DE102013200803A1 - Device for protecting AC supply against direct current fault current e.g. smooth direct current, has fault current generator coupled to circuit breaker and sensing unit and generating change current dependant on detection of fault current - Google Patents

Abstract

The device (2) has an earth-leakage circuit breaker (10) changing fault current. A sensing unit (12) detects direct current (DC) fault current. A fault current generator (13) is coupled to the earth-leakage circuit breaker and the sensing unit and generates change fault current dependant on the detection of the DC fault current. The sensing unit comprises a sum current transformer (14) for detecting the DC fault current. The fault current generator comprises an evaluation logic unit (16) for evaluation of a signal from the sensing unit. An independent claim is also included for a method for protecting an AC supply against DC fault current.

Description

The invention relates to a device and a method for protection against DC residual currents.

Residual current protection circuits are known in different versions. DE 28 51 381 C2 discloses, for example, a residual current protection circuit for direct and / or alternating current with a summation current transformer which is connected to a trigger, an alternating current source which generates a bias of the summation current transformer with a frequency deviating from the mains frequency, and a test circuit which generates a test current from the Mains voltage is derived.

For devices that cause smooth DC residual currents or fault currents with small residual ripple in the event of a fault, commonly used residual current circuit breakers of the so-called type A, which respond to alternating current and pulsating direct current, do not respond. An example is DC charging columns whose power section includes rectifiers that can produce smooth DC residual currents in the event of a fault that are not shut down by Type A residual current circuit breakers. For protection against fault currents, all-current sensitive residual current circuit breakers of the so-called type B are used for electrical installation in such devices. However, type B residual current circuit breakers are considerably more expensive than Type A residual current circuit breakers.

The invention has for its object to provide an improved device and an improved method for protection against DC residual currents.

The object is achieved with respect to the device by the features of claim 1 and in terms of the method by the features of claim 7.

Advantageous embodiments of the invention are the subject of the dependent claims.

An inventive apparatus for protection against DC residual currents comprises a residual current circuit breaker responsive to AC residual current, a sensor unit for detecting a DC residual current and a fault current generator coupled to the residual current circuit breaker and to the sensor unit for generating a DC fault current dependent generation of an AC fault current responsive to the residual current circuit breaker.

A DC residual current is understood here to mean a fault current which is a smooth DC current or a DC current with little residual ripple. An AC residual current is understood to mean a fault current which is an alternating current.

The invention makes it possible to use a residual current circuit breaker responding to AC residual current to protect against a DC residual current by superimposing a DC residual current on an AC fault current to which the residual current circuit breaker responds. In particular, lower cost type A residual current circuit breakers may be used instead of type B residual current circuit breakers for DC fault current protection. Thus, the invention advantageously makes it possible, on the one hand, to reduce costs in the protection against DC residual currents and, on the other hand, to increase the safety of devices in an installation with residual current circuit breakers that respond only to AC residual current.

A preferred embodiment of the invention provides that the sensor unit comprises a summation current transformer for detecting the DC residual current.

Summation current transformers have proven themselves for fault current detection in residual current circuit breakers and are therefore advantageous for detecting DC residual currents.

A further embodiment of the invention provides that the fault current generator comprises an evaluation logic unit for evaluating a sensor signal of the sensor unit and for generating a triggering signal for the generation of the AC error current as a function of the result of the evaluation.

By means of the evaluation logic unit, a trigger signal can advantageously be generated as a function of the signal strength of the sensor signal output by the sensor unit, and a response threshold for the generation of the AC error current can thereby be set.

A further embodiment of the invention provides that the fault current generator comprises an AC circuit member for generating the AC residual current, wherein the AC circuit member comprises a trigger switch, which allows the generation of the AC residual current in the closed state and prevents the generation of the AC residual current in the open state.

In this way, can be generated by closing the trigger switch in a simple manner by means of the AC circuit element of the AC residual current.

In this case, the AC circuit member preferably connects an outer conductor and either one Functional grounding or a protective grounding of an AC power supply connected to the residual current circuit breaker.

