Electrical protection system and method

Abstract

The method comprises the following steps: - measuring (102, 104) a voltage and a current in an electrical link; - repeatedly calculating (106, 108) a first moving average and a second moving average based on the measured current value, the second moving average being calculated over a longer duration than the first moving average; - comparing the measured voltage value with a predefined voltage threshold (120); - comparing the current value of the first moving average with the current value of the second moving average (132); - identifying (134) a triggering condition of a protection device when the measured voltage value is lower than the predefined voltage threshold for a duration longer than the predefined duration threshold and when the current value of the first moving average is higher than the current value of the second moving average.

Description

Technical Field

[0001] The present invention relates to the field of power distribution networks, and more particularly to microgrids or nanogrids. Background Art

[0002] Microgrids are typically used in residential, commercial or industrial buildings to generate and store electricity locally while also being connected to the mains distribution grid.

[0003] Microgrids facilitate the use of distributed energy resources, more specifically renewable energy sources, such as wind turbines, tidal stream generators, or photovoltaic panels. Microgrids may also include energy storage devices such as batteries. Microgrids can be used to ensure a stable and continuous supply of electricity when the main power grid is not reliable enough.

[0004] In practice, a microgrid is used to supply power to one or more electrical loads protected by electrical protection devices such as circuit breakers or fuse-based disconnect switches, whether or not those electrical protection devices are remotely controlled.

[0005] However, a disadvantage of microgrids is that it is difficult to manage electrical faults when the microgrid is disconnected from the main grid.

[0006] It is particularly desirable to be able to quickly isolate and locate the source of an electrical fault without affecting the power supply to the rest of the microgrid.

[0007] Typically, when a microgrid is connected to the main grid, the latter absorbs transient variations in load and ensures that the amplitude and frequency of the voltage are stable. Furthermore, in the case of an electrical fault of the short circuit or insulation fault type, the overcurrent caused by this fault has values ​​of high magnitude, for example, of the order of 10 to 20 times the nominal current value of the installation. The electrical protection devices affected by the fault react automatically and quickly, which allows the part of the microgrid that causes the electrical fault to be isolated without affecting the operation of the rest of the microgrid.

[0008] However, this performance is not guaranteed when the mains grid is disconnected.

[0009] Traditionally, many microgrids have included engine-generators in addition to energy storage and renewable energy, which has been satisfactory for a long time.

[0010] Generally, such engine-generators include an internal combustion engine (such as a diesel engine) coupled to a rotating machine (such as an alternator).

[0011] In particular, when the microgrid is disconnected from the main grid, the engine generator allows the microgrid to be stabilized and to play a role comparable to that normally played by the main grid in the event of an electrical fault, which allows ensuring that the electrical fault is handled satisfactorily.

[0012] However, due to new environmental standards and increased regulatory constraints, it is sometimes no longer desirable to use diesel engine-driven generators in microgrids. Nevertheless, it is still necessary to ensure that the microgrid performs satisfactorily in the event of an electrical fault.

[0013] In practice, in the absence of an engine-driven generator, when the microgrid is disconnected from the main grid, the power supply is ensured with the help of energy storage devices and inverters of renewable energy production devices, however, the inverter has different performance from the alternator of the engine-driven generator, in particular because the alternator has mechanical inertia due to its structure, which facilitates stabilization of the microgrid in the event of breakage and conveys significant overcurrents in the event of a short circuit.

[0014] Specifically, energy sources such as solar panels are generally current sources that are servo-controlled by a voltage source. In such a microgrid, the voltage source is formed by an inverter of an energy storage device.

[0015] One problem is that in the event of an electrical fault, the inverter of the energy storage device can only maintain power for a very short duration, typically a few seconds at most before failing and terminating power to the microgrid.

[0016] Furthermore, the magnitude of the inverter overcurrent is very close to the magnitude of the nominal current, for example, about 1.2 times the magnitude of the nominal current. Such overcurrent is not large enough in magnitude and duration to ensure that most conventional electrical protection devices such as fuses or electromechanical circuit breakers are actually triggered.

[0017] As a result, there is a risk that the protection devices will not be able to perform their functions and the inverter will stop supplying power to the microgrid before the electrical fault can be located and isolated. When the inverter is reinstalled, the fault will still exist and will cause the microgrid to fail again, thus complicating the search and isolation of the fault by the maintenance team.

[0018] There is also a risk that electrical faults will damage the microgrid and cause a fire due to the long reaction time of protection equipment in this environment.

[0019] In microgrids, it is not always possible or desirable to use devices such as ANSI 51V type protection devices to protect against voltage-related overcurrents, on the one hand due to the high cost of implementation (since this usually requires the addition of electronic protection relays external to the circuit breakers), and on the other hand due to the complexity of their installation and their parameterization (since this requires the adjustment of several additional parameters for each protection device, the calculation of specific protection plans, etc.), which takes more time and requires more advanced or extraordinary skills from the installer and the design team responsible for installing and maintaining the microgrid.

[0020] Therefore, there is a need for a solution that allows detection of electrical faults in electrical installations, in particular in microgrids, and more specifically in microgrids without diesel engine-driven generators, which solution is reliable, inexpensive and easy to implement. Summary of the invention

[0021] To this end, according to one aspect of the present invention, a method is provided, the method comprising the following steps performed by an electronic monitoring module associated with an electrical protection device:

[0022] - repeatedly measuring the voltage and current in an electrical link associated with said electrical protection device;

[0023] - repeatedly calculating a first moving average and a second moving average based on the measured current value, the second moving average being calculated over a longer duration than the first moving average;

[0024] - comparing the measured voltage value with a predefined voltage threshold;

[0025] - comparing the first moving average current value with the second moving average current value;

[0026] A triggering condition of the protection device is identified when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than the second moving average current value.

