Synchronization of data acquisition devices for an online monitoring system of an electrical distribution network

Abstract

The invention relates to the synchronization between at least two data acquisition devices of an online monitoring system for an electrical distribution network, each located at a known point in the network and configured to detect high-frequency events during passive data acquisition phases and to inject high-frequency signals. According to the invention, a first signal comprising at least one high-frequency pulse is injected into the network from a first data acquisition device at a first injection instant tA1 time-stamped by a first local time-stamping means;After the first signal is received by the second data acquisition device at a first reception time tB1, time-stamped by a second local time-stamping device, a second signal identical to the first signal is injected into the network from the second data acquisition device. This second signal is injected at a second injection time tB2, separated from the first reception time tB1 by a predefined duration T. Upon reception of the second signal by the first data acquisition device at a second reception time tA2, time-stamped by the first local time-stamping device, a synchronization difference is determined between the first and second local time-stamping devices based on the first injection time tA1, the second reception time tA2, and the predefined duration T. Figure for abbreviation: None;

Description

Title of the invention: Synchronization of data acquisition devices of an online monitoring system for an electrical distribution network. Technical field

[0001] The present invention relates to the general field of monitoring the proper functioning of elements present in an electrical distribution network, in particular electrical cables, and more specifically the synchronization between at least two data acquisition devices belonging to an online monitoring system of an electrical distribution network. Technological background

[0002] One of the main problems likely to affect the operation of an electrical transmission and / or distribution network is the occurrence of partial discharges on cables, transformers, switching equipment, cable junctions, etc., which can lead to their progressive degradation and, ultimately, to destructive faults.

[0003] The detection and localization of discharges can provide crucial information to the network operator regarding the condition of the insulation of distribution cables in operation and of equipment in general.

[0004] Monitoring systems have already been proposed based on measurements at one end of a network cable, using time-domain reflectometry (TDR) and signal processing techniques. However, these systems can mainly be used offline and have strict limitations regarding their effectiveness and scope of application.

[0005] Other known systems, called online monitoring systems, can detect and locate events that may represent anomalies, such as partial discharges, without affecting the normal operation of the network. Information regarding the progression of the phenomenon over time can prevent the occurrence of destructive faults, thereby improving network reliability indices and preventing short-circuit currents from stressing other equipment. Consequently, such online monitoring systems contribute to one of the important aspects of the smart grid, namely the optimal use of existing assets through the implementation of optimized preventive maintenance and intelligent asset condition monitoring.

[0006] As shown in [Fig. 1], which partially schematically illustrates an example of a meshed electrical distribution network, the principle of online monitoring consists of placing a plurality of data acquisition devices 1 online at predefined locations in the network, for example, at the ends of electrical cables within that network. In the non-limiting example of [Fig. 1], three of these online data acquisition devices 1 are shown placed at three known locations illustrated by points A, B, and C. The two devices 1 placed at points A and B can detect events corresponding to a partial discharge occurring at any position on a cable or piece of equipment in the network, for example, between points A and B or even outside of these points. Similarly, the two devices 1 placed at points B and C can detect events corresponding to a partial discharge occurring at any position on a cable or piece of equipment in the network, for example, between points B and C, or even outside of these points.

[0007] The known principle for locating a partial discharge with this type of online monitoring system is as follows: If a partial discharge 2 occurs between points A and B of the network, two corresponding pulse signals UA(t) and Ug(t) will propagate in opposite directions within the network. The signal UA(t) is detected by the data acquisition device 1 located at point A at time t0aA, and the signal UB(t) is detected by the data acquisition device 1 located at point B at time toaB. The location ZpB of the partial discharge 2 can thus be determined according to the following relationship: Z PD =i ^ J c (1 ) with At ° a= toa HAS ' toa B (2) tc, the flight time between points A and B; and lc the known length of cable separating points A and B.

[0008] In order to be able to determine the quantity Atoa, and consequently, the location ZpD, it is therefore necessary to synchronize the two data acquisition devices 1 located at points A and B. In other words, the arrival times toaA and toaB of the signals UA( t ) and uB( t ) acquired by each of the two data acquisition devices 1 must be determined in a common time reference frame.

[0009] As shown in Figure 1, it is already known to associate each data acquisition device 1 of the monitoring system with a receiver 10 of a satellite navigation system, for example a GPS receiver 10. Each event detected by each of the data acquisition devices 1, for example the preceding signal UA(t) or uB(t) generated by a partial discharge, can thus be time-stamped in a common reference system. This synchronization method is described, for example, in document WO 2021 / 138569. The difference between the arrival times of the signals uA(t) and UB(t) at the two data acquisition devices 1, expressed in a common time reference, and consequently, the location The ZpD of the partial discharge can then be determined by applying relations (1) and (2) above.

