Patent Description:
Transfer of electrical power may include supplying electrical power from an electrical grid to an electrical system, supplying electrical power from the electrical system to the electrical grid to an electrical system, or both. For example, electrical systems may include various types of electrical loads taking power from the grid, electrical generators such as solar inverters supplying power to the grid, and bi-directional chargers used for charging/discharging batteries. Protection devices are typically used to allow a separation between the electrical system and the electrical grid. For example, a residual-current circuit breaker (RCCB) is a device that monitors the flow of electrical current in a circuit, and automatically disconnects the power if it detects an imbalance. This imbalance can indicate a potentially dangerous situation, such as an electrical shock hazard or a ground fault. Typical safety and grid standards may require multiple protection mechanism so that the failure of one mechanism does lead to dangerous situations or bring down parts of the electrical grid. So, to connect a local electrical system to the grid it may be required to use protection devices having multiple contactors or relays with appropriate monitoring and control devices. Unfortunately, the resulting system may be overly complex and bulky, since effectively multiple protection devices are applied, which need to be integrated in the local electrical system. Some grid standards may allow separation of local and remote protection devices, in which case it may be required that a signal is sent from the local protection device to the remote protection device to enforce a power disconnect e.g. using a central switch. However, since the distance between the local electrical system and the central switch can be large, signaling is not trivial.

Known protection devices are described in <CIT>, <CIT>, <CIT> and <CIT>.

There is a need to reduce the complexity and size of protection devices for local electrical systems while maintaining or improving standards for safety and grid integrity.

The scope of this patent is defined by the independent claims. Aspects of the present disclosure relate to methods and systems for transferring, via a local interface, electrical power between a central interface and a local electrical system. Typically, the transferring of electrical power comprises sending electrical current back and forth via local power lines between the local interface and the central interface. The central interface is electrically connected to transfer the electrical power to and/or from an electrical grid via a central interface switch. For example, the local interface comprises a local charging station, e.g. to charge (or discharge) a battery, and the central interface comprises a central distribution point for distributing power from (or to) a main electrical grid. The central interface switch typically comprises a residual-current circuit breaker for severing the electrical connection to the electrical grid when an imbalance occurs in the electrical current being sent back and forth via the local power lines. This may help to protect integrity of the grid and/or safety of local systems.

As described herein a controller of the local interface, e.g. forming part of a charging station, monitors a status of the local electrical system, e.g. comprising a battery being charged/discharged by the system. Responsive to detecting a fault condition in the monitored status of the local electrical system, the controller can activate a leakage circuit of the local interface to generate a current imbalance on the local power lines. This may cause the central interface to sever the local electrical system from the electrical grid by triggering of the residual-current circuit breaker of the central switch. Advantageously, a leakage current can be easily and controllably generated in the case of a fault condition on the existing local power lines to activate the central switch, which may be situated remotely, without requiring further signal lines. Using the leakage current as a signal can take advantage of existing circuit breakers which are typically placed at central interfaces to protect the electrical grid. Also, the leakage current signal can reach relatively large distances without having to fear signal degradation. The remotely activated switch can act as alternative or additional means of protection, e.g. in addition to a local switch. So, the number of required switches, e.g. expensive relays, in the local interface can be reduced while maintaining the same protection using a simple leakage current circuit.

In some embodiments, the monitoring of the status of the local electrical system comprises monitoring the local power lines. In one embodiment, the monitoring comprises performing a measurement of a voltage, current, power, frequency, phase, and/or noise transferred via the local power lines to and/or from the local electrical system. In another or further embodiment, the detecting the fault condition comprises determining that the measurement deviates from a threshold tolerance value. Advantageously, the status of the local electrical system can thus be monitored using the power lines running though the local interface to the local electrical system, without requiring separate signals to be sent to and/or from the local electrical system. In other or further embodiments, the monitoring of the status of the local electrical system comprises receiving a status signal from the local electrical system. In one embodiment, the detecting the fault condition is based on the status signal indicating a fault condition in the local electrical system (or an absence of the status signal indicating a fault condition in the local electrical system).

