CA1081810A - Electric cable cooling apparatus with multiple cylinder pump - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Cooling apparatus and method for an electric cable installation in which the cable has a plurality of oil filled channels, the movement of the oil cooling the cable. The apparatus differs from prior art apparatus in that it uses a pair of multi-cylinder pumps, one at each end of the cable channels and having a number of oil operable cylinders equal to the number of channels, and a number of combination tanks at each end of the channels equal to the number of channels, each tank including an oil operable, bellows-type separator and the tanks and pump cylinders being connected so that the circuit for the cable oil is separate from the circuit for the actuating oil of the cylinders and from the fluid which opposes movement of the separator.
Electrovalves at each end of the channels control the insulating oil flow between the channels and the tanks, and the opening and closing of the electro-valves and the operation of the pumps is coordinated so that cooling oil in the channels oscillates and moves simultaneously in the same direction when enforced or higher cooling is required. When the pumps and electrovalves are de-energized (electrovalves open), the system operates in a conventional manner to compensate for cooling oil expansion and contraction with normal, e.g., ambient and normal load, temperature changes.

Description

o The present invention relates to a method and apparatus for the cooling of electric cables hav-ing distinct insulating oil channels and relates particularly methods and apparatus for causing the oil mass in the cable channels to oscillate.

It is known that cables for conveying electric energy, being as they are subject to heating caused by the current passage, require an adequate cooling for keeping the temperature within values consistent with both the life and service of said cables. For this reason, various inst~llations are used for moving the insulating oil longitudinally in a cable for the purpose of removing heat due to current passage and of avoiding the formation of localized overheated areas, coincident with the joints, if any, used for joining various cable units together. A known type of installation provides a pump inserted into the insulating oil circuit, so that oil under pressure is sent into one of the channels while oil is sucked from the remaining channels arranged in parallel with each other.

Unfortunately, in this known case, two unaccept-able inconveniences arise, as follows: -.~ .
(1) The first inconvenience originates ~-from the fact that mechanical impurities caused by pump parts cause deterioration of the insulating oil dielectric character-istics.

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(2) The second inconvenience, which, for example, can be noted in a tern of in-dividual cables, originates from the fact that longitudinal motion of the insulating oil would be obtained along the channel of one phase, in the forward direction and along the remaining two channels in the backward direction. Consequently, a non-uniformity in cooling conditions for the various phases would be obtained.

A further known type of installation provides the separation of the circuit in which the insulating oil flows from circuit in which the pump oil circulates. Sub-stantially, said installation includes, at a first extrem-ity of a cable channel, a centrifugal pump, a first tank containing a liquid and a second tank containing a number of lenticular cells filled with insulating oil and hav-ing deformable walls. Said cells are connected to each other by a collector pipe which in turn communicates the interior of the cells with cable oil, and said second tank, exteriorly of the cells, is filled with the same liquid as the first tank. At the cable second extremity, there is a third fluid-tight closed tank, in the interior of which there are a number of deformable closed cells filled with gas. Said third tank also communicates with the oil of the cable.

During operation, said pump takes liquid from the first tank and it introduces said liquid into the second tank, thereby causing a variation of the volume 8~ 0 of the cells and causing, therefore, an oil flow from the cells to the cable and, therefrom, into the third tank. Thereafter, the pumping direction of the pump is reversed, the pressure within the second tank decreases and oil flows from the third tank through the cable to-wards the second tank cells.

The latter described installation would allow for the elimination of the cited inconveniences, because the insulating oil would remain separate from the pump parts and each phase would be cooled down in the same manner as the other ones. However, it is evident that the use of a centrifugal pump for each cell-containing tank would involve a high cost when a number of cables and corresponding channels in which the insulating oil has to be oscillated are dealt with. Further, it should be particularly noted, that centrifugal pumps find a practical applieation only with pressure of 3 or 4 atmospheres, whereas present aooling installations may -require service pressures of over 10 atmospheres.

One might think that the wanted pressure could be attained by way of increasing the number ôf pumps.
However, in such a case only an inconvenience of a tech-nical nature would be overcome, while, onthe other hand, the inconvenience of an economic nature, the cost of numerous pumps, would be enhanced and worsened.

