Cooling system for an electric machine

Abstract

Cooling system (30) for an electric machine, with at least one cooling circuit (31) in thermal contact with the electric machine (25), in which a liquid cooling medium circulates; at least one circulation pump (32) for the liquid cooling medium, which is arranged in the cooling circuit (31); and at least one heat exchanger (33) arranged in the cooling circuit (31), characterized by that the circulation pump is designed as a submersible oil pump (31) comprising a pump head (36) and an electric drive motor (37) connected to the pump head (36), which has a motor housing (38) that defines a motor compartment (39) in which a rotatable motor shaft (40), a rotor (41) connected to the motor shaft in a rotationally fixed manner and a stator (43) connected to the motor housing are arranged, which are surrounded by the cooling medium of the cooling circuit (31).

Description

[0001] The present invention relates to a cooling system for an electrical machine, in particular a cooling system for the generator and / or transformer of a wind turbine.

[0002] A wind turbine uses the kinetic energy of the wind and converts it via a rotor into rotational energy in a rotor shaft. The rotor shaft drives a generator, which converts the mechanical rotational energy into electrical energy. Wind turbines have a mast or tower, at the top of which the rotor is mounted so it can rotate using a rotor shaft. The rotor shaft leads to a machine house, also located at the top of the mast and also called a nacelle, which contains the generator, which is set in rotation by the rotor shaft and converts the mechanical rotational energy into electrical energy. The rotor typically consists of three rotor blades, which are connected to the rotor shaft at a hub and convert the translational movement of the air, i.e. the wind, into a rotational movement of the rotor shaft.The rotor shaft transmits the rotary motion to the generator either via a gearbox or, in gearless systems, directly. Other subsystems, such as clutches, brakes, controls, hydraulic systems, and cooling systems, are housed in the nacelle. A wind turbine typically also includes a transformer, as the alternating current supplied by the generator is not typically fed directly into the power grid, but is first stepped up by the transformer to a medium-voltage level of the supply grid with low transmission losses. Depending on the type of wind turbine, the transformer can be housed in the nacelle at the top of the tower or as a separate unit at the base of the tower, where the grid connection is typically also located in a switch room.

[0003] The electrical machines of a wind turbine, especially the generator and transformer, are subject to losses that generate heat that must be dissipated by a cooling system. For this purpose, electrical machines typically have a cooling circuit in which a cooling medium is brought into thermal contact with subcomponents of the electrical machines, thereby heating up. The cooling medium is transported via a circulation pump to a heat exchanger in the cooling circuit, where the cooling medium cools through thermal contact with the ambient air and can thus be brought back into contact with the electrical machine.

[0004] Circulation pumps in wind turbine cooling systems are typically driven by cost-effective asynchronous motors controlled by a two-point control system. The temperature of the electric motor is monitored, and if a temperature threshold is exceeded, the circulation pump is switched on, thus cooling the electric motor. If the temperature falls below a further temperature threshold, which may be different from the first threshold, so that a certain hysteresis is provided in the control concept, the circulation pump is switched off again. However, this leads to a high thermal load on the components in contact with the cooling circuit—not only the electric motor, but also the cooling circuit itself and the heat exchanger located within the cooling circuit.

[0005] In recent decades, the size and rated power of newly constructed wind turbines have increased enormously. While in the 1980s, typical maximum rated powers were in the range of 30 kW, generated by wind turbines with rotor diameters of around 15 m, today's maximum rated powers of onshore turbines with rotor diameters of more than 100 m are in the range of 3,000 to 4,000 kW, while offshore turbines with rotor diameters of over 200 m even generate maximum rated powers of over 10,000 kW.

[0006] Although the electrical machines of a wind turbine typically have an efficiency of 95%, as the power of the wind turbine increases, the heat losses of the electrical machines, such as the generator and the transformer, also increase accordingly. The present invention is therefore based on the technical problem of providing a cooling system for electrical machines, in particular a cooling system for the electrical machines of a wind turbine, which is better adapted to the dissipation of larger amounts of heat and, in particular, allows adaptation to the heat quantities generated during operation, which vary with weather conditions.

