US2718709A - Process for drying electrical equipment disposed in a sealed casing - Google Patents

Process for drying electrical equipment disposed in a sealed casing Download PDF

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US2718709A
US2718709A US253253A US25325351A US2718709A US 2718709 A US2718709 A US 2718709A US 253253 A US253253 A US 253253A US 25325351 A US25325351 A US 25325351A US 2718709 A US2718709 A US 2718709A
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oil
casing
electrical
sealed casing
dielectric liquid
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US253253A
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James G Ford
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CBS Corp
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Westinghouse Electric Corp
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    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01FMAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
    • H01F27/00Details of transformers or inductances, in general
    • H01F27/08Cooling; Ventilating
    • H01F27/10Liquid cooling
    • H01F27/18Liquid cooling by evaporating liquids
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01GCAPACITORS; CAPACITORS, RECTIFIERS, DETECTORS, SWITCHING DEVICES OR LIGHT-SENSITIVE DEVICES, OF THE ELECTROLYTIC TYPE
    • H01G13/00Apparatus specially adapted for manufacturing capacitors; Processes specially adapted for manufacturing capacitors not provided for in groups H01G4/00 - H01G11/00
    • H01G13/04Drying; Impregnating

Description

Sept. 27, 1955 RD DISPOSED IN A SEALED CASING Filed Oct. 26, 1951 J. G. FO PROCESS FOR DRYING ELECTRICAL EQUIPMENT To Vacuum Pump I4 v w r- I Q A Heater Oil Punfler Trap I I g I8 I i 38 36 9' WITNESSES: INVENTOR fi/flzr/ g James 6. Ford.
7} A W BY ATTOR EY 2,718,709 Patented Sept. 27, 1955 United States Patent ()fiice PROCESS FOR DRYING ELECTRICAL EQUIPMENT DISPOSED' IN A SEALED CASING James G. Ford, Sharon, Pa, assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., 2 corpora! tion of Pennsylvania Application October 26, 1951, Serial No. 253,253
4 Claims. (Cl. 349) This invention relates to a process for rapidly and efiiciently dryingout electrical apparatus disposed in a sealed casing, prior to putting the apparatus in service.
At the present time, electrical apparatus disposed within a sealed casing is subjected to an involved and prolonged treatment to remove moisture, gases and other undesirable impurities therefrom prior to putting the electrical apparatus in service. Cellulosic insulation, such as paper, pressboard, cotton cloth or tape and the like, is employed as a component of the insulation of the electrical apparatus, and such cellulosic insulation contains substantial quantities of moisture. Under normal conditions, the cellulosic insulation will contain from 2% to 1.0% by weight of moisture. Other components of the insulation also contain substantial amounts of moisture. If normal electrical current were to be applied to the electrical apparatus under these conditions of high mois ture content, failure might occur because of the low. dielectric strength of the insulation due to such. large amounts of moisture being present.
It is an accepted procedure at the present time to thoroughly preheat electrical apparatus in an air oven before placing it in the sealed casing in which it will be disposed thereafter and to evacuate the hot, electrical apparatus when in the sealed casing in order to remove moisture and other undesirable volatile impurities. Such treatment provides for an adequate dielectric strength of the insulation to withstand operating voltages. Thereafter, the dried apparatus may be impregnated with a dielectric liquid which serves to cool and to insulate the electrical members.
The present drying: procedure, however, is time consuming, particularly with the larger size of electrical equipment, such as power transformers. From 3 to 5 days preheating in anair oven may be required tobring the temperature of the cores and coils of a large power transformer to a temperature of 85 C. Some deterioration of the cellulosic insulation may take place since the air inthe oven is at a temperature of from 125 C. to 135- C. The preheated core and coil are then removedfrom the heating oven, placed within a vacuum tank or, in some cases, in the transformer casing while still hot. Immediately thereafter, the treating tank or transformer casing are subjected to evacuation in order to withdraw any moisture or othervolatiles from the insulation of the transformer core and coils. The total time required for drying out a 100,000 kva. transformer by this procedure is in the order of from 7 to 8 days. No process known at the present time is available in which this drying out peri'odmay be substantially reduced.
When a transformer is being repaired afterhaving been in service, the insulation is impregnated withoiland, upon being dried in the: air oven-infollowingthe drying out procedure, the oil will oxidize. This results in an undesirable gummy sludge being present in the surfaces. Corrosive acids are also produced. Accordingly, such known procedures for drying out the. members. are. unsatisfactory.
The object of the present invention is to provide a process for-rapidly and efliciently drying out electrical apparatus while it is enclosed in a sealed casing.
A further object of the invention is to provide for simultaneously heating and evacuating electrical apparatus disposed in a sealed casing by spraying hot dielectric liquids over the electrical apparatus while evacuation is being carried out.
Other objects and advantages of the invention will in partbe obvious and will in part appear hereinafter. For a better understanding of the nature and objects of the invention, reference should be had to the following detailed description and drawing, in which the single figure is a view in elevation, partly broken, of a transformer being treated in accordance with the invention.
