MXPA98009993A - High voltage plants with electri motors - Google Patents

Abstract

In a plant comprising one or more electrical machines built with insulated conductors and connected via insulated conductors for high currents, the magnetic circuit of at least one of these electric machines is directly connected to a high supply voltage of 20-800 KV, preferably higher than 36 KV. The insulation of the electrical machine is constructed with a cable placed in its winding and comprising one or more current carrying conductors, with a number of filaments surrounded by the outer and inner semiconductor layers and intermediate insulating layers. The conductors can be connected in groups in parallel and, therefore, semiconductor layers are not required around each conductor of the group. If the conductors are connected in series with each other within the group, isolation of parts is required, which will support a few KV, while the connection of the conductors to all the phases requires a resistant isolation of parts, which will support the phase voltage of the High voltage supply network

Description

HIGH VOLTAGE PLANTS WITH ELECTRIC MOTORS TECHNICAL FIELD The present invention relates to electric power plants that comprise motors intended for connection with distribution or transmission networks, hereinafter referred to as industrial networks. The invention relates secondly to an engine intended for use in such a plant. The motors can be synchronous or asynchronous motors. The plant with electric motors can be a laminator, wastepaper basket, pulp dryer, mineral plant, spring structure, fan systems, pump or compressor, lifting devices, stroke (machine tool), crane, centrifugal machine, conveyor, plant of workshops, steel laminates, etc. Therefore, "plants with electric motors" should be understood in its broadest sense.

BACKGROUND ART The magnetic circuits of electric motors usually comprise a laminated core, for example of a steel sheet with a welded assembly. To provide ventilation and cooling, the core is often divided into blocks with axial ~ / 0 axial ventilation ducts. In the case of larger motors, the laminations are perforated in segments that are attached to the frame of the machine, keeping the REF: 28956 laminated core by means of pressure needles and pressure rings. The winding is arranged in the grooves of the laminated core, these grooves generally having a cross section in the shape of a rectangle or trapezoid. In ultiphase electric motors the windings are made as single-layer or double-layer windings. In the case of single-layer windings there is only one side of the turn per slot, while in the case of the double-layer windings there are two sides of a turn per slot. Spiral side means one or more drivers combined vertically or horizontally and provided with a common loop insulation, ie an insulation intended to support the rated voltage of the motor to ground. The double-layer windings are usually made as triangle windings whereas the single-layer windings of the present context can be made as triangle or planar windings. In the triangle windings there is only one winding width (possibly two), while the flat windings are made as concentric windings, that is, with a wide winding width. Spiral width means the distance of the dimension of the arc between the two sides of the coil belonging to the same winding. Normally, all large motors are made with double layer winding and turns of the same size. Each loop is placed with one side in one layer and the other side in the other layer. That means that all the turns cross each other at the end of the coil. If there are more than two layers these crisscrosses complicate the winding work and the coil end is less satisfactory. It is considered that rotary electric motor coils can be manufactured with good results up to a voltage range of 10 - 20 KV. Large AC motors are divided into synchronous and asynchronous motors; the former usually cover a higher power range, up to a few tens of MW, and are constructed so that they are normally supplied with a maximum voltage of 20 KV. The synchronous motor operates with a rotor speed synchronous with the frequency of the network. In contrast, in the asynchronous motor, the magnetic field rotates faster than the rotor, so that the induced currents provide torsion in the direction of rotation. The two types of engines are largely similar in construction. They consist of an estotro that has placed inside a rotor. The stator is made of a laminated core with perforated grooves for the winding. The estotro is placed in a lower box, coupled to the base by its foot. The rotor is suspended in the bearings mounted in the box. To protect active parts, in the lower box a frame of estotro is placed. The frame is provided with openings for cooling air to enter. The function of an AC motor is based on the interaction between magnetic fields, electric currents and mechanical movement. Magnetic fields are located mainly in the iron of the machine and electric currents, in the windings. A distinction is made between two main types of AC motors: synchronous and asynchronous machines. The main difference between the two is the way torsion occurs. The synchronous motor is excited by supplying power to the rotor from the outside via brushless exciters or slip rings, while the asynchronous motor obtains its excitation energy by induction of the current of the state. The speed of the synchronous motor, therefore, does not depend on the load as it does in the case of the asynchronous motor. According to the construction of the rotor, there are two types of synchronous motors: those with salient poles and those with a cylindrical rotor. In the operation of 2 poles and high speed, the mechanical stresses exerted on the rotor are very high and, in this case, it is convenient to use a cylindrical rotor. On the other hand, when it comes to motors with lower speeds, four poles or more, the diameter of the rotor is greater. As the speeds are lower and consequently so are the corresponding mechanical stresses, it is more convenient that the rotor has protruding poles. The boundary between these two types is undefined. At higher power and with four poles, cylindrical rotors are used long and thin. At lower power and with four poles, rotors with protruding poles are used. Asynchronous motors are also divided into two types: squirrel cage induction motors or slip ring motors. Both types have in common the rotor built with laminations with slots for winding. The difference lies in the construction of the winding. The squirrel-cage induction motors have a squirrel-cage winding, which consists of axial rods that, at the ends, short-circuit with a short-circuit generator ring. The asynchronous motors with slip rings have a three-phase winding in the rotor, with the phase terminals connected to the slip rings. Through the varied design of the rotor slots, the starting and operating properties of the squirrel-cage induction motor can be adjusted to different requirements. Slip ring asynchronous motors are used mainly in difficult starting conditions. The external resistance can be connected via the sliding hoops. By increasing the resistance of the rotor, the maximum torque can be shifted towards the lower speed, thereby increasing the starting torque. When the start is completed, the external starting resistance is short-circuited. The choice of a large AC motor in terms of type, nest class and cooling method depends on the following factors, among others: Torque characteristic of the load Type of load and load cycle Restrictions of starting power Characteristics of the network Cost of electrical energy Environment in which the motor must be installed Investment cost in relation to the estimated useful life of the plant The maximum aspiration with respect to an electric machine is that its cost of capital and operating costs result the lowest possible. Therefore, it is desirable to maintain efficiency as much as possible in certain power factors. The synchronous motor, in general, has an efficiency superior to that of the asynchronous motor.