In accordance with the claimed invention, the local interface comprises a local interface switch configured to selectively disconnect the local electrical system from the local power lines. Responsive to detecting the fault condition in the monitored status of the local electrical system, as a primary means of protection, the controller initially sends a control signal to the local interface switch causing the local interface to sever the local electrical system from the electrical grid. As a secondary means of protection, the controller, subsequently and only responsive to determining that the local interface switch is not operable to disconnect the electrical power, activates the leakage circuit to generate the current imbalance on the local power lines causing the central interface to sever the local electrical system from the electrical grid. In other or further embodiments, the local interface is operable for reconnecting the local electrical system based on the monitored status indication that the fault condition has been removed and/or a control signal indicating that the transferring of electrical power is to be resumed. For example, the local interface may comprise a user interface for manually resuming transfer of electrical power after a fault condition has been alleviated.

In some embodiments, the local interface comprises a bi-directional charging station. In other or further embodiments, electrical power is transferred over the local power lines by alternating current, AC. In one embodiment, the leakage circuit of the local interface is configured to generate an AC residual current on the local power lines. Preferably, the local interface comprises a (backup) power source, such as a battery, configured to supply electrical power for operating components of the local interface, such as the controller and leakage circuit. In this way operation of the local interface can be ensured independent of any fault conditions occurring in the electrical power transferred via the local power lines. Alternatively, or in addition, the local interface and/or battery may receive power from the power lines, e.g. via a power converter. Preferably, the power converter has relatively high tolerance for various fault conditions which may occur on the local power lines.

In some embodiments, the controller is configured, upon initiating of the local interface, to test whether the central interface switch is operable to disconnect the electrical power by activating the leakage circuit. In other or further embodiments, the controller is configured to allow the transferring of electrical power via the local interface only after determining the central interface switch is operable to disconnect the electrical power by the activating of the leakage circuit.

Some aspects of the present disclosure can be embodied as a local interface configured to transfer electrical power between an electrical grid and a local electrical system, e.g. in accordance with the methods and systems described herein. In some embodiments, the local interface comprises electrical connections, e.g. respective terminals, configured to connect to the local electrical system and connect to local power lines for the transferring of electrical power via the local interface between the local electrical system and a central interface to the electrical grid. Typically, the transferring of electrical power comprises sending electrical current back and forth via the local power lines between the local interface and the central interface. In other or further embodiments, the local interface comprises a leakage circuit which, when activated, is configured to generate a current imbalance on the local power lines for triggering a residual-current circuit breaker at the central interface. In other or further embodiments, the local interface comprises a controller configured to monitor a status of the local electrical system, and responsive to detecting a fault condition in the monitored status of the local electrical system, activating the leakage circuit for severing the local electrical system from the electrical grid. For example, the leakage circuit may be configured to generate a residual current larger than <NUM> mA DC and/or <NUM> mA AC.

In some embodiments, the local interface comprises a protective earth terminal for providing a ground connection. In one embodiment, the leakage circuit comprises a switchable electrical connection between at least one of the local power lines and the protective earth terminal. In another or further embodiment, the switchable electrical connection is switchable between a first position, in which an electrical connection between the at least one of the local power lines and the protective earth terminal is interrupted, and a second position, in which the electrical connection is closed. For example, the controller is configured arranged for controlling the switchable connection between the first and second position based on detecting the fault condition.

In some embodiments, the leakage circuit and/or the switchable connection comprises one or more active switching elements. In one embodiment, the active switching elements comprises a unipolar current switching circuit for generating a DC residual current. In another or further embodiment, the active switching elements comprises a bipolar current switching circuit for generating an AC residual current. In another or further embodiment, the active switching elements comprises a solid state relay switching circuit for generating both AC and DC residual currents. In another or further embodiment, the active switching elements comprises a relay switching circuit for generating both AC and DC residual current in case of high electrical insulation and infrequent activation of the leakage circuit. Also combinations of different types of active switching elements can be used.

Some aspects of the present disclosure can be embodied as a system comprising the local interface connected to the central interface via the local power lines. In some embodiments, the central interface is electrically connected to transfer the electrical power to and/or from the electrical grid via a central interface switch. In other or further embodiments, the central interface switch comprises the residual-current circuit breaker for severing the electrical connection to the electrical grid when an imbalance occurs in the electrical current being sent back and forth via the local power lines.