[0007] This technical problem is solved by a cooling system for electrical machines having the features of the present claim 1. Advantageous developments of the cooling system according to the invention are the subject matter of the dependent claims.

[0008] Accordingly, the present invention relates to a cooling system for an electrical machine having at least one cooling circuit in thermal contact with the electrical machine, in which a liquid cooling medium circulates, at least one circulating pump for the liquid cooling medium arranged in the cooling circuit, and at least one heat exchanger arranged in the cooling circuit. The cooling system according to the invention is characterized in that the circulating pump is designed as an oil-submerged pump comprising a pump head and an electric drive motor connected to the pump head, which has a motor housing defining a motor compartment in which a rotatable motor shaft, a rotor connected in a rotationally fixed manner to the motor shaft, and a stator connected to the motor housing are arranged, around which the cooling medium of the cooling circuit flows.

[0009] As the power of wind turbines increases, so does the cooling requirements of the electrical machines. Accordingly, the corresponding cooling system must also be equipped with more powerful circulation pumps. The use of an oil-immersed pump as provided for in the invention ensures more effective cooling of the electric drive motor of the circulation pump, since the cooling medium of the cooling system's cooling circuit is used to cool the drive motor. In contrast to frequently used canned motors, which can also be cooled by the pumped cooling medium, in an oil-immersed motor the cooling medium flows not only around the motor shaft and rotor, but also around the stator, ensuring better cooling of the drive motor overall. The temperatures of the rotor and stator are significantly lower than in a similarly powerful canned motor, which reduces the thermal load on the motor for the same power output.In other words, an oil-immersed engine can operate at a higher power level under the same thermal load.

[0010] According to an advantageous embodiment of the present invention, the drive motor is designed as a synchronous motor. Although a synchronous motor is more expensive to purchase than an asynchronous motor, it enables lower overall operating costs for the cooling system, as a synchronous motor enables continuous control of the temperature of the liquid coolant in the cooling circuit. In contrast, when using an asynchronous motor, a 2-point control is usually applied, i.e., temperature limits are defined for switching the circulation pump on and off. This overall leads to a higher thermal load on the components of the cooling system, as such a 2-point control is always associated with a certain temperature hysteresis.In contrast, when using a synchronous motor, the temperature of the liquid cooling medium can be kept largely constant within narrow limits, which reduces the thermal load on the components of the cooling system and extends their service life.

[0011] If the drive motor is designed as a synchronous motor, both the rotor and the stator can be designed as electromagnets with current-carrying windings. In an oil-immersed motor, these windings are also surrounded by the liquid cooling medium and thus effectively cooled. In a preferred embodiment of the present invention, the synchronous motor has a rotor consisting of permanent magnets, while the stator is the electromagnet, which consists of iron cores, each surrounded by an electrical winding.

[0012] The pump head is preferably designed as a radial impeller pump, which has a pump housing defining a working chamber into which a pump-side end of the motor shaft projects, on which a radial impeller is mounted in a rotationally fixed manner. The use of a radial impeller pump proves particularly efficient for use in a circulation pump for liquid cooling media, where the impeller is mounted directly on the motor shaft. The resulting compact design also facilitates the installation of the circulation pump in the cooling circuit, especially if the circulation pump is located in the nacelle of the wind turbine, where space is correspondingly limited.

[0013] In the submerged oil pump provided according to the invention, it is preferably provided that a partial flow of the liquid cooling medium is guided from the working chamber of the pump head into the engine compartment and from there back into the working chamber. For this purpose, passage openings are preferably provided in the pressure area of ​​the pump head through which the liquid cooling medium can flow from the working chamber of the pump head into the engine compartment, while passage openings are provided in the suction area of ​​the pump head through which the liquid cooling medium can flow from the engine compartment back into the working chamber of the pump head.

[0014] The motor shaft of the circulation pump is preferably supported by at least one plain bearing. Particularly preferably, the motor shaft is supported by two plain bearings, in particular by an axial and radial bearing near the pump head and by a radial bearing at the end of the motor shaft remote from the pump head.

