Residual current protective device for protecting an electrical direct current system

Description

TECHNICAL FIELD

[0001] The present invention relates to the protection of direct voltage electrical installations. In particular, it relates to a residual current device for the protection of a direct voltage electrical installation. STATE OF THE ART

[0002] In an electrical installation, an electric current that arrives through a contact of the electrical installation, then passes through one or more conductors, must exit through another contact of the electrical installation. Thus, if a current at one contact of the electrical installation is different from the current at another contact of the electrical installation, this means that there is a current leak. However, this current leakage can be dangerous for equipment linked to the electrical installation or for an operator handling the electrical installation. To overcome this inconvenience, residual current devices are already known. These differential devices protect electrical installations and the operator by detecting residual currents. When a residual current is detected, these devices emit a control signal called a "trip".This trigger then commands a circuit breaker to cut off all power to the electrical installation.

[0003] However, these differential devices do not exist for direct voltage electrical installations in an environment highly disturbed by electromagnetic interference.

[0004] US 2010 / 194354 discloses a residual current device for the protection of an electrical installation. STATEMENT OF THE INVENTION

[0005] The object of the present invention is to overcome this lack by proposing a residual current differential device for the protection of a direct voltage electrical installation according to claim 1.

[0006] To this end, the invention relates to a residual current differential device for protecting a direct voltage electrical installation, the installation comprising a positive contact and a negative contact.

[0007] Thus, thanks to the device, it is possible to protect direct voltage electrical installations from residual currents.

[0008] According to the invention, the function of the low-pass filter is to ensure justified triggering of the differential device in the event of detection of a direct current leakage, even if the environment is very noisy, and not to prevent potential false triggering due to disturbances.

[0009] Furthermore, the full-wave rectifier module without threshold comprises a plurality of operational amplifiers, a plurality of resistors and a plurality of diodes.

[0010] Additionally, the trigger module includes: a comparator sub-module configured to emit a signal representative of the result of a comparison between the rectified current and the predetermined threshold; a counter sub-module configured to emit a confirmation signal if the signal representative of the result of the comparison indicates that the rectified current is greater than or equal to the predetermined threshold for a duration greater than or equal to the predetermined duration; a flip-flop sub-module configured to emit the trigger command when the counter sub-module emits the confirmation signal.

[0011] In addition, the comparator sub-module comprises a comparator having an inverting input configured to receive a signal representative of the predetermined threshold, a non-inverting input connected to the rectifier module and configured to receive the rectified current, and an output configured to output the signal representative of the result of the comparison.

[0012] Furthermore, the counter sub-module comprises an inverter and a counter, the inverter having an output and an input connected to the output of the comparator and configured to receive the signal representative of the result of the comparison, the counter having a reset input connected to the output of the inverter, a clock input configured to receive a clock signal and an output configured to emit the confirmation signal.

[0013] According to a feature, the flip-flop sub-module comprises a D flip-flop, the D flip-flop having a clock input connected to the output of the counter and configured to receive the confirmation signal, a reset input configured to receive a reset signal representative of a reset of the D flip-flop, a data input configured to receive a signal complementary to the signal representative of the trigger command and an output configured to emit the trigger command signal.

[0014] The invention also relates to a direct voltage electrical installation according to claim 7, comprising a residual current differential device as specified above for the protection of said direct voltage electrical installation. The invention also relates to an aircraft according to claim 8, comprising a direct voltage electrical installation such as that specified above. BRIEF DESCRIPTION OF THE FIGURES

[0015] The invention, with its characteristics and advantages, will emerge more clearly on reading the description given with reference to the appended drawings in which: there figure 1 represents a schematic view of a direct voltage electrical installation which illustrates an embodiment of the invention, and the leakage currents which may appear, the figure 2 represents a side view of an aircraft carrying a direct voltage electrical installation and a residual current differential device which illustrates an embodiment of the invention, the figure 3 represents an electrical diagram of the residual current device which illustrates an embodiment of the invention, the figure 4 represents a curve showing an example of the evolution of the difference current over time, in the absence of a fault, the figure 5 represents a curve showing an example of the evolution of the rectified current over time, the rectified current corresponding to the difference current of the figure 4 , and the figure 6 represents a curve showing an example of the evolution of the difference current over time after being filtered by the low-pass filter, when a fault appears. DETAILED DESCRIPTION

[0016] There figure 3 represents an embodiment of the residual current differential device 1 for the protection of an electrical installation 2 with direct voltage represented in figure 1 . In the remainder of the description, the residual current device is referred to as “device 1”.

