WO2019101891A1

WO2019101891A1 - Method and device for diagnosing faults of an alternator

Info

Publication number: WO2019101891A1
Application number: PCT/EP2018/082280
Authority: WO
Inventors: Thierry JACQ; Mauricio CUEVAS-SALVATIERRA; Jean-Philippe Lecointe; Raphael Romary; Fabrice MORGANTI
Original assignee: Electricite De France
Priority date: 2017-11-24
Filing date: 2018-11-22
Publication date: 2019-05-31
Also published as: FR3074300A1; FR3074300B1

Abstract

A method, which is carried out by data-processing means, for diagnosing at least one fault of an alternator by measuring at least one physical parameter which represents an operation of the alternator, comprises:- acquiring a reference spectrum content which represents an initial state of the alternator, the initial state corresponding to a normal operating state of the alternator; - measuring, during ongoing operation of the alternator, a current spectrum content comprising at least one current signal of the physical parameter; - comparing the current spectrum content with the reference spectrum content for an amplitude which is associated with at least one predetermined frequency in order to estimate a variation between the amplitude which is associated with the at least one predetermined frequency in the current spectrum content and the amplitude which is associated with the same predetermined frequency in the reference spectrum content; and - if an absolute value of the variation is greater than a selected threshold, establishing the probability of the presence of a fault of the alternator.

Description

Method and device for fault diagnosis of an alternator

[001] The invention relates to the field of diagnostic methods of a fault of an alternator and a device for diagnosing a fault of an alternator.

More specifically, the invention relates to a method and a device for diagnosing a short circuit between turns of a rotor and / or a stator of an alternator from a measurement of minus one physical parameter chosen from one and / or the other of a vibration of the alternator carcass, an external dispersion flux of the alternator or a stator current of the alternator.

[003] Currently, a relatively large number of faults on the alternators of hydraulic, thermal but also nuclear parks contributes to the unavailability of slices. In order to detect such faults, some alternators have been instrumented.

[004] However, the expensive aspect of the installation of a specific instrumentation adapted to the high voltages and high currents of the alternators, as well as the obligation to wait for the alternators to be overhauled, makes it difficult to install such an instrumentation. In particular, the intrusive nature of the instrumentations currently used makes it difficult to install them on all hydraulic, thermal and nuclear power plants.

[005] Several diagnostic methods have been developed in recent years to detect the occurrence of a fault in alternators. The value of timely detection of an alternator fault, especially for power utility companies, is of crucial importance. In fact, the unavailability of generators leads to production losses and maintenance expenses, which motivates the development of new techniques in the field of engineering. Good monitoring should lead to an appropriate warning of imminent failures, an optimum schedule for preventive maintenance and, also, a preventive repair work plan.

[006] In the same way, a good diagnosis allows operators to have the necessary spare parts before the machine breaks down. Thus, it is possible to reduce the time of interruption of production and reduce the time taken for an effective and appropriate repair. [007] In general, physical parameter measurements are performed when the machine is running at full load. This data must be retrieved in such a way that information is accessible, reliable and secure. Most of the time, it is impossible to stop production to install a sensor inside the machine.

[008] Thus, the choice of the parameters to be monitored is important in the diagnosis of a defect. It is necessary to have a very good temporal knowledge of the indices or parameters selected to determine the state of the equipment, in particular at its amplitudes to determine the alarm thresholds in the event of a defect in the machine.

[009] The present invention improves the situation.

[010] For this purpose, it proposes a method, implemented by computer means, of diagnosing at least one fault of an alternator by measuring at least one physical parameter representative of an operation of the alternator. the method comprising:

obtaining a reference spectral content representative of an initial state of the alternator, the initial state corresponding to a normal operating state of the alternator;

a measurement, during a running operation of the alternator, of a current spectral content comprising at least one current signal of the physical parameter;

a comparison of the current spectral content with the reference spectral content, for an amplitude associated with at least one predetermined frequency, for estimating a variation between the amplitude associated with the said at least one predetermined frequency in the current spectral content and the associated amplitude at said at least one predetermined frequency in the reference spectral content; and

- If an absolute value of said estimated variation is greater than a chosen threshold, a determination of a probability of presence of a fault of the alternator.

