WO2014122647A1

WO2014122647A1 - System and method for protecting against electric current leakages

Info

Publication number: WO2014122647A1
Application number: PCT/IL2014/050125
Authority: WO
Inventors: Eran Genzel
Original assignee: Better Place GmbH; Reinhold Cohn And Partners
Priority date: 2013-02-06
Filing date: 2014-02-05
Publication date: 2014-08-14
Also published as: EP3005509A1; IL224590A0

Abstract

A system for use in detection of current leakages in an electrical power supply (51) device is presented. Current leakages in an electrical power supply device operating under a residual current device (57d) are detected by a sensing unit (54n) that measures residual currents in the electrical power device. A control unit (54r) processes measured signals from the sensing unit and generates output signals corresponding to leakage fault indications according to predetermined permissible amplitude and time duration defined according to operational boundaries of the residual current device. The control unit comprises an analyzing unit (54z) for receiving and processing the measured signals. The analyzing unit is capable of identifying that amplitude of the measured signals is greater than the predetermined permissible amplitude, and responsively generating indication signals indicative of current leakage conditions. A processing unit (54p) of the control unit determines a time duration of the current leakage conditions based on the indication signals from the analyzing unit and generates output signals corresponding to leakage fault indications whenever the time duration exceeds the predetermined permissible time duration.

Description

SYSTEM AND METHOD FOR PROTECTING AGAINST ELECTRIC

CURRENT LEAKAGES

TECHNOLOGICAL FIELD

The disclosure herein concerns protection against residual electric current leakages in electrical systems.

BACKGROUND

Residual current devices (RCDs) are typically used in low voltage electrical installations to protect against risks such as electric shock and fires by cutting off electrical power supplied to an electrical cabinet, or to a specific output branching therefrom, when leakage of electrical current to ground is detected. Typically, an electrical current leaking to ground is not measured directly by the RCD, but it is rather determined based on comparison of the vector sum of all electrical currents supplied to an electrical cabinet/utility and returned from it. When current is leaking to earth, this vector sum will not be zeroed.

There are three main types of RCDs used nowadays, also known as type 'AC, type 'Α', and type 'B' (in order of increasing cost and capabilities). All three types of RCDs provide protection against residual alternating currents (AC), however, RCDs of type 'AC do not provide protection against pulsating direct currents (DC / rectified AC) faults. While the type 'A' RCDs provide some protection against pulsating and smooth DC fault currents, there are certain situations and fault conditions within electric vehicles (EVs) which may result in excess residual DC current and therefore non- detection of faults by the 'A' type RCDs, resulting in loss of protection under these conditions.

The penetration of electric vehicles and plug-in hybrid electric vehicles (PHEV) to the market in recent years as a viable alternative to internal combustion engine (ICE) vehicles has accelerated standardization discussions and adoption of technologies, including safety aspects of the charging system used for charging batteries of the EVs under existing safety frameworks and standardization. For example, it is required by standards that each socket-outlet of such charging systems be protected by a dedicated residual current device (RCD) to reduce the risk of hazardous electrical shocks. The required type of RCD is at least of Type 'A' (with the exception of some countries which decide otherwise by local regulation).

Due to the electrical characteristics of the EV in multi-phase charging, it may impact the required level of electrical safety. Under certain conditions, including fault conditions, the EV may exhibit residual DC currents that can result in saturation and possibly even blinding of type 'A' RCD to even conventional faults and thus defeat its operation and impacting safety. Similar conditions may also occur in single-phase charging. There is therefore a need for solutions which allow maintaining an adequate level of safety during both single and multi-phase EV charging.

One possible solution to overcome such non-detection of faults is to use an expensive type 'B' RCDs, instead of type 'Α', as these offer better protection against residual DC currents. However, the cost of such devices is significantly higher than the standard type 'A' RCD.

GENERAL DESCRIPTION

The present application provides a system and method for detection and protection of electrical equipment from electrical DC leakage currents in an electric power supply of said equipment. The system of the present invention can generally be used with any AC leakage current detector as well as any switching mechanism capable of disconnecting the electric power supply within the electrical equipment. Typically, the system of the invention may operate in conjunction with a standard low cost RCD device (e.g. , RCD of type 'Α'), which provides the electrical safety protection.

As will be described further below, some standard RCD devices, such as the RCD of type 'Α', are capable of properly operating under residual DC current conditions but within a limited range and characteristics of such currents. Accordingly, the use of such RCDs does not solve the problem of protecting the equipment and user from electrical hazards in the presence of residual DC currents beyond the aforementioned limitations.

The present invention provides in some of its embodiments a novel system aimed to ensure the overall safety of the system and its users by detecting the residual DC current conditions in general, and when used in conjunction with the certain RCD, is configured to detect the residual DC current conditions outside the RCD guaranteed range of operation (also referred to herein as operational boundaries of the RCD) and disconnecting the power supply, should these conditions exist.

In one aspect there is provided a system for use in detection of current leakages in an electrical power supply equipment/device operating under a residual current device, the system comprising a sensing unit configured and operable to measure residual currents in an electrical power supply equipment/device and produce measured signals indicative thereof, and a control unit comprising an analyzing unit, configured and operable to receive and process the measured signals from the sensing unit and generate indication signals indicative of current leakage conditions (e.g. , DC leakages) upon identifying that amplitude of the measured signals is greater than a predetermined permissible amplitude (e.g. , greater or equal to 4 or 6 mA, or a specific value in the range of 4 to 6 mA), and a processing unit configured and operable to determine a continuous time duration of the current leakage conditions based on the indication signals from the analyzing unit, and generate output signals corresponding to leakage fault indications whenever said time duration exceeds a predetermined permissible time duration (e.g. , equivalent to 150 degrees of the 360 degrees time cycle of the electrical power supply, for example about 8.3 milliseconds for 50 Hz electric power supply). The predetermined permissible amplitude, and time duration can be defined according to operational boundaries of the residual current device.

In some embodiments, the processing unit is configured and operable to generate the output signals responsive to determination that the measured residual currents have exceeded the permissible amplitude a predetermined number of times. This determination may be also dependent on the magnitude of fault conditions, e.g. , the duration of time, within one or more AC cycles, during which the measured residual currents exceeded the permissible amplitude, and may also be defined according to operational boundaries of the residual current device.

The output signal indications generated by the processing unit of the control unit responsive to the leakage fault indications may trigger various actions to resolve the faulty leakage conditions. For example, in some embodiments the system is configured and operable to regulate the electric power consumption responsive to the leakage fault indications, and if so needed, to reduce the power consumption to minimum consumption acceptable for proper operation of the system. Additionally or alternatively, the system may comprise a switching device configured and operable to disconnect the power supply to the equipment/device responsive to the leakage fault indications determined by the control unit.

