CN114336520A

CN114336520A - Electric protection unit

Info

Publication number: CN114336520A
Application number: CN202111158920.2A
Authority: CN
Inventors: B.博德特; J.默尼耶-卡鲁斯
Original assignee: Schneider Electric Industries SAS
Current assignee: Schneider Electric Industries SAS
Priority date: 2020-09-30
Filing date: 2021-09-30
Publication date: 2022-04-12
Also published as: FR3114681A1; FR3114681B1; AU2021236427A1

Abstract

An electrical protection unit (2) comprising-separable electrical contacts (14) associable with electrical conductors (4) of an electrical installation, -an electromagnetic actuator (10) configured to open the separable electrical contacts (14) when activated, -an electronic trip device (18) configured to activate the electromagnetic actuator when an electrical fault is detected in the installation, and-a power supply circuit (22) powered from the electrical conductors (4) and configured to power 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

Electric protection unit

Technical Field

The present invention relates to an electrical protection unit, and more particularly, to a differential protection unit.

Background

As is known, differential protection units allow to protect electrical installations from differential electrical faults. Such units are typically connected to an electrical line that includes a phase conductor and a neutral conductor, and allow an interrupting current to flow through the line by opening the separable electrical contacts in the event of a detected fault.

Among these known differential protection units, there is a class of units known as "voltage-dependent" units, which are powered by their associated wires, for example by being connected to phase conductors.

The electronic circuits installed in these protection units, in particular including the trip devices for detecting differential electrical faults, are therefore generally completely powered by the voltage obtained from the installation. The power supply may be realized via a power supply circuit including, for example, a rectifier.

This arrangement makes it possible to dispense with the provision of a separate power supply or a separate power supply and simplifies the use of the protection unit.

However, there is a risk that in case of a failure of the power supply circuit the trip device will no longer be powered, so that the protection unit cannot detect a differential failure or take action in case such a failure is detected, which may lead to serious safety problems.

More generally, similar problems occur with electrical protection units other than differential protection units.

Disclosure of Invention

There is therefore a need for electrical protection units supplied by electrical installations, which protect against faults and exhibit a more reliable operation, and which can do so irrespective of the position of the power supply in the installation relative to the protection units.

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

separable electrical contacts associable with electrical conductors of an electrical installation,

an electromagnetic actuator configured to open the separable electrical contacts when activated,

-an electronic trip device configured to activate the electromagnetic actuator when an electrical fault is detected in the installation, an

-a power supply circuit powered from the electrical conductor and configured to supply power to the electronic trip device.

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

According to the invention, the protection unit exhibits a reliable and safe behavior in case of a failure of the power supply circuit, since the control circuit automatically sends a trip command as soon as the detector detects a loss or a failure of the power supply.

According to some advantageous but not mandatory aspects, such protection units may incorporate one or more of the following features, alone or according to any technically allowable combination:

the auxiliary trip device comprises a control circuit, for example a pulse generator, configured to generate one or more pulses of a control signal so as to intermittently energize the coil of the electronic actuator.

The control circuit is coupled to a power switch, e.g. a thyristor, which controls the activation of the electromagnetic actuator.

-the pulses are separated by a duration longer than or equal to 500 milliseconds in duration or longer than or equal to 1 second.

-the ratio of the duration of the separation of the two pulses to the duration of each pulse is higher than or equal to 50, preferably higher than or equal to 100.

-the duration of each pulse is shorter than or equal to 50 milliseconds.

The auxiliary trip device comprises a detector, for example a window detector, connected at the output of the power supply circuit, said detector being 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 a pulse in the event of a loss of power supply at the output of the power supply circuit.

The auxiliary trip device is further configured to activate the electromagnetic actuator in a synchronized manner with a rising edge of the power supply voltage at the power supply circuit input in case a loss of power supply at the power supply circuit output is detected.

-the auxiliary trip means comprises a unijunction transistor.

The auxiliary trip device is configured to issue an alarm in case of tripping of the actuator after detection of loss of power supply at the power supply circuit output.

The invention will be better understood and other advantages thereof will become more apparent from the following description of one embodiment of an electrical protection unit, provided by way of example only and with reference to the accompanying drawings, in which:

drawings

Fig. 1 schematically shows an electrical protection unit according to an embodiment of the invention, configured to protect an electrical installation;

fig. 2 shows an example of a control signal for tripping the protection unit of fig. 1 in case of a fault in the power supply circuit of the protection unit;

fig. 3 schematically illustrates one embodiment of an auxiliary trip device of the protection unit of fig. 1;

fig. 4 illustrates an example of voltage measured over time at various locations of the auxiliary trip unit of fig. 3.

Detailed Description

Fig. 1 shows an electrical protection unit 2 intended to protect an electrical installation, such as a power distribution installation.

