Field

This relates to a residual current circuit breaker having auto-test functionality, the RCCB device having a bypass circuit configured to prevent disruption of power supply to a load during automatic testing.

Background

A residual current device (RCD) is a protection device which continuously monitors current through a circuit it protects to detect any leaking current (i.e. a current leak to the earth wire). It also protects against current shorts, as well as electric electrocution or shock caused by direct contact. Residual current devices include residual current circuit breakers (RCCBs, which provide leakage current protection) and residual current circuit breakers with overload protection (RCBOs, which also provides overload protection).

Current leakage protection is achieved by monitoring the current flow in the line and neutral. RCCBs operate by measuring the difference (e.g. using a differential current transformer) between the current flowing through the live conductor in one direction and that returning through the neutral (N) conductor or wire in the opposite direction. In a normal circuit, the current flow via the current line equals the return flow in the neutral. However, this return flow may not be equal to the line’s current flow in the event of any abnormalities or faults. In other words, an imbalance in the current flows indicates a fault. An RCCB will automatically stop electricity flowing through the circuit when it detects a fault by opening electrical contacts within the circuit. Hence the condition of the electrical contacts of the RCCB is crucial to the effectiveness and safety of the device. The

IEC 61008-1 product standard mandates the need for periodic testing of RCCBs to ensure human safety.

Existing RCDs (including RCCBs and RCBOs) have manual Test buttons, which allow a user to check the RCD by activating the tripping mechanism and causing contact movement. This is an entirely manual process, and it also disconnects the supply/power source from the load, which may stop some critical devices. Moreover, in application such as airports, oil and gas installations, or remote charging stations, access to RCDs is very difficult, making manual testing difficult and time consuming. There is therefore a need for an RCD with an automatic testing function, in which the RCD can generate its own fault signal and periodically check the trip mechanism and contact movement, without the need for manual operation. In particular, it is desirable to provide a compact, robust, RCD device with an automatic testing function.

Summary Described herein is a residual current circuit breaker device (RCCB) with an auto-test function. The device comprises: a residual current circuit configured to be connected to a first current line between a power source and a load, the residual current circuit comprising a first switch which is configured to open and close the first current line; means for performing an auto-test of the residual current circuit; and a bypass circuit configured to electrically connect the power source and the load via a second current line during the auto-test function, the bypass circuit comprising an electronic switch which is configured to open and close the second current line. The electronic switch can also be referred to as a solid state switch. Such a device can provide a reliable, robust, RCD device with an automatic testing function, without interruption of power supply to a load. The device may also be smaller than previous devices, and the auto-test function may be performed quicker, due to the use of an electronic switch with no moving parts.

In some examples, the first switch is a mechanical switch and is actuated by a mechanical drive. Optionally, the mechanical drive comprises a piezoelectric motor.

In some examples, the means for performing the auto-test further comprise: means for injecting a residual current into the residual current circuit to cause the first switch to open the first current line. In some examples, the means for injecting a residual current are configured to inject the residual current by causing a relay contact to close. For example, the device comprises a relay having a relay contact, and the means for injecting a residual current are configured to inject the residual current by causing the relay contact of the relay to close.

In some examples, the means for injecting a residual current comprises a first hardware logic unit. In other examples, the means for injecting a residual current comprises a controller.

In some examples, the controller is further configured to control the electronic switch to open and close the second current line.

In some examples, the means for performing the auto-test comprises a real time clock and is configured to perform the auto-test at periodic intervals based on the real time clock. In some examples, the bypass circuit further comprises one or more isolation contacts arranged in series with the electronic switch, the isolation contacts configured to open when a current between the source and the load falls below a predetermined threshold in order to electrically isolate the source and load along the second current line.

Some examples include a second hardware logic unit, wherein opening and closing of the one or more isolation contacts is driven by the hardware logic unit. The first and second hardware logic units maybe the same unit, or maybe different units. In some examples, the second hardware logic unit comprises a timer and is configured to close the one or more isolation contacts for a predetermined testing period.

In some examples, the electronic switch is configured to be opened and closed in response to a feedback signal indicative of a position of the one or more isolation contacts.

In some examples, the first switch is an electronic switch. In some examples, the device comprises a piezoelectric transform, wherein the means for injecting a residual current are configured to inject the residual current by controlling the piezoelectric transformer. In other words, the means for injecting a residual current comprise a piezoelectric transformer.

In some implementations the means for performing an auto-test of the residual current circuit comprises: a relay switch; a first module configured to control the relay switch to form a parallel current path within the RCCB device; and a second module configured to cause the first switch to open the first current line based on forming the parallel current path. In some implementations the means for performing an auto-test of the residual current circuit comprises: a piezoelectric transformer; a first module configured to control the piezoelectric transformer to form a parallel current path within the RCCB device; and a second module configured to cause the first switch to open the first current line based on forming the parallel current path. The piezoelectric transformer can optionally be implemented in combination with a relay or other isolation means.

The first module and/ or the second module may be implemented as hardware logic (i.e. in a control module as described herein) or as software code (i.e. in a controller as described herein). Any other means of forming a parallel current path other than the relay or piezoelectric transformer may also be used in the implementations described herein.

The following numbered clauses are also described herein. 1. A residual current circuit breaker device with an auto-test function, the device comprising: a residual current circuit configured to be connected to a first current line between a power source and a load, the residual current circuit comprising a first switch which is configured to open and close the first current line, wherein the first switch is a mechanical switch and is actuated by a first piezoelectric motor; means for performing an auto-test of the residual current circuit; and a bypass circuit configured to electrically connect the power source and the load via a second current line during the auto-test.

2. The device of clause i, wherein the bypass circuit comprises a second switch which is configured to open and close the second current line. 3. The device of clause 2, wherein the second switch is an electronic switch, optionally a solid state switch.

4. The device of clause 2, wherein the second switch is a mechanical switch. 5. The device of clause 4, wherein the second switch is actuated by a second piezoelectric motor.

6. The device of any of clauses 2 to 5, the bypass circuit further comprising one or more isolation contacts arranged in series with the second switch, the isolation contacts configured to open when a current between the source and the load falls below a predetermined threshold in order to electrically isolate the source and load along the second current line.

7. The device of clause 6, further comprising a first hardware logic unit, wherein opening and closing of the one or more isolation contacts is driven by the hardware logic unit.

8. The device of clause 7, wherein the first hardware logic unit comprises a timer and is configured to close the one or more isolation contacts for a predetermined testing period. 9. The device of any of clauses 6 to 8, wherein the second switch is configured to be opened and closed in response to a feedback signal indicative of a position of the one or more isolation contacts. io. The device of any of clauses 1 to 9, wherein the means for performing the auto-test further comprise: means for injecting a residual current into the residual current circuit to cause the first switch to open the first current line. 11. The device of clause 10, wherein the means for injecting a residual current are configured to inject the residual current by causing a relay contact to close.