In some embodiments the system is configured and operable to carry preventive actions responsive to the detection of the leakage fault conditions. Such preventive actions may include one or more of the following: (a) regulating the current consumption, and, if needed, reducing it to an acceptable operating minimum; (b) using a controllable switching device provided in the system to internally disconnect the electric power supply if regulating of the power consumption has not resolved the leakage fault conditions; and/or (c) tripping the residual current device if the actions of (a) and (b) have not resolved the leakage fault conditions.

In some embodiments the residual current device is configured and operable to disconnect the electrical power supply in response to AC and possibly also limited DC electrical residual current conditions detected in the electrical power supply. For example, the residual current device may be a type 'A' residual current device configured and operable to detect appearance of a limited range of DC current leakage conditions.

The control unit may be configured and operable to generate the indication signals indicative of the leakage fault conditions upon identifying that the amplitude and duration of the measured signals corresponding to the current leakage conditions is outside a predetermined range including a limited range of operation of the residual current device. Optionally, the control unit may be configured and operable to generate the indication signals when the leakage fault conditions repeatedly occur within some predetermined period of time. For example, the generation of the indication signals may be dependent on the magnitude of the fault conditions as reflected by the amplitude and the time duration of the measured residual currents, e.g. , the duration of time within which the measured residual currents exceeded the permissible amplitude in a single or in multiple AC cycles.

The system may be further adapted to calibrate errors in the sensing and analyzing units within the analyzing unit. The calibration by the analyzing unit may be based on a dedicated calibration function for ensuring maximal accuracy around a single point, or a plurality of points of interest. The calibration mechanism may comprise one or more constant electrical current sources looped via the sensing unit. The calibration process can be performed during equipment manufacture and/or during its operation in order to compensate for inaccuracies of the sensing and analyzing units which may occur due to variance in component characteristics, temperature response, gain linearity and aging.

More particularly, the calibration procedure may be carried out using one or more fixed current sources configured to emulate the leakage events to be detected by the sensing unit. The calibration is thus carried out by applying the emulating current(s) from the calibrating current source, recording the magnitude(s) data (also referred to herein as calibration data) measured by the sensing unit in response to the applied calibration currents, and thereafter scaling/offsetting measurement data from the sensing unit based on the magnitude(s) data recorded in the analyzing unit. Similarly, further calibrations may be carried out to reduce inaccuracies occurring due to temperature changes and exhaustion (deterioration) of the sensing and analyzing units.

In some embodiments the analyzing unit is configured and operable to generate the indication signals upon identifying that amplitude of the measured signals from the sensing unit is greater than a preset threshold value, which is optionally determined or refined during the calibration operation. Accordingly, the processing unit may be configured and operable to adjust the threshold value (e.g. , using the calibration techniques described above) according to the DC current leakage conditions to be detected.

In some implementations the system is configured and operable for use in detection of DC current leakages in the electric power supply of a charge spot used for charging electric vehicles. The electric power supply may be provided to the charge spot through an external residual current device, or possibly through an internal residual current device residing in the charge spot. The control unit may be further configured to generate pre-detection data indicating that current leakage fault(s) may occur based on the indication signals of the analyzing unit and processing unit, thereby enabling to interrupt a charging session of the charge spot and reduce the risk of potential electrical hazard which cannot be detected by the external/internal RCD. Optionally, the control unit is configured and operable to modify a charging profile of the charge spot based on the output signals from the analyzing unit and/or processing unit.

In possible embodiments the control unit is configured and operable to emulate features associated with physical behavior of the tripping mechanism of the residual current device to thereby ensure proper functioning thereof. Advantageously, the control unit may be adapted to detect potential blindness conditions of the residual current device associated with its operational boundaries, to thereby ensure overall safety of the system.

More specifically, the present invention may be used with a charge spot for the charging of batteries of electric vehicles. According to another broad aspect of the invention, there is thus provided a charge spot for charging batteries of electric vehicles, the charge spot connectable to an electric power supply provided through a residual current device and comprising a charge controller configured and operable to modify the charging profile of the vehicle responsive to changing levels of measured leakage currents, a charger unit connectable to a battery pack, and a device for detecting current leakage conditions in the electrical power supply, the device for detecting current leakage conditions comprising a sensing unit coupled to the electric power supply and configured and operable to measure residual currents in the electrical power supply and produce measured signals indicative thereof, and a control unit comprising an analyzing unit configured and operable to receive and process the measured signals from the sensing unit and generate indication signals indicative of current leakage conditions (e.g. , DC leakages) upon identifying that amplitude of the measured signals is greater than a predetermined permissible amplitude, and a processing unit configured and operable to determine a time duration of the current leakage conditions based on the indication signals from the analyzing unit and generate output signals corresponding to leakage fault indications whenever said time duration exceeds a predetermined permissible time duration.

In some embodiments the processing unit is configured and operable to generate the output signals when the leakage fault indications repeatedly occur a predetermined number of times within some predetermined duration of time. For example, in some embodiments, the generation of the output signals is dependent on the magnitude of the occurring fault conditions as reflected by the amplitude and the time duration of the measured residual currents exceeded the permissible amplitude e.g. , within a single or multiple AC cycles.

In some embodiments the charge controller is configured and operable to regulate the electric power consumption responsive to the leakage fault indications from the control unit (i.e. , generated by the processing unit). The charge spot may comprise a controllable switching device (e.g. , contactor) configured and operable to disconnect the electric power supply provided to the load / charger (e.g., at the electric vehicle). The control unit and/or charge controller may be configured to use the switching device to disconnect the vehicle from power supply in certain current leakage events responsive to leakage fault indications e.g. , if the regulation of the electric power supply by the charge controller has not resolved the leakage fault indications. Alternatively or additionally, the control unit may be configured to trip the RCD in certain current leakage events responsive to leakage fault indications e.g., if the regulation of the electric power supply by the charge controller and/or disconnection of the (internal) switching device did not succeed or did not resolve the leakage fault indications.

In some possible embodiments the electric power supply is provided by an electrical network. The RCD device through which the electric power is being supplied may be of a type that can detect only a limited range of current leakage characteristics, for example a type 'A' RCD device. In such cases the device for detecting current leakage conditions may be configured to detect current leakage events under which the RCD device cannot ensure proper operation.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which like reference numerals are used to indicate corresponding parts, and in which:

Figs. 1A and IB show conventional charge spot implementations;

Fig. 2 is a block diagram illustrating a charge spot implementation according to some possible embodiments;

Fig. 3 schematically illustrates the type of faults that can be sensed by RCDs of type AC, Ά', and 'Β';

Fig. 4 schematically illustrates a residual current transformer of typical RCDs;

Fig. 5 shows a magnetization curve of transformers used in RCDs of type 'AC;

Fig. 6 demonstrates changes of field intensity and flux density within the magnetization curve of RCDs of type 'AC being subject to alternating residual currents;

Fig. 7 demonstrates the reduction in flux density changes under alternating residual currents having a DC component in RCDs of type 'AC due to saturation; Fig. 8 shows the magnetization curve of RCDs of type 'A' and demonstrates their improved immunity to residual currents including DC components by achieving less saturation and greater changes in flux density than Type AC when such currents are present;

Fig. 9 demonstrates faults conditions (i.e. , saturation and blinding) of RCDs of type A';

Fig. 10 demonstrates situations in which RCDs of type 'A' can detect leakages despite the presence of a large DC offsetting current;

Fig. 11 illustrates marginal conditions for proper detection of leakages with a DC component in RCDs of type ' A;

Fig. 12 demonstrates a situation of sudden increase of DC leakage in RCDs of type A';

Fig. 13 illustrates the residual current conditions, required according to the IEC 60755 standard, under which operation of RCD of Type A is ensured; and

Fig. 14 is a block diagram of a possible embodiment usable for detecting residual currents having a DC component and controlling the supply of electrical power accordingly.

