FR3032837A1 - SELECTIVE PROTECTION SYSTEM OF AN ELECTRICAL NETWORK AND ASSOCIATED PROTECTION METHOD - Google Patents

Abstract

The invention relates to a system for selective protection of an electrical network comprising at least one main electrical line (5) and at least one secondary line (6 ', 6' ', 6' ''), the system comprising at least one main protection assembly (2), said head assembly, connected to a main power line, and secondary protection assemblies (3 ', 3' ', 3' '') each connected to a secondary line, the set of head comprising: a subset comprising an electric circuit, a cut-off device, and a control circuit connected to the subset and adapted to control the tripping of the subset, and each of the secondary assemblies comprising: a circuit breaker, said secondary circuit breaker (61 ', 61' ', 61' ''); the secondary circuit breaker (s) of each secondary line being adapted (s) to trip in the event of a short-circuit on the latter, independently of the control circuit, the control circuit of the head assembly not being connected to any of the secondary breakers.

Description

TECHNICAL FIELD The present invention relates to a system for selectively protecting an electrical network comprising at least one main line and at least one secondary line, and an associated protection method. .

More particularly, it relates to a system comprising current sensors adapted to detect short-circuit currents in such an electrical network and to selectively cut the current in the main line or in one of the secondary lines. The invention can be applied both to the protection of DC and AC networks. The invention thus aims to improve existing protection systems and methods. PRIOR ART Selective power failure is a crucial issue for the security of transmission and / or power distribution networks. An electrical network may include at least one main power line upstream and a number of secondary power lines downstream. The main line is equipped with a main cut-off device and the secondary lines are generally all equipped with circuit-breakers in case of short-circuit or overload, to cut the current respectively on the main line or on a secondary line, in order to to protect the installations fed by the network of currents of too high intensity, and / or the men of the electrocution. When it is necessary to cut power at a point in the network due to a short circuit, it is always desirable to turn off the power on a secondary line rather than on the main line. This makes it possible to continue to distribute power to the rest of the network. If it is not possible to do otherwise, it is necessary nevertheless to cut the power on the main line, always for the sake of protecting the installations and / or the men. In order to ensure the selectivity of the break, the circuit breakers are typically each equipped with sensors for measuring a current, a voltage or an impedance on their main or secondary line, and a control unit. The control units communicate with each other and exchange information as to the state of the line, that is to say the intensity of the current passing through it, or the voltage or the state of the circuit breaker, typically at the using a microprocessor.

3032837 2 A breaker may also fail to operate and not trip, even in the event of a short circuit or overload. For the sake of security, it is then necessary to provide robust and reliable security in order to secure the entire network. US Patent 5,905,616 discloses a network protection system comprising a circuit breaker upstream on a power line and several downstream circuit breakers on secondary power lines and connected to a microprocessor of the upstream circuit breaker. This microprocessor controls the tripping of downstream circuit breakers. The importance of downstream lines is prioritized and ranked in order of importance. The upstream circuit breaker has a microprocessor which is stored in the hierarchy of downstream circuit breakers. In case of network overload, the microprocessor can send a signal to a downstream circuit breaker and cause it to trip. The current on the electrical line of the circuit breaker is thus cut and, preferably on the lines of minor importance. The system disclosed in US Pat. No. 5,905,616 implements circuit breakers whose microprocessors communicate with each other. Such a protection system can not therefore be applied to an existing network. In other words, applying the disclosed system to an existing network involves the complete change of existing circuit breakers by circuit breakers adapted to communicate with each other via a microprocessor. In addition, no security is provided in case of non-tripping of a secondary circuit breaker. US patent application 2014/0078628 A1 discloses a system for protecting an electrical network comprising a plurality of circuit breakers cascaded over power lines. These circuit breakers communicate with each other by means of a microprocessor integrated in each circuit breaker. Each circuit breaker has a current sensor connected to an internal microprocessor. Downstream microprocessors are connected to upstream microprocessors. Each microprocessor has a memory in which several threshold values are stored.