[0027] The use of a moving average calculated from the measured current values ​​allows the detection of electrical faults with a triggering threshold which automatically adapts to the operating conditions of the electrical network of which the electrical link and the protection device form part.

[0028] By means of the invention, the detection of electrical faults is thus performed more reliably and in a relatively simple manner.

[0029] According to an advantageous but non-mandatory aspect, this method may combine one or more of the following features, which may be implemented individually or in any technically acceptable combination:

[0030] The method further comprises issuing a warning signal by the electronic monitoring module when a triggering condition is identified.

[0031] The method comprises, when a trigger condition is identified, sending, by the electronic monitoring module, a trigger signal for the protection device.

[0032] The method further comprises, when a trigger condition is identified, storing, by the electronic monitoring module, in a memory a state variable indicating the presence of the trigger condition, and starting from the start of the electronic monitoring module, if the state variable stored in the memory indicates the presence of the trigger condition, the trigger condition is identified.

[0033] When a trigger condition is identified, the method further comprises the steps of: waiting for a predefined duration, then measuring the voltage value again, and if the measured voltage value is below the voltage threshold, disabling the trigger condition.

[0034] - The method further comprises:

[0035] - acquiring status information emitted by a second electronic monitoring module similar to said electronic monitoring module and associated with a second protection device connected to the same electrical link downstream of said protection device;

[0036] If the acquired status information indicates that the second electronic monitoring module has identified a triggering condition for a second protection device, the triggering condition of said protection device is inhibited.

[0037] The first moving average is calculated over a first duration shorter than or equal to 1 second and preferably shorter than or equal to 500 milliseconds, and the second moving average is calculated over a second duration longer than the first duration and preferably at least five times longer than the first duration, the second duration being, for example, shorter than or equal to 10 seconds or shorter than or equal to 5 seconds.

[0038] According to another aspect, the invention relates to a system comprising an electrical protection device and an electronic monitoring module associated with the electrical protection device, the electronic monitoring module being programmed to implement the following steps:

[0039] - repeatedly measuring the voltage and current in an electrical link associated with said electrical protection device;

[0040] - repeatedly calculating a first moving average and a second moving average based on the measured current value, the second moving average being calculated over a longer duration than the first moving average;

[0041] - comparing the measured voltage value with a predefined voltage threshold;

[0042] - comparing the first moving average current value with the second moving average current value;

[0043] A triggering condition of the protection device is identified when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than the second moving average current value.

[0044] According to an advantageous but non-mandatory aspect, such a system may incorporate one or more of the following features, which may be implemented individually or in any technically acceptable combination:

[0045] The electronic monitoring module is integrated into the protection device, the electronic monitoring module being implemented, for example, by an electronic tripping device of the protection device.

[0046] - The electronic monitoring module is separated from the protection device and installed outside the protection device.

[0047] According to yet another aspect, the present invention relates to a power grid, in particular a microgrid, comprising:

[0048] - power storage and / or power generation equipment, which supplies power to the main link;

[0049] - At least one electrical load connected to the main link via a protection system as described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention will be better understood and other advantages of the invention will become more apparent from the following description of an embodiment of such a method, which description is given by way of example only and with reference to the accompanying drawings, in which:

[0051] Figure 1 is a schematic diagram of an example of a power distribution network;

[0052] Figure 2 is a schematic diagram of an electronic monitoring module according to an embodiment of the present invention, the electronic monitoring module and Figure 1 It is related to the electrical protection equipment of the China Power Grid;

[0053] Figure 3 According to the first embodiment Figure 2 A flowchart of an example method of operating an electronic monitoring module;

[0054] Figure 4 yes Figure 2 A timing diagram of a first example of operation of an electronic monitoring module;

[0055] Figure 5 yes Figure 2 a timing diagram of a second example of operation of the electronic monitoring module;

[0056] Figure 6 According to the second embodiment Figure 2 A flow chart of an example of a method of operation of an electronic monitoring module. DETAILED DESCRIPTION

[0057] Figure 1 An example of a power distribution network 2 , such as a microgrid, is schematically shown.

[0058] The electrical network 2 comprises a main electrical link 4 which is connected here via a protection device 10 , such as a circuit breaker, to a main distribution network 8 , such as a mains distribution network.

[0059] For example, the electrical link 4 comprises electrical conductors, such as cables or busbars of a switchboard.

[0060] The main grid 8 is capable of delivering an electrical power supply and can be selectively disconnected from the grid 2 .

[0061] According to an example, the electrical network 2 is installed in a residential, commercial or industrial facility.

[0062] The grid 2 comprises one or more power generation devices (preferably renewable energy sources such as wind turbines, tidal stream generators or photovoltaic panels) and one or more energy storage devices (such as batteries).

[0063] In the illustrated example, the power grid 2 includes:

[0064] a photovoltaic source SOL connected to the main link 4 via an inverter 12 and a protection device 14 , and

[0065] An energy storage device STOR connected to the main link 4 via an inverter 16 and a protection device 18 .

[0066] Preferably, the grid 2 is free of engine-driven generators, such as diesel engine-driven generators, or more generally, of any generators including rotating machinery, such as alternators. In the event that such an engine-driven generator is physically present in the grid 2, the engine-driven generator is preferably disconnected from the grid 2 or kept in a stopped state.