DETAILED DESCRIPTION OF EMBODIMENTS

As indicated above, the present invention can in particular be used with a charge spot device for charging batteries for electric vehicles, and will therefore be described below with respect to this specific application. It should however be understood that the invention is not limited to this specific application and can be advantageously used with any electric device connectable to an electric power supply. Further, in the description below the present invention is exemplified as being used with a standard RCD. However, as mentioned above, the principles of the invention are not limited to any additional RCD. The invention to be practically implemented might need an AC current leakage detector and a switching mechanism.

The conventional charge spot 44 shown in Figs. 1A and IB typically includes devices and logic required to receive electric power supply from the electric network and charge an electric vehicle (i.e. , a battery of the vehicle) via a flexible cable connected to the charge spot. These charge spots typically rely on the protection provided by conventional RCD of type A located within or upstream to the charge spot. Fig. 2 is a block diagram illustrating a possible implementation of a charge spot 54 according to some possible embodiments. The charge spot 54 receives electric power supply 51 (e.g. , from an electric network) which may be supplied through an electric safety device 57 including a main breaker 57b and a RCD device 57d. Though in this example the electric safety device 57 is provided in the charge spot 54, in some possible embodiments the electric safety device 57 is external to the charge spot 54 e.g. , in an electric cabinet of the power supply 51.

The charge spot 54 comprises a socket outlet 54u connectable via a connector 53t and cable 53e to a charger unit 53c of an electric vehicle 53 for charging a battery pack 53b installed therein. Alternatively, in possible embodiments, the charge spot 54 may integrally comprise the cable 53e, which may be adapted to be connectable to the charger unit 53c of the electric vehicle 53. Charging of the vehicle 53 may be commenced upon plugging the cable connector 53t to the socket 54u of the charge spot 54. It is noted that solid arrowed lines shown in Fig. 2 represent electric power supply lines, and broken arrowed lines represents data/control signals. It is however noted that the cable 53e that connects between the vehicle 53 and the charge spot 54 may be used for delivery of both electric charging currents and pilot control signals generated by the pilot control unit 54p of the charge spot 54.

The charge spot 54 further comprises a charge controller 54r configured and operable to communicate with the pilot control unit 54p for carrying out charging sessions for the charging of the battery pack 53b of the vehicle 53. The pilot control unit 54p is configured and operable to communicate with the charger 53c of the vehicle 53 (e.g. , over the cable 53e) and provide it with instructions to regulate the electrical charging currents consumed during the charging session. In some embodiments the pilot control unit 54p is further configured to temporarily halt the charging session and/or to split charging sessions into a plurality of charging cycles, as described in Israeli Patent Application No. 218213 of the same applicant hereof, and the disclosure of which is incorporated herein by reference.

In some embodiments the charge spot 54 further comprises a controllable switching device 54s (e.g. , contactor) configured and operable to disconnect the electric power supplied from the safety device 57 (i.e. , to disconnect electric power supplied to the charger 53c). For example, in some embodiments the charge controller 54r is configured and operable to receive control signals from the leakage detection device 54c and responsive to the received signals provide the charge controller 54r with control signals for modifying the charging profile of the battery (e.g. , by regulating or halting the charging session), and/or to disconnect the electrical power supply provided to the charger 53c of the vehicle 53 over the cable 53e by changing the state of the switching device 54s.

In this example, the current leakage detection device 54c comprises a sensing unit 54n configured and operable to measure leakage currents in the electric supply received via the safety device 57 and generate indication signals indicative thereof, and a control unit 54t configured and operable to process and analyze the indication signals from the sensing unit 54n and determine current leakage events based thereon.

More particularly, the control unit 54t of the leakage detection device 54c comprises in some embodiments an analyzing unit 54z and a processing unit 54p, which are employed for the determining of the current leakage events. For example, the analyzing unit 54z may be configured and operable to process the measured signals from the sensing unit 54n and generate indication signals indicative of current leakage conditions (e.g. , DC current leakages) upon identifying that amplitude of the measured signals is greater than a predetermined permissible amplitude, and the processing unit 54p may be configured and operable to determine leakage faults based on the indication signals generated by the analyzing unit 54z. For example, in some embodiments the processing unit 54p is configured and operable to determine a time duration of the current leakage conditions based on the indication signals from the analyzing unit 54z and generate output signals corresponding to leakage fault indications (e.g. , DC leakage faults) whenever said time duration exceeds a predetermined permissible time duration.

In some embodiments the processing unit 54p is configured and operable to determine if faulty current leakage conditions have occurred for some predetermined number of times within some predetermined time duration, based on the indication signals from the analyzing unit 54z, and generate corresponding fault output signals thereupon. In some embodiments, generation of the fault output signals by the processing unit may also depend on the magnitude of the fault conditions as reflected by the time duration within which the analyzing unit 54z generated the indication signals indicative of current leakage conditions e.g. , within a single or multiple AC cycles.

In some embodiments a predetermined residual current threshold and a predetermined time window are used by the control unit 54t to determine current leakage fault events. For example, in some applications the current leakage fault events are determined when determining that the current leakage indications measured by the sensing unit 54n are indicative that leakage current in the power supply 51 was continuously or intermittently greater than the predetermined residual current threshold for a duration of time that is greater than the predetermined time window.

The current leakage fault events may be determined based on a fixed time window approach i.e., by dividing the time axis into fixed time intervals of the time window and checking threshold crossing and their time durations within each fixed time interval, or based on a sliding window approach, i.e. , by identifying any continuous interval of time on the time axis within which there were threshold crossings over a total time durations greater than the predetermined time window.