With these provisions, the method of diagnosing at least one defect of an alternator comprises a reduced number of steps. In addition, the determination can be made through a measurement of different physical parameters, without interrupting the operation of the alternator.

[012] According to one embodiment, the method further comprises an emission of a presence signal of a fault of the alternator, if said estimated variation is greater than the threshold chosen. [013] Thus, the operator is alerted of the presence of a fault and may for example provide maintenance of the upstream alternator.

[014] In one embodiment, the reference spectral content is obtained by at least one measurement of the initial state of the alternator.

[015] In one embodiment, the reference spectral content is obtained by at least one modeling of the initial state of the alternator.

[016] In this way, the reference spectral content can be obtained in different ways. It is then also easy to apply the diagnostic method according to the invention to all types of alternator.

According to one embodiment, the method further comprises a determination of a predetermined number of frequencies of the current spectral content whose amplitude has undergone a variation greater than the chosen threshold before the determination of the probability of presence of a defect of the alternator.

[018] The calculation of the probability is therefore accurate since it can easily be integrated in the comparison step. On the other hand, the integration of a probability calculation step makes it possible to avoid maintenance or stopping of the alternator in the case where the probability of presence of a fault is low.

According to one embodiment, the comparison of the current spectral content with the reference spectral content is performed in at least one frequency window of the current spectral content, said frequency window being centered on said at least one predetermined frequency of the reference spectral content. , the frequency window comprising a width greater than 5% of the predetermined frequency of the reference spectral content.

[020] Thus, in the case where the mains frequency undergoes a variation, it remains possible to determine unambiguously the presence of a fault. Indeed, the widening of the frequency window for the comparison of the current spectral content to the reference spectral content makes it possible to avoid errors. For example, the determined frequency of the current spectral content can be shifted a few hertz on the current spectral content due to a variation of the network frequency.

[021] According to one embodiment, the physical parameter is chosen from at least one and / or the other of:

a stator current of the alternator;

- a vibration of the alternator;

an external dispersion flux of the alternator.

[022] Thus, at least one parameter, or even three parameters, can be measured to detect the presence of a fault. The accuracy of the result of the diagnostic process is increased. In addition, the chosen parameters make it possible to measure non-intrusively.

[023] In one embodiment, the faults comprise a short-circuit between turns for the rotor of the alternator and / or a short-circuit between turns for the stator of the alternator.

[024] The method according to the invention thus makes it possible to detect the presence of two distinct types of defects.

[025] The present invention also aims at a device for diagnosing at least one fault of an alternator by measuring at least one physical parameter representative of an operation of the alternator, the device comprising a processing circuit configured to the implementation of the method according to the invention.

[026] According to one embodiment, the device further comprises a measuring device comprising one and / or the other of:

at least one dispersion flux sensor capable of measuring an external dispersion magnetic field of the alternator;

at least one current sensor capable of measuring a stator current;

at least one vibration sensor capable of measuring a vibration of the alternator.

[027] The measuring device is therefore able to measure at least one of three, up to three, physical parameters. [028] According to one embodiment, the device further comprises a concentrator connected to the measuring device, and adapted to receive and sample the current signal of the physical parameter so as to obtain the current spectral content, then to transmit the current spectral content to the circuit treatment.

[029] In one embodiment, the concentrator is connected to the measuring device wirelessly.

[030] Thus, an operator can proceed to the fault diagnosis of a remote alternator.

[031] In one embodiment, the device comprises a server adapted to communicate remotely with the concentrator and able to store the current spectral content.

[032] In this way, the current spectral contents, but also the spectral reference contents, can be stored on a remote server. The data is then accessible remotely.

