Method for testing an electrical protection unit and a protection unit implementing the method

Abstract

The invention relates to a method for testing the operation of a unit for protecting an electrical network, the unit comprising a current sensor (2), a converter circuit (3), a capacitor (4) and a detection circuit (5). The method comprises a first test sequence for testing the current sensor (2), the converter circuit (3) and the capacitor (4) by means of a first generator circuit (6), and a second sequence for testing the detection circuit (5) by means of a second generator circuit (7). When the second test sequence is positive, the detection circuit (5) activates a control output (53). The invention also relates to a unit (1) for protecting an electrical network implementing this method.

Description

Technical Field

[0001] The invention relates to a method for testing the operation of a protection unit for protecting an electrical network, such as a circuit breaker, a differential protection relay or a switch. The invention also relates to a unit for protecting a network implementing such a method. Background Art

[0002] Electrical protection units are widely used in electrical installations to protect goods and people from electrical faults. Among them, one function of these protection units is to interrupt the power supply to the faulty part of the circuit once a fault is detected so as to isolate the faulty part from the rest of the circuit. The detected fault may be a short circuit, an overload, a ground insulation fault or a differential fault. These protection units usually have a test device for checking whether they are operating correctly. To this end, a test signal having the characteristics of the fault that is the protection target is applied to the protection unit in order to test the ability of the unit to detect faults. For example, a differential protection unit rated at 300mA is tested by applying a test current with a maximum amplitude that can reach 2.5 times the rated value (i.e. 750mA).

[0003] Reducing the size of the protection unit in order to incorporate a greater number of electrical monitoring and protection units within an electrical enclosure or on a switchboard, or to incorporate new functions within the protection unit has the disadvantage of increasing the heat inside the unit. Therefore, the unit must consume as little power as possible to limit self-heating. This limitation on power consumption is particularly important during the test phase, since the power used for testing is much higher than the power required for the operation of the unit. Returning to the previous example, the protection unit must be able to deliver a test current that can reach an amplitude of 750mA.

[0004] Patent US 5 371 646 is known which describes an assembly which allows to limit the duration of the test to that strictly necessary to open the circuit. However, the power required for the test comes from the electrical network and the power requirement is high: for example, for a 400V / 50Hz network, such a test requires 120W of power for a nominal 300mA. Although the test requires only a short time, the power dissipated in the product under test is not negligible.

[0005] The known patent application EP 1 936 771 A1 relates to a device for testing differential devices, which consists in selecting the minimum operating rating and the minimum delay. This solution is advantageous when applied to devices rated for several amperes (e.g. 30mA, 100mA and 300mA), since the test will be performed for the rated 30mA. However, this solution cannot be applied to units rated for only one ampere (e.g. 300mA).

[0006] Patent application FR 17 55699 describes a method for testing a protection unit without causing an open circuit in which the protection unit is installed. This solution saves a lot of energy but, according to its principle, does not test the circuit that is the object of protection for open circuits. Summary of the invention

[0007] The present invention therefore aims to overcome these drawbacks by making it possible to test the operation of a protection unit, whatever the chosen rating, without consuming significant additional power relative to nominal operation.

[0008] To this end, the subject of the invention is a method for testing the operation of a protection unit of an electrical network, said unit comprising:

[0009] - a current sensor which delivers a signal representative of an electrical fault current flowing through at least one electrical conductor;

[0010] a converter circuit connected at an input to the current sensor in order to receive a signal representative of the fault current and at an output to the capacitor, said converter circuit being designed to convert the signal representative of the fault current into a capacitor voltage and also designed to charge the capacitor to said capacitor voltage;

[0011] a detection circuit connected to the capacitor so as to compare a capacitor voltage across the capacitor with a predetermined threshold voltage and to activate a control output when the capacitor voltage across the capacitor is higher than the threshold voltage;

[0012] - a first generator circuit for generating a test current in the current sensor;

[0013] - a second generator circuit for generating a current for charging the capacitor,

[0014] The method comprises:

[0015] a first test sequence for testing the current sensor, the converter circuit and the capacitor by means of a first generator circuit; and when the first test sequence is positive,

[0016] The method includes a second test sequence for testing the detection circuit via a second generator circuit and activating the control output when the second test sequence is positive.

