Method and circuit arrangement for protecting metal parts from corrosion caused by stray currents

Abstract

This invention relates to a method and circuit arrangement for protecting metallic components in an electrolytic medium from corrosion caused by DC stray currents from a power supply system. In a first alternative, the DC stray current is recorded by a total DC differential current sensor as the sum of currents on all active conductors and the protective conductor of the power supply system. In a second alternative, a combined DC differential current sensor is configured to be switchable via a switching device to record differential currents on all active conductors of the power supply system, or to record the DC stray current as the total differential current on all active conductors and the protective conductor of the power supply system. In a third alternative, the differential currents on all active conductors of the power supply system are recorded by a separate DC current sensor located only on the protective conductor, and the DC stray current is calculated by forming the difference between the differential current recorded by the differential current transformer and the protective conductor current recorded by the separate DC current sensor.

Description

Technical Field

[0001] The present invention relates to a method and circuit arrangement for protecting metal components in an electrolytic medium from corrosion caused by DC stray currents from a power supply system. Background Technology

[0002] Unprotected metal components in an electrolytic environment, such as steel inserts in concrete foundations or buried metal equipment, can corrode due to DC stray currents from the power supply system. In reinforced concrete buildings, corrosion at the reinforcing steel can lead to static decay or leaks in buried pipes.

[0003] The negative static effects on a building, and in some cases even dangerous mitigating effects, are caused not only by DC stray currents in the ampere range, but also by DC stray currents as small as milliamperes, if these DC stray currents flow continuously over a long period of time and are mostly unnoticed.

[0004] A suitable means of preventing DC stray currents directly at the power source of a power supply facility is to install a power system (IT system; French: isoléterre) with an ungrounded network type and to ensure a particularly high level of insulation resistance to ground, while also monitoring the insulation condition composition through standardized insulation monitoring equipment (IMD).

[0005] In applications where this is not permissible and a grounding network type is used, the standard DIN EN 50162 sets forth requirements for considering and preventing corrosion caused by DC stray currents, and recommends various measures—such as the use of corrosion protection equipment, corrosion-resistant materials, or coating methods for insulating metal conductors from the electrolytic environment.

[0006] The standard DIN EN 50162 references known applications where negative corrosion due to DC stray currents has occurred, such as in the rail transport or electroplating industries.

[0007] What has been overlooked or given too little consideration is the increasing prevalence of DC power systems, particularly in the industrial sector and in the field of charging station infrastructure for electric vehicles (EV charging stations).

[0008] This raises the question of the long-term impact of a dramatic increase in the number of electric vehicles connected to charging stations in parking facilities, where these charging stations dissipate stray DC currents of up to 1 mA through the reinforced concrete foundations of the parking facilities via aging and pollution effects. In this context, instead of DC fault current circuits or DC leakage current circuits guiding through closed protective conductors, conductive current paths are observed in electrolytic building structures. Similar scenarios with negative impacts on building statics will also be considered for the increasing use of DC-powered machinery, such as production robots.

[0009] To date, in some applications, the corrosion of metal components in electrolytic media by DC stray currents has only been studied in terms of the negative corrosive effects of DC stray currents on these components. Therefore, the recommendations of standard DIN EN 50162 have been applied to the rail transport or electroplating industries.

[0010] For facilities at potential corrosion risks, the presence and magnitude of DC stray currents from power supply equipment have remained unsatisfactory in assessing until now whether and at what magnitude they enter the surrounding electrolyte and cause corrosion to metal components. Metered monitoring and assessment of DC stray currents are essential for critical facilities to implement appropriate corrosion protection measures under specific operating conditions.

[0011] In key facilities observed, for example, innovative electrical equipment will be widely available in the future (e.g., DC-powered machines, especially robots, in industrial facilities), or it is speculated that DC stray currents will flow permanently and thus effectively flow into building infrastructure after insulation degradation, making the danger of static degradation of buildings possible (e.g., EV charging stations in parking facilities). Summary of the Invention

[0012] Therefore, the object of the present invention is to design a method and apparatus for protecting metal components in an electrolytic environment from corrosion caused by DC stray current.

[0013] In the first alternative, this objective is achieved by recording the DC stray currents together as the sum of the currents on all active conductors and protective conductors of the power system using a DC total differential current sensor.

[0014] The basic idea of ​​this invention includes installing a DC differential current monitoring device with the highest possible sensitivity in facilities at risk of corrosion, which can distinguish and assess DC stray current from fault current and unavoidable leakage current.