Beyond one of these threshold values, the circuit breaker trips and informs if necessary the upstream circuit breaker. The upstream circuit breaker then adapts its threshold values according to the state of the downstream network. This system operates with circuit breakers having internal electronics communicating with each other and, like US Pat. No. 5,905,616, can not be implemented on an already existing network with secondary circuit breakers already installed without replacing them. The patent application WO 2006/108860 describes a protection system of a single-line electrical network comprising an upstream circuit breaker and a downstream circuit breaker, a current sensor and a voltage sensor being integrated in the upstream circuit breaker 3032837 . A circuit breaker serves as a backup circuit breaker or "back-up". The sensors are used to determine the impedance of the power line at the output of the circuit breaker. This protection system, relying on voltage and current measurements only at the upstream circuit breaker to calculate the impedance of the network, can not be implemented for a network comprising a plurality of secondary lines. In addition, whatever the protection system of the previous described, the need to operate a microprocessor during the protection reduces the robustness of the system, since it must both implement works on a program (or "software") and dedicated electrical circuits (or "hardware"). The risks of failure are thus cumulative. There is thus a general need to simplify and further improve the selectivity, reliability and safety of electrical networks in a simple and low cost manner. There is also a particular need to be able to find a protection system which meets the general need and which allows implementation on already existing protective installations. The object of the invention is to at least partially meet this (these) need (s). SUMMARY OF THE INVENTION To this end, the subject of the invention is a system for selective protection of an electrical network comprising at least one main electrical line with one or more current lines, at least one secondary line with one or more current lines and connected downstream to at least one main power line, the system comprising at least one main protection assembly, said head assembly, connected to a main power line, and secondary protection assemblies each connected to a secondary line the head assembly comprising at least: - a subassembly comprising an electric circuit and a cut-off device, said head cut-off device, this sub-assembly being adapted to cut the current of the main power line, a control circuit connected to the subassembly and adapted to control the tripping of the subassembly; a current sensor connected to each current line; current-adjusting device being adapted to measure as input the current flowing through the line to which it is connected and delivering at its output a current and / or voltage proportional (1c) to the current it measures, - means for comparing the current / or the voltage delivered at the output of each current sensor with a predetermined value said head threshold - means for transmitting a signal to the control circuit when the current and / or the output voltage of the current sensor is greater than head threshold, each of the secondary assemblies comprising at least: - a circuit breaker said secondary circuit breaker, - a current sensor connected to each current line, each current sensor being adapted to measure the current and / or the voltage running through the line current to which it is connected and delivering at its output a current and / or a voltage proportional (Ic) to the current and or the voltage it measures, - means for comparing the current t / or the voltage delivered at the output of each current sensor with a predetermined value called secondary threshold, - means for transmitting a signal to the control circuit when the current and / or the output voltage of the current sensor is greater than secondary threshold, the secondary circuit breaker (s) of each secondary line being adapted (s) to trip in the event of a short-circuit on the latter, independently of the control circuit, the control circuit of the head assembly not being connected to any of the secondary breakers. By "independently" is meant that a secondary circuit breaker can be tripped without receiving a signal from the control circuit of the head assembly, in the event of a short circuit on the secondary electrical line on which it is mounted. In other words, the secondary circuit breaker does not send a signal to the control circuit and also does not receive a signal from the control circuit. The tripping of a secondary circuit breaker is independent of that of the other circuit breakers.

Each comparator may advantageously be connected firstly to a reference voltage of a certain value, called a threshold, and secondly to the output of the rectifying means. This value is predetermined by design for each secondary circuit breaker according to the maximum current that the latter can withstand before being tripped. A secondary circuit breaker may therefore have a secondary threshold different from another secondary circuit breaker. It is easy to equip an existing installation with the system according to the invention. Indeed, it is not necessary to change the circuit breakers in place by new circuit breakers on each secondary line: simply install on each line a current sensor and associated electrical circuits. Only the head assembly requires the mounting of a suitable control circuit. In addition, the system according to the invention can operate with current sensors of different types, and can thus be adapted to all types of networks, whether high voltage, low voltage or very low voltage. tripping of a secondary circuit breaker, during a short-circuit, the system according to the invention makes it possible to detect the short-circuit current upstream and downstream and to cut the current on the main line to protect the powered electrical installations. through the power grid. If the current sensors on the secondary line 10 having the short circuit do not measure by a normal current after a given period of time, the current is cut off on the main line. The cut-off device of the head assembly thus serves as a backup circuit breaker or "back-up" to all secondary circuit breakers. The system according to the invention is also very robust since no control signal is sent by the circuit breakers themselves, and since the control circuit 15 is not necessarily a microprocessor. Indeed, it can be a logic circuit. This protects the system from malfunctions related to the use of programs ("software" in English). It is specified that a fault current other than a short circuit, such as an electrical overload, is interrupted by the head cut-off device or one of the secondary circuit breakers 20 independently without involving the system according to the invention. 'invention. The cutoff member of the head assembly may be a circuit breaker, a switch or a switch. Whatever the type of cut-off device envisaged, the intensity of the current flowing through it is constantly controlled by two parts, one of which operates by thermal effect and detects the overload currents and the other operates by effect. magnetic and detects short circuit currents. For example, a low voltage circuit breaker has a bimetallic strip as a thermal effect portion and an electromagnetic coil as a magnetic effect portion.

According to an advantageous embodiment, the head assembly comprises means for processing the signals coming from the output of each current sensor. According to this mode, the head assembly advantageously comprises comparator circuits connected to each of the outputs of the rectifying means, each comparator circuit being adapted to compare the current and / or the output voltage of the processing means with a predetermined value. said head threshold, and to output a signal to the control circuit when the current and / or the output voltage of the current sensor is greater than the head threshold.

According to another advantageous embodiment, at least one of the secondary assemblies comprises means for rectifying the signals coming from the output of each current sensor. According to this mode, the secondary assembly comprising comparator circuits connected to each of the outputs of the rectifying means, each comparator circuit being adapted to compare the current and / or the output voltage of the rectifying means with a predetermined value called secondary threshold and specific to each secondary line, and transmit a signal to the control circuit of the head assembly when the current and / or the output voltage of the current sensor is greater than the secondary threshold. According to an advantageous variant, the straightening means of the head assembly 15 and / or secondary assemblies are bridges made of diode, preferably arranged in so-called Graetz bridges. Alternatively, the rectifying means of the head assembly and / or secondary assemblies are bridges made of thyristors. According to a first embodiment, the main line delivers a continuous current. According to a second embodiment, the main line delivers an alternating current. According to a variant of the second embodiment, the main line comprises one, two, three or four current lines, possibly including a neutral current line.