[0015] Various suitable cooling liquids can be considered as cooling media that do not cause electrical problems when flowing through the electric motor, in particular oils that are not electrically conductive or poorly conductive.

[0016] According to one embodiment, at least one temperature sensor for measuring the temperature of the cooling medium is arranged in the cooling circuit.

[0017] Preferably, the circulation pump also comprises a pump control which implements a control strategy for operating the cooling system.

[0018] According to one embodiment of the cooling system according to the invention, the pump control controls the electric drive motor depending on the temperature of the cooling medium.

[0019] The invention also provides an electrical machine with a cooling system as described above. The electrical machine is particularly preferably an electrical generator or an electrical transformer, particularly preferably a generator or a transformer of a wind turbine.

[0020] Accordingly, the present invention also relates to a wind turbine comprising a generator and a transformer, which is characterized in that the generator and / or the transformer is thermally coupled to a cooling system of the type described above.

[0021] A wind turbine is typically connected to an electrical grid so that the power required to operate the cooling system's electric drive motor can be drawn from the grid. The wind turbine can also be part of a wind farm, with the individual wind turbines being networked together so that the power required to operate the cooling system's electric drive motor can also be drawn from the networked network of wind turbines. Since the cooling system only needs to be in operation when the wind turbine itself is in operation and therefore supplying power, the cooling system's electric drive motor can, according to a preferred embodiment of the invention, also be driven by a portion of the power generated by the wind turbine.

[0022] The invention will be explained in more detail below with reference to an embodiment illustrated in the accompanying drawings. This embodiment is purely exemplary and is not intended to limit the invention in any way.

[0023] The drawings show: Fig. 1 a schematic representation of a wind turbine in cross section; Fig. 2 a schematic representation of the main mechanical and electrical components of the wind turbine with cooling system for the wind turbine transformer; and Fig. 3 schematically shows a submerged oil motor in cross-section, as it is used as an electric drive motor for the circulation pump of the cooling system of the Fig. 2 can be used.

[0024] In Fig. Figure 1 shows a wind turbine, designated overall by the reference numeral 10, which has a tower 11 resting on a foundation 12. At the top of the tower 11 is a nacelle 13, also referred to as the machine house, in which the most important mechanical and electrical components of the wind turbine are located. A rotor shaft 14 is rotatably mounted in the nacelle 13 via a bearing 15. At the tip of the rotor shaft, outside the nacelle, there is a hub 16, on which the rotor blades 17 of the wind turbine 10 are adjustably mounted. For this purpose, the rotor blades 17 are connected to the hub 16 via typically hydraulically operated adjustment devices 18, so that the blade pitch of the rotor to the wind can be changed. The rotor shaft is usually connected via a gearbox 19 to a generator 20, which converts the rotational movement of the rotor shaft into an alternating electrical current.The power supplied by the generator 20 is transmitted via cables 21 laid on the tower 11 to a switchgear 22 located at the base of the tower, where it is fed into a medium-voltage grid via a grid connection 23.

[0025] How to Fig. 1, a wind measuring system 26 is arranged on the nacelle 13, which transmits data on wind direction and wind speed to the Fig. 2 provides the control system of the wind turbine 10 explained in more detail.

[0026] Since the feed into the power grid at the grid connection 23 must be made with a specific frequency and a specific voltage, but the wind turbine itself operates at a variable speed, further electrical components are provided between the generator 20 and the grid connection 23, which for the sake of clarity are shown in Fig. 1 are not shown, in particular those of Fig. 2, which is responsible for the mains frequency connection of the variable speed current supplied by the generator to the power supply network, while the transformer 25 ensures the voltage adjustment to the power supply network.

