DEVICES FOR MONITORING AND PROTECTING ELECTRICAL CIRCUITS

Description

Technical field

[0001] The present invention relates to the field of devices for monitoring and protecting power circuits controlled by switches with solid state or semiconductor power controllers (solid state power controller in English), hereinafter referred to as SSPC and in particular protection against current leakage faults known by the acronym GFI for Ground Fault Interrupt in English. Prior art

[0002] It is known to produce three-phase devices for which each power phase passes through a solid-state power controller provided with a switch for interrupting or allowing said phase to pass to a device to be powered and to have each of said power phases pass through a current detection transformer, the device comprising an earth fault circuit receiving an output from the current detection transformer, said earth fault circuit comprising an output connected to a monitoring module provided with a digital controller or processor, one or more outputs of which can be used to send to the controller(s) a command to cut off the power switches in the event of detection of a fault. Examples of solid-state power controllers are disclosed in documents CN 109672431, EP 2211437, US 3525019. Technical problem

[0003] These known solutions allow the detection of a phase leakage or an insulation fault but do not provide for distinguishing between several levels of earth leakage currents. Furthermore, it is desirable to be able to check the correct operation of the measuring circuit at the current detection transformer to ensure correct detection, particularly in cases where individuals may be in contact with the devices controlled by the SSPCs. Statement of the invention

[0004] In view of the prior art, the present application proposes an improved protection device comprising a means for testing at least one leakage current measurement channel.

[0005] More specifically, the present invention, as defined by the independent claims, relates to a monitoring and protection device for equipment powered by at least one solid state power controller called SSPC, said device comprising at least one current measurement circuit comprising: a current measuring transformer receiving at the primary at least the three phases of a three-phase power supply to the equipment or the phase and neutral of a single-phase power supply to the equipment and provided at the secondary with at least one winding for measuring the current in the primary, a measurement and test module comprising a controller provided with at least one analog input connected to said measurement winding by a measurement channel for measuring a current in the secondary I m , representative of a differential current I d in the primary and provided with a measurement program and a digital communication channel with said SSPC to control a switch in said SSPC in the event that said current I d exceeds a given threshold; such that said module comprises a current injection path into said transformer, said path comprising a current generator I inj driven by an output of the controller and connected to an injection winding on said transformer, said injection winding comprising a number of turns N inj adapted so that the current I inj produces in said measuring winding a current I m testing said secondary in the absence of current in the primary and said module comprises a test program adapted to control a current injection in parallel with a current measurement.

[0006] The injection channel of the invention makes it possible to test the correct operation of the measurement channel(s) of the device, in particular during a self-test of the solid-state power controller.

[0007] The following features correspond to embodiments which can be implemented optionally independently or in combination as appropriate.

[0008] According to an advantageous embodiment, the device comprises two measuring windings on the secondary, a first measuring winding being suitable for measuring a leakage current on the primary in a range of 0 to 100 milliamps, a second measuring winding being suitable for measuring a leakage current on the primary in a range of 0 to 2 Amps.

[0009] In a first embodiment suitable for a low-level measurement on a three-phase power supply, the device comprises three SSPC modules, the transformer is designed to receive the three phases of a three-phase power supply from said three SSPC modules and the neutral of the equipment, said primary current I d being the vector sum of the currents of said three phases and of the neutral and said controller is programmed to carry out one or more current measurements by means of the first measurement winding and to control the cutting of the switches of said three SSPC modules upon detection of a current I dB on the primary representative of a threshold called low-level GFI threshold of the order of 20 milliamps to 40 milliamps.

[0010] In a second embodiment suitable for a low-level measurement on a modified three-phase power supply, the device comprises three SSPC modules, the transformer is designed to receive the three phases from said three SSPC modules and the neutral of a three-phase power supply of the equipment, said primary current Id is the vector sum of the currents of said three phases and the neutral, said controller is programmed to carry out a series connection of said first measurement winding and second measurement winding, carry out one or more current measurements by means of the first winding and the second windings in series and control the cutting of the switches of said three SSPC modules upon detection of a current I dB on the primary representative of a threshold called low-level GFI threshold of the order of 20 milliamps to 40 milliamps.

