Synchronization of data acquisition devices of an online monitoring system of an electrical distribution network by detection of zero crossings

Abstract

The invention relates to the synchronization between at least two data acquisition devices of an online monitoring system of an electrical distribution network, each located at a known point A or B of the network and configured to detect high-frequency events during data acquisition phases. According to the invention, during a first phase of estimating the period of the electrical signal traveling through the network, each data acquisition device samples the electrical signal traveling through the network and deduces therefrom an estimate T'A or T'B of the period of the electrical signal by detecting the zero crossing times of the sampled signal, locally time-stamped by a time-stamping means associated with each data acquisition device.One of the devices then sends an information signal at a first detection time tZCA1,1, locally time-stamped, of a new zero crossing of the sampled signal, and triggers a data acquisition phase at a first time TRA separated from the first detection time by a duration corresponding to the first estimate T'A of the period of the electrical signal. The time of reception of this signal at the other device is also time-stamped by a local time-stamping means. After the lapse of a duration corresponding to half of the second estimate T'B of the period of the electrical signal following the reception time, this other device triggers a phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, at a second trigger time tRB determined locally and corresponding to a second time of detection of a new zero crossing of the sampled signal at the local level.We can then determine a synchronization difference between two high-frequency events acquired, on a given cycle, by the two data acquisition devices by calculating the difference between the second triggering instant tRB and the first triggering instant tRA. Figure for the abstract: Figure 2.

Description

Title of the invention: Synchronization of data acquisition devices of an online monitoring system of an electrical distribution network by detection of zero crossings 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 precisely 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 that may affect the operation of an electrical transmission and / or distribution network is the occurrence of partial discharges on cables, transformers, switching equipment, cable joints, etc. which may lead to their progressive degradation and, ultimately, to destructive faults.

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

[0004] Monitoring systems have already been proposed based on measurements at one end of a network cable, which use time domain reflectometry (TDR) as well as 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 discharge, without affecting the normal operation of the network. Information relating to the progression of the phenomenon over time can prevent the occurrence of destructive faults, thus improving the reliability indices of the network and preventing the short-circuit current from stressing other equipment. Consequently, such online monitoring systems contribute to one of the important aspects of the smart network, namely the optimal use of existing assets by implementing optimized preventive maintenance and intelligent knowledge of the state of the assets.

[0006] As shown in [Fig. 1], which partially diagrams 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 present in this network. In the non-limiting example of [Fig.l], three of these online data acquisition devices 1 have been 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 of a cable or equipment in the network, for example located between points A and B or even outside 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 of a cable or equipment in the network, for example located between points B and C, or even outside these points.

[0007] The known principle of 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 uB(t) will propagate in opposite directions in the network. The signal uA(t) is detected by the data acquisition device 1 located at point A at a time toaA, and the signal uB(t) is detected by the data acquisition device 1 located at point B at a time îoaB. The location ZPD of the partial discharge 2 can thus be determined according to the following relationship: ZPD=^ -le ( 1 ) with Atoa= toaA ' (2) tc, the flight time between points A and B; and 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 frame.

[0009] As visible 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 previous 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 ZPD location of the partial discharge, can then be determined by applying relations (1) and (2) above.

[0010] However, although the accuracy of GPS can be very high, several factors can introduce errors, such as the effects of multiple propagation of the GPS signal, satellite location errors, atmospheric conditions and, above all, installation difficulties. Indeed, the correct use of GPS systems involves the use of antennas that must be installed in free space to allow the satellite signal to be picked up. However, in addition to the fact that these antennas are expensive, many high-voltage or medium-voltage electrical distribution networks are underground distribution networks for which it is desired to minimize the need to install equipment on the surface.

[0011] Another known method, described in WO 2004 / 013642 A2, consists of injecting high-frequency synchronization pulses into one end of a cable under monitoring of a distribution network, using an inductive coupler. The data acquired by the monitoring systems used 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 obtain the location of the partial discharge. This time synchronization method uses the power cable as the transmission medium for the synchronization pulses, which mitigates the disadvantage of satellite invisibility and the atmospheric conditions problems associated with GPS.However, the accuracy of this method is greatly affected by the attenuation and dispersion of the synchronization pulses propagating in the cable. This results in a loss of the time data sent over the cable. Summary of the invention

