Apparatus and method for stopping an electric machine of a turbine engine

Abstract

An electric assembly for an aeronautical turbine engine, comprising an electric machine (70) configured to be arranged in a turbomachine (100) and comprising a stator (72) and a rotor (71) comprising magnets, the assembly comprising short-circuit detection means (210), hot air injection means (80) configured to draw hot air from the turbomachine at a temperature higher than the demagnetization temperature of the magnets of the rotor (71) and to inject the drawn hot air onto the magnets of said rotor (71) when the short-circuit detection means (210) detect the presence of a short-circuit in the electric machine (70), and cold air injection means (90) configured to draw cold air from the turbomachine (100) and to inject it into an inner cavity cavity of the turbomachine, the temperature of the cold air drawn by the cold air injection means (90) being lower than the temperature of the hot air drawn by the hot air injection means (80).

Description

TECHNICAL FIELD

[0001] The present invention relates to the field of turbomachines. More precisely, the present invention relates to a device for stopping an electric machine of an aircraft turbomachine in case of short circuit, and to a method using such a device. BACKGROUND

[0002] The use of synchronous electric machines with permanent magnets is known, in particular for aeronautical turbomachines. These electric machines can be connected to one or more shafts of the turbomachine.

[0003] Permanent magnet synchronous machines (so-called "PMSM") represent an advantageous technology in terms of efficiency, mass density and power torque. These criteria are indispensable to allow performance gains with the electrification of turbomachines.

[0004] However, these machines present considerable challenges in terms of safety, in particular due to the risk of establishing a short circuit and causing a fire. The appearance of a short circuit in the windings of an electric machine can be the result of the deterioration of the insulating material, in particular due to the use or ageing conditions (in particular high temperature and / or overvoltage). The deterioration of the insulating material, combined with high altitudes, involves the appearance of partial discharges which further damage the insulating material. Electric arcs can be created with plasmas, leading to the deposition of material and the appearance of a short circuit. Very high currents can also lead to an explosion fire.

[0005] In addition, a PMSM cannot be de-energized as long as the magnets of the electric machine continue to generate a magnetic field supplying the short circuit. However, the rotor of the electric machine containing the magnets is generally coupled to the shaft of the turbomachine, making it difficult to stop the short circuit.

[0006] Devices exist for protecting against short circuits in PMSM, such as mechanical uncouplings, but are generally not very reliable and are relatively expensive and bulky. On systems of the dog clutch type for example, the electric machine must be set to zero torque or very low torque in order to be able to uncouple, which is difficult to achieve in the case of a short circuit. It is also possible to use a mechanical type fuse which makes it possible to break the mechanical connection above a certain torque. However, the short circuit torque must be much greater than the maximum torque to break the connection. This system is expensive and not very reliable.

[0007] There is therefore a need for a device which makes it possible to stop an electric machine for a turbomachine in case of short circuit, both effectively and compactly, while ensuring the temperature resistance of the equipment of the turbomachine. SUMMARY

[0008] The present invention relates to an electric assembly for an aircraft turbomachine, comprising:

[0009] - an electric machine configured to be arranged in the turbomachine and comprising a stator and a rotor configured to be rotationally fixed to a shaft of the turbomachine, and the electric machine comprising magnets,

[0010] - a short-circuit detector configured to detect the presence of a short-circuit in the electric machine,

[0011] - a hot air ejector configured to draw hot air from the turbomachine at a temperature higher than the demagnetization temperature of the magnets of the rotor, and to eject the drawn hot air onto the magnets of the rotor when the short-circuit detector detects the presence of a short-circuit in the electric machine, and

[0012] - a cold air ejector configured to draw cold air from the turbomachine when the short-circuit detector detects the presence of a short-circuit in the electric machine, and to eject the cold air into an inner chamber of the turbomachine, the temperature of the cold air drawn by the cold air ejector being lower than the temperature of the hot air drawn by the hot air ejector.

