CONTROLLING AN ELECTRICAL SUPPLY TO AN APPLIANCE

Abstract

An electrical apparatus comprises an earth input (10a) for connection to an earth wire (10) of an electrical supply from a distribution network, an earth interface for providing an earth connection from the earth input (10a) to an appliance (2) and current sensing means (40) for sensing a current flow through the earth input (10a). The electrical apparatus further comprises earth-wire disconnection means (48) for disconnecting the earth interface from the earth input (10a) when a sensed current flow through the earth input (10a) satisfies an earth-wire disconnection condition and live-wire disconnection means (42) for initiating a disconnection of a live wire (4) of the electrical supply to the appliance (2) before or at the same time as the disconnecting of the earth interface.

Claims

1. An electrical apparatus comprising: an earth input for connection to an earth wire of an electrical supply from a distribution network; an earth interface for providing an earth connection from the earth input to an appliance; a current sensor for sensing a current flow through the earth input; earth-wire disconnection circuitry for disconnecting the earth interface from the earth input when a sensed current flow through the earth input satisfies an earth-wire disconnection condition; and live-wire disconnection circuitry for initiating a disconnection of a live wire of the electrical supply to the appliance before or at the same time as the disconnecting of the earth interface.

2. The electrical apparatus of claim 1, wherein the appliance is an electric vehicle or is electric vehicle supply equipment.

3. The electrical apparatus of claim 2, wherein the current sensor comprises a current transformer positioned around an earth conductor that is electrically connected to the earth input.

4. The electrical apparatus of claim 1, wherein the earth-wire disconnection condition requires the sensed current flow to exceed a predetermined threshold.

5-6. (canceled)

7. The electrical apparatus of claim 1, wherein the appliance is separate from the electrical apparatus, and wherein the earth interface is an earth output for connection to the appliance.

8. (canceled)

9. The electrical apparatus of claim 1, wherein the live-wire disconnection circuitry is configured to initiate the disconnection of the live wire before the disconnecting of the earth interface from the earth input.

10. The electrical apparatus of claim 1, wherein the live-wire disconnection circuitry is further configured to initiate a disconnection of a neutral wire of the electrical supply to the appliance, before or at the same time as the disconnecting of the earth interface.

11. The electrical apparatus of claim 1, comprising reconnection circuitry for reconnecting the earth interface to the earth input, and for initiating reconnection of the live wire to the appliance, wherein the reconnection circuitry is configured to reconnect the earth interface to the earth input before initiating reconnection of the live wire to the appliance.

12. The electrical apparatus of claim 1, comprising an interlock for preventing the live wire from being connected to the appliance while the earth interface is disconnected from the earth input.

13. The electrical apparatus of claim 1, further comprising: a live input for connection to a live wire of the electrical supply from the distribution network; and a live interface for providing a live connection from the live input to the appliance, wherein the live-wire disconnection circuitry is configured to disconnect the live interface from the live input before or at the same time as the disconnecting of the earth interface from the earth input.

14. The electrical apparatus of claim 1, wherein the live-wire disconnection circuitry is configured to transmit an analogue or digital signal to a separate control apparatus, not part of the electrical apparatus, for instructing the separate control apparatus to disconnect the appliance from the live wire of the electrical supply.

15. (canceled)

16. The electrical apparatus of claim 1, wherein the live-wire disconnection circuitry comprises a mechanical actuator for operating a switch, not part of the electrical apparatus, for the live wire of the electrical supply.

17. The electrical apparatus of claim 1, wherein the earth-wire disconnection circuitry comprises an electrically-operated contactor, actuator or relay.

18. The electrical apparatus of claim 1, wherein the earth-wire disconnection circuitry and the live-wire disconnection circuitry comprise control circuitry configured to receive a signal from the current sensor and to determine when the sensed current satisfies the earth-wire disconnection condition.

19. (canceled)

20. The electric apparatus of claim 1, configured for connection to the earth wire of a protective earth and neutral (PEN) conductor of a TN-C-S electrical supply.

21. A method of controlling an electrical supply to an appliance, comprising: sensing a current flow through an earth conductor connected between an earth wire, of an electrical supply from a distribution network, and an appliance; determining that the sensed current flow satisfies an earth-wire disconnection condition and, in response, disconnecting the appliance from the earth wire of the electrical supply; and disconnecting the appliance from a live wire of the electrical supply before or at the same time as disconnecting the appliance from the earth wire.

22. The method of claim 21, wherein the appliance is an electric vehicle or is electric vehicle supply equipment.

23. The method of claim 21, wherein the electrical supply is a TN-C-S electrical supply and the earth wire is a protective earth and neutral (PEN) conductor.