[0012] The present invention aims to overcome the drawbacks of the 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 of synchronization between at least a first device and a second data acquisition device of an online monitoring system of an electrical distribution network, each data acquisition device being located at a known point of the network and being configured to detect high-frequency events during data acquisition phases, the method comprising: a first phase of estimations of the period of the electrical signal traveling through the network consisting of: - taking the electrical signal traveling through the network at the first data acquisition device and deducing therefrom a first estimate T'A of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a first time-stamping means associated with the first data acquisition device; - taking the electrical signal traveling through the network at the second data acquisition device and deducing therefrom a second estimate T'B of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a second time-stamping means associated with the second data acquisition device; followed by a second synchronization phase comprising the following steps: - sending by the first data acquisition device of an information signal at a first detection instant tZCAi,i, locally time-stamped, of a new zero crossing of the signal taken at the level of the first data acquisition device; - local timestamp of the time of receipt of said information signal by the second data acquisition device; - triggering, by the first data acquisition device, of a first phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the first acquisition phase being triggered at a first triggering instant ^determined locally by the first time-stamping means and separated from the first detection instant by a duration corresponding to the first estimate T'A of the period of the electrical signal; - after the lapse of a duration corresponding to half of the second estimate T'B of the period of the electrical signal following said reception time, triggering, by the second data acquisition device, of a second phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the second acquisition phase being triggered at a second trigger time tRB determined locally by the second time-stamping means and corresponding to a second time of detection of a new zero crossing of the signal taken at the level of the second data acquisition device; and - determination of an Atoa synchronization difference between a first high-frequency event and a second high-frequency event acquired, over a given cycle, respectively by the first data acquisition device at a first acquisition instant locally time-stamped by the first time-stamping means and by the second data acquisition device at a second acquisition time locally time-stamped by the second time-stamping means by calculating the difference between the second trigger time tRB and the first trigger time Ira-

[0014] In a possible embodiment, the predefined cycle duration for each cycle of the first data acquisition phase corresponds to the first estimate T'A of the period of the electrical signal, and the predefined cycle duration for each cycle of the second data acquisition phase corresponds to the second estimate T'B of the period of the electrical signal.

[0015] In one possible embodiment, the successive cycles in the first phase and the second phase of data acquisition are consecutive.

[0016] Alternatively, the successive cycles in the first phase and the second phase of data acquisition are separated two by two by a predefined spacing duration Ts corresponding to a predefined number of consecutive zero crossings.

[0017] In a 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 device on a given cycle correspond to two signals generated by the same partial discharge at a point of the network located between the first and second data acquisition devices, and the method further comprises a step of calculating the ZPD location of the partial discharge according to the relationship । in which lc is a cable length between the first and second data acquisition devices.

[0018] 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 data acquisition phases, the online monitoring system being characterized in that it comprises: - a first local timestamping means and a first zero crossing detection module, associated with the first data acquisition device, and configured to sample the electrical signal traveling through the network at the first data acquisition device and detect the zero crossing times of the sampled signal, locally timestamped by the first timestamping means; - a second local time-stamping means and a second zero-crossing detection module, associated with the second data acquisition device, and configured to sample the electrical signal traveling through the network at the level of the second data acquisition device and detect the zero crossing times of the sampled signal, locally time-stamped by the second time-stamping means; and - synchronization means configured to: during a first estimation phase, deducing a first estimation T'A of the period of the electrical signal from zero crossing instants successively time-stamped locally by the first time-stamping means, and a second estimation T'b of the period of the electrical signal from zero crossing instants successively time-stamped locally by the second time-stamping means, and to carry out a second synchronization phase comprising the following steps: - sending by the first data acquisition device of an information signal at a first detection instant tZCAi,i, locally time-stamped, of a new zero crossing of the signal taken at the level of the first data acquisition device; - local timestamp of the time of receipt of said information signal by the second data acquisition device; - triggering, by the first data acquisition device, of a first phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the first acquisition phase being triggered at a first triggering instant ^determined locally by the first time-stamping means and separated from the first detection instant by a duration corresponding to the first estimate T'A of the period of the electrical signal; - after the lapse of a duration corresponding to half of the second estimate T'B of the period of the electrical signal following said reception time, triggering, by the second data acquisition device, of a second phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the second acquisition phase being triggered at a second trigger time tRB determined locally by the second time-stamping means and corresponding to a second time of detection of a new zero crossing of the signal taken at the level of the second data acquisition device; and - determination of a difference in Atoa synchronization between a first high-frequency event and a second high-frequency event acquired, over a given cycle, respectively by the first data acquisition device at a first acquisition instant locally time-stamped by the first time-stamping means and by the second data acquisition device at a second acquisition instant locally time-stamped by the second time-stamping means by calculating the difference between the second triggering instant tRB and the first triggering instant Ira-

[0019] In one possible embodiment, the first timestamping means and the second timestamping means are N-bit counters, N being an integer greater than or equal to 16.