[033] In one embodiment, the device further comprises a system for transmitting a presence signal of a fault of the alternator.

[034] The invention also relates to a computer program characterized in that it comprises instructions for implementing the method according to the invention, when the program is executed by a processor.

Other features and advantages of the invention will emerge from the description which is given below, with reference to the drawings in which:

FIG. 1 is a schematic view of the fault diagnosis device according to one embodiment of the invention,

FIG. 2 illustrates the main steps of the fault diagnosis method according to one embodiment of the invention,

FIG. 3 illustrates certain steps of the fault diagnosis method, in which three parameters are measured, according to one embodiment of the invention. [036] Hereinafter a detailed description of several embodiments of the invention with examples and reference to the drawings.

[037] We first refer to Figure 1 in which an example of a diagnostic device DIS of a defect of a machine according to the invention is shown. The machine is for example a synchronous machine. The machine comprises a rotor and a stator. For example, the machine is an alternator with a power of between 10kW and 100MW. Such an alternator ALT is illustrated in FIG. 1. The alternator ALT may be provided with an external structure of cylindrical shape.

[038] There is also provided a measuring device DM capable of measuring a physical parameter representative of a functioning of the alternator ALT. The measuring device DM is for example placed directly on the external structure of the alternator ALT.

[039] In an exemplary embodiment according to the invention, the measuring device DM is chosen to measure at least one physical parameter representative of an operation of the alternator, in a non-intrusive manner, and making it possible to diagnose a defect in the device. 'alternator.

The measuring device DM is for example able to measure at least one physical parameter chosen from a stator current of the alternator ALT, a vibration of the external structure of the alternator ALT, a dispersion flux. , around the alternator ALT.

[041] By "dispersion flow" means a dispersion flow resulting from the magnetic field from the windings of the alternator, not channelized by the magnetic circuit or the external structure of the alternator. The dispersion flux is external to the alternator.

[042] The choice of these parameters may be related to operational constraints imposed by an operator of the alternator. On the other hand, the choice of these parameters also makes it possible to develop a non-intrusive fault diagnostic device capable of detecting a defect of a machine.

[043] The measuring device DM then comprises at least one current sensor CAPT1, a flow sensor CAPT2 and a vibration sensor CAPT3. The current sensor CAPT1 of the measuring device DM is for example suitable for measuring a signal of the stator current I, for example example at the STAT stator supply terminals. The current sensor CAPT1 is for example amperometric clamp type or Rogowski loop.

[044] The current sensor CAPT1 can be used when the stator supply terminals STAT of the alternator ALT are safely accessible to the operator. If this is not the case, the only physical parameters of the vibrations and of the dispersion flux can be used for the implementation of the diagnostic method according to the invention.

[045] The flow sensor CAPT2 is for example placed mid width of the external structure of the ALT alternator to measure a signal of the dispersion flux F most representative of the air gap flow. In this way the effects of coil heads, or coils, of the alternator ALT are minimized.

[046] The vibration sensor CAPT3 is placed on the external structure of the alternator ALT in order to measure a vibration signal V of the external structure. The vibration sensor CAPT3 comprises for example an accelerometer.

[047] Thus, the measuring device DM is able to perform measurements of the physical parameters (current, dispersion flux and vibration) in a non-intrusive manner.

[048] With reference to FIG. 1, the measurement device DM is connected to a concentrator CONC. The concentrator CONC receives the signals measured by the measuring device DM. The concentrator CONC processes the signals measured by the measuring device DM. For example, the signals are sampled in order to be able to diagnose at least one fault of the alternator ALT. The concentrator CONC makes it possible to obtain spectral contents for each measured signal of the physical parameters.

[049] Spectral contents can also be digitized and stored in the CONC concentrator. The concentrator CONC may also comprise a communication interface COM, in order to transmit the digitized spectral contents to a remote SER server. The communication interface COM can be a wireless communication interface, allowing for example a GSM connection or radio waves.

