EA001129B1 - Rotary electric machine with radial cooling - Google Patents

Abstract

1. A rotating electric machine, comprising a stator (1) wound with a high-voltag e cable and provided with stator teeth (4) extending radially inwards from an outer yoke portion (5), characterized in that the machine comprises a winding comprising an insulation system including at least two semi-conducting layers, each layer constituting essentially an equipotential surface and also including solid isolation disposed therebetween, and that at least one stator tooth (4) is connected to at least one cooling tube (18) running radially in the stator tooth (4) and connected to a cooling circuit (34) in which coolant (36) is arranged to circulate and that the cooling is arranged to take place over at least most of the axial extension of the stator tooth (4). 2. A machine as claimed in claim 1, characterized in that at least one of the layers has substantially the same coefficient of thermal expansion as the solid insulation. 3. A machine as claimed in any of claims 1-2, characterized in that the cooling tube (18) is arranged to extend from the outer yoke portion (5) in through a cooling clamp tooth (25) and at the tip of the cooling clamp tooth (25) passes over to the tip of the next cooling clamp tooth (25) and then again out through this cooling clamp tooth (25) to the outer yoke portion (5), forming a cooling tube loop. 4. A machine as claimed in any of claims 1-3, characterized in that the cooling tube (18) is arranged to extend from the outer yoke portion (5) in through a cooling clamp tooth (25) and at the tip of the cooling clamp tooth (25) turn and passes back out through the said cooling clamp tooth (25) to the outer yoke portion (5), forming a cooling loop (21). 5. A machine as claimed in either of claim 3 or claim 4, characterized in that cooling tube loops (21) are arranged in at least one cooling clamp (19) of substantially identical shape as a stator cross section. 6. A machine as claimed in claim 5, characterized in that cooling tubes (18) are arranged to be cast in the cooling clamp (19). 7. A machine as claimed in claim 6, characterized in that the axial distance between the cooling clamps (19) is maximum 200 mm. 8. A machine as claimed in any of claims 3-7, characterized in that the cooling tube loop (21) is provided with at least one beam (30) arranged in the loop. 9. A method of cooling a rotating electric machine provided with high-voltage stator windings as claimed in claim 1, characterized in that the stator is cooled by a coolant (36) being caused to circulate in a cooling circuit (34) through cooling ducts running radially through the stator teeth (4). 10. A method as claimed in claim 9, characterized in that the coolant (36) is caused to circulate in a closed circuit which passes through a heat exchanger (41) cooling the circuit (34) with water from a water reservoir. 11. A machine as claimed in any of claims 1-8, characterized in that the potential of said first layer is substantially equal to the potential of the conductor. 12. A machine according to claim 11, characterized in that said second layer is arranged to constitute substantially an equipotential surface surrounding said conductor. 13. A machine according to claim 12, characterized in that said second layer is connected to a predetermined potential. 14. A machine according to claim 13, characterized in that said predetermined potential is earth potential. 15. A machine according to any one of the claims 11-14, characterized in that at least two adjacent layers have substantially equal thermal expansion coefficients. 16. A machine according to any one of the claims 1-8 or any one of the claims 11-15, characterized in that said current-carrying conductor comprises a number of strands, only a minority of said strands being non-isolated from each other. 17. A machine according to any one of the claims 1-8 or any one of the claims 11-16, characterized in that each of said three layers is fixed connected to adjacent layer along substantially the whole connecting surface. 18. A machine having a magnetic circuit for high voltage comprising a magnetic core and a winding, characterized in that said winding is formed of a cable comprising one or more current-carrying conductors, each conductor having a number of strands, an inner semiconducting layer provided around each conductor, an insulating layer of solid insulating material provided around said inner semiconducting layer, and an outer semiconducting layer provided around said insulating layer. 19. A machine according to claim 18, characterized in that said cable also comprises a metal shield and a sheath.

