Electrical protection unit

Abstract

An electrical protection unit (2) comprises: a separable electrical contact (14) capable of being associated with an electrical conductor (4) of an electrical facility, an electromagnetic actuator (10) configured to open the separable electrical contact (14) when activated, an electronic trip device (18) configured to activate the electromagnetic actuator when an electrical fault is detected in the facility, and a power supply circuit (22) powered from the electrical conductor (4) and configured to supply power to the electronic trip device (18), wherein the electrical protection unit (2) further comprises an auxiliary trip device (24, 26) configured to detect a loss of power supply at an output of the power supply circuit (22) and to activate the electromagnetic actuator (10) in response to such a loss of power supply.

Description

Technical Field

[0001] The invention relates to an electric protection unit, in particular to a differential protection unit. Background Art

[0002] As is known, differential protection units allow protection of electrical installations against differential electrical faults. Such units are generally connected to an electrical line comprising a phase conductor and a neutral conductor and, in the event of a detected fault, allow interruption of the current flowing through the line by opening separable electrical contacts.

[0003] Among these known differential protection units there is a class of units known as "voltage dependent" units, which are powered by the electrical line to which they are associated, for example by connection to a phase conductor.

[0004] Therefore, the electronic circuits installed in these protection units, including in particular the tripping devices for detecting differential electrical faults, are generally powered entirely by the voltage obtained from the installation. This power supply can be achieved via a power supply circuit comprising, for example, a rectifier.

[0005] This arrangement makes it unnecessary to provide an independent or separate power supply and simplifies the use of the protection unit.

[0006] However, there is a risk that in the event of a fault in this power supply circuit, the tripping device will no longer be powered, so that the protection unit cannot detect a differential fault or take action if such a fault is detected, which may lead to serious safety problems.

[0007] More generally, similar problems may occur with electrical protection units other than differential protection units. Summary of the invention

[0008] Therefore, there is a need for electrical protection units powered by an electrical facility that protect and exhibit more reliable operation in the event of a fault, and that can do so regardless of the location of the power source relative to the protection unit in the facility.

[0009] To this end, one aspect of the present invention relates to an electrical protection unit, comprising:

[0010] - separable electrical contacts capable of being associated with electrical conductors of an electrical installation,

[0011] - an electromagnetic actuator configured to open the separable electrical contacts when activated,

[0012] - an electronic trip device configured to activate the electromagnetic actuator when an electrical fault is detected in the facility, and

[0013] - a power supply circuit, supplied with power from the electrical conductor and configured to supply power to the electronic trip device.

[0014] The electrical protection unit further includes an auxiliary trip device configured to detect a loss of power supply at an output of the power supply circuit and to activate the electromagnetic actuator in response to such loss of power supply.

[0015] According to the invention, in the event of a fault in the power supply circuit, the protection unit exhibits a reliable and safe behavior, since the control circuit automatically sends a tripping command as soon as the detector detects a loss or a fault in the power supply.

[0016] According to some advantageous but non-mandatory aspects, such a protection unit may combine one or more of the following features, alone or in any technically permissible combination:

[0017] The auxiliary tripping device comprises a control circuit, for example a pulse generator, configured to generate one or more pulses of a control signal in order to intermittently energize the coil of the electronic actuator.

[0018] - A control circuit is coupled to a power switch, such as a thyristor, which controls the activation of the electromagnetic actuator.

[0019] - The pulses are separated by a duration longer than or equal to 500 milliseconds or longer than or equal to 1 second.

[0020] The ratio of the duration separating two pulses to the duration of each pulse is higher than or equal to 50, preferably higher than or equal to 100.

[0021] - The duration of each pulse is less than or equal to 50 milliseconds.

[0022] - the auxiliary tripping device comprises a detector connected at the output of the power supply circuit, such as a window detector, which is configured to disable the pulse generator as long as the power supply circuit delivers a voltage at the output and to allow the control circuit to transmit pulses in the event of a loss of power supply at the power supply circuit output.