12. The device of clause 10 or clause 11, wherein the means for injecting a residual current comprises a second hardware logic unit.

13. The device of clause 10 or clause 11, wherein the means for injecting a residual current comprises a controller.

14. The device of clause 13, wherein the controller is further configured to control the bypass circuit to open and close the second current line.

15. The device of any of clauses 1 to 14, wherein the means for performing the autotest comprises a real time clock and is configured to perform the auto-test at periodic intervals based on the real time clock.

16. A residual current circuit breaker device with an auto-test function, the device comprising: a residual current circuit configured to be connected to a first current line between a power source and a load, the residual current circuit comprising a first switch which is configured to open and close the first current line; means for performing an auto-test of the residual current circuit; and a bypass circuit configured to electrically connect the power source and the load via a second current line during the auto-test, the bypass circuit comprising a second switch which is configured to open and close the second current line, wherein the second switch is a mechanical switch and is actuated by a piezoelectric motor.

17. The device of clause 16, wherein the first switch is a mechanical switch and is actuated by a mechanical drive. 18. The device of clause 17, wherein the mechanical drive is second piezoelectric motor. 19. The device of clause 16, wherein the first switch is an electronic switch, optionally a solid state switch.

20. The device of any of clauses 16 to 19, the bypass circuit further comprising one or more isolation contacts arranged in series with the second switch, the isolation contacts configured to open when a current between the source and the load falls below a predetermined threshold in order to electrically isolate the source and load along the second current line.

21. The device of clause 20, further comprising a first hardware logic unit, wherein opening and closing of the one or more isolation contacts is driven by the hardware logic unit.

22. The device of clause 21, wherein the first hardware logic unit comprises a timer and is configured to close the one or more isolation contacts for a predetermined testing period.

23. The device of any of clauses 20 to 22, wherein the second switch is configured to be opened and closed in response to a feedback signal indicative of a position of the one or more isolation contacts.

24. The device of any of clauses 16 to 23, wherein the means for performing the autotest further comprise: means for injecting a residual current into the residual current circuit to cause the first switch to open the first current line.

25. The device of clause 24, wherein the means for injecting a residual current are configured to inject the residual current by causing a relay contact to close.

26. The device of clause 24, wherein the means for injecting a residual current are configured to inject the residual current using a piezoelectric transformer.

27. The device of any of clauses 24 to 26, wherein the means for injecting a residual current comprises a second hardware logic unit. 28. The device of any of clauses 24 to 26, wherein the means for injecting a residual current comprises a controller. 29. The device of any of clauses 16 to 28, wherein the means for performing the autotest comprises a real time clock and is configured to perform the auto-test at periodic intervals based on the real time clock.

30. A residual current circuit breaker device with an auto-test function, the device comprising: a residual current circuit configured to be connected to a first current line between a power source and a load, the residual current circuit comprising a first switch which is configured to open and close the first current line; means for performing an auto-test of the residual current circuit, comprising a piezoelectric transformer; and a bypass circuit configured to electrically connect the power source and the load via a second current line during the auto-test, the bypass circuit comprising a second switch which is configured to open and close the second current line. 31. The device of clause 30, wherein the first switch is a mechanical switch or wherein the first switch is an electronic switch.

32. The device of clause 30 or clause 31, wherein the second switch is a mechanical switch or wherein the second switch is an electronic switch.

List of Figures

Figure 1 illustrates an RCCB with manual testing functionality for illustrative purposes;

Figure 2 illustrates a first example RCCB with auto-testing functionality with an electronic second switch; Figure 3 illustrates a second example RCCB with auto-testing functionality with an electronic second switch;

Figure 4 illustrates a third example RCCB with auto-testing functionality with an electronic second switch;

Figure 5 illustrates a fourth example RCCB with auto-testing functionality with an electronic second switch;

Figure 6 illustrates a fifth example RCCB with auto-testing functionality with an electronic second switch; Figure 7 illustrates a sixth example RCCB with auto-testing functionality having a mechanical first switch with a piezoelectric mechanical drive; and

Figure 8 illustrates a seventh example RCCB with auto-testing functionality having a mechanical second switch with a piezoelectric mechanical drive.

Detailed Description

With reference to Figure 1, operation of a manually operated RCCB too is described. The following description is with reference to a residual current circuit breaker device (RCCB), but it will be understood that the principles described herein can be applied to any residual current devices with current leakage protection (such as RCBOs).

A current line 102 connects a source or power supply 104 to a load 106. Under normal operating conditions, the current flow via the current line equals the return flow in the neutral N. However, in the event of current leakage, some of the current takes a different return path (i.e. not through the N line), leading to a current imbalance. There are provided means 108 for sensing this imbalance in the current through current line 102 (here a 3 phase current line, see in particular the portion within the dashed lines) and the return current through the neutral N. Means 108 can comprise a core balance current transformer, CBCT, or any other suitable components. When an imbalance in the current is sensed (indicating a current leakage), a signal is provided from means 108 to control a mechanical drive 110 to cause a switch 112 (here a 4 pole switch, shown within the dotted lines) to open, thereby opening the current line 102 and isolating the load 106 from the source 104. Due to the nature of the current leakage detection, a RCCB device will always include a neutral pole, so will be a 2 pole or 4 pole device.

RCCB too can be manually tested by manual actuation of test button T to close test switch 114. Closing switch 114 introduces a parallel path through which the current can flow. The magnitude of this current is controlled by choosing an appropriate value for resistor 107. This parallel path provides a different return path, reducing the current flowing on the neutral N line. This mechanism of introducing a parallel path is referred to herein as injecting a residual current (also referred to herein as a test current or fault current). The reduction in current flow on the neutral line causes means 108 to sense an imbalance in the current, in turn causing mechanical drive 110 to open switch 112. After the test, the RCCB too can be reset, causing switch 112 to close again. It is this test process which it is desirable to automate. Various RCCBs with different auto-test implementations will now be described, with additional circuitry overlaid on the device of Figure 1 for ease of understanding only. It is understood that, in some applications, the auto-test functionality may be provided without the manual testing features T, 114 described above. With reference to Figures 2 to 6, a residual current circuit breaker device 200 (e.g. an RCCB, though the principles can be applied to other RCDs) with an auto-test function is described.

The device 200 comprises a residual current circuit (such as that described with reference to Figure 1, e.g. comprising means 108 and mechanical drive 110). The residual current circuit is configured to be connected to a first current line 102 (as described above with respect to the current line of Figure 1, here shown by dashed lines) between a power source 104 and a load 106. The residual current circuit comprises a first switch 112 (as described above with respect to the switch of Figure 1, here shown within dotted box) which is configured to open and close the first current line 102.