[0011] In a third embodiment suitable for a high-level measurement on a three-phase power supply, the device comprises three SSPC modules, the transformer is designed to receive the three phases of a three-phase power supply of the equipment from said three SSPC modules with or without the neutral, said primary current I d is the vector sum of the currents of said three phases and for which said controller is programmed to carry out one or more current measurements by means of the second measurement winding and to control the cutting of the switches of said three SSPC modules upon detection of a primary current I dH greater than a threshold called high-level GFI of the order of 1 Ampere to 2 Amperes.

[0012] In a fourth embodiment suitable for a low level or high level measurement on a single-phase power supply, the device comprises an SSPC module, the transformer is designed to receive the phase and the neutral of a single-phase power supply of the equipment, said primary current I d is the difference between the phase current and the neutral current and for which said controller is either programmed to carry out one or more current measurements by means of the first measurement winding and to control the cutting of the SSPC switch upon detection of a current I dB on the primary representative of a threshold called the low level GFI threshold of the order of 20 milliamps to 40 milliamps or programmed to carry out one or more current measurements by means of the second measurement winding, or of the first and second windings placed in series,and to control the cutting of the SSPC module switch upon detection of a current I dH on the primary greater than a threshold called high level GFI of the order of 1 Ampere to 2 Amperes.,

[0013] Advantageously, to obtain easy current detection with a low level of injected current, the current generator can be configured to inject an alternating current of a frequency ten to fifty times higher than the frequency of the current controlled by the SSPC(s).

[0014] The invention further relates to a method for measuring current by means of a device of the invention which comprises a self-test sequence for which at least one injection of current representative of one or more given primary current thresholds on said injection winding and at least one measurement of the currents at the level of the measurement winding(s) are carried out and in that the measurement and test module issues a command to cut off the switches of the SSPC module(s) in the event of non-detection of a measurement current on said measurement winding(s).

[0015] The method may comprise, after a self-test sequence, successive current measurement sequences and the transmission by the measurement and test module of a command to cut off the switches of the SSPC modules if the current differential of the 3 phases supplied by the 3 channels of the SSPC modules and the neutral return is greater than a threshold of 30 mA during two successive current measurements or if the sum of the currents of the 3 supply phases is non-zero and greater than a defined current level for a defined minimum period.

[0016] The method may comprise, after a self-test sequence, successive current measurement sequences and the transmission by the measurement and test module of a command to cut off the switch of the SSPC module if the current differential between phase and neutral is greater than a defined threshold during two successive current measurements or during a defined minimum period. Brief description of the drawings

[0017] Other characteristics, details and advantages of the invention will appear on reading the detailed description below of non-limiting exemplary embodiments, and on analyzing the appended drawings, in which: [ Fig. 1 ] shows a schematic view of the device described; [ Fig. 2A ] shows a first embodiment; [ Fig. 2B ] shows a second embodiment; [ Fig. 3 ] shows a schematic view of an example of a known type SSPC module; Description of the embodiments

[0018] The following drawings and description contain elements which may not only serve to better understand the present invention, but also contribute to its definition, where appropriate.

[0019] Reference is now made to the figure 1which represents an electronic device provided with three phase inputs 1, 2, 3 and a neutral input 4, three solid-state power controllers 5, 6, 7 each crossed by a phase, a current detection transformer 8 crossed by the three phases and the neutral to measure the current imbalances between these conductors and carry out a differential current measurement, a measurement and test module 9 comprising a microcontroller 9a, voltage measurement channels 10, 11 and a current injection channel 12 each connected to a winding 13, 14, 15 on the transformer 8 and control channels shown diagrammatically by the link 16 to allow the measurement and test module to communicate with the SSPC(s) 5, 6, 7.

[0020] An example of a known type SSPC 30 module for controlling a phase is shown diagrammatically in figure 3. Such a module constitutes a static electronic circuit breaker controlled by a microcontroller 33. This circuit breaker can be configured to adapt to different aircraft wiring configurations. The parameters generally include information such as "protection rating I 2 < t", "default state", "lockout" and many others.

[0021] The static electronic circuit breaker is composed of two MOSFETs (English acronym for insulated gate field effect transistor) head to tail 31, 32 in alternating current but can comprise a single MOSFET in the case of a direct current SSPC for the power switch part and the microcontroller 33 to control and monitor the evolution of the power current passing through the SSPC from the input VP to the output S in accordance with the configuration parameters received. Several protection functions (I 2 < T, Thermal memory function) can be managed in parallel by the microcontroller through an acquisition of the current passing through the SSPC carried out via a measurement shunt 35.