[0023] The auxiliary tripping device is further configured to, in case of detection of a loss of power supply at the power supply circuit output, activate the electromagnetic actuator in a manner synchronized with a rising edge of the power supply voltage at the power supply circuit input.

[0024] - The auxiliary tripping device comprises a unijunction transistor.

[0025] The auxiliary tripping device is configured to issue an alarm in case of tripping of the actuator after detecting a loss of power supply at the power supply circuit output.

[0026] The invention will be better understood and other advantages of the invention will become more apparent from the following description of an embodiment of an electrical protection unit provided by way of example only and with reference to the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 An electrical protection unit according to an embodiment of the present invention is schematically shown, which is configured to protect electrical facilities;

[0028] Figure 2 A method for using the protection unit in the event of a fault in the power supply circuit is shown. Figure 1 Example of a control signal for tripping a protection unit;

[0029] Figure 3 Schematically shows Figure 1 An embodiment of an auxiliary tripping device of a protection unit;

[0030] Figure 4 Shown in Figure 3 Example of voltage measured over time at multiple locations of an auxiliary trip device. DETAILED DESCRIPTION

[0031] Figure 1 An electrical protection unit 2 is shown which is intended to protect an electrical installation, such as an electrical distribution installation.

[0032] In some preferred embodiments, the protection unit 2 is a differential protection unit.

[0033] For example, the unit 2 is associated with an electric line 4 comprising a phase conductor and a neutral conductor.

[0034] The unit 2 comprises an electromagnetic actuator 10 including at least one coil 12 configured to initiate movement of a separable electrical contact 14 associated with the electrical wire 4 when said coil 12 is energized by injecting an electric current, for example a current pulse.

[0035] The unit 2 further comprises a sensor 16 configured to detect electrical faults in the electrical wires 4, for example mounted in a differential measurement torus around the phase conductors and the neutral conductor.

[0036] The unit 2 comprises an electronic tripping device 18 connected to the sensor 16 and configured to activate an electromagnetic actuator when an electrical fault is detected in the installation.

[0037] For example, the electronic trip device 18 is configured to detect a fault condition based on measurements made by the sensor 16. In response, the electronic trip device 18 is configured to generate a trip signal to activate the actuator 10.

[0038] In many embodiments, the electronic trip device 18 is implemented by one or more electronic circuits. For example, the electronic trip device 18 includes a processor, such as a programmable microcontroller or a microprocessor. According to some variations, the electronic trip device 18 may include a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or an application-specific integrated circuit (ASIC), or any equivalent element.

[0039] Preferably, the electromagnetic actuator 10 is configured to be powered by the electrical line 4 when the unit is tripped and the electromagnetic actuator 10 is activated. In other words, the electromagnetic actuator 10 relies on power delivered by the electrical utility to ensure its operation when activated during a trip.

[0040] For example, one end of the coil 12 is connected to the line 4 and the other end is connected to the power switch 20, which is connected to the electrical ground of the circuit. The power switch 20 can be switched between an on state and an off state. In order to power the coil 12, the switch 20 is switched to the on state, thereby allowing current to flow between the line 4 and the electrical ground.

[0041] For example, the switch 20 is switched under the action of a control signal sent by the electronic trip device 18 .

[0042] According to some exemplary embodiments, the switch 20 is a thyristor.

[0043] The unit 2 also comprises an electric power supply circuit 22 supplied by the electric conductor 4 .

[0044] Power supply circuit 22 is configured to supply power to electronic trip device 18. In other words, electronic trip device 18 operates indirectly using power delivered by the electric utility.

[0045] For example, the power supply circuit 22 includes a rectifier and / or a filter circuit for regulating the voltage received from the line 4. In practice, this voltage may come from a power source that supplies power to the electrical facility, such as a generator or a distribution network.

[0046] According to some embodiments, the electrical protection unit 2 further comprises an auxiliary trip device configured to detect a loss of power supply at the output of the power supply circuit 22 and to activate the electromagnetic actuator 10 in response to such loss of power supply.