The rotor of a synchronous motor is often manufactured with protruding poles. Its main use is in the power range between 1 MW and a few tens of MW, for example, for crushing and refining machines of the paper industry, for pumps both in the processing industry and in connection with weak networks, for example, for Irrigation facilities in desert countries. The oil industry also uses large synchronous motors for pumps and compressors. The main reason for the use of synchronous motors instead of the less expensive asynchronous motors, is that the former produce less voltage in the network, in the form of lower starting current, and that the overexcitation of the synchronous motor can also be used to improve the power factor. Large synchronous motors can also have slightly higher efficiency than equivalent asynchronous motors. The winding must be isolated, both between the winding windings of the coil and between the coil and the surroundings. Often different forms of plastic material, enamel and fiberglass are used as the insulating material. The ends of the coil are often supported in order to counteract the forces that arise between the different turns, particularly when short circuits are generated.

Motors of the type described above are connected to high voltage networks of, for example, 45 KV by the use of a transformer that lowers the voltage. The use of an engine in this way, connected to the high voltage network via a transformer, brings a number of disadvantages. Among others, the following can be mentioned: the transformer is expensive, increases transport costs and requires space; the transformer decreases the efficiency of the system; the transformer consumes reactive power; conventional transformers contain oil, with the risks that entails; it involves delicate operation, since the motor via the transformer works with a weak network.

BRIEF DESCRIPTION OF THE INVENTION An object of the invention is, therefore, to enable the use of one or more electric motors in a plant that is directly connected to high voltage supply networks, which here means sub-transmission networks and distribution, without the connection mediated by a transformer.

The benefit obtained by achieving the aforementioned objective is to avoid the use of an intermediate transformer in an oil bath, the reactance of which, otherwise, consumes reactive power. This objective is achieved according to the invention, in the sense that a plant of the type described in the preamble of claim 1, is granted the special characteristics defined in the characterization part of such clause, and in the sense of that an electric motor of the type described in the preamble of claim 25, is granted the special characteristics defined in the characterization part of that clause. Thanks to the solid insulation specially produced, the motors of such a plant can be supplied directly, with a voltage level in excess considerably compared to what is possible using the known technology, and at a voltage that can reach the maximum stresses applicable in high voltage industrial networks. In this way, the advantage is obtained that the transformer becomes superfluous, thus eliminating all the problems mentioned above, inherent in a plant in which the tension must be reduced in a staggered manner, as well as other significant advantages.