I have discovered a process by means of which electrical equipment disposed in a sealed casing, particularly large electrical equipment, may be dried outin a fraction of the time required heretofore and with no damage or deterioration occurring. Briefly, the electrical elements such as coils or windings and magnetic cores, are disposed within the sealed casing in which they are to function thereafter, then hot oil or other dielectric liquid is, introduced into the casing and sprayed, flowed or otherwise distributed over the electrical elements proper in order to impartheat to them. The oil running off the apparatus collects at the bottom of the casing and is withdrawn, and the withdrawn oil is passed through a purifying means and a heater inorder both to remove impurities thatmay have accumulated therein and to reheat the oil, then the oil: is returned to be resprayed or otherwise applied to theapparatus. The casing is evacuated during this procedure.
Spraying, flowing or otherwise distributing hot oil or other liquid dielectric, has been found to heat. electrical members promptly without causing any deterioration. of the insulation thereof. It is preferred to use petroleum oils and synthetic dielectric liquids, such as chlorinated diphcnyl, for the spraying procedure to provide for heating of the electrical, apparatus in the process. The oil or other dielectric liquid should have a low vapor pressure at the temperatures to which it is heated while under a low vacuum of the order of 1 inch of mercury absolute pressure or less. Inasmuch as oil or other dielectric liquid will be used to fill, the sealed casing after drying out has been efiected, it usually is desirable to employ the same dielectric liquid for the drying out of the transformer as will be employed thereafter in the casing as the permanent liquid dielectric.
Referring to the figure of the drawing, there is illustrated a transformer 10 comprising a tank 12 and a cover 14 cooperating to produce a sealed casing. Disposed Within the tank 12. is an electrical coil 16 and a core 18 having. insulation which contains substantial amounts of moisture, oxygen and other gases and volatile impurities which it is desired to remove before the transformer is put into service. Accordingly, there is introduced through the cover 14 a conduit 20 carrying a hot dielectric liquid, such as oil. The conduit 20 is connected to a series of nozzles or sprays 22 which distribute streams 24 of the hot oil over the coil 16 and core 18. As the streams of hot oil flow over the surfaces of the coil and core, they impart heat thereto rapidly. The oil runs off to the bottom of the tank 12 and collects as a small pool at a considerably lower temperature than in sprays 24'. The oil collected in the bottom of the tank 12 is withdrawn by means ofa conduit 28 connected to a pump 30' which forces the oil into a purifying device 32. Within the purifying device 32 is present an adsorptive material, such for example as fullers earth, charcoal, activated alumina or silica gel in the form of bricks, pellets or fragments. Any water or other impurities acquired by the oil in its passage over the transformer coil and core is removed therefrom within the purifier 32. The purified oil then enters the conduit 20 which passes through a heater 26 illustrated as an electrical heating element. It should be also understood that the position of the heater 26 and purifier 32 may be transposed, or they may be associated in one unit. Then the hot purified oil is returned to the spray heads 22 for respraying whereby the coil 16 and core 18 are further heated to a still higher temperature. In a matter of a few hours large sized coils and cores may be heated to a suitable temperature under these conditions.
It is ordinarily sufficient to heat the coil and core to a temperature of from 80 C. to 100 C. However, in some cases a temperature as low as 50 C. may be suflicient. In other cases, where the apparatus is prepared from more heat resistance insulation than paper, for instance glass cloth, the temperature to be applied may substantially exceed 100 C. Therefore, the oil or other dielectric liquid used in heating the apparatus is heated to at least 50 C., and preferably to from 80 C. to 110 C. or slightly higher.
Connected to the tank 12 is a vacuum pipe 36 leading to an oil trap 38 and thence to a tube 40 connected to a vacuum pump or other suitable source of vacuum. Oil vapor flowing to the trap 38 assists in driving out the moisture in the tank. A vacuum may be applied through the vacuum pipe 36 previous to the spraying of hot oil over the coil and core or simultaneously therewith or, if desired, application of vacuum may be delayed until the coil and core have reached a substantial temperature. The most rapid drying out of transformers has been secured when the evacuation is begun at or before the time that hot oil is sprayed on the coil and core. There are substantial quantities of moisture in the insulation which require prolonged vacuum treatment to be applied to remove it to the necessary degree and a substantial period of time is required to accomplish this.
It is necessary that the introduction of the hot oil or other dielectric liquid through the conduit 20 and withdrawal of the cooled collected dielectric liquid by the conduit 28 be so correlated that there will be no substantial portion of the coil and core immersed in the dielectric liquid during the process. Any substantial amount of immersion of the coil and core will develop a hydrostatic pressure in that portion of the apparatus which is immersed and will hinder the withdrawal of moisture and gases therefrom.
The following is one example of the practice of the present process. A transformer comprising a sealed casing was connected to a vacuum pump and the internal pressure in the casing was reduced in 8 hours to between to 10 millimeters of mercury absolute pressure. Oil heated to 100 C. was sprayed over the coil and core in the casing, and the coil and core were heated to a temperature of approximately 85 C. in another 12 hours and the coil and core maintained at this temperature for 12 hours, vacuum being maintained throughout this time. The spraying of oil was then discontinued and all of the oil within the casing was withdrawn. The transformer was then filled with refined transformer oil to the normal operating level. Tests indicated that the transformer was comparable in electrical properties to one that had been dried by conventional processes which took approximately three times as long to carry out.
The same process can be applied with considerable advantages to electrical apparatus that has been in service and has been repaired or reconditioned. The oil adhering to the apparatus does not constitute a nuisance or detriment to the drying out process of this invention. In particular the drying out process disclosed herein will not cause oxidation of the oil.