This advantageously makes it possible to impress the AC residual current in the functional grounding or protective grounding of an AC power supply and thereby reliably and quickly trip the residual current circuit breaker.

In the method according to the invention for protection against DC residual currents by means of a residual current circuit breaker responding to AC residual current, a DC fault current is detected by means of a sensor unit and generated by means of a fault current generator a AC error current responsive to the residual current circuit breaker when the DC residual current detected by the sensor unit exceeds the threshold.

Thus, the method according to the invention makes it possible to use a fault current circuit breaker which responds to alternating fault current with the advantages already mentioned above for protection against DC fault currents.

A preferred embodiment of the method provides that, in addition to the generation of an AC fault current, a DC component causing the DC residual current is switched off when the DC residual current detected by the sensor unit exceeds the threshold.

As a result, not only the fault current circuit breaker is triggered at a detected DC fault current, but advantageously also switched off the cause of the DC residual current.

Corresponding to the above-mentioned embodiments of devices for protection against DC residual currents, embodiments of the method provide that the AC residual current is preferably generated between an outer conductor and either a functional ground or a protective ground by an AC power supply connected to the residual current circuit breaker.

A further embodiment of the method provides that a threshold for the DC residual current is set, which is below a threshold for a malfunction of the residual current circuit breaker. The threshold for the DC residual current is preferably at most 6 mA.

As a result, the response threshold is advantageously dimensioned so small that the sensitivity of Type A residual current circuit breakers is not impaired.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they will be achieved, will become clearer and more clearly understood in connection with the following description of exemplary embodiments, which will be described in detail in conjunction with the drawings. Showing:

1 schematically a first embodiment of a device for protection against a DC residual current in a charging station, and

2 schematically a second embodiment of a device for protection against a DC residual current in a charging station.

Corresponding parts are provided in the figures with the same reference numerals.

1 shows a DC charging station 1 with a first embodiment of a device 2 for protection against DC residual currents.

The DC charging station 1 has a power unit 3 connected to an AC power supply. The AC power supply is three-phase and has three outer conductors 4 . 5 . 6 , a neutral conductor 7 , as well as a protective earth 9 and / or a functional grounding 8th on. The power section 3 includes rectifiers not shown in detail, which can produce smooth DC residual currents in case of failure.

The device 2 for protection against DC residual currents includes a residual current circuit breaker responsive to AC residual current 10 of type A, in a building installation 11 arranged and to the outer conductor 4 . 5 . 6 and the neutral conductor 7 the AC power supply is connected. Furthermore, the device comprises 2 a sensor unit 12 for detecting DC residual currents and one to the sensor unit 12 coupled fault current generator 13 for the generation of a fault current protection switch depending on the detection of a DC fault current 10 responsive AC error current. The sensor unit 12 and the fault current generator 13 are in the DC charging station 1 arranged.

The sensor unit 12 comprises a DC-capable summation current transformer 14 who with the outer conductors 4 . 5 . 6 and the neutral conductor 7 the AC power supply is connected, and a signal conditioning unit 15 ,

The fault current generator 13 includes an evaluation logic unit 16 , a driver 17 and a AC circuit element 18 with a trigger switch 19 , The AC circuit member 18 connects an outer conductor 4 . 5 . 6 and functional grounding 8th , for example via a resistor, with each other. The trigger switch 19 is open in error-free case.

The device 2 for protection against DC residual currents further includes a DC test circuit 22 with a supply voltage 20 , a button 21 and a test circuit resistor 23 , By pressing the button 21 is a test DC current to verify the DC residual current detection and tripping of the residual current circuit breaker 10 through the device 2 generated, ie by means of the DC test circuit 22 can be activated by pressing the button 21 the functionality of the device 2 be checked. The test direct current is the signal conditioning unit 15 fed. In normal operation of the device 2 is the button 21 open.