[0017] The electrical installation 2 can be carried on board an AC aircraft, in particular a transport aircraft.

[0018] As represented in figure 1 , the electrical installation 2 comprises a positive contact 3 and a negative contact 4. The positive contact can be connected to a positive polarity conductor 31 allowing the electrical installation 2 to be supplied with current i1 from a supply circuit. The negative contact can be connected to a negative polarity conductor 41 allowing the current i2 to return to the supply circuit. As shown in the figure 1 , current leaks may occur: a leakage current i4 from the positive polarity conductor 31, a leakage current i5 from the negative polarity conductor 41 and a leakage current i3 at the electrical installation 2.

[0019] According to Kirchhoff's node law, the sum of the currents arriving at a node is equal to the sum of the currents leaving it. Therefore, the difference between current i1 and current i2 is equal to the sum of leakage currents i3, i4 and i5. If the difference between current i1 and current i2 is not zero, there is one or more leakage currents. If this difference reaches a certain threshold, electrical installation 2 is cut off from the supply circuit in order to protect electrical installation 2. figure 1 represents the electrical installation 2 cut off from the power supply circuit by switches 51 open for each of the conductors 31 and 41. For example, these switches 51 are included in a circuit breaker. The device 1 thus allows the protection of the electrical installation 2.

[0020] As shown in the figure 3 , the device 1 comprises a current difference measurement module 5, a full-wave rectifier without threshold module 6 and a trigger module 7.

[0021] The current difference module 5 is configured to produce a voltage U6 which corresponds to a difference current i6 corresponding to the absolute value of the current difference between the current i1 flowing in the positive contact 3 and the current i2 flowing in the negative contact 4. On the figure 3 , U6 = f (i6) means that the voltage U6 is a function of the difference current i6.

[0022] The device 1 further comprises a low-pass filter 8 configured to filter the difference current i6 before being rectified by the full-wave rectifier module without threshold 6.

[0023] The order of the low-pass filter 8, its cutoff frequency and its damping coefficient can be defined so that the low-pass filter meets two conditions.

[0024] The first condition is based on knowledge of the spectrum of normal earth fault currents in an electrical network. The low-pass filter is sized to obtain a differential peak current, after filtering, lower than the difference between the minimum current dangerous for humans and the detection threshold (predetermined threshold). In other words, the low-pass filter is configured so that a differential peak current after filtering is lower than or equal to the difference between the minimum current dangerous for humans and the predetermined threshold. This makes it possible to avoid having a reset of a counter 11 of the trigger module 7 before the end of the predetermined duration, caused by low peaks of a noisy signal.

[0025] For example, the minimum current dangerous for humans is equal to 90 mA and the detection threshold is chosen to be equal to 70 mA. The deviation is therefore equal to 20 mA for this example.

[0026] The second condition is based on the fact that the addition of the response time of the filter to a current dangerous to humans and the confirmation time should not exceed the predetermined duration for cutting off the electrical installation 2 from the supply circuit. In other words, the sum of the response time of the filter to a current dangerous to humans and the confirmation time of this response time is less than or equal to the predetermined duration for cutting off the electrical installation 2 from the supply circuit.

[0027] For example, the response time is 5 ms and the predetermined duration is 150 ms. The confirmation time is therefore 145 ms.

[0028] Thus, in the example presented above, the low-pass filter 8 chosen to meet both conditions is a second-order low-pass filter having a cut-off frequency of 100 Hz and a damping coefficient of 0.7.

[0029] There figure 6 shows a curve representing an example of the evolution of the difference current i6 after filtering by the low-pass filter 8. The predetermined threshold is set at 70 mA. Low peaks are smoothed and remain above the predetermined threshold, but do not reset the counter 11 if the time D where these peaks are above the predetermined threshold is less than the predetermined duration, which prevents the emission of a trigger command T by a D flip-flop 12 of the trigger module 7. If the time D is greater than or equal to the predetermined duration, a trigger command T can be issued. This thus allows the detection of leakage currents which were not detectable without filtering.