The device 200 further comprises means for performing an auto-test of the residual current circuit. Performing an auto-test comprises causing the first switch to open the first current line 102. After the auto-test is complete, the first switch is closed again to close the first current line and electrically connect the source and load via the first current line. In some examples, the means for performing the auto-test can be configured to (automatically) control or initiate opening and/or closing of the first switch. In other words, the means for performing an auto-test can automatically open and/or close the first switch to replicate the testing function provided by manual testing features T, 114 described above with respect to Figure 1. In other examples, the first switch is otherwise caused to be opened and/or closed (i.e. by way of a different mechanism than the means for performing the auto-test). The means for performing an auto-test can be implemented in any suitable manner, some specific examples of which will be discussed in more detail below.

The device 200 further comprises a bypass circuit. The bypass circuit is configured to electrically connect the power source 104 and the load 106 via a second current line 202 (shown as a solid line) during the auto-test. In contrast to the mechanical first switch 112, the bypass circuit comprises an electronic switch 212 which is configured to open and close the second current line 202. The second current line is arranged in parallel with respect to the first current line. Here, each pole of the first current line 102 is shown with an associated bypass circuit, but any suitable arrangement can be provided to bypass the first switch 112 with a second current line 202 so that current continues to flow to the load 106 even when the first switch 112 is open during performance of the auto-test. In other words, the first switch and the second, electronic, switch are arranged in parallel. Mechanical switches (such as first switch 112) are physical switches, which must be activated physically, by moving, pressing, releasing, or touching its contacts. Electronic switches, on the other hand, do not require any physical, moving, contacts to control a circuit. Instead, electronic switches are activated by semiconductor action. Electronic switches (such as second switch 212) are generally called ‘solid state switches’. Electronic, or solid state, switches, have no physical moving parts (and hence no physical contacts). There are different types of solid state switches are available, with different sizes and ratings. Second switch 212 can be any suitable electronic switch or combination of electronic switches, including a solid state switch comprising one or more: diodes, transistors, silicon controlled rectifiers (SCRs), MOSFETs, diode or triode AC switch (DIACs or TRIACs) and/or insulated gate bipolar transistors (IGBTs). Any suitable solid state switch may be used.

An electronic or solid state switch can be more robust than a mechanical or electromechanical switch. Since there is no need to make/break physical contact to control a circuit, and no moving parts, an electronic switch can be more reliable and have a higher degree of repeatability and accuracy than a mechanical switch. A more robust and reliable device may therefore be provided than approaches which use a mechanical switch or actuator to control the bypass circuit. The device may also have a quicker switching time, and be a smaller device (since there is no need for a mechanical drive for the second switch within the device).

With further references to Figures 2 to 6, means for injecting a residual current into the residual current circuit to cause the first switch to open the first current line are provided as part of the means for performing an auto-test function. The means for closing the first switch can be further configured to close the first switch a predetermined period of time after the residual current is injected to close the first current line. The means to inject a residual current can be configured to inject the residual current by causing a relay contact to close. Said means may be by way of one or more controllers or processors (controllers comprising software code), or may be implemented in hardware logic.

With further reference to Figures 2 to 6, a controller 216 is provided. Controller 216 may be implemented in any suitable manner, for example as a microprocessor, or a microcontroller or microcontroller unit (MCU). Control signals from the controller 16 are indicated by solid arrows, and feedback signals received at the controller are indicated by dashed arrows. In the particular embodiments of Figures 2 to 5, the means for performing the auto-test are implemented by controller 216. In other words, the device 200 comprises a controller 216 configured to perform an auto-test function to cause the first switch to open the first current line (i.e. by injecting a residual or fault current into the residual current circuit). The controller can be further configured to control the means for closing the first switch to cause the first switch to close a predetermined period of time after the residual current is injected. In other words, after the auto-test is complete, the controller controls the position of the first switch to cause the source and load to be again electrically connected via the first current line. However, it will be seen that other means to inject a residual current can be provided, as discussed in more detail below with respect to the embodiment of Figure 6.

In the specific implementations of Figures 2 to 5, the controller 216 is configured to inject a residual current into the residual current circuit to cause the first switch 112 to open the first current line 102. In other words, the controller is configured to mimic the effect of closing switch 114 during a manual testing process to cause a current imbalance. The current imbalance is detected by the means 108, which can be implemented as a core balance current transformer CBCT, or in any other suitable manner. In some examples, the current through the first current line can be sensed by a current sensor Ci, and the auto-test function can be performed in dependence on the detected current. Current sensor Ci senses the load current (current flowing to the load) and ensures that the rated current is flowing through the device before performing an auto-test function.

In some specific examples, the controller 216 is configured to inject the residual current by causing a relay contact or switch 218 of relay Ri (shown here in an open state or open position) to close. Controller 216 is configured to send an independent control signal 224 to relay Ri to cause Ri to close contact or switch 218. A relay is an electrically operated switch. It consists of input terminals for receiving control signals, and a set of operating contact terminals. The relay switch may have any number of contacts 218 in multiple contact forms, such as make contacts, break contacts, or combinations thereof. The traditional form of a relay uses an electromagnet to close or open the contacts, but relays using other operating principles may also be used for relay Ri, such as solid state relays which use semiconductor properties for control without relying on moving parts. In other examples (not shown here), a piezoelectric transformer maybe used to inject the residual current instead of a relay (discussed further with respect to Figure 8).

The action of closing switch 218 of relay Ri injects a residual current into the neutral line, causing means 108 to sense an imbalance in the current. The first switch 112 is then caused to be opened in response to said sensing. After the auto-test is completed, the means for closing the first switch can be controlled to close the first switch 112. In some examples, the controller 216 is configured to control the means for closing the first switch to close the first current line 102 after a first predetermined period of time. The first predetermined period of time (or first predetermined time period) can be an expected test duration or period, or can be a predetermined time interval after the first switch 112 is opened.

The position of the first switch (i.e. open or closed) can be controlled by means for opening and means for closing the first switch. The means for opening and closing the first switch can be implemented separately (i.e. as separate means) or as a single component or apparatus. The means for opening and closing the first switch 112 can be provided by mechanical drive 110. In other words, the first switch can be a mechanical switch which is actuated by a mechanical drive.