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

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

The unit 2 comprises an electromagnetic actuator 10, the electromagnetic actuator 10 comprising at least one coil 12, the coil 12 being configured to initiate movement of the separable electrical contacts 14 associated with the electrical wires 4 when said coil 12 is energized by injecting an electrical current (e.g. a current pulse).

The unit 2 further comprises a sensor 16, the sensor 16 being configured to detect an electrical fault in the electrical line 4, for example a differential measurement ring (differential measurement torus) mounted around the phase and neutral conductors.

Unit 2 includes an electronic trip device 18 connected to sensor 16, electronic trip device 18 being configured to activate an electromagnetic actuator when an electrical fault is detected in the facility.

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

In many embodiments, electronic trip device 18 is implemented by one or more electronic circuits. For example, electronic trip device 18 includes a processor, such as a programmable microcontroller or microprocessor. According to some variants, electronic trip device 18 may comprise a signal processing processor (DSP), or a reprogrammable logic assembly (FPGA), or an Application Specific Integrated Circuit (ASIC), or any equivalent element.

Preferably the electromagnetic actuator 10 is configured to be powered by the electrical cord 4 when the unit is tripped and the electromagnetic actuator 10 is activated. In other words, the electromagnetic actuator 10 relies on the power delivered by the electrical installation to ensure its operation when activated during tripping.

For example, the coil 12 is connected at one end to the line 4 and at the other end to a power switch 20, the power switch 20 being connected to the electrical ground of the circuit. The power switch 20 is switchable between an on state and an off state. To power the coil 12, the switch 20 is switched to an on state, allowing current to flow between the line 4 and electrical ground.

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

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

The unit 2 further comprises a power supply circuit 22 powered by the electrical conductor 4.

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

For example, the power supply circuit 22 comprises 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, such as a generator or a distribution network, that powers the electrical installation.

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 a loss of power supply.

For example, the auxiliary trip device includes a detector 24, such as a window detector, connected at the output of the power supply circuit 22. For example, the output of power supply circuit 22 carries a power supply voltage that powers electronic trip device 18.

The auxiliary trip device includes a control circuit 26, such as a pulse generator 26.

The control circuit 26 is configured to generate one or more pulses of a control signal when activated in order to energize the coil 12 of the electronic actuator.

When unit 2 is operating, control circuit 26 remains inactive as long as power supply circuit 22 is operating normally and supplying power normally to electronic trip device 18.

In many embodiments, activation of the control circuit 26 is 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.

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

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

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 the voltage value, the power supply circuit 22 is considered to be operating normally. It will therefore be appreciated 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.

In the example shown, the control output of electronic trip unit 18 and the output of control circuit 26 are connected to the control electrode of switch 20, for example through an or logic gate, here bearing reference numeral 28 in fig. 1.

An example of the operation of the auxiliary trip device is explained with the aid of fig. 2.

The graph 30 shows the variation over time of a control signal (denoted "Trig"), also called trip signal, delivered at the output of the control circuit 26, which is used to switch the switch 20, thus driving the electromagnetic actuator 10.

Graph 32 shows the variation over time of the status signal (denoted "Sensor") delivered at the output of detector 24 and supplied to the input of control circuit 26.

In the example shown, the status signal may take two possible values, a first value corresponding to an active state of the detector 24 (e.g. a high value) and a second value corresponding to an inactive state (e.g. a low value lower than the first value).

For example, detector 24 is configured such that detector 24 remains in an active state as long as power supply circuit 22 is operating normally and providing proper power to electronic trip device 18. In the event of a loss of power supply, the detector 24 transitions to an inactive state.

In fig. 2, at the beginning of the example, the power supply circuit 22 is operating normally, so the detector 24 is initially in an active state. The status signal is delivered to remain at the first value thereby disabling the control circuit.

Then, at a time indicated by reference numeral 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.

The control circuit 26 then ends the disabled state and sends one or preferably a plurality of electrical pulses 36. The pulses may be current pulses or voltage pulses, depending on the nature of the switch 20.

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 energised by a current pulse causing the activation of the actuator 10 and the opening of the separable contacts 14.

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

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

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.

According to one illustrative example, the pulses 36 are separated by a duration D2 that is 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.

Similarly, the duration D1 of each pulse 36 is less than or equal to 50 milliseconds.

According to some advantageous embodiments, which will be explained in more detail below, the auxiliary trip device is also configured such that the activation of the electromagnetic actuator 10 in the event of a loss of power supply at the output of the power supply circuit 22 is detected, is synchronized with the rising edge of the power supply voltage.

Here, the power supply voltage is a voltage obtained from the line 4, and is delivered to an input of the power supply circuit 22.

One example of an implementation of the control circuit 26 is shown below the label 40 in fig. 3.

Particularly advantageously, the control circuit 26 is constructed on the basis of components of the unijunction transistor type, preferably programmable unijunction transistors.