[0015] For measurement purposes, the indicative factor is, on the one hand, the difference between an existing differential current transformer (residual current device or residual current monitor (RCM)) used to identify fault and / or leakage current flowing through the protective conductor, and on the other hand, a DC differential current sensor installed according to the present invention used to identify DC stray current flowing through the surrounding electrolytic medium.

[0016] Even though the differential current transformer is designed as a DC measuring current transformer to identify DC fault currents to ensure the functionality of Type A (RCD) residual current protection devices, the fact that a 5mA DC differential current can be determined by measurement does not mean that the recorded 5mA DC differential current is also a 5mA DC stray current that causes corrosion effects. If this 5mA DC differential current actually flows only through the insulated protective conductor and not through the electrolytic environment into the center grounding point of the power supply facility, no corrosion effect is expected.

[0017] The differential current measurement techniques used to date cannot distinguish between DC fault and / or leakage currents in a protective conductor system designed in an insulated manner and DC stray currents in the electrolytic medium, because all current portions that do not flow through the active conductor are recorded as differential currents through differential current transformers installed according to the prior art. Therefore, in addition to DC fault and / or leakage currents, DC stray currents leaking through the electrolytic environment are also recorded.

[0018] The ideas described above also apply to the second and third alternatives.

[0019] In the first alternative, the invention employs an additional DC total differential current sensor—in most cases, in addition to the differential current transformer already installed as a fault current measuring device—which, unlike what is known in the prior art which measures differential current only through active conductors and compares with common installation instructions, measures differential current together on all active and protective conductors.

[0020] Therefore, the DC total differential current sensor only records the DC stray current as the total differential current. The DC stray current leaks into the electrolytic medium and is suitable for causing corrosion in metal components (e.g., building infrastructure).

[0021] The dynamic range of a DC total differential current sensor does not need to be configured for much larger expected DC fault and leakage currents, thus allowing for precise resolution of particularly small expected DC stray currents.

[0022] In particular, DC stray current has high sensitivity with a resolution of less than 1 mA.

[0023] A DC total differential current sensor can have a limited measurement range (dynamic range) that is advantageous for high resolution because the fault / leakage current, which is much larger than the DC stray current, is self-compensated by including a protective conductor in the total differential current. The remaining total differential current corresponds to the DC stray current to be detected, and the shared DC total differential current sensor can be adjusted in terms of measurement range and resolution to accommodate this DC stray current. Therefore, small DC stray currents of less than 1 mA can also be identified.

[0024] In the second alternative, this objective is achieved by a combined DC differential current sensor designed to be switchable via a switching device. In a first switching setting, differential currents on all active conductors of the power supply facility are recorded, while in a second switching setting, DC stray currents are recorded as the total differential current on all active and protective conductors of the power system.

[0025] In this second alternative, only one, namely a combined, DC differential current sensor, is required, which operates according to a switch setting, acts as a typical differential current transformer used in the prior art and (only) includes the active conductors of the power supply facility (first switch setting), or records the total differential current on all active conductors of the power supply facility and (also) the protective conductors (second switch setting)—acting as a DC total differential current sensor as in the first alternative.

[0026] However, compared to the DC total differential current sensor described in the first alternative, the dynamic range of the combined DC differential current sensor must also be designed for much larger expected DC fault and leakage currents, and therefore can only identify the particularly small expected DC stray currents with a tiny resolution.

[0027] In the third alternative, this objective is achieved by having a differential current transformer record the differential current on all active conductors of the power supply facility, a separate DC current sensor recorded the protective conductor current by means of a separate DC current sensor located only on the protective conductor, and a DC stray current calculated by forming the difference between the differential current recorded by the differential current transformer and the protective conductor current recorded by the separate DC current transformer.

[0028] In this third alternative, it is assumed that a differential current transformer installed according to existing technology is used to identify fault currents. This differential current transformer records all currents as differential currents, and the circuit for the differential currents is not closed solely through the active conductors of the power supply facility; therefore, in addition to DC fault / leakage currents, DC stray currents are also recorded.

[0029] In contrast, the additionally installed separate DC current sensor only records the DC fault / leakage current as an absolute current (protective conductor current).

[0030] The DC stray current can be determined in the calculation unit by forming the difference between the differential current recorded by the differential current transformer and the protective conductor current recorded by the DC current sensor.

[0031] In the same situation, the dynamic range of the differential current transformer and the dynamic range of the individual DC current sensor must be designed for the much larger expected fault and leakage currents, which becomes apparent in an unfavorable manner compared to the first alternative.