24. The method of claim 21, comprising disconnecting the appliance from the live wire of the electrical supply in response to determining that the sensed current flow satisfies the earth-wire disconnection condition.

25. The method of claim 21, comprising disconnecting the appliance from the live wire before disconnecting the appliance from the earth wire.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Certain preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0065] FIG. 1 is a schematic diagram showing a conventional single-phase TN-C-S supply to a consumer installation.

[0066] FIG. 2 is a schematic diagram showing a conventional TN-C-S supply to a consumer installation in which a “broken PEN” fault is present.

[0067] FIG. 3 is a schematic diagram showing a conventional approach to mitigating a “broken PEN” fault, in which a consumer installation is provided with a separate earth.

[0068] FIGS. 4a, 4b and 4c are schematic diagrams showing three different stages in the operation of apparatus embodying the present invention.

[0069] FIG. 5 is a schematic diagram showing a conventional electric vehicle supply equipment (EVSE).

[0070] FIG. 6 is a schematic diagram showing an embodiment of the present invention in which an electric shock protection device is integrated within electric vehicle supply equipment (EVSE).

[0071] FIG. 7 is a schematic diagram showing a variant embodiment, including an interlock mechanism.

[0072] FIG. 8 is a schematic diagram showing another variant embodiment, in which the control unit is connected to a protected supply source.

[0073] FIG. 9 is a schematic diagram showing an alternative embodiment in which an electric shock protection device is a separate unit which can be attached to an EVSE.

[0074] FIG. 10 is a schematic diagram showing a variant embodiment in which the electric shock protection device includes an override device.

[0075] FIG. 11 is a schematic diagram showing a variant embodiment, in which additional switches are included on the live and neutral wires, controlled by the protection device.

[0076] FIG. 12 is a schematic diagram showing an alternative embodiment in which an electric shock protection device is included within an electrical installation as a separate device upstream of an EVSE to be protected.

DETAILED DESCRIPTION

[0077] Throughout the figures, like reference numerals have been used for like elements.

[0078] FIGS. 4a-4c show an electrical apparatus embodying the present invention, in three states which may occur in use. The apparatus protects a user in the event of a “broken PEN” fault, whilst overcoming the shortcomings of the known approaches to this issue.

[0079] FIG. 4a shows a TN-C-S electrical supply system, as already described with reference to FIG. 1, but now connected to an appliance 2′ which embodies the invention. The appliance 2′ contains a live switch 42, a neutral switch 44 and an earth switch 48. When the appliance 2′ is connected to the supply, a live wire 4 of the supply enters the appliance 2′ at a live input 4a, a neutral wire 6 of the supply enters the appliance 2′ at a neutral input 6a, and a protective earth wire 10 of the supply enters the appliance 2′ at an earth input 10a. These inputs may all be located in a removable socket or plug of the appliance 2′, or the appliance 2′ may be permanently connected such that each input 4a, 6a, 10a is a fixed connection between two conductors, or is a notional point along a continuous conductor (e.g., adjacent an aperture in a casing of the appliance 2′). The live switch 42 is connected to the live wire 4, the neutral switch 44 is connected to the neutral wire 8, and the earth switch 48 is connected to the protective earth wire 10. The earth switch 48 is positioned between the earth input 10a and the earthed chassis 2a′ of the appliance 2′.

[0080] The appliance 2′ also includes a current sensor 40, positioned around an earth conductor 10b within the appliance 2′. The current sensor is thus located along a path between the earth input 10a and the outer casing 2a′ of the appliance 2′, when the earth switch 48 is closed, and can sense current flowing through the earth input 10a from the protective earth wire 10.

[0081] FIG. 4a shows the appliance 2′ connected to the supply, in a situation in which there is no “broken PEN” fault.

[0082] FIG. 4b illustrates a scenario in which there is a damaged section 28 present on the PEN conductor 6 and a user 34 touches the “earthed” casing 2a′ of the appliance 2′. As described with reference to FIG. 2 the PEN fault results in a flow of current IPE 18 through the protective earth wire 10, and therefore a current 32 briefly flows through the user 34 who is connected to true earth 38 and is in contact with the outer casing 2a′ of the appliance 2′. However, in contrast to the conventional appliance 2 of FIG. 2, the present appliance 2′ prevents the user 34 from receiving a dangerous ongoing electric shock due to the fault. In particular, the situation shown in FIG. 4b, in which current 32 is flowing through the user 34, persists only momentarily. Before a dangerous amount of charge can flow through the user 34, the appliance 2′ transitions to the state shown in FIG. 4c.