[0017] Advantageously, the first test sequence comprises:

[0018] - a step of taking a first measurement of the voltage across the capacitor;

[0019] - a step of generating a test current in the current sensor during the first delay; and

[0020] - A step of taking a second measurement of the voltage across the capacitor.

[0021] Advantageously, the first delay is determined such that the second measure of voltage is below a threshold voltage.

[0022] Preferably, the first delay is determined according to:

[0023] - a first measurement of the voltage across the capacitor;

[0024] - a predetermined value of the first target voltage;

[0025] - the capacitance of the capacitor; and

[0026] -Amplitude of the test current.

[0027] Advantageously, the value of the first target voltage is lower than the threshold voltage.

[0028] Preferably, the first delay is calculated according to the following equation:

[0029] [Equation 1]

[0030]

[0031] in:

[0032] Tempo_1 is the first delay;

[0033] V_cap1 is the first measurement of the voltage across the capacitor;

[0034] V_s1 is the value of the first target voltage;

[0035] C is the capacitance of the capacitor; and

[0036] I_tst1 is the amplitude of the test current.

[0037] Advantageously, the first test sequence is positive when the difference between the second voltage measurement and the first voltage measurement is above a predetermined second threshold value.

[0038] Preferably, the second test sequence comprises the step of generating, by the second generator circuit, a current for charging the capacitor during a predetermined second delay period.

[0039] Preferably, the second delay is determined according to:

[0040] - a second voltage measurement;

[0041] - a predetermined second target voltage;

[0042] - the value of the capacitance of the capacitor; and

[0043] -The magnitude of the current used to charge the capacitor.

[0044] Preferably, the second delay is calculated according to the following equation:

[0045] [Equation 2]

[0046]

[0047] in:

[0048] Tempo_2 is the second delay;

[0049] V_s2 is the second target voltage;

[0050] V_cap2 is the second voltage measurement;

[0051] C is the value of the capacitance of the capacitor; and

[0052] I_tst2 is the magnitude of the current used to charge the capacitor.

[0053] Advantageously, the value of the second target voltage is between 1 and 1.2 times the threshold voltage.

[0054] The invention also relates to a protection unit for an electrical network, the unit comprising:

[0055] - a current sensor which delivers a signal representative of an electrical fault current flowing through at least one electrical conductor;

[0056] a converter circuit connected at an input to the current sensor and at an output to the capacitor, the converter circuit being designed to convert a signal representative of the fault current into a capacitor voltage and to charge said capacitor to said voltage;

[0057] - a detection circuit connected to the capacitor so as to compare the capacitor voltage across the capacitor with a predetermined first threshold voltage and to activate the control output when the voltage across the capacitor is higher than the threshold voltage;

[0058] - a first generator circuit for generating a test current in the current sensor;

[0059] - a measuring circuit connected to the capacitor in order to measure the capacitor voltage across the capacitor;

[0060] - a second generator circuit for generating a charging current for charging the capacitor; and

[0061] - a processing circuit connected to the first generator circuit for controlling the generation of the test current, connected to the second generator circuit for controlling the generation of the charging current, and connected to the measurement circuit for receiving a measurement of the capacitor voltage across the capacitor, the processing circuit comprising circuitry for running the above-described test method.

[0062] Advantageously, the converter circuit comprises a load resistor and a rectifier circuit for a signal representative of the fault current.

[0063] Preferably, the protection unit comprises:

[0064] - a current switch for establishing or interrupting a current flow through at least one current conductor,

[0065] - an actuator connected to the control output of the detection circuit, said actuator actuating the opening of the current switch when the control output is activated.

