Method for recognizing digitally a partial discharge in electrical equipment in a severe aeronautical environment and computer program product

Abstract

The invention relates to a method for detecting and recognizing a partial discharge in electrical equipment (10) in an aeronautical environment, the method comprising a step of detecting (E10), by means of a sensor (91), an electrical signal to be analysed (1), the method being characterized in that it further comprises steps of computing (E2) at least one value of a distance parameter (3) representative of a distance between the electrical signal to be analysed (1) and at least one signature signal (2) representative of a partial discharge, the distance parameter being dependent on a difference between the electrical signal to be analysed and the signature signal, and of comparing (E3) the value of the distance parameter with a detection threshold (4) and detecting a potential partial discharge depending on a result of the comparison.

Description

[0001] METHOD FOR DIGITALLY RECOGNIZING A PARTIAL DISCHARGE IN ELECTRICAL EQUIPMENT IN A SEVERE AERONAUTICAL ENVIRONMENT AND COMPUTER PROGRAM PRODUCT TECHNICAL FIELD

[0002] The invention relates to the digital recognition of partial discharge signatures in an electrical chain in an aeronautical environment. STATE OF THE ART

[0003] A partial discharge is a localized electrical discharge that only partially short-circuits the insulating gap between conductors or electrodes. The presence of these discharges leads to accelerated degradation of the insulation, whether liquid, by oxidation, or solid, by erosion, and can lead to significant reliability problems.

[0004] Hybridization and / or electrification of propulsion systems leads to an increasing demand for electrical energy and consequently to an increase in voltage levels. This increase in voltage, accompanied by severe pressure and temperature conditions, increases the risk of these partial discharges occurring.

[0005] It is therefore necessary to be able to reliably detect and recognize these discharges as soon as they appear without requiring excessive computing power. In addition, while partial discharge detection is relatively simple under sinusoidal voltage, under pulse stress or Pulse Width Modulation (PWM), the noise generated tends to overlap with the partial discharge signals, thereby complicating detection.

[0006] Since discharges have very low charge values, complex and robust measuring devices must be implemented.

[0007] Detection methods exist but are not very easy to implement because they require suitable electronics and high requirements in terms of acquisition frequency, for example. Expert advice is also often necessary to confirm whether or not this phenomenon is present. DISCLOSURE OF THE INVENTION

[0008] A general aim of the invention is to identify the presence of partial discharges in electrical signals in a simple and automated manner, avoiding complex processing.

[0009] To this end, the invention proposes a method for detecting and recognizing a partial discharge in electrical equipment in an aeronautical environment, the method comprising a step of detecting, by means of a sensor, an electrical signal to be analyzed, the method being characterized in that it further comprises steps of:

[0010] - calculation of at least one value of a distance parameter between the electrical signal to be analyzed and at least one signature signal representative of a partial discharge, the distance parameter being a function of a difference between the electrical signal to be analyzed and the signature signal,

[0011] - comparison of the value of the distance parameter with a detection threshold and detection of a possible partial discharge based on a result of the comparison.

[0012] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations: the calculation comprises the calculation of a series of values ​​of the distance parameter between the electrical signal to be analyzed and at least one signature signal, the calculation comprising the sub-steps of:

[0013] - selection of a portion of the electrical signal to be analyzed in an analysis window, the analysis window having a predefined width,

[0014] - calculation of a value of the distance parameter between the selected portion of the electrical signal to be analyzed and the signature signal,

[0015] - shift of the analysis window, and

[0016] - repeating steps c), d) and e) in order to obtain the series of values ​​of the distance parameter; the calculation of each value of the distance parameter comprises the comparison between the portion of the signal to be analyzed delimited by the analysis window and a plurality of different signature signals; the value of the distance parameter is calculated as a normalized Euclidean distance between the electrical signal to be analyzed, centered and reduced, and the signature signal, centered and reduced; the value of the distance parameter is calculated as a dynamic time deformation function, the variables of this function being centered and reduced; the detection threshold is determined as a function of characteristic parameters of the series of values ​​of the distance parameter; the characteristic parameters of the series of values ​​of the distance parameter comprise the mean and / or the standard deviation of the series of values ​​of the distance parameter;the detection threshold is determined as a function of the average of the series of values ​​of the distance parameter from which n times the value of the standard deviation of the series of values ​​of the distance parameter is subtracted, n being a real number; the detection comprises a step of processing the electrical signal to be analyzed, the processing comprising filtering the electrical signal to be analyzed by means of a high-pass filter, and an acquisition step by means of an acquisition device; the filtering of the signal is carried out by means of a high-pass filter whose cut-off frequency is of the order of magnitude of a hundred MHz and above;the method comprises a step of generating a database of signature signals representative of partial discharge signals, the generation comprising detection, filtering, acquisition and saving of these signatures in the database, the database comprising a plurality of partial discharge signature signals taking into account variable test conditions and influencing these signature signals; a detection device is adapted to implement the calculation and comparison steps of the method according to the invention; the sensor is a capacitive coupling type sensor, the sensor comprises a needle which is in contact during detection with a section of the conductive cable of the electrical signal to be analyzed, the section comprising a copper layer; a computer program product, comprises code instructions for executing a method according to the invention when executed on computer means.;