[0013] The turbomachine comprises one or more rotating shafts. The electric machine can be arranged at different locations in the turbomachine by being fixed to a rotating component which is mechanically coupled to one of the shafts. For example, the rotor can be mounted directly around a shaft or coupled to a module of a rotating turbomachine (compressor, turbine, reduction gear). The stator can be attached to a fixed casing of the turbomachine and the rotor is rotationally fixed to a shaft of the turbomachine, for example a low pressure shaft or a high pressure shaft. When the rotor rotates, the windings in the stator and the permanent magnets in the rotor generate an electric current. This generated electric current can in particular be used to power a power electronics unit installed in the turbomachine. The opposite effect, i.e. the introduction of a mechanical torque on the shaft, can also be sought.

[0014] The hot air ejecting device, in particular the hot air ejector, makes it possible to stop this machine as soon as a short-circuit is detected by the short-circuit detector. More precisely, as soon as a short-circuit is detected, the hot air ejecting device immediately ejects hot air onto the magnets. The stopping time of the electric machine after the ejection of hot air is less than 30 seconds, preferably less than 20 seconds, still more preferably less than 10 seconds.

[0015] The hot air ejecting device can in particular comprise at least one duct, a first end of which is arranged in the turbomachine at the location where the air is drawn and a second end of which is arranged close to the rotor. The term "close to" is understood to mean that the second end is close enough to the rotor so that the heat transfer is as efficient as possible. In particular, the second end is close enough to the magnets of the rotor so that the temperature of the air at the outlet of the second end is substantially equal to the temperature of the air which impacts the rotor, in particular the magnets of the rotor. The maximum distance between the second end and the rotor, in particular the magnets of the rotor, is for example less than 1 cm.

[0016] Preferably, the suction of hot air by the hot air injection means is carried out through a secondary air suction system already installed in the turbine (so-called SAS for secondary air system) and / or through the addition of an additional suction at different stages of the turbine. More precisely, in the case of a bypass turbine, the main flow and the secondary flow extend from upstream to downstream of the turbine, passing through different stages of the turbine, in particular the low pressure and high pressure compressors, the combustion chamber, and the high pressure and low pressure turbines. The suction of hot air by the injection means can be carried out from one or the other or even several of these stages. The choice of the hot air suction site can be made according to the type of electric machine used, in particular according to the demagnetization temperature of the magnets of the rotor, or the Curie temperature of the material of which the magnets are composed. In other words, it is at this temperature that the magnets lose their ferromagnetic properties. The term "hot air" should therefore be understood as meaning air at a temperature higher than the Curie temperature of the magnets.

[0017] The fact of sucking hot air from the first end of the duct of the injection means, passing it through the duct all the way to the second end to inject it onto the magnets of the rotor, makes it possible to demagnetize the magnets if the short-circuit detector detects a short circuit, and thus to de-energize the electric machine, thereby limiting the risk of a fire outbreak.

[0018] The suction of cold air by the cold air injector can be carried out through a secondary air system already installed in the turbine (so-called SAS).

[0019] In addition, the inner chamber can be a chamber located in the turbine and which needs to be kept at low temperature, inside or outside which the electric machine can be arranged, but close to the chamber, in particular adjacent to the chamber. At the beginning of the process for stopping the machine in the case of a short circuit, the supply of hot air increases the temperature by heating the magnets, increasing the risk of overheating inside the inner chamber. The supply of cold air inside it makes it possible to prevent this overheating. The flow rate and the temperature of the cold air drawn are preferably determined according to the architecture of the chamber and the arrangement of the electric machine with respect to the chamber. Preferably, the temperature of the cold air sucked by the cold air injector is much lower than the temperature of the hot air sucked by the hot air injector, for example twice as low. The temperature of the cold air can be between -55°C and 150°C.

[0020] In addition, the fact of using hot air and cold air sucked directly from the turbine, in particular using a secondary air system already present in the turbine, makes it possible to limit the volume and the cost of the means for stopping the electric machine. In addition, there is no need to incorporate additional means for passing the hot air and the cold air inside the turbine, such additional means could provide uncontrolled problems and could increase the risk of malfunction in the turbine. Direct suction from the turbine therefore makes it possible to improve the reliability of the means.