[0066] Advantageously, the current sensor is a sensor for a differential current flowing through at least two electrical conductors. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] The accompanying drawings illustrate the present invention:

[0068] Figure 1 A test device for a protection unit of an electrical network is shown in the form of a block diagram.

[0069] Figure 2 A flow chart of a method for testing a protection unit comprising a testing device according to the invention is shown.

[0070] Figure 3A , Figure 3B and Figure 3C Shows Figure 2 Detail of the flow chart of the test method is shown.

[0071] Figure 4 The voltage levels measured when the test method is run and the predefined or calculated threshold levels are illustrated graphically.

[0072] Figure 5 is a schematic representation of a test device according to the present invention.

[0073] Figure 6 is a schematic representation of a protection unit comprising the test device of the present invention. DETAILED DESCRIPTION

[0074] Figure 1A test device for a current measurement chain of an electrical protection unit 1 according to a preferred embodiment of the invention is shown in the form of a block diagram. The protection unit 1 comprises a current sensor 2 designed to deliver a signal Is representative of an electrical fault current Idf flowing through at least one electrical conductor 21. The current sensor 2 is preferably a differential current sensor and in this case at least two electrical conductors 21 are used. The output of the current sensor 2 is connected to the input of a converter circuit 3. The converter 3, comprising an input and an output, is designed to convert a signal representative of a fault current (Is) received at its input into a capacitor voltage V_cap and to charge a capacitor 4 of capacitance C connected at its output to said capacitor voltage V_cap. The voltage across the capacitor 4 is thus representative of the electrical fault current Idf. The capacitor 4 is connected to the input of a detection circuit 5. The detection circuit 5 compares the capacitor voltage V_cap received at its input with a predetermined threshold voltage V_sd and activates a control output 53 when the capacitor voltage V_cap is higher than the threshold voltage V_sd. The threshold voltage V_sd is related to a limit value known as the rated value of the electrical protection unit. The rated value may be predefined as 30 mA, 100 mA, 300 mA or any other value that provides appropriate protection for the electrical installation in which the protection unit is incorporated. The threshold voltage V_sd is the capacitor voltage V_cap obtained when the electrical fault current Idf is equal to the rated value of the protection unit. Thus, when the electrical fault current Idf is higher than the rated value of the protection unit, the control output 53 is activated.

[0075] The protection unit 1 must be able to be tested to verify that it operates correctly. To this end, a test device and method are used to test the operation of the assembly consisting of the current sensor 2, the converter 3, the capacitor 4, the detection circuit 5 and the control output 53. To this end, a first generator circuit 6 is connected to the current sensor 2 so as to generate a test current I_tst1 in the current sensor 2. The test current I_tst1 must represent the fault current Idf. However, in the case of testing a unit with a rated value of 300 mA, the first generator circuit 6 must deliver a current with an amplitude higher than 300 mA. To this end, the first generator circuit 6 must include components whose dimensions are suitable for dissipating several watts, which makes there a problem in terms of temperature rise inside the protection unit 1 and another problem in terms of capacity (bulk) related to the volume of the generator components, especially when the volume of the unit is small. The test current I_tst1 can be reduced by using, for example, a current sensor 2 (such as a current transformer), the required reduction of the test current I_tst1 being inversely proportional to the number of turns of the test winding constituting the sensor. Such solutions known from the prior art usually require that the current transformer and its test winding be constructed in such a way as to be adapted to the rating of the protection unit or to a limited range of ratings. Such solutions result in as many industrial variations as ratings, thus increasing the manufacturing costs.