[0020] In one possible embodiment, the first time-stamping means is integrated into the first data acquisition device, and / or the second time-stamping means is integrated into the second data acquisition device.

[0021] In one possible embodiment, the first zero crossing detection module is integrated into the first data acquisition device, and / or the second zero crossing detection module is integrated into the second data acquisition device. Brief description of the figures

[0022] The description which follows with reference to the appended drawings, given as non-limiting examples, will make it clear what the invention consists of and how it can be implemented. In the appended figures: [Fig.l] [Fig.l], 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 manner 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 a possible embodiment of the invention; [Fig.3] [Fig.3] schematically illustrates a data acquisition device according 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 certain steps of the method of [Fig.4]; [Fig.6] [Fig.6] schematically illustrates other steps of the method of [Fig.4]. Description of embodiment(s)

[0023] In the figures, identical or equivalent elements will bear the same reference signs. The various diagrams are not to scale.

[0024] 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 with multiple data acquisition devices that need to be synchronized.

[0025] [Fig. 2] partially illustrates an electrical distribution network similar to the network of [Fig. 1], comprising 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 hook-up accessories, equipment and / or transformers. The system comprises a plurality of acquisition devices 1 placed at different known points of the network, such as points A, B and C shown in [Fig. 2]. Points A, B, C where the data acquisition devices are located are preferably located 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 at easily accessible locations, for example at the transformers.

[0026] The devices 1 being here dedicated, in a non-limiting manner, to the detection and location of partial discharges, each device 1 conventionally comprises, as illustrated schematically in [Fig. 3], detection means 11 capable of detecting pulse events caused in the cables by the partial discharges, such as the high-frequency pulses uA(t) and uB(t) generated by the pulse 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 location point of the device. Instead of the GPS receiver 10 of [Fig. 1], the online monitoring system further comprises: - a first local time-stamping means 13 and a first zero-crossing detection module 12, associated with the first data acquisition device 1, and configured to sample the electrical signal traveling through the network at the first data acquisition device 1 and detect the zero-crossing instants of the sampled signal, locally time-stamped by the first time-stamping means 13; - a second local time-stamping means 13 and a second zero-crossing detection module 12, associated with the second data acquisition device 1, and configured to sample the electrical signal traveling through the network at the level of the second data acquisition device 1 and detect the instants of zero crossings of the sampled signal, locally time-stamped by the second time-stamping means 15.

[0027] By "associated" is meant that each local time stamping means 13 and / or each zero crossing detection module 12 is either electrically and functionally connected to each device 1, or integrated into each device 1, as illustrated in [Fig.3].

[0028] Each data acquisition device 1 may further advantageously comprise a mobile communication module 14 (4G or more) or by Ethernet, allowing it in particular to receive or 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 or to any other device 1 of the monitoring system. Each device 1 is also capable of emitting information signals to any other device 1 included in the monitoring system, or of receiving such information signals. These information signals can be transmitted via the detection means 11, used in an active mode, the information signal then being injected into the network, in particular into the cable at the location point of the device 1, and recovered via the detection means of another device 1. Alternatively, the information signals can be emitted / received via the mobile communication modules 14 (or by Ethernet included in each device 1.

[0029] Each local time-stamping means 13 is preferably a precise local clock, or a 16-bit or more counter. Such a local time-stamping means 13 makes it possible to locally time-stamp everything that happens at each device 1, in particular the detections of zero crossing, the transmission or reception of any information signal, and each event detected by the high-frequency sensor 11 at the location point of the data acquisition device 1, during a data acquisition phase.

[0030] Each zero crossing detection module 12 comprises a low-frequency sensor 15 capable of sampling the electrical sinusoidal signal traveling through the network at the fundamental frequency of 50 Hz or 60 Hz depending on the country at the location point (A, B or C) of the device 1 considered, and a zero crossing detection circuit 16 receiving the signal sampled by the low-frequency sensor 15. The low-frequency sensor 15 is preferably a non-invasive sensor, for example a contactless ELF magnetometer or an inductive ELF sensor (ELF being the Anglo-Saxon initials for “Extremely Low Frequency”). Low-frequency capacitive sensors can nevertheless be considered. The circuit 16 can implement any known zero crossing detection algorithm.The zero crossing detector circuit 16 can be any known comparator circuit for detecting the voltage of the sampled signal as it changes from positive to negative and from negative to positive.