It can thus include in particular four current lines including a neutral current line. According to an advantageous embodiment, the comparator circuits of the head assembly and / or secondary assemblies are adapted to transmit an "all-or-nothing" signal (TOR) to the control circuit. Such a signal can be generated and read in a simple manner and this contributes to the robustness of the protection system. Advantageously, the comparator circuits are operational amplifiers each configured as a comparator.

A logic circuit may advantageously be connected between the output of the comparator circuits of the head assembly and the control circuit, the logic circuit performing the sum of the output signals of the comparator circuits. By sum, we mean the logical function "or inclusive" ("OR" in English).

According to another embodiment, a logic circuit is connected between the output of each comparator circuit of the secondary assemblies and the control circuit, each logic circuit performing the sum of the output signals of the comparator circuits of the secondary assembly to which it is connected. connected. This allows in particular to configure the control circuit with a single signal for each main or secondary power line. In fact, it suffices that only one of the current sensors of one of the lines causes, at the output of a comparator circuit, the transmission of an "all" signal, and therefore one of the inputs of a logic circuit. either an "all" signal so that the output of the same logic circuit is also an "all" signal in the case of a current greater than the leading threshold or the secondary threshold. The system advantageously comprises means adapted to connect the output of each logic circuit and the control circuit. These means may consist of an optocoupler, which has the additional advantage of being able to electrically isolate the circuits from each other. One can also consider instead of an optocoupler, a transistor. According to an alternative embodiment, the control circuit comprises a memory in which at least the cut-off times of the secondary breakers and, if appropriate, a margin time, are recorded. By "cut-off time" is meant the time during which the circuit-breaker performs its breaking action as a whole, from its tripping to the total breaking of the current. For example, the cut-off time of a secondary circuit breaker for a circuit breaker 25 having a magneto-thermal effect is the sum of the trip duration, the opening time of the poles of the circuit-breaker and the extinction duration of the circuit breaker. electric arc. Advantageously, the head cutoff device and / or the secondary circuit breakers is (are) selected from magneto-thermal circuit breakers or self-blowing or self-pneumatic circuit breakers.

The invention also relates to a method for protecting an electrical network comprising at least one main electrical line at one or more current lines, at least one secondary line with one or more current lines and connected downstream to at least one main electrical line, at least one cut-off member being mounted on each main electrical line and at least one secondary circuit breaker being connected to each secondary line, the method comprising the following steps: a / measuring the currents flowing through the current lines of the main line by means of current sensors, b / process the signals from the current sensors, c / compare the intensity of the currents with a predetermined value called the leading threshold, and, if the value of the intensity of the current flowing through a current line of the main line is greater than the leading threshold, then d / emit a signal to a circuit of command that causes the launch of a main countdown of initial value greater than or equal to the longest break time of the secondary circuit breakers, then perform for each a given secondary line, the following successive steps: a '/ measure the currents traversing the current lines of the secondary line by means of current sensors, b '/ processing the signals from the current sensors, c' / comparing the intensity of the currents to a predetermined value called secondary threshold, a secondary threshold being specific to each secondary line, and, if the value of the intensity of the current flowing through a current line of a given secondary line is greater than its secondary threshold, then of transmitting a signal to a control circuit which causes the launch of a secondary countdown of initial value greater than or equal to the cut-off time of the secondary circuit breaker of the secondary line, the account to be secondary market canceling the main countdown, and, at the end of the secondary countdown, repeat steps (a ', b', c ', d') for the given secondary current line, and, if the value of the intensity of the current flowing through a current line of the given secondary line is greater than its secondary threshold, cut off the current of the main line, if the value of the intensity of the current in each current line of the given secondary line is below its secondary threshold, then repeat the steps for the other secondary current lines, if the value of the intensity of the current in all the secondary lines is less than their secondary threshold, then the end of the main countdown without have been canceled 5 and cut the power of the main line. Advantageously, the transmitted signals are "all-or-nothing" (TOR) signals. The invention also relates to the application of such a method for protecting a three-phase electrical network or a DC network. DETAILED DESCRIPTION Other advantages and features of the invention will become more apparent upon reading the detailed description given with reference to the following figures among which: FIG. 1A is a diagrammatic representation of a head assembly of an embodiment of FIG. 1B shows a schematic view of one of the secondary assemblies of a protection system according to one embodiment of the invention; FIG. 2 represents a flow chart of an example; 3 is a schematic view of the different steps of the protection method according to FIG. 2; FIGS. 4A and 4B show examples of tripping curves of circuit breakers; magneto-thermal values from which threshold values of the secondary assemblies according to the invention are determined, - FIGS. steps of the protection process in the event of a short-circuit at different points in the electrical network; FIG. 7 illustrates the rectification operation of a current or a voltage; FIG. 8 represents the tripping curves of circuit breakers; magneto-thermal signals from which threshold values of three secondary assemblies according to the invention are determined; FIGS. 9A to 9D show the trip curves of a magneto-thermal circuit breaker from which the thresholds and the values of the circuit are determined. main countdown for the head assembly according to the invention, - Figures 10A to 10D and 11A to 11E show the voltage curves recorded at different locations of a system according to the invention, during a simulation, 3032837 FIG. 12 is a schematic view of an electrical network with a protection part common to both a system according to the invention and a system according to the state of the invention. rt. FIG. 12 shows an electrical network as it currently exists with a protection part common to both a system according to the invention and a system 5 according to the state of the art. The network comprises firstly a main power line 5, with three current lines 50b, 50c, 50d each carrying a phase and a neutral current line 50a. A cutoff member 51 is mounted on this main line 5. In the illustrated example, the main line 5 is a three-phase star-coupled line (Y) with neutral output.