Unfortunately, for the reasons given herein-before, said present known types of installations have various inconveniences which, up to date, have not been solved.

In addition, further difficulties have been observed in cases where one wishes to associate an installation suitable for enforced cooling by means of pumps, to another installation provided with traditional tanks containing insulating oil and capable of counterbalancing oil volume variations due to cable temperature changes. Such tanks are arranged at the ends of the channels in a manner such that they send out or absorb insulating oil according to oil volume variations within cable channels, e.g. because of lowering ambient temperature as between day and night.
In general, the difficulties as hereinbefore described present a number of problems to be solved. In fact, a solution thereof should be ;~
reached which permits obtaining a single installation which does not foul the insulating oil, which is effective in enforced cooling and also effective for counterbalancing oil volume in channels due to cable tempera-ture variations, and which at the same time is also simple and has a low cost both for materials used and for the necessary equipment installation.
Unfortunately, up to date, all of the known solutions do not allow for the simultaneous solution of all said problems.
One object of the present invention, is, therefore, to provide an installation for oil mass oscillation in distinct channels of electric cables which is capable of solving the cited problems and overcoming the cited inconveniences.
According to the present invention, there is provided a pumping installation for cooling electric energy cables, said cables having a plurality of channels for the flow of insulating oil, said channels having first adjacent ends and opposite, second adjacent ends, said installation comprising: a pair of pumps, each having a plurality of cylinders equal in number to the number of said channels, each cylinder having a suction side and a delivery side and a bellows-like separator which is fluid actuable and which separates said suction side and said delivery side from said fluid and each pump having a common actuating means for its cylinders, one pump being adjacent said first adjacent ends and the other pump being adjacent said second adjacent ends; a first plurality of insulating oil tanks equal ` ~f, -4-.

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lQ81~10 in number to the number of said channels disposed adjacent to said one pump; a second plurality of insulating oil tanks equal in number to the number of said channels disposed adjacent said other pump; a plurality of valves equal in number to the number of cylinders; means connecting each of the delivery sides of the cylinders of said one pump respectively to one of the first adjacent ends of said channels; means connecting the suction sides of the cylinders of said one pump respectively to one of said first pl~rality of tanks; means connecting the delivery sides of the cylinders of said other pump respectively to the said second adjacent ends of said channels; means cGnnecting the suction sïdes of the cylinders of said other pump respectively to one of said second plurality of tanks; and means connecting said valves respectively between the delivery side and the suction side of each cylinder whereby when a valve is open, direct flow of insulating oil from the associated channel to its corresponding tank is permitted and when a valve is closed, oil is pumped by a pump to its associated channel from its corresponding tank.
Said installation of the invention is of particular advantage with electric cables for which oil volume variations within cable channels have to be counter-balanced and for cooling down the cables by means of enforced oil mass oscillations in the channels, for example, for limiting within acceptable values the cable temperatures each time electric energy at a higher power than the nominal one has to be conveyed. This advantage arises from the characteristics of said installation, which ~818~0 ~ ~

are substantially the following:

a) the use of pumps with volumetric cylinders and bellows-cylinders capable of sucking and compressing cable insulating oil in circuits : ~.
wholly free from mechanical impurities;

b) a first system for enforced cooling of cables including, in practice, only two multi-cylinder pumps with each cylinder associated, through a driving mechanism, with a motor and a tank for each channel end. In this first sy~tem each pump is -at the respective cable ends, each pump cylinder has a portion for oil delivery associated with a channel and a portion ;.
for oil suction associate with a tank;

c) a second system for counterbalancing oil volume variations in channels, including the same tanks as used in said first system, and simple piping for hydraulically connecting said tanks to said channels by means of elec-trovalves. ..