Description

The present invention relates to rotating electrical machines, for example, synchronous machines, as well as to dual excitation machines, devices for use in asynchronous static current converter stages, machines with an external pole and synchronous flow machines, and in addition to AC machines, intended primarily for work at power plants and the production of electricity. The invention relates primarily to the design of the stators of such machines and the cooling of the stator teeth and thus indirectly isolated electrical conductors constituting the stator winding.

The level of technology

Such machines have traditionally been developed for voltages in the range of 6-30 kV, with a voltage of 30 kV considered as the upper limit. In the case of generators, it was usually understood that the generator should be connected to a power supply network through a transformer that amplifies the voltage to the level of the power supply network, i.e., to a range of approximately 100-400 kV. The present invention is intended for use at high voltages, which are primarily meant electrical voltage in excess of 10 kV. A typical operating range for a device made according to the invention is from 36 to 800 kV.

When using high-voltage insulated electrical conductors, hereinafter referred to as cables, in a stator winding with solid insulation, similar to that used in electric power transmission cables, for example, cable with insulation made of polyethylene with intermolecular bonds (ХЬРЕ), the voltage in the machine can be increased to such a level that It can be connected directly to the power supply network without an intermediate transformer. Thus, there is no need for a conventional transformer. This concept generally provides that the stator grooves in which cables are placed will be deeper than with known technology (thicker insulation due to higher voltage and more turns in the winding). This means that the distribution of losses will differ from the corresponding distribution of losses in a known machine, which, in turn, entails new problems associated with cooling, for example, the stator teeth.

Two different air cooling systems are known: radial cooling, in which air passes through a rotor through its sleeve and radial channels in the rotor, and axial cooling, in which air is blown through the air gap using axial fans.

In the case of radial cooling, the stator is divided into radial channels formed by (usually straight) spacers, which are welded into place. Due to the insufficient thermal conductivity of the stator core in the axial direction, the channels must be located frequently. The disadvantage of air cooling is that the ventilation losses are significant and that the stator must be longer due to the presence of ventilation ducts. Ventilation ducts can also weaken the mechanical structure, especially in the above-mentioned high-voltage generators with long teeth.

The advantage of a water-cooled system for high-voltage generators, used, for example, instead of air-cooled systems, is that radial ventilation ducts may be missing, resulting in a shorter machine with the same efficiency. Water-cooled systems for stators in large AC machines are often based on the use of hollow winding parts, i.e. The electrical wires are hollow and have longitudinal channels for the cooling agent in combination, in some cases, with the introduction of cooling tubes in the axial direction of the stator yoke. Constructions are known in which the stator yoke is cooled using aluminum blocks inserted in the stator at equal intervals in the axial direction. However, there are no examples of direct cooling of the stator teeth with the help of such cooling clamps, since they are not cooled directly, but by water cooling the stator winding.

It is believed that high-quality coils for rotating generators operating in the 3-25 kV voltage range can be manufactured.

For a long time, attempts were made to develop a generator with higher voltages, as can be seen, for example, from Е1ес1пса1 \ Wag1D. OSGOEG 15 1932, p. 524525. The development of a 33 kV generator is described here. A generator in Langerbrugge, Belgium, is also described at 36 kV. Although the article discusses the possibility of further increasing the voltage, the concept of designing such generators is missing. This is primarily due to the shortcomings of the insulation systems, which use varnish-impregnated mica foil and paper.

The report of the Scientific and Research Institute of Electric Power (EPA), ЕB-3391, 1984, reviewed the concepts for building an overvoltage rotating electrical machine for connecting it to a power grid without an intermediate transformer. Such a decision, according to research, is capable of increasing efficiency and economy. The main reason for considering in 1984 the project of generators for direct connection to the power grid was that at that time a superconducting rotor was manufactured. The large magnetic fields created by the superconductor make it possible to use a winding with air gaps with sufficiently thick insulation to counteract electrical loads.