[0083] FIG. 4c shows a state in which an ongoing electric shock to the user 34 has been prevented. In the broken PEN fault scenario, the current 18, shown in FIG. 4b, briefly flows through the current sensor 40. The current sensor 40 is connected to circuitry (e.g., a microcontroller) that controls the live, neutral and earth switches 42, 44 and 48, such that, when the current exceeds a predetermined threshold, optionally for a predetermined threshold period of time, all of the switches 42, 44, 48 are opened, thereby disconnecting the supply from the appliance and preventing an ongoing shock to the user. Preferably, the live wire 4 and the neutral wire 8 are disconnected before the earth wire 10—e.g. with a predetermined time delay between the disconnections.

[0084] As each of the earth switch 48, the neutral switch 44 and the live switch 42 have been opened, no current flows through any of the wires within the appliance 2′ in FIG. 4c and the user 34 will receive no more than a momentary small shock. These switches 42, 44, 48 provide isolation of the appliance 2′ when open. They may each have a minimum contact gap, e.g. rated for isolation to 4000V or more.

[0085] The current sensor 40 may comprise a current transformer that has linear sensitivity and a fast response to small currents (in the range 0 mA to 50 mA). It may comprise a commercially-available device marketed as a “zero current” transformer or a “zero-phase current” transformer. The current sensor 40 may provide a quantitative or qualitative measure of current (analogue or digital) to control circuitry, for determining when the current exceeds the predetermined threshold.

[0086] If the appliance 2′ is located in the UK, the mains supply is nominally at 230V, or possibly up to 400V due to the grid being three phase; therefore, due to the PEN fault shown in FIG. 4c, point Y of the neutral wire 8 could be at a nominal voltage of approximately 230V. Due to the link 12, point X of the earth wire 10 will therefore also be raised to approximately 230V. In the case where the appliance 2′ comprises an outdoor appliance, for example an electric vehicle, the person 34 shown in FIG. 4c is standing outside on moist ground and is therefore at approximately true earth i.e. 0V. If the earth switch 48 were not present or were not open, then any conductive exterior 2a′ of the appliance 2′, which may be metal, would be raised to the same 230V as point X, and therefore if the person 34, who is earthed, touched the appliance, they would receive a very large electric shock. However, since the earth switch 48 is opened momentarily (e.g., within a few milliseconds) after any such touch is made, the point Z on the chassis 2a′ will be rapidly isolated from the mains supply 3, therefore preventing a person who touches the appliance from receiving an ongoing shock. The earth switch 48 may be specified to open within 40 ms or quicker.

[0087] The advantageous effect of preventing harmful ongoing electric shocks to the user in this instance could be achieved by opening only the earth switch 48. It is important that not only the earth wire 10, but also the live wire 4 and the neutral wire 8 are disconnected in the event of the current in the earth wire 10 exceeding a threshold, in order for the earth wire 10 to perform the normal function of an earth. Consider, for example, if a fault in the live wire 4 were to result in the live wire connecting directly to the casing 2a′ of the appliance 2′ in normal usage (without any broken PEN fault being present); then a standard earth would conduct this excess voltage away such that the appliance 2′ remained grounded and therefore safe to touch. However, at least in some embodiments of the present invention, the current sensor 40 and associated control circuitry (together providing a current condition sensing module) may not distinguish between positive and negative currents, so a sufficiently high current in the earth wire, even in a direction towards the PEN conductor 6, would result in the earth switch 48 opening, so that the earth wire 10 was no longer conducting.

[0088] In this instance, if only the earth wire 10 were disconnected then the faulty live wire 4 would raise the voltage of the outer casing 2a′ of the appliance 2′, and thereby put a person 34 at risk if they were to touch the appliance 2′. It is therefore advantageous that the appliance 2′ be configured also to disconnect the live wire 4, and optionally to disconnect the neutral wire 8, so that the earth wire 10 also performs the standard function of an earth and keeps the appliance 2′ safe in the event of a live wire fault.

[0089] Preferably, the device is configured so that the live switch 42 is opened before the earth switch 48. Optionally the neutral switch 44 is also opened before the earth switch 48. If the earth wire 10 were disconnected first, with the live wire 4 still connected, then there could be a voltage on the chassis 2a′, if there were a wiring fault, since the live wire 4 would still be connected to the appliance 2′. Similarly, when restoring the supply, the earth switch 48 is closed before the live switch 42 and neutral switch 44 are closed. This isolation and restoration sequence may be implemented with timing delays, generated by hardware circuitry, or by the means of one or more integrated programmable components or by any other suitable engineering technique. Additionally, an interlock may be provided to ensure that the sequence is followed, as described in more detail below.