[0010] However, although GPS accuracy can be very high, several factors can introduce errors, such as the effects of multiple propagation of the GPS signal, satellite positioning errors, atmospheric conditions, and, above all, installation difficulties. Indeed, the correct use of GPS systems requires the use of antennas that must be installed in open space to receive the satellite signal. Besides the fact that these antennas are expensive, many high-voltage and medium-voltage power distribution networks are underground, and it is desirable to minimize the need to install equipment on the surface.

[0011] Another known method, described in WO 2004 / 013642 A2, involves injecting high-frequency synchronization pulses at one end of a cable being monitored by a distribution network, using an inductive coupler. The data acquired by the monitoring systems at both ends of the cable, generated by partial discharge pulses in the cable, thus contain both partial discharge pulses and synchronization pulses. By aligning the data sets and using the time delay between the partial discharge pulse and the synchronization pulse, it is possible to determine the location of the partial discharge. This time synchronization method uses the power cable as the transmission medium for the synchronization pulses, thereby mitigating the drawbacks of satellite invisibility and weather conditions associated with GPS.However, the accuracy of this method is significantly affected by the attenuation and dispersion of the synchronization pulses propagating through the cable. This results in a loss of the time-domain data transmitted through the cable. Summary of the invention

[0012] The present invention aims to overcome the drawbacks of methods and systems for synchronizing at least two data acquisition devices of an online monitoring system of an electrical distribution network.

[0013] More specifically, the present invention relates to a method for synchronizing at least a first and a second data acquisition device of an online monitoring system for an electrical distribution network, each data acquisition device being located at a known point in the network and being configured to detect high-frequency events during passive data acquisition phases and to inject high-frequency signals, the method comprising the following steps: - inject into the network a first signal comprising at least one high-frequency pulse from the first data acquisition device at a first injection instant time-stamped by a first local time-stamping means; - receive said first signal at the level of the second data acquisition device at a first reception instant tBi time-stamped by a second local time-stamping means; - inject into the network a second signal identical to said first signal from the second data acquisition device, the second signal being injected at a second injection instant tB2 time-stamped by the second local time-stamping means and separated from the first reception instant tBi by a predefined duration T; - receive said second signal at the first data acquisition device at a second reception time tA2 time-stamped by the first local time-stamping method; and - determine a synchronization difference Atoa between the first local timestamping method and the second local timestamping method based on the first injection instant tAb of the second reception instant tA2, and the predefined duration T.

[0014] In one possible embodiment, said predefined duration T is greater than at least an estimated time-of-flight value of a signal between the first and second data acquisition devices.

[0015] In one possible embodiment, said first injected signal and said second injected signal comprise a sequence of high-frequency pulses of predefined period.

[0016] In one possible embodiment, said predefined duration T is greater than the sum of the estimated value of flight time and said predefined period.

[0017] In one possible embodiment, the synchronization difference Atoa is determined according to the following relationship: △toa= t^+TOF' where TOF' corresponds to the time of flight of a signal between the first and second data acquisition devices calculated according to the relation: TOF'^VD

[0018] In one possible embodiment, the method further includes time-stamping high-frequency events detected by the first data acquisition device during a first passive data acquisition phase, via the first local time-stamping means, and high-frequency events detected by the second data acquisition device during a second passive data acquisition phase, via the second local time-stamping means.

[0019] The first passive data acquisition phase is preferably triggered at the second reception instant tA2 timestamped by the first local timestamping means.

[0020] The second passive data acquisition phase is preferably triggered at the second injection instant tB2 time-stamped by the second local time-stamping means.

[0021] The first passive data acquisition phase and the second passive data acquisition phase can advantageously be carried out over a time window of the same predetermined duration.

[0022] In one possible embodiment, the first high-frequency event detected by the first data acquisition device and the second high-frequency event detected by the second data acquisition device correspond to two signals generated by the same partial discharge at a point in the network located between the first and second data acquisition devices, and the method further comprises a step of calculating the location Zp^ of the partial discharge according to the relation _TOF'- Atoa, in which lc is a cable length between the first and the ^PD- 2TOF' Jc second data acquisition devices.

