upon the oxidation of the oil by oxygen contained in 20 the air that is absorbed by the oil. The elimination of oxygen from the gas space above the oil is also desirable in order to prevent the formation of explosive gaseous mixtures that might occur upon the formation of such gases as hydrogen and acetylene by decomposition of the insulating oil, under certain conditions of operation of the apparatus, such, for example, as upon the occurrence of a local or stewing are between adjacent turns of the winding. It has been proposed to provide a cushion of inert gas in the space above the oil, either by supplying such a gas from a tank containing the same, or by employing deoxidizing material for removing the oxygen from such gas as may enter the casing of the apparatus by chemically combining with it. Since, as stated above, insulating oil will absorb oxygen from air in contact with its surface, it is possible, within certain limitations, to use the oil as a deoxidizing 4 material for removing oxygen from the gas cushioning space above the oil. In view, however, of the undesirable effects of oxygen upon the ordinary insulating oils, forming sludge and acids, the effectiveness in the use of such oils as a deoxidizer is limited.

I have found that the use of an oil which oxidizes readily and which has a high oxygen absorbing capacity insures the rapid creation of an inert atmosphere above the oil and minimizes sludging. By employing a casing equipped with a breathing regulator to restrict the breathing, and by using a dehydrating agent within the casing to absorb moisture from a .ny. air breathed into the casing, and also to absorb moisture and other oxidation products from the space within 125 centigrade for .each of the commercial the casing that may be given oi as a result of absorption of oxygen by the oil. It is possible, by using an oil having a high oxidation absorptive capacity, to produce an oil-immersed electrical apparatus in which the oil will absorb oxygen from the adjacent gas space within the casing in suflicient quantities before sludging occurs to provide an apparatus in which the oil will require no reconditions for the normal life of the apparatus.

I propose to make use of the oxidation characteristics of a water-white oil that has been refined by concentrated sulphuric acid, oleum, or other similar refining agent to the extent that the natural occuring anti-oxidants have been 1'. removed. Such an oil has a rate of oxygen absorption that is many times that of the ordinary commercial types of insulating oils used for insulatmg and cooling electrical apparatus. For example, in tests made on a large number of 1. available types of yellow transformer oil exposed to an unlimited supply of air, such tests showed an absorption of about 2 cubic centimeters of oxygen for a 6 hour period at a temperature of types of oil, while the water-white oil that I propose to use showed an absorption of 181 cubic centimeters for the same volume of oil for a similar period of time at the same temperature.

The water-white oil, showed a solubility of substantially zero in a 94.5% solution of sulphuric acid, while the usual insulating oils have a solubility of between 15% and 25% in sulphuric acid of the same concentration. The water-white oil shows no coloration in or 50% solutions of sulphuric acid and is in this respect unlike the usual insulating oils which show brown or yellow colorations.

An object of my invention is to provide for greatly increasing the life of the oil employed in oilimmersed electrical apparatus.

Another object of my invention is to provide an 'inert atmosphere in the space above insulating oil in oil-immersed electrical apparatus and thereby to prevent the formation of acids and sludges by oxidation of the oil, without the necessity for employing the usual deoxidizing or inert gas supplying equipment.

Another object of my invention is the provision of oil-immersed electrical apparatus in which the original insulating properties of the oil will be maintained for a. very long time, that is, substantially the life of the electrical apparatlills without the necessity of reconditioning the o of the insulating material.

In the drawing, the single figure is a view in vertical section of a transformer arranged in accordance with my invention.

The tank or casing 1 is provided with a tight cover 2 by the use of suitable gaskets 3 or by other suitable means. I have shown an electrical apparatus in the form of a transformer 4 having terminal conductors 5 and 6 that connect the apparatus with an outside circuit through terminal bushings 7 and 8 that extend through the cover 2 of the casing 1.

The apparatus is immersed in cooling and insulating oil 9, the level of which is such as to completely immerse the electrical apparatus, and, at the same time, provide a gas space within the casing above the oil level. Preferably, about 10% of the volume of the tank or an equivalent space connected to the tank above the oil should be left as a gas cushioning space to provide for the normal contraction and expansion of the oil as a result of its natural change in volume as the temperature of the apparatus-varies as a result of varying load conditions. A rack or container 11 is shown in the upper part of the tank for containing suitable dehydrating material, such as a mixture of sodium carbonate and calcium chloride, in contact with the gas in the space above the oil for removing from the gas cushioning space water and volatile organic acids resulting from oxidation of the oil- A breathing regulator 12 is connected between the gas space in the casing and the outside atmosphere and is, in effect, a U tube passageway partially filled with mercury or an equivalent sealing liquid, shown at 13, for the purpose of preventing gas from passing from the casing to the outside atmosphere until a predetermined pressure exists within the casing, and also for preventing the passage of air from the outer atmosphere into the casing until the pressure within the case has reached a predetermined low value. As will be seen, the regulator operates to restrict the breathing from the casing to the outside atmosphere and thus to reduce the amount of oxygen that will come in contact with the oil to a very low value. The regulator may be so adjusted as to entirely eliminate breathing except under very abnormal conditions of operation resulting in a correspondingly abnormal expansion and contraction of the oil within the volume of the casing.

After the transformer 4 is assembled in its casing 1 and the casing supplied with oil to the proper level, the gas space above the oil may be blown out with nitrogen, if desired, or the transformer can be energized and heated to a temperature of about centigrade during which time the oxygen in the air above the oil will be very rapidly absorbed by the oil. The ratio of the gas space to the oil volume is so determined that under the worst breathing conditions, the amount of air drawn in through the breather 12 is insufiicient to permit an explosion if mixed with other gases resulting from decomposition As soon as air is breathed into the casing, the oxygen contained therein starts to combine with the oil and is thereby soon removed from the gas space. The rate of oxidation is a function of the temperature of the oil and is quite rapid at 75 C. or higher temperatures.