The network comprises downstream of the main line 5, three secondary lines 6 ', 6 "and 6". Each of these secondary lines 6 ', 6 "and 6' also comprises four current lines 60'a, 60'b, 60'c, 60'd, the current line 60'a is a neutral line and the three 60'b, 60'c, 60'd current lines each carry a phase, a circuit breaker 61 ', 61 ", 61"' is mounted on each of these secondary lines 6 ', 15 6 "and 6"'. it can be seen in FIG. 1A, the head assembly 2 according to the invention is mounted on a main electrical line 5. On each of these current lines is mounted a current sensor 40a, 40b, 40c, 40d delivering output A voltage proportional to the current it measures, each of these sensors can be adapted to measure an intensity traversing the network as a function of the type of power supply of the high voltage, low voltage or very low voltage network. arrive at the rectifying means 41. In the illustrated embodiment, the rectifying means are Grae diode bridges. tz 41a, 41b, 41c and 41d. The straightening operation performed is illustrated in FIG. 7: the output of this type of bridge approaches the absolute value of the input. The rectifying means 41 are connected at their output to comparator circuits 42. In the illustrated embodiment, the comparator circuits are operational amplifiers 42a, 42b, 42c, 42d configured as comparators. Each of the operational amplifiers 42a, 42b, 42c, 42d receives at its inverting input an input voltage of a predetermined value, called the head threshold. Thresholds are typically the same for the same power line. The non-inverting input of each of the operational amplifiers 42a, 42b, 42c, 42d is connected to the output of one of the rectifying means 41.

Thus, if the two supply inputs of each of the operational amplifiers 42a, 42b, 42c, 42d have respectively connected to a positive voltage and to a zero voltage, an output of zero voltage signal is obtained at the output if the voltage at non-inverting input point is less than the leading threshold, a signal equal to the saturation voltage of the operational amplifier. Such a signal is a digital signal (acronym for "all or nothing"). These digital signals are then sent to a logic circuit 43 making the sum of these signals. The output of the logic circuit 43 is zero only if all its inputs are "nothing" signals. If only one of its inputs is an "all" signal, then the output of the logic circuit is also an "all" signal. The logic circuit 43 thus also emits a digital signal. This digital signal coming from the logic circuit 43 is then sent to the control circuit 40. The control circuit 44 receives digital signals coming from the output of the logic circuit 43. The control circuit is adapted to, if it receives a signal "All", 15 trigger a main countdown C. The main countdown C has an initial value equal to a predetermined duration. At the end of the countdown C, if the signal is always an "all" signal, ie, at the end of the countdown still one of the current sensors 40a, 40b, 40c, 40d measures a current With an intensity greater than a threshold, the control circuit orders the tripping of the head cutoff 51. In the illustrated embodiment, the head cutoff 51 is a quadrupole breaker. The control circuit 44 may comprise only logic elements and therefore not run a program, in order to overcome the risks of failure related to the use of a program (software). This makes the protection system according to the invention more robust. Alternatively, the control circuit 44 may also include a microprocessor. It may also include a memory including in particular the duration of the main countdown C.

The control circuit 44 is also connected to three optocouplers 31, 31 ", 31" ', each connected to a secondary assembly whose operation is detailed below. In FIG. 1B, there is shown a secondary assembly 3 'connected to the input of an optocoupler 31'.

This secondary assembly is connected to a secondary electrical line 6 'located downstream of the main power line 5. It also comprises four current lines 60'a, 60'b, 60'c, 60'd, the line current 60'a being a neutral line and the three current lines 60'b, 60'c, 60'd each carrying a phase. On the line 6 'is a quadrupole circuit breaker 61' not connected to the rest of the protection system. Each of the current sensors 70'a, 70'b, 70'c, 70'd is connected to each of the current lines 60'a, 60'b, 60'c, 60'd and is adapted to measure the currents traversing the corresponding current line. They deliver at their output a voltage proportional to the current they measure.

The output of the current sensors is connected to the input of the rectifying means 71 '. In the illustrated embodiment, these are Graetz diode bridges 71'a, 71'b, 71'c, 71'd. They are connected at their output to comparator circuits 72 '. These circuits comprise operational amplifiers 72'a, 72'b, 72'c, 72'd configured as comparators, each connected to the output of one of the rectifying means 71 '.