[0022] In the event of a detected fault, the microcontroller 33 sends a cut-off order to the control component 34 responsible for controlling the gate of the power MOSFETS. The SSPS comprises an internal part 36 galvanically isolated by isolation means 37, 38 from a network bus 39 of the aircraft 39 and an external power supply for the microcontroller. The power input VP leaves the SSPC after passing through the MOSFETs.

[0023] In the case of a three-phase application, three single-phase SSPC channels can be grouped together to form a single three-phase SSPC channel capable of driving three-phase loads. In this case, one upstream controller and three channel controllers will be used.

[0024] The invention can also be applied to a single-phase switch.

[0025] Within the framework of the invention, it is necessary to provide two types of protection depending on the type of equipment to be controlled.

[0026] A first protection is a very sensitive protection that interrupts the power circuit in the event of earth leakage. This protection, hereinafter referred to as low-level GFI (GFI being the acronym in English for Ground Fault Interrupt), is achieved by a differential protection with a programmable value generally set at 30mA using the neutral return to be able to compare the vector sum of the current of the 3 outgoing phases and that of the neutral return. This is a protection of people, for example in the event of an insulation fault in a device.

[0027] A second protection is a less sensitive protection called high level GFI, for example for loads such as hydraulic pumps, for which the vector sum of the currents of the 3 phases and therefore the leakage current of one or other of the phases must not exceed a programmable threshold generally around 1.5A. This protection is a protection in the event of an earth fault on one phase of the device.

[0028] These two types of protections cover applications using an electrified function or device in an aircraft in contact with a human being. They can be generalized to any other vehicle containing electrical or electronic equipment for passengers, entertainment or cooking, for example.

[0029] This description relates to a monitoring and protection device suitable for achieving one or other type of protection depending on its programming and wiring.

[0030] According to the Figure 2A, the device is adapted to carry out a measurement of the vector sum of the currents of the 3 phases coming from the SSPC(s) 5 and the neutral return 4 to carry out the 30 mA differential protection (low level GFI). This measurement is carried out in the example by means of secondary windings 13, 14 connected to measurement channels 10, 11 of a measurement and test module 9 such as a microcontroller module 9a provided with analog measurement inputs 10a, 11a. The current transformer 8 receives the power conductors 1, 2, 3 and the neutral conductor 4 of the three-phase load supplied through the SSPC. In order not to increase the impedance at the primary, these conductors can only make a loop on the toroidal ferrite of the transformer or pass through it.The number of turns of the secondary windings is determined to obtain an output voltage offering a level of measurement precision on a scale around 30 mA, for example a scale 0 mA - 100 mA and providing a very low impedance brought back to the primary.

[0031] The choice of using two secondary windings is to allow the same transformer and the same assembly to be used for high-level GFI protection (1.5A current). For this protection, the vector sum of the currents of the 3 phases must be measured. In this case, the neutral return may not be wired to the current transformer as shown in Figure 2B. This measurement is then carried out by means of only one of the secondary windings 13 or 14 at the level of one of the measurement channels 10 or 11 and the corresponding analog input 10a or 11a of the measurement and test module 9. The current transformer 8 is crossed only by the power conductors 1, 2, 3 supplying the three-phase load supplied through the SSPC. The number of turns of the secondary winding considered is determined to obtain an output voltage offering a sufficient level of measurement precision to avoid triggering the protection inadvertently.

[0032] To fix the ideas, considering that the power conductors are wound on a single turn for each phase and for the neutral, on the ferrite of the toroidal transformer 8 to limit the impedance of the transformer to the primary, a first secondary winding of N1 turns makes it possible to measure a current range around 1.5 A. Advantageously, this winding placed in series with a second secondary winding of N2 turns makes it possible to measure a current range around 30 mA. Putting the two windings in series makes it possible to have a lower transformation ratio. Furthermore, the output shunt changes depending on whether one winding or two is used.

[0033] According to one aspect of the present disclosure, a means for testing these protection functions to ensure a self-test at startup of the SSPC card is provided.

