DE1690153A1 - Method and arrangement for cooling a power transmission line - Google Patents

Description

Patent attorney Dipl.-Phys. Gerhard Liedl 8 Munich 22 Steinsdorfstr. 21-22- Tel. 29 84

B 3590

SUMITOMO ELECTRIC INDUSTRIES, LTD. No. 15, 5-chome, Kitahama, Higashi-ku, Osaka / Japan

Method and arrangement for cooling a power transmission line

The invention relates to a method and an arrangement for cooling a Closed power transmission line in which the conductor and insulation are protected from the atmosphere by a jacket.

The technical terms used below become as follows clarified:

^{H / o} 109Ö19 / 03S6

The expression "closed power transmission line ¹¹ is to be understood as meaning all transmission lines which have a jacket by which the conductor or conductors and the insulator or insulators are protected from the atmosphere and which is filled with an electrical insulating liquid. Such a transmission line includes a high-voltage pressure cable, e.g.

The term "cable" means all cables that are around a - to be carried - reel can be wound, as well as conductors and insulators, which have great flexibility.

Under the term "transmission facility" are all arrangements except for those with a cable-like structure. A closed transmission line is used to transmit a large one Power used in large cities or in the vicinity of large cities where it is difficult to use a normal overhead transmission line or to use an underground transmission line. Recently, the density of closed transmission lines has become considerable -

3590 109819/0356

loan increased, from 200,000 KVA to 300,000 KVA per network a big city. This high power is transmitted over a long distance of several kilometers. It is expected that Even transmissions of 1,000,000 KVA per network are possible, using a high voltage cable over a large distance shall be. By means of the previous state of the art relating to closed Transmission lines, however, it is very difficult to find one to transmit great power with maximum voltage over a great distance, which is always the demand for suitable further developments get stronger.

The means of increasing the transmission capacity of underground, closed transmission lines that have been proposed so far can be summarized as follows:

1 * Using a large scale conductor and an insulator with low dielectric loss tangent;

2. Increase in working temperatures of conductor and insulator;

3. Reducing the thermal resistance of the earth in which a cable is located;

109819/0356

- ⁴ - I b901 53

4. Separation of the transmission lines from each other if several are used be, and

5. Using a forced circulation cooling system for a conductor as well an isolator.

Even if initially with the means used under 1 to 4 above Certain successes could be achieved, but considerable difficulties arose in the transmission capacity over a certain one Amount, which is why the main focus was on the appropriations proposed under 5.

To implement a forced circulation cooling system, the suggested the following solutions:

1. The heat generated in a cable is by means of an insulating oil if the cable is an OF cable of the tubular or closed type, the oil in the Sheath is passed through a heat exchanger provided on the outside of the cable.

3590 109819/0366

2. The thermal resistance of the soil is reduced by placing a water cooling pipe near an underground cable is provided,

3. It becomes a value of the thermal resistance of the soil against Aimed at zero by providing a large diameter water cooling pipe and immersing a cable in water will.

4. The cable is cooled by the fact that the air in the tunnel in which the cable is arranged to be circulated with the atmosphere.

The heat generated in the conductors and insulators is generally radiated into the ground through the jacket and protective layer. R ₁ , R ₀ and R "represent thermal resistances of the insulators, etc., of the casing and protective layer as well as of the floor, so that the amount of heat that has escaped _{depends on these thermal resistances R-, R 0} and R". According to the proposal listed under 1 “above, it is possible to _{lower the thermal resistances R 0} and R_ almost to a value of zero, while according to the methods mentioned above under 2., 3. and 4. it is only possible to reduce the thermal resistance R ₃

3590 109819 / O356

I b 9 Ü1 5

down to a certain amount. The aforementioned known methods of cooling have several disadvantages.