[0047] For example, the auxiliary trip device comprises a detector 24, such as a window detector, connected at the output of the power supply circuit 22. Said output of the power supply circuit 22 delivers a power supply voltage, which supplies the electronic trip device 18, for example.

[0048] The auxiliary trip device comprises a control circuit 26 , such as a pulse generator 26 .

[0049] The control circuit 26 is configured to generate one or more pulses of a control signal when activated so as to energize the coil 12 of the electronic actuator.

[0050] When the unit 2 is operating, the control circuit 26 remains inactive as long as the power supply circuit 22 operates normally and supplies power to the electronic trip device 18 normally.

[0051] In many embodiments, activation of the control circuit 26 is performed by the detector 24 , which allows the control circuit 26 to issue a trip signal in the event of a loss of power supply at the output of the power supply circuit 22 .

[0052] More specifically, detector 24 is configured to disable control circuit 26 as long as power supply circuit 22 is operating normally.

[0053] For example, as long as the power supply circuit 22 delivers a voltage at the output, it is considered to be operating normally.

[0054] In practice, a "window" may be defined, i.e. an interval of voltage values ​​defined by two predefined thresholds. As long as the voltage delivered by the power supply circuit 22 remains within the interval of voltage values, the power supply circuit 22 is considered to be operating normally. It will therefore be understood that the detector 24 performs a comparison of the voltage value measured at the output of the power supply circuit 22 with one or more predefined thresholds.

[0055] In the example shown, the control output of the electronic trip device 18 and the output of the control circuit 26 are connected to the control electrode of the switch 20, for example via an OR logic gate, which here has Figure 1 The figure number 28 in.

[0056] With the help of Figure 2 An example of the operation of the auxiliary trip device is explained.

[0057] The graph 30 shows the variation over time of a control signal, also referred to as a trip signal (denoted “Trig”), delivered at the output of the control circuit 26 for switching the switch 20 and thereby driving the electromagnetic actuator 10 .

[0058] Graph 32 shows the variation over time of a status signal (denoted “Sensor”) delivered at the output of the detector 24 and provided to the input of the control circuit 26 .

[0059] In the example shown, the state signal can take two possible values: a first value corresponding to an active state of the detector 24 (eg, a high value) and a second value corresponding to an inactive state (eg, a low value lower than the first value).

[0060] For example, the detector 24 is configured to remain in an active state as long as the power supply circuit 22 operates normally and properly powers the electronic trip device 18. In the event of a loss of power supply, the detector 24 transitions to an inactive state.

[0061] exist Figure 2 In the example, at the beginning, the power supply circuit 22 operates normally, so the detector 24 is initially in an active state. The delivered status signal remains at the first value, thereby disabling the control circuit.

[0062] Then, at a time indicated by reference 34 on the graph 32 , the status signal delivered by the detector 24 transitions to a second value, for example after a loss of power supply due to a fault in the power supply circuit 22 .

[0063] The control circuit 26 then exits the inhibited state and sends one or preferably a plurality of electrical pulses 36. Depending on the nature of the switch 20, the pulses may be current pulses or voltage pulses.

[0064] In the example shown, the pulses 36 cause the switch 20 to switch rapidly and sequentially between the on and off states. The or each coil 12 is then energized by a current pulse, causing activation of the actuator 10 and opening of the separable contacts 14.

[0065] According to some advantageous embodiments, the duration of the pulse 36 denoted D1 and the duration separating the two pulses 36 denoted D2 are selected so as to have a predefined duty cycle.

[0066] Preferably, the pulses 36 are sent periodically by the control circuit 26 so that the duration D2 separating two consecutive pulses 36 is the same for all pulses.

[0067] Thus, in general, the ratio of the duration D2 separating two pulses 36 to the duration D1 of each pulse 36 is higher than or equal to 50, preferably higher than or equal to 100.

