ELECTRICAL PROTECTION DEVICES AND CORRESPONDING PROCEDURES

Description

[0001] Aspects of the invention relate in particular to electrical protection apparatuses and associated methods of operation.

[0002] In the field of electrical protection, it is known to use differential protection devices to protect electrical distribution installations in the event of the occurrence of a differential fault current.

[0003] For example, an electrical switching device, such as a residual current device, may include a detection device designed to identify the occurrence of a fault current in an electrical conductor of the installation and, in response, trigger the switching device to interrupt the flow of current in the conductor.

[0004] Changing needs and regulatory constraints lead to the design of detection devices capable of reacting to the appearance of an electrical fault with a very short response time, for example less than or equal to 40 milliseconds.

[0005] However, it is desirable to avoid premature or unjustified tripping, as this could have adverse consequences on the operation of the electrical installation. Such premature tripping may be caused by short-term transient electrical disturbances.

[0006] Finally, these devices must be simple to manufacture and integrate into switching or electrical protection devices, such as differential circuit breakers. Their power consumption must also be moderate.

[0007] It is these drawbacks that the invention more particularly intends to remedy by proposing a detection device and an electrical protection device comprising such a detection device.

[0008] To this end, one aspect of the invention relates to an electrical protection apparatus as defined by claim 1.

[0009] The addition of a temporary overconsumption of energy by the processing circuit allows the quantity of energy stored in the energy reserve to be reduced in a controlled manner, and thus the emission of a trigger signal to be delayed. This prevents false triggering of the device caused by short-term parasitic phenomena, while ensuring that a trigger signal will nevertheless be emitted in the event of a proven fault.

[0010] According to advantageous but not mandatory aspects, such a detection device may incorporate one or more of the following characteristics, taken in isolation or in any technically admissible combination: The device is configured to, following detection of the occurrence of a fault current, wait for a predetermined delay time before starting to consume a predefined quantity of energy stored in the energy reserve. The predetermined delay time is between 1 ms and 4 ms, preferably equal to 2 ms. The device is configured to consume the predefined quantity of energy stored in the energy reserve only for a predefined time. The device comprises a resistor and a switch configured to selectively connect the resistor to the energy reserve, to consume said predefined quantity of energy stored in the energy reserve. The device further comprises a pulse generator coupled to the switch and configured to connect the resistor only for the duration of a pulse emitted by the pulse generator. The current sensor comprises a measuring toroid. The energy reserve comprises a capacitor.The protection apparatus further comprises a switching mechanism configured to open separable electrical contacts capable of being associated with an electrical conductor of an electrical installation, said switching mechanism being configured to be triggered when the triggering condition is identified.

[0011] According to another aspect, the method of detecting an electrical fault implemented by an electrical protection device comprises steps according to claim 10.

[0012] The invention will be better understood and other advantages thereof will appear more clearly in the light of the following description of an embodiment of an electrical protection apparatus and an associated operating method given solely by way of example and with reference to the appended drawings, in which: [ Fig 1 ] there figure 1 is a block diagram of an electrical protection device used in an electrical installation and comprising a detection device according to embodiments of the invention; [ Fig 2 ] there figure 2 is a graph representing an electrical voltage across an energy reserve of the detection device of the figure 1 given as a function of time; [ Fig 3 ] there figure 3 is a simplified diagram of a current pulse generated by the detection device of the figure 1 ; [ Fig 4 ] there figure 4 ; is an electrical diagram illustrating a mode of implementation of the detection device of the figure 1 ; [ Fig 5 ] there figure 5 is a functional diagram illustrating part of the detection device of the figure 4 ; [ Fig 6 ] there figure 6 is a diagram illustrating a method of detecting an electrical fault in accordance with embodiments of the invention.

[0013] There figure 1 represents an electrical protection device 2, such as a differential protection device.

[0014] The device 2 can in particular be used in an electrical installation, such as an electricity distribution installation, to detect a differential electrical fault between electrical conductors 4 of the electrical installation.

[0015] For example, the electrical installation is configured to distribute alternating electric current.

[0016] Generally, according to embodiments of the invention, the device 2 is configured to detect and react to a differential fault with a very short response time, for example less than or equal to 40 milliseconds (ms), while being immune to short-term parasitic electrical phenomena, for example less than 10 ms, in order to avoid untimely triggering.

