METHODS AND ELECTRIC CIRCUIT ARRANGEMENTS FOR PROTECTION OF METALLIC COMPONENTS FROM CORROSION VIA STRAY CURRENTS

Abstract

Methods and electric circuit arrangements for protecting metallic components in an electrolytic medium from corrosion due to direct-current (DC) stray current (Is) from a power supply system. The DC stray current may be jointly registered as a total sum current across all active conductors together with the protective conductor of the power supply system by a DC total differential-current sensor. Alternatively, a combined DC differential-current sensor is switchable by a switching device, a differential current being registered across all active conductors or the DC stray current being registered as a total differential current across all active conductors and the protective conductor. Alternatively, a differential current may be registered across all active conductors by a DC current sensor at the protective conductor and the DC stray current computed by forming differences of the differential current registered by the differential-current transformer and of the protective conductor registered by the DC current sensor.

Claims

1. A method for protecting metal components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), characterized in that the DC stray current (Is) is jointly registered as a total differential current (32) across all active conductors (6) together with the protective conductor (8) of the power supply system by a DC total-differential-current sensor (30).

2. The method according to claim 1, characterized in that the DC stray current (Is) is registered in a highly sensitive manner at a resolution of less than 1 mA.

3. A method for protecting metallic components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), characterized in that a combined DC differential-current sensor (40) is configured so as to be switchable by means of switching device (42), a differential current being detected across all active conductors (6) of the power supply system (4) in a first switch setting (S1) and the DC differential current (Is) being registered as a total differential current across all active conductors (6) and the protective conductor (8) of the power supply system (4) in a second switch setting (S2).

4. A method for protecting metallic components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), the method comprising the following steps: registering a differential current across all active conductors (6) of the power supply system (4) by means of a differential-current transformer (20), characterized in that a protective-conductor current (52) is registered by means of a separate DC current sensor (50) disposed exclusively at the protective conductor (8) and the DC stray current (Is) is computed via forming difference of the differential current registered by the differential-current transformer (20) and of the protective-conductor current (52) registered by the separate DC current transformer (50).

5. The method according to claim 1, characterized by registering an exceedance of a settable DC stray-current threshold value via the DC stray current (Is) and signaling this exceedance.

6. An electric circuit arrangement for protecting metallic components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), characterized by a DC total differential-current sensor (30) which jointly registers the DC stray current (Is) as a total differential current (32) across all active conductors (6) together with the protective conductor (8) of the power supply system (4).

7. The electric circuit arrangement according to claim 6, characterized in that the DC total differential-current sensor (30) is configured to be highly sensitive for a resolution of less than 1 mA.

8. An electric circuit arrangement for protection of metallic components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), characterized by a combined DC differential-current sensor (40) which is configured to be switchable by means of a switching device (42), the combined DC differential-current sensor (40) registering a differential current across all active conductors (6) of the power supply system (4) in a first switch setting (S1) and the DC stray current (Is) being registered as a total differential current across all active conductors (6) and the protective conductor (8) of the power supply system (4) in a second switch setting (S2).

9. An electric circuit arrangement for protection of metallic components (14) in an electrolytic medium (16) from corrosion as a consequence of a DC stray current (Is) from a power supply system (4), the electric circuit arrangement having a differential-current transformer (20), which registers a differential current across all active conductors (6) of the power supply system (4), characterized by a separate DC current sensor (50) which is disposed exclusively at the protective conductor (8) and registers a protective-conductor current (52), and having a computing unit (24), which is configured for computing the DC stray current (Is) by forming a difference of the differential current registered by the differential-current transformer (20) and of the protective-conductor current (52) registered by the separate DC current sensor (50).

10. The electric circuit arrangement according to claim 6, characterized by a computing unit (24), which is configured for identifying an exceedance of a settable stray-current threshold value by the DC stray current (Is), and a signaling device (34), which signals the exceedance.

11. The method according to claim 2, characterized by registering an exceedance of a settable DC stray-current threshold value via the DC stray current (Is) and signaling this exceedance.

12. The method according to claim 3, characterized by registering an exceedance of a settable DC stray-current threshold value via the DC stray current (Is) and signaling this exceedance.

13. The method according to claim 4, characterized by registering an exceedance of a settable DC stray-current threshold value via the DC stray current (Is) and signaling this exceedance.

14. The electric circuit arrangement according to claim 7, characterized by a computing unit (24), which is configured for identifying an exceedance of a settable stray-current threshold value by the DC stray current (Is), and a signaling device (34), which signals the exceedance.

15. The electric circuit arrangement according to claim 8, characterized by a computing unit (24), which is configured for identifying an exceedance of a settable stray-current threshold value by the DC stray current (Is), and a signaling device (34), which signals the exceedance.