[0090] In a preferred set of embodiments, the appliance 2′ of FIGS. 4a-4c may not be a single appliance, such as an electric car, but may instead comprise one or more components, such as an electric vehicle supply equipment (EVSE) and/or a standalone protection device for the EVSE, either of which may implement principles of the invention, and/or an electric vehicle. Various possible embodiments are described in more detail below. However, it will be appreciated these are not exhaustive.

[0091] FIG. 5 shows a standard electric vehicle supply equipment (EVSE) 53 for charging an electric vehicle, such as a family car. A mains electricity supply 3 is connected to an electric vehicle 51, through the EVSE 53, by a live wire 4, a neutral wire 8, and a protective earth wire 10.

[0092] A control unit 50 controls a double-pole contactor 52 (an electrically-controlled switch) which can connect and disconnect the live wire 4 and the neutral wire 8 simultaneously.

[0093] When it is desired to supply current to charge the connected electric vehicle, the control unit 50 signals the contactor 52 to close, and thus the electric vehicle battery recharge session starts. The signalling may be digital or analogue. In such a device, known in the art, there is no protection against a “broken PEN” fault, so expensive countermeasures are required, such as installing a local earth or providing a large isolation transformer.

[0094] FIG. 6 shows an EVSE device 60 embodying the present invention. In addition to the components as described with reference to FIG. 5, and shown in FIG. 6 with corresponding reference numerals, the EVSE device 60 contains a current sensor 40, and a single-pole earth contactor 54. In the embodiment of FIG. 6 these components are all included within an outer housing of the EVSE device 60.

[0095] The control unit 50′ of the EVSE device 60 may be voltage-dependent, receiving a supply from the mains supply 3, or it could be voltage-independent (e.g., being battery powered). It may be entirely analogue or may include digital logic such as one or more microcontrollers or ASICs. The control unit 50′ and earth contactor 54 together constitute earth-wire disconnection means as disclosed above.

[0096] In the event that the current in the earth wire 10 exceeds a preset threshold, optionally for more than a preset threshold period of time, this is detected by the control unit 50′ based on current measurements obtained from the current sensor 40. The control unit 50′ signals the double-pole live and neutral contactor 52′ to open, so that the appliance is no longer supplied with power. The control unit 50′ and live and neutral contactor 52′ together constitute live-wire disconnection means as disclosed above. The control unit 50′ also signals the earth contactor 54 to open, preferably a short delay after the live and neutral contactor 52′ has opened.

[0097] FIG. 7 shows a variation of the embodiment of FIG. 6. Many elements of the device are the same as in FIG. 6, and are therefore labelled with the same reference numerals, however the EVSE device 60 of FIG. 7 differs from the EVSE device 60 of FIG. 6 in that it further includes an interlock mechanism 70. The interlock mechanism 70 uses a double-pole earth contactor 54, one pole of which switches the earth wire 10, with the other pole being wired in series with the control line of the live and neutral contactor 52. In this way, the live and neutral contactor 52 can be closed only if the earth contactor 54 is already closed. This means that the live and neutral wires 4, 8 can be connected to the vehicle 51 only when the earth wire 10 is already connected to the vehicle 51. This provides failsafe protection in case of a mechanical or electrical fault in the normal connection sequencing implemented by the controller 50′.

[0098] FIG. 8 shows a further variant embodiment in which the control unit 50′ has a connection 80 to the live wire 4 and a connection 82 to the neutral wire 8. This provides power to the circuitry (e.g., processors etc.) in the control unit 50′ and for operating the contactors 52′, 54. Furthermore, the control unit 50′ is connected to the earth wire 10 by a connection 84, downstream of the earth contactor 54 and the current sensor 40. This earth connection 84 can be used to earth the device 60, but also provides a reference to the control unit 50′ for monitoring the supply to the vehicle 51. In this way, the power supply to the control unit 50′ will never have an earth that is held at the live potential in the case of a broken PEN fault. To increase the safety of the device 60 when the earth contactor 54 is open, the connections 80, 82 preferably provide galvanic isolation of the control unit 50′ from the supply 3—e.g., using a transformer, such as a transformer within an AC-to-DC power supply. Such isolation may be used in any of the embodiments disclosed herein that power the control unit from the main supply (rather than from a separate battery, for example).

