US3452147A - Non-condensable gas-condensable vapor cooled electrical transformer - Google Patents

Description

`luneI 24, 1969 P. NARBUT ET AL NON-CONDENSAELE GAS-CONDENSABLE VAPOR COOLED Filed Sept. 8. 1967 ELECTRICAL TRANSFORMER n 1111: F) C Sheet FIG.7.

June 24, 1969 P NARBUT ET AL. v 3,452,147

NoN-CONDENSABLE GAS-CONDENSABLE VAPOR COOLED ELECTRICAL TRANSFORMER WITNESSES INVENTORS MM Paul Nurbm und Curtis L, Moore BY ,ZM bmw w ATTORNEY U.S. Cl. 174-16 United States Patent XO 3,452,147 NON-CONDENSABLE GAS-CONDENSABLE VAPOR COOLED ELECTRICAL TRANSFORMER Paul Narbut, Sharpsville, and Curtis L. Moore, Sharon,

Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 8, 1967, Ser. No. 666,385 Int. Cl. H01b 7/34, 9/06 1 Claim ABSTRACT OF THE DISCLOSURE Transformer apparatus comprising a casing having a core and coil assembly therein wherein a fluid dielectric is sprayed over the core and coil assembly for cooling. The fluid dielectric evaporates upon contact with the hot core and coil assembly and forms a condensable vapor, which condensable vapor is mixed with a non-condensable gas. The non-condensable gas-condensable vapor mixture provides the dielectric and cooling medium for the transformer apparatus. Cooling devices are attached to the casing for cooling the non-condensable gas-condensable vapor mixture and means are provided for maintaining a pressure difference between the input and output of the cooling devices, such pressure Idifference serving to increase the thermocycling action of the non-condensable gas-condensable vapor mixture through the cooling devices to maintain the proper mixture of the non-condensable gas-condensable vapor in the casing for proper cooling of the core and coil assembly.

Descriptz'on of the invention This invention relates to electrical transformers and particularly to electrical transformers housed in a casing and utilizing a non-condensable gas-condensable vapor atmosphere for cooling, with a cooling device attached to the casing for dissipating heat from the non-condensable vapor developed during operation of the transformer.

An object of this invention is to improve the efficiency of the cooling device by increasing the flow of noncondensable gas through the cooling devices.

Another object is to improve the efficiency of the cooling devices Iby creating a gas pressure head in the cooling devices in the natural direction in which the non-condensable gas-condensable vapor circulates by thermocycling.

Another object is to improve the eiciency of the cooling devices by increasing the ilow of non-condensable gas through the cooling devices by creating a gas pressure head in the cooling devices and maintaining the natural segregation of non-condensable gas and condensable Vapor in the casing.

Other objects of this invention will become apparent from the following description when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a -diagrammatic view illustrating the observed positions of the isothermal non-condensablecondensable vapor lines of a transformer constructed according to this invention;

FIGURE 2 is a diagrammatic view illustrating the observed positions of the isothermal non-condensable-condensable gas vapor lines for a prior art device;

FIGURE 3 is another embodiment of the `apparatus similar to that shown in FIG. l;

FIGURE 4 is a diagrammatic View of another embodiment of the apparatus provided by this invention;

FIGURE 5 is a partial `diagrammatic view of still another embodiment of the apparatus provided by this invention; and

FIGURES 6 and 7 are detailed views of corner coolers shown in FIGS. l and 2.

Like reference characters indicate like parts throughout the various figures of the drawings.

The liquid coolants used in this invention may be any of these disclosed in the Hill Patent 2,561,738. The noncondensable gas may be nitrogen, argon, neon, carbon, dioxide, air, sulfur-hexauoride, or any of the other gases of the electro-negative group, or any other suitable non-condensable gas.

Referring to the drawings in detail, FIG. 1 illustrates transformer apparatus 10 as provided by this invention. The transformer illustrated in FIG. 1 comprises a casing 12 having a sump portion 14, and a core 16 and coil 18 positioned in the casing. The usual connections to the coil 18 and `bushings have not been shown for the purpose of clarity. The core 16 `.and coil 18 rest on the bottom of the casing 12. The sump 14 contains a quantity of liquid coolant 20, such as one of the coolants described in the Hill Patent 2,561,738. The casing 12 also contains a noncondensable gas such as described hereinbefore.