Each of these comparators 72'a, 72'b, 72'c, 72'd has an inverting input voltage of a predetermined value, called secondary threshold. The thresholds are typically the same for the same power line, but may be different between the secondary power lines. The outputs of the rectifying means are connected to the non-inverting input of the operational amplifiers. Thus, if the two power supply inputs of each of these comparators 72'a, 72'b, 72'c, 72'd are respectively connected to a positive voltage and to a zero voltage, one obtains at the output either a signal zero voltage if the voltage at the non-inverting entry point is less than the secondary threshold, or a signal equal to the saturation voltage of the operational amplifier. Such a signal is a digital signal ("all or nothing").

These digital signals are then sent to a logic circuit 73 'carrying out the sum of these signals. The output of the logic circuit 73 'is zero only if all its inputs are "nothing" signals. If only one of its inputs is an "all" signal, then the output of the logic circuit is also an "all" signal. The logic circuit 73 'thus also emits a digital signal. This digital signal from the logic circuit 73 is then sent to the optocoupler 31 '. The optocoupler 31 'is adapted to initially transform the signal "everything" from its input into a light signal. This light signal is then transformed into an "all" signal at the output of the optocoupler. A "nothing" signal coming from the input of the optocoupler is not transformed into a light signal and remains at the output of the optocoupler a "nothing" signal. The output of the optocoupler 31 'therefore also emits a digital signal. The other two secondary assemblies 3 "and 3" 'are identical to the secondary assembly 3' which has just been described and not a concern for clarity and brevity are not shown and described. Each of these two other secondary assemblies is respectively connected to the input of one of the other two optocouplers 31 ", 31 '". Each of the outputs of the optocouplers 31 ', 31 "and 31"' is connected to the control circuit 44. Thus, the output of the logic circuits 43, 73 'emits an "all" signal if the currents 10 measured by their associated current sensors are greater than a threshold value or a secondary threshold value. An "all" output value corresponds to the detection of a short circuit current. A short circuit can occur in many places on the power grid. Several short-circuit cases are illustrated in FIGS. 5 and 6. In FIG. 5, the short-circuit occurs on line 6 'downstream of circuit breaker 61'. In FIG. 6, the short circuit occurs downstream of the head assembly 5 and upstream of the secondary assemblies 3 ', 311, 3111. Thus, as illustrated in FIG. 5, in the event of a short-circuit on the line 6 ', 6 "and 6"', if the control circuit 44 receives both an "all" signal from the head assembly 2 and a secondary assembly 3 ', 3 ", 3"' of the secondary line affected by the short circuit, the main countdown C is started as explained above. The control circuit 44 cancels the main countdown initiated by the head assembly 2, then launches a secondary countdown C1, C2 or C3 on receipt of an "all" signal from a secondary set 3 ', 3 "or 3" '.

The initial values of the secondary countdowns C1, C2 and C3 are predetermined values that may be different for the different subsets 3 ', 3 "or 3"'. This value corresponds, at least, to the cut-off time of the secondary circuit breaker of the secondary electrical line connected to the secondary assembly which emitted the "all" signal. At the end of a secondary countdown C1, C2 or C3, if the secondary unit always transmits an "all" signal, the control circuit orders the triggering of the head cut-off device 51. Thus, as illustrated in FIG. 5, for a short-circuit on the line 6 'downstream of the circuit breaker 61', if the latter succeeds in cutting off the current and making the short-circuit current disappear, then this short-circuit current circuit is no longer measured on the current line 6 '. The head cutoff member 51 is then not triggered. This allows selective protection if the secondary circuit breaker 61 'operates correctly. On the other hand, if the short-circuit current is upstream of the secondary circuit breaker 61 'as shown in FIG. 6, or if the short-circuit current is downstream as illustrated in FIG. 5, but the secondary circuit breaker 61 'has a fault, the secondary countdown expires. The short-circuit current persists and the head cut-off device 51 is triggered by a command of the control circuit 44. The current is thus cut off on the main power line 5 upstream and therefore on all the secondary lines 6 ' , 6 ", 6" 'downstream. The installations fed by the electrical network and the men are thus protected from short circuits. The steps of the protection method according to the invention of an electrical network such as that of FIG. 12 are presented in FIG. 3. Firstly, the currents of the current lines of the main power line 15 are measured (step a ). Current sensors output image signals proportional to the measured current to the rectifying means. These image signals are then rectified (step b) and then compared (step c) with the leading threshold. If the value of the intensity of a current line is greater than the threshold of the head, a signal is emitted towards the control circuit 44. The latter then starts the main countdown 20 of value C equal to a predetermined duration ( step d). At the end of the main countdown C, if the measured current is always greater than the leading threshold, the current is cut on the main power line. The currents in the secondary power lines are also measured for each current line (step a ', a ", a"), rectified (step b', b ", b") and then compared with a secondary threshold specific to each line. current for each power line (step c ', c ", c"). If the intensity of a current of a line of current of a secondary power line is greater than a secondary threshold, a signal is emitted, this signal causing if necessary the cessation of the main countdown C and the launching a secondary countdown C1, C2 or C3 (step d ', d ", d") according to the line concerned. At the end of the secondary countdown, if the current measured in the secondary power line is still greater than the secondary threshold specific to this line, the current is cut on the main power line.