In the specific examples of Figures 2 to 6, the mechanical drive 110 comprises a piezoelectric motor 220, which can optionally be controlled by a piezoelectric driver PZD. A piezoelectric driver is an amplifier type power supply selected for the stable driving of each piezo element of the piezoelectric motor. Operation of a piezoelectric motor 220, or piezo motor, is based on the change in shape of a piezoelectric material when an electric field is applied, as a consequence of the converse piezoelectric effect. An electrical circuit makes acoustic or ultrasonic vibrations in a piezoelectric material (for example, zirconate titanate, lithium niobate or other single-crystal materials), which can produce linear or rotary motion depending on the mechanism. Any suitable piezo motor design or mechanism may be used. Piezoelectric motors typically use a cyclic stepping motion, which allows the oscillation of the crystals to produce a large displacement motion (as opposed to most other piezoelectric actuators where the range of motion is limited by the static strain that may be induced in the piezoelectric element). Rapid opening of the first switch 112 can therefore be provided by way of the piezo motor 220, facilitating rapid breaking of the circuit through the first current line 102 in response to a fault. Similarly, the first switch 112 may be rapidly closed after an auto-testing operation to make the circuit.

Furthermore, the use of a piezoelectric motor as described herein (as compared to e.g. a servomotor or electromechanical actuation) results in less interference between signals since there is no electromagnetic force arising from e.g. induction. Moreover, there is no electronic noise. The size of the motor can also be smaller than a standard servomotor (which needs a gear box mechanism, suitable lever ratio, etc.). In other words, a piezoelectric motor provides a high speed, small, mechanical.

It will be understood that in some examples (not illustrated in the Figures) the first switch may be an electronic switch rather than a mechanical switch. An electronic first switch may be implemented as described above with respect to the electronic second switch.

With further reference to Figures 2 to 6, means for causing the electronic switch to close the second current line and means for causing the electronic switch to open the second current line are provided. These means can be configured to open the electronic switch 212 a second predetermined time interval after the first switch 212 is closed. For example, the means can be configured to switch off a current supply to the electronic switch, thereby opening that switch and deactivating the bypass circuit (disconnecting the source and the load via the second current line 202). In the specific examples illustrated, these means comprise controller 216. The controller 216 can be configured to cause the electronic switch 212 to close the second current line 202 and cause the electronic switch to open the second current line. In other words, the controller is further configured to control the electronic switch to open and close the second current line. In this way, electrical connection of the source 104 and load 106 via the second current line 202 can be controlled by the controller 216. However, it will be understood that a separate controller/ controlling logic, whether implemented in hardware or software, or any other means maybe additionally or alternatively used to control the electronic switch 212.

Controller 216 can further be configured to receive a signal 222 indicative of a position of the first switch 112. Signal 222 can provide feedback to the controller 216 as to a status of the first switch (i.e. whether the switch is open or closed). Signal 222 can be received from a proximity sensor, or any other suitable sensing arrangement. In some examples, the second predetermined time interval, after which the electronic switch is opened, can be calculated from receipt of signal 222 indicating the first switch is closed and the source and the load are electrically connected via the first current line.

The above-described features facilitate a robust residual current circuit breaker device 200 having an auto-test function/feature, which enables the operation of the device to be periodically tested in an automatic manner, without manual operation. Furthermore, the bypass circuit facilitates testing of the device without disconnecting the source and load, facilitating deployment or use in safety critical and uninterruptable power applications. An example sequence for performance of an auto-test operation of device 200 will now be described.

1. Favourable condition for auto-test detected using controller 216, along with real time data and/ or measurement means (such as the feedback from current sensor Ci and the feedback from switch 336 regarding manual/ automatic operation). Real time data can comprise day, month, and year and/or time data from a real time clock (RTC).

2. Controller 216 will switch ON the electronic switch 212 (close the electronic switch) and bypass circuit will become active.

3. Controller will inject residual current into the residual current circuit via relay Ri; as a result, the first switch 112 will open.

4. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220.

5. A proximity sensor gives feedback 222 to controller 216 indicating a position or status of the contacts of the first switch 112. 6. After another small pre-set interval (second period of time), controller 216 will switch OFF the electronic switch 212 (open the switch); as a result, the bypass circuit will be deactivated and no current will flow through the second current line 202.

7. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line 102.

Further implementations and examples of such devices will now be described with reference to Figures 3 to 6. The below described devices incorporate the above-described features of Figure 2, and further description of these features will therefore be omitted. Like reference numerals refer to like features.

Figure 3 illustrates a device 300, which is an example of a residual current circuit breaker device 200. The bypass circuit(s) of device 300 each comprise an additional galvanic isolation means (called herein isolation contacts) 330. The isolation contacts 330 are arranged in series with the electronic switch 212. In other words, the bypass circuit further comprises one or more isolation contacts 330 arranged in series with the electronic switch 212. The second current line 202 is defined through the isolation contacts 330. The isolation contacts are configured to open when a current between the source and the load falls below a predetermined threshold to electrically isolate the source and load along the second current line. This isolates the source from the load along the second current line when the load 104 is switched off, or when a fault is detected.

Galvanic isolation can therefore be achieved by way of isolation contacts 330. In this example, isolation contacts 330 are implemented as relay switches, but any suitable galvanic isolation means may be used. The isolation contacts 330 are controlled by current sensor C2. Current sensor C2 is positioned after the residual current circuit and after the bypass circuit (i.e. on an uninterrupted portion of current path between the source 104 and the load 106). Control signals from the current sensor to the isolation contacts 330 are represented by the dotted arrows in Figure 3. In this example there is one isolation contact 330 per bypass circuit, and an individual current sensor C2 per isolation contact 330. However, other arrangements are possible, depending on the configuration of the bypass circuit. Once the current between the source and the load detected by current sensor C2 is at or above the predetermined threshold level (i.e. a rated current is detected), the control signals from the current sensor C2 cause the isolation contacts (e.g. the relay contact) to close. The contact will remain closed as long as the rated current flows between the source and the load. If the current falls below the threshold level, the contact 330 will open again. The actuation of the isolation contacts 330 is in this implementation controlled by the current sensor C2.

Once the isolation contacts 330 are closed, the controller 216 can receive a feedback signal 332 indicative of the isolation contacts being closed. The controller 216 can then activate (close) the electronic switch 212 to activate the bypass circuit and allow current to flow through the second current line 202. The auto-test can then be performed by controller 216, as discussed above (inject a residual current into the residual current circuit via relay Ri to cause the first switch 112 to open). After the first predetermined time threshold (first period of time), the controller 216 can close the first switch 112 using the piezo motor 220. After the second predetermined time threshold (second period of time), the controller 216 can open the electronic switch 220. A proximity sensor can provide feedback signals 220 to the controller 216 about the status/position of the first switch. The isolation contacts 330 remain closed; the activation and deactivation of the electronic switch 212 controls current flow through the bypass circuit.