[0023] The present invention also relates to an online monitoring system for an electrical distribution network comprising at least a first and a second data acquisition device, each data acquisition device being located at a known point in the network and being configured to detect high-frequency events during passive data acquisition phases and to inject high-frequency signals, the online monitoring system being characterized in that it comprises a first local time-stamping means associated with the first data acquisition device, a second local time-stamping means associated with the second data acquisition device,and synchronization means configured to: - inject into the network a first signal comprising at least one high-frequency pulse from the first data acquisition device at a first injection instant time-stamped by the first local time-stamping means; - receive said first signal at the level of the second data acquisition device at a first reception instant tBi time-stamped by the second local time-stamping means; - inject into the network a second signal identical to said first signal from the second data acquisition device, the second signal being injected at a second injection instant tB2 time-stamped by the second local time-stamping means and separated from the first reception instant tBi by a predefined duration T; - receive said second signal at the first data acquisition device at a second reception time tA2 time-stamped by the first local time-stamping method; and - determine a synchronization difference Atoa between the first local timestamping method and the second local timestamping method based on the first injection time tAb of the second reception time tA2, and the predefined duration T.

[0024] In one possible embodiment, the first local timestamping method and the second local timestamping method are N-bit counters, where N is an integer greater than or equal to 16.

[0025] In one possible embodiment, the first local timestamping means is integrated into the first data acquisition device, and / or the second local timestamping means is integrated into the second data acquisition device. Brief description of the figures

[0026] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will clearly explain what the invention consists of and how it can be implemented. In the accompanying figures: [Fig.1] The [Fig.1], already described above, partially and schematically illustrates an example of an electrical distribution network with an online monitoring system comprising data acquisition devices synchronized in a known way on the basis of a GPS-type navigation system; [Fig.2] Fig.2 partially and schematically illustrates an example of an electrical distribution network with synchronized data acquisition devices according to one possible embodiment of the invention; [Fig.3] Fig.3 schematically illustrates a data acquisition device conforming to a possible embodiment according to the invention; [Fig.4] Fig.4 illustrates possible steps for a synchronization method according to the invention; [Fig.5] Fig.5 schematically illustrates some steps of the process of Fig.4. Description of method(s) of implementation

[0027] In the figures, identical or equivalent elements shall bear the same reference numerals. The various diagrams are not to scale.

[0028] In the following, the synchronization between at least two data acquisition devices of a monitoring system according to the invention will be described in the non-limiting case where the online monitoring system is configured to identify and locate partial discharges in the network. The synchronization principle can nevertheless be extended to any online monitoring system having several data acquisition devices that need to be synchronized.

[0029] Figure 2 partially illustrates an electrical distribution network similar to the network in Figure 1, including an event monitoring system. The electrical distribution network is, for example, a high-voltage or medium-voltage network. composed of a plurality of electrical cables, connection or linking accessories, switchgear, and / or transformers. The system includes a plurality of data acquisition devices 1 placed at various known points in the network, such as points A, B, and C shown in [Fig. 2]. Points A, B, and C, where the data acquisition devices are located, are preferably situated at the ends of cables or cable sections. In the non-limiting case of an underground network, the data acquisition devices 1 are preferably placed in easily accessible locations, for example, at transformers.

[0030] Since the devices 1 are herein dedicated, without limitation, to the detection and localization of partial discharges, each device 1 conventionally comprises, as schematically illustrated in Figure 3, detection means 11 capable of detecting impulsive events caused in the cables by the partial discharges, such as the high-frequency pulses U^(t) and Ug(t) generated by the impulsive discharge 2 of [Fig. 2]. The means 11 are, for example, a non-invasive sensor, preferably an inductive sensor 11, located around the cable at the device's location point. In place of the GPS receiver 10 of [Fig. 1], the online monitoring system further comprises a local timestamping means 12 associated with each data acquisition device 1, and time synchronization means configured to implement the steps of a synchronization method according to the invention.By "associated," it is understood that each local timestamping means 12 is either electrically and functionally connected to each device 1, or integrated into each device 1 as illustrated in [Fig. 3]. Each device 1 also includes injection means 13 configured to generate high-frequency signals and inject these high-frequency signals via the detection means 11. These injection means 13 are part of the time synchronization means, as will become clearer later. Each data acquisition device 1 may further advantageously include a mobile (4G or higher) or Ethernet communication module 14, enabling it, in particular, to receive or see control signals emitted by a remote server (not shown) included in the online monitoring system, or to transmit information, such as acquired data, to this server.

[0031] Each local timestamping means 12 is preferably a precise local clock, or a counter of 16 bits or more. Such a local timestamping means 12 makes it possible to timestamp each injection of a high-frequency signal, each reception of a high-frequency signal, and each event detected by the high-frequency sensor 11 at the location point of the data acquisition device 1, during a passive data acquisition phase.