[0017] The device 2 comprises a sensor 6 and a processing circuit 8 connected to the output of the sensor 6. The sensor 6 and the processing circuit 8 together form a detection device of the device 2.

[0018] The sensor 6 is configured to measure a differential fault current between two electrical conductors 4. When the device 2 is in service, the sensor 6 is coupled to the electrical conductors 4, for example mounted around the electrical conductors 4.

[0019] According to examples of implementation, the sensor 6 comprises a magnetic core around which a coil is wound. In the presence of a differential fault current, an electrical voltage appears between the terminals of the coil and forms the measurement signal delivered at the output of the sensor 6. This electrical voltage is representative of the differential fault current between the conductors 4.

[0020] In practice, since the primary electric current flowing in the conductors 4 is an alternating current, the voltage delivered by the sensor 6 is not always constant and can vary over time.

[0021] For example, each half-period of the primary current can be divided between a first operating phase and a second operating phase.

[0022] In the first phase, sensor 6 operates as a current generator. The first phase ends when the magnetic core of sensor 6 reaches saturation.

[0023] In the second phase, the sensor 6 generates a voltage to restore at least part of the magnetic energy stored in the winding. The second phase ends when the half-cycle of the primary current ends.

[0024] For example, for alternating currents with a frequency of 50Hz or 60Hz, the maximum half-period of the primary current is 10 ms.

[0025] The processing circuit 8 is configured to generate a trigger signal when an electrical fault current is measured by the sensor 6.

[0026] The trigger signal is then used by device 2 to interrupt the flow of current in conductor 4.

[0027] According to exemplary implementations, the device 2 further comprises a relay 10, a switching mechanism 12 and separable electrical contacts 14 coupled to the conductor 4.

[0028] The relay 10 is connected to the output of the processing circuit 8 and is configured to actuate the switching mechanism 12 as soon as it receives the trigger signal emitted by the processing circuit 8.

[0029] Relay 10 can be an electromechanical relay, in order to consume little energy for its operation.

[0030] The switching mechanism 12 is configured to, when actuated, switch the separable electrical contacts 14 from a closed and electrically conductive state to an open state preventing the flow of current in the conductor(s) 4.

[0031] Alternatively, the relay 10, the mechanism 12 and the separable electrical contacts 14 may be replaced by a component having equivalent functionality, for example a solid-state relay, such as a transistor.

[0032] Preferably, the device 2 is a device self-powered by electrical energy, also called a “self-powered” device. For example, the processing circuit 8 is powered electrically only by taking a portion of the electrical power delivered by the sensor 6.

[0033] In particular, the processing circuit 8 is not supplied with electrical energy via a dedicated electrical power supply device, such as a power converter supplied by the electrical installation (for example via a connection to the conductors 4) or by an on-board power source such as a battery. The apparatus 2 therefore does not need to include power conversion equipment.

[0034] According to embodiments, the processing circuit 8 may be implemented by one or more electronic circuits, comprising one or more discrete analog components and / or by one or more integrated circuits. The processing circuit 8 may also comprise a processor, such as a microcontroller.

[0035] According to variants, the processing circuit 8 may comprise a signal processing processor (DSP), or a reprogrammable logic component (FPGA), or a specialized integrated circuit (ASIC), or any equivalent element.

[0036] In the example illustrated, the processing circuit 8 comprises a protection and rectification stage 20, a clipping stage 22, a processing stage 24, a rechargeable energy reserve 26 and a comparator 28.

[0037] Stages 20, 22 and 24 are configured to filter and / or process the measurement signal from sensor 6. Stage 24 makes it possible to modify the dynamic behavior of processing circuit 8 in order to comply with standardized trigger times.

[0038] In the example illustrated, stage 20 is placed at the input of circuit 8 and receives the measurement signal from sensor 6. Stages 20, 22 and 24 are connected in series one behind the other.

[0039] Floors 20, 22 and 24 can be constructed conventionally and are not described in further detail below.

[0040] The energy reserve 26 is configured to accumulate the energy coming from the sensor 6 when the latter emits a measurement signal.

[0041] In other words, the energy reserve is charged by the electrical voltage delivered by the sensor 6 when a fault current flows in the conductor(s) 4.