[0034] To do this, the invention proposes to use a channel 12 for injecting a current linj into the current transformer 8. This injection channel is adapted to generate on the measurement load at the secondary at the level of the measurement channels 10, 11 a current in the secondary windings providing a test value. It should be noted that the test value is independent of the current measurement because the test is carried out at a frequency different from the frequency of the supply current of the equipment. To do this, the injection channel uses an output channel of the measurement and test module 9, which will control a current generator or an oscillator providing a current and a current injection winding on the current transformer. This winding has a number of turns Ninj adapted to provide at output the current equivalent to that generated during the fault to be detected.

[0035] To generate the test current, it is for example possible to use the microcontroller to drive a mosfet connected to a pull-up resistor or to oscillate an amplifier to generate a current source. Furthermore, by using a high frequency current, for example 10 to 50 times the frequency of the equipment supply current and a high number of turns, the transformation ratio being very different from the primary secondary ratio, the cut-off frequency of the transformer is not the same as between the primary and the secondary which allows to use a low current.

[0036] The low intensity injected current is injected by a signal generated at a high frequency so as not to overload the output of the microcontroller generating the signal.

[0037] For example, for a current transformer operating with a primary frequency of the order of 400Hz to 800Hz, the frequency of the injected current will be of the order of 8kHz to 20kHz and typically 10kHz. During current injection, which can be carried out during power circuit cuts by the SSPC or in an open power circuit self-test sequence, the measurement and test module 9 checks the current levels present on the measurement channels 10 and 11 to confirm their correct operation.

[0038] To communicate with the SSPC(s), the measurement and test module comprises a bidirectional link 16 through which it can receive a test request or transmit the results of a test carried out as well as transmit an order to cut off the power circuit in the event of detection of a fault. In the case where the test confirms the correct operation of the measurement circuit, the measurement and test module authorizes the SSPC(s) to close the power circuit and in other cases the measurement and test module commands the SSPC to open this circuit.

[0039] It should be noted that the test cannot be done during the operating phase.

[0040] The measure may, for example, include: In the case of non-use of the neutral return and if the sum of the currents of the 3 supply phases is non-zero and greater than a defined current level for a defined minimum time of the order of 5ms to 20ms then the card interface function can open the 3 SSPC channels to ensure high level GFI protection. In the case of use of the neutral return, the card interface function will ensure low level GFI protection by checking whether the current differential in the 3 phases supplied by the 3 SSPC channels and the neutral return is greater than a threshold of 30mA during two successive current measurements with a step depending on the application and function of the microcontroller sampling frequency.

[0041] According to a card start-up test (Power Up Built In Test in English terminology), the card interface function injects current into a secondary of the current transformer to test the current readings of the two high-level and low-level GFI protections.

[0042] In each case, a current value taking into account the shunt resistance at the output of the transformer to be controlled is injected by a current source at a higher frequency, in order to read the protection winding. This source is controlled by the microcontroller of the protection function and not by the SSPC channels.

[0043] The invention is not limited to the examples described above, only by way of example, but it encompasses all the variants that a person skilled in the art may envisage within the framework of the protection sought. In particular, the threshold currents may be different and the measurement channels may be completely separate.

Claims

1. A device for monitoring and protecting equipment powered by at least one solid-state power controller called SSPC (5, 6, 7), said device including at least one current measurement circuit characterised in that it includes: - a current measuring transformer (8) receiving at the primary at least the three phases (1, 2, 3) of a three-phase power supply of the equipment or the phase and the neutral of a single-phase power supply of the equipment and provided at the secondary with at least two windings (13, 14) for measuring the current at the primary, - a measuring and testing module (9) including a measuring and testing controller (9a) provided with at least one analog input (10a, 11a) connected to at least one of said measurement windings (13, 14) by a measurement channel (10, 11) for measuring a current at the secondary Im, representative of a differential current Id at the primary and provided with a measurement program and a digital channel (16) for communication with said SSPC for controlling a switch of said SSPC in the event that said current Id exceeds a given threshold; wherein said module (9) includes a channel for injecting current into said transformer, said channel comprising a current Iinj generator controlled by an output of the measuring and testing controller (9a) and connected to an injection winding (15) on said transformer, said injection winding including a number of turns Ninj adapted so that the current Iinj produces in said measurement windings (13, 14) a test current Im of said secondary in the absence of current at the primary characterized in that said module (9) includes a test program adapted to control a current injection in parallel with a current measurement; and wherein said two measurement windings (13, 14) at the secondary are such that a first measurement winding (13) is adapted for a measurement of a leakage current at the primary in a range 0 to 100 milliamps and a second measurement winding (14) is adapted for a measurement of a leakage current at the primary in a range of 0 to 2 amps.