[0068] According to one illustrative example, pulses 36 are separated by a duration D2 longer than or equal to 500 milliseconds or longer than or equal to 1 second or even more preferably longer than or equal to 2 seconds.

[0069] Similarly, the duration D1 of each pulse 36 is shorter than or equal to 50 milliseconds.

[0070] According to some advantageous embodiments explained in more detail below, the auxiliary tripping device is also configured such that activation of the electromagnetic actuator 10 upon detection of loss of power supply at the output of the power supply circuit 22 is synchronized with a rising edge of the power supply voltage.

[0071] Here, the power supply voltage is a voltage obtained from the line 4 and is supplied to the input of the power supply circuit 22 .

[0072] An example of an implementation of the control circuit 26 is shown in Figure 3 Below the mark 40 in the middle.

[0073] The control circuit 26 is particularly advantageously constructed on the basis of components of the unijunction transistor type, preferably programmable unijunction transistors.

[0074] For example, the two transistors T1 and T2 are connected to each other between a first point P1 and a second point P2. The two transistors T1 and T2 may be bipolar transistors connected end to end through their respective collectors and bases (the collector of each transistor is connected to the base of the other transistor).

[0075] According to one illustrative example, the first transistor T1 may be a PNP bipolar transistor and the second transistor T2 may be an NPN bipolar transistor.

[0076] In practice, transistors T1 and T2 measure the potential difference between point P1 and point P2.

[0077] In the illustrated example, the terminal labeled “Input” represents a power supply terminal connected to an electric utility and at the same potential as the line 4. The power supply terminal is connected to a conductor connecting the switch 20 to the coil 12, for example.

[0078] The terminal “Trip output” is connected to the output terminal of the switch 20 , to which the control signal including the pulse 36 is delivered.

[0079] Terminal "Inhib" is an input terminal, here shown with a dashed line, connected to the output of detector 24. The reference "GND" denotes the electrical ground of the circuit.

[0080] Point "OUT" represents an intermediate point connected to the emitter of the second transistor T2 and indirectly connected to the output "Trip output". In the example shown, point P1 is connected to the emitter of the first transistor T1 and point P2 is connected to the base of the second transistor T2.

[0081] These points P1 , P2 , and OUT are defined for illustrative purposes to explain certain aspects of the operation of circuit 40 .

[0082] The circuit 40 further includes resistors R1 , R2 , R3 , R4 , R5 , diodes D1 , D2 , and capacitors C1 , C2 .

[0083] With the help of Figure 4 Explaining the operation of circuit 40, Figure 4The variation over time (denoted t, expressed in milliseconds) of the potential measured at the points P1 , P2 , OUT (or, equivalently, the voltage between these points and ground GND) and of the network voltage received by the input “Input” is shown.

[0084] In the example shown, curves 54, 52, 56 and 50 correspond to the voltage at point P1, the voltage at point P2, the input voltage and the voltage at point OUT, respectively. To simplify the explanation, these voltages are represented on an arbitrary magnitude scale (on the y-axis).

[0085] In practice, the inhibition performed by the detector 24 consists in short-circuiting the terminals of a capacitor C1 connected in parallel with the detector 24 between ground and the terminal “Inhib”, this capacitor C1 also being connected in series with a resistor R1 and a diode D1 between ground GND and the input “Input”. A point P1 is connected between the resistor R1 and the capacitor C1.

[0086] Therefore, as long as there is a non-zero voltage across the capacitor, the potential at point P1 will not increase.

[0087] Furthermore, as long as the potential at point P1 is lower than that at point P2, the assembly is in a static state and nothing happens. The potential at point P2 is stable at the value produced by the voltage divider bridge formed by resistors R2, R3 and R4 at point OUT, which are connected in series between the input terminal "Input" and ground GND.

[0088] The residual ripple observed in curve 52 depends on the value of a second capacitor C2 connected in parallel with resistors R3 and R4 between point P2 and ground GND.