[0032] A time synchronization method, according to the present invention, between the data acquisition devices 1, will now be described with reference to Figures 4 and 5. For the sake of simplicity, the explanation is given with regard to the two devices 1 located at points A and B, but can easily be extended to all the data acquisition devices 1 present in the online monitoring system of the electrical grid. In the following, the device 1 located at point A is called the "first data acquisition device," and the device 1 located at point B is called the "second data acquisition device." Since the two devices are identical, their role can nevertheless be reversed:

[0033] The synchronization process begins with a step 110 in which the first data acquisition device 1 generates a first signal SA(t) and injects this first signal into the network, more precisely into the cable. This first signal SA(t), generated or delivered by the injection means 13 of the first device 1, comprises at least one high-frequency pulse. It is thus possible to inject this first signal into the network at point A, using the detection means 11 in an active mode (as opposed to the passive mode in which the detection means 11 receive signals). In one possible embodiment, this first signal SA(t) corresponds to a sequence of high-frequency pulses of predetermined period. The use of several successive pulses, instead of a single pulse, advantageously improves the signal resolution and mitigates the effects of signal attenuation and dispersion during its propagation in the cable.The injection time tAi of this first signal is time-stamped by the local time-stamping means 12 integrated, or more broadly associated, with the first device 1, and recorded locally or transmitted for recording to the central server via the communication module 14 of the first device 1.

[0034] The first injected signal propagates through the various network components (cables and transformers and / or switching equipment, and / or cable junctions, etc.) until it reaches the second data acquisition device 1. This first signal SA(t) is therefore received by the second device 1 at a step 120 via its detection means 11. The time of reception tBi of this first signal is time-stamped by the local time-stamping means 12 integrated into, or more broadly associated with, the second device 1, and recorded locally.

[0035] After a predefined duration T following the reception time tBi, the second data acquisition device 1 generates a second signal SB(t), identical to the first signal, and injects this second signal at point B of the network, more precisely into the cable, using its detection means 11 in active mode (step 130 in Figures 4 and 5). The injection time tB2 of this second signal SB(t) is time-stamped by means of local time-stamping 12 integrated into, or more broadly associated with, the second device 1, and recorded locally. The predefined time T separating the reception time tBi and the injection time tB2 of this second signal Sg(t) is preferably chosen to be greater than at least one estimated time-of-flight value of a signal between the first and second data acquisition devices 1. In the case where the first and second signals correspond to a sequence of high-frequency periodic pulses with a predefined period Ta / b, the predefined time T is preferably chosen to be greater than the sum of the estimated time-of-flight value and said predefined period Ta / B. The estimated time-of-flight value through the network does not need to be precise. It can be an average time-of-flight value across the network components.

[0036] This second injected signal SB(t) propagates through the various network components (cables and transformers and / or switching equipment, and / or cable junctions, etc.) undergoing the same effects as those encountered during the propagation of the first signal SB(t), until it reaches the first data acquisition device 1. This second signal SB(t) is therefore received by the first device 1 at a step 140 via its detection means 11. The time of reception tA2 of this second signal is time-stamped by the local time-stamping means 12 integrated into, or more broadly associated with, the first device 1, and recorded locally or transmitted for recording to the central server via the communication module 14 of the first device 1.

[0037] It is then possible, in a step 150, to determine a synchronization difference Atoa between the first local timestamping means 2 and the second local timestamping means 12 of the two data acquisition devices 1 based on the first injection instant tAb of the second reception instant tA2, and the predefined duration T. More precisely, the synchronization difference Atoa is determined by calculation according to the following relationship: Atoa = t^+TOF' where TOF' corresponds to the time of flight of a signal between the first and second data acquisition devices (1) calculated according to the relation: TOF'^d^-tAj-T)

[0038] This calculation can be carried out locally (at the level of the first device 1) or centrally at the level of the remote server.

[0039] Any high-frequency event that can be detected by the detection means 11 of the first device 1 or the second device 1 during passive data acquisition phases can therefore be time-stamped first locally, via the local time-stamping means 12, and then in a reference database common thanks to knowledge of the difference in Atoa synchronization between the two data acquisition devices 1.

[0040] In the non-limiting case where the data acquisition devices 1 are dedicated to the detection of high-frequency events corresponding to signals U^(t) and Ug(t) generated by the same partial discharge 2, the method therefore includes the triggering of a first passive phase and a second passive phase of detection of these events at the level of the first data acquisition device 1 and the second data acquisition device 1 respectively, during a time window of the same predetermined duration for the two phases (step 160).

