Method for locating an insulation fault in a direct current electrical circuit.

Abstract

Automated method for locating an insulation fault in an isolated type electrical circuit (2) in an aircraft (1), the electrical circuit comprising a pair (4) of supply rails, and power lines (51, 52, 61, 62, 63, 64, 71, 72) connected to the pair of supply rails, each power line comprising a piloted switch (8), the method comprising the steps of: If an absolute value of a determined common-mode voltage is greater than a predetermined threshold voltage, then search for an insulation fault successively: For each power line (51, 52) classified as a sensitive load; then if not found, For each power line (61, 62, 63, 64) classified as a non-sensitive load; then if not found, For each power line (71, 72) classified as a source; and, Command to close each piloted switch open except the piloted switch of the power line which led to the output of step a). Figure for the abridged version: [Fig.1]

Description

Title of the invention: Method for locating an insulation fault in a direct current electrical circuit. Technical field of the invention

[0001] The invention relates to the field of electrical power systems implemented within an aircraft. In particular, the invention relates to an automated method for locating an insulation fault in an isolated or impedance-isolated direct current electrical circuit located in all or part of an aircraft. Prior art

[0002] Climate change is a major concern for many legislative and regulatory bodies worldwide. Indeed, various restrictions on carbon emissions have been, are being, or will be adopted by various states. In particular, an ambitious standard applies to both new types of aircraft and those currently in operation, requiring the implementation of technological solutions to bring them into compliance with current regulations. Civil aviation has been actively contributing to the fight against climate change for several years now.

[0003] Technological research efforts have already led to very significant improvements in the environmental performance of aircraft. It is therefore necessary to consider the factors impacting all phases of design and development in order to obtain aeronautical components and products that are less energy-intensive, more environmentally friendly, and whose integration and use in civil aviation have moderate environmental impacts, with the aim of improving aircraft energy efficiency. Consequently, it is necessary to continuously work towards reducing climate impact by employing methods and operating virtuous development and manufacturing processes that minimize greenhouse gas emissions to the minimum possible in order to reduce the environmental footprint of the activity.

[0004] This sustained research and development work focuses in particular on the development of the use of electrical technologies, for example to provide propulsion.

[0005] In this context, in an aircraft environment, isolated or impedance-isolated direct current electrical circuits are developed using high-voltage direct current (HVDC) electrical networks (acronym for "High Voltage Direct Current"), with a high voltage, for example 540V or 800V. This choice allows for the parallel connection of driven electrical sources. by low pressure and high pressure shafts (as well as potentially putting the aircraft's sources in parallel), and thus makes it possible to ensure the functions of power distribution control and power transfer control between shafts, without interruption of the electrical network.

[0006] This high voltage is called "differential" because it exists between a positive conductor and a negative conductor. Thus, these positive and negative conductors also have a voltage measured with respect to ground (for example, a metallic structure of the aircraft) which can be measured separately as Vpos and Vneg. A so-called "common-mode" voltage Vcm is defined as follows: Vcm = (Vpos + Vneg) / 2. Thus, with, for example, a differential voltage of 800V, it is possible to have: Vpos = +400V and Vneg = -400V with Vcm = 0V; Vpos = +420V and Vneg = -380V with Vcm = 20V; Vpos = +800V and Vneg = 0V with Vcm = 400V; etc.

[0007] In most applications, the preferred operation is that where Vpos = +400V and Vneg = -400V with Vcm = 0V, i.e., Vpos and Vneg voltages symmetrical with respect to ground, because this reduces the stress on the electrical insulators within the electrical circuit.

[0008] In an isolated or impedance-isolated electrical circuit, the common-mode voltage Vcm can vary (or "float") during operation depending on the insulation resistance values ​​of electrical equipment connected to said circuit. If one of the connected electrical devices has a short circuit between one of the positive and negative conductors and ground, the leakage current through such an insulation fault is practically zero to very low (a few mA), which theoretically allows operation to continue without interruption. However, the voltages Vpos and Vneg become significantly unbalanced. Since these voltages Vpos and Vneg are common to the entire electrical circuit, measuring a voltage with respect to ground gives the same result across the entire circuit and therefore does not allow for the localization of the connected electrical device exhibiting the insulation fault.

[0009] Therefore, within an aircraft, there is a need to implement mechanisms for detecting and locating insulation faults in insulated or impedance-insulated high-voltage direct current electrical circuits.

[0010] Currently, a localization solution, generally implemented during maintenance operations, consists of disconnecting the connected electrical equipment one after the other until the insulation fault disappears. However, this solution does not ensure the minimum continuity of service provided by an isolated or impedance-isolated direct current electrical circuit. Description of the invention

[0011] An object of the invention is to provide an automated method for locating insulation faults in a direct current electrical circuit of the isolated or impedance-isolated type provided in all or part of an aircraft which allows optimal continuity of service while being robust and reliable, allowing the correct location of insulation faults present, but also being able to avoid untimely detections of insulation faults in the face of possible disturbances such as lightning for example.