In the method proposed under 1, it is difficult to obtain a Maintain flow of insulating oil over a great distance since the viscosity of insulating oil is greater than that of water. Because the specific heat of insulating oil is very high compared to that of water is small, in order to dissipate the heat generated in the conductors and insulators, a large amount of oil must be circulated, so that the application this procedure is only limited to short transmission lines. Since the thermal resistances R-, R and R are negligible If the oil flows within the conductor, an increase in the transmission capacity can only be achieved with short transmission lines to be expected.

The procedure mentioned under 2. enables the reduction of the thermal Resistance R «· However, it is difficult to determine the transmission capacity to increase over a certain amount.

If the number of water cooling pipes is increased, the aforementioned Ratios can be achieved, but the disadvantage must be accepted that the manufacturing costs increase.

3590 1098 19/0356

" ⁷ "! 690153

The procedure mentioned under 3. is more effective than the one mentioned under 2., however, has the following disadvantages; The manufacturing costs are high; it is difficult to cool the coupling part of the cable; the method is limited in terms of the cooling effect because of the difference between the conductor temperature and the increased cooling water temperature becomes small.

The method mentioned under 4 also has the disadvantage of high production costs on. Furthermore, it is disadvantageous that the cooling capacity is small due to the use of air. There is still the difficulty the transfer of a great achievement.

In all of the above processes, it is not possible to determine the temperature difference to increase significantly between the cooling medium and the heated part. Due to the fact that the temperature of the cooling medium changes along the transmission line, the temperature near the inlet of the cooling medium differs considerably the temperature near the outlet, so that there is a poor cooling effect.

Based on the aforementioned prior art, it is now the task

3590 109819 / Π356

of the invention, an improved method and arrangement for cooling a transmission line in proposal, whereby the disadvantages mentioned are avoided. This object is achieved according to the invention in that a supply and inside the jacket a return line for a cooling medium can be arranged that a gas in the liquid state is supplied to the supply line as a cooling medium which is gaseous at normal temperatures and at atmospheric pressure and liquid at superatmospheric pressure and at least in the gaseous state acts like an electrical insulator that a lower pressure in the return line than in the supply line it is maintained that the cooling of the transmission line is carried out using the heat of evaporation that occurs, when the cooling medium flows out of the supply line and evaporates, and that the evaporated cooling medium is conducted to the outside by means of the return line from the jacket.

It is preferred that the cooling medium led out of the jacket is liquefied and circulated.

A preferred transmission line cooling arrangement formed in accordance with the invention is characterized in that a feed and a

3590.109819/0356

Return line for a cooling medium in a jacket of the transmission line it is provided that a condenser is arranged at least at one point on the transmission line and with the supply and return line is connected that means are provided for supplying a gas serving as a cooling medium in the liquid state to the supply line are, wherein the gas is gaseous at normal temperature and atmospheric pressure and liquid at superatmospheric pressures and acts at least in the gaseous state as an electrical insulator, and that means are provided that the evaporated cooling medium to the Return the condenser.

The feed line is preferred with an evaporation layer for the Cooling medium provided, which provides a uniform and uniform resistance to the outflow of the cooling medium along the length of the transmission line so that uniform and uniform evaporation takes place.

The amount of evaporation is preferred by controlling the difference regulated between the pressures of the supply and return lines when the amount of heat generated in the cable is low.

3590 109819 / Π356

The cooling method according to the invention has a number of advantages and Difference in comparison to the known cooling method. In the known cooling method, the cooling medium is at one temperature which is lower than that of the transmission line to be cooled, whereby the thermal conductivity is used for cooling, d. H. the longitudinal extension of the transmission line is cooled using the specific heat of the cooling medium. In contrast for this purpose, in the cooling method according to the invention, the transmission line is cooled in the radial direction, with the heat of vaporization of the cooling medium is used. The method according to the invention also has the advantage that the production of the transmission line it is much easier that the cooling effect is greater than in the known methods and that a long transmission line is cooled very effectively by using a material as the coolant is used, which acts as an insulator at least in the gaseous state.