As will better appear from the description given hereafter, said characteristics allow for the cooling of electric cables, without altering the characteristics of insulating oil, in an effective manner for every elec-tric load condition, with a simple construction and a low installation cost. In addition, an installation according ~6--: .. :

to the present invention is, in particular, suitable for the cooling down of three unipolar cables of a three-phase system with three distinct insulating oil channels. -A further object of the present invention is a method for operating an electric cable cooling installa-tion, as herein described, which method is characterized in.-that it includes the following steps:

a) the alternate actuation of said pumps, the closing of electrovalves at ends of channels next to the actuated pump and the opening of electrovalves at ends of the channels opposite to the actuated pump;

b) the withdrawing of oil from tanks by the actuated pump;

c) the sending of oil under pressure from actuated pump cylinders toward the adjacent channel ends and from the latter towards the tanks at the channel en~s opposite to the actuated pump;

d) the stopping of the actuated pump and opening of the ~previously closed electro-valves;

e) the actuation of the pump and closing of electrovalves at the channel ends opposite to p~eviously actuated pump, and repeating with opposite oil flow steps a), b), c) and;d).

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The objects and advantages of the invention will be better understood from the following description of the presently preferred embodiments thereof, which description should be considered in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram of a cable cooling installation of the invention;

Fig. 2 is a cross-sectional, end view of three separate electrical cables illustrated diagramatically in Fig. 1 which may be part of a three phase system;

Fig. 3 is a cross-sectional view of one cylinder of the groups forming part of the pumps illustrated in Fig. l; and Fig. 4 is a perspective view of the driving mechanism forming part of a pump.

The installation 1 shown in Fig. 1 is suitable for the cooling of a three-phase system formed by three individual -cables 2, 3, 4, each of them with an insulating layer 5, 6, 7 (Fig. 2) around conductors 8, 9, 10 which in turn include a central channel for insulating oil 11, 12, 13, respectively. These channels 11-13 are schematically shown in Fig. 1 and extend from terminals A, B, C, and to terminals A', B', C'. The installation 1 includes two pumps 14, 15, each of them having three equal cylin-ders 16, 17, 18 and 19, 20, 21 respectively, which are capable of sucking and delivering insulating oil under pressure through suction and delivery valves illustrated in detail in Fig. 3 and described in connection therewith.

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The pumps 14 and 15 are driven by two motors 22, 23, .
two actuation mechanisms 24 and 24' between said motors and said pumps (as illustrated in Fig. 4 and described in connection therewith). The installation also includes three tanks 28, 29, 30 in proximity to terminals A', B', C' .

Cylinders 16, 17, 18 of pump 14 have delivery valves connected at terminals A, B, C with first delivery pipes 31, 32, 33 and suction valves connected to second suction pipes 34, 35, 36. Tanks 25, 26, 27 are connected at terminals k, B, C, with third pipes 37, 38, 39. Said second pipes 34, 35, 36 have a limited length between suction valves of cylinders 16-18 and connections 40, 41, 42 between the ends of the third pipes 37-39.

Oil flow between the tanks 25-27 and the oil channels 11~13 is permitted, or shut off, by appropriate conventional electrovalves 43, 44, 45 connected to the third pipes 37, 38, 39 between the connections 40, 41, 42 and the terminals A, B, C.

Connections of the pump 15 with the tanks 28, 29, 30 and of said pump 15 and said tanks 28, 29, 30 with the terminals A', B', C' are the same as those already described for pump 14. Accordingly, in Fig. 1, conn-ections in proximity to the terminals A', B', C', which are the same as those in proximity to the terminals A, B, C are indicated with the same numbers, but primed.

The general diagram of the installation has _g_ o been set forth hereinbefore, and a description of the individual parts thereof, i.e. pump cylinders, actuating mechanism and the tanks will be given hereinafter.
For simplification-reasons the description which follows hereinafter will be limited to the cylinder 16, the mechanism 24 and the tank 25, it being understood that the remaining actuating mechanism and tanks are the same in~construction and operation.