A DC residual current is by means of the summation current transformer 14 detected and converted into a voltage proportional to the DC fault current. This voltage signal is the signal conditioning unit 15 supplied, processed by it and the evaluation logic unit 16 fed. When the DC _{residual current} exceeds a threshold _IΔN , the evaluation _{logic unit} generates 16 a trigger signal to the driver 17 and the power section 3 the DC charging station 1 is supplied. The threshold I _ΔN is chosen so small that the sensitivity of the residual current circuit breaker 10 is not affected. Preferably, a response threshold I _{ΔN is} selected which does not exceed 6 mA.

The driver 17 closes after the trigger signal the trigger switch 19 of the AC circuit member 18 which generates thereon an AC error current to which the residual current circuit breaker 10 responds. In the power section 3 the electrical component causing the DC fault current is switched off in response to the trip signal.

2 shows a DC charging station 1 with a second embodiment of a device 2 for protection against DC residual currents. The second embodiment differs from that in FIG 1 illustrated first embodiment only in that the AC circuit member 18 an outer conductor 4 . 5 . 6 and the protective earth 9 the AC power supply connects.

While the invention has been further illustrated and described in detail by way of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 2851381 C2 [0002]

Claims (12)

Contraption ( 2 ) for protection against DC residual currents, comprising - a residual current circuit breaker responsive to AC residual current ( 10 ), - a sensor unit ( 12 ) for detecting a DC residual current - and one to the residual current circuit breaker ( 10 ) and to the sensor unit ( 12 ) coupled fault current generator ( 13 ) for the detection of a DC fault current generation of the residual current circuit breaker ( 10 ) responsive AC fault current. Contraption ( 2 ) according to claim 1, characterized in that the sensor unit ( 12 ) a summation current transformer ( 14 ) for detecting a DC residual current. Contraption ( 2 ) according to one of the preceding claims, characterized in that the fault current generator ( 13 ) an evaluation logic unit ( 16 ) for evaluating a sensor signal of the sensor unit ( 12 ) and for generating a trigger signal for the generation of the AC error current as a function of the result of the evaluation. Contraption ( 2 ) according to one of the preceding claims, characterized in that the fault current generator ( 13 ) an AC circuit element ( 18 ) for generating the AC residual current, wherein the AC circuit member ( 18 ) a trigger switch ( 19 ), which allows the generation of the AC residual current in the closed state and prevents the generation of the AC residual current in the open state. Contraption ( 2 ) according to claim 4, characterized in that the AC circuit member ( 18 ) a functional grounding ( 8th ) and an outer conductor ( 4 . 5 . 6 ) one with the residual current circuit breaker ( 10 ) connected AC power supply. Contraption ( 2 ) according to claim 4, characterized in that the AC circuit member ( 18 ) a protective earth ( 9 ) and an outer conductor ( 4 . 5 . 6 ) one with the residual current circuit breaker ( 10 ) connected AC power supply. Method for protection against DC residual currents by means of a residual current circuit breaker which responds to an alternating error current ( 10 ), wherein - a threshold for the DC residual current is specified, - the DC residual current by means of a sensor unit ( 12 ), and - by means of a fault current generator ( 13 ) the residual current circuit breaker ( 10 ) is generated when the fault of the sensor unit ( 12 ) detected DC residual current exceeds the threshold. Method according to Claim 7, characterized in that, in addition to the generation of an AC fault current, an electrical component causing the DC residual current is switched off when the voltage supplied by the sensor unit ( 12 ) detected DC residual current exceeds the threshold. A method according to claim 7 or 8, characterized in that the AC error current between a functional grounding ( 8th ) and an outsider ( 4 . 5 . 6 ) by one with the residual current circuit breaker ( 10 ) connected AC power supply is generated. A method according to claim 7 or 8, characterized in that the AC error current between a protective ground ( 9 ) and an outsider ( 4 . 5 . 6 ) by one with the residual current circuit breaker ( 10 ) connected AC power supply is generated. Method according to one of claims 7 to 10, characterized in that a threshold for the DC residual current is set below a threshold for a malfunction of the residual current circuit breaker ( 10 ) lies. A method according to claim 11, characterized in that the threshold for the DC residual current is at most 6 mA.

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