Such a method advantageously makes it possible to allow each secondary circuit breaker time to perform its current-breaking action on a secondary line before making the decision to cut off the current on the main power line. The initial value of a secondary countdown, for each secondary power line, is the time it takes the secondary breaker to turn off the power on that secondary line, i.e., its cut-off time. This duration can vary from one circuit breaker to another and is intrinsic to the type of circuit breaker, and is therefore part of the manufacturer's data. For a low voltage or very low voltage network, the circuit breakers are preferably magneto-thermal. In this case, the initial value of the main countdown is preferably chosen to be equal to the longest cut-off time, plus a margin time. Secondary thresholds are also chosen based on the manufacturer's data for each secondary breaker. As already stated, according to the invention, even if the secondary thresholds are defined as a function of the secondary circuit breakers, the latter do not receive a control signal. FIGS. 4A and 4B illustrate a method of predetermination by the inventor of the secondary thresholds for magneto-thermal circuit breakers. The secondary threshold is preferably equal to the tripping threshold of the secondary circuit breaker considered. The circuit breaker trip curve has a high envelope and a low envelope, and each envelope has a portion that corresponds to the thermal operation of the circuit breaker, and a portion that corresponds to the magnetic operation of the circuit breaker. The thermal operation corresponds to the case of an overload on the secondary electrical line, and the magnetic operation corresponds to the case of a short-circuit on the line. According to the method defined by the inventor, the secondary threshold is chosen as being the lowest magnetic tripping threshold of the upper envelope of the tripping curve of the secondary circuit breaker considered. FIG. 2 illustrates a detailed flowchart that shows the logical relationships between the state of a current sensor of a head or secondary assembly (detection of a current greater than a threshold and transmission of a digital signal) and the commands issued by the control circuit during a protection process implemented by the system illustrated in FIGS. 1A and 1B. The control method is first initialized (step SO).

In the first place, the intensity of the current in each current line of the main power line 5 is measured and compared with the leading threshold (step S101). If one of these intensities exceeds the threshold of head, one checks whether a main countdown has already been started or not (step S102).

If no, the main countdown is started (step S103). If so, it is verified that it has not completed (step S108). If so, the intensity of the current in each current line of the main power line 5 is measured again and compared to the leading threshold (step S109). If not, the control method is re-initialized (step SO).

The completion of the main countdown causes the triggering by the control circuit 44 of the head cutoff 51 (step S107). Then, if the countdown is still running or if no current greater than the leading threshold is detected, the current intensity in each line of current of a secondary power line is measured and compared to the secondary threshold. a first secondary power line, in this case line 6 '(step S104'). If no current greater than the secondary threshold specific to the line 6 'is detected, this step is repeated for the next line 6 "(step S104"). If again, no current greater than the secondary threshold specific to the line 6 ", this step is repeated for the line 6 '" (step S104 "'). If, again, no current greater than the secondary threshold specific to the line 6 '"is not detected, it returns to step S101. On the other hand, if a short-circuit current is detected on a secondary electrical line, for example the line 6 ', i.e. the intensity of a current measured on a current line is greater than only secondary clean line 6 ', then the main countdown is, if necessary, canceled and a secondary countdown is initiated by the control circuit 44 (step S105 "). At the end of this secondary countdown the current is measured again on each current line of the secondary electrical line 6 '(step S106').

If no current greater than the secondary threshold is detected on the secondary electrical line 6 ', no action is taken and step S104 "is carried out, if, on the other hand, a current higher than the secondary threshold is still detected at the same time. secondary countdown time, that is to say that the circuit breaker 61 'has not properly cut the current in a predetermined time because of a fault, or that the short circuit is in upstream of the circuit breaker 61 ', the control circuit 44 triggers the cut-off member 51 and the main power line current is cut off (step S107) In the same way, the same steps can be performed on each secondary line 6 "and 6 'when a current of intensity greater than the threshold value specific to each line 6", 6' is detected (steps S105 ", S105", S106 ", S106") Figures 8 and 9A to 9D illustrate the method of choice by the inventor of the values of the princess countdowns and in the secondary thresholds of the head threshold and the secondary thresholds for the implementation of a prototype protection system applicable to a network as shown in FIG. 12. In these figures, a current of 16A crosses the line 6 ', a current of 250A crosses the line 6 "and a current of 400A crosses the line 6" The secondary circuit breaker 61 'mounted on the secondary line 6' has a tripping curve 9 'threshold is1 (160A) and tripping time tdi (0,03s).