The oxidation of the oil results in the formation of oxidation products such as soluble acids, neutral products, water and carbon dioxide. The water is gradually taken up by the dehydrating material in the gas space above the oil and the carbon dioxide remains partly in the gas space and partly in solution in the oil as an inert substance. Basic material, such as anhydrous potassium hydroxide can be used as the dehydrating material in which case volatile acids would be absorbed and the carbon dioxide removed. A number of other dehydrating agents may be employed.

The oil used is of a water-white type, which is generally made by refining with fuming sulphuric acid and should be refined to the extent that the natural occurring anti-oxidants have been removed and the solubility of the oil in concentrated sulphuric acid is substantially zero. These oils have the characteristics of being readily oxidized after an inductive period that is characterized by'very slow oxidation, during which time certain oxidation products accumulate which later become catalytic and speed up the rate of oxidation quite considerably. Therefore it is desirable to use the oil in a slightly oxidized condition so as to speed up the initial removal of oxygen from the transformer.

The rate of absorbtion of oxygen by the oil may be still further increased, especially during the inductive period, by adding a catalyst to the oil. Such substances as copper, manganese, cobalt form soaps which act as catalytic agents, speed up the rate of oxidation.

The oils of the yellow type, such as are ordinarily used for insulating electrical apparatus, do not show an inductive period and are characterized by a slow and gradual oxidation, while oil of the water-white type, after the initial inductive period, will absorb oxygen very rapidly and will absorb immense quantitiesof oxygen before changing its characteristics as a dielectric, such as by forming destructive acids and sludge. The difference in behavior of these two types of oil is attributed to the presence of small amounts of resins in the yellow oil. which are absent in the white oil. These resins apparently act as antioxidants and, in general, are present in the yellow transformer oils in amounts ranging from 0.5 to 2.0 percent depending upon the degree of refining of the oil.

Tests made on transformers arranged in accordance with my invention in which the temperature, oxidation and other conditions were controlled, indicated that oil would be good for the life of the transformer without attention. Such a test in which the deoxidized gas was removed from the space above the oil and this space supplied with atmospheric air a sufllcient number of times to correspond to the quantity of air breathed into the transformer in about 60',

years service showed the teriorated.

The above description of one embodiment of my invention is to be taken as illustrative only, and not in a limiting sense. Modifications may be made in the apparatus illustrated and described, without departing from the spirit of my invention, and I do not wish to be limited other than by the scope of the appended claims.

I claim as my invention:

1. In an oil-cooled transformer, a casing therefor having a breathing regulator for permitting oil only slightly dethe entrance or escape of gas if the pressure with- 1 in the casing falls below or rises above predetermined limits, and oil within the casing to a sufficient level to completely surround the transformer and to provide suificient gas space above the oil to allow for its expansion under normal working conditions, said oil being of the white type and refined to the extent that the natural occurring anti-oxidants have been substantially all removed.

2. An electrical apparatus adapted for operation in a cooling and insulating fluid comprising a sealed casing, a breather valve for permitting the passage of gas between the interior of the casing and the outside atmosphere under predetermined pressure conditions, and an oil of the ,white type that has been refined to the extent that the natural occurring anti-oxidants have been substantially completely removed, the level of the oil being such as to immerse the electrical apparatus and to provide a substantial gas space in the casing above the oil.

3. In an oil cooled transformer, a casing therefor, a breathing regulator for permitting the entrance or escape of gas if the pressure within the casing falls below or rises above predetermined limits, and an insulating fluid within the casing to such level as to completely surround the transformer while, at the same time, allowing a sufficient gas space above the fluid to permit its expansion under normal working conditions, said fluid being a water-white type of oil from which the natural occurring anti-oxidants have been substantially removed.

4. In an oil-insulated electrical apparatus, the combination comprising a casing having an ex-- pansion space in which the insulating oil comes in contact with a. body of gas, said insulating oil being a water-white type of oil from which the natural occurring anti-oxidants have been substantially removed.

5. In combination, an air-tight casing, an electrical transformer within the casing, and an oil of the water-white type, that has been refined to the extent that the natural occurring antioxidants have been removed, within the casing and surrounding said transformer, and above the surface of which there is suflioient space to allow for the expansion of the oil under normal working conditions.

6; In an electrical transformer, in combination, a sealed casing, transformer windings within the casing, and an oil within the casing to a level above the transformer windings that has been refined to the extent that the natural occurring anti-oxidants have been sufficiently removed to permit the oil to absorb about 180 times its volume of oxygen when exposed to the atmosphere for six hours at 125 C.

'7. In an electrical transformer, in combination, a sealed casing, transformer windings within the casing, and an oil, that has been refined to the extent that the natural occurring anti-oxidants have been removed and then slightly oxidized, within the casing and immersing the transformer windings.

8. In combination, a sealed casing, an electrical apparatus within the casing, and a partly oxidized oil of a water-white type that is insoluble in concentrated sulfuric acid within the casing and immersing the transformer windings.

9. In combination, a sealed casing, an electrical apparatus within the casing, an oil of the waterwhite type that has been refined to the extent that the natural occurring anti-oxidants have been removed, and a catalytic agent for aiding the rate of absorption of oxygen by the oil from any gas in contact therewith.

I JAMES G. FORD.

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