[0027] Fig. Figure 2 shows a schematic representation of the main mechanical and electrical components of the wind turbine, as well as the corresponding control systems. Fig. The components shown in Figure 1 are designated by the same reference numerals. Fig. 2 which are already in Fig. 1, on which the rotor blades 17 are arranged via an adjustment device 18. The rotor shaft 14 is connected via the gearbox 19 to the generator 20, which supplies power to a grid connection 23. Between the generator 20 and the grid connection 23, the aforementioned power electronic frequency converter 24 is provided, which is typically designed in a so-called "back-to-back" arrangement, i.e., a generator-side and a grid-side partial converter are connected via a DC link to a capacitor bank (shown only schematically here). The frequency-stable alternating current supplied by the frequency converter 24 is transformed by the transformer 25 to the required voltage level for feeding into the grid.Also shown schematically is a control system 27 for the wind turbine 10, which receives information about wind speed and wind direction via the wind measuring system 26, as well as information about the torque of the generator from the generator 20 and information about the rotation frequency of the rotor shaft 14. The control system 27 can adjust the blade angle of the rotor blades via a hydraulic system 28.

[0028] While the Fig. 2 shown switchgear 22 with the mains connection 23 are usually arranged at the base of the tower, the remaining Fig. 2 may be located in the nacelle 13. However, in some wind turbines, the frequency converter 24 and transformer 25 are also located in the switchgear 22 at the base of the tower.

[0029] The electrical machines of the wind turbine, such as the generator 20 or the transformer 25, have, especially in the case of high-performance wind turbines, not insignificant heat losses, which are dissipated via a Fig. 2 schematically shown for the transformer 25. The cooling system 30 comprises a cooling circuit 31 in thermal contact with the transformer, in which a liquid cooling medium (not shown in the figures) circulates. For this purpose, a circulating pump 32 is arranged in the cooling circuit, which transports the liquid cooling medium, which has absorbed heat from the transformer 25, through a heat exchanger 33 also arranged in the cooling circuit and feeds it back to the transformer via the cooling circuit 31. The heat exchanger 33 can, for example, be a plate heat exchanger, wherein the liquid cooling medium is pumped through the plates of the heat exchanger, which in turn are in thermal contact with the ambient air on their outer surfaces.

[0030] A temperature sensor 34 is arranged in the cooling circuit 31, which measures the temperature of the cooling medium and supplies it to a pump control 35, which controls the circulation pump 32 so that the temperature of the cooling medium is maintained within a predetermined temperature window.

[0031] According to the invention, the circulation pump 32 is designed as a sub-oil pump. A preferred variant of the sub-oil pump 32 provided according to the invention is shown in Fig. 3 in more detail.

[0032] Fig. 3 shows a cross section of a preferred embodiment of a sub-oil pump as used in the cooling circuit 31 of the cooling system 30 of the Fig.2 can be used as a circulation pump. The sub-oil pump 32 comprises a pump head 36 and an electric drive motor 37 connected to the pump head, which in the present case is designed as a synchronous motor. The synchronous motor 37 has a motor housing 38 which defines a motor chamber 39 in which a rotatable motor shaft 40 is arranged. A rotor 41 is rotatably mounted on the motor shaft 40 and is formed by permanent magnets 42 in the example shown. The rotor 41 is surrounded by a stator 43 which is connected to the motor housing 38 and consists of iron cores 44, each of which is surrounded by current-carrying windings 45 which, during operation, generate a rotating magnetic field which the rotor 41 follows synchronously.The motor shaft 40 is rotatably mounted at the end remote from the pump head by means of a radial plain bearing 46 remote from the pump head and at the transition between the motor housing 38 and the pump head 36 by means of a radial plain bearing 47 close to the pump head and an axial bearing 48. The pump-side end 49 of the motor shaft 40 projects into a pump housing 50 of the pump head 33. The pump housing 50 has an axial suction port 51 and a radial pressure port 52 and defines a working chamber 53 between the suction port 51 and the pressure port 52. The pump-side end 49 of the motor shaft 40 projects into the working chamber 53. A radial impeller 54 is mounted non-rotatably on the pump shaft at the pump-side end 49 of the motor shaft 40, so that the radial impeller 54 can rotate in the working chamber 53, driven by the synchronous motor 37.