[0012] To this end, the invention provides a method for locating an insulation fault in an isolated or impedance-insulated direct current electrical circuit located in all or part of an aircraft, the electrical circuit comprising a pair of power rails and a series of power lines connected to the pair of power rails, each power line comprising a controlled switch, wherein the method comprises the steps of: a. Determination of a common mode voltage at the level of the power supply rail pair; b. Comparison of a determined absolute value of the common-mode voltage with a predetermined threshold voltage; c. If the absolute value of the determined common-mode voltage is greater than the predetermined threshold voltage, then search for an insulation fault in the series of connected power lines: i. For each power line in the series of power lines classified as a sensitive load, the process disconnects the power line in question by opening the associated pilot-operated switch, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less than the threshold voltage, the process performs step d), otherwise the process proceeds to the next sensitive load; ii. For each power line in the series of power lines classified as an insensitive load, the process disconnects the power line in question by opening the associated pilot-operated switch, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less than the threshold voltage, the process performs step d), otherwise the process closes the associated pilot-operated switch and proceeds to the next insensitive load; and, iii. For each power line in the series of power lines classified as a source, the process disconnects the power line in question by opening the associated pilot-operated switch. then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less than the threshold voltage, the process performs step d), otherwise the process closes the associated controlled switch and proceeds to the next source; and, d. Command to close each pilot switch open except the pilot switch of the power line which led to the output of step c) and which presents the insulation fault sought.

[0013] Advantageously, but optionally, the method for locating an insulation fault according to the invention has at least one of the following technical characteristics: • during step c), the process measures the duration of the threshold voltage overrun and triggers the search for the insulation fault if the measured duration of overrun is greater than a predetermined threshold duration; • during step ii., each non-sensitive load being associated with a predefined short power interruption tolerance, the disconnection of each non-sensitive load is carried out in a decreasing order of short power interruption tolerances; • during step c), each power line being associated with a predefined probability of occurrence of an electrical fault, the disconnection of each power line is carried out in a decreasing order of the probabilities of occurrence of an electrical fault; • during step d), if the insulation fault is located on a source during step iii., the process controls the pilot-operated switches associated with the power lines classified as sensitive loads in opening; • during step iii., the process controls the controlled switches of a portion of the loads to open in order to remain compatible with a capacity of the connected sources; • during step d), if the insulation fault is located on a source during step iii., the process opens the controlled switches of a portion of the loads so as to remain compatible with a capacity of the connected sources; • wherein, during steps i and ii respectively, the method first simultaneously opens the controlled switches associated with the power lines in question, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is greater than the threshold voltage, the method performs step ii. and iü. respectively, otherwise the process continues with the current step; and, • During step ii., the insensitive loads are distributed into subgroups, and the process simultaneously opens the controlled switches associated with the insensitive loads of a given subgroup, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is greater than the threshold voltage, the process moves on to the next subgroup, otherwise the process continues step ii. for each of the insensitive loads of the current subgroup.

[0014] According to the invention, an aircraft is also provided comprising a first direct current electrical circuit of the isolated or impedance-isolated type, the electrical circuit comprising a first pair of supply rails, and a first series of electrical lines connected to the first pair of supply rails, each of the electrical lines comprising a controlled switch, in which the aircraft comprises a first computer arranged to implement a method for locating an insulation fault having at least one of the preceding technical characteristics.

[0015] Advantageously, but optionally, the aircraft according to the invention has at least one of the following technical characteristics: • the aircraft comprising a second direct current electrical circuit of the isolated or impedance-isolated type comprising a second pair of supply rails, and a second set of electrical lines connected to the second pair of supply rails, each of the electrical lines comprising a piloted switch, wherein the aircraft comprises a second computer arranged to implement a method for locating an insulation fault having at least one of the preceding technical characteristics, the first and second computers comprising means of communication between them; • the first and second pairs of power rails are electrically connected to each other; • the first and second computers are arranged so as to implement the localization process respectively on the second and first electrical circuits; • which each step a) to d) is implemented successively by the first and second computers. • in which the process includes a consolidation step between the locations possibly established by the first and second computers. • in which the first and / or second electrical circuits belong to a high-voltage direct current electrical network of the isolated or impedance-isolated type. Brief description of the figures

[0016] Other features and advantages of the invention will become apparent from the following description of an embodiment of the invention. See the accompanying drawings:

[0017] [Fig-1] is a schematic view of an embodiment of an electrical circuit in isolated or impedance-isolated direct current within an aircraft;

[0018] [Fig.2] is a schematic view of an aircraft comprising two direct current electrical circuits of the isolated or impedance isolated type;

[0019] [Fig.3] is a logic diagram illustrating a first embodiment of a method for locating an insulation fault according to the invention;

[0020] [Fig.4] is a flowchart illustrating step 300 of the method for locating an insulation fault according to the method of [Fig.3];

[0021] [Fig.5] is a flowchart illustrating step 400 of the method for locating an insulation fault according to the method of [Fig.3];

[0022] [Fig.6] is a flowchart illustrating step 500 of the method for locating an insulation fault according to the method of [Fig.3];

[0023] [Fig.7] is a chronogram illustrating an implementation of the process of [Fig.3]; and,

[0024] [Fig.8] is a timing diagram illustrating an implementation of a second embodiment of a method for locating an insulation fault according to the invention.