[0067] The electrical network 2 also comprises one or more electrical loads intended to be powered by means of electricity delivered by the main electrical network 8 and / or an energy storage device and / or a power generation device.

[0068] The electrical loads are connected to the main supply link 4 via electrical protection devices 20 such as circuit breakers or fuse-based disconnect switches, or equivalent protection devices, whether or not they are remotely controlled.

[0069] For example, according to the prior art, each protection device 20 is configured in a known manner to switch the flow of current in an electrical link of the electrical network 2 when the current flowing through the electrical network 2 is above a triggering threshold.

[0070] Specifically, each protective device is switchable between an electrically open state that prevents the flow of current and an electrically closed state that allows the flow of current.

[0071] According to an example of embodiment, the protection device 20 employs electromechanical technology and may comprise separable electrical contacts or any other electrical disconnecting means that can be switched by means of a controllable actuator, for example an electromagnetic actuator.

[0072] The electrical network 2 also includes an electronic monitoring module 22 associated with one or more protection devices 20, the function of which will be described in more detail below.

[0073] In the illustrated example, a first group of electrical loads, such as the critical loads indicated by reference Q1 , are connected to the main power supply link 4 , for example via an uninterruptible power supply UPS and a first protection device 20 equipped with a monitoring module 22 .

[0074] A second group of electrical loads LOAD is connected to the main power supply link 4 via a second protection device 20 equipped with a monitoring module 22 .

[0075] The third group of electrical loads is connected to the main power supply link 4 via a plurality of protection devices 20 installed in cascade, here by means of secondary power supply links connected in parallel and arranged, for example, in a hierarchical manner.

[0076] For example, reference 24 denotes a secondary power supply link associated with the foremost protection device 20 , here denoted by reference Q2 , and forming a first level of the hierarchy of the microgrid 2 .

[0077] Downstream of the foremost protection device 20 , a secondary power supply link 24 is shared between three branches, each branch comprising one protection device 20 and a monitoring module 22 associated with one protection device 20 , here forming a second level.

[0078] exist Figure 1 In FIG. 2 , the protection devices 20 of the second level have been denoted by reference numeral “ 20 - 3 ”, and one of them is denoted here by reference numeral Q3 .

[0079] One or more electrical loads may be connected directly or indirectly downstream of the protection device of level Q3.

[0080] Also in the illustrated example, one of these branches, downstream of its protection device 20, is itself subdivided into three other branches, for each of which one or more electrical loads are connected to the branch via the protection device 20, where the protection device 20 does not include a monitoring module 22, which defines a third level.

[0081] exist Figure 1 , the protection devices 20 of the third level have been denoted by reference numeral “ 20 - 4 ”, one of which has been denoted by reference numeral Q4 .

[0082] In order to Figure 1 For easier reading, not all electrical loads are illustrated and shaded parts of the electrical network 2 are schematically represented by dots.

[0083] It will be understood that reference Figure 1 The described electrical network 2 is given by way of example, which is not necessarily limiting, and as a variant, the electrical network 2 may be different and may, for example, have a different architecture and / or a different topology and / or include electrical loads and / or generation devices and / or energy storage devices which differ in their nature and / or number and / or in their arrangement in the electrical network 2. However, the invention relates primarily to applications in which the energy source is connected to the power supply link 4 and is not placed downstream of the protection device 20.

[0084] According to some embodiments, as in the illustrated example, not all protection devices 20 are equipped with a monitoring module 22 .

[0085] In practice, in a preferred variant, only the rated current I n The protection device 20 is equipped with a monitoring module 22 which is higher than or equal to about 1 / 10 of the nominal current of the inverter 16 of the energy storage device.

[0086] Figure 2 One of the monitoring modules 22 associated with one of the protection devices 20 is shown, for example a monitoring module 22 installed on a power supply link to which the protection device 20 is connected.

[0087] In the illustrated example, the power supply link 24 is a three-phase link and comprises three electrical conductors 26 , each associated with one electrical phase.

[0088] According to other variants (not shown), the embodiments described below can be extended to other types of power grids, such as a single-phase two-conductor (neutral and phase) power grid, a two-phase two-conductor (two phases) power grid or a three-conductor (two phases and neutral) power grid, or even a three-phase four-conductor (three phases and neutral) power grid.

[0089] The protection device 20 is therefore suitable for switching the three-phase current flowing in these conductors 26 .

[0090] Reference numeral 28 denotes a system formed by the association of the protection device 20 and the monitoring module 22 .

[0091] For example, the monitoring modules 22 of the electrical network 2 are similar or identical to each other and operate similarly.

[0092] The monitoring module 22 comprises an electronic processing unit 30 , a set of sensors 32 for measuring current and voltage values ​​in the power supply link 24 , and a communication interface.

[0093] According to an embodiment, the electronic processing unit 30 comprises a computing logic unit, such as a programmable microcontroller or microprocessor, and a computer memory forming a computer-readable data storage medium.

[0094] For example, the memory is a ROM, a RAM or a non-volatile memory such as an EPROM, an EEPROM, a FLASH memory or an NVRAM or an optical memory or a magnetic memory.

[0095] Here, the memory comprises executable instructions or modules of software code, which, when executed by the computing logic unit, are preferably suitable for implementing a detection method, such as the detection method described in the following examples.

[0096] As a variant, the electronic processing unit 30 comprises a programmable logic component such as an FPGA or an application-specific integrated circuit such as an ASIC configured to implement the detection method.