Cylinder 16 (Fig. 3) is essentially the same as the cylinder illustrated in Fig. 1 of our copending Canadian application Serial No. 260, 663, filed Septem-ber 7, 1976 and entitled "Bellows Pump and Pumping Plant for Oil-filled Electric Cables" and includes an internal chamber 46 with bases 46' and 46", and a central horizontal axis, a delivery valve 47 and a suction valve 48, and a cylindrical bellows 49, the axis of which is aligned with the axis of the chamber 46. One extremity of the bellows 49 is arranged in fluid-tight relation to the base 46' of the chamber 46, and the opposite extremity of the bellows 46 is secured, in the interior of chamber 46, to a plate 49'. The~cylinder 16 also includes a fluid-dynamic cylinder 50, completely internal to and co-axial with the bellows 49, a piston 51 sliding in the interior of the second cylinder 50, and a cylindrical stem 52 secured to the center of the bellows plate 49' which stem 52 slides in a central guide 53 at an extremity 50' of said second fluid-dynamic cylinder 50.

Said piston 51, in its resting condition, is 1:. ' . ' ~ 8~

pushed from the left to the right hand side of Fig. 3 by means of a spring 59 arranged between a bearing shoulder 59' of said piston 51 and the extremity 50' of said cylinder 50. Between the base 46" of the chamber 46 and a circular flange 49" carried by the plate 49', there is arranged an oppositely acting spring 54 which acts on one extremity of bellows 49.

~he internal space of the chamber 46 is occupied by two distinct and wholly separate fluids which are in-dependent of each other, and specifically there are:

(1) an actuation fluid which fills the space between the second fluid-dynamic cylinder 50 and the bellows 49, and which through the ports 50" at the extremity 50' of this second cylinder, occupies the remaining space in the interior of the bellows 49 interior;

(2) insulating oil at installation rated pressure which occupies the space between the internal walls of the chamber 46 and the external walls of the bellows 49.

Valves 47 and 48 can be of any known type and, merely by way of example, a particular embodiment thereof is hereinafter described in connection with Fig. 3.
Delivery valve 47 includes an internally truncate con-ical seat 47' w~ith a central port 47" which aligns ~ith a corresponding port 47'n in the wall of the chamber 46 81~

and an upper opening F communicating with the first delivery pipe 31 associated with the terminal A of oil channel 11 (Fig. 1). Said valve 47 has an operating element M, the truncate conical end portion of which is pushed against the truncate conical seat 47' by means of a spring N, engaging a stop surface N' of said valve, and has an upper portion with guide spokes R contacting the internal walls of the valve 47. Said spring N is selected in a manner such that it permits the element M
to move away from the truncate conical seat 47' only when the insulating oil pressure within chamber 46 reaches a pre-set value selected for the enforced cooling of cables.

Suction valve 48 has, internally, a truncate conical seat 48' with a central port 48" communicating with the second suction pipe 34, and an upper opening F' communicating with a port 48llt in the wall of the chamber 46. The valve 48 has an operation element M', the truncate conical end portion of which is~lpressed by its own weight against the truncate conical seat 48', and has an upper portion with guide spokes R' contacting the internal wall of the valve.

The pump cylinders and the associated suction and delivery valves having been described, the actuating mechanism 24 which is capable of causing shifting of the pistons in interior of t~e cylinders 16, 17, 18 (Fig.l) will now be described.

The actuating mechanism 24 (Fig. 4) has an : : ' ' ' ', ' ' B~

eccentric or cam 55 carried by a shaft 56 drivable by motor 22 (Fig. 1), and a multi~faced prismatic member 57, of which three faces 57' are provided with roller bearings 58 arranged with their axes parallel to the axis of the shaft 56, and three further faces 57" alter-nating with the faces 57' and not engaging bearings.
Said prismatic member 57 extends around the eccentric 55 and is held in place due to the thrust that the three pis-tons 51, 51', 51" of the cylinders 16, 17, 18 (Fig. 1), through the springs 59, 60, 61, bring to bear on the faces 57'.

During the rotation of the eccentric 55, the piston 51 always remains in contact with the same face 57' provided with bearings, receiving, first, a thrust which, in Fig. 4, is directed away from the axis of shaft 56 towards the exterior, and, in Fig. 3 from the right to the left hand side in the interior of the chamber 46 of the cylinder 16, and thereafter, when said eccentric 55 permits said face 57' to move towards the axis of the shaft 56 (Fig. 4) and back into its original position due to the action of ~previously loaded spring 59. In a similar manner, during the rotation of the 55, the pistons 51' and 51" similarly move, remaining always in contact, through the corresponding bearings, with the same faces. The presence of roller bearings is of advan-tage in that sliding friction between the pistons and the faces 57' is avoided.