[0025] For clarity, identical or similar elements are identified by identical reference signs throughout the figures. Detailed description of an implementation method

[0026] With reference to [Fig. 1], we will describe an embodiment of a direct current electrical circuit 2 of the isolated or impedance-isolated type, on which a method for locating an insulation fault according to the invention is intended to be implemented. The electrical circuit 2 is provided here in all or part of an aircraft 1.

[0027] The electrical circuit 2 comprises a pair 4 of power rails, and a series 5, 6, 7 of power lines connected to the pair 4 of power rails, each of the power lines comprising a piloted switch 8. The pair 4 of power rails comprises a positive conductor and a negative conductor, each of the conductors forming a power rail of the pair 4 of power rails. Similarly, each of the power lines has a positive conductor and a negative conductor electrically connected to the positive and negative conductors, respectively, of pair 4 of the power supply rails. On each power line, the controlled switch 8 acts in either the opening or closing direction on both the positive and negative conductors of the associated power line. In an alternative embodiment, the controlled switch 8 has two single-pole controlled switches, each acting on a single conductor: a first single-pole controlled switch on the positive conductor and a second single-pole controlled switch on the negative conductor. The two single-pole controlled switches are then simultaneously controlled either in the opening or closing direction and thus act as a single controlled switch 8.

[0028] The series of electrical lines 5, 6, 7 is here divided into three groups. The first group 5 comprises the electrical lines classified as sensitive loads. Here, the first group 5 comprises two electrical lines 51, 52, each of the electrical lines 51, 52 including current-consuming electrical equipment that is not capable of withstanding a high common-mode voltage Vcm for a long duration. In an aircraft 1, a sensitive load is, for example, an electrical line including a de-icing system for the blades of a turbomachine. It is understood that a high common-mode voltage Vcm is a common-mode voltage Vcm that is greater than a predetermined threshold voltage (for example, a predetermined voltage between 50V and 200V, preferably 150V) beyond which there is significant and detrimental stress on the insulators and certain electronic components of the electrical equipment of sensitive loads.Furthermore, it is understood that a long duration within the meaning of the invention is a duration greater than 1 second.

[0029] The second assembly 6 comprises the electrical lines classified as non-sensitive loads. Here, the second assembly 6 comprises four electrical lines 61, 62, 63, 64, each of the electrical lines 61, 62, 63, 64 including current-consuming electrical equipment capable of withstanding a high common-mode voltage Vcm for a long duration. Within an aircraft 1, a non-sensitive load is, for example, an electrical line including an electric pump related to thermal management functions, or an electric pump related to the fuel system, or a converter to aircraft electrical loads.

[0030] The third assembly 7 comprises the power lines classified as a source. Here, the third assembly 7 comprises two power lines 71, 72, each of the power lines 71, 72 including electrical equipment generating current or voltage that supplies the first 5 and second 6 assemblies of power lines consuming current. Within an aircraft 1, a source is, for example, a power line including a high-voltage battery, or a current or voltage generator driven by one of the shafts of a turbomachine.

[0031] Furthermore, the aircraft 1 includes a computer 3 arranged to manage and control the electrical circuit 2. The computer 3 is configured to implement the method for locating an insulation fault according to the invention described later. The computer 3 can act as a permanent insulation monitor for the electrical circuit 2.

[0032] With reference to [Fig. 2], we will briefly describe an alternative embodiment of an aircraft 1 comprising first and second electrical circuits 2 and 12, respectively, operating in direct current, of the isolated or impedance-isolated type. For example, the first electrical circuit 2 is provided in a turbomachine of the aircraft 1, and the second electrical circuit 12 is provided in a fuselage of the aircraft 1.

[0033] It should be noted that, in [Fig. 2], assemblies 5 and 6, respectively 15 and 16, have been simplified for better readability: each of the power lines 51, respectively 151, and following, 61, respectively 161 and following, is individually connected to the pair 4, respectively 14, of power rails via a dedicated pilot-operated switch 8, respectively 18, as illustrated in detail in [Fig. 1]. Thus, each power line 51, respectively 151, and following, 61, respectively 161, and following, can be individually connected / disconnected.

[0034] The structure of the two electrical circuits 2 and 12 is similar to that described previously with regard to [Fig. 1], the diagram of the two electrical circuits 2 and 12 having been simplified by grouping the electrical lines 51, 52, respectively 151 and following of the first set 5, respectively 15 and the electrical lines 61, 62, 63, 64, respectively 161 and following of the second set 6, respectively 16. Briefly, the second electrical circuit 12 comprises elements similar to the elements of the first circuit 2, the references having been prefixed with the number “1”: a second computer 13, a second pair 14 of supply rails and controlled switches 18.

[0035] The first 3 and second 13 computers are arranged to be able to communicate with each other via a 313 link.