<FIG> illustrates a method and corresponding local interface <NUM> for triggering a central interface switch <NUM>, e.g. suitable for network and system protection using a standard grid compliant installation. The method and local interface <NUM> described herein can e.g. be applied in AC or DC charging products, intended for private and public use. Also, the method and local interface <NUM> can be applied in AC or DC power generators, such as solar inverters, battery walls, and wind turbines. Preferably, the local interface <NUM> is integrated in, or otherwise forms part of, a local power station <NUM> configured to received and/or supply power to the local electrical system <NUM>, e.g. charging station configured to charge and/or discharge a battery.

In some embodiments, the local electrical system <NUM> is arranged for receiving electrical power E from the central interface <NUM>, for generating and supplying electrical power E to the central interface <NUM>, or for both receiving and generating electrical power E. In other or further embodiments, the local electrical system <NUM> comprises a power load, such as an electrical charging device <NUM> or other power consuming device, arranged for receiving electrical power E from the central interface <NUM>, e.g. for charging a plug-in hybrid or full electric vehicle <NUM>. In other or further embodiments, the local electrical system <NUM> comprises a power source <NUM> or generator, such as a photovoltaic system, arranged for generating and supplying electrical power E to the central interface <NUM>. In other or further embodiments, the local electrical system <NUM> comprises a chargeable battery unit <NUM>, and the local interface <NUM> is be arranged for both charging the chargeable battery unit using electrical power from the central interface <NUM>, as well as discharging the chargeable battery unit to the central interface <NUM>, e.g. to provide auxiliary electrical power to the central interface <NUM>.

The central interface <NUM> may e.g. be part of a central power distribution, and/or be accessible from any residential, industrial, or commercial structure or facility, such as a home or office building, factory or distribution site, charging station, parking area, or electrical power junction. In one example, the central interface <NUM> may be accessible from a building on a real estate parcel, and the local electrical system <NUM> may be an electric charging device provided on the real estate parcel nearby the building and arranged for charging an electric vehicle, e.g. at a distance up to fifty meter from the building, or more.

In accordance with the invention as claimed, electrical power E is transferred, via the local interface <NUM>, between a central interface <NUM> and a local electrical system <NUM>. The central interface <NUM> is connected to a main grid <NUM>. The electrical power E is transferred between the central interface <NUM> and the main grid <NUM> via a central interface switch <NUM> comprising a residual-current circuit breaker. The residual-current circuit breaker can e.g. be with or without over-current protection (RCD or RCBO).

The central interface <NUM> and the local electrical system <NUM> are spatially separate, e.g. by electrically conductive cabling spanning a distance larger than <NUM> meter, larger than <NUM> meter, or larger than <NUM> meter. As such, the central interface switch <NUM>, e.g. residual-current circuit breaker, is spatially separated from the local electrical system <NUM> as well.

As illustrated in <FIG>, controller <NUM> of the local interface <NUM> monitors a status "S" of the local electrical system <NUM>. The monitored status "S" can for example comprise health parameters indicative of normal operating conditions or fault conditions of the local electrical system, and/or any devices thereof, such as an electric vehicle, a charging device, a battery unit, or a local power generator. The status "S" can e.g. be monitored by the controller <NUM> being in communication with the local electrical system <NUM> and/or individual devices thereof, for example by a wired or wireless data connection. The controller <NUM> can for example be provided by a processor or microcontroller, e.g. implemented on an integrated circuit chip. The controller <NUM> may comprise any type of software and/or hardware control circuit.

Responsive to detecting a fault condition based on the monitored status "S" of the local electrical system <NUM>, the controller <NUM> activates a leakage circuit <NUM> of the local interface <NUM> to generate a residual current on the central interface <NUM>. This causes a triggering of the residual-current circuit breaker of the central interface switch <NUM> for disconnecting the electrical power E. For example, the leakage circuit <NUM> may be activated in case the local interface switch <NUM>, e.g. an internal switch of the local interface <NUM>, fails to respond and/or fails to cut the connection.

According to some regulatory bodies, introduction of a leakage current may not be allowed during normal operating conditions. For this reason, the method and local interface <NUM> described herein introduce a leakage current after detection of a fault condition. Hence the local electrical system <NUM> is no longer in a state of normal operating condition.