In embodiment shown in Fig. 4, the prismatic ':, - ' ' , . ' ' . .

P~lg18~0 member 57 has only three active faces 57' to effect shifting of the pistons. However, the number of pistons and related active faces can also be increased when an higher oil delivery within the cables is wished. For example, the use of two cylinders for each oil channel extremity could be provided, and in this case also, the faces 57" could be made so-that they are plane, as are the faces 57', and through roller bearings would be in contact with as many pistons.

Having described the pumps and their actuation mechanism, the tanks containing insulating oil will now be described. Tank 25 is of a known type, e.g., is of the type described in Italian patent No. 893,A~2 of the present applicant, and therefore, the internal details of the tank 25 are not illustrated in the present patent application. In general, said tank 25 has a substantially cylindrical shape, and has in its interior an elastic cylindrical chamber composed of a rigid bottom coinciding with tank base, a peripheral surface formed by an elastic, ;~
bellows-like diaphragm, and a mobile rigid closure applied to upper edge of diaphragm. Said elastic chamber con-tains degasified insulating oil at the rated installation pressure, and it communicates with the third pipe 37 (Fig. 1), associated with the terminal A of the oil channel 11, and through the connection 40 with the second suction pipe 34. Around the bellows-like diaphragm, there is a space which is subject to a gas which is under the same pressure as insulating oil within elastic chamber.

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~818~0 When, for example, the insulating oil pressure in third pipe 37 lowers below a pre-set value, gas pressure at elastic chamber exterior prevails, and therefore, a deformation of the diaphragm and oil flow from said chamber towards the inlet of said pipe occurs.

The operation of the installation of the in-vention will now be described.

When an enforced cooling of cables is desired, first one and then the other of the pumps 14, 15 is actuated so that enforced oscillations of the oil mass within the individual channels 11-13 in alternately opposite direc-tions are caused. For example, for a better understand-ing of what is meant, the operation may be started with the pump 14 in operation, the pump 15 stopped, electro-valves 43lï 441, 45' simultaneously deactivated, i,e., open, so that oil flow between the channels 11, 12, 13 and the tanks 28, 29,30 is allowed, whereas electrovalves 43, 44, 45 are activated, i.e., closed, for preventing a portion of the insulating oil sent under pressure by cylinders 16, 17, 18 from flowing back into the tanks 25, 26, 27 through the third pipes 37, 38, 39. Under such conditions, motor 22 rotates, and therefore, the eccentric 55, driven by the shaft 56, cyclically applies thrust to the faces 57 of the prismatic member 57, and cyclically permits them to return to their original position (Fig. 4).

Accordingly, when the pistons 51, 51', 51" are subject to thrust as transmitted by said eccentric 55, .. .. .

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a shift of said pistons occurs, which, in Fig. 4, is directed away from the axis of the shaft 56. In particular, for a more ready understanding, reference is made to Fig. 3 and the operation of the cylinder 16 is taken into consideration, wherefrom it can be noted that there is a shift of piston 51 from the right to the left hand side, in the interior of the second fluid-dynamic cylinder 50, causing movement of the driving fluid through the ports 50" and against the plates 49'. Such driving ftluid movement causes dilation of bellows 49 whose stem 52 slides in the central guide 53 overcoming the force of the opposing spring 54. Then, when said eccentric 55 permits the face 57' of said prismatic member to move towards the axis of the shaft 56 (Fig. 4) a return of the piston 51 to its original position due to the action of spring 59 occurs, and the bellows 49 (Fig. 3) is com-pressed by the action of said spring 54, as well as by pressure of insulating oil which corresponds to the rated one for the installa~on and which in any case exists even when the pumps are stopped.