[0036] The first 4 and second 14 pairs of supply rails are electrically connected to each other via a connecting line 414 comprising, at the level of the first electrical circuit 2, a first piloted switching element 9 and, at the level of the second electrical circuit 12, a second piloted switching element 19.

[0037] The first 2 and second 12 computers are configured to implement the insulation fault location method according to the invention described later. The fact that the two computers 3 and 13 can communicate with each other via link 313 and that the first 4 and second 14 pairs of power rails are electrically connected to each other will allow redundancy in the implementation of the insulation fault location method according to the invention on each Electrical circuits 2 and 12. This allows for improved monitoring of the insulation of the high-voltage DC electrical network, whether isolated or impedance-isolated, formed by the first 2 and second 12 electrical circuits. Alternatively, the previous implementation redundancy is partial and resembles complementarity and coordination, with each computer 3, 13 acting on its associated electrical circuit 2, 12 to control the operated switches 8, 18 (open or close command). Redundancy is present for detection (the electrical circuits share the same voltage via the connecting line 414) and for localization, provided that each computer 3, 13 informs the other of the open / close commands on the operated switches 8, 18.

[0038] Each calculator 3,13 can isolate the electrical circuit 2,12 to which it is associated from the other by closing the associated controlled switching element 9,19.

[0039] Thus, during the implementation of the insulation fault localization method according to the invention, each computer 3, 13 applies the insulation fault localization method according to the invention to the electrical circuit 2, or 12 to which it belongs and to the other electrical circuit 12, or 2 via the connection line 414. A consolidation is then performed between the two results obtained. In particular, if the two results differ, the consolidation can then be performed either by a complementary means (not shown) available in the electrical network (such as other sensors), or by a default choice (insulation fault confirmed if at least one of the computers 3, 13 locates an insulation fault, or insulation fault confirmed if and only if both computers 3, 13 locate an insulation fault).

[0040] The implementation of the method for locating an insulation fault according to the invention is carried out entirely by one of the computers 3,13 and then by the other of the computers 3,13. In a variant of the implementation of the method for locating an insulation fault according to the invention, each step of the method for locating an insulation fault according to the invention is carried out successively by the first 3 and second 13 computers.

[0041] If one of the computers 3,13 does not return control to the other of the computers 3,13 after a predetermined time (or in the event of absence or loss of communication between the first 3 and second 13 computers), a fallback mode is implemented in which each computer 3,13 carries out the different steps of the method of locating an insulation fault according to the invention on its area of ​​authority, i.e. on the electrical circuit 2,12 to which it belongs.

[0042] Now, with reference to Figures 3 to 6, we will describe an embodiment of a method for locating an insulation fault according to the invention which is intended to be implemented by a computer 3.13 within an electrical circuit 2.12 as previously described.

[0043] First, each of the electrical lines in the electrical circuit 2,12 is classified as either a source, a sensitive load, or a non-sensitive load. Furthermore, each electrical line is assigned a priori probability of being a source of insulation fault during operation (evaluated based on the complexity of said electrical line, predicted failure reliability, experience feedback, etc.). In addition, each electrical line is assigned a parameter quantifying its capacity to tolerate a short power interruption without leading to a loss of a function performed by the electrical equipment of said electrical line: for example, electrical equipment providing a heating function (e.g., frost protection) for which the reaction times of the thermal phenomenon are only slightly affected by an interruption on the order of one second.

[0044] In a first step, the insulation fault location method according to the invention determines a common-mode voltage Vcm at the pair of supply rails. To do this, the insulation fault location method according to the invention measures the voltages Vpos and Vneg between ground and the positive and negative conductors, respectively. Then, the insulation fault location method according to the invention calculates the common-mode voltage Vcm as follows: Vcm = (Vpos + Vneg) / 2.

[0045] In a second step, the insulation fault location method according to the invention compares a previously determined absolute value of the common-mode voltage Vcm with a predetermined threshold voltage. This avoids searching for an insulation fault due to the presence of slight current leakages, below this threshold voltage, which are due to the normal operation of certain electrical equipment connected to the 4,14 pair of power rails. In a further step, the insulation fault location method according to the invention measures a threshold voltage overrun time and triggers a search for the insulation fault if the measured overrun time is greater than a predetermined threshold time.This prevents the localization of an insulation fault from being triggered during a transient overshoot of the threshold voltage due to the normal operation of at least one of the electrical devices connected to the 4.14 pair of supply rails.

[0046] If the preceding conditions require it, the method of locating an insulation fault according to the invention proceeds to a third step of locating 300,400,500 an insulation fault among the electrical lines 51,52, 61,62,63,64, 71,72, 151 and following, 161 and following, 171,172 of the electrical circuit 2,12.

[0047] During this step of locating an insulation fault, the method of locating an insulation fault according to the invention performs firstly a first localization 300 within the first set 5,15 of electrical lines classified as sensitive load.

