Location of ground faults in a dc grid

Abstract

The invention relates to a method for locating a ground fault in a DC grid (1) which has access to a plurality of load areas (3, 4, 5). In the method, a time window is predefined and, after detection of a ground fault, the ground fault is associated with a load area (3, 4, 5) which has accessed the DC grid (1) within the time window before the ground fault was detected.

Description

Technical Field

[0001] This invention relates to a method for locating ground faults in a DC power grid accessible to multiple load areas. Background Technology

[0002] A DC grid that is insulated from ground potential or grounded through high impedance can continue to operate even with a ground fault in its DC voltage potential. The ground fault itself can be easily detected during operation by measuring and evaluating the voltage between the DC voltage potential of the DC grid and the ground potential. However, it is difficult to identify the load area connected to the DC grid where the ground fault has occurred. Nevertheless, identifying the load area where the ground fault has occurred is important in order to disconnect the faulty load area and eliminate the ground fault. To identify the faulty load area, for example, at the connection point between each load area and the DC grid, such as at the input of the switchgear, the so-called common-mode current (CMFC), i.e., the fault current, can be measured. This fault current is the sum of the currents in the two connecting lines of the main line connecting the load area to the DC grid. If one of the CFCs is not zero, this indicates that a ground fault has occurred in the relevant load area. For example, the CFC measurement can be performed permanently or manually by maintenance personnel. However, such a measurement is expensive in either case.

[0003] A method for locating ground faults in a fire protection system is known from DE 10 2017 108822 A1, wherein, upon or after a ground fault is identified by a ground fault identification module, a switching element is disconnected to isolate the connecting lines of one, several, or all connection points until at least the ground fault identification module can no longer identify a ground fault. Subsequently, the connecting lines are gradually reconnected for each connection point by closing the corresponding switching element. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an improved method for locating ground faults in a DC power grid accessible to multiple load areas.

[0005] According to the present invention, the above-mentioned technical problem is solved by a method having the features of claim 1, a DC power grid having the features of claim 14, and a DC power grid having the features of claim 15.

[0006] Advantageous designs of the present invention are the subject of the dependent claims.

[0007] In the method according to the invention for locating a ground fault in a DC power grid accessible to multiple load areas, a pre-defined time window is provided, and after a ground fault is detected, the ground fault is associated with a load area that was connected to the DC power grid within that time window prior to the detection of the ground fault. In other words, the ground fault is associated with a load area that, particularly prior to ground fault detection, was connected to the DC power grid for a time interval less than or equal to the pre-defined time window from which the ground fault was detected. Here and below, it is always assumed that the DC power grid is insulated from ground potential or grounded through a high impedance.

[0008] In other words, the method according to the invention correlates the detection of a ground fault in a DC power grid with the connection of a load area to the DC power grid to locate the load area where the ground fault occurred. The method is based on the consideration that if a ground fault is detected in the DC power grid immediately after the load area is connected, then it is clear that a ground fault already existed in the load area before the connection. To determine the load area, the method sets a pre-given time window to correlate the detection of the ground fault with the connection of the load area. The ground fault is associated with a load area that was connected to the DC power grid within the pre-given time window before the ground fault was detected. If no load area was connected to the DC power grid within the pre-given time window before the ground fault was detected, the ground fault is not associated with a load area, or the ground fault must be located in another way. The time window may be, for example, a pre-given duration of a few milliseconds. The method can be implemented very simply and with low overhead, and therefore also inexpensive, because only the time points of ground fault detection and load area connection must be evaluated. To detect the ground fault, only the voltage between the DC voltage potential of the DC power grid and the ground potential needs to be measured at a single location on the DC power grid.

[0009] In one design of the method, if multiple load areas are connected to the DC grid within a time window before a ground fault is detected, the ground fault is associated with the load area that was the last to be connected to the DC grid within that time window. This design of the method enables the location of ground faults even if two or more load areas are subsequently connected to the DC grid within a pre-given time window before a ground fault is detected.

[0010] In another design of the method, the load area associated with the ground fault is isolated from the DC power grid. Furthermore, it can be configured such that after isolating the load area from the DC power grid, it is checked whether a ground fault still exists in the DC power grid. If a ground fault still exists after isolating the load area from the DC power grid, then the association between the ground fault and the load area is severed, and the load area is reconnected to the DC power grid. This design of the method particularly enables the checking of the association between the ground fault and the load area. That is, if a ground fault always exists in the DC power grid after isolating the load area from the DC power grid, then it is clear that the ground fault is not in the load area, but elsewhere in the DC power grid, and thus the association between the ground fault and the load area may be incorrect.