With a plant according to the invention, the overload capacity also increases dramatically. This can be + 100% for one or two hours, which allows selecting the motors with the lowest nominal power output and thereby also saving costs. Higher output is also obtained by high voltage in the motors, because it is proportional to the square of the voltage. In this way, the invention allows electric motors with greater power to be achieved. The invention thus extends the application area corresponding to electric machines to the range of 1-300 MW and even allows applications at higher power levels still. The main and essential difference between the known technology and the embodiment according to the invention is, therefore, that this is achieved with a magnetic circuit included in at least one electric motor, which is arranged to be connected directly to a circuit high voltage supply, via coupling elements such as circuit breakers and insulators. In that way the magnetic circuit comprises one or more laminated cores. The winding consists of a threaded cable with one or more permanently insulated conductors, which have a semiconductor layer both on the conductor and on the outside of the insulation, connecting the outer semiconductor layer with the ground potential.

To solve the problems associated with the direct connection of electric motors, both rotary and static, in all types of industrial high-voltage networks, at least one motor of the plant according to the present invention has a number of characteristics such as as mentioned above, they differ in a distinctive way from known technology. The additional features and further embodiments are defined in the corresponding claims and are discussed below: The winding is produced from a cable having one or more permanently insulated conductors with a semiconductor layer in both the conductor and the cover. Some typical conductors of this type are PEX cables or a cable with EP rubber insulation, which, however, are more developed for the purposes of the present in terms of the conductor filaments as well as the nature of the outer cover. PEX = crosslinked polyethylene (XLPE). EP = ethylene propylene. Cables of circular cross-section are preferred, but cables with some other cross section can also be used, for the purpose of obtaining, for example, better packing density.

Such a cable makes it possible to design the laminated core according to the invention in a new and optimum way with respect to grooves and teeth. The winding is preferably manufactured with insulation in the steps corresponding to the best use of the laminated core. The winding is preferably manufactured as a multilayer concentric cable winding, thus allowing the number of intersections of coil ends to be reduced. The groove design is adapted to the cross-section of the winding cable, so that the grooves are in the form of a number of cylindrical apertures, extending axially and / or radially outwardly from each other and with a part central extending between the winding layers of the stator. The design of the slots is adjusted to the cross section of the relevant cable and to the stepped insulation of the winding. The stepped insulation allows the magnetic core to have a substantially constant tooth width, regardless of the radial extent. The additional development mentioned above with respect to the filaments implies that the conductors consist of a number of layers / layers impacted, ie, isolated filaments that from the point of view of an electric machine are not necessarily transposed, not isolated and / or isolated from each other in the correct way. The additional development mentioned above, with respect to the outer cover, implies that the cover is cut at suitable points along the conductor, each sectional length connecting directly with the ground potential. The use of a cable of the type described above allows the total length of the outer shell of the winding, as well as the other parts of the plant, to be maintained at ground potential. An important advantage is that the electric field closes to zero within the region of the coil end, outside the outer semiconductor layer. With the ground power in the outer casing, there is no need to control the electric field. This means that no field concentration will occur either in the core, or in the coil end regions, or in the transition between them. The mixture of impacted filaments, isolated and / or uninsulated, or transposed filaments results in little loss by deviation. The high voltage cable used in the winding is made of an inner core / conductor with multiple filaments, at least two semiconductor layers, the innermost one of which is surrounded by an insulating layer which, in turn, is surrounded by a layer external semiconductor with an external diameter of the order of 10-250 mm and a conductive area of the order of 40-3000 mm2. If at least one of the motors of the plant according to the present invention is constructed in the specified manner, the starting and control of that engine or of those engines can be achieved with the starting methods known per se, mentioned by way of reference. According to a particularly preferred embodiment of the invention, at least two of those layers, preferably three, have the same coefficient of thermal expansion. In this way, the decisive benefit is achieved in the sense of avoiding defects, breaks and other things by style during the thermal movement in the winding. According to another important preferred embodiment of the invention, at least one of the motors of the plant has one or more connection voltages. From the perspective of another aspect of the invention, the stated objective has been achieved in the sense that the plant of the type described in the preamble of claim 23 is granted the special characteristics defined in the characterization part of that clause.