As will be explained below with reference to Fig. 13, in some embodiments, the predetermined permissible amplitude and time duration may be defined according to a combination including the operation boundaries of the residual current device 57d and the expected behavior of a superior residual current device, such as of a type "B" RCD. Similarly, in some embodiments, the predetermined number of occurrences of the leakage fault conditions, and the predetermined time duration within which such repeated occurrence of the leakage fault conditions is determined to be faulty, may be also defined according to a combination including the operation boundaries of the residual current device 57d and the expected behavior of a superior residual current device such as one of type "B". In some embodiments, the predetermined number of occurrences of the leakage fault conditions, and the predetermined time duration within which such repeated occurrence of the leakage fault conditions is determined to be faulty, may also depend on the magnitude of the fault conditions as reflected by amplitude and the time duration of the measured residual currents e.g. , within a single or multiple AC cycles.

In some possible embodiments the leakage detection device 54c is configured and operable to carry out preventive actions responsive to current leakage faults. For example, in certain current leakage fault events the leakage detection device 54c may be configured to carry out the following actions:

(a) provide the charge control unit 54r with control signals for regulating the electric power consumed by the charger 53c of the vehicle 53 (e.g. , to reduce the consumed electric charging power or even halt the charging session, if so needed); (b) if, after regulating/halting the charging session, the current leakage fault events still persist, provide the charge controller 54r with a control signal for disconnecting the electric power supplied from the safety device 57 by changing the state of the switching device 54s to a disconnected state, to thereby disconnect the electrical power supplied to the charger 53c of the vehicle 53;

and

(c) if, after regulating the charging session and disconnecting the electric power supply through the switching device 54s the current leakage fault events still persist, e.g., possibly due to failure of switching device operation, generate a control signal to trip the RCD device 57d, to thereby disconnect the electric power supplied to the charge spot 54.

In certain current leakage fault events, e.g., slowly developing residual currents, the leakage detection device 54c and charge controller 54r are configured and operable to alert the user, and/or a system administrator, that hazardous electric current leakages may evolve during current or future charging of the vehicle 53, and that certain components of the vehicle 53 and/or of the charge spot 54 may require repair and/or maintenance.

The present application may be advantageously employed for detecting residual currents having a DC component. The techniques of the present application may be used to improve the protection provided by a standard RCD e.g., of the 'A' type. For example, the current leakage detection device 54c may be configured and operable to detect DC current leakage conditions that a conventional RCD device (type 'A' RCD) may not be able to detect. As will be explained herein below, some types of RCD devices are blinded (e.g. , due to the saturation effect) to certain leakage current events and thus cannot detect them. This blinding effect is typically caused due to the presence of a residual DC current (also referred to herein as a DC component) under which the total residual current does not fall sufficiently close to zero, for a sufficient amount of time.

With reference to Fig. 13, according to the IEC 60755 standard, detection current leakage fault requires that the residual current must have zero contact of at least 8.3 ms (curve 18 e.g., main frequency f=50Hz) or a maximal permissible superimposed smooth DC residual current of 6mA (curve 17), irrespective of the residual current rating. Particularly, in order to ensure proper operation of RCDs of type 'Α', the residual current must fall below 6mA for at least 150 degrees during the 360 degrees of the AC power supply cycle (i.e. , for at least 8.3ms out of 20ms for electrical supply of 50Hz). Accordingly, in some embodiments the leakage detection device 54c is configured and operable to generate current leakage fault indications in a 50Hz electric power supply 51 whenever the amplitude of the leakage current measured by the sensing device 54n is greater than 6mA for time duration greater or equal to 8.3ms.

In some possible embodiments the leakage current detector device 54c may be configured and operable to generate alerts, typically for slowly developing residual currents, whenever the amplitude of the leakage current measured by the sensing device 54n is greater than 4mA, or any other preselected threshold value smaller than 6mA, for a predetermined time duration. For example, in possible embodiments, such alerts may be generated whenever the amplitude of the leakage current measured by the sensing device 54n is greater than a preselected threshold value smaller than 6mA during a time duration which is greater or equal to the time duration equivalent to 150 degrees of the 360 degrees of the AC power supply cycle. The generation of the alerts may be conditioned such that the alerts be generated if the leakage conditions are consistent (i.e. , the measured leakage current remains greater than the preselected value) or worsen (e.g., the measured leakage current increases towards 6mA) over a predetermined time duration (e.g. , lsec), to thereby indicate to the user/system that electric current leakage fault conditions are evolving in the system.

As demonstrated hereinbelow with reference to Figs. 9 and 10, the critical parameter for tripping the type 'A' RCD is not the level of DC offset 26c or 26d (i.e., the pure DC residual currents component) but rather the overall magnetic field intensity generated by both AC and DC residual currents. Accordingly, in some embodiments, the leakage detection device 54c of the present application is configured to emulate the characteristic physical behavior of the tripping mechanism of RCD of type 'Α', and thus confirm it can function correctly and prevent any undesired impact on the system and service, and take appropriate action if not. This is different from the detection of residual current which indicates electric shock hazards as performed by RCDs, and from mere detection of DC fault currents for protecting the RCD operation, which may cause false detection as elaborated herein below.

In some embodiments the leakage detection device 54c is configured to detect and react only to hazardous scenarios wherein the type 'A' RCD cannot operate properly. For example, the device 54c in some possible embodiments is not configured to detect the fault conditions which present the electrical shock hazards (which the type 'A' RCD effectively detects), but rather configured to detect situations (e.g. , caused by the load) where a potential fault condition would not be detected by the protection device (RCD) due to its inherent limitations, and thereby ensure overall safety.

While residual current measurement devices used nowadays typically measure (or more accurately calculate) true RMS of the residual current signal for imitating the RCD operation, or possibly measure only the DC component level, the leakage detection device 54c of the present application, in some embodiments, determines that the combined (AC and DC components) residual current signal is below a predetermined threshold (e.g. , about 6mA) for a predetermined time duration, which indicates a potential negative influence on the RCD operation. The residual current measurement devices used nowadays and which are based on RMS calculated values, or only on measured DC component values, do not reliably represent the potential fault conditions. This failure in reliably representing the potential fault conditions is either due to averaging period of the RMS calculation over one or more cycles, or due to filtering of the residual AC components that are inherent in the system, and are therefore less suitable for this application and may generate false indications, or not detect true fault conditions altogether.

Fig. 14 exemplifies a battery charging implementation 60 employing the leakage detection device 70, according to some embodiments of the present application, for improving the protection provided using a conventional RCD of type 'A' 63. In this example the RCD 63 is utilized for feeding electrical power for charging the battery 66b of the electric vehicle 66. The leakage detection device 70 comprises a sensing unit 72 (e.g. , configured to identify the combined AC and DC leakage current) electrically coupled to the electrical current-carrying conductors 13 (e.g. , the mains) fed via the RCD 63, a residual current analyzing and processing part 70p configured to receive and process output signals produced by the sensing unit 72 and issue responsive control signals, and a controllable switching device 71 configured to controllably connect/disconnect the electrical power supplied to the EV 66 over the electrical current-carrying conductors 13 responsive to control signals received from the residual current analyzing and processing part 70p. The switching device 71 enables to controllably break the electrical contact between the EV 66 and the RCD 63 whenever faults are detected, and cease operation of the charging system. The switching device 71 is also configured to reestablish the electrical contact between the EV 66 and the RCD 63 to allow fault recovery and a new charging session to commence.