[0048] To perform this first localization 300, for each power line 51, 52, 151 and following of the first set 5, 15 of power lines classified according to their a priori probability of being a source of insulation fault during operation in descending order, the insulation fault localization method according to the invention disconnects 310 the power line in question 51, 52, 151 and following by opening the associated pilot-operated switch 8, 18, then determines a common-mode voltage at the level of the pair 4, 14 of supply rails (as in the first step). If an absolute value of this determined common-mode voltage is less than 320 the threshold voltage, the insulation fault localization method according to the invention has then located the insulation fault sought on the power line in question and proceeds to a fourth step 600 which will be described later.Otherwise, the method for locating an insulation fault according to the invention proceeds 330 to the next sensitive load in the first set 5, 15 of power lines. If all power lines 51, 52, 151 and following have been tested without locating an insulation fault, the method for locating an insulation fault according to the invention performs a second localization 400. Power lines 51, 52, 151 and following are not reconnected until the insulation fault is located during the subsequent steps. Thus, the disconnection performed in this first localization step 300 meets two needs simultaneously: protection of sensitive loads (by keeping them disconnected) and localization of the insulation fault (by doing so one at a time).

[0049] The second location 400 relates to the second set 6.16 of power lines classified as non-sensitive load.

[0050] To perform this second localization 400, for each power line 61, 62, 63, 64, 161 and following of the second set 6, 16 of power lines classified according to their parameter quantifying their capacity to tolerate a short interruption of power supply without leading to a loss of function, first in descending order and then according to their a priori probability of being a source of insulation fault during operation in descending order, the insulation fault localization method according to the invention disconnects 410 the power line in question 61, 62, 63, 64, 161 and following by opening the associated pilot switch 8, 18, then determines a common-mode voltage at the level of the pair 4, 14 of supply rails (as in the first step). The insulation fault localization method according to the invention sends prior to the disconnection of the The line in question sends a message to the electrical equipment of the power line in question to warn of the impending interruption, and this electrical equipment can thus prepare itself in such a way as to reduce the disruption to the associated service (the details depend on the nature of the electrical equipment). If an absolute value of this determined common-mode voltage is less than the threshold voltage, the insulation fault location method according to the invention has then located the insulation fault being sought on the power line in question and proceeds to the fourth step, which will be described later. Otherwise, the insulation fault location method according to the invention controls the associated pilot-operated switch to close in order to restore power to the power line in question. Then, the insulation fault location method according to the invention proceeds to the next insensitive load in the second set of power lines.If all the power lines 61, 62, 63, 64, 161 and following have been tested without locating any insulation fault, the method of locating an insulation fault according to the invention proceeds to a third location 500. .

[0051] It should be noted that, during this second localization 400, the order of the tested power lines 61, 62, 63, 64, 161 and subsequent lines makes it possible that the insensitive loads located at the end of the list do not need to be disconnected. Indeed, it is the insensitive loads in the second set 6, 16 of power lines that are least tolerant of a short-duration interruption. From the point of view of these insensitive loads, the further they are positioned in the list, the lower the probability of being disconnected during the second localization 400.

[0052] The third location 500 relates to the third set 7.17 of power lines classified as source.

[0053] To perform this third localization 500, for each power line 71, 72, 171, 172 of the third set 7, 17 of power lines classified according to their a priori probability of being a source of insulation fault during operation in descending order, the insulation fault localization method according to the invention disconnects 510 the power line in question 71, 72, 171, 172 by opening the associated pilot-operated switch 8, 18, and then determines a common-mode voltage at the pair 4, 14 of supply rails (as in the first step). If an absolute value of this determined common-mode voltage is less than 520 the threshold voltage, the insulation fault localization method according to the invention has then located the insulation fault sought on the power line in question and proceeds to the fourth step 600, which will be described later.Otherwise, the method for locating an insulation fault according to the invention controls the associated pilot switch 8, 18 in the closed position so as to restore power to the electrical line in question. Then, the method for locating an insulation fault according to the invention. proceeds to the next source in the third set 7,17 of power lines. If all power lines 71,72, 171,172 have been tested without locating an insulation fault, the method for locating an insulation fault according to the invention returns to the first step.

[0054] It should be noted that the third location 500 concerns power lines connected to power sources. Since disconnecting these sources significantly affects the electrical circuit 2,12 (reducing electrical generation capacity), precautions must be taken when implementing the third location 500. Two solutions are possible, to be chosen according to the priority objectives allocated to the system.

[0055] In a first solution, if the priority is to allow the operation of loads that cannot withstand a high common-mode voltage (i.e., sensitive loads), then the method for locating an insulation fault according to the invention can perform a step of disconnecting sufficient loads to remain compatible with a remaining partial generation capacity when disconnecting the generation sources (power lines 71, 72, 171, 172) one by one, followed by verification that the insulation fault has disappeared each time, and then reconnecting them. The generation source responsible for the insulation fault is kept disconnected until the next maintenance operation on aircraft 1.

[0056] In a second solution, if the priority is to maintain the generation capacity, and it is acceptable to continue the flight of aircraft 1 without the common mode voltage sensitive loads, then the isolation of the generation sources is not achieved, the sensitive loads disconnected during the first localization 300 remain disconnected until the end, and all other loads remain connected.