[0021] In certain embodiments, the hot air sucked by the hot air ejector has a temperature higher than 250°C, and preferably higher than 400°C.

[0022] If a short circuit is detected, this temperature makes it possible to demagnetize the rotor, to de-energize the electric machine, and thus to prevent a fire outbreak.

[0023] In certain embodiments, the hot air ejector is configured to suck hot air from a high pressure compressor of the turbomachine.

[0024] Sucking the high pressure compressor makes it possible to obtain a higher air temperature in the turbomachine before combustion.

[0025] In certain embodiments, the hot air ejector is configured to suck hot air downstream of a combustion chamber of the turbomachine.

[0026] Sucking downstream of the combustion chamber makes it possible to obtain hot air at an even higher temperature (for example 1000°C), and thus to demagnetize magnets having a particularly high Curie temperature.

[0027] In certain embodiments, the hot air ejector is configured to suck hot air from a high pressure compressor of the turbomachine and downstream of a combustion chamber of the turbomachine.

[0028] Mixing the hot air sucked upstream of the combustion chamber, in particular in the high pressure compressor, and downstream of the combustion chamber makes it possible to control the temperature level of the air injected at the magnets. This allows greater flexibility in temperature regulation, and adapts the system to the characteristics of the electric machine used and the magnets it comprises.

[0029] In certain embodiments, the short circuit detector comprises a temperature measurer attached to the machine and / or a leakage current measurer and / or a measurement and impedance comparator.

[0030] Preferably, the temperature measuring device is a thermocouple attached to the stator. The threshold temperature, which can be a short circuit, can be determined in advance, in particular based on the type of electric machine considered. Thus, if this given threshold is exceeded, for example by comparing it to the temperature read by the thermocouple, hot air can be injected by the hot air ejector onto the magnets of the rotor.

[0031] Preferably, the measurement and impedance comparator and the leakage current measurer are arranged in a monitoring and control unit of the electric machine, which is generally incorporated in the power electronics unit of the electric machine. Similarly, threshold values or nominal values can be determined in advance to allow comparison and monitoring. Thus, if one or more of these given threshold values are exceeded, hot air can be injected via the hot air ejector onto the magnets of the rotor. The use of these devices has the advantage of being simple and inexpensive to implement and incorporate.

[0032] In certain embodiments, the hot air injector comprises at least one valve movable between a closed position preventing the injection of hot air onto the magnets of the rotor and an open position allowing the injection of hot air onto the magnets of the rotor.

[0033] The valve makes it possible to inject hot air onto the magnets only when a short circuit is detected. In particular, when this demagnetization is not desired, the closed position of the valve makes it possible to maintain the temperature level of the magnets at a value low enough (the operating limit can vary between 80°C and 350°C) to avoid the demagnetization of these magnets and to avoid affecting their performance. In particular, under nominal operation, the temperature of the magnets must of course be maintained below the limit value specified by the manufacturer (strictly speaking, below the Curie temperature), above which irreversible demagnetization occurs. The use of such a valve has the advantage of being simple and inexpensive.

[0034] In certain embodiments, the electrical assembly comprises a control unit to which the short circuit detector and the valve are connected, the control unit being configured to open the valve when the short circuit detector detects the presence of a short circuit in the electric machine.

[0035] The control unit can be of the ECU (Electronic Control Unit) type. Such a control unit makes it possible to automate the injection of hot air onto the rotor in particular if the detector detects a short circuit. This improves the efficiency of the device.

[0036] In certain embodiments, the hot air injector comprises an air circuit arranged in the stator of the machine and comprising a plurality of passages configured to inject hot air onto the magnets of the rotor.

[0037] This improves the efficiency of the device by injecting hot air as closed as possible onto the magnets of the rotor.

[0038] In certain embodiments, the electric machine is configured to be arranged in an inner chamber, which is a pressurized chamber or a cryogenic chamber of the turbomachine containing oil. The term "cryogenic chamber" is understood to mean a region of the turbomachine that needs to be maintained at a low temperature (for example, below 140°C) during operation.

