US3903355A

US3903355A - Cooling arrangement for electrical transmission system

Info

Publication number: US3903355A
Application number: US454237A
Authority: US
Inventors: Werner Rasquin
Original assignee: Felten and Guilleaume Kabelwerke GmbH
Current assignee: Felten and Guilleaume Kabelwerke GmbH
Priority date: 1973-05-29
Filing date: 1974-03-22
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02
Also published as: FR2232113B1; GB1451274A; JPS5021283A; NL7400560A; FR2232113A1; IT1005238B

Abstract

An arrangement for cooling high voltage electric power transmission cables, comprising cooling fluid channels located in the core of the cables, cooling means located at the beginning and end of said channels, and means for circulating cooling fluid in predetermined directions through each of said channels.

Description

United States Patent Rasquin Sept. 2, 1975 1 1 COOLING ARRANGEMENT FOR 2.969.415 1/1961 Hartill et al 174/19 ELECTRICAL TRANSMISSION SYSTEM 3.105.883 10/1963 Higson, Jr. 174/1 1 R X 3.187.080 6/1965 Ball 1 1. 174/11 R [75] Inventor: Werner Rasquin, Cologne. Germany 339101 12 1966 Kafka 174/15 C 3.485930 12/1969 Priaroggia .t 174/15 C [73] Assgnw Felte Gumeaume Kabelwerke 3,800,062 3/1974 Kataoka 174/15 0 AG, Cologne. Germany [22] Filed. Man 22, 1974 FOREIGN PATENTS OR APPLICATIONS 1,573,685 7/1969 France 174/l5 C [2]} Appl- 454,237 1,124.08] 8/1968 United Kingdom 174 15 c [30] Foreign Application Priority Data Primary Examiner-Arthur T. Grimley May 29. 1973 Germany N 2327316 Attorney, Agent, or Firm-Michael S. Striker Aug. 9, 1973 Germany.... 2340328 Sept 15. 1973 Germany... 2340507 [57] ABSTRACT 2 U.S. l ..174l5C; 17411 R;17414 R; [5 1 C l/74/27 An arrangement for cooling high voltage electric [5!] Int Cl 2 018 7/34 power transmission cables, comprising cooling fluid [58] Field 14 R 27 channels located in the core of the cables, cooling H means located at the beginning and end of said chan- [56] References Cited nels, and means for circulating cooling fluid in predetermined directions through each of said channels. UNITED STATES PATENTS 873,216 12/1907 Davis 174/l5 C 13 Claims, 4 Drawing Figures PATENTEDSEP zms sum 1 BF 4 PATENTEM 975 sum 2 BF 4 FIG. 2

PATENTEU SEP 2 I975 sum 3 BF 4 FIG. 3

COOLING ARRANGEMENT FOR ELECTRICAL TRANSMISSION SYSTEM BACKGROUND OF THE INVENTION The present invention relates to high voltage electrical transmission systems, particularly to three phase alternating current systems with associated cooling means.

It is generally known to provide circulating fluid cooling devices, such as oil or water ducts, in the fabrication of high voltage transmission systems. Such systems, however, only include one cooling station or heat-exchanging device. After cooling. the fluids enter the system and flow in the same direction. Following circulation and heating by the cable, the fluids are generally returned to the cooling unit in external return flow tubes, which are separate from the transmission cables.

The construction of return flow pipes may be made as separate pipes or tubes, or with three possibly conical isolated electrical conductors distributed in a known manner in the return flow pipes (see, for example, West German published Pat. application No. 1,067,099). In such an arrangement, should one con ductor or return flow pipe fail, then the entire cable system would become inoperative.

SUMMARY OF THE INVENTION It is an object of the invention to provide a cooling arrangement for high voltage electric power transmission cables utilizing a plurality of cooling fluid channels and at least two cooling units.

Another object of the invention is to provide a novel and improved means for maintaining the system in operation should one of the conductors, or one of the cooling channels, fail.

The invention is embodied in an arrangement of four parallel cables, with a cooling fluid, such as oil or water, flowing in a cooling channel in the center of each cable. At the beginning and end of the cables is a cooling station, with cooling means, connected to said cooling channels so as to receive and cool the cooling fluid therein. The cooling fluid is then recirculated in the system in predetermined specified channels and directions.

Three of the four cables normally carry electric cur rent, such as in a three phase alternating current sys tem, and the fourth cable serves as a reserve. Should the conductor in one cable or one of the cooling channels fail, it would be possible to immediately switch over to the reserve cable, and thereby maintain continuous operation of the system.