[0076] exist Figure 2 The subject of the invention, shown in the form of a flow chart in FIG. 1 , is a test method comprising a first sequence 100 for testing a current sensor 2, a converter circuit 3 and a capacitor 4 in a first instance while using less power than a test using a test current above the unit rating. During said first test sequence 1, the capacitor voltage V_cap is kept below a threshold voltage V_sd to avoid activating the control output 53. When the first test sequence is positive, the method proceeds to a second sequence 200 for testing the capacitor 4 and the detection circuit 5, and the control output 53 is activated when the second test sequence is positive. The innovative splitting of the test operation into two test sequences using different test criteria and signals makes it possible to reliably test all circuits and components without excessive power consumption and therefore without generating a lot of heat.

[0077] Figure 3A and Figure 3BThe first test sequence 100 is shown in the form of a detailed flow chart. The first test sequence 100 starts with a step 110 where a first measurement V_cap1 of the capacitor voltage across the capacitor 4 is taken. The method may proceed to a step 120 where a first delay Tempo_1 is initialized with a first predetermined duration T1. Preferably, after the measurement step 110, a step 115 is performed where the first measurement V_cap1 of the capacitor voltage is compared with a predetermined control voltage V_ct. When the first measurement V_cap1 of the capacitor voltage is higher than the control voltage V_ct, then a first delay Tempo_1 is calculated in a step 125. The first delay Tempo_1 is calculated such that at the end of the delay Tempo_1 the voltage across the capacitor 4 reaches a target voltage V_s1 that is lower than the threshold voltage V_sd. This particularity makes it possible to verify that the current sensor 2, the converter circuit 3 and the capacitor 4 operate correctly without activating the control output 53. The value V_s1 of the first target voltage is lower than the threshold voltage V_sd. Preferably, the value V_s1 of the first target voltage is between 0.1 and 0.9 times the threshold voltage V_sd. This value depends on the rating of the unit and the magnitude of the test current that will be drawn.

[0078] The value of the first delay Tempo_1 is determined according to:

[0079] - the value of a first voltage measurement V_cap1;

[0080] - the value of the first target voltage V_s1;

[0081] - the value of the capacitance C of the capacitor 4; and

[0082] - The amplitude value of the test current I_tst1.

[0083] Preferably, the value of the first delay Tempo_1 is calculated according to the following equation:

[0084] [Equation 3]

[0085]

[0086] The step 120 of initializing the first delay Tempo_1 or the step 125 of calculating said first delay Tempo_1 is followed by a step 130 of resetting the timer t, then a step 135 of incrementing the timer t and delivering the test current I_tst1 via the first generator circuit 6. Next, in a first comparison step 140, the elapsed time t is compared with the first delay Tempo_1. As long as the time t is shorter than the first delay Tempo_1, the method stays at the step of delivering the test current I_tst1. When the elapsed time t is longer than the first delay Tempo_1, the method proceeds to a step 145 in which the delivery of the test current I_tst1 is stopped, then to a step 150 in which a second measurement V_cap2 of the voltage across the capacitor 4 is taken. Next, a theoretical difference Delta_V is calculated in a step 160. The theoretical difference Delta_V corresponds to a theoretical increase in the voltage V_cap across the capacitor 4 due to the presence of the test current I_tst1 during the duration of the first delay Tempo_1.

[0087] Preferably, the value of the theoretical difference Delta_V is calculated according to the following equation:

[0088] [Equation 4]

[0089]

[0090] In a comparison step 170, the theoretical difference Delta_V is compared to the potential difference between the second voltage measurement V_cap2 and the first voltage measurement V_cap1. If they are not equal, in particular if the potential difference between the second voltage measurement V_cap2 and the first voltage measurement V_cap1 is smaller than the theoretical difference Delta_V, the test is considered negative in a step 180. However, if they are equal, the first sequence 100 is considered positive and the method proceeds to the second sequence 200. In a preferred embodiment, equality is considered to have been achieved when the voltage difference between V_cap2 and V_cap1 is within the theoretical difference Delta_V-20% and Delta_V+20%.