[0011] In another design of the method, the evaluation unit stores the detection time point and time window of the ground fault, and for each access to the load area, it stores the access time point and the access association between the access time point and the access to the load area. Based on the stored data, the evaluation unit associates the ground fault with the load area. Here, the evaluation unit can be implemented independently, or it can be a control unit that controls the access to the load area, or it can be a ground fault monitoring unit configured to detect ground faults. If the evaluation unit is implemented independently or as a ground fault monitoring unit, then, for example, the control unit that controls the access to the load area reports each access time point and its access association to the evaluation unit. If the evaluation unit is implemented independently or as a control unit, then the ground fault is detected and reported to the evaluation unit, for example, by the ground fault monitoring unit.

[0012] In other words, in the design of the method mentioned above, the evaluation unit stores and evaluates the time points of access to the load area and detection of ground faults. Here, the evaluation unit can be advantageously implemented as a control unit that controls the access to the load area, or as a ground fault monitoring unit configured to detect ground faults, especially when such a unit is originally located in the DC power grid.

[0013] In an alternative design of the method, the DC grid has an access unit associated with each load area, through which the load areas can be connected to the DC grid. Each access unit stores a time window and, for each connection of the load area associated with the access unit, determines whether the connection was made within that time window before a ground fault was detected. For example, a ground fault monitoring unit detects the ground fault and reports it to each access unit, or each access unit is configured to detect ground faults independently.

[0014] In other words, instead of evaluating the access time points for all load areas, the aforementioned method is designed such that, for each load area, the corresponding access unit evaluates these time points individually. Additionally, the access unit can also independently detect ground faults in the DC power grid.

[0015] In another design of the method, after a ground fault is detected, all load areas are first isolated from the DC grid. Then, at different connection times, each load area is sequentially connected to the DC grid for a duration greater than the time window and not overlapping with the connection duration of other load areas. For each connection of a load area, it is checked whether a ground fault occurs within that time window after connection. This design of the method enables a systematic search for load areas where ground faults have occurred.

[0016] Corresponding to one design of the method according to the invention mentioned above, the first DC power grid according to the invention, which can be connected to multiple load areas, has an evaluation unit configured to store the detection time point of a ground fault, a pre-given time window, and for each connection of a load area, store the connection time point and the connection association between the connection time point and the connected load area, and associate the ground fault with a load area that was connected to the DC power grid within the time window before the ground fault was detected.

[0017] Corresponding to one design of the method according to the invention mentioned above, the second DC grid according to the invention, which can be connected to multiple load areas, has an access unit associated with each load area. The load area can be connected to the DC grid through the access unit, and the access unit is configured to store a pre-given time window and, for each connection of the load area associated with the access unit, determine whether the connection was made within the time window before a ground fault was detected. Attached Figure Description

[0018] The features, characteristics, advantages, and implementations of the present invention described above will become clearer and more readily understood in conjunction with the following detailed description of the embodiments in conjunction with the accompanying drawings.

[0019] The only accompanying drawing schematically shows a DC power grid 1 that can be connected to multiple load areas 3, 4, and 5. The DC power grid 1 is insulated from ground potential or grounded through a high impedance. Detailed Implementation

[0020] The DC power grid 1 has two main electrical lines 7 and 9, multiple access units 10 to 12, a control unit 13, a ground fault monitoring unit 15, and an evaluation unit 17.

[0021] The accompanying drawings exemplarily illustrate three load areas 3, 4, and 5. The first load area 3 and the second load area 4 each have converters 9 and 20 and motors 21 and 22, respectively. The third load area 5 has a converter 23, a switch and protection unit 25 for AC power, and an AC power grid 27, wherein the switch and protection unit 25 is connected between the AC power grid 27 and the converter 23. Each converter 19, 20, and 23 is connected to access units 10, 11, and 12.

[0022] The first main line 7 is at the first DC voltage potential of DC power grid 1. The second main line 9 is at the second DC voltage potential of DC power grid 1.

[0023] Each access unit 10, 11, 12 is associated with a load area 3, 4, 5, which can be connected to the DC power grid 1 through access switch units 10, 11, 12.

[0024] The access to load areas 3, 4, and 5 is controlled by control unit 13. For this purpose, access units 10, 11, and 12 can be controlled by control unit 13. Furthermore, control unit 13 is configured to report the access time point and the association between the access time point and the access to the load areas 3, 4, and 5 to evaluation unit 17 for each access to load areas 3, 4, and 5.