[050] The spectral contents stored on the SER server are for example accessible to an operator from a terminal TER, for example computer, tablet, telephone smart, or a dedicated diagnostic terminal. The TER terminal comprises a processing circuit TRAIT able to process the spectral contents. The TER terminal may further include an output interface for communicating the diagnostic results to the operator. The terminal TER may also include a system for transmitting a presence signal of a fault of the alternator ALT.

[051] Thus, the use of the method in the sense of the invention is advantageous in the context of fault detection on an alternator for several reasons. Firstly, the diagnostic device DIS makes it possible to perform a measurement of physical parameters representative of an operation of the ALT alternator in a non-intrusive manner. The installation of the measuring device DM is particularly easy. Indeed, when the operator wishes to make a diagnosis of an alternator, he can place at least one of the sensors CAPT1, CAPT2, CAPT3 on the alternator ALT to make the measurements. The operator is not obliged to stop the alternator ALT. On the other hand, it is also possible to leave in place the measuring device DM on the alternator and to measure the signals of at least one of the physical parameters as soon as the operator deems it necessary, or else to measure the signals continuously.

[052] Overall, the fault diagnosis method of an ALT alternator is based on the analysis of a current spectral content of at least one physical parameter. By "current spectral content" is meant spectral content measured during operation of the alternator ALT. The current spectral content includes, for example, the signals sampled by the concentrator CONC.

[053] More precisely, the detection of a fault of an alternator ALT is carried out by the correlation of measured signals of at least one, up to three, physical parameters. The analysis of the measured signals makes it possible to characterize the fault of the alternator ALT.

[054] The diagnostic method according to the invention comprises in particular the detection of a short circuit type fault between the turns of the rotor and / or short circuit between the turns of the stator of the ALT alternator. Indeed, a short circuit between the turns of the rotor and / or short-circuit between the turns of the stator can be identified by a modification of the current spectral content of the physical parameters measured with respect to a reference spectral content described below, in particular a modification of the amplitude of certain predetermined frequencies. In order to identify an amplitude change, the method according to the invention is for example based on a comparison between a current spectral content, corresponding to a spectral content comprising a current signal of at least one physical parameter, with a reference spectral content.

[055] Figure 2 illustrates the main steps of the diagnostic method within the meaning of the invention.

[056] In step S1, a reference spectral content representative of an initial state of the alternator ALT is obtained. By initial state, is meant a healthy state, in which the ALT alternator has normal operation, that is to say without defects. Indeed, the diversity of alternators ALT implies an initial identification of the initial state for each type of alternator ALT. This initial state can be obtained in different ways, illustrated in steps SlA and SlB.

[057] In step S1A, it is possible to obtain the reference spectral content of the alternator ALT by measurements of the chosen physical parameters (stator current, dispersion flux, vibration) on a "healthy" alternator. For example, a "healthy" alternator is an alternator that has never worked before. For example, the alternator leaves the construction plant. A "healthy" alternator may also be a refurbished alternator following a substantial maintenance program, including for example a rotation of rotors. The spectral content of each physical parameter is measured, for example by means of the measuring device DM.

[058] Alternatively, in step S1B, it is possible to obtain the reference spectral content by modeling a faultless alternator ALT. A faultless ALT alternator is for example modeled by means of a software or a computer program. Modeling makes it possible to obtain the spectral reference contents for each physical parameter. The physical parameters are, for example, the stator current, the vibrations and the dispersion flux of the alternator ALT.