16. The electric circuit arrangement according to claim 9, characterized by a computing unit (24), which is configured for identifying an exceedance of a settable stray-current threshold value by the DC stray current (Is), and a signaling device (34), which signals the exceedance.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Further advantageous embodiments are derived from the following description and drawings, which describe preferred embodiments of the invention by means of examples.

[0042] FIG. 1 shows a differential-current measurement for determining a fault current according to the state of the art;

[0043] FIG. 2 shows a DC total differential-current measurement according to the invention;

[0044] FIG. 3 shows a combined DC differential-current measurement according to the invention; and

[0045] FIG. 4 shows a separate DC current measurement according to the invention.

DETAILED DESCRIPTION

[0046] FIG. 1 shows a differential-current measurement according to the state of the art for determining a DC fault/leakage current If in the example of a power supply system 4 deemed a critical installation 2 and having a charging station 10. Power supply system 4 is connected to an electric vehicle 9 via two active conductors 6 and protective conductor 8 on the DC side.

[0047] For monitoring and determining DC fault/leakage current If, a differential-current transformer 20 is provided via which (only) active conductors 6 are guided as stipulated by regulations, whereas protective conductor 8 is guided past differential-current transformer 20 on the outside.

[0048] Consequently, DC fault/leakage current If which flows in the electric vehicle via an insulation fault Rf1 to conductible parts connected to protective conductor 8 (fault to frame) is registered. (a DC stray current (FIG. 2) is not observed in FIG. 1)

[0049] In a first alternative solution, a DC total differential-current measurement according to the invention in the case of a possible DC stray current Is is shown in FIG. 2, DC stray current Is leaking in the electric vehicle via an electrolytic medium 16 (ferroconcrete) of a building 12 (parking facility), caused by an insulation fault Rf2.

[0050] Additionally to differential-current transformer 20 installed as per regulation as a fault-protection measure, a DC total differential-current sensor 30 preferably designed as a toroidal core transformer is connected in such a manner that the currents of all active conductors 6 and the current flowing in protective conductor 8 are registered jointly as total differential current 32.

[0051] Since protective conductor 8 is measured along with active conductors 6 using DC total differential-current sensor 30, DC fault/leakage current If cancels itself out, meaning only DC stray current Is remains as total differential current 32 and can be evaluated in a computing 24 regarding the exceedance of a settable DC stray-current threshold.

[0052] Consequently, only corrosion-effective stray current Is caused by insulation fault Rf2 is registered, stray current Is flowing in electric vehicle 9 past electrically conductive parts connected to protective conductor 8 directly via electrolytic ferroconcrete foundation 16 of parking facility 12.

[0053] In differential-current transformer 20 connected as stipulated by regulations for fault current measuring, however, DC stray current Is flowing via electrolytic ferroconcrete 16 is registered in addition to DC fault/leakage current If, though it cannot be distinguished from DC fault/leakage current If or be resolved for measurement reasons since DC stray current Is to be presumed smaller by a factor of at least 10 than DC fault/leakage current If in the charging current application described here.

[0054] FIG. 3 shows a combined DC differential-current measurement according to the invention in a second alternative solution, having a combined DC differential-current sensor 40 which is preferably configured as a toroidal core transformer and is designed to be switchable by means of a switching device 42.

[0055] As a function of switch settings S1, S2, either only active conductors 6 (switch setting S1) or active conductors 6 and protective conductor 8 (switch setting S2 are guided via combined DC differential-current sensor 40.

[0056] In switch setting S1, combined DC differential-current sensor 40 is effective as a differential-current transformer 20 (FIG. 1) which registers the sum of all currents caused by insulation faults Rf1 and Rf2 as differential current 22.

[0057] In switch setting S2, only DC stray current Is is registered as total differential current 32 in function of DC total differential-current sensor 30 (FIG. 2).

[0058] Since switch device 42 switches protective conductor 8, this solution can prove to be normatively critical. Switch device 42 has to switch protective conductor 8 without interruption; requirements made to the low impedance of the protective-conductor loop impedance must not be exceeded at any point and the shut-off time of an overcurrent protective device must not be negatively impacted by the properties of switch device 42.

[0059] FIG. 4 shows a separate DC current measurement in a third alternative solution, having a separate DC current sensor 50, preferably configured as a toroidal core transformer.

[0060] DC current sensor 50 encircles only protective conductor 8 and thus registers protective-conductor current 52 which is caused by insulation fault Rf1 and corresponds to DC fault/leakage current If.

[0061] Differential-current transformer 20 registers—in the manner installed only via active conductors 6 as stipulated by regulations-differential current 20 which corresponds to the sum of all currents caused by insulation faults Rf1 and Rf2, i.e., DC fault/leakage current If and DC stray current Is.

[0062] By forming the differences of differential current 20 and protective-conductor current 52, corrosion-effective DC stray current Is is computed in computing 24.

[0063] An exceedance of a settable DC stray-current threshold via DC stray current Is is identified in computing unit 24 and signaled by a signaling device 34.