WO2023105160A1

WO2023105160A1 - Electric machine comprising a de-energising valve

Info

Publication number: WO2023105160A1
Application number: PCT/FR2022/052267
Authority: WO
Inventors: Sabrina Siham AYAT; Rémi Luc Stéphane DORGET; Rémy BIAUJAUD
Original assignee: Safran; Universite De Lorraine
Priority date: 2021-12-10
Filing date: 2022-12-07
Publication date: 2023-06-15
Also published as: FR3130466A1

Abstract

The invention relates to an electric machine that comprises a rotor (7), a stator (2), and a vacuum chamber (10), the rotor (7) and/or the stator (2) comprising a superconducting material, the rotor (7) and/or the stator (2) that comprises the superconducting material being placed in the vacuum chamber (10). The electric machine further comprises a cooling system (11), placed in the vacuum chamber (10), for cooling the rotor and/or the stator, and a valve (12) passing through a peripheral wall (13) of the vacuum chamber (10).

Description

DESCRIPTION

TITLE: Electrical machine with de-excitation valve

Technical area

The present invention relates to the de-excitation of superconducting electrical machines.

The present invention is applicable to entirely or partially superconducting electrical machines, in configurations in which the armature or the inductor alone can (can) be superconductive.

A particularly interesting application of the invention relates to turbomachines intended for supplying electrical energy to aircraft on-board networks.

Prior techniques

Propulsion systems for electric or hybrid aircraft require the use of electric motors capable of competing with, or even exceeding, the performance of internal combustion engines.

Electrical machines intended for the propulsion of electric aircraft are characterized by electrical power densities greater than about 20 kW per kg.

In this context, the use of the most efficient machines possible is advantageous in order to be able to achieve these levels of power density.

The use of superconducting machines makes it possible in the first place to obtain good efficiency.

Indeed, when they are cooled to a temperature below their critical temperature, superconducting materials have zero resistivity, which allows direct currents to circulate without losses.

At this temperature, they also exhibit a diamagnetic response to any change in the magnetic field. This behavior is analogous to that of a magnetic field barrier. The absence of resistivity of superconducting materials at a temperature below their critical temperature therefore makes it possible to increase the current density flowing in the conductors.

Indeed, the absence of losses by Joule effect in the superconducting conductors makes it possible to avoid a linear increase in the needs in cooling with the increase in the power of the superconducting electric motors. It is nevertheless necessary to cool them to temperatures below their critical temperatures, typically below 100 Kelvin or even 150 Kelvin.

An exemplary embodiment of a superconducting electrical machine 1 with flux barriers and axial flux without magnetic core, also called without iron, has been represented in figure 1. Figure 1 illustrates in particular the rotor and stator of such an electric machine 1.

The electric machine 1 comprises a stator 2 comprising an annular superconducting inductor 3 as well as one or more arrangements 5 of electromagnetic coils 6 forming an armature, the inductor 3 being coaxial with the arrangements 5 of electromagnetic coils 6. More precisely, the stator 2 comprises a part of the inductor 3. In particular, the part of the inductor 3 included in the stator 2 comprises for example a superconducting DC coil.

The electric machine also comprises a rotor 7 comprising superconducting pads 8 arranged radially inside the annular inductor and rotating with respect to the stator 2. The inductor 3 therefore comprises a superconducting DC coil 3 placed at the stator 2 and superconducting pellets 8 placed in the rotor 7. The axis of rotation of the rotor corresponds to the axis of the axial flow of the electric machine 1. The superconducting pellets 8 are cooled, with helium, nitrogen or hydrogen for example, and realize the variation of the magnetic field thanks to the diamagnetic response of the superconducting pellets 8. The superconducting pads 8 have for example a circular shape or a section annular, the latter shape improving the power density of the electric machine.

The example more particularly illustrated in FIG. 1 corresponds to an axial flux machine comprising a rotor 7 flanked by two stators 2. In this case, a set of pellets 8 is flanked on either side by an arrangement 5 of coils electromagnetic 6. As a variant, one could also have a stator framed by two rotors. In this variant, an arrangement 5 of electromagnetic coils is flanked on either side by a set of superconducting pads 8.

In a generator operating mode, the inductor 3 creates an intense magnetic field, the superconducting pads 8 cause the variation of this magnetic field, and the electromagnetic coils 6 are exposed to the variable magnetic field created by the rotation of the rotor 7. A electromotive force is thus generated according to Faraday's law.

In the context of aviation, the management of breakdowns within electrical machines is essential in order to guarantee the overall reliability of aircraft. In the event of a breakdown, it is imperative to limit its impact. For example, a faulty generating electrical machine continuing to rotate can disrupt surrounding systems by injecting unwanted and uncontrolled currents or voltages into them.