When combining an excitation circuit with a winding (the so-called monolithic cylindrical armature), when two cylinders with conductors are enclosed in three insulation cylinders, and the entire system is installed on an iron core without teeth, the high-voltage rotating electrical machine could possibly be directly connected to the power grid . This solution implies that the main insulation must be made thick enough to withstand the network-to-network and network-to-ground voltages. The obvious drawbacks of the proposed solution are that, in addition to the requirements arising from the presence of a superconducting rotor, very thick insulation is required, which increases the size of the machine. In order to withstand large electric fields, the end ends of the windings must be insulated and cooled with oil or freon. The entire machine must be hermetically sealed to prevent the dielectric from absorbing moisture from the atmosphere.

Some attempts to implement a new approach to the development of synchronous machines are described, among other things, in the article \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ L1, 1, 1970, pp. 6-8, in US Pat. No. 4,429,244. Generator stator and in USSR Pat. No. 955369.

The water-cooled and oil-cooled synchronous machine, described in the TE1ek1to1eshka journal, is designed for voltages up to 20 kV. The article describes a new insulation system consisting of oil / paper insulation, which allows you to immerse the stator completely in oil. At the same time oil can be used as coolant and at the same time as isolation. To prevent oil from seeping from the stator to the rotor, there is a dielectric oil retaining ring on the inner surface of the core. The stator winding is made of hollow oval-shaped conductors with oil and paper insulation. The side parts of the coil with insulation are fixed in grooves of rectangular section by means of wedges. Both in hollow conductors and in holes in the stator walls, oil is used to cool them. However, such cooling systems require a large number of both electrical and hydraulic connections at the ends of the coils. In addition, thick insulation leads to an increase in the radius of curvature of the conductors, which, in turn, causes an increase in the departure of the winding.

The aforementioned U.S. patent relates to a part of a stator in a synchronous machine, which contains a sheet magnetic core with trapezoidal grooves for the stator winding. The grooves narrow as the need for isolation of the stator winding decreases towards the inside of the rotor, where the part of the winding nearest to the neutral point is located. In addition, part of the stator contains a dielectric oil-holding cylinder located near the inner surface of the core. This part may increase the requirements for the magnetic part of the device compared to a machine without this ring. The stator winding is made of oil-filled cables of the same diameter for each layer of the coil. The layers are separated from each other by spacers installed in the slots, and secured with wedges. A feature of the winding is that it contains two so-called semi-windings connected in series. One of the two semi-windings is located centrally inside the tubular insulation. The stator conductors are cooled by the surrounding oil. The disadvantages of a system with such a large amount of oil are the risk of leakage and a lot of cleaning work in the event of an accident. Those parts of the tubular insulation that are located outside the grooves have a cylindrical part and a conical end, reinforced by current-carrying layers, the purpose of which is to control the electric field in the area where the cable enters the end of the winding.

It is clear from USSR patent No. 955369 that another attempt to increase the nominal voltage of a synchronous machine is that the oil-cooled stator winding contains a known high-voltage cable of the same size for all layers. The cable is placed in the grooves of the stator, made in the form of circular radially arranged holes, the dimensions of which correspond to the cross-sectional area of the cable and the necessary place for their installation and for the refrigerant. Various radially arranged layers of the winding are surrounded by tubular insulation and fixed in it. In the groove of the stator tube is fixed insulating struts. Due to the oil cooling in the internal air gap, it is necessary to install an internal dielectric ring to create a seal to prevent leakage of the oil coolant. The above-described disadvantages associated with the presence of oil in the system are inherent in this design. The design does not show the narrowing of the insulation and grooves of the stator. In addition, the design is characterized by very small radial gaps between different grooves in the stator, which implies a large leakage flow in the grooves and significantly affects the machine requirements associated with magnetization.

ΌΕ 2917717 shows the cooling segment for the cooling agent in an electric machine. The segment contains internal cooling channels.