[0033] During operation, the cooling medium is drawn in via the intake port 51 and, after flowing through the radial impeller 54, enters the pressure area of ​​the working chamber 53, from where it is expelled via the discharge port 52. A partial flow of the cooling medium flows from the pressure area of ​​the working chamber 53 into the motor chamber 39, flows around the windings 45 of the stator, and returns to the suction area of ​​the pump head via passages between the working chamber 53 of the pump head 36 and the motor chamber 39 of the motor housing 38. Thus, the cooling medium of the cooling circuit can effectively cool the drive motor of the circulation pump and extend its service life. List of reference symbols 10 wind turbines (WT) 11 Tower 12 Foundation 13 Nacelle / machine house 14 Rotor shaft 15 warehouses 16 Hub 17 rotor blades 18 Adjustment device 19 gearboxes 20 generators 21 power cables 22 Switchgear 23 Mains connection 24 frequency converters 25 Transformer 26 Wind measurement system 27 Control system for wind turbines 28 Hydraulic system 29 30 Cooling system 31 Cooling circuit 32 Circulation pump, sub-oil pump 33 heat exchangers 34 Temperature sensor 35 Pump control 36 Pump head 37 electric drive motor, synchronous motor 38 engine housing 39 Engine compartment 40 Motor shaft 41 Rotor 42 permanent magnet 43 Stator 44 iron core 45 winding 46 radial plain bearing remote from pump head 47 radial plain bearing near the pump head 48 thrust bearings 49 pump-side end of the motor shaft 40 50 pump housings 51 suction nozzle 52 pressure nozzles 53 work space 54 Radiallaufrad

Claims

[1] Cooling system (30) for an electrical machine, with at least one cooling circuit (31) which is in thermal contact with the electrical machine (25) and in which a liquid cooling medium circulates; at least one circulation pump (32) for the liquid cooling medium, which is arranged in the cooling circuit (31); and at least one heat exchanger (33) arranged in the cooling circuit (31), characterized by , that the circulation pump is designed as a sub-oil pump (31) which comprises a pump head (36) and an electric drive motor (37) connected to the pump head (36), which has a motor housing (38) which defines a motor chamber (39) in which a rotatable motor shaft (40), a rotor (41) connected in a rotationally fixed manner to the motor shaft and a stator (43) connected to the motor housing are arranged, around which the cooling medium of the cooling circuit (31) flows. [2] Cooling system according to claim 1, characterized by that the electric drive motor (37) is designed as a synchronous motor. [3] Cooling system according to one of claims 1 or 2, characterized by that the pump head (36) is designed as a radial wheel pump having a pump housing (50) defining a working chamber (53) into which a pump-side end (49) of the motor shaft (40) projects, on which a radial impeller (54) is mounted in a rotationally fixed manner. [4] Cooling system according to claim 3, characterized by that a partial flow of the liquid cooling medium is guided from the working chamber (53) of the pump head (36) into the motor chamber (39) and back into the working chamber (53). [5] Cooling system according to one of claims 1 to 4, characterized by that the motor shaft (40) is mounted by means of at least one plain bearing (46,47). [6] Cooling system according to one of claims 1 to 5, characterized by that a temperature sensor (34) for measuring the temperature of the cooling medium is arranged in the cooling circuit (31). [7] Cooling system according to one of claims 1 to 6, characterized by that the circulation pump (32) comprises a pump control (35). [8] Cooling system according to claims 6 and 7, characterized by that the pump control (45) controls the electric drive motor (37) depending on the temperature of the cooling medium. [9] Electric machine with a cooling system according to one of claims 1 to 8. [10] Electric machine according to claim 9, characterized by that the electrical machine is an electrical generator (20) or an electrical transformer (25). [11] Wind turbine (10) with a generator (20) and a transformer (25), characterized by that the generator (20) and / or the transformer (25) are thermally coupled to a cooling system (30) according to one of claims 1 to 8. [12] Wind turbine according to claim 11, characterized bythat the electric drive motor (37) of the cooling system is driven by part of the electricity generated by the wind turbine.

Images