[0032] In another implementation, an excess of a settable DC stray current threshold is identified by DC stray current, and the excess is signaled.

[0033] If an excess of the DC stray current threshold is established in the calculation unit, the signaling device signals, for example, through field notification or notification distributed via the interface, that the DC stray current that is harmful to corrosion has been identified.

[0034] In this context, the DC stray current threshold can be adjusted to suit the critical facilities being monitored, particularly to suit the conductivity of the electrolyte and the stray current corrosion susceptibility of the installed metal components.

[0035] In the three circuit arrangements according to the present invention, the corresponding method steps of the three alternative schemes are implemented by utilizing the corresponding structural features.

[0036] Therefore, the technical effects and advantages obtained by using the method claimed are applied in the same way to the circuit layout.

[0037] Therefore, three alternative arrangements for the circuit layout to be protected are proposed, each corresponding to the method to be protected, but different from each other, especially from the existing technology for the arrangement and implementation of differential current measurement technology.

[0038] In this context, the first alternative is characterized by a DC total differential current sensor; the second solution is characterized by a switchable combined DC differential current sensor with switching devices; and the third alternative is characterized by a separate DC current sensor that interacts with the differential in the computing unit.

[0039] In order to distinguish between DC fault / leakage current and corrosion-induced DC stray current, the wiring of the DC current sensor technology according to the present invention is implemented in a manner that deviates from and is the opposite of that described in the prior art. In particular, by including the protective conductor in the record passing through the differential current transformer, which is even described as faulty according to the prior art. Attached Figure Description

[0040] Further advantageous embodiments will be derived from the following description and figures, which illustrate preferred embodiments of the invention through examples.

[0041] Figure 1 A differential current measuring device for determining fault current according to the prior art is shown;

[0042] Figure 2 A DC total differential current measuring device according to the present invention is shown;

[0043] Figure 3 A combined DC differential current measuring device according to the present invention is shown; and

[0044] Figure 4 A separate DC current measuring device according to the present invention is shown. Detailed Implementation

[0045] Figure 1 A differential current measuring device for determining the DC fault / leakage current If, according to existing technology, is shown in an embodiment where the power system 4 is considered a critical facility 2 and has a charging station 10. The power system 4 is connected to the electric vehicle 9 via two active conductors 6 and a protective conductor 8 on the DC side.

[0046] To monitor and determine the DC fault / leakage current If, a differential current transformer 20 is provided through which the active conductor 6 is guided (only) in accordance with regulations, while the protective conductor 8 is guided on the outside through the differential current transformer 20.

[0047] Therefore, the DC fault / leakage current If flowing through the insulation fault Rf1 in the electric vehicle to the conductive components connected to the protective conductor 8 (fault to frame) was recorded. Figure 1 No DC stray current was observed. Figure 2 ))

[0048] In the first alternative, Figure 2 The diagram illustrates a DC total differential current measuring device according to the invention in the presence of a possible DC stray current Is, caused by an insulation fault Rf2, which leaks into the electric vehicle through the electrolytic medium 16 (reinforced concrete) of building 12 (parking facility).

[0049] In addition to the differential current transformer 20 installed in accordance with regulations as a fault protection measure, the DC total differential current sensor 30, preferably designed as a toroidal core transformer, is connected in such a way that the currents of all active conductors 6 and the currents flowing in the protective conductor 8 are recorded together as the total differential current 32.

[0050] Since the DC total differential current sensor 30 is used together with the active conductor 6 to measure the protective conductor 8, the DC fault / leakage current If cancels itself out, which means that only the DC stray current Is remains as the total differential current 32, and can be evaluated in the calculation unit 24 regarding the excess amount of the settable DC stray current threshold.

[0051] Therefore, only the stray current Is caused by the corrosion of the insulation fault Rf2 is recorded. The stray current Is flows through the electric vehicle 9 through the electrolytic reinforced concrete foundation 16 of the parking facility 12 and is directly connected to the conductive parts of the protective conductor 8.

[0052] However, in the differential current transformer 20 connected in accordance with the regulations for fault current measurement, in addition to the DC fault / leakage current If, a DC stray current Is flowing through the electrolytic reinforced concrete 16 is also recorded, although it cannot be distinguished from the DC fault / leakage current If, or can be differentiated for measurement purposes, since in the charging current application described herein, the DC stray current Is is assumed to be at least 10 times smaller than the DC fault / leakage current If.

[0053] Figure 3 A combined DC differential current measuring device according to the invention is shown in a second alternative, which has a combined DC differential current sensor 40, which is preferably configured as a toroidal magnetic core transformer and is designed to be switched by a switching device 42.