In US Pat. No. 3,447,002, a stator core is shown in which there are a plurality of annular recesses in which thermally conductive bodies are installed, arranged one after the other in the tangential direction in each recess, and there are cooling tubes in these cooled bodies.

In US Pat. No. 2,217,430, an electric machine is shown with stator cooling means by circulating water in the stator core.

According to the present invention, direct cooling of the teeth is necessary and therefore the stator winding is cooled indirectly. In addition, the teeth are exceptionally long compared to those in known generators, and therefore, direct cooling of the teeth is also required.

Purpose of the invention

The aim of the present invention is to provide a structure as described above, which allows direct cooling of the stator teeth while indirectly cooling the cable constituting the stator winding. Preferred embodiments of the invention will be given in the following description.

Summary of Invention

The present invention relates to a structure for cooling the stator teeth and indirectly the stator winding in a high-voltage electric machine, for example, in a high-voltage alternator.

The design contains radially running tubes with electrical insulation, installed in the form of loops in the stator teeth at a certain distance along the axis from the adjacent loops. The design also includes radially running cooling clamps containing cooling tubes in which the refrigerant circulates. The cooling clamps are located in the stator at approximately the same axial distance as the normal ducts for air ventilation. The tubes go to the full radial length of the stator teeth.

According to the most preferred embodiment of the invention, at least one of the semiconducting layers preferably both have the same coefficient of thermal expansion as solid insulation. The decisive advantage that is achieved in this is that there are no defects, cracks, etc. during expansion due to the heating of the winding.

Brief Description of the Drawings

The invention will be described in more detail in connection with the accompanying drawings.

FIG. 1 schematically shows a perspective view with a cross section along the stator diameter of a rotating electric machine;

in fig. 2 shows a cross section of a high voltage cable made in accordance with the present invention;

in fig. 3 schematically shows the sector of a rotating electric machine;

in fig. 4 shows a first embodiment of the present invention;

in fig. 5 schematically shows a second embodiment of the present invention;

in fig. ba-bb shows cross-sections of each of the four embodiments of the teeth with cooling tubes according to the invention;

in fig. 7 shows a cooling circuit according to the present invention.

Detailed Description of the Invention

FIG. 1 shows a part of an electrical machine in which the rotor is removed to more clearly show the structure of the stator 1. The main parts of the stator 1 include a stator housing 2, a stator core 3 comprising stator teeth 4 and an outer yoke part 5 bounding a stator yoke. In addition, the stator includes a stator winding, consisting of a high-voltage cable located in space 7, which has the shape of a bicycle chain, see FIG. 3, and is located between the individual teeth 4 of the stator. FIG. 3, only electrical conductors are shown in the stator winding. As seen in FIG. 1, the stator b forms a package of 8 winding ends on both sides of the stator 1. In addition, from FIG. 3 it is clear that the insulation of high-voltage cables has several dimensions depending on the radial position of the cables in the stator 1.

In known large-sized machines, the stator housing 2 is often made of welded sheet steel structures. In large machines, the stator core 3, also known as a lamellar core, is usually made of 0.35 mm thick sheets, combined into packages with an axial length of approximately 50 mm, separated from each other by dividers, forming 5 mm ventilation channels. However, in the machine made according to the present invention, there are no ventilation ducts. In large machines, each plate pack is formed by fitting the stamped segments 9 of a suitable size so that they form the first layer, after which each subsequent layer is placed at right angles to create a complete flat part of the stator core 3. These parts and dividers are held together by presser legs 1 0, resting against the clamping rings, fingers or segments (not shown). FIG. 1 shows only two presser legs.

FIG. 2 shows a cross section of a high voltage cable 11 made in accordance with the invention. High-voltage cable 11 contains many lived 12, for example, from copper, having a circular cross-section. These conductors 12 are located in the middle of the high-voltage cable 11. Around the conductors 1 2 there is a first semiconducting layer 13, and around the first semiconducting layer 13 there is an insulating layer 14, for example, with insulation from polyethylene with intermolecular bonds. Around the insulating layer 1 4 there is a second semiconducting layer 15. Thus, in the present invention, the concept of high-voltage cable does not include an outer protective sheath, which usually surrounds such cables intended for electrical distribution networks.