In some embodiments, for detecting the fault condition, the method may comprise measuring a value in voltage, current, power, frequency, phase, or noise on power lines <NUM>, <NUM> arranged for transferring the electrical power E between the central interface <NUM> and the local electrical system <NUM>. The power lines <NUM>, <NUM> can e.g. be provided by electrically conductive wiring or cabling, extending between the central interface <NUM> and the local electrical system <NUM> via the local interface <NUM> and arranged for transferring the electrical power E therebetween. The step of measuring a value can e.g. be performed by the controller <NUM>, e.g. by having one or more signal lines connecting the power lines <NUM>, <NUM> with the controller <NUM>. It is noted that, while the present figures show only two power lines (<NUM>,<NUM>), in general these could be any number of power lines, e.g. three or more power lines in case of using <NUM>-phase power. For example, the leakage circuit <NUM> may create a leakage current on any one or more of the power lines, e.g. between a respective power line and ground.

Alternatively, the step of measuring can be performed by an external measurement device arranged for measuring the value on the power lines <NUM>, <NUM> and coupled to the controller <NUM> for transmitting the measured value. Such measurement devices may include a voltage meter, an ampere meter, a power meter, an oscilloscope, a noise meter, or an electro-magnetic interference EMI meter.

The measured value may be compared with a predetermined tolerance value to calculate a deviation from the predetermined tolerance value. The predetermined tolerance value can e.g. be derived from a regional applicable technical standard, such as EN <NUM> or IEC <NUM>-<NUM>, or can be defined as a comparative parameter based on properties of the local electrical system <NUM>, such as nominal voltage, nominal current, nominal continuous power, peak power, terminal resistance, inductance, time constant, thermal resistance, and ambient temperature, as well as on properties of the central interface <NUM>, such as applied voltage, current and power. The comparison can e.g. be performed by the controller <NUM>, or by an external processing unit.

Subsequently, e.g. responsive to the calculated deviation exceeding a threshold, it may be established that a fault condition occurs. For example, after calculating a deviation from the predetermined tolerance value, the controller <NUM> or any other processing unit may compare the calculated deviation to the threshold. Upon determining that the calculated deviation exceeds the threshold, the controller <NUM> may establish that there is a fault condition in the local electrical system. The threshold may be a constant value, or may be adjusted in time e.g. to compensate for wear or thermal effects. The threshold can e.g. be a safety factor ranging between -<NUM>% and <NUM>% of the predetermined tolerance value, preferably ranging between -<NUM>% and <NUM>% of the predetermined tolerance value, more preferably ranging between -<NUM>% and <NUM>% of the predetermined tolerance value. Accordingly, the threshold can provide an additional safety margin for establishing the fault condition, to prevent inadvertently generating a false positive signal that would activate the leakage circuit <NUM> of the local interface <NUM>, e.g. due to a noisy measurement signal.

In some exemplary embodiments, a leakage current of the local electrical system <NUM> may be measured, and responsive to the measured leakage current exceeding a threshold, it can be established that a fault condition occurs. Measurement of the leakage current of the local electrical system can be performed by any residual current detection device, e.g. coupled to the controller <NUM>. Alternatively, or additionally, the method may comprise detecting any other issue with the local electrical system to establish that a fault condition occurs, e.g. by a measurement device or controller <NUM> of the local interface <NUM>. For example, detecting that a cable is improperly connected, that electronic components or connectors are wet, or in case the local electrical system is arranged for charging a battery unit, detecting e.g. that the battery unit is malfunctioning or defect.

In accordance with the claimed invention, the local interface <NUM> comprises a local interface switch <NUM>, or contactor, and the method further comprises, prior to the step of activating the leakage circuit of the local interface <NUM>, determining, by the controller <NUM>, whether the local interface switch <NUM> is activatable for disconnecting the electrical power. Responsive to determining that the local interface switch <NUM> is activatable, the method comprises generating a control signal, e.g. by the controller <NUM>, for activating the local interface switch <NUM>. For example, the local interface switch <NUM> may be activatable when a recoverable failure occurs in the local electrical system <NUM>, such as a failure caused by a software error.

The method further comprises the step of otherwise, thus responsive to determining that the local interface switch <NUM> is not activatable, activating the leakage circuit <NUM> to generate a residual current on the central interface <NUM> causing a triggering of the residual-current circuit breaker of the central interface switch <NUM> for disconnecting the electrical power. For example, the local interface switch <NUM>, or contactor, may not be activatable when an unrecoverable failure occurs in the local electrical system <NUM>, such as a failure caused by contact welding. In this way, a distinction can be made between recoverable and unrecoverable failures, wherein the leakage circuit <NUM> is activated only in response to detecting an unrecoverable failure, for disconnecting the electrical power E via the residual-current circuit breaker. Recoverable failures, in contrast, can be resolved by the controller <NUM> activating the local interface switch <NUM>.