The sensing unit 72 is configured to measure the residual currents passing through the electrical current-carrying conductors 13, and responsively output a voltage signal 5,· proportional to the vector summation of the sensed residual currents. In possible embodiments the sensing unit 72 is configured to operate in bandwidths suitable to support both DC and AC currents i.e., any core balance CT (CBCT) or similar CT construction, capable of measuring also DC frequency.

The residual current analyzing and processing part 70p generally includes a signal analyzing stage 74, a signal processing stage 76, and a controller 77. In the signal analyzing stage 74, signals from the sensor unit 72 are analyzed to determine whether residual current via the mains 13, measured by the sensing unit 72, have exceeded the predetermined threshold (e.g. , 6mA), and responsive signals are produced indicative of the exceeding (and its complementary) time period durations. In the signal processing stage 76 signals from the analyzing stage 74 are processed to determine time periods in which the sensed residual currents have exceeded a predetermined threshold value, and responsive signals are produced indicative of the fault occurrence, or of conditions to issue an alert to indicate that a current leakage fault may occur. The controller 77 is configured to receive such fault indications from the signal processing stage 76 and issue control signals responsively for disconnecting the electric power supplied via the switching device 71.

The controller 77 may be further configured to adjust the threshold value used in the signal analyzing stage 74 based on the calibration data to accurately determine whether the residual current via the mains 13, measured by the sensing unit 72, has exceeded the predetermined threshold value. Furthermore, the controller 77 may also be configured to adjust the threshold value used in the signal analyzing stage 74 to modify the leakage current threshold (e.g., from 6mA to 4mA) for pre-warning or increased safety purposes. For example, in possible embodiments the residual current analyzing and processing part 70p includes an adjustable voltage source 75 (implemented in Fig. 12 by variable reference voltage units 75p and 75n) configured to produce a reference threshold voltage in response to control signals produced by the control unit 77. The control unit 77 may be configured to perform various decisions as to whether a fault condition has been detected, and/or is expected to occur.

For example, in possible embodiments, the control unit 77 may be configured to modify the reference voltage level provided by the adjustable voltage source 75 and monitor the indications received from the signal processing stage 76, to thereby set different threshold fault levels (e.g., 4mA) to pre-detect slowly developing faults. Alternatively or additionally, the control unit 77 may be configured to apply signal filtering capabilities to eliminate transitional events (e.g., ignoring and filtering out events of crossing of the threshold fault level for a single and short duration of time, such that these events do not affect the charging process) prior to decision to reduce the charging current or to disconnect the electric power supplied through the controllable switching device 71.

The device 70 may further include a calibration unit 73 configured to calibrate the sensing unit 72 and signal analyzing stage 74 to an accurate desirable level. In some embodiments the calibration unit 73 may be configured to receive control signals (not shown) from the controller 77 to adequately calibrate the output voltage signal 5,·. A possible calibration point according to some embodiments may be a residual current of 6mA DC. For example, independent calibration circuitry 73 may be employed to ensure maximal detection accuracy around the 6mA point (the current level under which the RCD is influenced) based on signals 5,· received from the sensing unit 72, analyzed by the signal analyzing stage 74 and on control signals received from the controller 77, to confirm correct detector operation, and to prevent any misdetection.

During calibration, the disconnect switch 71 may be operated to terminate charging and disconnect the electric vehicle 66 from charging currents, causing the only true leakage signal measured by the signal processing stage 76 to be that driven by the calibration unit 73.

In some embodiments the signal analyzing stage 74 includes two signal sheer units, a positive slicer 74p and a negative slicer 74n, configured to output a pulse-width modulated (PWM) signal whose duty cycle is indicative of the time periods during which the measurement signals 5; from the sensing unit 72 exceeded respective positive or negative thresholds i.e., depending on the residual current flow direction. In other words, the slicer units, 74p and 74n, are used to determine whether the sensed residual currents Si departed from the detectable range of the RCD 63 and issue respective indications accordingly. Each slicer unit, 74p and 74b, may include an analog front end 74a (AFE) circuitry configured to match the sensing unit 72 to the electrical characteristics of the analyzing unit 74 so as to enable the device 70 to achieve the required dynamic range and accuracy, and handle unwanted signal noise.

Accordingly, the signal processing stage 76 may also comprise two respective signal processing units, 76p and 76n, each configured to receive PWM signals from respective slicer unit, 74p and 74n, determine from the received signals the time durations during which the sensed residual currents Si exceeded respective positive and/or negative threshold values, and the number of such positive and/or negative threshold crossing. For example, in some embodiments, the signal processing units 76p and/or 76n are configured and operable to issue respective positive and negative residual fault indications, for input to the control unit 77, whenever determining that the time durations during which the sensed residual currents Si departed from the detectable range of the RCD device 63 were greater than a permissible time period (e.g., greater than 8.3 ms) and that the number of occurrences of these events is greater than some predetermined number, which may also depend on the magnitude of the event, i.e. , the amount of time in which the permissible time duration (e.g. , 8.3ms) has been exceeded within a single AC cycle (e.g. , 20ms).

This design may also employ two respective variable reference voltage units 75p and 75n configured to set the threshold of the respective slicer units, 74p and 74n. In some embodiments the variable reference voltage units 75p and 75n are configured to output a voltage level which is equivalent to residual current measurement of about 6mA.

It is noted that the various units/components of the leakage detection device 70 may be implemented by hardware as discrete components or as software modules e.g., as part of System-On-Chip. For example, using a processing unit or micro-controller which samples the signal amplitude and converts it to digital samples (ADC), sufficient samples below a threshold are scanned and it is determined whether a current leakage fault has occurred. Accordingly, the residual current analyzing and processing part 70p may be implemented in some embodiments by one or more integrated circuits configured to carry out digital signal processing and corresponding computations, and to facilitate determination of leakage, using one or more memories and processing units. In some embodiments the controller 77 is configured to identify excursions of the magnetic field in the core of the current transformer of the conventional RCD of type 'A' 63 (which are caused by, and proportional to, the currents of the primary coil and are therefore indirectly measurable at the output of the sensing unit 72) over time (typically one cycle of the fundamental supply frequency - i.e., 20mS) based on the signals from the signal processing stage 76 and/or the signals from the signal analyzing stage 74. In some embodiments the controller 77 is further configured to determine, based on the size of the excursions (whether or not they exceeded a slicer threshold), and their time length (whether this excess existed for greater than a certain proportion of the full cycle), whether the core of the conventional RCD of type 'A' 63 is at risk of being saturated and therefore at risk of not detecting certain fault currents.