FIG. 3 schematically shows the radial sector of the machine with a segment 9 of the stator 1 and with a rotor pole 16 on the rotor 17 of the machine. In addition, it is seen that the stator winding 6 is laid in the space 7, having the form of a bicycle chain between the teeth 4 of the stator. Each prong 4 of the stator extends radially inward from the outer part 5 of the yoke.

FIG. 4 is a simplified illustration of a first embodiment of the invention with a cooling tube 18 forming a loop in a cooling clip 19 having essentially the same shape as segment 9, with a characteristic groove between the parts 20 of the teeth, similar to a bicycle chain. FIG. 4 and 5, for simplicity, the clips are shown rectangular to simply illustrate the principles of the invention. According to FIG. 4 and 5, the loop 21 of the cooling tube is formed by connecting one end of the cooling tube 1 8 with the inlet loop 22, and its other end with the output loop 23.

The coolant flows in the cooling tube 18 from the inlet loop 22 on the outer side 24 of the cooling clip to the cooling clip 1 9 and to the tooth 25 of the cooling clip to its tip, from where the cooling tube 18 passes to the adjacent tooth in the space 26 formed between the air gap and the uppermost high-voltage cable 27. This space is occupied by a mortise wedge (not shown), which may have external notches at the site of the passage of the tube, which ensures the passage of the specified tube. This mortise wedge can also be divided into approximately thirty small wedges to provide space for tube bends. In a preferred embodiment of the cooling clip in the present invention, it can be made by bending rectangular tubes, which are laid in the form of loops, and then the cooling loops of the tubes are cast with aluminum on the plate.

FIG. 5 shows a simplified view of a second embodiment of the invention with a cooling tube 18 forming a loop in a cooling clip 19 having essentially the same construction as segment 9 with parts of 20 teeth, between which a characteristic groove similar to a bicycle chain is formed. According to FIG. 5 in this embodiment of the invention, the cooling tube loop 21 is formed by connecting one end of the cooling tube 1 8 to the input loop 22, and its other end to the output loop 23.

Thus, the refrigerant flows in the cooling tube 1 8 from the inlet loop 22 on the outer side 24 of the cooling clip to the cooling clip 1 9 and into the tooth 25 of the cooling clip to its tip, then the cooling tube 18 turns in the tip (see arrow) and goes to reverse outward along the same prong of the clamp to form a similar loop again in the next prong.

In this embodiment, the cooling clip can also be made by bending a tube of rectangular cross section. Then loops are formed from the tube, and the loops of the cooling tube are cast with aluminum on the plate or attached to the intermediate steel bar with the compound to be cast. Tubes of polyethylene with intermolecular bonds can also be combined with intermediate steel bars to form cooling clamps consisting of stator profiles separated by steel spacers partially filled with compound with filler, for example, hardened plastic.

The advantage of the embodiment of the invention shown in FIG. 4 is that the bending radius of the tube is larger than when the tube must return along the same tooth, as shown in FIG.

five.

The adjacent cooling clips shown in FIG. 4 and 5 by dotted arrows, connected in parallel to the input and output loops.

