CN114336520A - Electrical protection unit - Google Patents

Abstract

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

Description

electrical protection unit

technical field

The present invention relates to electrical protection units, in particular to differential protection units.

Background technique

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

Among these known differential protection units, there is a class of units called "voltage dependent" units, which are powered by the wires associated with them, eg by connecting to phase conductors.

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

This arrangement makes it unnecessary to provide an independent power source or a separate power source, and simplifies the use of the protection unit.

However, there is a risk that in the event of a failure of this power supply circuit, the tripping device will no longer be supplied with power, so that the protection unit cannot detect a differential fault or take action in the event of such a fault being detected, This can lead to serious security issues.

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

SUMMARY OF THE INVENTION

Therefore, there is a need for electrical protection units powered by electrical installations that protect in the event of a fault and exhibit more reliable operation, and can do so independently of the location of the power source relative to the protection unit in the installation.

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

- separable electrical contacts capable of being associated with the electrical conductors of the electrical installation,

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

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

- a power supply circuit, powered from the electrical conductors, 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 loss of power supply.

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

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:

- The auxiliary tripping device comprises a control circuit, eg a pulse generator, configured to generate one or more pulses of a control signal for intermittently energizing the coil of the electronic actuator.

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

- Pulses are separated by durations longer than or equal to 500 milliseconds or longer than or equal to 1 second.

- the ratio of the duration separating 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 less than or equal to 50 ms.

- the auxiliary tripping device comprises a detector, such as a window detector, connected at the output of the power supply circuit, the detector being configured to disable the pulse generator as long as the power supply circuit is delivering voltage at the output, and at the output of the power supply circuit Allows the control circuit to transmit pulses in the event of a loss of power supply.

- The auxiliary tripping device is further configured to activate the electromagnetic actuator in synchronization with the rising edge of the power supply voltage at the power supply circuit input in the event of detection of a loss of power supply at the power supply circuit output.

- Auxiliary tripping devices include unijunction transistors.

- The auxiliary trip device is configured to issue an alarm in the event of tripping of the actuator after detecting a loss of power supply at the output of the power supply circuit.

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, wherein:

Description of drawings

Figure 1 schematically shows an electrical protection unit according to an embodiment of the present invention, which is configured to protect an electrical installation;

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

Fig. 3 schematically shows an embodiment of the auxiliary trip device of the protection unit of Fig. 1;

FIG. 4 shows an example of voltage measured over time at various locations of the auxiliary trip device of FIG. 3 .

Detailed ways

Figure 1 shows an electrical protection unit 2 intended to protect electrical installations, such as power distribution installations.

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

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

The unit 2 includes an electromagnetic actuator 10 including at least one coil 12 configured to be associated with the wire 4 when said coil 12 is energized by injecting a current (eg, a current pulse) The separable electrical contacts 14 begin to move.

The unit 2 also includes sensors 16 configured to detect electrical faults in the electrical wires 4, eg differential measurement torus installed around the phase and neutral conductors.

The unit 2 includes an electronic trip device 18 connected to the sensor 16, the 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 fault conditions based on measurements made by sensor 16 . In response, the electronic trip device 18 is configured to generate a trip signal to activate the actuator 10 .

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 microprocessor. According to some variations, the electronic trip device 18 may comprise a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or an application specific integrated circuit (ASIC), or any equivalent element.

Preferably, the electromagnetic actuator 10 is configured to be powered by the wire 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 facility to ensure its operation when activated during a trip.

For example, one end of coil 12 is connected to line 4 and the other end is connected to power switch 20, which is 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 the on state, allowing current to flow between the line 4 and electrical ground.

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

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

The unit 2 also includes a power supply circuit 22 powered by the electrical conductors 4 .

The power supply circuit 22 is configured to supply power to the 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 includes a rectifier and/or filter circuit for regulating the voltage received from the line 4 . In practice, this voltage may come from the power source that powers the electrical installation, such as a generator or distribution grid.

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 electromagnetic induction in response to such loss of power supply Actuator 10.

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 the power supply circuit 22 delivers the power supply voltage that powers the 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 the control signal when it is activated in order to energize the coil 12 of the electronic actuator.

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

In many embodiments, activation of the control circuit 26 occurs through 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, as long as the power supply circuit 22 is delivering voltage at the output, it is considered to be operating normally.

In practice, a "window" can be defined, ie the 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. Thus, it should be understood that the detector 24 performs a comparison of the voltage value measured at the output of the power supply circuit 22 to one or more predefined thresholds.

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 electrodes of the switch 20 , for example by an OR logic gate, here with the reference numeral in FIG. 1 . 28.

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

Graph 30 shows the control signal (denoted "Trig") delivered at the output of control circuit 26, also known as the trip signal, as a function of time, which is used to toggle switch 20, thereby driving the electromagnetic actuator 10.

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

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

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

In Figure 2, at the beginning of the example, the power supply circuit 22 is operating normally, so the detector 24 is initially active. The delivered status signal remains 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, eg 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 more electrical pulses 36 . Depending on the nature of the switch 20, the pulses may be current pulses or voltage pulses.

In the example shown, pulses 36 cause rapid and sequential switching of switch 20 between 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 .

According to some advantageous embodiments, the duration of the pulse 36 denoted D1 and the duration of the split two pulses 36 denoted D2 are chosen 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 the 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 shorter 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 to enable activation of the electromagnetic actuator 10 with power in the event of a detected loss of power supply at the output of the power supply circuit 22 The rising edge of the supply voltage is synchronized.

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

An example of an implementation of the control circuit 26 is shown in FIG. 3 below the reference numeral 40 .

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 through their respective collectors and bases (the collector of each transistor is 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 point P1 and point P2.