[0099] FIG. 9 shows an alternative embodiment in which a protection device 96 embodying the invention is not integrated within an EVSE device (i.e. in the same housing), but is attached to an electrical supply system to which a separate EVSE 94 is also installed. Such an arrangement is suitable for retrofitting to a pre-existing EVSE 94. The EVSE 94 includes a charging control unit 90, which in turn controls a live and neutral contactor 52′, which controls the live and neutral supply to the vehicle 51.

[0100] The separate protection device 96 includes a protection control unit 92. As previously described, when the current in the earth wire 10 exceeds a threshold value, the protection control unit 92 causes an earth contactor 54 to disconnect the earth wire 10 from the vehicle 51. In this embodiment when the current in the earth wire 10 exceeds the threshold value the protection control unit 92 additionally transmits a signal 98 to the charging control unit 90, which causes the charging control unit 90 to open the live and neutral contactor 52′ so that the live and the neutral wire are no longer connected to the vehicle 51. The signal 98 may be sent over a digital interface (e.g., USB) or over an analogue interface. In this way, the protection control unit 92 can also control the timing and order of the opening (and the closing) of the contactors 52′, 54 as previously described.

[0101] In FIG. 9, the protection device 96 is positioned between the EVSE 94 and the vehicle 51. However, it could alternatively be positioned between the EVSE 94 and the supply 3.

[0102] FIG. 10 shows a variation of the embodiment shown in FIG. 9. In this embodiment, in addition to the elements already described with reference to FIG. 9, the protection control unit 92 provides a physical override device 100, instead of the electrical signalling between the protection device 96 and the EVSE 94. The override device 100 is physically installed within the EVSE 94 (e.g., during a retrofitting) but is controlled from the protection device 96. It is connected to the live and neutral contactor 52′ in the EVSE 94 using auxiliary contactors, or mechanically linked contactors, for example a shunt trip. In the event of the current in the earth wire 10 exceeding a threshold, the protection control unit 92 transmits a signal to the override device 100, which can override the EVSE's control of the live and neutral contactor 52′ to force the contactor 52′ open. Override device 100 is configured to be able to override the charging control unit 90, which normally controls the charging switches, so that the switches of the live and neutral wires 4, 8 can be disconnected in case of a broken PEN fault, and cannot be reconnected until the override device 100 allows it.

[0103] As before, the protection control unit 92 may ensure that the live and neutral contactor 52′ is opened before the earth contactor 54 is opened, and is closed only after the earth contactor 54 is closed.

[0104] FIG. 11 shows an alternative to the arrangement described with reference to FIG. 10. In this embodiment a separate external unit 110, which may be a DIN Rail component assembly, is installed between the supply 3 and the EVSE 94. The external unit 110 contains a double-pole miniature circuit breaker (MCB), connected to live and neutral, and a shunt trip 112 for tripping the MCB. The shunt trip 112 is controlled by leads extending from the protection control unit 92 of the protection device 96. In this way, when the current sensor 40 senses a current in the earth wire 10 which exceeds a threshold level for a threshold time, the protection control unit 92 transmits a signal to the shunt trip 112 in the external unit 110, which isolates the live and neutral supplies. Such an embodiment may be attractive where it is undesirable or impossible to interface with an existing EVSE 94 as shown in FIG. 9, or to install an override device 100 as shown in FIG. 10, since it requires no additional connections to the EVSE 94.

[0105] FIG. 12 shows a standalone protection device 120 embodying the invention. This is electrically connected upstream of a conventional EVSE device 94 which is desired to be protected. This standalone protection device 120 provides a shunt trip 121 which can be used to control an existing miniature circuit breaker (MCB) or residual current device (RCD) to disconnect the live wire 4 and neutral wire 8 when the current sensor 40 detects current above a threshold level on the earth wire 10. Alternatively, rather than controlling an existing MCB or RCD, an external live and neutral contactor may be fitted alongside the standalone protection device 120.

[0106] With any of these embodiments, it will be appreciated that the same principles can be used to protect any appliance or apparatus, not just an electric vehicle supply equipment (EVSE) charge point, or could even be used to protect a whole property or other wiring installation. For example, the electric vehicle 51 could be substituted for any appliance or apparatus in the embodiments described above.

[0107] In some embodiments the disconnection conditions may be more complex than a simple threshold level—e.g., depending additionally or alternatively on a rate of change of current, or one or more other factors.

[0108] It will be appreciated by those skilled in the art that the invention has been illustrated by describing one or more specific embodiments thereof, but is not limited to these embodiments; many variations and modifications are possible, within the scope of the accompanying claims.