[0041] In one possible embodiment, the first passive data acquisition phase is triggered at the second reception instant tA2 and the second passive data acquisition phase is triggered at the second injection instant tB2. Upon detection of the signals UA(t) and uB(t), it is then possible to calculate the location Zpg of the partial discharge according to the relation _TOF'- Atoa, in which lc is a cable length between the first and the ^PD- 2TOF' Jc second data acquisition device 1. This calculation step 170 can, for example, be carried out at the remote central server level.

[0042] Steps 110 to 150 are preferably repeated periodically (for example, once or several times a day) in order to compensate for drifts that may affect the network, such as temperature changes, overloads, and / or dispersion in the meters 12.

Claims

1. Demands Method for online monitoring of an electrical distribution network, using at least a first device (1) and a second device (1) for data acquisition, each device (1) for data acquisition being located at a known point in the network and being configured to detect high-frequency events during passive phases of data acquisition and to inject high-frequency signals, the method comprising the following steps: - injecting (110) into the network a first signal comprising at least one high-frequency pulse from the first device (1) for data acquisition at a first injection time timed by a first local time-stamping means (12); - receive (120) said first signal at the level of the second data acquisition device (1) at a first reception instant tBi time-stamped by a second local time-stamping means (12); - inject (130) into the network a second signal identical to said first signal from the second data acquisition device (1), the second signal being injected at a second injection instant tB2 time-stamped by the second local time-stamping means (12) and separated from the first reception instant tBi by a predefined duration T; - receive (140) said second signal at the level of the first data acquisition device (1) at a second reception time tA2 time-stamped by the first local time-stamping means (12);and - determine (150) a synchronization difference Atoa between the first local time-stamping means (12) and the second local time-stamping means (12) on the basis of the first injection instant tAb of the second reception instant tA2, and the predefined duration T, the method further comprising a time-stamping (160) of the high-frequency events detected by the first data acquisition device (1) during a first passive data acquisition phase, via the first local time-stamping means (12), and of the high-frequency events detected by the second data acquisition device (1) during a second passive data acquisition phase, via the second local time-stamping means (12), the first high-frequency event detected by the first data acquisition device (1) and the second event; high frequency detected by the second data device (1) corresponding to two signals generated by the same partial discharge (2) at a point in the network located between the first and second data acquisition devices (1).

2. A method according to claim 1, wherein said predefined time T is greater than at least an estimated time-of-flight value of a signal between the first and second data acquisition devices (1).

3. A method according to any one of the preceding claims, wherein said first injected signal and said second injected signal comprise a sequence of high-frequency pulses of predefined period.

4. A method according to claims 2 and 3, wherein said predefined duration T is greater than the sum of the estimated value of flight time and said predefined period.

5. A method according to any one of the preceding claims, wherein the synchronization difference Atoa is determined according to the following relation: △toa= ÏA2+TOF1 in which TOF' corresponds to the time of flight of a signal between the first and second data acquisition devices (1) calculated according to the relation: TOF'=J(tA2-tA1-T)

6. A method according to any one of the preceding claims, wherein the first passive data acquisition phase is triggered at the second time-stamped reception time tA2 by the first local time-stamping means (12).

7. Method according to claim 6, wherein the second passive data acquisition phase is triggered at the second injection instant tB2 time-stamped by the second local time-stamping means (12).

8. A method according to any one of the preceding claims, wherein the first passive data acquisition phase and the second passive data acquisition phase are carried out over a time window of the same predetermined duration.

9. A method according to any one of the preceding claims, characterized in that the method further comprises a step (170) of calculating the location Zpp of the partial discharge according to the relation _TOF'-Atoa, ^PD- 2TOF' in which lc is a cable length between the first and second data acquisition devices (1), and in which TOF' corresponds to the time of flight of a signal between the first and second data acquisition devices (1) calculated according to the relation: TOF1=2 (t^2- Ïai ” T)'

10. An online monitoring system for an electrical distribution network comprising at least a first and a second data acquisition device (1), each data acquisition device (1) being located at a known point in the network and being configured to detect high-frequency events during passive data acquisition phases and to inject high-frequency signals, the online monitoring system being characterized in that it comprises a first local time-stamping means (12) associated with the first data acquisition device (1), a second local time-stamping means (12) associated with the second data acquisition device (1), and synchronization means, the monitoring system being configured to implement a method according to one of the preceding claims.

11. A system according to claim 10, characterized in that the first local timestamping means (12) and the second local timestamping means are N-bit counters, N being an integer greater than or equal to

12. 1U. System according to any one of claims 10 and 11, wherein the first local timestamping means (12) is integrated into the first data acquisition device (1), and / or the second local timestamping means (12) is integrated into the second data acquisition device (1).

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