FIG. 6a-6b depict cross-sections of the teeth of the cooling clip, illustrating various embodiments of the invention according to the embodiments shown in FIG. 4-5. FIG. 6a is a sectional view of a tooth of a cooling clip according to FIG. 4, illustrating a preferred embodiment in which the cooling tube 1 8 of steel has a substantially rectangular cross section and is poured into an aluminum block 28 having a metal cover 29. The aluminum block can also be made of two halves that dock around the cooling tube. FIG. 6b shows a cross section of the tooth of the cooling clip, made in accordance with FIG. 4, with the cooling tube 1, 8 of the teeth passing between the two bars 30, preferably made of steel and acting as spacers and reinforcing bars during the assembly of the cooling tube. After assembling the cooling tube with steel bars, gaps are formed, which are then filled with a cast compound 31. In FIG. 6c shows a cross section of a tooth of the cooling clip, made according to FIG. 5. In this embodiment of the invention, the cooling clip is made of flexible hollow reinforcement laid in a loop around a bar 30, preferably made of steel, and the intermediate space is filled with compound 31, after which the hollow reinforcement is removed, thus forming a pipe channel 32. On FIG. 66 also shows a cross section of the tooth of the cooling clip according to FIG. 5, in this embodiment, a flexible cooling tube 33 of polyethylene with intermolecular bonds is placed in a loop around a bar 30, preferably made of steel.

Embodiments of the channels for the cooling medium in the tooth of the cooling clip shown here can be modified in many ways within the scope of the claims. For example, a cast block of aluminum can be made of two parts with channels for insertion of cooling tubes made of steel or polyethylene with intermolecular bonds. The cross section of the cooling tube can vary from round to oval or be essentially rectangular.

FIG. 7 shows an external cooling circuit in which all cooling tubes 18 are connected to a closed cooling circuit 34, which in the shown embodiment includes a reservoir 35 containing refrigerant 36, which may be water, hydrogen gas or other refrigerant. In tank 35 there is a level indicator to control and monitor the level of the refrigerant. The tank 35 is also connected to two distribution circuits consisting of an inlet loop 37 and an output loop 38. Between the inlet loop 37 and the output loop 38, there are a plurality of cooling clamps 19, schematically shown in FIG. 7, each of which contains at least one loop 21 of the cooling tube. All cooling clamps 1 9 are installed in parallel between the inlet loop 37 and the output loop 38. Thus, refrigerant 36 circulates from the inlet loop 37 at the same time through all parallel-connected loop 21 of cooling tubes to the output loop 38, circulation pump 39, circulation filter 40, through a heat exchanger 41, for example, a flat heat exchanger, and then back to the inlet loop 37. Water with a temperature of approximately 15 ° flows from the water reservoir through a heat exchanger filter (not shown) in the heat exchanger pump 42. Water is pumped through the heat exchanger and returns to the water tank.

The water cooling system according to the present invention may comprise, for example, cooling clamps with tubes inserted approximately every 5 cm along the entire stator. If the stator segments are glued together, the spacing between the cooling clamps may be greater than 5 cm.

Since the cooling clip must be able to withstand the weight of the entire stator when it is vertically installed plus the pressure from any pressure rings (total pressure in the range of 0.5 MPa), a mechanical support structure is embedded in the cooling clip, as shown in FIG. 6a-6. The cooling tubes can be made of stainless steel or can be polymer, as mentioned above, for example, of polyethylene with intermolecular bonds of the brand ^ ίτδΒο-ίηΡΕΧ, and they can be bent in a hot state directly on the cooling plate using steel spacers as a template for flexion. Steel spacers are welded in the same way as in the known air-cooled stators, and also assume axial forces. Polyethylene tubes with intermolecular bonds can be given a flat shape in a furnace at a temperature of approximately 130 °, and then placed them properly, pressing the plates. Then the plates are welded or glued. It is important that the cooling tubes be flat and relatively large in order to provide a sufficient cooling surface. Steel tubes may be smaller than polyethylene tubes with intermolecular bonds. Poured compound can be made sufficiently heat-conducting using, for example, epoxy resin filled with quartz. Air pockets can then be filled with compound to be filled in, as shown above.

The invention is not limited to the embodiments shown as examples. Several modifications are possible within the scope of the invention. So, the cooling tubes can be metal or plastic. The cooling plates can also be cast aluminum blocks. An interesting possibility is also the use of stacked stator plates as supporting structures with filling the remaining gaps with a cast compound.