During the compression phase of the bellows 49 in the cylinder 16 (Fig. 3) in the interior of chamber 46, a lowering of pressure occurs which is sufficient for lifting the element M' from the truncate conical seat 48' of valve 48. Consequently, insulatfmg oil from the tank 25 flows into the interior of chamber 46 through the second pipe 34 and the port 48'~ of the valve 48.

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During the bellows dilation phase which is directed from the base 46' toward the base 46" of the chamber 46, insulating oil previously sucked is pushed against operating element of the valve 47 causing said element to move away from the truncate conical seat 47' against the resistance of the spring N, and moves operating element M' against the truncate conical seat 48', thus causing the valve 48 to shut. Under such conditions, insulating oil, through the central port 47"'`of valve and the open-ing F, flows into the first pipe 31 (Fig. 1), into channel11 and then, through the third pipe 37', into the tank 28.

Cylinders 17 and 18 similarly operate and pro-duce similar oil flows. Subsequently, after a selected pre-set time, the pump 14 is stopped, the valves 43, 44.
45 are deactivated (opened) so that the insulating oil from channels 11, 12, 13 is allowed to flow towards the tanks 25, 26, 27, and the valves 43', 44', ~5' are activated, i.e., closed, for preventing insulating oil as sent into the channels from flowing back to the tanks 28 30 through the third pipes. Under such conditions, there are the suction and compression phases of the pump 15, with delivery of oil under pressure into channels 11, 12, 13 towards tanks 25, 26, 27. Said phases are the same as those which have been hereinbefore explained with reference to the pump 14, and, for simplicity reasons, will not be repeated.

It will be noted that the operation cycles whichhave been described hereinbefore advantageously provide i~8~8~0 a uniform cooling down of all of channels. In fact, the same elements having been arranged at the extremity of each channel, and cyclical actuation of the elements at either of the ends of the cables, produces oscillations of oil mass in all channels. Consequently, all of the electrical phases are cooled down in an equal manner.

The operation cycle which has been described is repeated by alternate actuation of the pumps 14 and 15 and control of the electrovalves until the temperature of the cables is brought to an acceptable pre-set value.
When then the operating conditions correspond to normal service temperatures for the cables, both said pumps 14 and 15 are stopped and the electrovalves 43, 44, 45 and 43', 44', 45' are simultaneously deactivated so that all tanks 25-30 are directly connected with the respective channels 11-13. Therefore, the installation, always with the same tanks used in its enforced cooling system and with the help of simple electrovalves is capable of counter-balancing, in a known manner, the oil volume variations within the cable channels due to normal temperature varia-tions of cables, by means of the insulating oil contained in the elastic chambers of the tanks. Because of this feature said installation is simple.

Further, the use of only two pumps and of only two motors together with the consequent possibility of housing such active units in places of limited dimensions, makes the installation advantageous and of low cost.

, ~0~3~810 A further advantage of the installation of the present invention is offered by the special arrange- -ment of the hydraulic circuits as hereinbefore described, which provide that the oil mass oscillations of the individual channels are independent of each other. Such arrangement is important, for the possible oil pollution, if any, in a channel, does not spread to oil of the other channels, and in addition, in the case of a breakdown, inactivity time of the installation is limited to the time required for oil purification steps in only one channel.

Another advantage of the installation originates from the fact that operating personnel are not necessary because all of the operation phases can be easily made automatic with a pre-fixed program capable of defining for each extremity of channels the operation of a single motor or of three normal electrovalves. For example, the motors 23 and 24 and the electrovalves 43-45 and 43'-45' may be electrically connected in an obvious manner to a conventional timed switching means 70 (Fig. 1) so as to energize and de-energize the motors 23 and 24 and the electrovalves 43-45 and 43'-45' in the sequences described hereinbefore when forced cooling is required and to de-energize all of them when forced cooling is not required.
The switching means 70 may be controlled by any device which is responsive to conditions which indicate that en-forced cooling is required, e.g., cable current or temperature, or by a power distribution supervisor located at a remote point and having a communication line extend-~8~8~0 ing to the means 70 from such remote point.

Further, due to the reduced numbers of activeparts in the installation, the cost for control equip-ment for said parts is lower, and a smaller breakdown percentage is attained.