[0039] If the electric machine is incorporated into a pressurized chamber containing oil, for example, and at the beginning of the process of stopping the machine in the event of a short circuit, the supply of hot air increases the temperature by heating the magnets, thereby increasing the risk of overheating of the oil in this chamber. The supply of cold air inside it can prevent this overheating of the oil.

[0040] In certain embodiments, the cold air injector comprises at least one valve movable between a closed position preventing the injection of cold air into the inner chamber and an open position allowing the injection of cold air into the inner chamber.

[0041] The valve is also connected to the control unit and is used to inject cold air into the inner chamber only when a short circuit is detected.

[0042] In certain embodiments, the electric machine is a permanent magnet synchronous machine.

[0043] The application also relates to a turbomachine comprising an assembly as described in any one of the above embodiments.

[0044] The application also relates to a method for stopping an electric machine of a turbomachine using an assembly as described in any one of the above embodiments, the method comprising the steps of:

[0045] - detecting, by the short circuit detector, a short circuit in the electric machine,

[0046] - injecting hot air onto the magnets of the rotor of the electric machine when a short circuit in the electric machine has been detected in the detection step, the hot air having a temperature higher than or equal to the demagnetization temperature of the magnets of the rotor of the electric machine,

[0047] - injecting cold air into the inner chamber of the turbomachine when a short circuit in the electric machine has been detected in the detection step, the cold air having a temperature lower than the temperature of the hot air injected onto the magnets of the rotor.

[0048] The injection of cold air can be simultaneous with the injection of hot air when a short circuit is detected, or in a slightly delayed manner, for example less than 10 seconds after the hot air has started to be injected. BRIEF DESCRIPTION OF DRAWINGS

[0049] The application and its advantages will be better understood by reading the following detailed description of different embodiments given by way of non-limiting examples. The description makes reference to the attached pages of drawings, in which:

[0050] Figure 1 is a longitudinal section view of a turbomachine equipped with a secondary air system.

[0051] Figure 2 shows Figure 1 a turbomachine equipped with an electrical assembly according to the application.

[0052] Figure 3 is a detail view of the electric machine of the turbomachine of Figure 2

[0053] Figure 4 shows Figure 2 a modified embodiment of the embodiment of

[0054] Figure 5 shows the different steps of a method for stopping an electric machine according to the application. DETAILED DESCRIPTION ​

[0055] In the remainder of the text, the terms "upstream" and "downstream" are defined relative to the direction of gas flow through the turbine, by... Figure 1 and Figure 2 The arrow F in the diagram indicates this.

[0056] Figure 1 A bypass turbine 100 is shown, which, in a known manner, sequentially comprises from upstream to downstream at least one fan 10, an engine section comprising at least a low-pressure compressor 20, a high-pressure compressor 30, a combustion chamber 40, and at least 50 high-pressure turbine stages and 60 low-pressure turbine stages. Turbine 100 is an exemplary embodiment of the invention. However, the type (architecture and size) of the turbine is not limiting in this description. The invention also relates to turboshaft engines or turboprop engines.

[0057] The rotor, which rotates around the main shaft X of the turbine 100 and is connected together by a system of different transmission devices and gears, corresponds to these different components.

[0058] In a known manner, the turbine is equipped with a secondary air system, wherein, as required, air is drawn from several different points on the turbine 100, more specifically from different stages, and from one of the two air paths of the bypass turbine. The air drawn from these points is then delivered to another part of the turbine 100.

[0059] exist Figure 1 In the illustrated embodiment, the secondary air system includes suction channels 1 and 2 that draw air from the low-pressure compressor 20 or the high-pressure compressor 30 and allow for chamber pressurization; suction channel 3 in the high-pressure compressor 30 allows for de-icing of the front end and pod; and suction channels 4 and 5 upstream of the combustion chamber 40 for cooling the high-pressure turbine 50. This enumeration is not limiting, and the secondary air system can include other suction points.

[0060] Figure 2 It shows Figure 1 The turbine 100 is equipped with electrical components according to the invention. The turbine 100 also includes the aforementioned different suction channels. For clarity, these are not shown in the text. Figure 2 It is shown again in the text.