The secondary circuit breaker 61 "mounted on the secondary line 6" has a tripping curve 9 "is2 (419A) and tripping time td2 (0.085s) The secondary circuit breaker 61" 'mounted on the secondary line 6' has a tripping curve 9 'is3 (3536A) and tripping duration td3 (0.085s). The thresholds is1, isz and is3 are chosen on the curves as each being the lowest value for the high envelope of the secondary circuit breaker concerned. The tripping times tdi, td2 and td3 are chosen by correspondence to these values on the curve. The respective values of each of the corresponding secondary countdowns C1, C2 and C3 are then calculated by adding to the tripping time, the data of the circuit-breaker manufacturer, namely the opening time of the poles of the circuit-breaker (t01, to2). , you) and the duration of extinction of the internal electric arc (tai, tcz, tc3). The value of each secondary countdown is thus obtained by summing for each circuit-breaker the trip duration, the opening time of the poles and the extinction time of the internal electric arc, that is, that is, by making the following sum for each secondary countdown: Cn = tan ton tcn 30 where n is the numerical subscript corresponding to the secondary line concerned (1 for line 6 ', 2 for line 6 "and 3 for line 6 "Cn is the secondary countdown specific to the index line n, 3032837 18 td is the trip time specific to the breaker of the index line n, tone is the opening time of the specific poles to the circuit breaker of the index line n, and tcn is the cut-off time of the circuit-specific arc of the index line n, the value of the countdown is thus chosen as at least equal to the cut-off time 5 of the secondary circuit breaker, all of these values are summarized in the following table. Line Threshold Type (A) duration of opening time of breaker poles duration Count to electric circuit breaker tripping (ms) of arc extinction (ms) countdown (ms) (ms) 5 630 / / / 135 head cut 51 6 'Secondary 61' 160 30 25 5 60 6 "Secondary 61" 419 85 45 5 135 6 "Secondary 3536 85 45 5 135 61" Figures 10A to 10D and 11A to 11E illustrate measurements taken on the prototype protection system according to the invention, with the previous values.

The conditions for the measurements are as follows. A signal simulating a short circuit of 270A for 110 ms is injected on the main electrical line 5 and on the secondary electrical line 6 '. We thus place ourselves in the case where the short circuit is not eliminated by the secondary circuit breaker of the line 6 '. The signals measured at the head (main) assembly 2 are shown in FIGS. 11A-11E and the signals measured at the secondary assembly 3 'are shown in FIGS. 10A-10D. The injected signal is first measured at the current sensors of the head assembly 2 mounted on the line 5 (Figure 11A) and the secondary assembly 3 'mounted on the line 6' (Figure 10A).

The image signals of the current sensors are then rectified at the rectifying means 41: only the rectified current of the main assembly 2 is shown in FIG. 11B. The rectified signals are then compared to the thresholds at the comparator circuits 42 of the head assembly 2 (Fig. 11C) and those 72 of the secondary assembly 3 '3032837 (Fig. 10C). The threshold for the head set is the head threshold ist and the threshold for the secondary set 3 is the secondary threshold is1. Since the head threshold equal to 630A is greater than the injected signal equal to 270A, the comparator circuits output a "nothing" signal and a "nothing" signal is observed at the output of the logic circuit 43 after the comparator circuits 42 (Figure 11D). On the other hand, the output of the logic circuit 73 emits "all" signals, which results in a signal at the output of the optocoupler 31 '(FIG. 10D). The secondary countdown, equal in this case to 60ms, is triggered. The head value thus makes it possible to trigger, as desired by the operator, the head assembly or a secondary assembly according to the value of the head threshold with respect to the secondary threshold. Since the length of the injected signal is 110ms, the secondary countdown of the line 6 'expires. The control circuit 44 then transmits to the head cut-off device 51 a signal controlling the breaking of the current on the main electrical line 5 (FIG. 11E). The current is then cut off on the electrical network. The invention is not limited to the examples which have just been described; it is possible in particular to combine with one another characteristics of the illustrated examples within non-illustrated variants. Thus, if in the illustrated examples, the breaker of the main line is a circuit breaker, it may equally well be a contactor or a switch depending on the applications. Similarly, the circuit breakers may be other than magneto-thermal circuit breakers implemented in the illustrated examples. The circuit breakers can also be, for high voltage ac application, circuit breakers commonly called auto-blow or auto-pneumatic. If in the illustrated examples, the cut-off device and the circuit-breakers are mounted directly on their respective power lines, they can also be connected indirectly to them, in particular by being mounted in an electrical cabinet and / or remote from line.

Claims (20)