[0097] According to an embodiment, the sensor 32 allows measuring the magnitude of the current flowing in the power supply link associated with the monitoring module 22 , so as to measure, for example, the magnitude of the current in each phase 26 .

[0098] The sensor 32 also allows the voltage on the two phase lines 26 and / or on one or more individual phase lines 26 to be measured, for example relative to a reference potential.

[0099] For example, the set of sensors 32 includes one or more current sensors and one or more voltage sensors. The current sensor may include a Rogowski coil, a current transformer, a Hall effect sensor or a shunt. The voltage sensor may include a shunt, a transformer or a capacitive sensor.

[0100] For example, the communication interface comprises a first output 34 for sending a trigger control signal to the protection device 20 and eg to an actuator 36 or a tripping device of the protection device 20 , in particular for switching the protection device 20 to an open state if an electrical fault is detected.

[0101] Advantageously, the monitoring module 22 is also connected to the protection device 20 in order to determine the open or closed state of the protection device 20 .

[0102] According to an example, the communication interface further comprises a second output 38 for sending a warning signal, in particular to a user.

[0103] For example, the second output 38 includes a connector or dry contacts for controlling a remote device, such as a relay, indicator light, or sounder, that is directly connected to the second output 38 .

[0104] As a variant, the communication interface may incorporate a communication device capable of sending such a warning signal, such as an indicator light or a sounder, or an electronic human-machine interface device comprising, for example, a display screen.

[0105] According to other variants, the second output 38 comprises a radio frequency interface for sending the warning signal via a radio communication link, for example a telelink.

[0106] Depending on the implementation possibilities, Figure 2 As shown, the monitoring module 22 is separate from the protection device 20, ie it is a matter of a separate and independent element from the protection device 20. Here, the monitoring module 22 is mounted outside the protection device 20.

[0107] According to other possibilities of embodiment, the monitoring module 22 is integrated into the protection device 20. For example, the monitoring module 22 can be a separate and independent element from the protection device 20, while being accommodated in the housing of the protection device 20.

[0108] As a variant, the monitoring module 22 is implemented, for example in the form of software, by an electronic control unit belonging to the protection device 20 , such as an electronic tripping device.

[0109] In this case, the monitoring module 22 does not necessarily have a communication interface or input / output dedicated thereto, but can instead use a communication interface or input / output of the electronic control unit of the protection device 20 .

[0110] Generally, each of the monitoring modules 22 is programmed to implement the following steps:

[0111] - measuring voltages and currents in an electrical link 24 associated with a protection device 20 associated with a monitoring module 22 ;

[0112] - calculating a first moving average, called short average, and a second moving average, called long average, from the measured current values;

[0113] - comparing the measured voltage value with a predefined voltage threshold;

[0114] - comparing the first moving average current value with the second moving average current value;

[0115] A triggering condition of the protection device 20 is identified when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than or equal to the second moving average current value.

[0116] The steps of measuring, calculating and comparing are for example performed repeatedly over time, and for example repeated periodically.It will therefore be appreciated that the first moving average and the second moving average are constituted by a plurality of measurements of the current performed over time at a plurality of moments.

[0117] For example, a comparison of the currents and a comparison of the voltages may be performed for each phase line or for a plurality of phase lines.

[0118] According to one example, on the one hand, for one phase line, the voltage is compared with said threshold value and, on the other hand, for the same phase line, a moving average calculated from the measured current is compared.

[0119] According to another example, the voltage developed between the two phase lines is compared with the threshold value and the moving averages are compared in order to detect an increase in the current on the two phase lines.

[0120] In practice, the trigger condition indicates the presence of an electrical fault of the short circuit or insulation fault type.

[0121] Depending on the embodiment, once a trigger condition has been identified, the monitoring module 22 may take one or more actions to remedy the cause of the fault, such actions including, for example, sending a trigger signal via output 34, and / or sending a warning signal via output 38 or any suitable element of the communication interface.

[0122] Advantageously, the presence of the triggering condition is recorded in a memory of the unit 30 , for example in the form of a first state variable.

[0123] For example, the first state variable may take a first value (inactive state) indicating that the trigger condition does not exist or a second value (active state) indicating that the trigger condition exists.

[0124] In practice, the first moving average is calculated based on first samples of current values, which are accumulated during a first duration. The second moving average is calculated based on second samples of current values, which are accumulated during a second duration that is longer than the first duration. In other words, the second moving average is calculated over a longer duration than the first moving average.

[0125] Advantageously, the first duration is shorter than or equal to 1 second or shorter than or equal to 500 milliseconds, preferably shorter than or equal to 200 milliseconds or even equal to 100 milliseconds. The second duration is at least five times longer than the first duration, while preferably shorter than or equal to 10 seconds or shorter than or equal to 5 seconds, for example.

[0126] According to an example, the first moving average is an exponential moving average. The second moving average is an arithmetic average.

[0127] As a variant, the first moving average and the second moving average may be selected differently.

[0128] The use of a moving average calculated from the measured current values ​​allows the detection of electrical faults with a triggering threshold that automatically adapts to the operating conditions of the electrical network 2 .

[0129] By means of the invention, electrical faults are thus detected more reliably and in a relatively simple manner.

[0130] According to an optional embodiment, when a trigger condition is identified, the monitoring module 22 waits for a predefined duration (represented as T4 here) and then measures the voltage value again. If the measured voltage value becomes higher than the voltage threshold again, the trigger condition is disabled.