Solutions exist to limit the impact of an electrical machine breakdown. A mechanical solution consists in segmenting a shaft of the machine in such a way as to prevent drive-in in the event of a breakdown, which however leads to the destruction of the shaft of the machine. An electromagnetic solution is to turn off magnetic field sources, for example magnets or electromagnets.

However, these solutions are not directly applicable to superconducting electrical machines which usually require vacuum insulation and cooling. Indeed, the large magnetic fields implemented in superconducting machines complicate their demagnetization. Disclosure of Invention

The object of the present invention is therefore to overcome the aforementioned drawbacks and to facilitate rapid and reliable de-energization of an electrical machine, for example during a breakdown.

The subject of the present invention is an electric machine comprising a rotor, a stator, and a vacuum enclosure, the rotor and/or the stator comprising a superconducting material, the rotor and/or the stator which comprises the superconducting material being placed in the 'vacuum enclosure, the electric machine further comprising a system for cooling the rotor and/or the stator placed in the vacuum enclosure, and a valve placed through a peripheral wall of the vacuum enclosure.

Thus, during a breakdown, the opening of the valve makes it possible to connect the interior of the vacuum enclosure with the exterior in order to rapidly increase the internal temperature of the enclosure and to eliminate the superconducting effects of the material. superconductor. Indeed, the thermal insulation provided by the vacuum is broken and heat transfers by convection take place between the air and the rotor and/or the stator.

Advantageously, the vacuum chamber is placed in an environment comprising air whose temperature is at least 5 Kelvin higher than the temperature of the rotor and/or of the stator placed in the vacuum chamber.

In one embodiment, the electric machine further comprises a solenoid valve controlling the opening and closing of the valve according to a setpoint.

Advantageously, the vacuum chamber includes a temperature sensor.

In one embodiment, the stator includes an annular inductor and an armature including at least one arrangement of electromagnetic coils, and wherein the rotor includes superconducting pads mounted radially within the inductor.

Advantageously, the inductor is made of superconducting material. The invention also relates to a turbomachine comprising at least one electric machine as defined above.

In addition, another subject of the invention is an aircraft comprising at least one turbomachine as defined above.

Finally, the subject of the invention is a method for de-energizing an electrical machine as defined above, the method comprising the following steps:

Detection of a breakdown in the electrical machine; And

Opening of the valve until the temperature of the rotor and/or the stator placed in the vacuum chamber increases above a predefined temperature threshold for which the superconducting material no longer has a superconducting effect.

Brief description of the drawings

Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[Fig 1] which has already been mentioned, illustrates schematically and in exploded view the rotor and stator of an electrical machine with flux barriers according to the state of the art;

[Fig 2] schematically illustrates an embodiment of an electric machine according to the invention; And

[Fig 3] illustrates the steps of the method according to the invention.

Detailed description of at least one embodiment

There is shown schematically in Figure 2 a simplified diagram of an embodiment of an electrical machine 1.

The rotor 7 and stator 2 visible in FIG. 1 represent a particular embodiment of rotor 7 and stator 2 of the electric machine 1 illustrated in FIG. 2. Any other superconducting machine or any other arrangement of rotor and stator may also be suitable. . Said electrical machine 1 therefore comprises a rotor 7, a stator 2, a vacuum chamber 10 and a cooling system 11.

In this embodiment the rotor 7 and the stator 2 each comprise an element made of superconducting material.

As illustrated in FIG. 1, the stator 2 comprises for example a superconducting annular inductor 3 and an armature comprising at least one arrangement 5 of electromagnetic coils 6.

The rotor 7 comprises for example superconducting pads 8 mounted radially inside the inductor 3 of the stator 2.

In this embodiment, the rotor 7 and the stator 2 are placed within the vacuum enclosure 10 and the vacuum enclosure 10 is connected to the cooling system 11. In operation, the electric machine 1 places the enclosure vacuum 10 under vacuum and cools the rotor 7 and the stator 2 using the cooling system 11 in order to promote the superconducting behaviors of the stator 2 and the rotor 7.

In another embodiment, only the rotor 7 comprises a superconducting element. In this embodiment, only the rotor 7 is placed in the vacuum chamber 10 and only the rotor 7 is cooled.

Conversely, in a last embodiment, only the stator 2 comprises a superconducting element and only the stator 2 is placed in the vacuum enclosure 10 to be cooled.

In the embodiment illustrated in Figure 2, the electric machine 1 comprises a valve 12 placed through a wall 13 of the vacuum chamber 10. In particular, the wall 13 of the vacuum chamber 10 is perforated in order to be able to introduce the valve 12 therein. The valve 12 can thus be introduced into vacuum enclosures for electrical machines that already exist, simply and at low cost. The valve 12 can reach an open position and a closed position.