The type 'A' RCD 63 is typically worst affected by slowly developing fault currents (unlike immediate fault currents), which cause the saturation and possibly blinding of the RCD 63. In some embodiments the controller 77 of the leakage detection device 70 is configured to identify gradually developing fault events which typically do not trip the type 'A' RCD 63. For example, the controller 77 of the leakage detection device 70 may be configured to detect trends of detected residual currents 5; e.g. , by setting lower detection levels for the signal processing stage 76 (reducing the slicer thresholds) and signal analyzing stage 74 (reducing the proportion of the full cycle that must be exceeded in order to give output indication). Then upon detection of lower- level excesses, the detection levels are returned to normal values to detect the required excess, and react in a manner that minimize their impact, for example by accelerating the charging schedule to maximize the amount of charge delivered to the electrical vehicle 66 before the leakage currents reach unacceptable levels while attempting to avoid continued loss of service (e.g., in cases where accelerated charging may solve moisture compensation issues). This option may be used to track and manage a battery charger under slow rising fault conditions.

Commonly, residual current measurement devices are required to measure a relative large range of currents. For example, typical RCD tripping current of 30mA RMS requires a measurement range of at least 42mA peak current. This wide range may impact the sensitivity and accuracy required to detect leakage currents less than 6mA. The leakage detection device 70 of the present application, in some embodiments, narrows the range to as low as 6mA by properly adapting the sensing unit 72 accordingly, which enables it to have better sensitivity in the range relevant for battery charging applications.

Common residual current measurement devices include pre-detection functionality (the ability to detect fault conditions prior to achieving a certain level of interest) of RMS current at a level which can prevent tripping of the RCD or present electrical hazard (e.g. , 30mA RMS current). In some embodiments the leakage detection device 70 is configured to carry out pre-detection on parameters which indicate the limit where RCD of type 'A' are influenced (blinded or saturated). For example, the leakage detection device 70 may be configured to carry out the pre-detection functionality based on the amplitude of the sensed residual current and the phase appearance period.

The amplitude threshold parameter usable to ensure the proper operation of type 'A' RCDs is typically 6mA. The leakage detection device 70 of the present application may be configured to operate using different threshold values e.g. , 4mA, which may be used for pre-detection to indicate possible occurrence fault conditions. This enables better management of the fault, for example, by alerting the user that the battery charge may not be fully completed.

The design also permits the use of superior type A' RCDs, should they become available. For example, the amplitude threshold parameter may also be set to values higher than 6mA in order to match the use of superior type 'A' RCDs that are not blinded unless such higher currents are present.

To further demonstrate the advantages of the techniques disclosed herein, it should be considered that in addition to the residual DC fault current, the EV 66 also has inherent residual AC fault currents. A trivial implementation that detects DC level over one or more periods (e.g. , to give average DC content), and does not take into consideration the minimal time within a single period in which the leakage current falls below 6mA, may cause false detection and therefore negative impact on the functionality of the overall system by disconnecting the electric vehicle from the electric power in situations where type 'A' RCD is not actually blinded and the residual currents do not actually exceed any permitted threshold. It is therefore a disadvantage to disregard the AC content of the residual current when constructing a device which ensures proper operation of the Type 'A' RCD in situations where residual DC currents may be present. In some embodiments the leakage detection device 70 may be configured to gather statistics of the detected residual currents 5,· in a memory 70m, which may be used to assist in better analysis and handling of the fault conditions, including gathering statistics on the basis of specific vehicles or particular models of vehicles that may become prone, over time, to unsafe leakage currents. Such statistics may also be shared in a distributed or centralized manner between multiple charge spots.

In some embodiments, the leakage detection device 70 may be configured to exhibit different behavior depending on the type of electrical vehicle 66 connected to the charge spot. For example, certain types of vehicles may exhibit high DC leakage currents for a limited time at certain points of the charge cycle, and the leakage detection device 70 may be configured to ignore such high DC leakage currents and accept a temporary blinding of the type 'A' RCD 63 by this known behavior.

It is likely that there will be system leakage currents that are influenced by condensation and similar effects that are a function of the temperature of the EV, its environment and charging circuitries. In some embodiments, the pre-detection functionality of the leakage detection device 70 may be used to alter the charging profile of the battery 66b in real time. For example, the leakage detection device 70 may be configured to issue control signals instructing a battery charger to increase the charging rate upon appearance of leakage currents 5,·, in order to ensure that the maximal charging power possible is delivered prior to the 6mA threshold being reached, or to increase the charging rate in order to cause increased charging-related heating at the EV which may reduce condensation.

In some embodiments a phase appearance period parameter may be defined to ensure that the operation of the type 'A' RCD 63 is 150°. Analysis of the detected period can indicate a possible fault, and better handling of the fault condition.

In some embodiments the leakage detection device 70 is configured to measure raw analog signal samples and compare corresponding analog signals indicative of the measured leakage currents to an analog threshold level. Such implementations are simple to implement since they preclude the need for an analog-to-digital converter, and allow all calculations to be performed as a function of time and not time and magnitude. It is also understood that the leakage detection techniques of the present application are less costly to implement than conventional implementations based on RMS calculations, which require processing to perform mathematical operations of square and mean root. In order to better understand the difficulties involved in effectively protecting against DC leakages using conventional low cost RCDs a brief review of the limitations of such RCDs will be discussed herebelow.

Fig. 3 schematically illustrates the types of faults that can be sensed by the type 'AC, Ά', and 'B' RCDs. As shown in Fig. 3, RCDs of type 'A' do not detect pulsating DC faults 6, 2, 3 and 7(the fault numbers are according to fault numbers specified in annex B of the IEC60755 standard). A main element in the RCD is a current transformer which has to deliver sufficient power to trip electromechanical relay of the RCD. Fig. 4, schematically illustrates a current transformer 10 of a typical RCD of type 'Α'. Such transformers 10 include a toroidal core 11 made of steel or other magnetic material that is magnetically soft (i.e., unlike a permanent magnet, its magnetic field is not fixed). The four electrical current-carrying conductor lines, namely, the three phase conductor lines 13p and the neutral conductor line 13n (collectivity referenced by numeral 13) passing through the toroid opening lip, form the primary coil winding, and a fifth wire is wound around the toroid 11 to form the secondary coil winding 14.

Whenever the vector sum of the electrical currents flowing through the four conductors 13 of the primary coil is not zeroed (i.e., there are electrical currents flowing through the load from some other connection, which means that there is a hazardous current leaking to earth) an electrical voltage evolves in the secondary coil 14, which is the fault indication that causes the RCD to trip. Specifically, any net non-DC current flowing through the primary coil 13 will create a magnetic field around the transformer core 11. This will result in a change in the magnetic flux in the core 11, which in turn will create a magnetic field around the secondary coil 14. The change in magnetic field around the secondary coil 14 will induce an electrical voltage in the secondary coil 14. It should be noted that since changes in the magnetic flux are actually sensed by the secondary coil 14, steady DC currents flowing through the primary coil 13 will not result in an output voltage at the secondary coil 14.