[0030] The full-wave rectifier module without threshold 6 is configured to produce a voltage U7 which is an image of the rectified current i7 corresponding to the filtered difference current rectified by the full-wave rectifier module without threshold 6. On the figure 3 , U7 = f (i7) means that the voltage U7 is a function of the rectified current i7.

[0031] The trigger module 7 is configured to issue a trigger command T when the rectified current i7 is greater than or equal to a predetermined threshold for a predetermined duration.

[0032] The predetermined threshold and the predetermined duration have values ​​allowing sufficient protection so that current leaks are not dangerous for humans.

[0033] Generally, the minimum current that can be dangerous for humans is equal to 90 mA for an exposure time of 150 ms.

[0034] According to a first non-limiting example, a predetermined threshold is equal to 150 mA and the predetermined duration is equal to 70 ms.

[0035] According to a second non-limiting example, a predetermined threshold is equal to 70 mA and the predetermined duration is equal to 150 ms.

[0036] This trip command T can be transmitted to a circuit breaker which will cut off the electrical installation 2 from the supply circuit when it has received said trip command T.

[0037] The full-wave rectifier module without threshold 6 may comprise two operational amplifiers 61 and 62, seven resistors R1, R2, R3, R4, R5, R6 and R7 and two diodes D1 and D2. This full-wave rectifier module without threshold 6 may be formed of a single-wave rectifier comprising the operational amplifier 61, the diodes D1 and D2 and the resistors R1, R2 and R3 and an inverse adder comprising the operational amplifier 62, and the resistors R4, R5, R6 and R7.

[0038] There figure 4 shows an example of the evolution of a difference current i6 as a function of time t. The figure 5 shows the rectified current i7 corresponding to the filtered difference current rectified by the full-wave rectifier module without threshold 6. As shown in these figures, the full-wave rectifier module without threshold 6 makes it possible to rectify the negative half-waves A1, A2, A3 of the difference current i6. The figure 5 represents, in curved dotted lines, the negative alternations A1, A2, A3 straightened out shown on the figure 4 The horizontal dotted line S represents the predetermined threshold.

[0039] The letters a, b, c, d and e on the figure 5 represent the durations for which the rectified current i7 is greater than or equal to the predetermined threshold. If one of these durations a, b, c, d or e is greater than or equal to the predetermined duration, a trip command T is issued by the trip module 7.

[0040] As shown in the figure 3 , the trigger module 7 may comprise a comparator sub-module 71, a counter sub-module 72 and a flip-flop sub-module 73.

[0041] The comparator sub-module 71 is configured to emit a signal S1 representative of the result of a comparison between the rectified current i7 and the predetermined threshold.

[0042] The comparator sub-module 71 may comprise a comparator 9 having an inverting input E1, a non-inverting input E2 connected to the rectifier module 6 and an output F1. The voltage U7 which corresponds to an image of the rectified current i7 is intended to be applied to the non-inverting input E2. A signal S3 representative of the predetermined threshold is intended to be applied to the inverting input E1. The signal S1 representative of the result of the comparison is intended to be emitted by the output F1 of the comparator 9.

[0043] The counter sub-module 72 is configured to emit a confirmation signal S2 if the signal S1 representative of the result of the comparison indicates that the voltage U7 is greater than or equal to the predetermined threshold for a duration greater than or equal to the predetermined duration.

[0044] The counter sub-module 72 may comprise an inverter 10 and a counter 11. The inverter 10 has an output F2 and an input E3 connected to the output F1 of the comparator 9. The counter 11 has a reset input E4 connected to the output F2 of the inverter 10, a clock input E5 and an output F3. The output F2 of the inverter 10 is connected to the reset input E4 of the counter 11. The signal S1 representative of the result of the comparison is intended to be applied to the input E3 of the inverter 10. A clock signal S4 is intended to be applied to the clock input E5 of the counter 11. The confirmation signal S2 is intended to be emitted by the output F3 of the counter 11.

[0045] Without limitation, the clock signal has a clock cycle of 1 ms duration.

[0046] The flip-flop sub-module 73 is configured to issue the trigger command T when the counter sub-module 72 issues the confirmation signal S2.