In its closed position, the valve 12 makes it possible to keep the vacuum chamber 10 airtight. In its open position, the valve 12 creates a communication between the inside and the outside of the vacuum chamber 10.

Depending on the quality of vacuum desired inside the vacuum chamber 10, active pumping carried out by a pump included in the vacuum enclosure may be required to maintain the vacuum inside the enclosure. During the opening of the valve 12, there are two scenarios. In one mode of implementation, the pump is active and draws in the air which will enter even more quickly inside the enclosure (acceleration of the heating). In another mode of implementation, the pump can be turned off at the same time as the opening of the valve 12.

During operation of the electric machine 1, the valve 12 is in the closed position. If it is desired to de-energize the electric machine 1, for example if a fault is detected, the valve 12 is opened. The vacuum from the vacuum vessel 10 creates a suction and the air outside the vacuum vessel 10 enters the vacuum vessel 10 and increases the internal temperature of the rotor and stator in the vacuum vessel 10 by due to the loss of thermal insulation provided by the vacuum.

In particular, the vacuum chamber 10 is preferably placed in an environment comprising air whose temperature is at least 5 Kelvin higher than the internal temperature of the vacuum chamber 10 when the latter is cooled. In this way, the opening of the valve 12 ensures an increase in the internal temperature of the vacuum chamber 10.

For a superconducting material maintained at its critical operating temperature, for example 50 Kelvin, an increase of 5 Kelvin is enough to suppress the superconducting effect and therefore de-energize the electrical machine 1.

The valve 10 is for example kept open for the time necessary for the temperature to increase. The vacuum enclosure 10 comprises for example a temperature sensor 15, for example a thermocouple, in order to supply the temperature information to a remote computer 16 controlling the de-energization of the electric machine 1. In one embodiment, the temperature sensor temperature is placed on the rotor and/or the stator, so as to precisely measure their temperature. In addition, the electric machine 1 comprises a solenoid valve 17 controlling the opening and closing of the valve 12. The solenoid valve 17 is for example controlled by an instruction sent from the remote computer 16. The remote computer 16 implements a method of de-energizing the electric machine 1 by implementing a first step 21 of detecting a fault in the electric machine 1. The fault may come from a mechanical or electrical problem.

Then, a step 22 of opening the valve 12 is performed for the time that the internal temperature of the vacuum chamber 10 increases beyond a predefined temperature threshold. For example, an operator predetermines in the remote computer 16 a temperature at which the superconducting materials no longer have any effect. The temperature sensor 15 measures the temperature and sends it to the remote computer 16.

Optionally, a step 23 of stopping the cooling system 11 is carried out in parallel with the opening of the valve 12 in order to accelerate the increase in the internal temperature of the vacuum chamber 10.

Claims

9 CLAIMS

1. Electrical machine comprising a rotor (7), a stator (2), and a vacuum chamber (10), the rotor (7) and / or the stator (2) comprising a superconducting material, the rotor (7) and /or the stator (2) which comprises the superconducting material being placed in the vacuum chamber (10), characterized in that it further comprises a cooling system (11) for the rotor and/or the stator placed in the vacuum chamber (10) and a valve (12) placed through a peripheral wall (13) of the vacuum chamber (10), the vacuum chamber (10) being placed in an environment comprising the air whose temperature is at least 5 Kelvin higher than the temperature of the rotor and/or of the stator placed in the vacuum chamber (10).

2. Electrical machine according to claim 1, comprising a solenoid valve (17) controlling the opening and closing of the valve (12) according to a setpoint.

3. Electrical machine according to one of claims 1 and 2, wherein the vacuum chamber (10) comprises a temperature sensor (15).

4. Electrical machine according to any one of claims 1 to 3, wherein the stator (2) comprises an annular inductor (3) and an armature comprising at least one arrangement (5) of electromagnetic coils (6), and wherein the rotor (7) comprises superconducting pads (8) mounted radially inside the inductor (3).

5. Electrical machine according to claim 4, in which the inductor (3) is made of superconducting material.

6. Turbomachine comprising at least one electric machine (1) according to any one of claims 1 to 5.

7. Aircraft comprising at least one turbomachine according to claim 6.

8. A method of de-energizing an electric machine (1) according to any one of claims 1 to 5, characterized in that it comprises the following steps: Detection (step 21) of a fault in the electrical machine (1); And

Opening (step 22) of the valve (12) until the temperature of the rotor and/or of the stator placed in the vacuum chamber (10) increases beyond a predefined temperature threshold for which the superconducting material no longer has a superconducting effect.