[0091] Figure 3CThe second test sequence 200 is shown in the form of a detailed flow chart. The second test sequence 200 starts with a step 210 of calculating a second delay Tempo_2. Similar to sequence 1, the second delay Tempo_2 can be predefined so as to last long enough to activate the control output 53. Preferably, the second delay Tempo_2 is calculated in order to verify the accuracy of the threshold used to activate the control output 53 via the detection circuit 5. Therefore, the second delay Tempo_2 is calculated so that the voltage across the capacitor 4 reaches a second target voltage V_s2, which is significantly higher than the threshold voltage V_sd, so that the control output 53 is activated. The term "significantly higher" is understood to mean that the value of the second target voltage V_s2 is preferably between 1 and 1.5 times the threshold voltage V_sd. Limiting the range in this way makes it possible to verify the switching accuracy of the detection circuit 5. For example, in a specific embodiment, the target voltage V_s2 is equal to 1.2 times the threshold voltage V_sd. Thus, in the worst case, the detection circuit 5 activates the control output when the capacitor voltage V_cap across the capacitor 4 exceeds the threshold voltage V_sd by 20%. It is thus verified that the threshold for activating the control output has deviated from the intended activation threshold by no more than 20%.

[0092] The value of the second delay Tempo_2 is determined as follows:

[0093] - the value of the second voltage measurement V_cap2;

[0094] - the value of the second target voltage V_s2;

[0095] - the value of the capacitance C of the capacitor 4; and

[0096] - the amplitude value of the charging current I_tst2 delivered by the second generator circuit 7 .

[0097] Preferably, the value of the second delay Tempo_2 is calculated according to the following equation:

[0098] [Equation 5]

[0099]

[0100] The step 210 of calculating the second delay Tempo_2 is followed by a step 220 of resetting the timer t, then a step 230 of incrementing the timer t and delivering the charging current I_tst2 via the second generator circuit 7. The charging current I_tst2 will charge the capacitor 4 so as to increase the voltage V_cap across said capacitor 4 to the value of the second target voltage V_s2. Said target voltage V_s2 is slightly higher than the threshold voltage V_sd, so when the voltage V_cap across the capacitor 4 is equal to the threshold voltage V_sd, in a step 240, the detection circuit 5 activates the control output 53. The method ends with a step 250 of signaling a positive test.

[0101] In a first comparison step 260, the elapsed time t is compared with the second delay Tempo_2. As long as the time t is shorter than the second delay Tempo_2, the method stays in the step 230 of delivering the test current I_tst2 and incrementing the timer t. When the elapsed time t is longer than the second delay Tempo_2, the method proceeds to a step 270 in which the delivery of the test current I_tst2 is stopped, and then to a step 280 for signaling a negative test: specifically, for the duration of the second delay Tempo_2, the voltage V_cap across the capacitor 4 does not equal or exceed the threshold voltage V_sd, and therefore the control output 53 is not activated.

[0102] Figure 4 The diagram shown illustrates the voltage level across the capacitor 4 and the predefined or calculated threshold level when the test method is run through. In the first sequence of steps 110, the voltage across the capacitor 4 is equal to V_cap1. Since the voltage V_cap1 is higher than the control voltage V_ct, the method calculates a first delay Tempo_1 in step 125, and then in step 135, the method commands the delivery of a test current I_tst1 via the first generator circuit 6 and increments the timer t. The voltage across the capacitor 4 increases and tends to the first target voltage V_s1. However, the end of the first delay Tempo_1 sets the voltage across the capacitor 4 to the value V_cap2. Since the current sensor 2, the converter circuit 3 and the capacitor 4 have been operating normally, the potential difference between the second voltage measurement V_cap2 and the first voltage measurement V_cap1 is substantially equal to the theoretical difference Delta_V. The method proceeds to the second test sequence 200, in which the charging current I_tst2 is delivered by the second generator circuit 7 during the second delay Tempo_2. The voltage across the capacitor 4 increases and tends towards the second target voltage V_s2. However, when the voltage across the capacitor 4 exceeds the threshold voltage V_sd, the detection circuit 5 activates the control output 53, the test is positive, and the method process stops.