In some other examples (not shown in Figure 3), the isolation contacts may not remain closed. Instead, hardware logic which can sense the output of the current sensor C2 may be used to provide a timing signal to control closing of the isolation contacts 330 for a predetermined period of time.

In some examples described with reference to Figure 3, an additional reference signal 334 is provided to the controller 216, the reference signal 334 being indicative of a position of switch 336. Switch 336 indicates whether the device 300 is set to a manual or automatic test position. Controller 216 (or other means for performing the auto-test function) will only perform the auto-test function when the device 300 is set to “automatic” by switch 336. It will be understood that switch 336 is an optional feature, which feature may also be provided in the embodiment of Figure 2 (i.e. without the isolation contacts).

In some examples, reference signal 334 is used to determine whether conditions are favourable for performing an auto-test function. For example, an auto-test function may be performed when the load 104 is on and/or the current is at the rated current and/or there is no detected fault (examples of load condition status), and the reference signal 334 indicates the switch 336 is set to the automatic position. The controller can optionally (additionally or alternatively) monitor one or more other conditions to determine whether to perform the auto-test function, such as: a time of day, a number of days from a previous test, etc. (examples of a real time clock status). An example sequence for performance of an auto-test operation of device 300 will now be described.

1. Once a rated current is detected by sensor C2, sensor C2 will activate the galvanic isolation contacts 330. These contacts will remain closed while the rated current is present between the source and the load (while the rated current flows from the RCCB). If the rated current falls below a threshold limit, then the one or more contacts 330 will open.

2. Once the controller 216 has confirmation that the isolation contacts 330 are closed, then the auto-test is initiated by controller 216. Favourable conditions like the position of switch 316, a real time clock status, and/or load condition status can be detected and may also be used by the controller 216 to determine whether to initiate the auto-test sequence.

3. The controller 216 will activate the electronic switch 212 and the bypass circuit will become active. The isolation contacts 330 open once a timer delay is over (i.e. remain closed for a testing time period). 4. Controller will inject residual current into the residual current circuit via relay

Ri; as a result, the first switch 112 will open.

5. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220.

6. A proximity sensor gives feedback 222 to controller 216 indicating a position or status of the contacts of the first switch 112.

7. After another small pre-set interval (second period of time), controller 216 will switch OFF the electronic switch 212 (open the switch); as a result, the bypass circuit will be deactivated and no current will flow through the second current line 202. 8. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line 102.

The auto-test feature of device 300 described above can ensure periodic testing by automatically creating a residual fault current, and the bypass circuit will ensure that supply to the load 106 is not interrupted while testing the RCCB. The galvanic isolation contacts 330 are inserted to meet isolation requirements in an OFF state (i.e. when the bypass circuit is open and no current flows through the second current line). Figure 4 illustrates a device 400, which is an example of a residual current circuit breaker device 200. As in Figure 3, the bypass circuit(s) of device 400 each comprise an additional galvanic isolation means (called herein isolation contacts) 330. The isolation contacts 330 are arranged in series with the electronic switch 212. As discussed above, controller 216 receives feedback from the position of switch 336, which indicates whether the device 400 is set to a manual or automatic test position. For example, controller 216 can receive a feedback signal (such as reference signal 334) from the switch 336 so that the controller can sense whether device 400 is in a manual or automatic position or state. In this particular example, reference signal 334 is provided by a signal source 440, which provides reference signal 334 to the controller via the switch 336. However, it will be understood that reference signal 334 may be provided in any suitable manner in the embodiments described herein. Controller 216 (or other means for performing the auto-test function) will only perform the auto-test function when the device 400 is set to “automatic” by switch 336. Controller can also receive feedback from an inbuilt real time clock. For example, auto-tests can be periodically performed based on the clock and an associated schedule (i.e. weekly, monthly, or yearly, as appropriate). It will be understood that the inbuilt real time clock is an optional feature, which feature may also be provided in the embodiment of Figure 2 (i.e. without the isolation contacts) and/or Figure s.

Device 400 further comprises a control module 440 configured to control the isolation contacts 330. Control module 440 is hardware logic; there is no software code in control module 440. The control module 440 switches the galvanic isolation contacts on and off based on feedback signals from the controller 216 and the sensing output from the current sensor C2. The control signals from the control module to the isolation contacts are shown by the dotted arrows in Figure 4. In other words, the isolation contacts are driven by a first hardware logic unit of control module 440. Once the current between the source and the load detected by current sensor C2 is at or above the predetermined threshold level (i.e. a rated current is detected), a feedback signal is provided from the current sensor C2 to the control module 440. The control module also receives a trigger signal from the controller 216. In response to the feedback signal from the current sensor C2 and the trigger signal from the controller, the control module activates the isolation contacts 330 to close the contacts. The current sensor can also provide a reference signal 442 to the controller, which reference signal can be indicative of a load condition; load condition signal 442 may be used by controller in determining whether to initiate the auto-test function (i.e. whether conditions are favourable for a test) and thus whether to output the trigger signal to the control module 440.

Once the isolation contacts are closed, the controller will activate the electronic switch 212, causing the electronic switch to close and activating the bypass circuit. In particular, the controller 216 can receive a feedback signal 332 from the isolation contacts 330 (not shown, but as in Figure 3) indicative of the isolation contacts being closed. In other words, the status of the isolation contacts can be provided to the controller by feedback signal 332. In response to receiving the feedback signal, the controller 216 can activate (close) the electronic switch 212 to allow current to flow through the bypass circuit along the second current line 202. The source 104 and load 106 are thus electrically connected through the second current line 202.

The auto-test can then be performed by controller 216, as discussed above (inject a residual current into the residual current circuit via relay Ri to cause the first switch 112 to open). After the first predetermined time threshold (first period of time), the controller 216 can close the first switch 112 using the piezo motor 220. After the second predetermined time threshold (second period of time), the controller 216 can open the electronic switch 220. A proximity sensor can provide feedback signals 220 to the controller 216 about the status/position of the first switch. The control unit 440 is configured to open the isolation contacts 330 a third predetermined time period after closing the contacts (e.g. after a third time period, which is greater than a sum of the first period of time and the second period of time). The hardware logic of the control unit 440 comprises timer logic, and is configured to open the isolation contacts at the end of the auto-test function (i.e. after the third time period) based on the timer logic. The third time period can also be referred to as a testing time period or testing duration (period of time in which the auto-test function is performed).

An example sequence for performance of an auto-test operation of device 400 will now be described. 1. Once a rated current is detected by sensor C2, sensor C2 will send a signal to hardware logic control module 440.

2. Control module 440 will receive a trigger signal from the controller 216 and in response will activate (close) the galvanic isolation contacts 330. Triggering of the auto- test function can be based on feedback from switch 316, a real time clock status, and/or load condition status.