[0061] The turbine 100 is equipped with a motor 70, which is a permanent magnet synchronous system arranged within the turbine's inner chamber E. This motor 70 includes a rotor 71 and a stator 72; the rotor 71 includes magnets, and the stator 72 includes copper windings 73. The type of motor (material, size, power, etc.) and its arrangement within the turbine are not limiting in this specification. In this embodiment, the inner chamber E is a pressurized chamber upstream of the low-pressure compressor 20.

[0062] The stator 72 of the electric machine 70 is attached to the fixed casing 22 of the turbomachine 100. The rotor 71 is fixed to the rotating shaft (e.g. the low pressure shaft) of the turbomachine, for example, through a connecting arm 24. The windings 73 located in the stator 72 and the magnets located in the rotor 71 allow to generate an electric current when the rotor 71 rotates. The electric current thus generated can be used, in particular, to power a power electronics unit (not shown) located in the turbomachine 100.

[0063] There is also provided a device for stopping the electric machine 70 in the turbomachine 100. It comprises a short-circuit detection device (e.g. a short-circuit detector 210) and a hot air injection device, for example, a cold air injector 80.

[0064] In this embodiment, the short-circuit detector 210 comprises a plurality of thermocouples arranged in the stator 72. Figure 2 and 3 Only one of them is shown in the figure. These thermocouples 210 are connected to the computing unit 200 so that the temperatures measured by the thermocouples 210 in the stator 72 can be read. This embodiment is not limiting; other devices for detecting a short-circuit can be envisaged, such as impedance measurement devices (e.g. impedance measurers) or leakage current measurement devices (e.g. leakage current measurers), which can be incorporated into the power electronics unit.

[0065] The hot air injection device 80 comprises one or more ducts 81 Figure 2 and Figure 3 Only one of them is shown in the figure), each duct comprising an injection end 81a and a suction end 81b. In this embodiment, the suction end 81b is connected to a downstream stage of the high pressure compressor 30 in such a way as to be in fluid communication with this downstream stage. Thus, a portion of the gas flowing along the high pressure compressor 30 can be sucked and flow through the duct 81. Alternatively, the duct 81 can also be connected as a bypass of one of the ducts of the secondary air system previously described. More specifically, depending on the temperature required to demagnetize the magnets, the hot air can be obtained using the already installed secondary air system (SAS) and / or by adding an additional suction of the same compressor, sucking different stages of the high pressure compressor 30.

[0066] The injection end 81a is arranged in proximity of the rotor 71 of the electric machine 70. For example, the injection end 81a is arranged at a distance of less than 1 cm from the rotor 71. More precisely, the injection end 81a is arranged facing the rotor 71, i.e. substantially at the same position as the rotor 71 along a radial direction perpendicular to the axis X. Thereby, the gas sucked at the suction end 81b can be directly injected onto the rotor 71, in particular onto the magnets of the rotor 71. When the hot air injection device 80 comprises several ducts 81, each suction end 81b is connected to the high pressure compressor 30 and each injection end 81a is arranged in proximity of the rotor 71, for example in a way to distribute around the rotation axis of the rotor 71, in order to inject hot air onto the largest possible surface of the rotor 71.

[0067] Further, the hot air injection device 80 comprises a valve 82 arranged on each duct 81. The valve 82 can be an electronic valve and is connected to the computing unit 200. According to the value measured by the short circuit detector 210, the computing unit 200 can control the opening or the closing of the valve 82. For example, if the thermocouple 210 detects at least one temperature higher than or equal to 300°C, which is characteristic of the presence of a short circuit in the electric machine 70, the computing unit 200 controls the opening of the valve 82. The hot air, which has been sucked from the high pressure compressor 30 and is present in the duct 81 upstream of the valve 82, can then flow to the injection end 81a and thereby be injected onto the magnets arranged in the rotor 71. The term "hot air" is to be understood as meaning that the air sucked from the high pressure compressor 30 has a temperature higher than the Curie temperature of the magnets of the rotor 71, thereby allowing the demagnetization of these magnets.