It is particularly advantageous in such an arrangement to have the cooling fluid flowing in one direction in two of the cables, and flowing in the opposite direction in the other two of the cables. Such an arrangement of continuous recirculation of the cooling fluid is more economical than utilizing separate flow lines to return and recirculate the fluid. The fourth cable serves the purpose of providing return flow of the cooling fluid, and also serves as a back-up conductor in case of malfunction of another cable.

Another feature of the invention is to obtain the maximum technical advantage at the least cost. One method of achieving this goal is to utilize intermediate pumping means along the channel and cable, in addition to the pumping stations at the beginning and end of the cable. Activating the intermediate pumps for the cooling fluid will increase the throughput of the cooling channels. (i.e., increase the quantity of fluid flowing through the channel), and thereby increase the rate of heat dissipation in the cable. In this manner, one can have a higher maximum permissible power in the cable system than without the intermediate pumps.

Increasing the maximum permissible system power also increases the cost of the system, due on the one hand to both the manufacture and assembly of the intermediate pumps themselves, and a loss due to high installation costs on the other hand, bringing about higher overall cost, as well as the costs from construc tion of the cooling station. These higher costs however are associated with a higher output of the transmission system, more advantageous system length, and increased lifetime. Thus, when these costs are compared in the long run with the advantages of long term operation, it would appear to be an economical choice in spite of higher construction costs.

A particular embodiment of the invention envisions that the distance between cooling stations is more than 10 kilometers, the inner diameter of the cooling fluid channel is from 40 to mm.

The number n of intermediate pumps to be located in the cable system between cooling stations may be calculated from the equation where:

K Total cost of the cable system before the installation of intermediate pumps;

K,. Capital costs for the cooling stations before the installation of intermediate pumps;

K ,v Cost of the power loss before the installation of intermediate pumps.

From the above analysis it follows that operation is most economical if small diameter fluid channels are used with relatively long distances between cooling stations, and wherein the cost of the cooling stations (K together with the cost of power loss (K is less than half of the total cost (K,,,,,,,).

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a cross-sectional view of the cable system arrangement relative to the surface of the earth;

FIG. 2 is a cross-sectional view of a single cable, showing the various component elements;

FIG. 3 is a diagram of the cable cooling and flow system arrangement; and

FIG. 4 is a graph relating pressure variables and temperature variables in the system to electrical power transmitted.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view of an electrical cable system for power transmission of high intensity. such as over 2 million voltamperes. The figure shows the cable system 1 located beneath the surface of the earth there are four separate parallel cables in the system, three normally carrying current (such as in a threephase or three-wire system), and the fourth serving as a back-up or reserve cable. The axes of the four cables are situated at the corners of a square, one diagonal of which is parallel to the surface of the earth 5 and has a length 2a, as shown. The reserve cable is the one furthest from the surface of the earth, since it would be used only rarely, it would be subject to the least deterioration over time.

The figure also shows the spacing a, of the cables 2 from the center of the square (not shown), and a schematic cross-section of each cable, with conductor 4, provided with a central channel 3 for cooling fluid.

FIG. 2 illustrates the cross-section of a cable 2 in more detail. In the center of the cable a cylindrical tube 6 forming a channel 3 for passage of the cooling fluid, and a concentric conductor 4 of copper or aluminum piping or wire braid. The tube 6 can be constructed of either metal or plastic.

Outside of the conductor 4 is a smooth conductive lining member 7; and finally an insulator 8, composed of plastic or oil treated paper. Outside of the insulator 8 is an electrical shield 9, composed of a copper band, for example. This

central portion

3, 6, 4, 7, 8, 9 rests inside of an enclosure defining an open space 23 between the central portion and the enclosure.

The enclosure of the cable is composed of a corrugated tube 10, preferably of aluminum, surrounded by a covering layer 11 of plastic material, and finally another outer sheathing 12 of plastic or other synthetic material.

FIG. 3 is a diagram of the cooling system arrangement. The diagram shows the four cables 2, which, in one particular embodiment, have intermediate pumps 21 uniformly distributed over the length of the cable. The length of the cable may be more than kilometers.

Also shown are fluid monitoring means 20, to measure various parameters such as temperature and pressure of the fluid at least at one point of each cable, electrical insulating means 13; and three-phase electric grid wires R,S,I, connected to the electrical conductor 4 of the cable through switches 14.