Another advantageous feature of the present invention is the fact that whatever the number of side-by-side channel terns, it is always possible to only use two-multi-cylinder pumps, only two motors and only two actuating mechanisms. In addition, in this manner, installation active parts are easily and simply arranged even when extremities of channels involved are in proximity to small spaces.

Although preferred embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various modifica-tions may be made without departing from the principles of the invention.

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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A pumping installation for cooling electric energy cables, said cables having a plurality of channels for the flow of insulating oil, said channels having first adjacent ends and opposite, second adjacent ends, said installation comprising:

a pair of pumps, each having a plurality of cylinders equal in number to the number of said channels, each cylinder having a suction side and a delivery side and a bellows-like separator which is fluid actuable and which separates said suction side and said delivery side from said fluid and each pump having a common actuating means for its cylinders, one pump being adjacent said first adjacent ends and the other pump being adjacent said second adjacent ends;

a first plurality of insulating oil tanks equal in number to the number of said channels disposed adjacent to said one pump;

a second plurality of insulating oil tanks equal in number to the number of said channels disposed adjacent said other pump;

a plurality of valves equal in number to the number of cylinders;

means connecting each of the delivery sides of the cylinders of said one pump respectively to one of the first adjacent ends of said channels;

means connecting the suction sides of the cylinders of said one pump respectively to one of said first plurality of tanks;

means connecting the delivery sides of the cylinders of said other pump respectively to the said second adjacent ends of said channels;

means connecting the suction sides of the cylinders of said other pump respectively to one of said second plurality of tanks; and means connecting said valves respec-tively between the delivery side and the suction side of each cylinder whereby when a valve is open, direct flow of insulating oil from the associated channel to its corresponding tank is permitted and when a valve is closed, oil is pumped by a pump to its associated channel from its corresponding tank.

2. A pumping installation as set forth in claim 1 wherein the number of said channels is at least three and said valves are electrovalves.

3. A pumping installation as set forth in claim 1 or 2 wherein said cables are three individual cables each having its own channel.

4. A pumping installation as set forth in claims 1 or 2 wherein said actuating means comprises an eccentric and a motor for driving said eccentric, the cylinders of a pump being disposed around said eccentric and operable thereby.

5. In pumping installation for cooling electric energy cables, said cables having a plurality of channels for the flow of insulating oil, said channels having first adjacent ends and opposite, second adjacent ends, said installation comprising:

a pair of pumps, each having a plurality of cylinders equal in number to the number of said channels, each cylinder having a suction side and a delivery side and a bellows-like separator which is fluid actuable and which separates said suction side and said delivery side from said fluid and each pump having a common actuating means for its cylinders, one pump being adjacent said first adjacent ends and the other pump being adjacent said second adjacent ends;

a first plurality of insulating oil tanks equal in number to the number of said channels disposed adjacent to said one pump;

a second plurality of insulating oil tanks equal in number to the number of said channels disposed adjacent said other pump;

a plurality of valves equal in number to the number of cylinders;

means connecting each of the delivery sides of the cylinders of said one pump respectively to one of the first adjacent ends of said channels;

means connecting the suction sides of the cylinders of said one pump respectively to one of said first plurality of tanks;

means connecting the delivery sides of the cylinders of said other pump respectively to the said second adjacent ends of said channels;

means connecting the suction sides of the cylinders of said other pump respectively to one of said second plurality of tanks; and means connecting said valves respectively between the delivery side and the suction side of each cylinder whereby when a valve is open, direct flow of insulating oil from the associated channel to its corresponding tank is permitted and when a valve is closed, oil is pumped by a pump to its associated channel from its corresponding tank;

a method of cooling said cables which comprises:

alternately actuating said pumps for selected periods of time; and closing the valves connected to an actuated pump and opening the valves connected to the unactuated pump to cause the actuated pump to withdraw insulating oil from the tanks to which it is connected and deliver the oil to said channels while permitting oil to flow into the tanks associated with the unactuated pump.

6. A method as set forth in claim 5 further comprising deactivating both pumps and opening all valves to permit insulating oil to flow out of said tanks to said channels and vice versa with normal temperature changes of said cables.