In the illustrated example, the terminal labeled "Input" represents the power supply terminal connected to the electrical utility and at the same potential as line 4 . For example, the power supply terminals are connected to conductors that connect the switch 20 to the coil 12 .

The terminal "Trip output" is the output terminal connected to the switch 20 to which the control signal containing the pulses 36 is delivered.

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

The 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, the point P1 is connected to the emitter of the first transistor T1 and the point P2 is connected to the base of the second transistor T2.

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

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 with the aid of Fig. 4, which shows the potentials measured at points P1, P2, OUT (or, equivalently, the voltage between these points and ground GND) and the voltage received through the input "Input" The change in network voltage over time (denoted as t, expressed in milliseconds).

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).

In practice, the inhibition performed by the detector 24 consists in short-circuiting the terminals of the capacitor C1, which is connected in parallel with the detector 24 between ground and the terminal "Inhib", which capacitor C1 is also connected to the ground GND and the input "Input". The resistor R1 and diode D1 are connected in series between them. Point P1 is connected between resistor R1 and capacitor C1.

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

Also, as long as the potential at point P1 is lower than the potential at point P2, the component is at rest and nothing happens. The potential at point P2 stabilizes at the value created 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.

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

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 on the circuit branch connecting point OUT to the output "Trip output" . At the output, resistor R5 limits the current output through the output "Trip output".

For example, the turn-on threshold of diode D2 may be chosen to be approximately 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 under the action of the trip device 10 .

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

This behavior can be achieved by adjusting the dimensions of 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 associated with the first capacitor C1 constant to obtain.

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

Thus, the turn-on threshold voltage of the unijunction transistor (referred to hereinafter as Vth) can be achieved by appropriately adjusting the dimensions of the components of the circuit 40 such that during the phase in which the potential measured at the second point P2 is decreasing, at the first point The increase in the magnitude of the potential measured at P1, which occurs periodically as the input voltage oscillates, as shown by curves 50 and 52 of FIG. 4, is defined as being less than twice the turn-on threshold voltage Vth.

Similarly, during the phase in which the potential measured at the first point P1 is decreasing, the magnitude of the change in 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 supply voltage zero crossings.

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

For example, in a 230V AC grid operating at 50Hz, with resistors R1, R2, R3 and R4 having values equal to 2M, 500k, 100k and 1k, respectively, and capacitor C2 having a capacitance value equal to 1 μF, the value of the first capacitor C1 Capacitance values between 1.5µF and 10µF will give a duration D2 between 550ms and 3.6s.

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

Normally, when the inhibition is no longer performed, the voltage at point P1 increases until the voltage at point P2 is exceeded. Transistor T1 switches to the conducting state, transistor T2 follows it and then switches to the conducting state.

A cascading effect is then observed, as the sudden turn-on of the second transistor T2 results in a rapid discharge of capacitor C1, which produces pulse 36 and corresponds to the voltage peak observed at 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 is charged through the resistor R1.

The same steps are repeated cyclically as capacitor C1 is discharged and then charged again.

In general, the auxiliary trip device for Unit 2 is configured to:

- automatic disabling of the control circuit 26, for example by a signal sent by the detector 24 to the control circuit 26, as long as the power supply circuit 20 supplies the trip device 18 normally;

- When the power supply circuit 20 stops supplying the trip device 18 normally, a trip signal is generated by the control circuit 26 . For example, the detector 24 detects the loss of power supply and then stops disabling the control circuit 26 .

By means of the present invention, the protection unit 2 exhibits reliable and safe behavior in the event 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 the loss or failure of the power supply .

Furthermore, the use of the auxiliary trip device according to the above-described embodiments allows the protection unit 2 to operate and guarantee this safe behavior, regardless of how the protection unit 2 is connected in the electrical installation.

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

In particular, the use of electrical pulses to control the switch 20 makes it possible to avoid overheating and any risk of thermal damage to the protection unit 2 . In particular, the actuator 10 may be optimized in the size of the coil 12 or exhibit a degree of compactness, and thus the actuator 10 may not be able to withstand the heating of the coil 12 when the coil 12 is continuously powered resulting in an increase in temperature.

Now, this happens when the protection unit 2 is connected upstream of the power supply source of the installation when tripping. Specifically, since the connection to the wires 4 for powering the actuator 10 and the power supply circuit 22 is located downstream of the separable contact 14, as shown in FIG. 1, even when the separable contact 14 is tripped and opened , the actuator 10 will also continue to be powered continuously.

In the present case, the duration of the pulse is relatively short relative to the duration between the two pulses, which allows the actuator to cool down between the two pulses, while still guaranteeing the tripping of the unit 2 and the separable contact 14 's open.

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 therefore has no risk of potential failure in its own auxiliary power supply, which guarantees a more reliable behavior in the event of a failure.

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

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

- 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

- 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 corresponding transistor, eg to the gate of the transistor.

For example, the transistors are metal oxide semiconductor (MOS) transistors, although other technologies may be used.

The first transistor is additionally connected (here via its drain) to the output terminal of the detector 24 through which the status signal is transmitted when the detector 24 is operating. The output terminal of the detector 24 is intended to be connected to the 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 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 to the input terminals of the detector 24 through their cathodes. 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.

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 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.

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

Therefore, 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 also possible.

According to a first variant, the detector 24 can 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 reprogrammable logic component (FPGA), or application specific integrated circuit (ASIC), or any equivalent element.

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

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 .

For example, an electronic fault monitoring device may include a measurement probe coupled to the sensor 16 in order to detect faults in the sensor 16 or an 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 above-conceived embodiments and variants can be combined with each other in order to create new embodiments.

Claims (10)

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).

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