[0103] Another subject of the invention is an electrical protection unit 1, which preferably provides protection against differential electrical faults, such as a circuit breaker, a protection relay or a switch. A test device for such a protection unit 1 is schematically shown at Figure 5 The protection unit 1 comprises:

[0104] - a current sensor 2 delivering a signal Is representative of an electrical fault current Idf flowing through at least one electrical conductor 21;

[0105] a converter circuit 3 connected at an input to the current sensor 2 and at an output to the capacitor 4, said converter circuit 3 being designed to convert the signal Is representative of the fault current into a capacitor voltage V_cap and to charge said capacitor 4 to said voltage V_cap;

[0106] a detection circuit 5 connected to the capacitor 4 so as to compare the capacitor voltage V_cap across the capacitor 4 with a predetermined first threshold voltage V_sd by means of a comparator 52 and to activate a control output 53 when the voltage across the capacitor 4 is higher than the threshold voltage V_sd provided by a voltage reference 51;

[0107] a first generator circuit 6 for generating a test current I_tst1 in the current sensor 2;

[0108] a measuring circuit 8 connected to the capacitor 4 in order to measure the capacitor voltage V_cap across the capacitor 4 and to provide a measurement of said voltage V_cap;

[0109] a second generator circuit 7 for generating a charging current I_tst2 for charging the capacitor 4; and

[0110] a processing circuit 9 connected to the first generator circuit 6 in order to control the generation of the test current I_tst1, connected to the second generator circuit 7 in order to control the generation of the charging current I_tst2, and connected to the measurement circuit 8 in order to receive the measurement of the capacitor voltage V_cap across the capacitor 4. Optionally, a communication line 91 is intended to send information about the state of the protection unit 1 and / or to receive commands, an indicator 92 allows information about the state of the protection unit 1 to be displayed.

[0111] The processing circuit 9 comprises circuits for executing the above-mentioned test method, such as logic gates, a microprocessor, a microcontroller or an ASIC.

[0112] The capacitor 4 preferably has a capacitance C between 0.5 and 10 μF.

[0113] The current sensor 2 preferably comprises a magnetic circuit 22 and a secondary winding 23 for delivering a signal Is representative of the electrical fault current Idf. Preferably, the current sensor 2 is a differential current sensor intended to detect a difference in the amplitude of currents flowing through at least two electrical conductors 21 .

[0114] The converter circuit 3 comprises a load resistor 31 for adjusting the rating of the protection unit 1. The rectifier circuit 32 is designed to rectify the signal Is representative of the electrical fault current Idf delivered by the current sensor 2 into a DC voltage V_cap and to charge the capacitor 4 to this voltage V_cap.

[0115] like Figure 5 As shown, the first generator circuit 6 consists of a current limiting resistor 62 and a thyristor 63. The trigger gate of the thyristor is connected to the processing unit 9 in order to control the generation of the test current I_tst1 in the current sensor 2. The test current I_tst1 is taken from one of the electrical conductors 21, for example the phase conductor Ph. The test current is limited by the current limiting resistor 62 and flows through the conductor 61 through the current sensor 2. For example, for a nominal value of 300 mA, the test current I_tst1 is equal to 50 mA. By reducing the test current of the sensor by a factor of 15, i.e. 750 / 50, in this way, the power dissipated during the test is divided by 225 with respect to the test with the test current I_tst1 equal to 750 mA. Therefore, the size of the components for generating the test signal is proportionally reduced, which is a significant advantage of the test method according to the invention. Figure 5 The illustrated embodiment of the first generator circuit 6 is preferred; however, other embodiments are conceivable.