[0054] Depending on the switch settings S1 and S2, the combined DC differential current sensor 40 can either guide the active conductor 6 (switch setting S1) or guide both the active conductor 6 and the protective conductor 8 (switch setting S2).

[0055] In switch setting S1, the combined DC differential current sensor 40 serves as the differential current transformer 20. Figure 1 It is effective, and it records the sum of all currents caused by insulation faults Rf1 and Rf2 as differential current 22.

[0056] In switch setting S2, the DC total differential current sensor 30 ( Figure 2 In the function of ), only the DC stray current Is is recorded as the total differential current 32.

[0057] Since switchgear 42 switches the protective conductor 8, this solution can be proven to be critical in terms of specifications. Switchgear 42 must switch the protective conductor 8 uninterruptedly; it must not exceed the low impedance requirement for the protective conductor loop impedance at any time, and the turn-off time of the overload current protection device must not be negatively affected by the characteristics of switchgear 42.

[0058] Figure 4 A separate DC current measuring device is shown in the third alternative, which has a separate DC current sensor 50, preferably configured as a toroidal magnetic core transformer.

[0059] The DC current sensor 50 surrounds only the protective conductor 8, thus recording the protective conductor current 52 caused by the insulation fault Rf1 and corresponding to the DC fault / leakage current If.

[0060] Differential current transformer 20—installed in accordance with regulations via only the active conductor 6—records differential current 20, which corresponds to the sum of all currents caused by insulation faults Rf1 and Rf2, namely the DC fault / leakage current If and the DC stray current Is.

[0061] The corrosion-effective DC stray current Is is calculated in calculation unit 24 by forming the difference between differential current 20 and protective conductor current 52.

[0062] In the calculation unit 24, the amount of excess of the settable DC stray current threshold is identified by the DC stray current Is, and the excess is notified by the signaling device 34.

Claims

1. A method for protecting metal parts (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), characterized in that the DC stray current (Is) is recorded jointly by a DC total differential current sensor (30) as a total differential current (32) over all active conductors (6) of the power supply system and a protective conductor (8).

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

3. A method for protecting metal parts (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), characterized in that a combined DC differential current sensor (40) is configured to be switchable by a switching device (42) to detect a differential current over all active conductors (6) of the power supply system (4) in a first switching setting (SI) and to record the DC stray current (Is) as a total differential current over all active conductors (6) of the power supply system (4) and a protective conductor (8) in a second switching setting (S2).

4. A method for protecting metal parts (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), the method comprising the steps of: - recording a differential current over all active conductors (6) of the power supply system (4) by a differential current transformer (20), characterized in that - a protective conductor current (52) is recorded by a separate DC current sensor (50) arranged only at the protective conductor (8), and - the DC stray current (Is) is calculated by forming a difference between the differential current recorded by the differential current transformer (20) and the protective conductor current (52) recorded by the separate DC current sensor (50).

5. The method according to any one of claims 1 to 4, characterized in that an exceedance of a settable DC stray current threshold value is recorded by the DC stray current (Is) and signaled.

6. A circuit arrangement for protecting metal parts (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), characterized in that a DC total differential current sensor (30) jointly records the DC stray current (Is) as a total differential current (32) over all active conductors (6) of the power supply system (4) and a protective conductor (8).

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

8. A circuit arrangement for protecting metal parts (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), characterized in that A combined DC differential current sensor (40) which is configured to be switchable by a switching device (42) in a first switching setting (S1) records the differential current on all active conductors (6) of the power supply system (4) and in a second switching setting (S2) the DC stray current (Is) is recorded as the total differential current on all active conductors (6) and the protective conductor (8) of the power supply system (4).

9. A circuit arrangement for protecting a metal component (14) in an electrolytic medium (16) from corrosion due to a DC stray current (Is) from a power supply system (4), The circuit arrangement has a differential current transformer (20) which records the differential current on all active conductors (6) of the power supply system (4), characterized in that a separate DC current sensor (50) which is arranged only on the protective conductor (8) and records a protective conductor current (52), and has a computing unit (24) which is configured to calculate the DC stray current (Is) by forming the difference between the differential current recorded by the differential current transformer (20) and the protective conductor current (52) recorded by the separate DC current sensor (50).

10. The circuit arrangement according to any one of claims 6 to 9, characterized in that a computing unit (24) which is configured for identifying an excess of a settable stray current threshold value by the DC stray current (Is), and a signaling device (34) which signals the excess.

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