[0131] This delay makes it possible to avoid triggering the protection device 20 if the voltage has returned to nominal amplitude by this time, which reduces the risk of false alarms.

[0132] In an advantageous but still optional embodiment, the monitoring module 22 comprises an output 40 and an input 42 intended to be connected to other monitoring modules 22 , for example when a plurality of protection devices 20 are installed in cascade.

[0133] This allows, in particular, electrical faults to be isolated at the correct level between a plurality of circuit breaker devices connected in cascade within the electrical network 2 .

[0134] For example, output 40 delivers a signal, noted Sel_out, to a monitoring module 22 associated with an upstream protection device 20. Input 42 receives a signal, noted Sel_in, originating from one or more monitoring modules 22 associated with one or more protection devices 20 installed downstream.

[0135] exist Figure 1 In the example of FIG. 4 , the output 40 of the monitoring module 22 of the Q3 stage is connected to the input 42 of the monitoring module 22 of the Q2 stage located upstream.

[0136] For example, when multiple downstream monitoring modules 22 are connected downstream of the monitoring module 22 , the downstream modules are connected in parallel so that the input 42 can receive the signal Sel_in when one or more of the downstream monitoring modules 22 sends a corresponding signal.

[0137] Advantageously, but still optionally, the monitoring module 22 may store in a memory, for example in the form of a second state variable, information representative of the state of one or more downstream monitoring modules 22 connected to the input 42 .

[0138] For example, the second state variable can take a first state and a second state, wherein the first state corresponds to the absence of the signal Sel_in on the input 42, indicating that there is no trigger condition in the downstream module 22, and the second state corresponds to the presence of the signal Sel_in received on the input 42, indicating that there is a trigger condition in one of the downstream modules 22.

[0139] Thus, according to an embodiment including such selective management, the method may further include:

[0140] - obtaining status information issued by a downstream second monitoring module 22 associated with a second protection device 20 connected downstream of the protection device 20;

[0141] If the acquired status information indicates that the second monitoring module 22 has identified a triggering condition for the second protection device 20 , the triggering condition of the protection device 20 is disabled.

[0142] This makes it possible not to trigger the protection device 20 situated upstream when one of the downstream protection devices 20 has detected a fault. Thus, neutralization of the power supply of branches of the network 2 that are not related to the electrical fault is avoided.

[0143] According to an example of implementation, when a delay of the application waiting time T4 is used in a plurality of monitoring modules 22 associated with a cascade-installed protection device 20, the waiting time of the monitoring module located downstream is preferably shorter than the waiting time of the monitoring module located upstream. For example, for the monitoring module 22 of the Q2 level, the waiting time T4 is equal to 300 milliseconds, while for the monitoring module 22 of the Q3 level, the waiting time is equal to 200 milliseconds.

[0144] This makes it possible in particular to ensure the selectivity of the triggering of cascade-connected circuit-breaking devices within the electrical network 2 , for example in the same branch of the electrical network 2 originating from the link 24 .

[0145] Figure 3 An example of the operation of the monitoring module 22 according to the first embodiment is now shown.

[0146] The first embodiment can be particularly advantageously used for multiple monitoring modules 22 and protection devices 20 connected in cascade (such as Figure 1 even though other uses are possible.

[0147] In step 100 , the monitoring module 22 is turned on.

[0148] In a step 102 which is repeated over time, a measurement of the voltage is performed by the sensor 32. In parallel, in a step 104 which is also repeated over time, a measurement of the current is performed by the sensor 32.

[0149] As the current and voltage measurements are repeated, a first moving average is calculated in step 106 and a second moving average is calculated in step 108 .

[0150] For example, the calculation is automatically performed by the unit 30 , and the calculated first and second moving average current values ​​are stored in a memory of the unit 30 .

[0151] According to an alternative embodiment, in parallel, the monitoring unit 22 carries out one or more diagnostic steps immediately after its switching on.

[0152] For example, in step 110 the unit 22 determines whether the protection device 20 is in the open state and, if this is the case, resets the first state variable to a first value in step 112 .

[0153] Where appropriate, in step 114 the second state variable is reset to indicate that the trigger condition is not present in the downstream module.

[0154] In the event that the protection device 20 is identified as being in the closed state, then in step 116 the module 22 checks whether the first state variable is in the first state.

[0155] If this is not the case, step 114 is carried out.

[0156] If the first state variable is equal to the first value, then in step 118 the measured voltage is compared with a first predefined voltage threshold, for example equal to 70% of the nominal voltage for an adjustable minimum time, for example at least 50 milliseconds.

[0157] If the measured voltage is above the first threshold, step 112 is performed.

[0158] If the measured voltage is below the first threshold, step 120 is implemented, in which module 22 checks whether the second state variable is in the second state. If this is the case, the method passes to step 112.

[0159] In the opposite case, ie if the second state variable is equal to a second value indicating that no trigger condition is present downstream, a trigger condition is identified.

[0160] Thus, in this example, in step 122 , the module 22 sends a trigger signal in order to switch the protection device 20 to the open state.

[0161] As a variant, step 118 may be omitted and the method directly proceeds to step 120 .

[0162] In this first embodiment, after step 114, in a step 130 repeated over time, the measured voltage value is compared with a predefined voltage threshold in order to determine whether the measured voltage value is below the predefined voltage threshold for a first duration t1 that is longer than the predefined duration threshold.

[0163] For example, the voltage threshold is the same as the first predefined threshold. Here, the first duration is greater than or equal to the adjustable duration, for example, set to be equal to 50 milliseconds.