[0042] In the following example, the energy reserve 26 includes a capacitor.

[0043] In practice, in certain embodiments, the energy reserve 26 can receive the measurement signal after processing or filtering of the latter by the stages 20, 22, 24, or instead receive a voltage which is representative of this measurement signal.

[0044] The comparator 28 is configured to compare the energy level stored in the energy reserve 26 with a single predefined value and to generate the trigger signal when the stored energy level exceeds the predefined value.

[0045] For example, to do this, the comparator 28 is connected with the energy reserve 26 and compares the voltage across the energy reserve 26 with a predefined voltage threshold.

[0046] Thus, when a certain level of energy is stored in the energy reserve 26, a trigger condition is considered to be identified by the processing circuit 8 and a trigger signal is emitted. Advantageously, the energy stored in the energy reserve 26 is consumed to trigger the relay 10.

[0047] In this way, the processing circuit 8 is able to react quickly to the occurrence of a fault current, while requiring only little energy to operate. This is particularly appreciable since, as explained above, the device 2 is self-powered and must therefore have very low power consumption.

[0048] According to aspects of the invention, the device 2 further comprises an auxiliary circuit 30 which is configured to temporarily inhibit the triggering of the device 2 in the event of the occurrence of an electrical fault.

[0049] Advantageously, the inhibition is ensured by consuming part of the energy stored in the energy reserve 26 following the detection of a fault current.

[0050] In the illustrated example, the circuit 30 comprises a detection module 32, a module 34 for generating a delay and a module 36 for triggering the consumption of a predefined quantity of energy in the energy reserve 26.

[0051] The auxiliary circuit 30 may be associated with the processing circuit 8 or be part of the processing circuit 8.

[0052] For example, the detection module 32 is configured to detect a start condition, in order to identify an increase in the fault current. The start condition may be a rising wavefront of the electrical voltage delivered by the sensor 6, or the moment from which the received electrical voltage is clipped by the stage 22.

[0053] The module 34 comprises a pulse generator configured to generate a pulse, for example an electrical current or voltage pulse, after detection by the detection module 32 of the start condition.

[0054] Preferably, the module 34 is configured to introduce a predefined waiting time after detection by the detection module 32 of the start condition before generating the pulse.

[0055] In the example illustrated by graph 60 of the figure 3 , the module 34 generates a current or voltage pulse 62 for a predefined duration “T-pulse” after a predefined delay “T-on” counted from the moment when the module 32 detects the start condition.

[0056] The reference "I 0" designates the amplitude of the pulse, which in practice can be chosen arbitrarily. Outside the T-pulse duration, the current or voltage of the signal at the output of module 34 remains zero.

[0057] For example, the values ​​of the preset duration "T-pulse" and the preset delay "T-on" can be stored in a memory of the auxiliary circuit 30.

[0058] The module 36 is preferably configured to consume energy stored in the energy reserve 26 only for the duration of the pulse generated by the module 34.

[0059] According to examples, the module 36 may comprise a resistor and a switch for selectively connecting or disconnecting the resistor from the energy reserve 26.

[0060] For example, the switch is driven by the pulse generated by the module 34. In practice, the module 34 can be coupled to a control electrode of the switch to send the pulse to said control electrode in order to drive the switch. In the presence of a pulse, the resistor is not connected to the energy reserve 26. In the absence of a pulse, the resistor is disconnected from the energy reserve 26.

[0061] Thus, the resistor is only connected to the energy reserve 26 for the duration of the pulse.

[0062] According to exemplary implementations, the switch is a mechanical switch, or an electromechanical switch such as a relay, or a solid-state switch, such as a transistor.

[0063] It is understood that, when the resistor is connected to the reserve 26, it dissipates at least part of the energy of the reserve 26.

[0064] It is thus possible to reduce a predefined amount of energy by choosing the duration of the pulse and the sizing of the resistor.

[0065] According to implementation modes, which will be better understood upon reading the examples which follow, the auxiliary circuit 30 can be implemented by one or more electronic circuits comprising one or more discrete analog components and / or one or more integrated circuits and / or a processor, such as a microcontroller.

[0066] An example of operation of the auxiliary circuit 30 is explained with reference to the figure 2 .