In the cooling method according to the invention, which utilizes the heat of vaporization of the cooling medium, the conductor of the transmission line can at a low, e.g. B. at normal temperature can be used. It is also possible to keep the conductor at high temperatures

3590 109819/0356

- ¹¹ - 16 9 Ü1 p

of absolute zero by lowering the temperature of the transmission line and shielding the thermal radiation from the outside. When the conductor is used at normal temperatures, a number of problems relating to thermal expansion and contraction of the cable can be solved very easily. If the conductor is used at temperatures close to λ absolute zero, there is the advantage of utilizing the superconductivity of the conductor. In both cases it is possible to reduce the electrical resistance in accordance with the lowering of the temperature, so that an increase in performance is obtained which is equivalent to the increase in the effective cross-sectional area of the conductor.

A cooling medium that can be used in the method according to the invention must meet the following conditions:

1. The cooling medium must be at room temperature and normal atmospheric Gaseous pressure and liquid at higher pressure.

2. The cooling medium must not be flammable or explosive. This requirement arises essentially from the fact that the

3590 109819 / Π356

! 690153

th lines should be used in or around a large city to ensure that there is no fire and a Explosion can be avoided if a dielectric breakdown occurs due to some external circumstance.

™ 3. The cooling medium must not be toxic or only slightly toxic,

so that damage can be avoided in the event of a discharge.

4. The cooling medium must be good electrical, at least in the gaseous state Have insulating properties as well as a low dielectric coefficient, a low dielectric tangential Loss and high dielectric strength.

| 5. The coolant may be used in the conductor, which is made of copper or aluminum, for example can exist, not corrode and attack. This requirement also applies to a casing made of steel, lead or Aluminum as well as with regard to the insulating material, which can consist of plastic or paper.

6. The refrigerant must have a large latent heat of vaporization.

109819/0356 3590

.13-Ib9ü153

7. The coolant must not have too high a viscosity in the liquid state to have.

The coolant must be stable in terms of its chemical properties be. The decrease in reaction sensitivity must be at least below

be low under the given conditions. f

Cooling media that meet the aforementioned conditions are, for example, CCl ₀ F ₀ , SF _ß , CO ₀ and CHClF ₀ . This results in the following values:

ei Δ Xi Δ Δ

Gas pressure ο

kg / cm

0.5-5 1-20

Fluid pressure
kg / cm ^CC1 2 ^F 2 5-30 SF ₆ 10-100 co ₂
CHClF

When it comes to cooling, a distinction can be made between internal and external cooling will.

₃₅₉₀ , 109819/0356

.14-lb90153

Internal cooling:

Here, the inflow for the cooling medium is on the part of the insulator. The evaporation of the cooling medium therefore takes place on the inside of the conductor or on an outer circumference or on part of the Insulating material. As evaporation progresses towards the thickness of the insulator, the insulator must be suitable for the flow of the cooling medium be. In this way of working, it is theoretically possible to reduce the thermal resistance It. To zero.

External cooling:

In this case, the cooling medium evaporates starting from the inflow into the space within the casing, but does not cross the insulator. This mode of operation is therefore particularly suitable for insulators with low gas permeability, e.g. B. solid insulators from a tubular deformed plastic. Furthermore, this mode of operation can be used regardless of the type of isolator used.

Further details and features of the invention are from the following Description of preferred embodiments and based on

3590 109819 / Π356

) b 9 01 5 3

can be seen in the accompanying drawings. Figures 1 to 8 relate to preferred embodiments of the method according to the invention and the arrangement according to the invention for cooling a closed Power transmission line. The power transmission line is shown in cross section. The simplicity and clarity For the sake of this, the references to the meaning of the individual Figures 1 to 8 of the drawing are shown in the following table:

Type Cool way Number of nuclei 3 cores tubular type Internal cooling 1 core Fig. 1 ' "completed
ner guy " External cooling Fig. 2 "mechanical"
Type Internal cooling Fig. 5 External cooling Fig. 3 Fig. 6 Internal cooling Fig. 4 Fig. 7 External cooling Fig. 8

-ie-lb9Ü153

9 and 10 relate to schematic diagrams of a inventive connection of a closed power transmission line.