[0057] In a fourth step 600, the insulation fault location method according to the invention, having located the insulation fault during the preceding third location step 300, 400, 500, the insulation fault location method according to the invention closes each pilot-operated switch 8, 18 that was open during the location step 300, 400, 500, except for the pilot-operated switch 8, 18 of the power line that led to the output of said location step 300, 400, 500 and that presents the insulation fault being sought. However, if the insulation fault is located on a source during the third location step 500, the insulation fault location method according to the invention opens the pilot-operated switches 8, 18 of a portion of the loads so as to remain compatible with the capacity of the remaining connected sources.

[0058] An example of implementation of the method for locating an insulation fault according to the invention described above is illustrated in [Fig.7].

[0059] This timing diagram shows the evolution over time of the voltages Vpos and Vneg of the pair 4 of the power supply rails (V4), of the power lines 51 and 52 classified as sensitive loads (V51 and V52), and of the power lines 61, 62, 63, and 64 classified as non-sensitive loads (V61, V62, V63, V64). For the sake of illustration, the insulation fault F occurs on the power line 63 at time TF. The sources have not been shown, as they are not considered by the method for locating an insulation fault according to the invention in this illustrative example.

[0060] At time TF of occurrence of the insulation fault F, the insulation fault localization method according to the invention detects a change in the common-mode voltage on pair 4 of the supply rails beyond the threshold voltage. The insulation fault localization method according to the invention then triggers the third localization step 300, 400, 500.

[0061] First, the insulation fault location method according to the invention performs the first location 100. The controlled switch 8 of the power line 51 is opened at the first instant T. The common-mode voltage does not fall below the threshold voltage. The insulation fault location method according to the invention then opens the controlled switch 8 of the next power line 52 at a second instant T. The common-mode voltage does not fall below the threshold voltage. Since all the power lines 51, 52 of the first assembly 5 have been processed without insulation fault location, the insulation fault location method according to the invention proceeds to the second location 400.

[0062] During the second location 400, the controlled switch 8 of the power line 61 is opened at the third instant T. The common-mode voltage does not fall below the threshold voltage. The insulation fault location method according to the invention closes the controlled switch 8 of the power line 61, then opens the controlled switch 8 of the next power line 62 at a fourth instant T. The common-mode voltage does not fall below the threshold voltage. The insulation fault location method according to the invention closes the controlled switch 8 of the power line 62, then opens the controlled switch 8 of the next power line 63 at an instant TD. The common-mode voltage falls below the threshold voltage. The insulation fault F was then found on the power line 63.The following power line 64 is not tested, nor are the power lines classified as sources not shown (the third location 500 is not implemented here). In all cases, the duration TP preceding the opening of the considered controlled switch 8 allows an anticipation message of power interruption to be sent to the associated electrical equipment behind said controlled switch 8.

[0063] Therefore, the method for locating an insulation fault according to the invention implements the fourth step 600 by closing the controlled switches 8 of the lines electrical 51,52 which had remained open and keeps open the piloted switch 8 of the electrical line 63 presenting the insulation fault F. The implementation time of the method of locating an insulation fault according to the invention is TS.

[0064] To quantify the advantages provided by the implementation of the method for locating an insulation fault according to the invention described, we denote: - N the number of electrical lines within the electrical circuit 2; - Ntol the number of lines that tolerate unbalanced voltages; - Nintol the number of lines that do not tolerate it; - i the position of an electrical line (between 1 and N); -1 the time to isolate and test an electrical line; - Pi the probability for line n° i of creating an insulation fault.

[0065] Testing an electrical line involves disconnecting it, checking the common-mode voltage, and reconnecting it. The typical duration t is on the order of a few milliseconds to a few tens of milliseconds (typically 2 ms to 100 ms max). It depends on the load and the speed of the associated controlled switch (fast if static, such as an SSPC, or slower if electromechanical, such as a contactor). It may also be necessary to wait a short time for the common-mode voltage to stabilize, which depends on the electrical characteristics of the circuit (line inductance, total common-mode capacitance).

[0066] Thus, the total probability of obtaining an insulation fault corresponds to the sum of the Pi values. If all the power lines have the same probability P, then this is simply equal to N*P. The maximum duration of the implementation of the insulation fault location method according to the invention is N*t: the more power lines there are, the longer the implementation time. If, for example, we have a duration t of 100 ms and twenty power lines, then the implementation of the insulation fault location method according to the invention lasts two seconds.

[0067] More precisely, for a power line in the first set 5,15 at position i (rather at the beginning, i being small), the power line at the considered position i experiences a common-mode voltage above the threshold voltage for a duration less than or equal to i*t. It has an interruption probability of (N-i+l)*P, or on the order of N*P for small i. It experiences a power interruption for a duration less than or equal to N*t.

[0068] For a power line of the second set 6,16 in position i (rather in the middle or at the end), the power line in position i under consideration experiences a common-mode voltage above the threshold voltage for a duration approximately equal to N*t. It has a probability of interruption less than or equal to (N-i+l)*P. It experiences a power interruption for a duration equal to t.