Following another electrical insulating means 15, the fluid channel tube 6 extends from the cable and is grounded at 16. The channel preferably has a diameter of between 40 and 70 mm.

In normal operation of the system, the cooling fluid circulates in the channel in the direction shown by the arrows 17, due to the action of the circulating pumps 18. The fluid is pumped through two cables, through a first cooling means 5, then back through the other two cables, then through a second cooling means 5, and once again through the two original cables. Valves l9 permit adjustment or cutoff of circulation in any of the channels.

The fluid monitoring devices are able to sense key parameters like temperature and pressure of the fluid in the channels. In the event of disturbance or malfunction of a particular cable and channel, these parameters would change, thereby alerting the operator of the system. The operator then may immediately switch the grid wire connections by changing switches 14 to another combination of cables. Furthermore, the operator may selectively close certain valves 19, to shut off the cooling fluid flow from the channel experiencing a malfunction.

In normal operation, the cooling fluid flow would be in one direction in two of the cables, and in the opposite direction in the other two cables. In the case of malfunction or disorder in one cable, the cooling fluid would be shut off in that one cable; the fluid would then flow in one direction in two cables, and in the opposite direction in the remaining cable. This circulation distribution makes it possible to maintain the power level in the transmission system, although the cooling fluid throughput in the cooling channel system, with one channel inoperative, is necessarily lower.

Although it is desirable to avoid lowering the fluid throughput, the effect is not so great as to require a drastic reduction in power. The two cables in which the water is flowing in the same direction will merely experience a higher operating temperature; and the fluid flowing in the remaining will experience a rise in operating pressure, compared with the operating parameters under normal system operation. Repairs to the defective cable are not expected to take too much time, and the effect of higher-than-normal operating temperatures on certain cables for a relatively short period of time is not expected to shorten the life expectancy of such cables significantly.

One consequence of the high electric current able to be carried by the transmission system is the production of a strong magnetic field in the region of the conductors. In conventional cable systems, the magnetic induction with neighboring cables will set up eddy currents, creating additional heating of the cables.

Another feature of the invention is the'particular arrangment of the four cables. In the particular embodiment seen in FIG. 1 the axes of the cables are located at the corners of a square; one diagonal of the square is parallel to the surface of the earth. Thus, the three cables carrying current lie on the vertices of an isosceles triangle, and the single magnetic field associated with a single cable effectively neutralizes the other magnetic fields, at any given time. Furthermore, the cable not carrying current does not sense any significant magnetic field. The region of the transmission system has only a small, stable, net magnetic field, which is independent of which of the three cables are energized.

The three cables lying closest to the surface of the earth are preferably the ones used to carry current. In this way, should one of the cables require repair, they are relatively close to the surface, and can therefore, be more easily repaired or replaced.

FIG. 4 is a graph illustrating various relationships be tween key parameters of the system.

S transmission system power during undisturbed operation.

S transmission system power during disturbed operation.

AT temperature increase in the channel when fluid is flowing in a first direction during undisturbed operation.

AT =temperature increase in the channel when fluid is flowing in a first direction during disturbed operation.

AP,, pressure drop along the channel in a second opposite direction of flow during undisturbed operation.

AP pressure drop along the channel in a second opposite direction of flow during disturbed operation.

The term undisturbed operation is to be understood as the normal operation of the system with fluid flowing in two channels in one direction, and two channels in the other direction. Disturbed operation is to be understood as the operation when one of the fluid channels is blocked, so that fluid flows in one channel in one direction, and in two channels in the opposite direction.

Examining the curves in FIG. 4, one can see that the combination of operating parameters expressed above correspond to the 5/5 1 curve, i.e. the electrical power transmission during disturbed operation is the same as during undisturbed operation.

lf the operating range of the pressure and temperature parameters of the system do not allow particular levels (96C and 84 bar), then the electrical power transmission during disturbed operation will be somewhat less than during undisturbed operation, corresponding to /8,, curves below the S/S 1 curve in FIG. 4. On such curves the pressure difference and/or the temperature difference during disturbed operation would be lower.

The form of the curves themselves are derived as follows: The electrical power capable of being transmitted through the cable is proportional to the fluid throughput. Thus 5,, -AT,, V AP and the curves are given by An example using specific operating parameters should clarify the relationships expressed in FIG. 4.