The step of determining whether the local interface switch <NUM> is activatable can for example be performed by measuring a voltage on auxiliary contacts <NUM> of the local interface switch <NUM>. For example, the local interface switch <NUM> may comprise one or more auxiliary contacts <NUM>, or diagnostic terminals, electrically connected to the main conductive path of the local interface switch <NUM>, and arranged for diagnosing an applied voltage, current, or power on the local interface switch <NUM>. The controller <NUM>, or an external measurement device coupled to the controller <NUM>, can e.g. be connected to the auxiliary contacts <NUM> to measure the voltage, to determine whether the local interface switch <NUM> is activatable. For example, in case a measured voltage on the auxiliary contacts <NUM> is higher than a predetermined threshold, the controller <NUM> may establish that the local interface switch <NUM> is activatable. Conversely, in case a measured voltage on the auxiliary contacts <NUM> is lower than a predetermined threshold, the controller <NUM> may establish that the local interface switch <NUM> is not activatable. Accordingly, the activatability of the local interface switch <NUM> can be diagnosed by the local interface <NUM>.

After the step of generating a control signal for activating the local interface switch <NUM>, the local interface <NUM> may be manually operable for reconnecting the electrical power E. For example, the local interface <NUM> may comprise a button or lever, that is manually operable for reconnecting the electrical power. In this way, operation of the local electrical system can be resumed by a deliberate user action, e.g. as opposed to an automatic signal generated by the controller <NUM>, to prevent that the local electrical system is inadvertently activated before removing the root cause of the failure.

As illustrated, the central interface <NUM> is typically distanced, or spatially separated, from the local electrical system <NUM>, e.g. by at least one meter of wiring or other power lines, more typically at least five meter, or even more than ten meter. In some embodiments, the wiring can have a length of more than one hundred meters, e.g. up to a kilometer, or more, depending on the physical distance between the central interface, which may be accessible from a building on a real estate parcel, and the local electrical system, e.g. a local power generator such as a PV system or an EV charging device, which may be located e.g. anywhere on a real estate parcel. In relatively sparsely populated rural areas, for example, a real estate parcel can cover multiple square km, with limited access to the central interface. In other examples, e.g. in relatively densely populated urban areas, the distance between the central interface <NUM> and the local electrical system <NUM> is limited, for example in a range up to <NUM> meter, up to <NUM> meter, or less.

The local interface <NUM> may comprise a bi-directional charging station, e.g. arranged for charging and/or discharging a battery such as a vehicle battery or home battery. The bi-directional charging system can also be coupled to other types of electrical power E sources in a one-directional fashion, e.g. to a photo voltaic PV system arranged for generating and supplying electrical power E, to charge one or more devices or power storage units. In both directions, the controller <NUM> may be able to activate the leakage circuit <NUM> of the local interface <NUM> responsive to detecting a fault condition based on the monitored status "S" of the local electrical system <NUM>, to generate a residual current on the central interface <NUM> causing a triggering of the residual-current circuit breaker of the central interface switch <NUM> for disconnecting the electrical power E.

As an example, the local interface <NUM> can comprise an AC/AC charger, wherein, during transferring via the local interface <NUM>, AC electrical power E is transferred between the central interface <NUM> and the local electrical system <NUM>, and activating a leakage circuit <NUM> of the local interface <NUM> generates an AC residual current on the central interface <NUM> causing a triggering of the residual-current circuit breaker of the central interface switch <NUM> for disconnecting the electrical power E.

Alternatively, AC electrical power E may be transferred between the central interface <NUM> and the local electrical system <NUM>, and the step of activating a leakage circuit <NUM> may comprise generating a DC residual current on the central interface <NUM>, causing a triggering of the residual-current circuit breaker for disconnecting the electrical power E. In another variant, DC electrical power E may be transferred between the central interface <NUM> and the local electrical system <NUM>, and the step of activating a leakage circuit <NUM> may comprise generating a DC residual current on the central interface <NUM>, to trigger the residual-current circuit breaker and disconnect the electrical power. In this way, the step of responding to a fault condition is independent of the type of electrical power E transferred between the central interface and system <NUM>, <NUM>, as well as the type of residual-current circuit breaker.