2. The monitoring and protection device according to claim 1, wherein the device includes three SSPC modules, the transformer receiving the three phases of a three-phase power supply derived from said three SSPC modules and the neutral of the equipment, said current at the primary Id is the vector sum of the currents of said three phases and of the neutral and wherein said controller is programmed to proceed with one or more current measurement(s) by means of the first measurement winding and order the switching off of the switches of said three SSPC modules on detection of a current IdB at the primary representative of a threshold called low-level GFI threshold in the range of 20 milliamps to 40 milliamps.

3. The monitoring and protection device according to claim 1, wherein the device includes three SSPC modules, the transformer is designed to receive the three phases derived from said three SSPC modules and the neutral of a three-phase power supply of the equipment, said primary current Id being the vector sum of the currents of said three phases and of the neutral, said controller is programmed to proceed with a serial connection of said first measurement winding and second measurement winding, carry out one or more current measurement(s) by means of the first winding and the second winding in series and order the switching off of the switches of said three SSPC modules on detection of a current IdB at the primary representative of a threshold called low-level GFI threshold in the range of 20 milliamps to 40 milliamps.

4. The monitoring and protection device according to claim 1, wherein the device includes three SSPC modules, the transformer is designed to receive the three phases of a three-phase power supply of the equipment derived from said three SSPC modules with or without the neutral, said primary current Id is the vector sum of the currents of said three phases and wherein said controller is programmed to proceed with one or more current measurement(s) by means of the second measurement winding and order the switching off of the switches of said three SSPC modules on detection of a current IdH at the primary higher than a so-called high-level GFI threshold in the range of 1 amp to 2 amps.

5. The monitoring and protection device according to claim 1, wherein the device includes an SSPC module, the transformer is designed to receive the phase and the neutral of a single-phase power supply of the equipment, wherein said current at the primary Id is the difference between the phase current and the neutral current and wherein said controller is either programmed to proceed with one or more current measurement(s) by means of the first measurement winding and order the switching off of the switches of the SSPC on detection of a current IdB at the primary representative of a so-called low-level GFI threshold in the range of 20 milliamps to 40 milliamps or programmed to proceed with one or more current measurement(s) by means of the second measurement winding, or of the first and second winding(s) connected in series, and order the switching off of the switch of the SSPC module on detection of a current IdH at the primary higher than a so-called high-level GFI threshold in the range of 1 amp to 2 amps.

6. The monitoring and protection device according to any one of the preceding claims, wherein the current generator is configured to inject an alternating current with a frequency of ten to fifty times higher than the frequency of the current controlled by the SSPC(s).

7. A method for measuring current by means of a device of any one of the preceding claims, characterised in that it includes a self-test sequence for which at least one injection of current representative of one or more given primary current threshold(s) on said injection winding, for which a measurement of the currents at each of said first measurement winding and second measurement winding is carried out and in that the measuring and testing module emits an order for switching off the switches of the SSPC module(s) in case of nondetection of a measurement current on at least either one of said first measurement winding and second measurement winding during said current injection.

8. The method according to claim 7 applied to the device of claim 2 or 3, characterised in that it includes, after the self-test sequence, successive current measurement sequences and the emission by the measuring and testing module of an order for switching off the switches of the SSPC modules if the current differential of the 3 phases supplied by the 3 channels of the SSPC modules and the neutral return is higher than a 30mA threshold during two successive current measurements or if the sum of the currents of the 3 supply phases is non-zero and higher than a defined current level for a defined minimum period.

9. The method according to claim 7 applied to the device of claim 5, including, after a self-test sequence, successive current measurement sequences and the emission by the measuring and testing module of an order for switching off the switches of the SSPC modules if the current differential between the phase and the neutral is higher than a defined threshold for two successive current measurements or for a defined minimum period.