[0069] In all cases, in an isolated or impedance-isolated electrical circuit, electrical equipment can anticipate an interruption of its power supply.

[0070] By comparison, the same quantities can be represented in the case of a conventional TN-type electrical circuit where there is only one electrical conductor and a ground connection, for which an insulation fault on an electrical line at position i immediately results in a significant fault current (short circuit) on said electrical line, allowing a protective device to directly disconnect the electrical line concerned in a time independent of the number N of electrical lines. The electrical line at position i under consideration does not experience the high voltage associated with the fault current during the duration of the fault. It has a probability of interruption of N*P. The duration of the interruption is typically less than or equal to 5 seconds. No anticipation of the interruption is possible.

[0071] It therefore appears that for the power lines treated during the second localization 400, the method of locating an insulation fault according to the invention does indeed have the following advantages: - better continuity of service, by reducing the probability of interruption of supply (all the more so as the power line is positioned at the end of the sequence) and the possibility of anticipating the interruption, as opposed to a classic TN type electrical circuit (where all loads are affected until the fault is clarified); and interruption duration independent of the number of power lines in the electrical circuit 2,12, just as on a classic TN type electrical circuit.

[0072] We will now describe an alternative embodiment of the method for locating an insulation fault according to the invention described above. In this embodiment, the electrical lines classified as sensitive or non-sensitive loads are divided into subgroups: for example, a first subgroup consisting of the electrical lines 51, 52 of the first set 5, a second subgroup consisting of the electrical lines 61, 62 of the second set 6, and a third subgroup consisting of the electrical lines 63, 64 of the second set 6. The number of groups and the distribution of the electrical lines within the groups can vary and depend on the complexity of the electrical circuit 2. At a minimum, the first set 5 forms a first subgroup and the second set 6 forms a second subgroup. It should be noted that this embodiment is possible with the sets 15 and 16 described above with reference to [Fig. 2].

[0073] In this embodiment of the method for locating an insulation fault according to the invention, the first localization 300 comprises a preliminary step of simultaneously opening the controlled switches 8,18 associated with the sensitive loads of the subgroup considered (here the first subgroup), followed by determination of the common-mode voltage at the level of the pair 4,14 of supply rails; if the absolute value of the common-mode voltage is greater than the threshold voltage, the method for locating an insulation fault according to the invention moves on to the next subgroup, otherwise the process continues the first localization for each of the sensitive charges of the current subgroup.

[0074] Similarly, the second localization 400 includes a preliminary step of concurrently opening the piloted switches 8,18 associated with the non-sensitive loads of a considered subgroup (here the second subgroup for example), then determining the common mode voltage at the level of the pair 4,14 of supply rails; if the absolute value of the common mode voltage is greater than the threshold voltage, the method of localizing an insulation fault according to the invention closes the piloted switches 8,18 associated with the non-sensitive loads of a considered subgroup and moves on to the next subgroup (here the third subgroup), otherwise the method continues the second localization 400 for each of the non-sensitive loads of the current subgroup.

[0075] The timing diagram in [Fig.8] illustrates an implementation of this variant of the method for locating an insulation fault according to the invention under the same conditions as for the timing diagram in [Fig.7].

[0076] At time TF of occurrence of the insulation fault F, this variant of the insulation fault localization method according to the invention detects a change in the common-mode voltage on pair 4 of the supply rails beyond the threshold voltage. The variant of the insulation fault localization method according to the invention then triggers the third localization step 300, 400, 500.

[0077] First, the variant of the insulation fault location method according to the invention performs the preliminary step of the first location 100. The controlled switches 8 of the power lines 51, 52, forming a subgroup T5, are opened at the first instant T. The common-mode voltage does not fall below the threshold voltage. The variant of the insulation fault location method according to the invention proceeds to the second location 400.

[0078] Initially, the variant of the insulation fault location method according to the invention performs the preliminary step of the second location 400. The controlled switches 8 of the power lines 61, 62, forming a first subgroup T61, are opened at the second instant T. The common-mode voltage does not fall below the threshold voltage. The variant of the insulation fault location method according to the invention closes, at instant TR, the controlled switches 8 of the power lines 61, 62, then opens the controlled switches 8 of the power lines 63, 64, forming a subsequent second subgroup T62, at an instant TD1. The common-mode voltage falls below the threshold voltage. The insulation fault F has then been found in the second subgroup T62. Then the variant of the insulation fault location method according to the invention proceeds with the second location 300 on each of the power lines 63, 64 of the second subgroup T62, as previously described, to locate the insulation fault F on the power line 63.

[0079] Therefore, the variant of the method for locating an insulation fault according to the invention implements the fourth step 600 by closing the pilot-operated switches 8 of the power lines 51, 52 that had remained open and keeps open the pilot-operated switch 8 of the power line 63 exhibiting the insulation fault F. The implementation time of the variant of the method for locating an insulation fault according to the invention is TS2, which is then less than the previous time TS.