11 and 13 relate to preferred embodiments of the invention? ' to shape of conductors and insulators that can be used according to the invention in a get closed power transmission line.

The meaning of the individual reference symbols used in FIGS. 1 to 8 For the sake of simplicity and clarity, it is shown in the following table:

Fig. 1 Reference number
2 3 32 4th 5 6th 7th 8th Element: 33 corrosion-resistant
protective layer « 21st 4! 51 61 71 81 a coat 12th 22nd 34 42 52 62 72 82 Reflux 13th 23 35 43 53. 63 73 83 Sliding wire 14th 24 36 Spacer 37 44 - Protective layer 15th 25th 38 55 insulator 16 26th 46 56 66 76 86 ladder 17th 27 47 57 67 77 87 Inflow 18th 28 48 58 68 78 88

109819/0356

-π- lb9Ü153

With regard to the following description of the individual figures of In the drawing, it should be noted that the two-digit reference numerals evident from the table above begin with the first digit refer to the figure of the drawing and with the second digit to the element to be identified. So z. B. uniform for the head The number 7 is used in all the figures, so that the designation 17 is to be understood as the conductor 7 of FIG. I.

As can be seen from FIGS. 1 to 6, a conductor 7 is an insulator 6 surrounded. The insulator 6 has an electrical protective layer (not shown) on its outermost circumference. Furthermore, the conductor is provided on its outside with a protective layer 5 for internal pressure or for mechanical protection. To adhere to a certain Spacer spacers 34 and 44 are expediently provided. ι

In the embodiments according to FIGS. 7 and 8, in which an insulating layer is absent, a jacket 2 is provided on the outer circumference. The space between the jacket 2 and the protective layer or the Spacers or the space between the jacket 2 and the insulator 6 is used as reflux 3 for the cooling medium. In the middle

109819/0356

.is- fb9U153

leren part of the conductor 7 or at a point in the area of the return flow 3 an inlet 8 is provided for the cooling medium. In the arrangements according to FIGS. 2, 6 and 8, the inflow 8 is independent of the Head 7 and the spacers.

A corrosion-resistant protective layer 1 serves both for a complete Termination and protection of the cable as well as corrosion protection. The jacket 2 consists of a steel pipe or a plastic pipe (forced plastic pipe). The cooling medium - in the gaseous state flows through the reflux 3. The sliding wire 14 or 24 is used for sliding or inserting the conductor 7 into a pipe if a tubular transmission line is used.

If a transmission line with internal cooling is used, the protective layer 5 and the insulating layer 6 produced by winding a paper, plastic or cloth tape around the conductor 7, whereby the resistance to the gas flow is reduced, which arises when the cooling medium flowing through the supply line within the conductor evaporates and flows through the protective layer 5 and the insulating layer 6 imdial to the conductor 7. The conductor consists of stranded wires or from a single wire, with the supply for the cooling medium being provided inside the same.

³⁵⁹⁰ 1G9819 / 0356

While the transmission line is operating, there is a resistive loss and a dielectric loss due to the current flowing in the conductor and a loss in the clad due to the eddy current in the same. In the process of internal cooling, the ohmic loss in the conductor is carried through directly from the cooling medium radially to the conductor an evaporation of the cooling medium dissipated. In the process of external cooling, the heat generated as a result of this loss is lost through the insulating layer due to the thermal flow and is absorbed by evaporation of the cooling medium. The due The heat generated by the eddy current loss is absorbed by the cooling medium within the reflux line and through the insulating layer the internal cooling blasted outside of the jacket or absorbed by an evaporation of the cooling medium directly with external cooling. The dielectric loss is relatively small, so that there is no significant loss Difficulties arise in practice. To the ohmic and to eliminate the eddy current loss in the jacket as simply and largely as possible, an application of both the line and the line is recommended the external cooling.