[0089] However, the voltage at point OUT depends on the value of resistor R4, which is chosen to remain below the conduction threshold of diode D2, which is connected here in the circuit branch connecting point OUT to output "Trip output". At the output, resistor R5 limits the current output through output "Trip output".

[0090] For example, the conduction threshold of diode D2 may be selected to be approximately 0.2V.

[0091] As mentioned above, the tripping of the actuator 10 must be synchronized with the occurrence of the rising edge of the network voltage. This makes it easier to interrupt the current in the line 4 when the separable contacts 14 are opened under the action of the trip device 10.

[0092] For this purpose, preferably, the trip command represented by the first pulse 36 must be sent by the control circuit at the moment when the potential ripple at the point P2 starts to decrease.

[0093] This behavior can be obtained by sizing capacitors C1 and C2 (and resistors R1 and R2) so that the time constant of the charging circuit associated with the second capacitor C2 is lower (faster) than the time constant associated with the first capacitor C1.

[0094] Furthermore, in order to ensure the above-mentioned synchronization, it may be desirable that the voltages measured at points P1 and P2 remain confined to a certain range of values ​​related to the turn-on threshold voltage of the unijunction transistor.

[0095] Therefore, the turn-on threshold voltage (hereinafter indicated as Vth) of the unijunction transistor can be adjusted by appropriately adjusting the dimensions of the components of the circuit 40 so that during the stage when the potential measured at the second point P2 is decreasing, the increase in the amplitude of the potential measured at the first point P1 (which occurs periodically with the oscillation of the input voltage, as shown in FIG. Figure 4 It is defined as being less than twice the turn-on threshold voltage Vth) as shown in curves 50 and 52.

[0096] Similarly, during the phase in which the potential measured at the first point P1 is decreasing, the amplitude variation of the potential measured at the second point P2 (visible in curves 50 and 52 ) is greater than five times the turn-on threshold voltage Vth to avoid delays in trip commands associated with zero crossings of the supply voltage.

[0097] The choice of the capacitance values ​​of capacitors C1 and C2 also makes it possible to adjust the duration D2 separating the two pulses.

[0098] For example, in an AC grid of 230 V operating at 50 Hz, for values ​​of resistors R1, R2, R3 and R4 equal to 2M, 500k, 100k and 1k respectively, and for a capacitance value of capacitor C2 equal to 1 μF, a capacitance value of the first capacitor C1 between 1.5 μF and 10 μF, a duration D2 between 550 milliseconds and 3.6 seconds will be given.

[0099] exist Figure 4 , the tripping occurs a short time after the time marked at 540 milliseconds on the x-axis.

[0100] Typically, when inhibition is no longer performed, the voltage at point P1 increases until it exceeds the voltage at point P2. Transistor T1 switches to the conducting state, transistor T2 follows it and in turn switches to the conducting state.

[0101] A cascade effect is then observed, since the sudden switching on of the second transistor T2 causes a rapid discharge of the capacitor C1 , which generates a pulse 36 and corresponds to the voltage peak observed at the point OUT (curve 56 ).

[0102] Once the first capacitor C1 has been discharged, the circuit returns to its initial position and the voltage at point P1 increases again due to the charging of capacitor C1 through resistor R1.

[0103] The same steps are repeated cyclically as capacitor C1 discharges and then charges again.

[0104] Generally speaking, the auxiliary trip device of unit 2 is configured to implement the following operations:

[0105] - automatically inhibiting the control circuit 26, for example by means of a signal sent to the control circuit 26 by the detector 24, as long as the power supply circuit 20 supplies the trip device 18 normally;

[0106] - When the power supply circuit 20 stops supplying normal power to the trip device 18, a trip signal is generated by the control circuit 26. For example, the detector 24 detects the loss of power supply and then stops inhibiting the control circuit 26.

[0107] By means of the invention, the protection unit 2 exhibits a reliable and safe behavior in the event of a fault in the power supply circuit 22, since the pulse generator 26 automatically sends a tripping command as soon as the detector 24 detects a loss or a fault of the power supply.