[0164] In parallel, in a step 132 which is repeated over time, the respective current values ​​of the first and second moving averages are compared to each other in order to determine whether the current value of the first (short) moving average has become higher (optionally with a predefined margin) than the current value of the second (long) moving average.

[0165] If the results of both comparisons performed in step 130 and step 132 are positive, a trigger condition is identified in step 134 .

[0166] In the opposite case, steps 102, 104, 106, 108, 130 and 132 continue to be repeated until the method ends.

[0167] Advantageously, the presence of a fault is stored in the memory in step 136. For example, the first state variable is equal to the second value.

[0168] Next, in step 138, the module 22 issues a status signal indicating the presence of a trigger condition. For example, the signal Sel_out is transmitted via the output 40 to one or more monitoring modules 22 connected upstream, where appropriate.

[0169] Preferably, in step 140 , module 22 starts counting down a predefined duration T4 , for example by means of a clock of circuit 30 .

[0170] In step 142, the monitoring module 22 checks the state of the input 42, in particular in order to detect a state message issued by the downstream monitoring module 22 indicating that the protection device 20 connected downstream is in a triggering condition. For example, in step 142, the module 22 detects whether the signal Sel_in received on the input 42 has a high value.

[0171] In this case, in step 144, the second state variable is changed to a second value to indicate that a trigger condition exists downstream of protection device 20. Next, in step 146, the first state variable is reset to its first value because the protection device located downstream has detected an electrical fault.

[0172] In the event that no status information is received when step 142 ends, step 141 is implemented to check whether delay T4 has reached its end point, ie whether the countdown of duration T4 started in step 140 has ended. If this is not the case, step 142 is implemented again.

[0173] Upon expiration of the predefined duration T4 , the module 22 automatically checks, in step 148 , whether the measured voltage is still below (or equal to) the voltage threshold.

[0174] If not, ie if the measured voltage value becomes higher than the voltage threshold again, the trigger condition is disabled and the module 22 stops emitting a status signal indicating the presence of the trigger condition in step 150 . The method restarts from step 114 .

[0175] If yes, ie the measured voltage value remains below (or equal to) the voltage threshold, module 22 checks whether the second state variable is equal to the second value in step 152. In other words, module 22 checks whether the second state variable indicates the presence of a downstream trigger condition.

[0176] If this is the case, the trigger condition is again disabled, since the module located downstream has detected the fault even if the voltage has not returned to normal levels. Step 154 ​​is then implemented, in which the waiting time T5 is counted down. The method then passes to the above-mentioned step 150. For example, the waiting time T5 is equal to 50 milliseconds.

[0177] This delay allows the downstream monitoring module to have sufficient time to trigger the corresponding downstream protection device.

[0178] In the event that the power supply to the grid 2 is interrupted before the protection device 20 has time to open, the indication that a fault exists is still stored in the memory during this time.

[0179] Generally, the use of the first state variable and / or the second state variable, although optional, is nevertheless advantageous since it allows information relating to fault detection in module 22 or in downstream modules to be stored in the memory even when the power supply of the grid 2 is interrupted prematurely, in particular due to a fault in the inverter 16.

[0180] If such an interruption occurs, the module 22 can still handle the electrical fault once the power supply is reestablished, by means of the information stored in the non-volatile memory of the circuit 30 , in particular by means of the above-mentioned diagnostic steps 116 , 118 and 120 .

[0181] At the end of step 152 , if the module 22 has not detected a trigger condition downstream, a trigger signal is sent in step 122 already described above to switch the device 20 to the disconnected state.

[0182] Advantageously, in step 156, a warning signal is also issued, for example using the above-mentioned communication interface.

[0183] In step 158, the module 22 checks whether the protection device 20 is in the disconnected state. If so, in step 160, the first state variable is reset to a first value indicating that no fault is present. Specifically, at this stage, since corrective actions have been taken via steps 156 and 158, storage in the memory is no longer necessary.

[0184] Optionally, in step 162, the module 22 checks whether the protection device 20 has been closed, for example after a manual reloading and reclosing operation performed by an operator. Step 162 is repeated until the protection device 20 is closed.

[0185] Once it is detected that the protection device 20 has been closed, the module 22 resets the warning signal in step 164. For example, the light signal is turned off, or the emission of the audio signal is stopped, or the transmission of the radio frame is stopped. The method then returns to step 150 described above.

[0186] Optionally, at the end of step 158, if the module 22 detects that the protection device 20 is not disconnected, the module 22 sends the control signal again (step 166), and then checks again whether the protection device 20 is in the disconnected state (step 168). If yes, the method goes to step 160. If not, the module 22 sends an error signal (step 170), for example using a communication interface, to indicate a fault of the protection device 20.

[0187] Figure 4 A timing diagram illustrating another example of the operation of the above-described method, which is implemented for the monitoring module 22 and the protection device 20 of the branch Q1 of the power grid 2 , is shown.

[0188] Curves 200 and 202 show the variation over time t (in arbitrary units) of the magnitude of the current I (expressed in amperes) and the voltage V (expressed as a percentage relative to the nominal value) respectively for an electrical link on which the protection device 20 is installed.

[0189] In the example shown, the electrical fault occurs at time t 1 , and at the subsequent time t 2 The current I as a function of time is constant except at time t 1 and t 2 In parallel, the average amplitude of the voltage V remains relatively constant except for the period t 1 and t 2 Therefore, module 22 is relatively constant at time t 1 Identify the triggering condition.