As the suitably permanent insulation system is designed so that from a thermal and electrical point of view it is designed for more than 36 KV, the plant can be connected to industrial high-voltage networks without any step-down intermediate transformer, thus achieving the advantages to which reference has been made. Such a plant is preferably, but not necessarily, constructed to include the characteristics defined for the plants, as claimed in any of clauses 1-22. The above-mentioned and other advantageous embodiments of the invention are defined in the corresponding clauses.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in more detail in the following detailed description of a preferred embodiment of the construction of the magnetic circuit of an electric motor of the plant, with reference to the accompanying drawings, in which: 1 shows a schematic view of the axial end of a sector of the stator of an electric motor of the plant, according to the invention; Figure 2 shows an end view of a cable whose layers have been removed stepwise and which is used in the winding of the stator according to Figure i; And Figures 3-7 show examples of different energization circuits known per se.

DESCRIPTION OF A PREFERRED EMBODIMENT According to FIG. 1, in the schematic axial view through a sector of the stator 1, belonging to the motor or electric motors included in the plant, the rotor 2 of the motor is also indicated. The stator 1 is composed in a conventional manner by a laminated core. Figure 1 shows a sector of the motor corresponding to the assembly of a single pole. From a part of the yoke 3 of the core located in the outermost part in a radial direction, a number of teeth 4 extend radially inward towards the rotor 2 and are separated by slots 5, in which the winding of the stator is arranged. The cables 6 forming this stator winding are high voltage cables, substantially of the same type as those used for power distribution, ie PEX cables. One difference is that the outer mechanical protection cover and the metal shield that normally surrounds such power distribution cables are removed, so that the cable corresponding to the present application comprises only the conductor and at least one semiconductor layer at each side of an insulating layer. So the semiconductor layer sensitive to mechanical damage is laid bare on the surface of the cable. The cables 6 are illustrated schematically in the Figure 1 only with the central conductive part of each cable part or retracted side of the loop. As can be seen, each slot 5 has the variable cross section, in which wide parts 7 and narrow parts 8 alternate. The wide parts 7 are substantially circular and surround the wiring and the central section parts between them form the narrow parts 8. Central section parts serve to radially fix the position of each cable. The cross section of the slot 5 also narrows radially inwardly. This is due to the fact that the lower the tension in the wire parts closer to them, they are located in the radially inner part of the stator 1. There, therefore, the thinnest wiring can be used, while the thicker wiring is necessary more outside. In the illustrated example, different three-dimensional cables are used, arranged in the three correspondingly dimensioned sections 51, 52 and 53 of the slots 5. Figure 2 shows an end view of a high voltage cable, which has been The layers were removed for use in an electric motor according to the present invention. The high voltage cable 6 comprises one or more conductors 31, each of which comprises a quantity of filaments 36 which together give a circular cross section of copper (Cu), for example. These conductors 31 are arranged in the middle of the high-voltage cable 6 and surrounded, in the embodiment shown, by an isolation of parts 35. However, it is feasible that the isolation of parts 35 in one of the conductors 31 is omitted. In the present embodiment of the invention the conductors 31 are jointly surrounded by a first semiconductor layer 32. Around this first semiconductor layer 32 there is an insulating layer 33, for example of PEX insulation, which in turn is surrounded by a second semiconductor layer 34. So the concept "high voltage cable" in this application does not need to include any metallic screen or outer cover of the type that normally surrounds such power distribution cable. Figures 3-7, in the form of basic diagrams, show examples of known energization procedures, applicable to the rotating motors of the plant, according to the present invention. In the figures, the following designations are used: U: High voltage network Xt: Impedance of the transformer Xn: Impedance of the network R: Reactor B: Circuit breaker Xr: Impedance of the reactor M: Motor C: Capacitor Xm: Motor impedance Xc: Capacitor impedance T: Transformer L: Three-phase stator windings So Figure 3 refers to the energizing procedure of the transformer, Figure 4 to the reactor energization procedure, Figure 5 shows the energization procedure of the winding of parts, Figure 6 shows the energization procedure of the capacitor and Figure 7 shows the combined energization procedure of the reactor and the capacitor. Of course, other combinations of energization procedures in the plant, according to the invention, are also applicable. The different energization procedures described in the corresponding literature are considered as a reference. So that with one or more rotating electric motors constructed in accordance with the invention, the industrial plants comprising one or more of such motors can be directly connected to high voltage supply networks, that is, to networks having supply voltages of 20 KV or higher, thus enabling the elimination of at least one transformer. The use of the permanent isolation power cable, according to the invention, between the electric motors included in the plant and the achievement of a compact settlement of these motors thus ensures that the electric fields are small and that the bearings / terminals can be eliminate completely. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects or products to which it refers.