In both cooling methods, it is advantageous to adjust the size of the return line to increase the pressure loss of the cooling medium lengthways

109819/0366

-20- I b9Ü 1

reduce the length of the transmission line and a to get the most uniform evaporation heat possible. In practice the arrangement must be designed in such a way that the resistance to the gas flow and the pressure loss are as low as possible. Farther it is necessary, the deviation of the evaporated amount of cooling medium along the length of the transmission line so to be kept as low as possible, which is important to note in the manufacturing process.

As can be seen from Fig. 10, condensers 97 are at one end of the transmission line or provided at both ends or in the middle. With each of these three possibilities for the arrangement of the condenser However, care must be taken to ensure that the condensers are distributed and arranged in such a way that the amount of evaporation is in the longitudinal direction is essentially constant. Known liquefaction processes can be used for liquefaction can be used, e.g. a process in which first compression to high pressure with subsequent cooling and liquefaction is provided or a method in which without compression is cooled and liquefied. The latter liquefaction process is particularly recommended in cold northern zones.

-21- ib9Ü153

In Figs. 9 and 10 embodiments are shown which the Connection between a closed power transmission line cooled according to the invention and an above-ground line or a concern another line. A waveguide 101, which is part of an above-ground Line 92 is connected to a condenser 97 by an isolating coupling 91 and a line. A cooled according to the invention, The closed transmission line 96 is connected to the waveguide 101 via a three-way junction 95, a line 94 and a connection 93 in connection. The three-way junction 95 is connected to the condenser 97 via a line 99. As can be seen from FIG. 10, the Transmission line 96 has a coupling 100 with a large span.

When the transmission line is in operation, the cooling medium is liquefied in the condenser 97 and via line 98 which Isolierkupplung 91 or the interior of the waveguide 101, the interior of arrival (circuit 93, the line 94 and the Dreiwegverzweigung 95 of the transmission line The cooling medium evaporated in the transfer line 96 is returned to the condenser 97 via the line 99.

Figures 11 to 13 relate to preferred embodiments of conductors

109819/0356

-22- lb9Ü153

and isolators, which according to the inventive method for Cooling a closed transmission line are formed. The meaning of the reference symbols of the arrangements according to FIGS. 11 to 13 can be seen in the table below.

Fig. 11 Fig. 12 Fig. 13

Reference number 1104 1204 1304 Sliding wire 1105 1205 1305 Protective layer 1106 1206 1306 insulator 1107 1207 1307 ladder 1108 1208 1308 Supply line Data and dimensions 250 250 500 Voltage (KV) 1000 1000 1000 Power (MVA) / circuit 20th 10 10 Length (km) Inside Inside Inside Cooling method 70 50 40 Feed line diameter (mm)

Cross-sectional area of the ₄₅₀₀

Conductor (mm), aluminum

109819/0356

Fig. 11 Fig. 12 Fig, 13

Data and dimensions

Outside diameter of the conductor (mm) 110

Number of conductor segments 12

Thickness of the insulating layer (mm). 20th

Final outside diameter

(mm), approximate values 160

Inner diameter of the pipe (mm),
approximate values; Metal foil or 600 metal sheet

90 70 8th 8th 20th 30th 140 140 550 450

When comparing the internal and external cooling of the transmission line the following results.

With internal cooling, it is possible to change the density of the transmission power to increase considerably, because the thermal resistance R- can be up to can be reduced to zero, while the density of power transmission is limited in the case of external cooling, since the thermal resistance R- only can be reduced to a very limited extent.

With internal cooling, the cooling medium can either be liquid or

109819/0356

BATH ORIGINAL

b9U153

can be used in the gaseous state, while in external cooling can only be used in the gaseous state.

With internal cooling, the insulator must be made by winding it up, thus a good passage in the direction of the thickness of the insulating layer is guaranteed, while such a good passage is not required for external cooling, so that all manufacturing processes are used can find.

With internal cooling, the supply for the cooling medium is within the Arranged conductor and has a high potential with respect to earth, so that it is necessary to also use the coupling part that connects to the condenser is connected to isolate against this high potential, while with external cooling, since the supply is independent of the conductor, the supply line does not have a high potential, so that there is no corresponding insulation problem.