Suppose, in normal operation. the temperature T, of the fluid entering the channel is 30C, and the temperature T of the fluid leaving the channel is 85C. The corresponding pressure P, of the fluid entering the channel is 31 bar, and the pressure P of the fluid leaving the channel is 1 bar. Therefore A7), 8530C 55C; and AP 3ll bar 30 bar.

Further supposing that during disturbed operation T 30C, T 96C, so that AT= 66C. The corresponding pressure difference is AP 83 bar.

The ratios of the l. differences A7}, and AI, and pressure differences AP,, and AP, during undisturbed and disturbed operation are:

In this case, if the temperature difference along the two cables which conduct cooling medium in one direction in the disturbance case increases by relative to the operating temperature difference in the undisturbed state, then the pressure difference along the individual cables with oppositely directed current direction must be more than doubled.

While the invention has been illustrated and described as embodied in a cooling arrangement for an electrical transmission system, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitutes essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended:

l. A three-phase power-transmission cable system, comprising, in combination, a first set of three phase lines at a first location, and a second set of three phase lines at a second location remote from said first location; three cables and a fourth cable constituting a reserve cable, said three cables and said fourth cable adjoining each other and each spanning the distance from said first location to said second location and having respective first ends at said first location and respective second ends at said second location, each cable including an electrical conductor and an internal channel for the flow of a cooling medium in heat-exchanging relationship with the respective electrical conductor along the length of the respective cable from one to the other of said first and second locations; electrical switching means operative during normal operation for electrically connecting said conductors of said three cables at the first ends thereof to respective ones of the three phase lines of said first set and at the second ends thereof to respective ones of the three phase lines of said second set while leaving at least one end of the conductor of said reserve cable electrically unconnected to said phase lines, and operative in the event of failure of one of said three cables for connecting the phase lines associated with the conductor of the failed cable to the respective ends of the conductor of said reserve cable; and cooling means operative during normal operation for establishing a flow of cooling medium through the internal channels of said three cables and also said reserve cable, whereby in the event of failure of one of said three cables and establishment of electrical connections between the phase lines associated with the failed cable and the respective ends of the conductor of said reserve cable the heat generated within said reserve cable will be immediately removed by the cooling medium already flowing therethrough.

2. A system as defined in claim 1, wherein said three cables and said reserve cable are each a one-conductor cable.

3. A system as defined in claim 1, wherein said cooling means includes a first cooling station at said first location and a second cooling station at said second location, and connecting means connecting said first cooling station to the first ends of said three cables and of said reserve cable and connecting said second cooling station to the second ends of said three cables and of said reserve cable to establish at least one closed flow circuit for the flow of cooling medium through the internal channels of said three cables and of said reserve cable and through said first and second cooling stations.

4. A system as defined in claim 1, wherein said cooling means includes a first cooling station at said first location and a second cooling station at said second location, each of said cooling stations having respective inlet means for receipt of higher-temperature cooling medium and respective outlet means for the discharge of cooled and therefore lower-temperature cooling medium, and connecting means connecting the internal channels of two of said cables at the first ends thereof to the inlet means of the first cooling station and at the second ends thereof to the outlet means of the second cooling station, and connecting the internal channels of the remaining two of said cables at the first ends thereof to the outlet means of the first cooling station and at the second ends thereof to the inlet means of the second cooling station, and fluid impelling means for effecting flow of cooling fluid from the outlet means of said first cooling station to the inlet means of said second cooling station through the channels of two cables in one direction and for effecting flow of cooling fluid from the outlet means of the second cooling station to the inlet means of the first cooling station through the channels of the two remaining cables in the opposite direction.

5. A system as defined in claim 4, wherein said cooling means includes means operative in the event of failure of one of said three cables and establishment of electrical connections between the phase lines associated with the failed cable and the respective ends of the conductor of said reserve cable for blocking flow of fluid through the internal channel of the failed cable so that cooling fluid flows in one direction through two of the three operating cables and in the opposite direction through the remaining one of the three operating cables.

6. A system as defined in claim 5, wherein the dimensions of said internal channels, of said connecting means, and of the flow passages in said cooling stations and in said fluid impelling means, the cooling capacity of said cooling stations and the throughput of said fluid impelling means are such that when the flow of fluid through the failed cable is blocked the temperature of the two cables through which cooling medium flows in the same direction and also the pressure of the cooling medium in the remaining one of the three operating cables are higher than during normal operation but such as to leave the transmission of electrical power through the cable system the same as during normal operation.

7. A system as defined in claim 1, wherein each of said three cables and said reserve cable is a oneconductor cable the conductor of which is hollow, with the hollow interior of the conductor defining the respective internal channel.