The bottom of the sump 14 is connected to a pump 22 and the output of the pump 22 is connected by a conduit 24 to asprayhead 26. During the operation of the transformer liquid coolant is pumped from the pump 14 and sprayed over the core 16 and coil 18 to dissipate the heat generated in the core 16 Iand the coil 18 during operation of the transformer. The liquid coolant when thus delivered to the core 16 and the coil 18 distributes itself as a thin film over the core 16 and coil 18 and is caused to evaporate freely when the electrical components are hot, thereby cooling the core 16 and the coil 18. As the liquid coolant thus vaporizes, the hot and heavy vapors mix with the non-condensable gas present in the casing 12. However, the vapors being heavy, they tend to concentrate toward the lower part of the casing 12, thus displacing the non-condensable gas component to concentrate in the upper part of the casing 12.

Side coolers 28 and corner coolers 34 are attached to the casing 12 for cooling the non-condensable gases and the condensable vapor. Any required number of coolers 28 and 34 may be attached to the casing 12. The side coolers 28 are attached to the casing 12 near the bottom thereof by a conduit or header 32 and they are attached to the casing 12 near the top thereof by a conduit or header 30. The corner coolers 34 are attached to the casing 12 near the bottom thereof with a conduit or header 38 and near the top thereof with aa, conduit or header 36. The non-condensable gases and condensable vapor circulate through the coolers 28 and 34 by entering the lower headers of the coolers passing upward as indicated by arrows shown on the cooling tubes and reenters the casing 12 near the top thereof. This circulation is strictly a thermocycling process. A shroud 40 may be located opposite the upper header 28 of the side coolers 30 Where the header is connected to the casing 12 and also opposite the upper header 36 of the corner coolers 34. The purpose of this shroud is to direct the flow of the gas-vapor downward and thus to help maintain the proper segregation of vaporizable medium and non-condensable gas in the casing 12.

Also shown in FIG. 1 is a jet or nozzle 44 which connects to the pump conduit 24 and is directed into the lower header 32 of the coolers 32. It is understood that if necessary a jet, such as 44, may be directed intoI the lower header of each of the coolers 30 or 34. The purpose of this jet is to direct a spray of liquid coolant into the lower header of the coolers to provide a pressure differential between the entry of the cooling medium into the lower header and the exit from the .upper header to provide improved flow or to accelerate the flow of the condensable vapor and non-condensable gas through the coolers 30.and 34. The reason for providing a pressure head on the coolers to increase the flow of lthe vapor and the non-condensable gas through the headers will be explained hereinafter. The pressure differential provided between the entrance to the coolers and the exit from the coolers is very slight. In fact a pressure differential of .72 inch of water or .028 1b. per square inch has been found to be adequate to provide excellent heat transfer for the heat contained in the condensable vapor and the non-condensable gas.

Referring to FIG. 2, which illustrates a diagra-mmatical transformer apparatus similar to that shown in FIG. 1, except that no pressure differential is provided on the coolers for accelerating the ow of the condensable vapor and the non-condensable gas through the coolers. From observation of a transformer constructed according to FIG. 2 it was observed that the cooling of the condensable vapor and the non-condensable gas was not sufficiently efficient to provide adequate cooling for the transformer apparatus. The dot-dash lines shown on FIG. 2 represent the isothermal gas-vapor lines in the transformer and the coolers. That is any point on any particular dot-dash line is at the same temperature in the transformer casing 12 and the coolers 28 and 34. It was found by actual observation of the transformer of this type that the side cooler 28 was only about 75% efficient and that the corner cooler 34 was only about 47% eicient. It was also determined that the inefficiency of the coolers 28 and 34 was the result of reduced effectiveness of the heat transfer by condensation of the coolant vapors in the coolers 28 and 34. This inefficiency was caused by the non-condensable gas in the coolers. This non-condensable gas formed a heat insulating blanket in the vicinity of the inside walls of the cooler tubes. This insulating blanket prevented the hea-t from the condensable vapor from reaching the outside of the cooling tubes where it could be dissipated by air. It was also found that the effect of this insulation by the non-condensable gas is directly related to the concentration of the non-condensable gas and the vapor mixture in the cooler tubes. A large percentage or concentration of non-condensable gas provides greater thermal insulation of the inside of the tube walls and consequently a less efficiency cooler. A high concentration of non-condensable gas laying in the cooler prevents circulation of enough condensable vapor through the coolers to provide adequate cooling for the transformers. It is observed from the dot-dash isothermal lines of FIG. 2 that at any point on the coolers 28 and 34 the tempera-ture outside of the cooler is lower than the temperature inside the casing 12. This means that the cooler is not operating efiiciently to cool the non-condensable gas-c-ondensable vapor mixture. In order to improve this efiiciency it is necessary to raise the dot-dash isothermal lines and to raise the temperature of the coolers so that at any point the temperature of the coolers will be more nearly the temperature of the inside of the casing 12. From an observation of FIG. 2 it is observed that the dot-dash isothermal lines of the corner coolers 34 are even lower than the isothermal lines of the side coolers 28. This is caused by restriction of the gas circulation in the restricted headers 36 and 38 of the corner coolers.