Since the cooling medium flows inside the conductor with internal cooling, it is possible to limit the conductor temperature to a normal temperature or even lower, which not only reduces the resistance of the conductor can be reduced, but also the problem of

109819 / Π356

BATH ORIGINAL

use of the sheathing, especially when pulling, is solved. aside from that there are no disadvantages due to the insulating effect of the insulator caused by thermal expansion and contraction of the transmission line can arise. In contrast to this, in the case of external cooling, since the path of the cooling medium is independent of the conductor, the aforementioned Points of great difficulty.

Cooling according to the invention of a closed transmission line is carried out as follows in the embodiments of a transmission line described below.

Two transmission lines A and B are provided.

Transmission line A:

Features: tubular structure, internal cooling, cable with three cores, λ

wrapped plastic insulation, cooling medium: SF «, tubular steel jacket,

275 KV, 1500 mm ² .

Transmission line B:

Features: Closed structure, external cooling, cable with three cores, wrapped plastic insulation, cooling medium: CCl ₃ F ₂ , aluminum jacket, 60 KV, 325 mm ² .

109819/0356

»690153

The manufacture, installation and commissioning of the two transmission lines A and B are described as follows:

Transmission line A (see Fig. 1).

The production includes the following steps: As a conductor segment a waveguide is used or a central opening is provided in the middle of a conductor. A polyester tape and a tape made of polyester cloth are alternately wound to insulate the conductor, so that the volume resistance in the direction of the thickness of the insulating material is reduced and stabilized. A metal tape is then wound up as a mechanical and electrical protective layer on which a Sliding wire is arranged.

When installing, three cores are put together in a steel pipe or drawn into a steel pipe, which has a corrosion-resistant protective layer and has previously been placed underground in the ground is. An insulation described above is used in the area of the couplings and connection points of the transmission lines, the clearances of several hundred meters, whereupon the measures evident from FIGS. 9 and 10 of the drawing

109819/0356

-27- (b90153

be realized. After closing the jacket, it is evacuated and _{filled with SF ß} as a coolant.

During commissioning, the coolant is at a condensing temperature at 35 C or less and at a pressure of about

30 kp / cm liquefied in the condenser. The cooling medium has a

2
A pressure of 5 kp / cm when it comes out of the return line to the |

Is returned to the condenser. The cooling medium is the supply line supplied to keep the temperature of the conductor at a predetermined value which is equal to or below the normal temperature. For this purpose, a valve is provided which enables the flow rate to be regulated in order to keep the temperature of the conductor constant. It is also possible to provide * m pressure regulating valve,

Transmission line B (see Fig. 6).

The manufacturing process is as follows. A polyester tape will Wrapped around a conductor made of stranded wire and then surrounded by an electrical protective layer on the outermost circumference. Three such Cores are twisted together with the supply line for the cooling medium. An aluminum jacket is provided as well as a PVC pipe as a corrosion-resistant protective layer.

³⁵⁹⁰ 109819/0356

) B9Q? 53

When installing the connection, as shown in Fig. 10, performed and CClgF «is used as a coolant after making a Vacuum filled, the line 98 of the condenser 97 is connected directly to a line 68 which is not through the isolation coupling 91 passes through.

fe During commissioning, the cooling medium is at a temperature of

35 C or less and liquefied at a pressure of approximately 8 kgf / cm in the condenser. The condenser is adjusted so that the Supply line a temperature of 15 ° C and a gas pressure of approx.

Has 4 kp / cm when the temperature inside the sheath of the cable should be set to a value of 15 ° C. A decrease in the energy of the condenser occurs when the temperature is less than 15 C, so that not yet evaporated cooling medium collects within the supply line and the pressure decreases. A sample of the condenser energy occurs as the temperature in the jacket rises.