[0108] Furthermore, the use of the auxiliary tripping device according to the above-described embodiment allows the protection unit 2 to operate and ensure such safe behavior regardless of the connection mode of the protection unit 2 in the electrical installation.

[0109] In other words, the protection unit 2 exhibits the described operation regardless of whether the power supply source of the facility is connected upstream or downstream of the protection unit 2 .

[0110] In particular, the use of electric pulses to control the switch 20 makes it possible to avoid any risk of overheating and thermal damage to the protection unit 2. Specifically, the actuator 10 may be optimized in terms of the size of the coil 12, or exhibit a certain degree of compactness, and therefore the actuator 10 may not be able to withstand the temperature increase caused by the heating of the coil 12 when the coil 12 is continuously powered.

[0111] Now, this is exactly what happens when the protection unit 2 is connected upstream of the power supply source of the installation. In particular, since the connection to the wire 4 for powering the actuator 10 and the power supply circuit 22 is located downstream of the separable contact 14, as shown in FIG. Figure 1 As shown, the actuator 10 will therefore continue to be continuously powered even in the event that the separable contacts 14 are tripped and opened.

[0112] In the present case, the duration of the pulse is relatively short relative to the duration between two pulses, which allows the actuator to cool down between two pulses while still ensuring tripping of the unit 2 and opening of the separable contacts 14 .

[0113] In addition, the pulse generator 26 here consists of relatively simple, reliable and cheap components. Due to this simplified design and its passive behavior, the pulse generator 26 therefore has no risk of potential failure in its own auxiliary power supply, which ensures a more reliable behavior in the event of a failure.

[0114] In many embodiments, the detector 24 may be implemented by an electronic circuit made up of discrete components (eg by transistors) in order to obtain the above described behavior.

[0115] According to one embodiment (not shown), the detector 24 comprises:

[0116] - a first transistor, a first resistor and a first zener diode, which are connected in series to form a first branch of the circuit, and

[0117] - a second transistor, a second resistor and a second Zener diode, which are connected in series to form a first branch of the circuit.

[0118] In both cases, the resistor is connected to the control electrode of the respective transistor, for example to the gate of the transistor.

[0119] For example, the transistors are metal oxide semiconductor (MOS) transistors, but other technologies may also be used.

[0120] The first transistor is additionally connected (here via its drain) to an output terminal of the detector 24, through which a status signal is transmitted when the detector 24 is operating. The output terminal of the detector 24 is intended to be connected to an input terminal "Inhib" of the circuit 40. The other terminal of the first transistor is connected to the ground of the circuit. The second transistor is additionally connected (here via its drain) to the first branch and is connected to the ground of the circuit via its other electrode.

[0121] One or more resistors may be connected between each branch and electrical ground.

[0122] Both the first and the second Zener diode are connected with their cathodes to an input terminal of the detector 24. This input is intended to be connected to the output of the power supply circuit 22 in order to measure the voltage to be monitored.

[0123] The threshold voltage of the Zener diode makes it possible to define the threshold of the window of values ​​to be monitored.

[0124] For example, the threshold voltage of the first Zener diode is used to define the lower limit value of the window to be monitored, and the threshold voltage of the second Zener diode is used to define the upper limit value of the window to be monitored.

[0125] In practice, however, one has to take into account the presence of various resistors, which act as a voltage divider bridge.

[0126] Therefore, when the voltage received through the input terminal is equal to the lower threshold of the window (which is determined by the first Zener diode), the first transistor is turned on.

[0127] When the voltage received through the input terminal is equal to the upper threshold of the window (which is determined by the second Zener diode), the second transistor is turned on.

[0128] However, other embodiments are possible.

[0129] According to a first variant, the detector 24 may be integrated into an electronic fault monitoring device forming part of the protection unit 2 .

[0130] Therefore, the electronic fault monitoring device can be implemented by one or more electronic circuits (such as a processor, in particular a programmable microcontroller or microprocessor), or by a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or an application-specific integrated circuit (ASIC), or any equivalent element.