[0116] The protection unit 1 is intended to protect the electrical installation from electrical faults by opening the monitored circuit. To this end, Figure 6 The protection unit 1 schematically shown in FIG. 1 comprises:

[0117] a current switch 12 connected in series with the at least one electrical conductor 21, said switch 12 being designed to establish or interrupt the flow of electric current through the at least one electrical conductor 21;

[0118] An actuator 11 connected to the control output 53 of the detection circuit 5 , said actuator 11 actuating the opening of the current switch 12 so as to interrupt the flow of electric current when the control output 53 is activated.

[0119] In a preferred embodiment, the actuator 11 has a predetermined operating threshold and it performs the function of the detection circuit 5 .

[0120] The power supply circuit 10 provides suitable power Vcc to the processing circuit 9, the measuring circuit 8, the second generator circuit 7 and the detection circuit 5. The power supply and the remaining circuits are referenced to a reference potential Vss. The power supply circuit 10 is preferably connected to an electrical conductor 21 in order to take the power required for the operation of the various power supply circuits.

[0121] The test method that is the subject of the invention allows an exhaustive and precise testing of circuits and components. This method greatly limits the power consumption required for the test, and therefore the heating of the components, by dividing the test operations into two test sequences, each of which uses a specific generator to deliver the minimum power required for the test. This method also makes it possible to verify that the circuits have not deviated from their correct operation. For example, if the first generator circuit 6 delivers a test current of amplitude different from I_tst1, or if the value of the capacitor C is abnormal, the difference in potential V_cap2-V_cap1 will be different from the theoretical difference Delta_V and the test will be negative. Finally, the rated values ​​do not significantly affect the test method or the choice of components and circuits used, so this method can be implemented in a very wide range of protection products.

Claims

1. A method for testing the operation of a protection unit (1) of an electrical network, the unit comprising: - a current sensor (2) which delivers a signal (Is) representative of an electrical fault current (Idf) flowing through at least one electrical conductor (21); a converter circuit (3) connected at an input to the current sensor (2) in order to receive the signal (Is) representative of the fault current (Idf) and at an output to a capacitor (4), the converter circuit (3) being designed to convert the signal (Is) representative of the fault current into a capacitor voltage (V_cap) and to charge the capacitor (4) to the capacitor voltage (V_cap); - a detection circuit (5) connected to the capacitor (4) to compare a capacitor voltage (V_cap) across the capacitor (4) with a predetermined threshold voltage (V_sd) and to activate a control output (53) when the capacitor voltage (V_cap) across the capacitor (4) is higher than the threshold voltage (V_sd); - a first generator circuit (6) for generating a test current (I_tst1) in the current sensor (2); - a second generator circuit (7) for generating a current (I_tst2) for charging the capacitor (4), The method is characterized in that: The method comprises a first test sequence (100) for testing the current sensor (2), the converter circuit (3) and the capacitor (4) by means of the first generator circuit (6); and when the first test sequence is positive, The method comprises a second test sequence (200) for testing the detection circuit (5) by means of the second generator circuit (7), and activating the control output (53) when the second test sequence is positive.

2. The testing method according to claim 1, characterized in that: The first test sequence (100) comprises: - a step (110) of obtaining a first measurement (V_cap1) of the voltage across said capacitor (4); - a step (135) of generating said test current (I_tst1) in said current sensor (2) during a first delay (Tempo_1); and - A step (150) of taking a second measurement (V_cap2) of the voltage across said capacitor (4).

3. The testing method according to claim 2, characterized in that: The first delay (Tempo_1) is determined such that the second measure of voltage (V_cap2) is below the threshold voltage (V_sd).

4. The test method according to any one of claims 2 and 3, characterized in that: The first delay (Tempo_1) is determined according to: - a first measurement (V_cap1) of the voltage across the capacitor (4); - a predetermined value of a first target voltage (V_s1); - the capacitance (C) of the capacitor (4); and - The amplitude of the test current (I_tst1).

5. The testing method according to claim 4, characterized in that: The value of the first target voltage ( V_s1 ) is lower than the threshold voltage (V_sd).