[0067] Graph 40 illustrates the evolution of the electrical voltage at the terminals of the energy reserve 26 (y-axis, expressed in volts and noted U c ) as a function of time (x-axis, expressed in seconds and noted “t”), for a first example in which the auxiliary circuit 30 is not used (curve 42), and a second example in which the auxiliary circuit 30 is used (curve 44).

[0068] In the first example, an electric current is measured by the sensor 6, which generates a corresponding electric voltage at the input of the processing circuit 8. Part of the corresponding electric power is consumed by the processing circuit 8 for its operation, and the other part partially recharges the energy reserve 26, which results in an increase in the electric voltage at the terminals of the energy reserve 26, as visible on the curve 42.

[0069] This increase is not, however, constant, in particular because of the behavior of the sensor 6 and the electrical consumption of the processing circuit 8, and the periodicity of the primary current.

[0070] In the example illustrated, the voltage U c increases up to a first instant t 1 , from which the magnetic core of the sensor 6 reaches saturation. This corresponds to the first operating phase of the sensor 6 mentioned previously.

[0071] The voltage U c then stabilizes, or even decreases slightly, since the electrical power delivered by the sensor 6 is then essentially consumed by the processing circuit 8 to ensure its operation.

[0072] Then, from a second instant t 2 , corresponding to the end of the first half-period of the primary current, here equal to 10ms, the voltage U c increases again, corresponding to the second phase of operation of the sensor 6 mentioned previously.

[0073] The increase in voltage U c continues until it reaches (arrow 46) the predefined voltage threshold U lim of comparator 28. The trigger signal is then emitted.

[0074] In practice, it is desirable to avoid such behavior, as it may lead to untimely or unjustified triggering of device 2, which may be detrimental to the proper functioning of the electrical installation.

[0075] In this situation, a simple half-sine wave of current may be sufficient to trigger device 2, which is not desirable for devices that must meet certain normative constraints, such as differential protection devices known as type F (for example as defined by standard IEC62423) and type G (for example as defined by the Austrian standard OVE E 8601).

[0076] The auxiliary circuit 30 makes it possible to resolve these drawbacks, as illustrated by the second example.

[0077] In the second example, like the first example, when a differential fault electric current is measured by the sensor 6, part of the electric power supplied by the sensor 6 is used to charge the energy reserve 26, which results in an increase in the voltage U c , as visible on the curve 44.

[0078] In the same way as in the first example, the voltage U c increases up to a first instant t 1 , from which the magnetic core of the sensor 6 reaches saturation.

[0079] However, in the second example, the auxiliary circuit 30 intervenes temporarily to consume part of the energy stored in the reserve 26. This consumption results in a reduction in the voltage U c between the instants t' 1 and t' 2 .

[0080] Thus, at the end of the half-period of the primary current wave, corresponding to the instant t 2 , the level of energy stored in the reserve 26 has dropped sufficiently so that the additional energy input caused by the discharging of the torus (during the second phase of operation of the sensor 6) does not allow the voltage threshold U lim to be reached.

[0081] An untimely triggering of device 2 is then avoided.

[0082] However, the energy level stored in the reserve 26 remains high enough to guarantee the triggering of the device 2 if a second current wave is received immediately afterwards. Such a second current wave is in fact indicative of the presence of an electrical fault justifying the triggering of the device 2.

[0083] In the illustrated example, arrow 48 indicates a further increase in voltage U c caused by such a second current wave, which leads to the triggering of device 2 when voltage U c reaches the voltage threshold U lim , as illustrated indicated by arrow 50.

[0084] Thanks to the auxiliary circuit 30, the device 2 is capable of reacting to the occurrence of an electrical fault with a very short response time, while being immune to premature or unnecessary triggering caused by short-term parasitic electrical phenomena.

[0085] More specifically, the addition of a temporary overconsumption of energy by the processing circuit makes it possible to reduce in a controlled manner the quantity of energy stored in the energy reserve, and therefore to delay the emission of a trigger signal. This makes it possible to avoid false triggering of the device caused by short-term parasitic phenomena, while ensuring that a trigger signal will nevertheless be emitted in the event of a proven fault.

[0086] Such operation is particularly suitable for self-powered differential protection devices, in which the detection of the fault current is ensured by accumulation thanks to the energy reserve (devices known as type VI for "Voltage Independent" in English). The auxiliary circuit 30 can be implemented simply, consuming only little energy, and without the need to significantly modify the existing architectures of the differential protection devices.