From the above it can be seen that a cooled according to the invention, closed power transmission line has a considerably increased transmission capacity, since the conductor and the insulator through

3590

.29- 16901 S3

the heat of evaporation of the cooling medium can be cooled and the cooling medium at least in the gaseous state as an electrical insulating material is used. This has the great advantage that the conductor and the insulator are kept approximately at room temperature can.

The essential features of an and ™ designed according to the invention

cooled transmission line can be summarized as follows:

1. The conductor and the insulator are sheathed from the atmosphere separated and protected from the same.

2. The jacket is filled with a cooling medium, which at least acts as an electrical insulator in the gaseous state.

3. The cooling medium inside the jacket circulates between the supply and return line.

4. The cooling medium changes from the gaseous state to the liquid State transferred by means of a condenser, which is provided outside of the shell.

1 ^ 9819/0356

BATH ORIGINAL

5. The cooling medium is in the liquid state through the supply line initiated into the coat.

6. The cooling medium becomes uniform in the radial direction of the conductor evaporated along the longitudinal direction of the transmission line.

7. The inside of the jacket is cooled by the evaporation heat.

8. The cooling medium together with the part that has not yet evaporated is collected in the return line,

9. The cooling medium serves both for cooling and for insulation.

The inventive cooling method and the inventive cooling arrangement of a closed transmission line can also be used for transformers, Reactors, capacitors or other electrical devices are used, with the advantages that the line capacitance increases, the size of the conductive parts is reduced, and electrical insulation is simplified.

BAD ORIGtNAU

Claims (7)

Claims 1. Method for cooling a closed power transmission line, in the case of conductors and insulation by a jacket in front of the atmosphere are protected, characterized in that within the jacket a supply and a return line for a cooling medium are arranged that a gas in the liquid state of the supply line as cooling medium is supplied, which is gaseous at normal temperatures and at atmospheric pressure and at superatmospheric pressure is liquid and acts at least in the gaseous state like an electrical insulator that a lower pressure than in the return line the supply line is maintained that the cooling of the transmission line is carried out taking advantage of the heat of evaporation that occurs when the cooling medium leaves the supply line flows out and evaporates, and that the evaporated cooling medium by means of the return line is routed from the jacket to the outside. 109819/0356 ' 690153 2. Process for cooling a closed power transmission line, in which the conductor and insulation are protected from the atmosphere by a jacket, characterized in that the supply line for the cooling medium is arranged in a conductor of the transmission line that a gas in the gaseous state is supplied to the supply line as a cooling medium which at normal temperature and at atmospheric Pressure is gaseous and liquid at superatmospheric pressure and acts like an electrical insulator at least in the gaseous state, that in the return line a lower pressure than in the supply line that the transmission line is maintained by the heat of the Evaporation is cooled, which occurs when the cooling medium flows out of the supply line through the conductors and insulators and evaporates, and that a space within the jacket is used as a return line for the cooling medium. 3. The method according to claim 1 or 2, characterized in that the cooling medium led out of the jacket liquefies and circulates will. 109819 / Π356 b9Ü153 4. The method according to one or more of the preceding claims, characterized in that the difference between the pressures of the supply and return lines is controlled to increase the amount of evaporation to regulate the cooling medium. 5. The method according to one or more of the preceding claims, characterized in that an evaporating layer ™ in the jacket is provided to provide a uniform and even resistance for the flow of the cooling medium along the entire length of the transmission line to create" 109819/0356 1090153 6. Arrangement for performing the method according to one or more of the preceding claims, characterized in that a supply and a return line for a cooling medium in one jacket the transmission line are provided that a condenser is arranged at least at one point on the transmission line and connected to the supply and return line is connected to that means for supplying a ^ serving as a cooling medium gas in the liquid state to the supply line are provided with the gas at normal temperature and atmospheric Pressure is gaseous and liquid at superatmospheric pressures and at least in the gaseous state like an electrical insulator acts, and that means are provided which return the evaporated cooling medium to the condenser. 7. Arrangement according to claim 6, characterized in that control devices are provided that regulate the difference between the pressures in the supply and return lines. 3590 109819 / ^ 356 ORIGINAL INSPECTED