[0068] According to Figure 4In a modified embodiment of this embodiment shown in the figures, the hot air injection device 80 can comprise a duct 81'connected as a bypass of the duct 81, the duct 81'comprising suction ends 81 b' each of which sucks hot air at a different stage of the turbine 100. For example, a first suction end 81 b can be connected to the high-pressure compressor 30 upstream of the combustion chamber 40, and a second suction end 81 b' can be connected downstream of the combustion chamber 40. According to this configuration, a second valve 82' is arranged on the bypass duct 81'and is connected to the calculation unit 200. The suction of two different stages of the turbine 100 makes it possible to control the temperature level of the air injected onto the rotor 71. Furthermore, the valves 82 and 82' can be configured to have an opening degree that can be adjusted, thus allowing the calculation unit 200 to adjust even more precisely the temperature of the air injected onto the rotor 71. In particular, hot air can be injected at a higher temperature, so that certain types of magnets can be demagnetized more efficiently. For example, the magnets of the rotor 71 can be rare-earth magnets of the neodymium-iron-boron (NdFeB) type, having a Curie temperature of 370°C and a maximum operating temperature of between 140 and 220°C. Thus, the mixing of air sucked from the high-pressure compressor 30, downstream of the combustion chamber 40, having a temperature of around 500°C, allows the demagnetization of these magnets of the rotor 71.

[0069] The above embodiments are non-limiting. In particular, electric machines 70 having different characteristics can be used, in particular comprising magnets of different materials. Thus, depending on the electric machine 70 used and its position in the turbine 100, the suction ends 81 b can be arranged at different stages of the turbine 100, for example at different stages of the high-pressure compressor 30.

[0070] Furthermore, according to another modified embodiment of this embodiment (not shown), the injection end 81 a can be arranged in the stator 72 and open radially towards the rotor 71. More specifically, the air circuit can be incorporated into the stator 72 of the electric machine 70 through the windings 73 and so that hot air can be supplied to the rotor 71 through a channel and blown over the entire surface of the magnets.

[0071] Furthermore, the turbine 100 comprises a cold air injection device 90( Figure 3), comprising a duct 91 which can also be connected as a bypass of one of the ducts of the secondary air system previously described. This cold air injection device 90 is configured to draw air from a stage of the turbine (for example, the low-pressure compressor 20) on which the gas has a temperature lower than the air drawn by the hot air injection device 80. The cold air thus drawn can be injected into the pressurized chamber E in which the electric machine 70 is arranged. More specifically, in the event of detection of any short circuit, the calculation unit 200 controls the opening of the valve 82 and / or of the valve 82' and of a valve 92 arranged on the duct 91 of the cold air injection device 90. Thus, in parallel to the injection of hot air onto the magnets of the rotor 71, the demagnetization of the magnets is allowed, the cold air injected into the pressurized chamber E making it possible to avoid an excessive increase in the temperature of the oil inside it.

[0072] Reference will now be made to Figure 5 A method for stopping an electric machine of a turbine is described in the remainder of the present description.

[0073] The short-circuit detector 210 (for example, a thermocouple) constantly measures the temperature in the machine 70 (step S1). The temperatures read are transmitted to the calculation unit 200. The calculation unit 200 compares these temperatures with a given threshold temperature (characteristic of a short circuit) (step S2). If, in step S2, the calculation unit 200 determines that the temperatures are lower than the given temperature threshold, the method returns to step S1. If, in step S2, the calculation unit 200 determines that at least one of the temperatures is higher than or equal to the given temperature threshold, the method proceeds to step S3. Thus, the short-circuit detection comprises a measurement step S1 and a comparison step S2. In step S3, when the machine 70 is arranged in a pressurized chamber E with oil or in a low-temperature chamber, i.e. in a zone which must be kept at low temperature, the calculation unit 200 controls the opening of the valve 82 and / or of the valve 82' and of the valve 92 of the cold air injection device 90. Thus, hot air can be injected onto the magnets of the rotor 71, allowing the demagnetization of these magnets, thus limiting the risk of overheating of the oil in this chamber.