3. Once the controller 216 has confirmation that the isolation contacts 330 are closed, then the auto-test is initiated by controller 216. Favourable conditions like the.

4. The controller 216 will activate the electronic switch 212 and the bypass circuit will become active.

5. Controller will inject residual current into the residual current circuit via relay Ri; as a result, the first switch 112 will open.

6. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220. 7. A proximity sensor gives feedback 222 to controller 216 indicating a position or status of the contacts of the first switch 112.

8. After another small pre-set interval (second period of time), controller 216 will switch OFF the electronic switch 212 (open the switch); as a result, the bypass circuit will be deactivated and no current will flow through the second current line 202. The isolation contacts 330 are also opened by the control module 440.

9. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line 102.

Figure 5 illustrates a device 500, which is an example of a residual current circuit breaker device 200. As in Figure 3, the bypass circuit(s) of device 400 each comprise an additional galvanic isolation means (called herein isolation contacts) 330. The isolation contacts 330 are arranged in series with the electronic switch 212. As in Figure 4, a hardware logic control module 440 is provided. In contrast to the approach of Figure 4, the control module 440 switches the galvanic isolation contacts 330 on and off based on the sensing output from the current sensor C2. In other words, the isolation contacts 330 of device 500 are driven based on output of the individual current sensors C2. There is no additional signal from controller 216. Once the current between the source 104 and the load 106 detected by current sensor C2 is at or above the predetermined threshold level (i.e. a rated current is detected), a feedback signal is provided from the current sensor C2 to the control module 440. In response to the feedback signal from the current sensor C2, the control module activates the isolation contacts 330 to close the contacts. In some examples, control module 440 of device 500 also receives feedback signal 552 from the position of switch 336, which indicates whether the device 500 is set to a manual or automatic test position. Control module 440 will only close the isolation contacts 330 when the device 500 is set to “automatic” by switch 336.

In other words, control module 440 will only close isolation contacts 330 once feedback signal 552 is received and once the current sensed by sensor C2 is above the predetermined threshold.

Once the isolation contacts are closed by the control module 440, the controller will receive a feedback signal 550. Feedback signal 550 is indicative of a status/position of the isolation contacts and can be generated using high voltage or optical isolator logic which can sense the high voltage at the isolation contacts 330 and provide a status signal to controller 216. Feedback signal 332 (described with reference to Figure 3) can be generated in a same way as signal 550, or maybe generated in any other suitable manner. In response to receiving signal 550, the controller 216 will cause the electronic switch 212 to close. The source 104 and load 106 are then electrically connected through the second current line 202. The auto-test can then be performed by controller 216, as discussed above (inject a residual current into the residual current circuit via relay Ri to cause the first switch 112 to open). In other words, the controller 216 performs the auto-test function, but the control module 440 initiates performance of the test by controlling the isolation contacts 330. After the first predetermined time threshold (first period of time), the controller 216 can close the first switch 112 using the piezo motor 220. A proximity sensor can provide feedback signals 220 to the controller 216 about the status/position of the first switch.

The control module 440 of this example further includes an in-built timer, and is configured to close the isolation contacts 330 for a predetermined testing period. In other words, the first hardware logic unit comprises a timer and is configured to close the one or more isolation contacts for the predetermined testing period. The testing period is greater than the first time threshold/first period of time, in order that the isolation contacts 330 remain closed for the duration of the auto-test function. Optionally, this testing period can be between 7 and 10 seconds.

At the end of the testing period, the isolation contacts are opened again to isolate the source and load along the second current line. Feedback signal 550 indicative of the opening of the isolation contacts is provided to controller 216. In response to this feedback signal 550, the controller is configured to open the electronic switch. In other words, the electronic switch 212 is configured to be opened and closed in response to a feedback signal 550 indicative of a position of the one or more isolation contacts 330. The electronic switch is thus controlled (here by the controller 216) based on the feedback signal 550. In other examples, the controller 216 can open the electronic switch 212 after the first switch 112 is closed (i.e. the electronic switch is not controlled based on the feedback signal 550). In this example, the isolation contacts can again open after the end of the predetermined testing period (e.g. the isolation contacts are closed for the predetermined testing time/period, or testing duration).

The control module 440 can also comprise a real time clock (RTC), which can be used to trigger initiation of the auto-test function. The RTC can process timestamp information from signals received at the control module, and provide day, month and year data. In some examples, the RTC can provide a counter for a predetermined number of hours, days, weeks, etc. to periodically trigger the auto-test. The RTC can be used to trigger performance of a test at any suitable interval (such as, every week, every 28 days, or every year). The RTC can also be used to modify the periodicity of the test, and/ or to set a specific time and/or data of an auto test function.

An example sequence for performance of an auto-test operation of device 500 will now be described. 1. Once a rated current is detected by sensor C2, sensor C2 will send a signal to hardware logic control module 440.

2. Control module 440 receives feedback from switch 316, an in-built real time clock status, and a timer circuit. Triggering of the auto-test function by the control module can be based on this feedback. 3. Once the control module triggers the auto-test function, it closes the isolation contacts 330.

4. The controller 216 will receive feedback indicating the isolation contacts are closed, and in response will activate the electronic switch 212 and the bypass circuit will become active. 5. Controller 216 will inject residual current into the residual current circuit via relay Ri; as a result, the first switch 112 will open.

6. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220.

7. A proximity sensor gives feedback 222 to controller 216 indicating a position or status of the contacts of the first switch 112.

8. After another small pre-set interval (second period of time), controller 216 will switch OFF the electronic switch 212 (open the switch); as a result, the bypass circuit will be deactivated and no current will flow through the second current line 202. 9. The isolation contacts 330 are also opened by the control module 440. The isolation contacts 330 can be opened by the control module after a predetermined testing period (based on the in-built timer of the control module). The testing period can be greater than the first and second period of times, so allow for performance of the auto-test function.

10. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line 102.

Figure 6 illustrates a device 600, which is an example of a residual current circuit breaker device 200. As in Figure 3, the bypass circuit(s) of device 400 each comprise an additional galvanic isolation means (called herein isolation contacts) 330. The isolation contacts 330 are arranged in series with the electronic switch 212. As in Figure 4, a hardware logic control module 440 is provided. The means for performing an auto-test function here comprise a second hardware logic unit of the control module 440 (in contrast to previously described embodiments where the controller 216 performs the auto-test function). The first and second hardware logic units may be implemented in a single unit within the control module, or may be in separate units, as appropriate.

As in the example of Figure 5, the control module 440 of device 600 switches the galvanic isolation contacts 330 on and off based on the sensing output from the current sensor C2 (and in some implementations also based on the feedback signal 552). There is no additional signal from controller 216. The control module 440 of this example further includes a timer, and is configured to close the isolation contacts 330 for a predetermined testing period. Once the isolation contacts are closed by the control module 440, the controller will receive feedback signal 550 and, in response, will cause the electronic switch 212 to close. The source 104 and load 106 are then electrically connected through the second current line 202.