Having described the invention as above, property is claimed as contained in the following:

Claims (27)

1. Claims 1. A high-voltage power plant consisting of one or more motors, each comprising at least one winding, characterized in that the winding of at least one of the electric motors comprises a high-voltage cable having a power system. insulation including at least two semiconductor layers, each layer essentially constituting an equipotential surface and intermediate solid insulation between the layers.
2. 2. The plant of clause 1, characterized in that at least one motor has one or more connection voltages.
3. 3. The plant of clauses 1 or 2, characterized in that at least one of the layers has substantially the same coefficient of thermal expansion as the solid insulation.
4. 4. The plant of any of clauses 1-3, characterized in that it is provided that all substantial power transformation takes place in the same electric motor.
5. 5. The plant of any of clauses 1-4, characterized in that the insulation is constructed with a cable intended for high voltage, comprising one or more current carrying conductors surrounded by at least two semiconductor layers, with intermediate insulating layers of solid insulation.
6. 6. The plant of clause 5, characterized in that the innermost semiconductor layer has substantially the same potential as the conductor (s).
7. 7. The plant of clauses 5 or 6, characterized in that one of the outer semiconducting layers is arranged to essentially form an equipotential surface surrounding the conductor (s).
8. 8. The plant of clause 7, characterized in that said outer semiconductor layer is connected to a predefined potential.
9. 9. The plant of clause 8, characterized because the predefined potential is land potential.
10. 10. The plant of any of clauses 5-9, characterized in that at least two of said layers have substantially the same coefficient of thermal expansion.
11. 11. The plant of any of clauses 5-7, characterized in that the current carrying conductor comprises multiple filaments, with only a few of the filaments not isolated from each other.
12. 12. The plant of any of clauses 1-11, characterized in that the winding consists of a cable comprising one or more current carrying conductors, each conductor consisting of a number of filaments, an inner semiconductor layer disposed around each conductor, an insulating layer of solid insulation disposed around each inner semiconductor layer and an outer semiconductive layer disposed around each insulating layer.
13. 13. The plant of clause 12, characterized in that the cable also comprises a metal mesh and a cover.
14. 14. The plant of any of the preceding clauses, characterized in that the stator of the motor is cooled by means of a flow of gas and / or liquid, at ground potential.
15. 15. The plant of any of the preceding clauses, characterized in that the high voltage cables have a conductive area between 40 and 3000 mm2 and have an outer cable diameter of between 10 and 250 mm.
16. 16. The plant of any of the preceding clauses, characterized in that the starting current and / or starting fault or current for the electric motor (s) is arranged so that it is limited by an electric machine. static, that is, a reactor / inductor that is temporarily and / or permanently connected in series with the winding of the armature of the rotating electric machine (Figure 4).
17. 17. The plant of any of the preceding clauses, of at least one motor is characterized in that the neutral point is connected to ground via an impedance.
18. 18. The plant of any of the characterized because the neutral point is directly connected to ground.
19. 19. The plant of any of the preceding clauses, characterized in that the engine is arranged to operate as a producer of reactive power with large temporary overload capacity.
20. 20. The floor of any of the preceding clauses, characterized in that the motor is arranged to be connected to a distribution network or transmission network via coupling elements and without any transformation to reduce the voltage level.
21. 21. The plant of any of the preceding clauses, characterized in that the motor is arranged to be connected to a distribution network or transmission network that has a supply voltage in excess of 36 KV.
22. 22. The plant of any of the preceding clauses, characterized in that the motor winding is arranged to self-regulate the field control and lacks auxiliary devices to effect field control.
23. 23. A high voltage power plant consisting of one or more motors, each of which comprises at least one winding, characterized in that the winding of at least one of the electric motors comprises an insulation system which, in terms of its thermal and electrical properties, allows a voltage level in excess of 36 KV and because the engine includes the characteristics that define the plant in accordance with any of clauses 1-21.
24. 24. The power plant of clause 23, characterized in that the winding comprises a high voltage cable having an insulation layer including at least two semiconductor layers, each semiconductor layer constituting essentially an equipotential surface and an intermediate solid insulation.
25. 25. The motor of clause 24, characterized in that its stator winding is divided into two parts in order to achieve partial winding start.
26. 26. The motor of clauses 25 or 26, characterized in that it has one or more connection voltages.
27. 27. The engine of any of clauses 25-27, characterized in that it includes the characteristics defined for the engine in the plant defined in any of clauses 2-23.