It was found that the efficiency of the coolers 30 and 34 would be raised sufficiently to cause improved cooling of the transformer by causing an increase in the condensable vapor content and a decrease in the non-condensable gas content in the coolers. This is accomplished by creating a gas pressure head in .the coolers in the natural direction of gas vapor circulation in the coolers suicient to raise the isothermal non-condensable gas-condensable vapor lines in the casing and the cooler to positions such as illustrated in FIG. 1 of the drawings. This is accomplished in the apparatus of FIG. 1 by providing the jet 44 which directs a stream of liquid coolant into the lower headers 32 and 38 of the coolers. This jet creates a pressure head of approximately 0.5 inch of water or .02

pound per square inch. It was found by observation that `a very slight pressure head on the coolers in the natural direction of circulation of the non-condensable gas and the condensable vapor mixture was sufficient to raise the isothermal non-condensable gas-vapor dot-dash isothermal lines as illustrated in FIG. 1. It is seen that the dotdash isothermal lines of FIG. 1 have been raised substantially from those of FIG. 2 in both the side coolers 28 and the corner coolers 34. In FIG. 1 the temperatures of the coolers are substantially higher than the temperatures inside the casing 12. This means that the coolers are doing a more efficient job in dissipating the heat from the non-condensable gas-condensable vapor mixture. It is important that in circulating the condensable gas and non-condensable vapor to the coolers 28 and 34 that the natural segregation of the non-condensable gas and the condensable vapor in the tank be maintained, that is disturbed as little as possible. Since the non-condensable gas is lighter than the condensable vapor there is a tendency for the non-condensable gas to collect in the Itop of the casing 12 and for the condensable vapor to settle nearer the bottom of the casing. In order t-o cause a minimum disturbance to this natural segregation of the non-condensable gas and the condensable vapor in the casing 12, in FIG. l, a shroud 40 is provided to direct the condensable vapor toward the lower part of the casing 12.

It is well known that the efficiency of the coolers 28 and 30 increases with the outside temperature of the coolers. By observation it was found that the average cooler surface temperatures in installations where no pressure head is provided on the coolers is less than the temperature of the non-condensable gas-condensable vapor in the casing. This is clearly illustrated by the disposition of the dot-dash isothermal lines in FIG. 2. It was also observed that by providing a pressure head on the coolers as disclosed in FIG. 1 that the outside temperature of the coolers 28 and 34 was substantially raised and more nearly approached the temperature of the non-condensable gas-condensable vapor mixture in the tank 12; therefore, the efficiency of the coolers 28 and 34 are substantially raised by increasing the rate of non-condensable gasoondensable vapor flow through the coolers 28 and 34. This increase of ow of the non-condensable gas through the coolers does not give the non-condensable gas an opportunity to linger in the cooler tubesf'and form an insulating blanket on the inside of the cooler tubes.

When maximum efiiciency of the coolers 28 and 34 is desired the rate of circulation of the non-condensable gascondensable vapor through the coolers 28 and 34 may be caused to be so high as to result in little or no temperature difference between the non-condensable gas-condensable vapor entering the lower headers 32 and 38 and the temperature of the mixture reentering the casing 12 through the upper headers 30 and 34. In this instance the upper headers 30 from the cooler 28 may be returned to the casing at some point 50, as indicated in FIG. 3, which may be nearer to the lower headers 32 or at the same level as the entrance to the lower headers 32. In such installations the non-condensable gas-condensable vapor thus circulated to the coolers 28 and 34 will have a maximum condensable vapor content, thereby resulting in maximum cooler efficiency `and the upper part of the casing 12 will serve as a storage reservoir fo-r the non-condensable gas.