Claims (19)

CLAIM one . A rotating electric machine comprising a stator (1) with a winding from a high voltage cable, having stator teeth (4) extending radially inward from the outer part (5) of the yoke, said machine comprising a winding including an insulation system comprising at least two semiconducting layers, each of which forms a substantially equipotential surface, and a solid insulation located between them, with at least one stator tooth (4) connected to at least one cooling tube (18) extending radially into prong stat pa (4) and connected to a circuit (34) cooling in which the coolant (36) for circulating and cooling is effected, at least along most of the tooth (4) of the stator in the axial direction. 2. A rotating electric machine according to claim 1, characterized in that at least one of the layers has substantially the same coefficient of thermal expansion as solid insulation. 3. A rotating electric machine according to claim 1 or 2, characterized in that the cooling tube (18) passes from the outer part (5) of the yoke through the tooth (25) of the cooling clamp to its tip, passes to the tip of the next tooth (25) of the cooling clamp and then goes through this tooth (25) of the cooling clamp again to the outer part (5) of the yoke, forming a loop of the cooling tube. 4. A rotating electric machine according to one of claims 1 to 3, characterized in that the cooling tube (18) passes from the outer part (5) of the yoke through the tooth (25) of the cooling clip to its tip, where it turns and goes back through the specified the tooth (25) of the cooling clip to the outer part (5) of the yoke, forming a loop (21) of the cooling tube. 5. A rotating electric machine according to claim 3 or 4, characterized in that the loops (21) of the cooling tubes are located in at least one cooling clamp (19) having substantially the same shape as the cross section of the stator. 6. A rotating electric machine according to claim 5, characterized in that the cooling tubes (18) are formed in the cooling clamp (19) by molding. 7. A rotating electric machine according to one of claims 1 to 3, characterized in that the maximum axial distance between the cooling clamps (19) is 200 mm. 8. A rotating electric machine according to one of claims 3 to 7, characterized in that the loop (21) of the cooling tube is provided with at least one bar (30) placed in the loop. 9. The method of cooling a rotating electric machine with high-voltage stator windings, made according to claim 1, according to which the stator is cooled with refrigerant (36), which is forced to circulate in the cooling circuit (34) through cooling channels going through the stator teeth (4) in the radial direction . 10. The method according to claim 9, characterized in that the refrigerant (36) is forced to circulate in a closed circuit that passes through the heat exchanger (41), cooling the circuit (34) with water from the water tank. 11. A rotating electric machine according to one of claims 1 to 8, characterized in that the potential of said first layer is substantially equal to the potential of a conductor. 1 2. A rotating electric machine according to claim 11, characterized in that said second layer forms a substantially equipotential surface surrounding said conductor. 1 3. The rotating electric machine according to claim 1, characterized in that a predetermined potential is applied to said second layer. 1 4. The rotating electric machine according to claim 1, 3, characterized in that said predetermined potential is the potential of the earth. 1 5. A rotating electric machine according to one of paragraphs. 11-14, characterized in that at least two adjacent layers have essentially equal coefficients of thermal expansion. 1 6. A rotating electric machine according to one of claims 1 to 8, 11-15, characterized in that said current-carrying conductor contains a plurality of cores, only a smaller part of which is not isolated from each other. 1 7. A rotating electric machine according to one of claims 1 to 8, 11-16, characterized in that each of these three layers is fixedly connected to the adjacent layer over substantially the entire surface of the joint. 18. A machine having a high-voltage magnetic circuit containing a magnetic core and a winding, said winding being made of a cable containing one or more current-carrying conductors, each of which contains a plurality of conductors, around each conductor there is an inner semiconducting layer, around this inner semiconducting layer there is an insulating layer of solid insulating material, and around said insulating layer there is an outer semiconducting layer. 19. The machine according to p. 18, characterized in that the cable also contains a metal screen and sheath.