[0017] Thus, the invention makes it possible to distinguish partial discharges from other parasitic noises, such as, for example, high-frequency noises relating to converters using pulse width modulation (PWM).

[0018] Furthermore, the invention makes it possible to identify the presence of partial discharges on any type of signal quickly and simply, without adding too much signal processing.

[0019] The invention also makes it possible to recognize the presence of partial discharges of low amplitude, i.e. of the order of a millivolt.

[0020] PRESENTATION OF FIGURES

[0021] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0022] - figure 1 illustrates the main steps of a recognition detection method according to the invention;

[0023] - Figure 2 illustrates the technical principle behind the recognition of partial discharges according to the invention;

[0024] - Figure 3 illustrates a partial discharge detection system for obtaining signatures according to an embodiment of the present invention. In all the figures, similar elements bear identical references.

[0025] DETAILED DESCRIPTION

[0026] Electrical systems

[0027] No electrical system can function without the use of insulators or dielectrics. Electrical insulators, by preventing the flow of electric current, enable the proper functioning of electrical systems. In power electronics, these materials are found either in passive components, for which the dielectric properties of the material (and its storage aspects) are exploited, or as insulation. In electrical engineering, the main purpose is to insulate parts brought to different potentials.

[0028] Insulating materials, whether solid, liquid or gaseous, are often the weak link in electrical systems; in particular, beyond a certain voltage, the phenomenon of Partial Discharges (PD) and its consequences (such as the appearance of short circuits or fault electric arcs) are likely to occur.

[0029] Until now, the existence of these partial discharges had been little taken into account in the design of aircraft equipment, given the low voltage levels used. However, and in the aeronautical field in particular, the hybridization and electrification of high-power propulsion systems leads to an increase in operating voltages; in fact, no current system can claim to be either exempt from or resistant to PDs.

[0030] Subsequently, partial discharge DP will be understood to mean a localized electrical discharge generated, under the effect of a high voltage or voltage variation, in an insulating gap separating conductors. And by electrical network any type of network that can be found in an aeronautical environment, for example in any aircraft: plane or helicopter, etc.

[0031] Detection and recognition method Figure 1 is the flowchart of the steps of a DP partial discharge detection and recognition method, the main steps of which are illustrated in Figure 2.

[0032] The method comprises a step E10 of detecting an electrical signal to be analyzed 1. Once detected, the electrical signal to be analyzed 1 is advantageously processed. The detection step is accompanied by a filtering E11 of the electrical signal to be analyzed 1 by means of a filter. The filter is preferably a high-pass filter, in order to reduce as much as possible the noise level present in the electrical signal to be analyzed 1. The cut-off frequency of the high-pass filter is of the order of magnitude of a hundred MHz and beyond.

[0033] The method then comprises a step E12 of acquiring an electrical signal to be analyzed 1. The electrical signal to be analyzed 1 is preferably acquired by means of the acquisition device (described below).

[0034] Once the electrical signal to be analyzed 1 is processed, a calculation step E2 of a value of a distance parameter 3 is carried out. The distance parameter 3 is a function of a difference between two signals or portions of signals.

[0035] The calculation E2 of a value of the distance parameter 3 is carried out between the electrical signal to be analyzed 1 and a signature signal 2. The signature signal 2 is a signal representative of the signal of a partial discharge DP. The value of the distance parameter 3 is therefore calculated between the electrical signal to be analyzed 1 and a signal representative of a partial discharge DP.

[0036] According to one embodiment, the value of the distance parameter 3 is calculated as a normalized Euclidean distance. That is to say, for each point of the electrical signal to be analyzed 1 whose magnitude is centered and reduced, its distance from the point of the corresponding signature signal 2, and whose magnitude is centered and reduced, is determined. In other words, the value of the distance parameter 3 is the result of the equation:

[0037] With N the number of points of the signature signal 2, x a magnitude of the point of the signature signal 2 and y a magnitude of the point of the electrical signal to be analyzed 1. The magnitudes of the points x and y are advantageously voltages. Preferably, the magnitudes are centered and reduced to obtain magnitudes independent of the unit or the chosen scale and having the same mean and the same dispersion.