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

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.

In practice, transistors T1 and T2 measure the potential difference between points P1 and P2.

In the illustrated example, the terminal labeled "Input" represents a power supply terminal connected to an electrical facility and at the same potential as the line 4. For example, the power supply terminal is connected to a conductor connecting the switch 20 to the coil 12.

The terminal "Trip output" is an output terminal connected to the switch 20 to which a control signal containing the pulse 36 is supplied.

Terminal "Inhib" is an input terminal connected to the output of detector 24, here shown in dashed lines. The label "GND" represents the electrical ground of the circuit.

The point "OUT" represents the middle point connected to the emitter of the second transistor T2 and indirectly 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.

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

The circuit 40 also includes resistors R1, R2, R3, R4, R5, diodes D1, D2, and capacitors C1, C2.

The operation of the circuit 40 is explained by means of fig. 4, which shows the variation over time (denoted t, expressed in milliseconds) of the potentials measured at the points P1, P2, OUT (or, equivalently, the voltages between these points and the ground GND) and of the network voltage received through the Input ".

In the illustrated example, 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. For simplicity of explanation, these voltages are represented on an arbitrary magnitude scale (on the y-axis).

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 ". The point P1 is connected between the resistor R1 and the capacitor C1.

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

Further, as long as the potential of the point P1 is lower than the potential of the point P2, the element is in a stationary state, and nothing happens. The potential of point P2 stabilizes at the value produced by the voltage divider bridge formed by resistors R2, R3 and R4 at point OUT, these resistors R2, R3 and R4 being connected in series between the Input terminal "Input" and ground GND.

The residual ripple (ripple) observed in curve 52 depends on the value of a second capacitor C2, which capacitor C2 is connected in parallel with resistors R3 and R4 between point P2 and ground GND.

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

For example, the conduction threshold of diode D2 may be selected to be about 0.2V.

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 by the trip device 10.

To this end, the tripping command, represented by the first pulse 36, must preferably be sent by the control circuit at the moment when the potential ripple at point P2 starts to decrease.

This behavior may be obtained by sizing the capacitors C1 and C2 (and the 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.

Furthermore, to ensure the above-described synchronization, it may be desirable that the voltages measured at points P1 and P2 remain limited to a certain range of values related to the turn-on threshold voltage of the unijunction transistor.

Thus, the turn-on threshold voltage (hereinafter Vth) of the unijunction transistor may be defined by means of appropriately sizing the components of the circuit 40 such that the increase in amplitude of the potential measured at the first point P1, which occurs periodically with the oscillation of the input voltage, as illustrated by curves 50 and 52 of fig. 4, is less than twice the turn-on threshold voltage Vth during the phase in which the potential measured at the second point P2 is decreasing.

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 the curves 50 and 52) is greater than five times the turn-on threshold voltage Vth, so as to avoid the delay of the trip command related to the zero crossing of the supply voltage.

The choice of the capacitance values of the capacitors C1 and C2 also makes it possible to adjust the duration D2 of the separation of the two pulses.

For example, in an AC grid of 230V operating at 50Hz, the values for the resistors R1, R2, R3 and R4 are equal to 2M, 500k, 100k and 1k, respectively, and the capacitance value for the capacitor C2 is equal to 1 μ F, the capacitance value of the first capacitor C1 is between 1.5 μ F and 10 μ F, giving a duration D2 of between 550 milliseconds and 3.6 seconds.

In fig. 4, the trip occurs a short time after the time marked at 540 milliseconds on the x-axis.

Generally, when the prohibition is no longer performed, the voltage at the point P1 increases until the voltage at the point P2 is exceeded. The transistor T1 switches to the conducting state, the transistor T2 follows it and switches to the conducting state in turn.

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 the pulse 36 and corresponds to the voltage peak observed at the point OUT (curve 56).

Once the first capacitor C1 is discharged, the circuit returns to its original position and the voltage at point P1 increases again as the capacitor C1 charges through resistor R1.

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

In general, the auxiliary trip device of the unit 2 is configured to perform the following operations:

as long as the power supply circuit 20 is supplying the tripping device 18 normally, the control circuit 26 is automatically disabled, for example by a signal sent by the detector 24 to the control circuit 26;

generating a trip signal by the control circuit 26 when the power supply circuit 20 stops supplying normal power to the trip device 18. For example, the detector 24 detects the loss of the power supply and then stops the inhibition of the control circuit 26.

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

Furthermore, the use of the auxiliary trip device according to the above-described embodiment allows the protection unit 2 to operate and guarantee such safety behavior regardless of the manner in which the protection unit 2 is connected in the electrical installation.

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.

In particular, the use of an electric pulse to control the switch 20 makes it possible to avoid any risk of overheating and thermal damage to the protection unit 2. In particular, 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 due to the heating of the coil 12 when the coil 12 is continuously powered.