[0190] Graph 204 shows the memory state and the state signal within module 22 over time t. Here, they are illustrated as being able to take low values ​​(indicating an inactive state) and high values ​​(indicating an active state), although in practice other implementations are possible.

[0191] In this example, here, the countdown of duration T4 is at time t 1 The fault disappears before the waiting time T4 expires at time t 2 occur.

[0192] Here, the signal “Sel_out_Q1” indicating the status information delivered at the output 40 is output at the time t 1 is activated and at time t 2 End. The first state variable "Trip_mem_Q1" is at time t 1 Go to the active state and at time t 2 Return to the inactive state.

[0193] Since the monitoring module 22 is not connected to a downstream module in the branch Q1 , the signal “sel_in_Q1 ” indicating the state of the input 40 and the second state variable “sel_mem_Q1 ” remain inactive.

[0194] In practice, step 142 is continuously executed from the start of the countdown, without waiting for the end of the waiting time T4 at the end of step 140 .

[0195] Since the voltage has returned to the normal value before the waiting time T4 expires, the protection device 20 is not triggered. Therefore, the control signal "coil_Q1" remains inactive.

[0196] Figure 5 A timing diagram illustrating another example of the operation of the above-described method, which is implemented by the monitoring module 22 of the protection devices 20 - 3 and 20 - 4 of the power grid 2 , is shown.

[0197] Curves 210 and 212 show the magnitude of the current I (expressed in amperes) of the protection device Q2 and the current I (expressed in amperes) of one of the second-level protection devices 20-3, respectively, over time t (in arbitrary units). Curve 214 shows the voltage V (expressed as a percentage relative to the nominal value) over time t.

[0198] In the example shown, at time t' 1 , an electrical fault occurs at level Q3 downstream of protection device Q2. Due to the fault of inverter 16, the power supply of grid 2 is interrupted at a subsequent time t' 2 Interrupt. At time t' 3 , the inverter is reinstalled by the operator.

[0199] Therefore, the magnitude of the current changes from time t' 1 Starts to increase at time t' 2 Then it drops to zero and then from time t' 3 The amplitude of voltage V at time t' 1 decreased by half, and then at time t' 2 remains stable before dropping to zero, then at time t' 3 Sudden increase.

[0200] Graph 216 shows the memory state and the state signal within module 22 over time t. Here, they are illustrated as being able to take low values ​​(indicating an inactive state) and high values ​​(indicating an active state), although in practice other implementations are possible.

[0201] In this example, the symbol Q2 or Q3 in the signal name indicates that the signal is associated with the monitoring module 22 placed upstream (device Q2) or downstream (device Q3), respectively.

[0202] Lines "Timer_Q2" and "Timer_Q3" indicate the start and end of the countdown implemented in step 140. Here, for both modules, the countdown starts at time t' 1 The time t' starts and ends at different times because the duration T4 of the downstream module 22 (denoted as T4-Q3) is preferably selected to be shorter than the duration T4 of the upstream module 22 (denoted as T4-Q2). 3 In each case this is after expiration of both waiting times T4.

[0203] The signals "Sel_out_Q2" and "Sel_out_Q3" indicating status information delivered at the output 40 of the corresponding module 22 are both at time t' 1 is activated and at time t' after the power outage 2The signal “Sel_in_Q2” corresponds to the signal “Sel_out_Q3” emitted by the downstream module 23 and received on the input 40 of the upstream module 22 .

[0204] At time t' after step 146 1 Shortly thereafter, the second state variable "sel_mem_Q2" of the downstream module is activated. By virtue of being stored in the non-volatile memory, the second state variable is maintained even during interruptions in the power supply.

[0205] Similarly, the first state variables "Trip_mem_Q2" and "Trip_mem_Q3" are at time t' 1 It goes to the active state shortly thereafter and remains in the memory even during power supply interruptions. Since the state variable "sel_mem_Q2" is in the active state, "Trip_mem_Q2" is quickly reset.

[0206] Specifically, in practice, the input signal “sel_in” of the protection device can be activated at any time during the countdown of the duration T4 and thus reset the corresponding variable “sel_mem”.

[0207] When the power supply is reconnected, the module 22 is at time t' 3 Restart and read the values ​​of the first and second state variables stored in the memory, such as in steps 116 and 120.

[0208] At time t' 3 Soon after, since the fault only exists downstream, the downstream module 22 activates the control signal “coil_Q3” to trigger and open the corresponding downstream protection device 20 .

[0209] Instead, by virtue of selectivity, the trigger condition is disabled in the upstream module 22 and the control signal “coil_Q2” remains inactive.

[0210] Figure 6 A second embodiment of the invention is shown. Elements of this embodiment similar to elements of the first embodiment have been given the same reference numerals and are not described in detail as the above description can be transferred to the elements of the second embodiment.

[0211] For example, this second embodiment may advantageously be implemented in power grids using protection devices 20 of low cost and / or simplified design, in particular for markets in developing countries and / or for applications for equipping existing power grids (retrofitting).

[0212] In particular, this second embodiment differs from the first embodiment in that, when a triggering condition is identified, the monitoring module does not trigger the protection device, but only displays a warning, which still allows locating the source of the electrical fault in the power grid and taking action accordingly. In addition, the steps corresponding to the selective management and the steps corresponding to the storage of the first and second state variables in the memory are omitted.

[0213] This embodiment includes, inter alia, steps 300 to 314 which are similar to steps 108 to 110 and 132 to 134 described above, respectively.