As illustrated, the local interface <NUM> may further comprise an auxiliary electrical power supply <NUM> arranged for supplying auxiliary electrical power E to the controller <NUM>, independent of the electrical power E transferred between the central interface <NUM> and the local electrical system <NUM>. The auxiliary electrical power supply <NUM> can for example comprise a battery unit, a capacitor, or a local power generator, such as a photovoltaic system. For example, the controller <NUM> may be arranged for primarily receiving electrical power E from the local electric grid <NUM> and/or the local electric system <NUM>, e.g. via wiring extending therebetween. The controller <NUM> may be arranged for receiving auxiliary electrical power E from the auxiliary power supply, e.g. via separate cabling or power lines.

Upon startup of the local interface <NUM>, the controller <NUM> may be arranged for testing whether the central interface switch <NUM> is operable for disconnecting the electrical power E, and responsive to determining that the central interface switch <NUM> is operable, allowing the transferring. The residual-current circuit breaker <NUM> of the central interface switch <NUM> may e.g. be a testable and resettable device - e.g. comprising a test button that safely creates a small leakage condition, and another button that resets the conductors after a fault condition has been cleared. Such a testable and resettable device can be tested by the controller <NUM>, e.g. upon startup or upon connecting the local electrical system to a device, such as an electric vehicle e.g. for charging the vehicle. In this way, it can be prevented that a detected fault condition cannot be addressed by a triggering of the residual-current circuit breaker of the central interface switch <NUM>.

<FIG> illustrates other or further embodiments of the local interface <NUM> configured to perform the method described herein. The local interface <NUM> comprises first electrical terminals <NUM>, arranged for electrically connecting with a central interface. Second electrical terminals <NUM> are arranged for electrically connecting with a local electrical system. In principle, the terminals may comprises any form of electrical connection. For example, the terminals may comprise screw or clamp connections, solder wire, press contact, or any other type of connector. The terminals may be internal or exterior of the local interface <NUM>. The local interface <NUM> is arranged for transferring electrical power (E) between the central interface and the local electrical system, and the central interface is connected to a main grid, for transferring the electrical power (E) therebetween, via a central interface switch comprising a residual-current circuit breaker.

A leakage circuit is arranged for generating a residual current on the central interface, and a controller <NUM> is configured to monitor a status "S" of the local electrical system <NUM>. Responsive to detecting a fault condition based on the monitored status "S" of the local electrical system, the controller <NUM> is configured to activate the leakage circuit <NUM>, causing a triggering of the residual-current circuit breaker of the central interface switch for disconnecting the electrical power.

The generated residual current can e.g. be larger than <NUM> mA DC and/or <NUM> mA AC. Alternatively, the generated residual current may be larger than an allowable residual current value defined in an applicable standard, e.g. for a specific technical field and/or geographical region, such as IEC <NUM>-<NUM> related to EV supply equipment for charging electric road vehicles. In this way, triggering of the residual-current circuit breaker can be performed independent of the type of fault condition detecting at the local electrical system. Some fault conditions, for example, may generate limited to no leakage currents at all, while they may still be indicative of an electrical shock hazard. By generating a residual current larger than <NUM> mA DC and/or <NUM> mA AC, the residual-current circuit breaker is triggered, thereby disconnecting the electrical power (E) regardless of the magnitude of the leakage current detected at the local electrical system.

Preferably, e.g. as illustrated in <FIG>, the first and second terminals <NUM>, <NUM> provide live, and optional neutral, connections for transferring the electrical power (E), and the local interface <NUM> comprises a protective earth terminal <NUM> for providing a ground connection. The leakage circuit <NUM> may comprise a switchable connection between the first and second terminals <NUM>, <NUM> and the protective earth terminal <NUM>, and the switchable connection may e.g. be switchable between a first position, in which an electrical connection between the first and second terminals <NUM>, <NUM> and the protective earth terminal <NUM> is interrupted, or disconnected, and a second position, in which the electrical connection is closed, or connected. Controller <NUM> can e.g. be arranged for controlling the switchable connection between the first and second position.