[0131] According to a second variant, as an extension of the first variant, the electronic fault monitoring device may also be combined with the electronic tripping device 18. In other words, the detector 24 and the electronic tripping device 18 then form part of the same device connected to the monitoring circuit 26.

[0132] In both variants, the electronic fault monitoring device can implement independent monitoring and diagnostic functions with respect to detecting faults in the power supply circuit 22 .

[0133] For example, the electronic fault monitoring device may include a measurement probe coupled to the sensor 16 in order to detect a fault in the sensor 16 or in an associated measurement and processing chain.

[0134] In case the sensor 16 is a differential measurement loop, the measurement probe may be configured to inject current into the loop by induction.

[0135] The embodiments and variants envisaged above can be combined with one another in order to create new embodiments.

Claims

1. An electrical protection unit (2) for protecting electrical facilities, the electrical protection unit (2) comprising: - a detachable electrical contact (14) capable of being associated with an electrical conductor (4) of said electrical installation, - an electromagnetic actuator (10) configured to open the separable electrical contacts (14) when activated, - an electronic trip device (18) configured to activate said electromagnetic actuator when an electrical fault is detected in said installation, and - a power supply circuit (22), supplied by the electrical conductor (4) and configured to supply power to the electronic tripping device (18), in, The electrical protection unit (2) also includes an auxiliary trip device (24, 26) configured to detect a loss of power supply at the output of the power supply circuit (22) and to activate the electromagnetic actuator (10) in response to such a loss of power supply.

2. The electrical protection unit according to claim 1, wherein the auxiliary tripping device (24, 26) comprises a control circuit (26) configured to generate one or more pulses (36) of a control signal so as to intermittently energize the coil (12) of the electromagnetic actuator (10).

3. The electrical protection unit of claim 2, wherein the control circuit (26) is coupled to a power switch (20), the power switch controlling activation of the electromagnetic actuator (10).

4. An electrical protection unit according to any one of claims 2 and 3, wherein the pulses (36) are separated by a duration longer than or equal to 500 milliseconds or longer than or equal to 1 second.

5. An electrical protection unit according to claim 4, wherein the ratio of the duration separating two pulses (36) to the duration of each pulse (36) is higher than or equal to 50.

6. The electrical protection unit according to any one of claims 2 to 3, wherein the duration of each pulse (36) is shorter than or equal to 50 milliseconds.

7. An electrical protection unit according to any one of claims 2 to 3, wherein the auxiliary tripping device (24, 26) comprises a detector (24) connected at the output of the power supply circuit (22), the detector (24) being configured to inhibit the pulse generator as long as the power supply circuit (22) delivers a voltage at the output and to allow the control circuit (26) to transmit pulses in the event of a loss of power supply at the output of the power supply circuit (22).

8. An electrical protection unit according to any one of claims 2 to 3, wherein the auxiliary tripping device (24, 26) is further configured to activate the electromagnetic actuator (10) in a manner synchronized with the rising edge of the power supply voltage at the input of the power supply circuit (22) when a loss of power supply is detected at the output of the power supply circuit (22).

9. The electrical protection unit according to any one of claims 2 to 3, wherein the auxiliary tripping device (24, 26) comprises a unijunction transistor (40).

10. An electrical protection unit according to any one of claims 2 to 3, wherein the auxiliary tripping device (24, 26) is configured to generate an alarm in the event of a tripping of the actuator (10) after detecting a loss of power supply at the output of the power supply circuit (22).

11. The electrical protection unit according to claim 2, wherein the control circuit (26) comprises a pulse generator.

12. The electrical protection unit according to claim 3, wherein the power switch (20) comprises a thyristor.

13. The electrical protection unit according to claim 4, wherein the ratio of the duration separating two pulses (36) to the duration of each pulse (36) is higher than or equal to 100.

14. The electrical protection unit of claim 7, wherein the detector (24) comprises a window detector.

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