[0087] As explained above, the amount of energy consumed in the reserve 26 can be adjusted in advance, in particular by choosing appropriate values ​​of the delay and / or the duration of the pulse and / or resistance.

[0088] For example, the preset delay "T-on" is between 1ms and 4ms, for example equal to 2ms. According to examples, the T-pulse duration of the pulse can be between 2ms and 5ms

[0089] According to examples, the resistance value RT of the resistor of the module 36 can be between 1 kΩ and 100 kΩ.

[0090] In practice, the energy consumption in the reserve 26 may only be active after the saturation of the sensor 6 (i.e. between the times t 1 and t 2 ), or only before the saturation of the sensor 6 (i.e. before the time t 1 ), or over a time range overlapping these different operating phases.

[0091] Other values ​​can be chosen depending on the characteristics of the device 2 and the circumstances of use.

[0092] By setting the predefined delay before triggering the overconsumption of energy, the processing circuit 8 is allowed to take part of the power coming from the sensor to ensure its operation, power which would otherwise be dissipated by the module 36.

[0093] There figure 4 illustrates an exemplary embodiment of the processing circuit 8, comprising in particular two protection diodes 70 which implement the protection function of the stage 20 previously described, as well as an electronic card 72 which implements the tuning and rectification functions of the stages 20 and 22.

[0094] The processing circuit 8 further comprises a first resistor 74 and a Zener diode 76 connected upstream of the energy reserve 26, which can implement functions of the clipping module 22.

[0095] For example, Zener diode 76 limits the voltage across energy reserve 26 in cases of high differential current. In this example, reference 80 designates the pull-up resistor of module 36.

[0096] There figure 5 represents a more detailed example of construction of the auxiliary circuit 30, given for illustrative purposes, it being understood that other embodiments are possible.

[0097] In this example, given solely for illustration purposes, the auxiliary circuit 30 comprises the pull-up resistor 80, a first transistor 82, a resistor 84, a capacitor 86, and a second transistor 88. The output terminals of the circuit 30 (arrow 90) are connected to the energy reserve 26. The reference GND designates an electrical ground of the device 2.

[0098] Transistor 82 is connected to Zener diode 76 and to the RC circuit formed by the parallel association of resistor 84 and capacitor 86, this circuit being connected to a control electrode of transistor 88. Transistor 88 is connected to resistor 80 and acts as the switch of module 36.

[0099] When Zener diode 76 becomes conductive, it closes transistor 82. Capacitor 86 charges during the delay time T-on, the value of which is defined by the resistance and capacitance of resistor 84 and capacitor 86.

[0100] Then, the capacitor 86 discharges by applying a voltage across the control electrode of the transistor 88.

[0101] The transistor 88 switches to the closed state, thus connecting the resistor 80 to the energy reserve 26, making it possible to consume, by thermal dissipation, part of the electrical energy stored in the reserve 26.

[0102] According to other embodiments, the auxiliary circuit 30 can be implemented differently, for example by means of a microcontroller associated with a resistor 80 coupled to a switch.

[0103] In the case where the processing circuit 8 is at least partly implemented by a microcontroller or by any equivalent processor, then the auxiliary circuit 30 can be implemented using this same microcontroller or this processor.

[0104] An example of operation of the apparatus 2 is now described with reference to the figure 6 .

[0105] The method starts at step S100 with the appearance of a differential fault current in the conductor(s) 4. The sensor 6 detects this fault current and generates a corresponding electrical voltage.

[0106] In step S102, the energy reserve 26 is charged by a portion of the corresponding electrical voltage received from the sensor 6.

[0107] In step S104, which can be repeated continuously or periodically, the comparator 28 checks whether the level of electrical energy stored in the energy reserve 26 reaches the predefined threshold.

[0108] If this condition is met, device 2 is triggered during a step S106.

[0109] If this condition is not met, the method returns to step S102 and step S104 is repeated.

[0110] In parallel, and as long as device 2 is not triggered, the received voltage is detected by auxiliary circuit 30.

[0111] For example, during a step S110, the module 32 checks whether the condition of the received voltage is clipped by the Zener diode 76.

[0112] In step S112, the module 32 detects whether a start condition is met.