[0047] The flip-flop sub-module 73 may comprise a D flip-flop 12. This D flip-flop 12 has a clock input E6 connected to the output F3 of the counter 11, a reset input E7, a data input E8 and an output F4. The confirmation signal S2 is intended to be applied to the clock input E6 of the D flip-flop 12. The trigger control signal T is intended to be emitted at the output F4 of the D flip-flop 12. A signal S5 complementary to the signal representative of the trigger control T is intended to be applied to the data input E8 of the D flip-flop 12. A reset signal S6 representative of a reset of the D flip-flop 12 is intended to be applied to the reset input E7 of the D flip-flop 12. The reset signal S6 may be applied by an operator in order to reset the D flip-flop 12 after this D flip-flop 12 has emitted a trigger control signal T.

Claims

1. A residual current differential device for protecting a DC-voltage electrical installation (2), the installation comprising a positive contact (3) and a negative contact (4), characterized in that the device comprises at least: - a current difference measurement module (5) configured so as to produce a voltage (U6) corresponding to a differential current (i6) that corresponds to a current difference between the current (i1) flowing in the positive contact (3) and the current (i2) flowing in the negative contact (4); - a low-pass filter (8) configured so as to filter the differential current (i6) and emit a filtered current, the low-pass filter being configured such that a peak differential current after filtering is less than or equal to the difference between a minimum current hazardous to humans and a predetermined threshold. - a full-wave rectifier without threshold module (6) configured so as to produce a voltage (U7) corresponding to a rectified current (i7) that corresponds to the filtered current rectified by the full-wave rectifier without threshold module (6); - a trip module (7) configured so as to emit a trip command (T) when the rectified current (i7) is greater than or equal to the predetermined threshold for a predetermined duration, the predetermined duration being greater than or equal to the sum of a response period of the low-pass filter for responding to a current hazardous to humans and a confirmation period for this response period.

2. The device as claimed in claim 1, characterized in that the full-wave rectifier without threshold module (6) comprises a plurality of operational amplifiers (61, 62), a plurality of resistors (R1, R2, R3, R4, R5, R6, R7) and a plurality of diodes (D1, D2).

3. The device as claimed in either one of claims 1 or 2, characterized in that the trip module (7) comprises: - a comparator submodule (71) configured so as to emit a signal (S1) representative of the result of a comparison between the rectified current (i7) and the predetermined threshold; - a counter submodule (72) configured so as to emit a confirmation signal (S2) confirming whether the signal (S1) representative of the result of the comparison indicates that the rectified current (i7) is greater than or equal to the predetermined threshold for a duration greater than or equal to the predetermined duration; - a flip-flop submodule (73) configured so as to emit the trip command (T) when the counter submodule (72) emits the confirmation signal (S2).

4. The device as claimed in claim 3, characterized in that the comparator submodule (71) comprises a comparator (9) having an inverting input (E1) configured so as to receive a signal (S3) representative of the predetermined threshold, a non-inverting input (E2) connected to the rectifier module (6) and configured so as to receive the rectified current (i7), and an output (F1) configured so as to emit the signal (S1) representative of the result of the comparison.

5. The device as claimed in claim 4, characterized in that the counter submodule (72) comprises an inverter (10) and a counter (11), the inverter (10) having an output (F2) and an input (E3) connected to the output (F1) of the comparator (9) and configured so as to receive the signal (S1) representative of the result of the comparison, the counter (11) having a reset-to-zero input (E4) connected to the output (F2) of the inverter (10), a clock input (E5) configured so as to receive a clock signal (S4) and an output (F3) configured so as to emit the confirmation signal (S2).

6. The device as claimed in claim 5, characterized in that the flip-flop submodule (73) comprises a D flip-flop (12), the D flip-flop (12) having a clock input (E6) connected to the output (F3) of the counter (11) and configured so as to receive the confirmation signal (S2), a reset-to-zero input (E7) configured so as to receive a reset signal (S6) representative of resetting of the D flip-flop (12), a data input (E8) configured so as to receive a signal (S5) complementary to the signal representative of the trip command (T) and an output (F4) configured so as to emit the trip command signal (T).

7. A DC-voltage electrical installation, characterized in that said installation comprises a residual current differential device (1) as claimed in any one of claims 1 to 6 for protecting said installation (2).

8. An aircraft, characterized in that the aircraft comprises an electrical installation (2) as claimed in claim 7.