[0031] The online monitoring system finally also comprises time synchronization means configured to implement the steps of a synchronization method according to the invention, which will now be explained.

[0032] The synchronization method used by the data acquisition devices 1, in accordance with the present invention, is illustrated in [Fig. 4]. For the sake of simplification, the explanation is made with respect to the two devices 1 located at points A and B, but can easily be extended to all data acquisition devices 1 present in the electrical network:

[0033] The synchronization method 100 begins with a phase of estimating the period of the electrical signal passing through the network, made at each data acquisition device 1, and in particular at each zero-crossing detection module 12. More precisely, the estimation phase 110 consists of: - on the one hand, sampling the electrical signal passing through the network at the first data acquisition device 1, located at point A, and deducing therefrom a first estimation T'A of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a first time-stamping means 13 associated with the first data acquisition device 1; - on the other hand, taking the electrical signal traveling through the network at the level of the second data acquisition device 1, located at point B, and deducing therefrom a second estimate T'B of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a second time-stamping means 13 associated with the second data acquisition device.

[0034] As schematically illustrated in [Fig.5], and taking into account the fact that the sampled signal corresponds to the sinusoidal electrical signal at the fundamental frequency of the electrical network (i.e. at 50 Hz or 60 Hz depending on the country), this signal passes through zero twice during each signal period. In other words, each zero crossing detection module will be able to detect a pair of zero crossings for each period of the periodic signal sampled at the device 1 located at point A, respectively of the periodic signal sampled at the device 1 located at point B. Each device will also be able to locally time-stamp each zero crossing detection via its time-stamping means 13. If we note: {( ZCAÎ,ZCA?) ,(Z^ ), respectively {(ZCB1,ZCB2),(ZCB1,ZCB2),...,(ZCbhZCB24)} M successive pairs of zero crossings detected by the device 1 located at point A, respectively at point B, and { (tzCA;,tZCA?), (tzCA,,tzCAi \ / A)}, respectively {( tzc^tzc^ ), ( tzc^tzc^ tzc^tzc^ )} the pairs of associated instants obtained by local timestamping via the timestamping means 13 associated with the data acquisition device 1 located at point A, respectively at point B, the estimate T'A, respectively T'B> of the period of the periodic signal is calculated according to the relation: rp' __ NI ^xL^tzc^-tzcJ respectively TB=2x£“ ( ( tzc <tzC|(} The larger the integer M, the more we avoid fluctuations that could affect the periodic signal due to overload or the presence of equipment in the network. The integer M can be, for example, 100, or even 200 or 300.

[0035] Once each device has been able to locally estimate the period T'A or T'B of the sampled periodic signal, the method 100 continues with a second synchronization phase comprising the following steps (see jointly figures 4 and 6):

[0036] The data acquisition device 1 located at point A sends, during a step 120, an information signal s(t) at a first detection instant tZCAi.i, locally time-stamped, of a new zero crossing of the signal taken at the level of this data acquisition device 1. As seen previously, this signal s(t) can be sent by any transmission channel (by the network itself by injecting the signal into the cable or by cellular communication or by Ethernet. The signal s(t) can be of any type.

[0037] During a step 130, the information signal s(t) is received by the data acquisition device 1 located at point B, after a duration corresponding to the flight time T between the two points A and B. Note that this flight time T is generally of the order of a microsecond for a maximum distance of approximately 15 km separating the two points A and B. During this step 130, the instant of reception of this information signal s(t) is locally time-stamped by the local time-stamping means 13 associated with this device 1.

[0038] During a step 140, the data acquisition device 1, localized triggering at point A, triggers a first phase of acquisition of high-frequency events by its sensor 11, over a plurality of successive cycles of predefined cycle duration Tm, the first acquisition phase being triggered at a first triggering instant tRA determined locally by the first local time-stamping means 13 and separated from the first detection instant tZCAi,i of a duration corresponding to the first estimation T'A of the period of the electrical signal.

[0039] Furthermore, after the elapse of a duration corresponding to T'B / 2 following the instant of reception of the signal s(t), the data acquisition device 1 located at point B triggers, during a step 150, a second phase of acquisition of high-frequency events by its own sensor 11, over a plurality of successive cycles of predefined cycle duration, the second acquisition phase being triggered at a second trigger instant tRB determined locally by the second means timestamp 13 and corresponding to a second instant of detection of a new zero crossing of the signal taken at the level of the second data acquisition device 1.