It should be understood that the above description and drawing are illustrative of the invention and not in limitation thereof.
I claim as my invention:
1. In the process of drying out electrical apparatus disposed within a sealed casing, the steps comprising introducing into the sealed casing a dielectric liquid heated to a temperature of at least C. but not exceeding C., the dielectric liquid having a low vapor pressure at these temperatures, distributing streams of the hot dielectric liquid over the electrical apparatus whereby the apparatus is heated by the distributed dielectric liquid, the hot dielectric liquid picking up moisture and other impurities from the electrical apparatus in passing over it, the cooled dielectric liquid running off the electrical apparatus and collecting in the bottom of the casing, withdrawing the cooled dielectric liquid from the bottom of the casing, the rate of introduction and withdrawal of the dielectric liquid being such that at any time there is insufficient dielectric liquid present in the casing to immerse any substantial portion of the electrical apparatus, passing the withdrawn dielectric liquid through a purifying means and a heating means to remove any impurities present in the dielectric liquid and to reheat the dielectric liquid to a temperature of at least 80 C. for reintroduction into the sealed casing, and continuing the introduction and withdrawal of the heated liquid into the casing, and evacuating the sealed casing to remove moisture, gases and other volatile impurities, the dielectric liquid not boiling under the temperatures and pressures present within the casing.
2. In the process of drying out electrical apparatus disposed within a sealed casing, the steps comprising introducing within the sealed casing oil heated to a temperature of at least 80 C. but not exceeding 110 C., the oil having a low vapor pressure at these temperatures, spraying the hot oil over the electrical apparatus within the casing, the amount of oil within the casing at any one time being insuflicient to immerse any portion of the electrical apparatus, the sprayed oil imparting heat to the electrical apparatus as it flows over it and runs off into the bottom of the casing, the hot oil picking up moisture and other impurities for the electrical apparatus in passing over it, removing the cooled oil in the bottom of the casing and passing it to a purifying means and a heating means to remove any impurities that may be present in the oil and to reheat the oil to at least 80 C. for return to the sealed casing, respraying the reheated oil and continuing the cycle, and evacuating the casing during the process to remove moisture, gases and other volatile impurities therefrom.
3. In the process of drying out electrical apparatus disposed in a sealed casing, the steps comprising distributing over the electrical apparatus in the casing a stream of a dielectric liquid at a temperature of above 50 C. but not exceeding 110 C., the dielectric liquid having a low vapor pressure at these temperatures, whereby heat is imparted by the heated dielectric liquid to the electrical apparatus, the hot oil picking up moisture and other impurities from the electrical apparatus in passing over it, collecting the cooled dielectric liquid in the bottom of the casing after it has run off the apparatus, the quantity of dielectric liquid present in the casing at any one time being insufiicient to immerse any substantial part of the electrical apparatus, passing the collected liquid through a purifying means and a heating means to remove any impurities that may have been picked up by the dielectric liquid and to restore it to a temperature of above 50 C., redistributing the reheated purified liquid over the electrical apparatus and continuing the steps of collecting, purifying, heating and distributing the dielectric liquid, and maintaining a vacuum within the casing during the process to withdraw any moisture, gases and impurities that volatilize under the temperature and vacuum present in the casing.
4. In the process of drying out a transformer comprising a coil and a core disposed within a sealed casing prior to putting the transformer in service, the steps comprising heating oil to a temperature of from 80 C. to 110 C., the oil having a low vapor pressure at these temperatures,
spraying the hot oil within the casing upon the coil and core whereby the coil and core are heated rapidly thereby, no substantial part of the electrical apparatus being immersed in the oil, evacuating the sealed casing to an absolute pressure of not over 5 inches of mercury to remove moisture and other volatiles from the casing, the sprayed oil running 01f the coil and core and collecting in the bottom of the casing, the hot oil picking up moisture and other impurities from the coil and core in passing over them, withdrawing the collected oil from the casing, passing the withdrawn oil through a body of absorbent material to purify the oil, reheating the oil to a temperature ofi from 80 C. to 110 C., respraying the hot oil Within the casing, and continuing this cycle until the transformer is dried out.
References Cited in the file of this patent UNITED STATES PATENTS 1,835,922 Zeiss et al. Dec. 8, 1931 2,086,072 Fauth et al. July 6, 1937 2,293,453 Clark Aug. 18, 1942 2,500,783 Anderson et al Mar. 14, 1950
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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3430351A (en) * 1966-06-14 1969-03-04 Asea Ab Method of drying objects such as electrical machines and electrical insulating material
US3802090A (en) * 1971-07-22 1974-04-09 Jeumont Schneider Process and installation for drying fibrous cellulose materials
US3859734A (en) * 1973-01-18 1975-01-14 Sintab Swedinventor Ab Methods and plants for drying material in liquid solid, suspended or granulated form, e.g. blood-plasma, digested sludge, forage, fish, cereals, etc.
US3884622A (en) * 1972-10-17 1975-05-20 Erich Kopp Method and apparatus for polymerizing molded dental pieces
RU2713879C1 (en) * 2019-08-15 2020-02-10 Федеральное государственное бюджетное образовательное учреждение высшего образования "Кубанский государственный аграрный университет имени И.Т. Трубилина" Device for drying power transformers in field conditions of rural electric networks
US10773192B1 (en) * 2019-04-09 2020-09-15 Bitfury Ip B.V. Method and apparatus for recovering dielectric fluids used for immersion cooling