REVENDICATIONS1. System for selective protection of an electrical network comprising at least one main power line (5) at one or more power lines (50a to 50d), at least one secondary line (6 ', 6 ", 6"') at a or several lines of current (60'a to 60'd) and connected downstream to at least one main power line, the system comprising at least one main protection assembly (2), said head assembly, connected to a power line main, and secondary protection assemblies (3 ', 3 ", 3"') each connected to a secondary line, the head assembly comprising at least: - a subassembly comprising an electric circuit and a breaking device, said head cutoff member (51), this subassembly being adapted to cut the current of the main power line, - a control circuit (44) connected to the subassembly and adapted to control the tripping of the subassembly a current sensor (40a to 40d) connected to each line of neck rant, each current sensor being adapted to measure as input the current flowing through the line to which it is connected and delivering at its output a current and / or voltage proportional (1c) to the current it measures, - means for comparing the current / or the voltage delivered at the output of each current sensor with a predetermined value called the head threshold, means for transmitting a signal to the control circuit when the current and / or the output voltage the current sensor is greater than the head threshold, each of the secondary assemblies comprising at least: - a circuit breaker, said secondary circuit breaker (61 ', 61 ", 61"'); a current sensor (70'a to 70'd) connected to each current line, each current sensor being adapted to measure the current and / or the voltage traversing the current line to which it is connected and delivering to its output a current and / or a voltage proportional (Ic) to the current and or the voltage it measures, - means for comparing the current / or the voltage delivered at the output of each current sensor with a predetermined value called secondary threshold Means for transmitting a signal to the control circuit (44) when the current and / or output voltage of the current sensor is greater than the secondary threshold, the secondary circuit breaker (s) of each secondary line being adapted to trip in the event of a short-circuit on the latter, independently of the control circuit, the control circuit of the head assembly not being connected to any of the secondary circuit-breakers. 2. System according to claim 1, the head assembly (2) comprising rectifying means (41) of the signals from the output of each current sensor. 5 3. System according to claim 2, the head assembly (2) having comparator circuits (42) connected to each of the outputs of the rectifying means, each comparator circuit being adapted to compare the current and / or the output voltage of the rectifying means at a predetermined value called the head threshold, and outputting at its output a signal to the control circuit when the current and / or the output voltage of the current sensor is greater than the head threshold, 4. System according to one of claims 1 to 3, at least one of the secondary assemblies (3 ') having rectifying means (71') of the signals from the output of each current sensor. 5. System according to claim 4, at least one of the secondary assemblies (3 ') having comparator circuits (72') connected to each of the outputs of the rectifying means, each comparator circuit being adapted to compare the current and / or the voltage output of the rectifying means to a predetermined value called secondary threshold and specific to each secondary line, and transmit a signal to the control circuit of the head assembly when the current and / or the output voltage of the current sensor is greater than the secondary threshold. 6. System according to one of claims 2 to 5, the rectifying means of the head assembly and / or secondary assemblies being bridges made of diode, preferably arranged in so-called Graetz bridges (41a to 41d, 71 'a to 71'd). 7. System according to one of claims 2 to 5, the rectifying means of the head assembly and / or secondary assemblies being bridges consisting of thyristors. 8. System according to one of the preceding claims, the main line delivering a direct current. 9. System according to one of the preceding claims, the main line delivering an alternating current. 10. System according to one of claims 3 to 9, the comparator circuits of the head assembly and / or secondary assemblies being adapted to transmit to the control circuit an "all-or-nothing" signal (TOR). 3032837 22 11. System according to claim 10, the comparator circuits being operational amplifiers each configured as a comparator. 12. System according to one of claims 10 or 11, a logic circuit (43) being connected between the output of the comparator circuits of the head assembly and the control circuit, the logic circuit carrying out the sum of the output signals. comparator circuits. 13. System according to one of claims 10 to 12, a logic circuit (73 ') being connected between the output of each comparator circuit of the secondary assemblies and the control circuit, each logic circuit performing the sum of the output signals of the circuits. 10 comparators of the secondary set to which it is connected. 14. System according to one of the preceding claims, comprising means (31, 31 ", 31" ') capable of connecting the output of each logic circuit and the control circuit (44). 15. System according to claim 14, the opto-coupler means (31, 31 ", 31" '). 16. System according to one of the preceding claims, the control circuit comprising a memory, wherein at least the cutoff times of the secondary circuit breakers and, where appropriate a margin time, are recorded. 17. System according to one of the preceding claims, the head cutter and / or the secondary circuit breakers being selected from magneto-thermal circuit breakers or self-blowing circuit breakers or auto-pneumatic circuit breakers. 18. A method of selectively protecting an electrical network having at least one main power line (5) at one or more power lines (50a-50d), at least one secondary line (6 ', 6 ", 6"') one or more lines of current (60'a to 60'd) and connected downstream to at least one main power line, at least one cutoff member being connected to the main power line and at least one secondary circuit breaker being connected at each secondary line, the method comprising the following steps a / measuring currents flowing through the main line current lines by means of current sensors, b) processing the signals from the current sensors, so as to c / compare the intensity of the currents at a predetermined value called the head threshold, and if the value of the intensity of the current flowing through a current line of the main line is greater than the leading threshold, then d / emit a signal for lan cer of a main countdown of initial value 5 greater than or equal to the longest cutoff time of the secondary circuit breakers, then perform for a given secondary line (6 ', 6 ", 6"), the following successive steps: a , / a / to measure currents flowing through the lines of current of the secondary line by means of current sensors, b /, b, or to process the signals from the sensors of the current, so that it is possible to compare the intensity of the currents with a predetermined value called the secondary threshold, a secondary threshold being specific to each secondary line, and, if the value of the intensity the current flowing through a current line of a given secondary line is greater than its secondary threshold, then of /, d "/, d" '/ cancel the main countdown, then emit a signal to start an account at secondary count of initial value greater than or equal to the cut-off time of the secondary circuit-breaker the secondary line, and, at the end of the secondary countdown, repeat the steps (a '/, b' /, c '/, d' /; a "/, b" /, c "/, d" /; a "'/ b"' /, c "'/ d") for the given secondary current line, and if the value of the intensity of the current flowing through a current line of the given secondary line is greater than its value. secondary threshold, cut the current of the main line, if the value of the intensity of the current in each current line of the given secondary line is less than its secondary threshold, then repeat the steps (a '/, b' / , c '/, d' /; a "/, b" /, c "/, d" / "a" '/, b "' /, c" '/, d "' /) for the other lines of secondary current, if the value of the intensity of the current in all the secondary lines is lower than their secondary threshold, then at the end of the main countdown, cut the current of the main line. 19. The method of claim 18, the transmitted signals being "all-or-nothing" (TOR) signals. 3032837 24 20. Application of the method according to claim 18 or 19 for the protection of an alternating electric network or for the protection of a DC network.