In this way, the leakage circuit <NUM> provides a switchable connection between at least one of the live power lines <NUM> and/or 8and the ground connection <NUM>. As a result, when the controller <NUM> activates the leakage circuit <NUM>, leakage current flows from the power terminals <NUM>, <NUM> towards the ground, thereby generating a residual current on the central interface, which causes a triggering of the residual-current circuit breaker of the central interface switch for disconnecting the electrical power.

The active switching element 4a, 4b, 4c, 4d can for example comprises one or more of a unipolar current (semiconductor) switching circuit for generating a DC residual current (<FIG>), a bipolar current (semiconductor) switching circuit for generating an AC residual current (<FIG>), a solid state relay switching circuit for generating both AC and DC residual currents (<FIG>), and a relay switching circuit for generating both AC and DC residual current in case of high electrical insulation and infrequent activation of the leakage circuit (<FIG>). For example, an implementation based on the relay switching circuit may be chosen in order to improve electrical insulation between the microcontroller and the first and second terminals.

The local interface <NUM> may further comprise an auxiliary electrical power supply <NUM> arranged for supplying auxiliary electrical power (E) to the controller, independent from the electrical power (E) between the central interface and the local electrical system, e.g. as illustrated in <FIG>. The auxiliary electrical power supply <NUM> can for example comprise a battery unit, a capacitor, or a power generator. In this way, the controller <NUM> can remain active in case the electrical power (E) transferred between the central interface <NUM> and the local electrical system <NUM> is interrupted or lost.

For the purpose of clarity and a concise description, features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. For example, while embodiments were shown for the method and corresponding local interface, also alternative ways may be envisaged by those skilled in the art having the benefit of the present disclosure for achieving a similar function and result. <FIG> and <FIG> may be combined or split up into one or more alternative components. The various elements of the embodiments as discussed and shown offer certain advantages, such as providing a dual protection mechanism for a local electric system. Of course, it is to be appreciated that any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide even further improvements in finding and matching designs and advantages. It is appreciated that this disclosure offers particular advantages to local electrical systems, and in general can be applied for any application wherein electrical protection devices are useful or required.

Claim 1:
A method comprising
transferring, via a local interface (<NUM>), electrical power (E) between a central interface (<NUM>) and a local electrical system (<NUM>), wherein the transferring of electrical power (E) comprises sending electrical current (I) back and forth via local power lines (<NUM>,<NUM>) between the local interface (<NUM>) and the central interface (<NUM>), wherein the central interface (<NUM>) is electrically connected to transfer the electrical power (E) to and/or from an electrical grid (<NUM>) via a central interface switch (<NUM>), wherein the central interface switch (<NUM>) comprises a residual-current circuit breaker for severing the electrical connection to the electrical grid (<NUM>) when an imbalance occurs in the electrical current (I) being sent back and forth via the local power lines (<NUM>,<NUM>);
monitoring, by a controller (<NUM>) of the local interface (<NUM>), a status (S) of the local electrical system (<NUM>); and
responsive to detecting a fault condition in the monitored status (S) of the local electrical system (<NUM>), activating a leakage circuit (<NUM>) of the local interface (<NUM>) to generate a current imbalance on the local power lines (<NUM>,<NUM>) for causing the central interface (<NUM>) to sever the local electrical system (<NUM>) from the electrical grid (<NUM>) by triggering of the residual-current circuit breaker of the central switch (<NUM>)
characterized in that the local interface (<NUM>) comprises a local interface switch (<NUM>) configured to selectively disconnect the local electrical system (<NUM>) from the local power lines (<NUM>,<NUM>), wherein responsive to detecting the fault condition in the monitored status (S) of the local electrical system (<NUM>),
as a primary means of protection, the controller (<NUM>) initially sends a control signal to the local interface switch (<NUM>) causing the local interface (<NUM>) to sever the local electrical system (<NUM>) from the electrical grid (<NUM>);
as a secondary means of protection, the controller (<NUM>), subsequently and only responsive to determining that the local interface switch (<NUM>) is not operable to disconnect the electrical power, activates the leakage circuit (<NUM>) to generate the current imbalance on the local power lines (<NUM>,<NUM>) causing the central interface (<NUM>) to sever the local electrical system (<NUM>) from the electrical grid (<NUM>).