The control module 440 then performs the auto-test function. In other words, the means for performing the auto-test comprises a second hardware logic unit of the control module 440. The control module 440 is configured to mimic the effect of closing switch 114 during a manual testing process to cause a current imbalance. In this example, the control module 440 (i.e. second hardware logic unit) is configured to inject the residual current by causing the relay contact or switch 218 of relay Ri (shown here in an open state or open position) to close. Control module 440 is configured to send an independent control signal 660 to relay Ri to cause Ri to close contact or switch 218. The action of closing switch 218 of relay Ri injects a residual current into the neutral line, causing means 108 (not shown in Figure 6) to sense an imbalance in the current. A first predetermined time threshold (first period of time) after the first switch 112 is caused to open (which opening may e.g. be detected at the controller byway of signal 222 indicative of a position of the first switch 112), the controller 216 can close the first switch 112 using the piezo motor 220. The first period of time is less than the testing period, in order that the isolation contacts 330 remain closed for the duration of the auto-test function.

At the end of the testing period, the isolation contacts are opened again to isolate the source and load along the second current line. Feedback signal 550 indicative of the opening of the isolation contacts can be provided to controller 216. In response to this feedback signal 550, the controller can be configured to open the electronic switch 212. In other words, the electronic switch 212 can be configured to be opened and closed in response to the feedback signal 550 indicative of a position of the one or more isolation contacts 330. The electronic switch can thus be controlled (here by the controller 216) based on the feedback signal 550. In other examples, the controller 216 is configured to open the electronic switch after a second period of time from the first switch being closed, without dependence on the feedback signal 550. It will be understood that the electronic switch 212 can be controlled by the controller 216 even when the control module 440 (i.e. the hardware logic unit) controls the injection of a residual current by causing relay contact 218 of relay Ri to close.

An example sequence for performance of an auto-test operation of device 600 will now be described. 1. Once a rated current is detected by sensor C2, sensor C2 will send a signal to hardware logic control module 440.

2. Control module 440 receives feedback from switch 316, an in-built real time clock status, and a timer circuit. Triggering of the auto-test function by the control module can be based on this feedback. 3. Once the control module triggers the auto-test function, it closes the isolation contacts 330.

4. The controller 216 will receive feedback indicating the isolation contacts are closed, and in response will activate the electronic switch 212 and the bypass circuit will become active. 5. Control module 440 will inject residual current into the residual current circuit via relay Ri; as a result, the first switch 112 will open.

6. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220. 7. A proximity sensor gives feedback 222 to controller 216 indicating a position or status of the contacts of the first switch 112.

8. The isolation contacts 330 are opened by the control module 440 after a predetermined testing period (based on the in-built timer of the control module). 9. After another small pre-set interval (second period of time), controller 216 will switch OFF the electronic switch 212 (open the switch). In some other examples, the controller may additionally/ alternatively switch OFF the electronic switch based on feedback 550 indicating the isolation contacts have been opened.

10. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line 102.

With reference to Figure 7, a residual current circuit breaker device 700 (e.g. an RCCB, RCB or ROD) with an auto-test function is described. The device 700 comprises a residual current circuit such as that described with reference to Figure 1, e.g. comprising means 108 and mechanical drive 110. The residual current circuit is configured to be connected to a first current line 102 (as described above with respect to the current line of Figure 1, here shown by dashed lines) between a power source 104 and a load 106. The residual current circuit comprises a first switch 112 (here shown within dotted box) which is configured to open and close the first current line 102.

In this specific example, the first switch is a mechanical switch and is actuated by a piezoelectric motor 220 (an example of the mechanical drive 110). The piezoelectric motor and operation of the first switch 112 can be as described above with respect to Figures 2 to 6. In some examples, the piezoelectric motor 220 can optionally be controlled by a piezoelectric driver PZD. Rapid opening of the first switch 112 can be provided by way of the piezo motor 220, facilitating rapid breaking of the circuit through the first current line 102 in response to a fault. Similarly, the first switch 112 may be rapidly closed after an auto-testing operation to make the circuit.

The device 700 further comprises means for performing an auto-test of the residual current circuit. Performing an auto-test comprises causing the piezoelectric motor to actuate the first switch to open the first current line 102. After the auto-test is complete, the first switch is closed again by the piezoelectric motor to close the first current line and electrically connect the source and load via the first current line. In some examples, the means for performing the auto-test can be configured to (automatically) control or initiate opening and closing of the first switch by way of the piezoelectric motor. In other words, the means for performing an auto-test can automatically control the piezoelectric motor to open and close the first switch to replicate the testing function provided by manual testing features T, 114 described above with respect to Figure 1. In other examples, the piezoelectric motor is otherwise caused to open and close the first switch (i.e. the piezoelectric motor is controlled by a different mechanism than the means for performing the auto-test). The means for performing an auto-test can be implemented in any suitable manner, some specific examples of which will be discussed in more detail below.

The device 700 further comprises a bypass circuit. The bypass circuit is configured to electrically connect the power source 104 and the load 106 via a second current line 202 (shown as a solid line) during the auto-test. The bypass circuit comprises a second switch 212 which is configured to open and close the second current line 202. The second current line is arranged in parallel with respect to the first current line. Here, each pole of the first current line 102 is shown with an associated bypass circuit, but any suitable arrangement can be provided to bypass the first switch 112 with a second current line 202 so that current continues to flow to the load 106 even when the first switch 112 is open during performance of the auto-test. In other words, the first switch and the second switch are arranged in parallel.

In some examples, second switch is an electronic switch 212 (a solid state switch). An electronic or solid state switch can be more robust than a mechanical or electromechanical switch. Since there is no need to make/break physical contact to control a circuit, and no moving parts, an electronic switch can be more reliable and have a higher degree of repeatability and accuracy than a mechanical switch. A more robust and reliable device may therefore be provided than approaches which use a mechanical switch or actuator to control the bypass circuit.

In other examples, the second switch 212 is a mechanical switch. The mechanical second switch 212 can be actuated by a mechanical drive, optionally by a second piezoelectric motor 220’. When a second piezoelectric motor 220’ (shown here in dashed lines) is used, it can optionally be controlled by a piezoelectric driver (either driver PZD, or another driver, as appropriate). Rapid opening/ closing of the second switch 212 can be provided by way of the piezo motor 220’, facilitating rapid breaking/making of the circuit through the second current line 202. A quicker auto-test function may therefore be provided than approaches which use other means to control a mechanical switch of the bypass circuit.