[0113] As explained previously, this starting condition may correspond to the detection of a rising wavefront, which may correspond to the transition to a conductive state of the clipping diode 76 of the clipping stage 22.

[0114] As soon as the start condition is detected, the auxiliary circuit 30 begins to count down the waiting time “T-on” (step S112).

[0115] At the end of the waiting time “T-on”, the module 34 generates a current pulse for a duration T-pulse (step S114).

[0116] In step S116, in response to the pulse generated by the module 34, the module 36 consumes a predefined amount of energy stored in the reserve 26. For example, the switch of the module 36 is closed to connect the resistor 80 with the reserve 26 for the duration of the pulse. At the end of the pulse, the switch 36 is reopened and the resistor 80 is disconnected. The method returns to step S110.

[0117] Alternatively, the steps could be performed in a different order. Some steps could be omitted. The described example does not preclude other steps from being performed in other embodiments in conjunction and / or sequentially with the described steps.

[0118] Any feature of one of the embodiments or variations described above may be implemented in the other embodiments and variations described in accordance with the claims.

Claims

1. An electrical protection device (2) for detecting a differential fault between two electrical conductors (4), this protection device (2) comprising: - a current sensor (6), the current sensor (6) comprising a magnetic toroid around which a coil is wound; characterised by: - an energy reserve (26) connected to the current sensor, the energy reserve (26) being configured to be charged by the electrical voltage supplied by the current sensor (6) during a first operating phase when a fault current flows in the electrical conductor or conductors (4); - a processing circuit (8) configured to identify (S106) a triggering condition when the energy stored in the energy reserve (26) exceeds a predefined threshold (Ulim); the protection device being configured to: - measure (S100) a differential fault current using the current sensor (6), - detect (S112) the occurrence of a fault current measured by the current sensor (6), - in response, consume (S116) a predefined amount of energy stored in the energy reserve during a second operating phase of the current sensor (6) after the magnetic toroid of the current sensor (6) has reached saturation.

2. An electrical protection device (2) according to claim 1, which is configured so as, following detection of the occurrence of a fault current, to wait (S114) for a predetermined delay time (T-on) before beginning to consume (S116) a predefined quantity of energy stored in the energy reserve.

3. An electrical protection device (2) according to claim 2, in which the predetermined delay time (T-on) is between 1ms and 4ms, preferably equal to 2ms.

4. An electrical protection device (2) according to any one of the preceding claims, which is configured to consume (S116) the predefined amount of energy stored in the energy store only for a predefined duration (T-pulse).

5. An electrical protection device (2) according to any one of the preceding claims, wherein the device comprises a resistor and a switch (36) configured to selectively connect the resistor to the energy reserve (26), to consume (S116) said predefined quantity of energy stored in the energy reserve.

6. An electrical protection device (2) according to claim 5, which further comprises a pulse generator (34) coupled to the switch (36) and configured to connect the resistor only for the duration of a pulse emitted by the pulse generator.

7. An electrical protection device (2) according to any of the preceding claims, in which the current sensor (6) comprises a measuring toroid.

8. An electrical protection device (2) according to any of the preceding claims, in which the energy reserve (26) comprises a capacitor.

9. An electrical protection device (2) according to any one of the preceding claims, wherein the protection device further comprises a switching mechanism (10, 12) configured to open selectable electrical contacts (14) capable of being associated with an electrical conductor of an electrical installation, said switching mechanism being configured to be triggered when the trigger condition is identified.

10. A method of detecting an electrical fault implemented by an electrical protection device (2) to detect a differential fault between two electrical conductors (4), the method comprising steps consisting of: - measure (S100) a differential fault current by means of a current sensor (6), , the current sensor (6) comprising a magnetic toroid around which is wound a coil is wound around, the protection device being configured to identify a tripping condition when the energy stored in an energy reserve (26) connected to the current sensor (6) exceeds a predefined threshold (Ulim), the energy reserve (26) being configured to be charged by the electric voltage delivered by the current sensor (6) during a first operating phase when a fault current flows in the electrical conductors (4), - detect (S112) the occurrence of a fault current measured by the current sensor (6), - in response, consume (S116) a predefined amount of energy stored in the energy reserve during a second operating phase of the current sensor (6) after the magnetic toroid of the current sensor (6) has reached saturation.