Fig. 5 shows the magnetization curve 21 (hysteresis loop) of the transformer of an 'old-fashioned' or type 'AC RCD i.e., plotting magnetic flux density B in the core 11 vs. the magnetic field intensity H in the primary coil 13. Applying a strong positive magnetic field H will cause the magnetic flux density B to rise to a high positive value as indicated by the curve path referenced by numeral 21b. Likewise, applying a strong negative magnetic field H will cause the flux density B to change to a highly negative value as indicated by the curve path referenced by numeral 21a.

Fig. 6 shows the effect of a net AC (i.e., without any DC components) current in the primary coil 13. As seen, the sinusoidal voltage 17 causes the magnetic field H to assume positive and negative values (i.e., to move left and right along the magnetic field H axis), as shown by the thick horizontal line referenced 17m. These alterations of the magnetic field intensity H cause the magnetic flux intensity B to rise and fall, as the magnetization curve 21 follows the path shown by the arrows on curves 21a and 21b. The entire magnetization curve enclosed within the dashed line box 22 is periodically traversed due to the alternating voltage 17, and substantial changes in the magnetic flux density B in the core 11 of the transformer thus result in AC voltage being induced in the secondary coil 14 that is sufficiently large to trip the relay mechanism of the RCD.

Fig. 7 demonstrates the main problems in detection of DC fault currents by RCDs of type 'AC. In this example the alternating voltage 17a over the primary coil 13 is of the same magnitude as that of the alternating voltage 17 in Fig. 4, but is offset by a DC current 26. Even though the axis of the magnetic flux density B axis is still being crossed by the magnetization curve 21 (and even though the overall power of the leakage current is greater), a much smaller part of the magnetization curve 21 is traversed (shown by the dashed line box 22a), and thus the change in flux density B (indicated by the height of the dashed line box 22a) is much smaller, possibly not sufficient for tripping the RCD.

The limitations of RCDs of type 'AC demonstrated in Fig. 7 are partially overcome in RCDs of type 'Α', in which different materials and/or constructions are used for the current transformer of the RCD device to provide a more linear magnetization curve. As seen in Fig. 8, the magnetization curve 20 of the RCDs of type 'A' is flat and narrower than that of the RCDs of type 'AC. From comparison of the type 'AC magnetization curve 21 and the type 'A' magnetization curve 20 it is seen that for a similar DC offset 26 and a smaller AC voltage 17b, a larger magnetic flux change (indicated by the larger height of the dashed line box 22b) is obtained with RCD of type 'Α', even though the magnetic field intensity H never returns to zero. Thus, for AC leakage currents 17b with a DC offset 26 that return to near zero, or pulsating currents that return to near zero, RCD of type 'A' are able to correctly detect the leakage currents using the secondary coil and correspondingly trips. However, the transformers of RCDs of type 'A' still have their limitations as demonstrated in Fig. 9, which shows that with a high enough offsetting DC current 26c in the primary coil, RCDs of type 'A' suffer from the same lack of flux density change (shown by the small height of the dashed line box 22c) due to AC currents, as with the RCDs of type 'AC. However, as demonstrated in Fig. 10 with a similar DC offset 26d, it is not the amount of DC offset that influences the RCD detection ability, but rather whether the overall value of magnetic field intensity H returns to near zero at some point in the AC cycle. In Fig. 9 the type 'A' RCD core is saturated (dotted line box 22c) as the magnetic flux intensity does not change sufficiently to activate the tripping mechanism due to the DC offset 26c, whereas in Fig. 10 though the level of the DC offset 26d is more or less identical, the overall magnetic field intensity returns to near zero level and therefore generates sufficient change in magnetic flux density (shown by the height of the dashed line box 23d) to activate the tripping mechanism.

From a comparison of Fig. 9 and Fig. 10 it may be seen that:

- Determining whether a transformer is stuck in saturation due to DC currents, should consider the excursion of the applied magnetic field (i.e., the deviation of an average magnetic field value, being proportional to the currents of the primary coil, from zero) over a segment of time (typically one cycle of the fundamental supply frequency - i.e., 20mS), and not the actual amount of presented DC offset.

- It is therefore unwise to filter out the AC portion of the field intensity when analyzing whether the RCD of type 'A' transformer is stuck in saturation.

The reference to section 3.1.3 of the IEC specification, regarding the requirement of RCDs of type 'A' (requirement to detect pulsating direct leakage currents that "assumes, in each period of the rated power frequency, the value 0 or a value not exceeding 0.006 A DC during one single interval of time, expressed in angular measure, of at least 150°") is a benchmark by which RCDs of type 'A' are assured that the magnetic field intensity will be near zero (for long enough) to ensure that the flux density will fall sufficiently to exit saturation, and thus assure inductions of electrical voltages in the secondary coil for AC and pulsating DC fault currents, and the transfer of sufficient power thereto to trip the type 'A' RCD device.

This can be generalized as follows, with reference to Fig. 11, provided that the magnetic field intensity H has fallen during 150° of a cycle to the safe level delimited by the thick lines 24a and 24b (representing the field intensity relating to the benchmark of less than 0.006A of either polarity), or below it (for both positive and negative net DC leakage currents), it is guaranteed that RCDs of type 'A' have sufficient headroom to allow them to detect an increase in magnetic flux density caused by any event.

The above examples considered the question of whether a type 'A' RCD is blinded by the presence of a DC offset in the applied magnetic field H, which represents the fault types 6 and 2, 3, 7 of Fig. 3. These situations can be detected by measuring the currents in the primary coil of the RCD for deciding whether to take preventative actions (such as cutting off the power supply). As shown in Fig. 12, in the case of a sudden increase of DC leakage 17e (such as may occur if these faults suddenly occur), when the magnetization curve 20 is below the safe level shown In Fig. 11, there will be a corresponding increase in magnetic flux density B, the rapid change of which will induce a current in the secondary coil, and therefore it is expected that a type 'A' breaker will trip.

Conversely, for a gradually developing fault of one of these types, the magnetization curve slowly ascents into saturation such that the power that will be delivered by the current transformer will be distributed over a longer time period and therefore will not be sufficient to activate the electromechanical relay of the RCD and cause tripping thereof. The present invention provides fault detection techniques that allow identifying such gradually developing fault events.