[0040] In a particularly advantageous embodiment, the predefined cycle duration for each cycle of the first data acquisition phase corresponds to the first estimate T'A of the period of the electrical signal, and the predefined cycle duration for each cycle of the second data acquisition phase corresponds to the second estimate T'B of the period of the electrical signal. Consequently, the cycle durations for the two phases correspond to each other.

[0041] As shown in [Fig.6], the triggering times TRA and TRB, although measured locally by each time-stamping means 13, are supposed to coincide in a common time frame.

[0042] As a result, it is possible to determine, during a step 160, determination, a difference in synchronization Atoa between a first high-frequency event and a second high-frequency event acquired, over a given cycle, respectively by the data acquisition device 1 located at point A, at a first acquisition instant locally time-stamped by its own time-stamping means 13, and by the second data acquisition device 1 located at point B, at a second acquisition instant locally time-stamped by its own time-stamping means 13 by simple calculation of the difference between the second triggering instant tRB and the first triggering instant t^. This calculation can be carried out locally (for example at the level of the first device 1 located at point A) or centralized at the level of the remote server.

[0043] In one possible embodiment, the successive cycles in the first phase and the second phase of data acquisition are separated two by two by a predefined spacing duration Ts corresponding to a predefined number of consecutive zero crossings.

[0044] Alternatively, the successive cycles in the first phase and the second phase of data acquisition are consecutive, which amounts to saying that the spacing duration Ts is zero.

[0045] In all cases, a cycle (n+1) for the device 1 located at point A, respectively at point B, begins at an instant 1ra, respectively 1rr, which can An+1 Bn+1 express itself as a function of the previous cycle n, according to the relationship: tR. = tOaA + Tm + T respectively tR - toa + Tm + T so that, for each cycle n, we keep the relation ^oat> “ ^oa» — R An+1 nn+l

[0046] Any high-frequency event capable of being detected by the detection means 11 of the device 1 located at point A or of the device 1 located at point B during data acquisition phases will subsequently be able to be time-stamped first locally, via the local time-stamping means 13, then in a common reference base thanks to the knowledge of the difference in Atoa synchronization between the two data acquisition devices 1.

[0047] In the non-limiting case where the data acquisition devices 1 are dedicated to the detection of high-frequency events corresponding to signals uA(t) and uB(t) generated by the same partial discharge 2, the method further comprises a step (not shown) of calculating the location ZPD of the partial discharge according to the relation „ TOF- Atoa 1 jans iaqueiie [ is a length of cable between the first and the ^PD- 2TOF' A ior second data acquisition device (1).

[0048] This calculation step can for example be carried out at the level of the remote central server.

[0049] Steps 110 to 160 are preferably repeated periodically (for example one or more times per day) so as to compensate for drifts which may affect the network, such as temperature changes, overloads, and / or dispersion in the meters 13).

Claims

1. Claims Method for synchronizing between at least a first device (1) and a second device (1) for acquiring data from an online monitoring system of an electrical distribution network, each data acquisition device (1) being located at a known point in the network and being configured to detect high-frequency events during data acquisition phases, the method comprising: a first phase (110) of estimations of the period of the electrical signal traveling through the network consisting of: - taking the electrical signal traveling through the network at the first data acquisition device (1) and deducing therefrom a first estimate T'A of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a first time-stamping means (13) associated with the first data acquisition device (1); - taking the electrical signal traveling through the network at the second data acquisition device (1) and deducing therefrom a second estimate T'B of the period of the electrical signal by detecting the instants of zero crossings of the sampled signal, locally time-stamped by a second time-stamping means (13) associated with the second data acquisition device; followed by a second synchronization phase comprising the following steps: - sending (120) by the first data acquisition device of an information signal at a first detection instant tZcAi.i, locally time-stamped, of a new zero crossing of the signal taken at the level of the first data acquisition device (1); - local timestamp (130) of the time of reception of said information signal by the second data acquisition device; - triggering (140), by the first data acquisition device, of a first phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the first acquisition phase being triggered at a first triggering instant tRA determined locally by the first time-stamping means (13) and separated from the first triggering instant detection of a duration corresponding to the first estimate T'A of the period of the electrical signal; - after the lapse of a duration corresponding to half of the second estimate T'B of the period of the electrical signal following said reception time, triggering (150), by the second data acquisition device (1), of a second phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the second acquisition phase being triggered at a second trigger time tRB determined locally by the second time-stamping means (13) and corresponding to a second time of detection of a new zero crossing of the signal taken at the level of the second data acquisition device (1);and - determination (160) of a difference in synchronization Atoa between a first high-frequency event and a second high-frequency event acquired, over a given cycle, respectively by the first data acquisition device (1) at a first acquisition instant locally time-stamped by the first time-stamping means (13) and by the second data acquisition device (1) at a second acquisition instant locally time-stamped by the second time-stamping means (13) by calculating the difference between the second triggering instant tRB and the first triggering instant tRA.;