[059] The spectral reference contents of each physical parameter thus obtained are stored in a database in step S2. The database includes for example all the spectral reference contents for each type of alternator ALT. This database is for example accessible by the TER terminal. When the operator wishes To diagnose an ALT alternator, it can enter the characteristics of the specific alternator for the diagnostic process to be performed according to the type of alternator ALT. [060] In step S3, the current spectral content of at least one physical parameter is measured, for example by the measuring device DM. Each current spectral content comprises at least one current signal of the measured physical parameter. The current spectral contents can furthermore be filtered in order to remove the non-exploitable frequencies. This makes it possible, for example, to limit the number of data to be compared to the next step. The current spectral contents are for example limited to frequencies whose amplitude is below a threshold below which their content is not exploitable. For example, frequencies whose amplitude is less than -100dB relative to 1 volt RMS (for "Root Mean Square", or "rms value" in French), or -100dBV, are removed from current spectral contents. [061] For each physical parameter, among the stator current, the dispersion flux and the vibrations of the alternator ALT, at least one predetermined frequency is obtained in step S4.

[062] The predetermined frequency corresponds to a frequency representative of the occurrence of a specific fault of the alternator ALT. For example, if the magnitude of the predetermined frequency varies between the reference spectral content and the current spectral content, it is possible to detect the presence of the defect represented by the predetermined frequency. Several predetermined frequencies may be representative, together or separately, of the appearance of a specific fault of the alternator ALT. For example, to determine the occurrence of an alternator fault ALT of rotor short-circuit or stator short-circuit type, different predetermined frequencies are obtained.

[063] The predetermined frequencies can be defined analytically for each type of fault, from a rotor short circuit and a stator short circuit in step S4.

[064] The tables below illustrate the analytical expressions for determining the value of the predetermined frequencies for each physical parameter, according to the type of fault sought, among a stator short circuit and a rotor short circuit.

[065] The number n of predetermined frequencies relating to a physical parameter and representative of a defect is thus obtained. Indeed, by varying one or the other of the parameters of each analytical expression of the predetermined frequencies for each physical parameter (vibration, dispersion flux and stator current), several predetermined frequency values can be obtained. Thus, a number n of predetermined frequencies relating to each physical parameter for each of the defects is obtained.

[066] After obtaining the predetermined frequencies, a comparison of the current spectral content to the reference spectral content is made in step S5. More precisely, the variation of the amplitude associated with each predetermined frequency between the amplitude of the predetermined frequency of the reference spectral content and the current spectral content is estimated. By "variation" is meant for example a difference between the amplitude of the predetermined frequency of the reference spectral content and the current spectral content. The "variation" may also correspond to a ratio of the magnitude of the predetermined frequency of the reference spectral content to the amplitude of the predetermined frequency of the current spectral content, or vice versa. When the absolute value of the variation is greater than a chosen threshold, the presence of a fault of the alternator is determined. For example, it has been determined that if the absolute value of the chosen threshold is greater than 10 dBV, a fault is detected.

[067] On the other hand, if a predetermined frequency, not present on the reference spectral content, appears on the current spectral content, it is possible to detect the presence of a defect.

[068] For example, for an alternator operating at 3000rpm and comprising two poles, if in the current spectral content comprising a current signal of the dispersion flux, a frequency of 25 Hz appears, a short-circuit fault between turns of the rotor is detected.

[069] However, the value of the predetermined frequencies of the current spectral content may vary around the value of the determined frequencies obtained in step S4. This can be due in particular to the variability of the rotational speed of the alternator, related to the frequency of the electrical network. On the other hand, one or more artifacts may appear in the current spectral content. The appearance of an artifact can occur during the sampling phase of the current signal by the CONC concentrator to obtain the current spectral content.

[070] Thus, in step S51, the comparison described with reference to step S5 can be performed on a frequency window of the current spectral content framing the predetermined frequency in step S4. An identical frequency window can also be applied to the reference spectral content. Thus, the comparison of the variation of the amplitude of the predetermined frequency between the reference spectral content and the current spectral content is for example made on the frequency window, and not on a predetermined frequency. The frequency window has for example a width equal to 5% of the predetermined frequency obtained in step S4. It is then possible, even if there is a large variation in the frequency of the grating, to determine the amplitude variation of the predetermined frequency in the current spectral content.

[071] In step S6, the number n 'of predetermined frequencies of the current spectral content whose absolute value of the amplitude variation is greater than the selected threshold is determined.