[0038] According to another embodiment, the value of the distance parameter 3 is calculated by means of a dynamic time warping function (or "Dynamic Time Warping" in English terminology). Such a function makes it possible to calculate the value of the distance parameter 3 between the electrical signal to be analyzed 1 and the signature signal 2 in a more robust manner in the face of time and amplitude expansion / contraction.

[0039] According to another mode of implementation, it is possible to calculate the value of the distance parameter 3 by means of any function suitable for evaluating a difference between two signals.

[0040] Furthermore, the calculation step E2 advantageously comprises the calculation of a series 8 of values ​​of the distance parameter 3. The series 8 of values ​​is obtained by implementing the following steps:

[0041] - a selection E21 of a portion 7 of the electrical signal to be analyzed 1 in an analysis window 6, the analysis window 6 having a predefined width 61;

[0042] - a calculation E22 of a value of the distance parameter 3 between the portion 7 selected by the analysis window 6 of the electrical signal to be analyzed 1 and the signature signal 2;

[0043] - the offset E23 of the analysis window 6 by a predefined step 62; and

[0044] - the renewal E24 of these selection steps E21, calculation E22 and shift E23 in order to obtain the series 8 of values ​​of the distance parameter 3.

[0045] In other words, the analysis window 6 selecting a portion 7 of the electrical signal to be analyzed 1, is moved temporally onto the electrical signal to be analyzed 1 and, for each of its positions, the calculation E22 of the distance parameter 3 is carried out. In this way, the series 8 of values ​​of the distance parameter 3 represents the difference between the electrical signal to be analyzed and the signature signal for each of the portions 7 of this electrical signal to be analyzed 1.

[0046] Advantageously, the width 61 of the analysis window 6 represents a time interval corresponding to the duration of the partial discharge DP represented on the signature signal 2. Advantageously, the step 62 of shifting the analysis window 6 along the time scale of the electrical signal to be analyzed 1 is equal to an acquisition period of the electrical signal to be analyzed 1. It is however possible to choose a step 62 different from this acquisition period such as for example a multiple of the acquisition period or any other time period.

[0047] Furthermore, it is advantageously possible to calculate E22 a value of a distance parameter 3 between a portion 7 of the electrical signal to be analyzed 1 and a plurality of signature signals 2 representative of different types of partial discharges DP.

[0048] According to one embodiment, the plurality of signature signals 2 comes from a database. A detection device C, described below, makes it possible to generate EO a database comprising a plurality of signature signals 2 representative of partial discharges DP. It is indeed possible to identify the signature signals and to record them in the database prior to the implementation of the other steps of the detection and recognition method. The signal signatures 2 can evolve according to the conditions in which the electrical network 10 is present during its use. It is therefore possible to generate, in the laboratory, signal signatures 2 representative of partial discharges DP as they would be under these conditions.In order to be able to monitor the state of the insulation of the electrical network 10, it is advantageous to implement the detection and recognition method comprising the use of the database 10 comprising a plurality of signature signals 2 representative of partial discharges DP.

[0049] After the calculation step E2, the detection and recognition method comprises a comparison step E3. During this step, the value of the distance parameter 3 is compared with a detection threshold 4. The comparison E3 is suitable for detecting a possible partial discharge DP depending on the results obtained, and therefore on the distance between the electrical signal to be analyzed 1 and the signature signal 2. Indeed, the lower the value of the distance parameter 3, the smaller the difference between the electrical signal to be analyzed 1 and the signature signal 2. A small difference between the electrical signal to be analyzed 1 and the signature signal 2 implies a significant similarity and a detection of a partial discharge DP is then probable.In the embodiment according to which a series 8 of values ​​of the distance parameter 3 is calculated, the comparison step E3 compares the series 8 with the detection threshold 4 in order to detect one or more possible partial discharges DP and their position in the electrical signal to be analyzed 1.

[0050] The detection threshold 4 is advantageously determined as a function of the average of the series 8 of values ​​of the distance parameter 3 from which we subtract n times the value of the standard deviation of the series 8 of values ​​of the distance parameter 3. The number n is a real number, advantageously an integer greater than or equal to 1.

[0051] According to one embodiment, the detection and recognition method presented above can be coupled with other methods in order to guarantee even more precise recognition. For example, the method can be combined with a partial discharge recognition method DP implementing a wavelet transform of the electrical signal to be analyzed 1.

[0052] Test bench

[0053] Figure 3 schematically illustrates a device C allowing both to detect beforehand and in the laboratory, signature signals 2 allowing to generate EO the database of signature signals 2, but also to obtain the electrical signal to be analyzed 1 in order to be able to implement the detection and recognition method as described previously. The device C is for example a test bench comprising an acquisition device 9 and a sensor 91. The sensor 9 is for example a sensor 91 of the capacitive coupling type. The sensor 91 advantageously comprises a metal tip which touches a part 11 of an electrical network 10. The part 11 of the electrical network 10 is advantageously covered with a layer 12 of copper to amplify the detected electrical signal.