Operation of device 700 maybe otherwise as described with reference to Figures 2 to 6.

For example, any of the examples or implementations of these Figures may be combined with the mechanical second switch 212 described with reference to Figure 7. For example, the bypass circuit may comprise one or more isolation contacts 330 and/or may comprise the control module 440 (hardware logic unit), etc. Moreover, the sequences of operations described above with respect to this Figures can incorporate operation of a mechanical second switch in place of the described electronic switch.

With reference to Figure 8, a residual current circuit breaker device 800 (e.g. an RCCB, RCB or RCD) with an auto-test function is described.

The device 800 comprises a residual current circuit (such as that described with reference to Figure 1, e.g. comprising means 108 and mechanical drive 110, though in some examples the first switch maybe an electronic switch rather than a mechanical switch). The residual current circuit is configured to be connected to a first current line 102 (as described above with respect to the current line of Figure 1) between a power source 104 and a load 106. The residual current circuit comprises a first switch, which can be implemented as first switch 112 described above. The first switch is configured to open and close the first current line 102.

In some examples, the first switch is an electronic switch (a solid state switch). An electronic or solid state switch can be more robust than a mechanical or electromechanical switch. Since there is no need to make/break physical contact to control a circuit, and no moving parts, an electronic switch can be more reliable and have a higher degree of repeatability and accuracy than a mechanical switch. A more robust and reliable RCCB may therefore be provided than approaches which use a mechanical switch or actuator. In other examples, the first switch is a mechanical switch. The mechanical first switch can be actuated by a mechanical drive, optionally by a piezoelectric motor 220 (shown in dashed lines). When a second piezoelectric motor 220 is used, it can optionally be controlled by the piezoelectric driver PZD, as discussed above with respect to switch 112 of Figure 2. Rapid opening of the first switch can be provided by way of the piezo motor 220, facilitating rapid breaking of the circuit through the first current line 102 in response to a fault. Similarly, the first switch may be rapidly closed after an auto-testing operation to make the circuit.

The device 800 further comprises means for performing an auto-test of the residual current circuit. Performing an auto-test comprises causing the first switch to open the first current line 102. After the auto-test is complete, the first switch is closed again to close the first current line and electrically connect the source and load via the first current line. In some examples, the means for performing the auto-test can be configured to (automatically) control or initiate opening and/or closing of the first switch. In other words, the means for performing an auto-test can automatically open and/or close the first switch to replicate the testing function provided by manual testing features T, 114 described above with respect to Figure 1. In other examples, the first switch is otherwise caused to be opened and/ or closed (i.e. by way of a different mechanism than the means for performing the auto-test). The means for performing an auto-test can be implemented in any suitable manner, some specific examples of which will be discussed in more detail below. The device 800 further comprises a bypass circuit. The bypass circuit is configured to electrically connect the power source 104 and the load 106 via a second current line 202 (shown as a solid line) during the auto-test. The bypass circuit comprises a second switch 212 (shown within the dotted lines) which is configured to open and close the second current line 202. The second current line is arranged in parallel with respect to the first current line. Here, each pole of the first current line 102 is shown with an associated bypass circuit, but any suitable arrangement can be provided to bypass the first switch 112 with a second current line 202 so that current continues to flow to the load 106 even when the first switch 112 is open during performance of the auto-test. In other words, the first switch and the second switch are arranged in parallel.

In this specific example, the second switch 212 is a mechanical switch and is actuated by a piezoelectric motor 220’. The piezoelectric motor and operation of the second switch 212 can be as described above. In some examples, the piezoelectric motor 220’ can optionally be controlled by a piezoelectric driver (either PZD or another driver, not shown). Rapid opening/ closing of the second switch 212 can be provided by way of the piezo motor 220’, facilitating rapid breaking/making of the circuit through the second current line 202. A quicker auto-test function may therefore be provided than approaches which use other means to control a mechanical switch of the bypass circuit. In this specific example, the means for injecting a residual current comprise a piezoelectric transformer, or PT, 880. A piezoelectric transformer PT is a solid state transformer device. Controller 216 is configured to provide an electrical signal 882 to a primary side of the PT 880. This electrical signal (or input electrical energy) is transformed into electrical energy output by means of a mechanical vibration within the PT. This output electrical energy is provided to an isolation relay device R2, which relay R2 is itself controlled by controller 216 via signal 884. Signal 884 causes the relay contact of relay R2 to close in order to enable performance an auto-test function with the PT 880. The output electrical energy from PT 880 is output through the closed relay R2 and thus injected into the residual current circuit to cause a current imbalance which can be detected by means 108 (such as a CBCT). The resistor 107 described with reference to Figure 1 can be retained in the circuit. Isolation relay R2 is optional, and may not be included in the circuit in some examples. In some other examples, relay R2 maybe replaced with any other form of isolation switch or isolation means. In some examples, relay R2 is implemented as relay Ri described above.

PT 880 is used in place of the relay Ri described previously as the primary means for injecting residual current. However, it will be understood that relay Ri maybe used in some examples of device 800. Use of a piezoelectric transformer 880 in place of a relay Ri can reduce or avoid issues with electromagnetic interference, since there are no copper windings (as there are in the relay Ri). Electromagnetic interference maybe further reduced by removing relay R2 shown in Figure 8, or replacing isolation relay R2 with other isolation means. There is also a high boost ratio at the output side. A PT is also small and lightweight, and can deliver a more uniform output. It is also non-flammable, which can improve safety of the device 800.

Operation of device 800 may be otherwise as described with reference to Figures 2 to 6.

For example, any of the examples or implementations of these Figures may be combined with the mechanical second switch 212 and/ or piezoelectric transformer 880 described with reference to Figure 8. For example, the bypass circuit may comprise one or more isolation contacts 330 and/or may comprise the control module 440 (hardware logic unit), etc. An example sequence for performance of an auto-test operation of device 800 will now be described.

1. Favourable condition for auto-test detected using controller 216, along with real time data and/or measurement means (as discussed above).

2. Controller 216 will close bypass circuit using a piezo driver and piezo motor 220’.

3. Controller will inject residual current into the residual current circuit via piezo transformer 880 (and optionally isolation relay R2); as a result, the first switch will open.

4. After a pre-set interval (first period of time), controller 216 will close the first switch contacts using piezo driver PZD and piezo motor 220 (when first switch is a mechanical switch).

5. After another small pre-set interval (second period of time), controller 216 will open the bypass contacts of the second switch again using the piezo driver and piezo motor 220’. 6. System will regain its normal state of operation with current flowing between the source 104 and load 106 through the first current line.

Any of the above-described features may be provided in any suitable combination within a residual current circuit breaker RCCB or other residual current device (RCD).