8. A system as defined in claim 1, wherein said cooling means includes four intermediate pumps, each connected in the flow path of the internal cooling channel of a respective one of said cables intermediate the first and second ends thereof.

9. A system as defined in claim I, wherein said cooling means includes four groups of intermediate pumps, the number of pumps being the same in each of said groups, and the pumps of each group being connected in the flow path of the internal cooling channel of a respective one of said cables intermediate the first and second ends of the respective cable and uniformly spaced along the length of the respective cable.

10. A system as defined in claim 1, wherein the distance between said first and second locations is greater than 10 kilometers, and wherein the flow diameter of each of said internal channels is between 40 and millimeters, and wherein the number of intermediate pumps in each of said four groups is equal to n, where n mml)/( cs loss) 1 1 wherein:

K the total cost of the cable system before installation of the intermediate pumps,

K capital cost of the cooling means before the installation of the intermediate pumps,

K cost of the power loss in the cables before the installation of the intermediate pumps.

11. A system as defined in claim 3, wherein the flow of cooling medium in said system from said first location to said second location and also from said second location back to said first location is exclusively through the internal channels of said cables.

12. In an electrical transmission system, particularly for the transmission of high voltage electrical power, a combination comprising a plurality of cables each spanning the distance between a first location and a second location remote from the first location, each cable comprising an electrical conductor and an internal channel for the flow of a cooling medium; cooling means comprising at least discrete first and second units, said first unit being at said first location and communicating with the first ends of said internal channels and said second unit being at said second location and communicating with the second ends of said internal channels; and means for circulating cooling medium in said channels, such that the flow in one of said channels is counter to the flow in another of said channels, wherein the number of said cables is four, and said system is a three-phase alternating current system, wherein a combination of three of said cables carries electric current while the fourth cable serves as a reserve, wherein said cables are located beneath the surface of the earth, wherein each of said cables is located at one of the corners of a quare, and wherein a diagonal of said square in parallel to said surface of the earth.

13. A combination as defined in claim 12, wherein said fourth cable is that which lies furthest from said surface of the earth.

Claims

1. A three-phase power-transmission cable system, comprising, in combination, a first set of three phase lines at a first location, and a second set of three phase lines at a second location remote from said first location; three cables and a fourth cable constituting a reserve cable, said three cables and said fourth cable adjoining each other and each spanning the distance from said first location to said second location and having respective first ends at said first location and respective second ends at said second location, each cable including an electrical conductor and an internal channel for the flow of a cooling medium in heat-exchanging relationship with the respective electrical conductor along the length of the respective cable from one to the other of said first and second locations; electrical switching means operative during normal operation for electrically connecting said conductors of said three cables at the first ends thereof to respective ones of the three phase lines of said first set and at the second ends thereof to respective ones of the three phase lines of said second set while leaving at least one end of the conductor of said reserve cable electrically unconnected to said phase lines, and operative in the event of failure of one of said three cables for connecting the phase lines associated with the conductor of the failed cable to the respective ends of the conductor of said reserve cable; and cooling means operative during normal operation for establishing a flow of cooling medium through the internal channels of said three cables and also said reserve cable, whereby in the event of failure of one of said three cables and establishment of electrical connections between the phase lines associated with the failed cable and the respective ends of the conductor of said reserve cable the heat generated within said reserve cable will be immediately removed by the cooling medium already flowing therethrough.

7. A system as defined in claim 1, wherein each of said three cables and said reserve cable is a one-conductor cable the conductor of which is hollow, with The hollow interior of the conductor defining the respective internal channel.

9. A system as defined in claim 1, wherein said cooling means includes four groups of intermediate pumps, the number of pumps being the same in each of said groups, and the pumps of each group being connected in the flow path of the internal cooling channel of a respective one of said cables intermediate the first and second ends of the respective cable and uniformly spaced along the length of the respective cable.

10. A system as defined in claim 1, wherein the distance between said first and second locations is greater than 10 kilometers, and wherein the flow diameter of each of said internal channels is between 40 and 70 millimeters, and wherein the number of intermediate pumps in each of said four groups is equal to n, where n ((Ktotal)/(Kcs + Kloss) - 1)2 - 1 wherein: Ktotal the total cost of the cable system before installation of the intermediate pumps, Kcs capital cost of the cooling means before the installation of the intermediate pumps, Kloss cost of the power loss in the cables before the installation of the intermediate pumps.