[0054] The device C makes it possible both to generate the database EO in advance, but also to obtain the electrical signal to be analyzed 1. To this end, the sensor 9 acquires the electrical signal, for example in millivolts, an image of an electrical quantity varying in the electrical network 10, for example the electric current.

[0055] A filtering E11, for example a filtering by means of a high-pass filter, is applied to the electrical signal in order to reduce as much as possible the noise level present. The cut-off frequency of the filter used is advantageously around a hundred megahertz or higher. Finally, the acquisition step E12 is necessary to obtain the electrical signal to be analyzed 1 or the signature signal 2. Once detected, filtered and acquired, the signal is either recorded in the database if it is a measurement aimed at enriching EO the database in the laboratory, or used as an electrical signal to be analyzed 1 to implement the detection and recognition method as described previously.

Claims

CLAIMS 1. Method for detecting and recognizing a partial discharge (PD) in electrical equipment (10) in an aeronautical environment, the method comprising a step of detecting (E10), by means of a sensor (91), an electrical signal to be analyzed (1), the method being characterized in that it further comprises steps of: a) calculating (E2) at least one value of a distance parameter (3) between the electrical signal to be analyzed (1) and at least one signature signal (2) representative of a partial discharge (PD), the distance parameter (3) being a function of a difference between the electrical signal to be analyzed (1) and the signature signal (2), and b) comparing (E3) the value of the distance parameter (3) with a detection threshold (4) and detecting a possible partial discharge (PD) as a function of a result of the comparison (E3).

2. Method according to claim 1, wherein the calculation (E2) comprises the calculation of a series (8) of values ​​of the distance parameter (3) between the electrical signal to be analyzed (1) and at least one signature signal (2), the calculation (E2) comprising the sub-steps of: c) selection (E21) of a portion (7) of the electrical signal to be analyzed (1) in an analysis window (6), the analysis window (6) having a predefined width (61), d) calculation (E22) of a value of the distance parameter (3) between the selected portion (7) of the electrical signal to be analyzed (1) and the signature signal (2), e) shifting (E23) of the analysis window (6), and f) renewal (E24) of steps c), d) and e) in order to obtain the series (8) of values ​​of the distance parameter (3).

3. Method according to claim 2, in which the calculation (E2) of each value of the distance parameter (3) comprises the comparison (E3) between the portion (7) of the signal to be analyzed (1) delimited by the analysis window (6) and a plurality of different signature signals (2).

4. Method according to any one of claims 1 to 3, in which the value of the distance parameter (3) is calculated as a normalized Euclidean distance between the electrical signal to be analyzed (1), centered and reduced, and the signature signal (2), centered and reduced.

5. Method according to any one of claims 1 to 4, in which the value of the distance parameter (3) is calculated as a dynamic time warping function, the variables of this function being centered and reduced.

6. Method according to any one of claims 2 to 5, in which the detection threshold (4) is determined as a function of parameters characteristic of the series (8) of values ​​of the distance parameter (3).

7. Method according to claim 6, wherein the characteristic parameters of the series (8) of values ​​of the distance parameter (3) comprise the mean and / or the standard deviation of the series (8) of values ​​of the distance parameter (3).

8. Method according to any one of claims 2 to 7, in which the detection threshold (4) is determined as a function of the average of the series (8) of values ​​of the distance parameter (3) from which n times the value of the standard deviation of the series (8) of values ​​of the distance parameter (3) is subtracted, n being a real number.

9. Method according to any one of claims 1 to 8, in which the detection (E10) comprises a step of processing the electrical signal to be analyzed (1), the processing comprising a filtering (E11) of the electrical signal to be analyzed (1) by means of a high-pass filter, and an acquisition step (E12) by means of an acquisition device (9).

10. Method according to claim 9, in which the filtering (E11) of the signal is carried out by means of a high-pass filter whose cut-off frequency is of the order of magnitude of a hundred MHz and beyond.

11. Method according to any one of claims 1 to 10, comprising a step of generating (E0) a database (10) of signature signals (2). representative of partial discharge (PD) signals, the generation (EO) comprising detection, filtering, acquisition and saving of these signatures (2) in the database (10), the database (10) comprising a plurality of partial discharge (PD) signature signals (2) taking into account variable test conditions and influencing these signature signals (2).

12. Computer program product, comprising code instructions for executing a method according to any one of claims 1 to 11 when executed on computer means.

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