The present disclosure provides techniques for detecting DC faults that RCDs of type 'A' do not detect, by using a leakage sensing device configured to sense and analyze the electrical currents of the primary coil of the RCD, identify problematic residual DC currents and ensure the conditions for the proper operation of the Type 'A' RCD. The leakage sensing device may be configured to take actions upon leakage detection events that the Type 'A' RCD cannot detect (e.g. , to disconnect electrical current supply by tripping the RCD and/or disconnecting the power supply provided to, or from, the RCD). Such a solution offers some benefits over using RCD of Type B, such as: (a) it can reduce the overall system cost; and (b) it enables recovery from such events as it can utilize electro-mechanical devices (e.g. , contactors) prior to critical fault conditions in order to prevent the tripping of the RCD.

The above examples and description have of course been provided only for the purpose of illustration, and are not intended to limit the invention in any way. As will be appreciated by the skilled person, the invention can be carried out in a great variety of ways, employing more than one technique from those described above, all without exceeding the scope of the invention.

Claims

CLAIMS:

1. A system for use in detection of current leakages in an electrical power supply device, comprising:

a sensing unit configured and operable to measure residual currents in the electrical power supply device operating under a residual current device, and produce measured signals indicative thereof; and

a control unit comprising:

an analyzing unit configured and operable to receive and process the measured signals from the sensing unit, the analyzing unit being capable of identifying that amplitude of the measured signals is greater than a predetermined permissible amplitude and responsively generating indication signals indicative of current leakage conditions; and

a processing unit configured and operable to determine a time duration of the current leakage conditions based on the indication signals from the analyzing unit and generate output signals corresponding to leakage fault indications whenever said time duration exceeds a predetermined permissible time duration, said predetermined permissible amplitude and time duration are defined according to operational boundaries of the residual current device.

2. A system according to claim 1, wherein the residual current device is configured and operable to detect AC electrical current leakage conditions in said electrical power supply, enabling to disconnect said electrical power supply, the residual current device being configured and operable to detect appearance of a limited range of DC current leakage conditions.

3. A system according to claim 2 wherein the residual current device is a type 'A' residual current device.

4. A system according to any one of the preceding claims, wherein the processing unit is configured and operable to calibrate the sensing and/or analyzing units in order to adjust it to the measured signals produced by the sensing unit according to the current leakage conditions to be detected.

5. A system according to claim 4, wherein the calibration of the analyzing and sensing units is based on a dedicated calibration function for ensuring maximal accuracy around a single point of interest, associated with the residual current device.

6. A system according to any one of the preceding claims, wherein the analyzing unit is configured and operable to identify that the amplitude of the measured signals from the sensing unit is greater than a preset threshold value and responsively generate the indication signals.

7. A system according to claim 6, wherein the control unit is configured and operable to adjust the threshold value according to the current leakage conditions to be detected.

8. A system according to any one of the preceding claims, wherein the analyzing unit is configured and operable to generate the indication signals whenever the amplitude of the measured signals from the sensing unit is indicative of leakage current being greater or equal to 6 niA.

9. A system according to any one of claims 1 to 7, wherein the analyzing unit is configured and operable to generate the indication signals whenever the amplitude of the measured signals from the sensing unit is indicative of leakage current being greater or equal to 4 mA.

10. A system according to any one of the preceding claims, wherein the predetermined permissible time is equivalent to 150 degrees of the 360 degrees time cycle of the electrical power supply.

11. A system according to any one of the preceding claims, wherein the predetermined permissible time is about 8.3 milliseconds.

12. A system according to any one of the preceding claims wherein the control unit is configured and operable to identify slowly developing current leakages.

13. A system according to any one of the preceding claims wherein the control unit is configured and operable to generate the output signals when the current leakage conditions occur a number of times that is greater than a predetermined number of times and within a predetermined duration of time, said predetermined number and time duration defined according to the operational boundaries of the residual current device.

14. A system according to claim 13 wherein the generation of the output signals depends on magnitude of the fault conditions as reflected by the time duration within a single or multiple AC cycles, in which the permissible time duration is exceeded.

15. A system according to any one of the preceding claims wherein the control unit is configured and operable to pre-detect leakage faults.

16. A system according to any one of the preceding claims wherein the control unit is configured and operable to emulate features associated with physical behavior of tripping mechanism of the residual current device to thereby ensure proper functioning thereof.

17. A system according to any one of the preceding claims wherein the control unit is configured and operable to detect a potential blindness condition of the residual current device associated with its operational boundaries to thereby ensure overall safety of the system.

18. A system according to any one of the preceding claims configured and operable for use in detection of DC current leakages in the electric power supply of a charge spot for charging electric vehicles.

19. A system according to claim 18 wherein the control unit is configured to generate data indicative of the pre-detection of leakage events, thereby enabling to interrupt a charging session of the charge spot.

20. A system according to claim 18 or 19 wherein the control unit is configured and operable to modify a charging profile of the charge spot based on the indication signals received from the analyzing unit and processing unit.

21. A system according to any one of claims 18 to 20 wherein the control unit is configured and operable to carry out preventive actions responsive to current leakage fault indications, comprising one or more of the following:

generate signals to modify a charging profile of the charge spot;

generate signals to disconnect the electric power supplied by the charging spot by changing a state of a controllable switching device of the charge spot; and

generate signals for tripping the residual current device.

22. A charge spot for charging batteries of electric vehicles, the charge spot being configured for connecting to an electric power supply provided through a residual current device, and to a charger unit connectable to a battery pack, and comprising a device for detecting current leakage conditions in the electrical power supply, said device for detecting current leakage conditions comprising:

a sensing unit coupled to the electric power supply and configured and operable to measure residual currents in the electrical power supply and produce measured signals indicative thereof; and

a control unit comprising:

an analyzing unit configured and operable to receive and process the measured signals from the sensing unit, identify that amplitude of the measured signals is greater than a predetermined permissible amplitude and responsively generate indication signals indicative of current leakage conditions; and

a processing unit configured and operable to determine a time duration of the current leakage conditions based on the indication signals from the analyzing unit, identify that the time duration exceeds a predetermined permissible time and responsively generate output signals corresponding to leakage fault indications,

said predetermined permissible amplitude and time duration are defined according to operational boundaries of the residual current device.

23. A charge spot according to claim 22, wherein said control unit is installed with reference data indicative of the operational boundaries of the residual current device.

24. A charge spot according to claim 22 or 23, wherein the analyzing unit is configured and operable to identify that the amplitude of the measured leakage current is greater than a preset threshold value and responsively generate the indication signals, and wherein the processing unit is configured and operable to adjust the threshold value according to the current leakage conditions to be detected.

25. A charge spot according to any one of claims 22 to 24, wherein the analyzing unit is configured and operable identify that the amplitude of the measured leakage current is greater or equal to 6 mA and responsively generate the indication signals, and wherein the predetermined permissible time period is equivalent to a 150 degrees duration of a time cycle of the electrical power supply.

26. A charge spot according to any one of claims 22 to 25, wherein said control unit is configured and operable to carry out the following actions responsive to current leakage fault indications:

generate signals to modify a charging profile of the charge spot;

generate signals for tripping the residual current device.