The apparatus disclosed and described in FIG. 1 is desirable since the pressure head on the lower headers of the coolers is provided by a static means, that is the jet 44.

FIG. 4 illustrates a second embodiment of the apparatus shown and described in FIG. 1 wherein the pressure head on the coolers is provided by a small fan 48 located opposite the non-condensable gas-condensable vapor exit from the header 30 of the cooler 28. This fan need only be powerful enough to provide a suction on the header 30 to provide a pressure differential of a fraction of an inch t of Water between the input to the lower header 32 and the exit from the upper header 30.

FIG. 5 is similar to FIG. 6 and shows only a single side header with a small fan 52 located opposite the input to the lower header 32 of the cooler 28. This fan need only be large enough to provide a pressure differential of approximately 0.5 inch of water or .02 pound per square inch between the input to the lower header 32 and the output from the upper header 30. It has been observed that both the embodiments shown in FIGS. 4 and 5 operate efficiently to increase the circulation of the non-condensable gas and condensable vapor through the cooler Z8 .to improve the elliciency of the cooler as illustrated by the dot-dash isothermal lines on FIG. l.

FIGS. 6 and 7 merely show the details of a corner cooler 34 of the type illustrated in FIGS. 1 and 2. As illustrated by the dot-dash isothermal lines in FIG. 2, the eiciency of the corner cooler 34 is substantially lower than the efiiciency of the side cooler 28 of FIG. 2. The reason for this lower efliciency of the corner cooler 34 is that the corner cooler 34 has smaller headers 36 and 38 than the headers 30 and 32 of the side cooler 28. These smaller headers considerably restrict the flow of the noncondensable gas and condensable vapor through the corner cooler when natural thermo-cycling of the non-condensable gas-condensable vapor is relied upon for cooling of the transformer. However, by providing a slight pres sure head, of say approximately 0.5 inch of water or .02 1b. per square inch between the input to the corner cooler 34 and the output from the corner cooler 34 as shown and described hereinbefore in FIGS. l, 3, 4 and 5 the circulation of the non-condensable gas-condensable vapor through the corner cooler is increased and the non-condensable gas is no-t allowed to lay in the cooler and form a thermal insulating blanket adjacent the inside of the tube walls, and the eiciency of the corner cooler is improved to be substantially equal that of the side coolers 28, as illustrated by the dot-dash isothermal lines of FIG. 1.

From the foregoing, it is seen that the arrangements shown and described herein have provided improved means for eiciently cooling a transformer which utilizes Y t5 condensable vapor to enter the coolers thereby improving the cooling eiciencies of the coolers and in the meantime maintaining the natural segregation of the non-condensable gas and condensable vapor in the transformer casing.

We claim as our invention:

1. Electrical apparatus comprising a casing having an electrical conductor disposed therein which is subject to temperature changes when in use, a non-condensable gas and a vaporizable liquid coolant contained by the casing, means for applying the liquid coolant to the electrical conductor to effect cooling of the electrical conductor by vaporization of the applied liquid coolant, the vapors of the liquid coolant and the non-condensable gas being intermixed within the casing when the vapors evolve to provide a dielectric medium for insulating the electrical conductor, `a cooling device, means connecting the lower end of the cooling device to the lower end of the casing and the upper end of the cooling device to the upper end of the casing, said means connecting said cooling device to said casing providing for thermo-Siphon ow of the non-condensable gas and condensable vapors between the casing and the cooling device, and means providing a pressure difference between the inlet to said cooling device and the outlet of said cooling device comprising a jet which directs a spray of liquid coolant into the input of said cooling device, said pressure difference enhancing the oW of the non-condensable gas through said cooling device.

References Cited UNITED STATES PATENTS 2,525,457 10/1950 Palvev 174-15 2,711,882 6/1955 Narbutovskih 174-15 2,717,319 9/1955 Bundy 336-58 X 2,990,443 6/1961 Camilli 174-15 3,034,796 5/1962 Wilk 174-15 X 3,275,893 9/1966 Phillips et al. 174-15 X -LEWIS H. MYERS, Primary Examiner. A. T. GRIMLEY, Assistant Examiner.

Us. c1. XR. 336-47, 5s

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