[072] If more than one physical parameter is measured, steps S3 to S5 are iterated for each physical parameter. [073] From the number n determined in step S4 and the number n 'of predetermined frequencies determined in step S6, a probability of presence of a fault is calculated in step S7. For example, the probability P can be calculated as follows:

P = n '/ n

[074] On the other hand, if the diagnostic method is applied to two physical parameters, for example the dispersion flux and the alternator vibration, the probability of fault existence Pi is calculated as follows:

With n _b and n respectively _has the total number of predetermined frequencies relating to the dispersion flux and to the vibration of the alternator identified by the analytical method described with reference to step S4,

and n 'n and _b' respectively _in the total number of predetermined frequency spectral content in the current of the stray flux and vibration whose absolute value of the variation of amplitude is greater than the selected threshold.

[075] In step S8 an alert signal is for example issued to warn the operator of the probability of presence of a fault of the alternator.

[076] Figure 3 illustrates the main steps of the ALT alternator fault diagnosis method using the three physical parameters: alternator ALT vibration, dispersion flux and stator current.

[077] The flow chart starts when an operator wishes to establish a diagnosis of an alternator ALT. The flow chart can also start without external intervention, for example if a periodic check has been planned. The initial state of the alternator has already been obtained. The steps of the logic diagram allow, for example, to diagnose a short circuit type fault. [078] In step S100, a comparison of the current spectral content to the reference spectral content is made. The current spectral content and the reference spectral content comprise respectively at least one current vibration signal and at least one vibration reference signal. The variation of the amplitude associated with each predetermined frequency between the amplitude of the predetermined frequency of the reference spectral content and the current spectral content is estimated. The predetermined frequencies comprise, for example, the predetermined frequencies relating to the diagnosis of a ro-ro circuit short circuit by means of a measurement of the vibrations of the alternator. Step S 101 makes it possible to obtain the predetermined frequencies in order to perform the comparison in step S 100.

[079] In step S102, the number of predetermined frequencies whose amplitude has varied, in absolute value, beyond the threshold chosen between the current spectral content of vibrations and the spectral reference vibration content is obtained. The threshold chosen is for example equal to 10 dB.

[080] Steps S 103 to S05 relate to the measurement of the alternator dispersion flux.

[081] In step S103, a comparison of the current spectral content to the reference spectral content is made. The current spectral content and the reference spectral content comprise respectively at least one current signal of the dispersion flux and at least one reference signal of the dispersion flux. The variation of the amplitude associated with each predetermined frequency between the amplitude of the predetermined frequency of the reference spectral content and the current spectral content is estimated. The predetermined frequencies include, for example, the predetermined frequencies relating to the diagnosis of a rotor circuit short-circuit by means of a measurement of the alternator dispersion flux. Step S104 makes it possible to obtain the predetermined frequencies in order to perform the comparison in step S103.

[082] In step S105, the number of predetermined frequencies whose amplitude has varied, in absolute value, beyond the threshold chosen between the current spectral content of the dispersion flux and the reference spectral content of the dispersion flux is obtained. The threshold chosen is for example equal to 10 dBV.

[083] The steps S 106 to S 109 relate to the measurement of the stator current of the alternator. [084] In step S106 the presence of a current sensor CAPT1 is determined. Indeed, if the STAT stator supply terminals of the alternator ALT are not accessible, it is not possible to install a current sensor CAPT1. Thus, the presence of a current sensor CAPT1 will not be detected. The process then proceeds to step S110.

[085] In contrast, if a current sensor CAPT1 is detected, a comparison of the current spectral content to the reference spectral content is made in step S 107. The current spectral content and the reference spectral content comprise respectively at least one current signal of the stator current and at least one reference signal of the stator current. The variation of the amplitude associated with each predetermined frequency between the amplitude of the predetermined frequency of the reference spectral content and the current spectral content is estimated. The predetermined frequencies comprise for example the predetermined frequencies relating to the diagnosis of a short circuit rotor circuit by means of a measurement of the stator current of the alternator. Step S 108 makes it possible to obtain the predetermined frequencies in order to perform the comparison in step S 107.