[0080] Such a variant of the method for locating an insulation fault according to the invention is therefore interesting if the priority is the reduction of the implementation time, for example to be able to reconnect as quickly as possible the loads sensitive to common mode voltage which were disconnected first to protect them.

[0081] Naturally, the invention is described above by way of example. It is understood that a person skilled in the art is able to carry out different embodiments of the invention without departing from the scope of the invention.

[0082] It is emphasized that all features, as they are apparent to a person skilled in the art from the present description, drawings and attached claims, even if in practice they have only been described in relation to other specific features, both individually and in any combinations, may be combined with other features or groups of features disclosed herein, provided that this has not been expressly excluded or that technical circumstances make such combinations impossible or meaningless.

Claims

1. Demands Method for locating an insulation fault in an isolated or impedance-insulated direct current electrical circuit (2,12) in all or part of an aircraft (1), the electrical circuit comprising a pair (4,14) of supply rails, and a series of power lines (51,52, 61,62, 63,64, 71,72, 151, 161, 171,172) connected to the pair (4,14) of supply rails, each of the power lines comprising a controlled switch (8,18), wherein the method comprises the steps of: a. Determination (100) of a common mode voltage at the level of the pair (4,14) of supply rails; b. Comparison (200) of an absolute value of the determined common-mode voltage with a predetermined threshold voltage; c. If the absolute value of the determined common-mode voltage is greater than the predetermined threshold voltage, then search (300, 400, 500) for an insulation fault in the series of connected power lines: i. For each power line (51, 52, 151) in the series of power lines classified as a sensitive load, the process disconnects (310) the power line in question by opening the associated pilot-operated switch, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less (320) than the threshold voltage, the process performs step d), otherwise the process proceeds (330) to the next sensitive load; ii. For each power line (61, 62, 63, 64, 161) in the series of power lines classified as a non-sensitive load, the method disconnects (410) the power line in question by opening the associated pilot-operated switch, and then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less than (420) the threshold voltage, the process performs step d), otherwise the process controls (440) the associated pilot switch to close and passes (430) to the next insensitive load; and, iii. For each power line (71,72, 171,172) in the series of power lines classified as the source, the process disconnects (510) the power line in question by controlling the associated pilot switch to open, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is less than (520) the threshold voltage, the process performs step d), otherwise the process controls (540) the associated pilot switch to close and passes to the next source; and, d. Controls (600) to close each open pilot switch except the pilot switch of the power line that led to the output of step c) and that has the insulation fault being sought.

2. A method according to claim 1, wherein, during step c), the method measures (250) a duration of overshoot of the threshold voltage and triggers the search (300,400,500) for the insulation fault if the measured duration of overshoot is greater than a predetermined threshold duration.

3. A method according to any one of claims 1 to 2, wherein, in step ii., each insensitive load being associated with a predefined short power interruption tolerance, the disconnection of each insensitive load is carried out in a decreasing order of short power interruption tolerances.

4. A method according to any one of claims 1 to 3, wherein, in step c), each power line being associated with a predefined probability of occurrence of an electrical fault, the disconnection of each power line is carried out in a decreasing order of the probabilities of occurrence of an electrical fault.

5. A method according to any one of claims 1 to 4, wherein, during step d), if the insulation fault is located on a source during step iii., the method controls the pilot-operated switches associated with the power lines classified as sensitive loads in opening.

6. A method according to any one of claims 1 to 5, wherein in steps i. and ii. respectively, the method first simultaneously opens the controlled switches associated with the power lines in question, then determines the common-mode voltage at the supply rail pair; if the absolute value of the common-mode voltage is greater than the threshold voltage, the method performs steps ii. and iii. respectively, otherwise the method continues with the current step.

7. Aircraft (1) comprising a first direct current electrical circuit (2) of the isolated or impedance-isolated type, the electrical circuit comprising a first pair (4) of supply rails, and a first series of electrical lines (51, 52, 61, 62, 63, 64, 71, 72) connected to the first pair of supply rails, each of the electrical lines comprising a piloted switch (8), wherein the aircraft comprises a first computer (3) arranged to implement a method for locating an insulation fault according to any one of claims 1 to 6.

8. Aircraft according to claim 7, wherein the aircraft comprises a second DC electrical circuit (12) of the isolated or impedance-isolated type comprising a second pair (14) of supply rails, and a second set of electrical lines (151, 161, 171, 172) connected to the second pair of supply rails, each of the electrical lines comprising a piloted switch (18), wherein the aircraft comprises a second computer (13) arranged to implement a method for locating an insulation fault according to any one of claims 1 to 6, the first and second computers comprising means for communication (313) between them.

9. Aircraft according to claim 8, wherein the first (4) and second (14) pairs of power rails are electrically connected (414) to each other, the first and second computers preferably being arranged to implement 22 the localization process respectively on the second and first electrical circuits.

10. Aircraft according to any one of claims 7 to 9, wherein the first and / or second electrical circuits belong to a high-voltage direct current electrical network of the isolated or impedance-isolated type.