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1835922A (en) * 1928-09-28 1931-12-08 Gen Electric Method of and heans for drying out and impregnating joints for cables
US2086072A (en) * 1933-05-08 1937-07-06 Verwertung Fauth Scher Patente Process for dehydrating and rendering flesh
US2293453A (en) * 1939-02-24 1942-08-18 Gen Electric Dehydrating treatment
US2500783A (en) * 1947-01-08 1950-03-14 Western Pine Ass Process of treating wood

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1835922A (en) * 1928-09-28 1931-12-08 Gen Electric Method of and heans for drying out and impregnating joints for cables
US2086072A (en) * 1933-05-08 1937-07-06 Verwertung Fauth Scher Patente Process for dehydrating and rendering flesh
US2293453A (en) * 1939-02-24 1942-08-18 Gen Electric Dehydrating treatment
US2500783A (en) * 1947-01-08 1950-03-14 Western Pine Ass Process of treating wood

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3430351A (en) * 1966-06-14 1969-03-04 Asea Ab Method of drying objects such as electrical machines and electrical insulating material
US3802090A (en) * 1971-07-22 1974-04-09 Jeumont Schneider Process and installation for drying fibrous cellulose materials
US3884622A (en) * 1972-10-17 1975-05-20 Erich Kopp Method and apparatus for polymerizing molded dental pieces
US3859734A (en) * 1973-01-18 1975-01-14 Sintab Swedinventor Ab Methods and plants for drying material in liquid solid, suspended or granulated form, e.g. blood-plasma, digested sludge, forage, fish, cereals, etc.
US10773192B1 (en) * 2019-04-09 2020-09-15 Bitfury Ip B.V. Method and apparatus for recovering dielectric fluids used for immersion cooling
RU2713879C1 (en) * 2019-08-15 2020-02-10 Федеральное государственное бюджетное образовательное учреждение высшего образования "Кубанский государственный аграрный университет имени И.Т. Трубилина" Device for drying power transformers in field conditions of rural electric networks

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