2. The method of claim 1, wherein the predefined cycle duration for each cycle of the first data acquisition phase corresponds to the first estimate T'A of the period of the electrical signal, and the predefined cycle duration for each cycle of the second data acquisition phase corresponds to the second estimate T'B of the period of the electrical signal.

3. Method according to any one of the preceding claims, characterized in that the successive cycles in the first phase and the second phase of data acquisition are consecutive.

4. Method according to any one of claims 1 to 2, characterized in that the successive cycles in the first phase and the second phase of data acquisition are separated two by two by a predefined spacing duration Ts corresponding to a predefined number of consecutive zero crossings.

5. Method according to any one of the preceding claims, characterized in that the first high-frequency event detected by the first data acquisition device (1) and the second high-frequency event detected by the second data device (1) on a given cycle correspond to two signals generated by the same partial discharge (2) at a point of the network located between the first and second data acquisition devices (1), and in that the method further comprises a step of calculating the location ZPD of the partial discharge according to the relationship Zpd-T2tof” 1 in which is a length of cable between the first and second data acquisition devices (1).

6. 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 data acquisition phases, the online monitoring system being characterized in that it comprises: - a first local time-stamping means (13) and a first zero-crossing detection module (12), associated with the first data acquisition device (1), and configured to sample the electrical signal traveling through the network at the first data acquisition device (1) and detect the zero-crossing instants of the sampled signal, locally time-stamped by the first time-stamping means (13);- a second local time-stamping means (13) and a second zero-crossing detection module (12), associated with the second data acquisition device (1), and configured to sample the electrical signal traveling through the network at the second data acquisition device (1) and detect the zero-crossing instants of the sampled signal, locally time-stamped by the second time-stamping means (15); and - synchronization means configured to: during a first estimation phase, deduce a first estimate T'A of the period of the electrical signal from zero-crossing instants successively locally time-stamped by the first time-stamping means (13), and a second estimate T'B; of the period of the electrical signal from zero crossing times successively time-stamped locally by the second time-stamping means (13), and to perform a second synchronization phase comprising the following steps: - sending (120) by the first data acquisition device of an information signal at a first detection instant tZCAi.i, locally time-stamped, of a new zero crossing of the signal taken at the level of the first data acquisition device (1); - local timestamping (130) of the instant of reception of said information signal by the second data acquisition device; - triggering (140), by the first data acquisition device, of a first phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the first acquisition phase being triggered at a first trigger instant ^determined locally by the first timestamping means (13) and separated from the first detection instant by a duration corresponding to the first estimate T'A of the period of the electrical signal; - after the lapse of a duration corresponding to half of the second estimate T'B of the period of the electrical signal following said reception time, triggering (150), by the second data acquisition device (1), of a second phase of acquisition of high-frequency events over a plurality of successive cycles of predefined cycle duration, the second acquisition phase being triggered at a second trigger time tRB determined locally by the second time-stamping means (13) and corresponding to a second time of detection of a new zero crossing of the signal taken at the level of the second data acquisition device (1); and - determination (160) of a difference in Atoa synchronization between a first high-frequency event and a second high-frequency event acquired, over a given cycle, respectively by the first data acquisition device (1) at a first acquisition instant locally time-stamped by the first time-stamping means (13) and by the second data acquisition device (1) at a second acquisition instant locally time-stamped by the second time-stamping means (13) by calculating the difference between the second triggering time tRB and the first triggering time tRA.

7. System according to claim 6, characterized in that the first timestamping means and the second timestamping means are N-bit counters, N being an integer greater than or equal to 16.

8. System according to any one of claims 6 and 7, wherein the first time-stamping means (13) is integrated into the first data acquisition device (1), and / or the second time-stamping means is integrated into the second data acquisition device (1).

9. A system according to any one of claims 6 to 8, wherein the first zero crossing detection module (12) is integrated with the first data acquisition device (1), and / or the second zero crossing detection module (12) is integrated with the second data acquisition device (1).

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