This now happens upon tripping, precisely in the case of a protection unit 2 connected upstream of the power supply of the installation. Specifically, since the connection to the electrical cord 4 for supplying power to the actuator 10 and the power supply circuit 22 is located downstream of the separable contacts 14, as shown in fig. 1, the actuator 10 will continue to be continuously powered even if the separable contacts 14 trip and open.

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

In addition, the pulse generator 26 here consists of relatively simple, reliable and inexpensive components. Due to this simplified design and its passive behavior, the pulse generator 26 is therefore free of a risk of potential failure in its own auxiliary power supply, which ensures a more reliable behavior in case of failure.

In many embodiments, the detector 24 may be implemented by an electronic circuit composed of separate components (e.g., by transistors) in order to achieve the above-described behavior.

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

-a first transistor, a first resistor and a first zener diode connected in series to form a first branch of the circuit, an

-a second transistor, a second resistor and a second zener diode connected in series to form a first branch of the circuit.

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

For example, the transistors are Metal Oxide Semiconductor (MOS) transistors, but other techniques may be used.

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

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

Both the first and second zener diodes are connected by their cathodes to the input terminal of detector 24. Which is intended to be connected to the output of the power supply circuit 22 in order to measure the voltage to be monitored.

The threshold voltage of the zener diode makes it possible to define the threshold of the window of values to be monitored.

For example, the threshold voltage of the first zener diode is used to define the lower limit of the window to be monitored, and the threshold voltage of the second zener diode is used to define the upper limit of the window to be monitored.

In practice, however, the presence of various resistors, which act as voltage divider bridges, must be considered.

Thus, the first transistor is turned on when the voltage received through the input terminal is equal to the lower threshold of the window (which depends on the first zener diode).

The second transistor is turned on when the voltage received through the input terminal is equal to the upper threshold of the window (which depends on the second zener diode).

However, other embodiments are possible.

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

Thus, the electronic fault monitoring device may 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 by a reprogrammable logic module (FPGA), or by an Application Specific Integrated Circuit (ASIC), or by any equivalent element.

According to a second variant, as an extension of the first variant, the electronic fault monitoring device can also incorporate an electronic tripping device 18. In other words, the detector 24 and the electronic trip device 18 then form part of the same device connected to the monitoring circuit 26.

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

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

Where the sensor 16 is a differential measurement loop, the measurement probe may be configured to inject current into the loop by induction.

The embodiments and variants envisaged above may be combined with each other in order to create new embodiments.

Claims

1. An electrical protection unit (2) comprising:

-separable electrical contacts (14) associable with electrical conductors (4) of an electrical installation,

an electromagnetic actuator (10) configured to open the separable electrical contacts (14) when activated,

-an electronic trip device (18) configured to activate the electromagnetic actuator when an electrical fault is detected in the installation, and

-a power supply circuit (22) powered by the electrical conductor (4) and configured to power 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.

2. Electrical protection unit according to claim 1, wherein the auxiliary trip device (24, 26) comprises a control circuit (26), such as a pulse generator, the control circuit (26) being configured to generate one or more pulses (36) of a control signal in order to intermittently energize the coil (12) of the electronic actuator (10).

3. Electrical protection unit according to claim 2, wherein the control circuit (26) is coupled to a power switch (20), e.g. a thyristor, which controls the activation of the electromagnetic actuator (10).

4. An electrical protection unit according to any one of claims 2 and 3, wherein said pulses (36) are separated by a duration (D2) longer than or equal to 500 milliseconds or longer than or equal to 1 second.

5. Electrical protection unit according to claim 4, wherein the ratio of the duration (D2) of the two pulses (36) separated to the duration (D1) of each pulse (36) is higher than or equal to 50, preferably higher than or equal to 100.

6. An electrical protection unit according to any one of claims 2 to 5, wherein the duration (D1) 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 6, wherein the auxiliary trip device (24, 26) comprises a detector (24), such as a window detector, connected at the output of the power supply circuit (22), the detector (24) being configured to disable the pulse generator whenever the power supply circuit (22) delivers a voltage at the output and to allow the control circuit (26) to transmit a pulse 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 the preceding claims, wherein the auxiliary trip device (24, 26) is further configured to activate the electromagnetic actuator (10) in synchronism with a rising edge of the power supply voltage at the input of the power supply circuit (22) in the event of a loss of power supply at the output of the power supply circuit (22) being detected.

9. An electrical protection unit according to any one of the preceding claims wherein the auxiliary trip means (24, 26) comprises a single junction transistor (40).

10. An electrical protection unit according to any one of the preceding claims, wherein the auxiliary trip means (24, 26) is configured to issue an alarm in the event of the actuator (10) tripping after detection of a loss of power supply at the output of the power supply circuit (22).