[0074] Although the present application has been described with reference to specific exemplary embodiments, it is evident that modifications and changes can be made thereto without departing from the scope of the application as defined by the claims. For example, if the architecture of the turbine does not allow the extraction before the combustion chamber at the correct temperature level, the extracted air can be further heated to the required correct temperature using an exchanger combined downstream of the combustion chamber (using the exhaust heat) or by any other overheating method, in particular electrical. Moreover, the individual features of the different embodiments shown / referred to can be combined in further embodiments. The description and drawings are therefore to be considered in an illustrative sense only and not in a restrictive sense.

[0075] It is also clear that all the features described with reference to the method can be transposed, individually or in combination, to the device, and vice versa, all the features described with reference to the device can be transposed, individually or in combination, to the method.

Claims

1. An electrical assembly for an aeronautical turbomachine, comprising: - an electric machine (70) configured to be arranged in a turbomachine (100) and comprising a stator (72) and a rotor (71) configured to be rotationally fixed to a shaft of the turbomachine (100) and comprising magnets, - a short-circuit detector (210) configured to detect the presence of a short-circuit in the electric machine (70), - a hot air ejector (80) configured to draw hot air from the turbomachine at a temperature higher than the demagnetization temperature of the magnets of the rotor (71) and to eject the drawn hot air onto the magnets of the rotor (71) when the short-circuit detector (210) detects the presence of a short-circuit in the electric machine (70), and - a cold air ejector (90) configured to draw cold air from the turbomachine (100) and to eject the cold air into an inner chamber (E) of the turbomachine when the short-circuit detector (210) detects the presence of a short-circuit in the electric machine (70), the cold air drawn by the cold air ejector (90) having a temperature lower than the temperature of the hot air drawn by the hot air ejector (80).

2. The assembly of claim 1, wherein, The temperature of the hot air drawn by the hot air ejector (80) is higher than 250°C.

3. The assembly of claim 1, wherein, The temperature of the hot air drawn by the hot air ejector (80) is higher than 400°C.

4. The assembly of claim 1, wherein, The hot air ejector (80) is configured to draw hot air from downstream of a high-pressure compressor (30) of the turbomachine and / or of a combustion chamber (40) of the turbomachine (100).

5. The assembly of claim 1, wherein, The short-circuit detector (210) comprises a temperature measurer and / or a leakage current measurer and / or a measurement and impedance comparator attached to the electric machine (70).

6. The assembly of claim 1, wherein, The hot air ejector (80) comprises at least one valve (82) movable between a closed position preventing the ejection of hot air onto the magnets of the rotor (71) and an open position allowing the ejection of hot air onto the magnets of the rotor (71).

7. The assembly according to claim 1, comprising a control unit (200), the short-circuit detector (210) and the valve (82) connected to the control unit (200), the control unit (200) being configured to open the valve (82) when the short-circuit detector (210) detects the presence of a short-circuit in the electric machine (70).

8. The assembly of claim 1, wherein, The electric machine (70) is configured to be arranged in an inner chamber (E) which is a pressurized chamber or a cryogenic chamber of the turbomachine containing oil.

9. The assembly of claim 1, wherein, The electric machine (70) is a permanent magnet synchronous system.

10. A turbomachine comprising the assembly according to any one of the preceding claims 1 to 9.

11. A method for stopping an electric machine of a turbomachine (100) using the assembly according to any one of the preceding claims 1 to 9, the method comprising the steps of: - detecting a short-circuit in the electric machine (70) by means of the short-circuit detector (210), - ejecting hot air onto the magnets of the rotor (71) when a short-circuit in the electric machine (70) has been detected in the detection step, the hot air having a temperature higher than or equal to the demagnetization temperature of the magnets of the rotor (71) of the electric machine (70), - ejecting cold air into an inner chamber (E) of the turbomachine when a short-circuit in the electric machine (70) has been detected in the detection step, the cold air having a temperature lower than the temperature of the hot air ejected onto the magnets of the rotor (71). - when, in the detection step, a short circuit in the electric machine (70) has been detected, cold air is injected into the inner chamber (E) of the turbomachine, the temperature of the cold air being lower than the temperature of the hot air injected onto the magnets of the rotor (71).

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