[0214] Therefore, the monitoring module 22 measures the voltage (step 302) and the current (step 304) after it is turned on (step 300), and then calculates the first moving average (step 306) and the second moving average (step 308). The measured voltage value is compared with the predefined voltage threshold (step 310), and the current value of the first moving average is compared with the current value of the second moving average (step 312) to identify the triggering condition of the corresponding protection device 20 (step 314).

[0215] Specifically, a trigger condition of the protection device is identified when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than the second moving average current value.

[0216] In parallel, if a fault has been previously stored in the memory, which is checked in step 324 , the module automatically issues a warning signal (step 326 ), for example similarly to step 156 .

[0217] The warning signal may be manually reset by the operator at any time, as shown in step 328. In this example, the method is relatively simple in implementation and no automatic check is performed on the actions taken by the operator to reset the warning signal.

[0218] Once the triggering condition has been identified, the module issues a warning signal and stores it in a memory in a step 316 similar to step 156 , and then waits for a predefined duration T4 in a step 318 similar to step 140 .

[0219] At the end of the countdown, in step 320 similar to step 148 , the monitoring module 22 automatically checks whether the measured voltage is still below (or equal to) the voltage threshold.

[0220] If not, ie if the measured voltage value becomes higher than the voltage threshold again, in a step 322 similar to step 164 , the module 22 ceases to emit the warning signal and the memory of the alarm is reset.

[0221] In the opposite case, step 320 is repeated until the waiting time T4 expires.

[0222] The embodiments and variations contemplated above may be combined together to form new embodiments.

Claims

1. A method comprising the steps of: performing, by an electronic monitoring module (22) associated with an electrical protection device (20), - repeatedly measuring (102, 104; 302, 304) a voltage and a current in an electrical link (24) associated with the electrical protection device; - repeatedly calculating (106, 108; 306, 308) a first moving average and a second moving average based on the measured current value, the second moving average being calculated over a longer duration than the first moving average; - comparing the measured voltage value with a predefined voltage threshold value (120; 310); - Comparing the first moving average current value with the second moving average current value (132; 312); - identifying (134; 314) a triggering condition of the electrical protection device when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than the second moving average current value.

2. The method according to claim 1, characterized in that The method also includes issuing (156; 316) a warning signal by the electronic monitoring module (22) when a triggering condition is identified.

3. The method according to claim 1 or claim 2, characterized in that: The method includes sending (122) a trigger signal for the electrical protection device (20) by the electronic monitoring module (22) when a trigger condition is identified.

4. The method according to claim 1 or claim 2, characterized in that: The method also includes, when a trigger condition is identified, storing (136) a state variable indicating the presence of the trigger condition in a memory by the electronic monitoring module (22), and is characterized in that, starting from the start of the electronic monitoring module (22), if the state variable stored in the memory indicates the presence of the trigger condition, the trigger condition is identified.

5. The method according to claim 1 or claim 2, characterized in that: When a trigger condition is identified, the method also The method comprises the following steps: waiting for a predefined duration (T4), then measuring the voltage value again, and if the measured voltage value is higher than the predefined voltage threshold, prohibiting the trigger condition.

6. The method according to claim 1 or claim 2, characterized in that: The method further comprises: - acquiring status information emitted by a second electronic monitoring module (22, Q3) associated with a second protection device (20, Q3) connected downstream of said protection device (20, Q2) to the same electrical link (24); - if the acquired status information indicates that the second electronic monitoring module (22, Q3) has identified a triggering condition for the second protection device (20, Q3), the triggering condition of the protection device (20, Q2) is inhibited.

7. The method according to claim 1 or claim 2, characterized in that: The first moving average is calculated over a first duration shorter than or equal to 1 second, and is characterized in that the second moving average is calculated over a second duration longer than the first duration, the second duration being shorter than or equal to 10 seconds or shorter than or equal to 5 seconds.

8. The method according to claim 7, characterized in that The first duration is shorter than or equal to 500 milliseconds.

9. The method according to claim 7, characterized in that: The second duration is at least five times longer than the first duration.

10. A system (28) comprising an electrical protection device (20) and an electronic monitoring module (22) associated with the electrical protection device, characterized in that: The electronic monitoring module (22) is programmed to implement the following steps: - repeatedly measuring (102, 104; 302, 304) a voltage and a current in an electrical link (24) associated with the electrical protection device; - repeatedly calculating (106, 108; 306, 308) a first moving average and a second moving average based on the measured current value, the second moving average being calculated over a longer duration than the first moving average; - comparing the measured voltage value with a predefined voltage threshold value (120; 310); - Comparing the first moving average current value with the second moving average current value (132; 312); - identifying (134; 314) a triggering condition of the electrical protection device when the measured voltage value is below a predefined voltage threshold for a duration longer than the predefined duration threshold and when the first moving average current value is higher than the second moving average current value.

11. The system according to claim 10, characterized in that The electronic monitoring module (22) is integrated into the electrical protection device (20), and the electronic monitoring module (22) is implemented by an electrical tripping device of the electrical protection device (20).

12. The system according to claim 10, characterized in that The electronic monitoring module (22) is separated from the electrical protection device (20) and is installed outside the electrical protection device (20).

13. A power distribution network (2), comprising: - a storage device (STOR) and / or a power generation device (SOL) which supplies power to the main link (4); - At least one electrical load connected to the main link via an electrical protection device according to claim 10.

14. The power distribution network (2) according to claim 13, characterized in that The distribution network (2) is a microgrid.

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