[086] In step S109, the number of predetermined frequencies whose amplitude has undergone a variation, whose absolute value is above the chosen threshold, between the current spectral content of the stator current and the reference spectral content of the stator current is obtained. The threshold chosen is for example equal to 10 dBV.

[087] In step S110, if the number of predetermined frequencies whose amplitude has varied in absolute value, beyond the threshold chosen, between the current and reference spectral contents of each physical parameter is less than a value, for example at 5, an absence of a stator short circuit is detected in step S111.

[088] On the other hand, if the number of predetermined frequencies whose amplitude has undergone a variation whose absolute value is beyond the chosen threshold, between the current and reference spectral contents of each physical parameter is greater than 5, a calculation of the presence probability of the stator short-circuit is made in step S112. In step S 113, a time stamp of the defect, with the probability of presence of the defect, is established.

[089] For the detection of a rotor short-circuit fault, the same steps described with reference to FIG. 3 can be applied. However, the predetermined frequencies of each physical parameter obtained in steps S 101 and S 104 will not be the same. On the other hand, the current sensor CAPT1 does not intervene in the diagnostic process of a short circuit ro tor.

Claims

claims

A method, implemented by computer means, for diagnosing at least one fault of an alternator by measuring at least one physical parameter representative of an operation of the alternator, the method comprising:

if an absolute value of said variation is greater than a chosen threshold, a determination of a probability of presence of a fault of the alternator.

2. Method according to claim 1, further comprising an emission of a presence signal of a fault of the alternator, if said estimated variation is greater than the threshold chosen.

3. Method according to one of claims 1 and 2, wherein the reference spectral content is obtained by at least one measurement of the initial state of the alternator.

4. Method according to one of claims 1 and 2, wherein the reference spectral content is obtained by at least a modeling of the initial state of the alternator.

5. Method according to one of claims 1 to 4, further comprising a determination of a predetermined number of frequencies of the current spectral content whose amplitude has undergone a variation greater than the chosen threshold, before said determination of the probability of presence. a fault of the alternator.

6. Method according to one of claims 1 to 5, wherein the comparison of the current spectral content to the reference spectral content is performed in at least one frequency window of the current spectral content, said frequency window being centered on said at least one predetermined frequency of the reference spectral content, the frequency window comprising a width greater than 5% of the predetermined frequency of the reference spectral content.

7. Method according to one of claims 1 to 6, wherein the physical parameter is chosen from at least one and / or the other of:

a stator current of the alternator;

- a vibration of the alternator;

an external dispersion flux of the alternator.

8. Method according to one of claims 1 to 7, characterized in that the defects comprise a short-circuit between turns for the rotor of the alternator and / or a short-circuit between turns for the stator of the alternator.

9. Device for diagnosing at least one fault of an alternator by measuring at least one physical parameter representative of an operation of the alternator, the device comprising:

- A processing circuit configured for implementing the method according to one of claims 1 to 8.

The device of claim 9, further comprising a measuring device comprising one and / or the other of:

at least one dispersion flux sensor capable of measuring an external dispersion flux of the alternator;

at least one current sensor capable of measuring a stator current;

11. Device according to claim 10, further comprising a concentrator connected to the measuring device, and adapted to receive and sample the current signal of the physical parameter so as to obtain the current spectral content, then to transmit the current spectral content to the circuit of treatment.

12. Device according to claim 11, wherein the concentrator is connected to the measuring device wirelessly.

13. Device according to one of claims 11 and 12, further comprising a server adapted to communicate remotely with the hub and able to store the current spectral content.

14. Device according to one of claims 10 to 13, further comprising a system for transmitting a presence signal of a fault of the alternator.

15. Computer program characterized in that it comprises instructions for the implementation of the method according to one of claims 1 to 8, when the program is executed by a processor.