6. The testing method according to claim 4, characterized in that: The first delay (Tempo_1) is calculated according to the following equation: [Equation 6] in: Tempo_1 is the first delay; V_cap1 is the first measurement of the voltage across the capacitor (4); V_s1 is the value of the first target voltage; C is the capacitance of the capacitor (4); and I_tst1 is the amplitude of the test current.

7. The testing method according to any one of claims 2, 3, 5 and 6, characterized in that: The first test sequence (100) is positive when the difference between the second voltage measurement (V_cap2) and the first voltage measurement (V_cap1) is above a predetermined second threshold value (Delta_V).

8. The testing method according to any one of claims 2, 3, 5 and 6, characterized in that: The second test sequence (200) comprises a step (240) of generating a current (I_tst2) for charging the capacitor (4) by means of the second generator circuit (7) during a predetermined second delay (Tempo_2).

9. The testing method according to claim 8, characterized in that: The second delay (Tempo_2) is determined according to: - a second voltage measurement (V_cap 2); - a predetermined second target voltage (V_s2); - the value (C) of the capacitance of the capacitor (4); as well as - the amplitude of the current (I_tst2) used to charge the capacitor (4).

10. The testing method according to claim 9, characterized in that: The second delay (Tempo_2) is calculated according to the following equation: [Equation 7] in: Tempo_2 is the second delay; V_s2 is the second target voltage; V_cap2 is the second voltage measurement; C is the capacitance value of the capacitor (4); and I_tst2 is the magnitude of the current used to charge the capacitor (4).

11. The testing method according to any one of claims 9 and 10, characterized in that: The value of the second target voltage (V_s2) is between 1 and 1.2 times the threshold voltage (V_sd).

12. A protection unit (1) for an electrical network, the unit comprising: - a current sensor (2) delivering a signal (Is) representative of an electrical fault current (Idf) flowing through at least one electrical conductor (21); - a converter circuit (3) connected at an input to the current sensor (2) and at an output to a capacitor (4), the converter circuit (3) being designed to convert the signal (Is) representative of the fault current into a capacitor voltage (V_cap) and to charge the capacitor (4) to said voltage (V_cap); - a detection circuit (5) connected to the capacitor (4) for comparing a capacitor voltage (V_cap) across the capacitor (4) with a predetermined first threshold voltage (V_sd) and activating a control output (53) when the voltage across the capacitor (4) is higher than said threshold voltage (V_sd); - a first generator circuit (6) for generating a test current (I_tst1) in the current sensor (2); The protection unit (1) is characterized in that it comprises: - a measuring circuit (8) connected to the capacitor (4) in order to measure the capacitor voltage (V_cap) across the capacitor (4); - a second generator circuit (7) for generating a charging current (I_tst2) for charging the capacitor (4); and - a processing circuit (9) connected to the first generator circuit (6) in order to control the generation of a test current (I_tst1), connected to the second generator circuit (7) in order to control the generation of a charging current (I_tst2), and connected to the measurement circuit (8) in order to receive a measurement of a capacitor voltage (V_cap) across the capacitor (4), the processing circuit (9) comprising circuitry for running a test method according to one of claims 1 to 11.

13. The protection unit (1) according to claim 12, characterized in that The converter circuit (3) comprises a load resistor (31) and a rectifier circuit (32) for the signal (Is) representing a fault current (Idf).

14. The protection unit (1) according to any one of claims 12 and 13, characterized in that The protection unit (1) comprises: - a current switch (12) for establishing or interrupting a current flowing through at least one electrical conductor (21); - an actuator (11) connected to a control output (53) of the detection circuit (5), the actuator (11) actuating the opening of the current switch (12) when the control output (53) is activated.

15. The protection unit (1) according to any one of claims 12 to 13, characterized in that: The current sensor (2) is a sensor for a differential current flowing through at least two electrical conductors (21).

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