[0025] The ground fault monitoring unit 15 is configured to detect ground faults in the DC voltage potential of the DC power grid 1. For this purpose, the ground fault monitoring unit 15 is connected to each main line 7, 9 and is configured to measure the voltage between the ground potential and the DC voltage potential at the location of the main line 7, 9. Furthermore, the ground fault monitoring unit 15 is configured to report detected ground faults to the evaluation unit 17.

[0026] Evaluation unit 17 is configured to store the detection time of a ground fault, a pre-defined time window, and the access time and access association reported to evaluation unit 17 by control unit 13, and to associate the ground fault with load areas based on the stored data. Here, the ground fault is associated with load areas 3, 4, and 5 that were connected to DC power grid 1 within the time window prior to the detection of the ground fault. If no load areas 3, 4, or 5 were connected to DC power grid 1 within the time window prior to the detection of the ground fault, evaluation unit 17 does not associate the ground fault with load areas 3, 4, or 5. If multiple load areas 3, 4, and 5 were connected to DC power grid 1 within the time window prior to the detection of the ground fault, evaluation unit 17 associates the ground fault with the load area 3, 4, or 5 that was the last to be connected to DC power grid 1 within that time window. The time window, for example, is a pre-defined duration of a few milliseconds and is stored by evaluation unit 17.

[0027] The DC power grid 1 according to the present invention and the embodiment of the method according to the present invention described in the accompanying drawings can be modified in different ways to other implementation examples.

[0028] For example, it can be configured so that the access time points and access associations of load areas 3, 4, and 5 are reported to the evaluation unit 17 by access units 10, 11, and 12, rather than by control unit 13.

[0029] Furthermore, for example, it can be configured to disconnect load areas 3, 4, and 5 associated with the ground fault from the DC power grid 1 via access units 10, 11, and 12 associated with load areas 3, 4, and 5, and after disconnecting load areas 3, 4, and 5 from the DC power grid 1, check whether the ground fault still exists. If the ground fault still exists after disconnecting load areas 3, 4, and 5 from the DC power grid 1, then the association between the ground fault and load areas 3, 4, and 5 is canceled, and load areas 3, 4, and 5 are reconnected to the DC power grid.

[0030] Furthermore, in the event of a ground fault, the system can be configured such that, after a ground fault, all load areas 3, 4, and 5 are first disconnected from the DC power grid 1 through their connection units 10, 11, and 12. Then, the system systematically searches for faulty load areas 3, 4, and 5 by sequentially connecting them to the DC power grid 1 at different connection times, within a time window longer than the connection duration and not overlapping with the connection durations of other load areas 3, 4, and 5. For each connection of load areas 3, 4, and 5, the system checks whether a ground fault occurs within the time window following the connection.

[0031] Alternatively, instead of a separate evaluation unit 17, either the control unit 13 or the ground fault monitoring unit 15 can be configured as the evaluation unit 17. When the control unit 13 is configured as the evaluation unit 17, the ground fault monitoring unit 15 reports a ground fault to the control unit 13, and the control unit 13 is configured to check, in the presence of a ground fault, whether load areas 3, 4, and 5 were connected to the DC power grid 1 within a time window prior to the detection of the ground fault. When the ground fault monitoring unit 15 is configured as the evaluation unit 17, the control unit 13 or the access units 10, 11, and 12 report the access time and access association of load areas 3, 4, and 5 to the ground fault monitoring unit 15, and the ground fault monitoring unit 15 is configured to check, in the presence of a ground fault, whether load areas 3, 4, and 5 were connected to the DC power grid 1 within a time window prior to the detection of the ground fault.

[0032] Furthermore, instead of evaluation unit 17, it can be configured so that, in the presence of a ground fault, each access unit 10, 11, 12 automatically determines whether the load areas 3, 4, 5 associated with access units 10, 11, 12 were accessed within a time window prior to the detection of the ground fault. Here, each access unit 10, 11, 12 is configured to store the access time point and time window of the load areas 3, 4, 5 associated with access units 10, 11, 12, and, in the presence of a ground fault, check whether the access time point was within the time window prior to the detection of the ground fault. The ground fault monitoring unit 15 reports the ground fault to all access units 10, 11, 12, or each access unit 10, 11, 12 is configured to independently detect ground faults.

[0033] Although the invention has been described and illustrated in detail with reference to preferred embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variations therefrom without departing from the scope of protection of the invention.

Claims

1. A method for locating ground faults in a DC power grid (1), wherein multiple load areas (3, 4, 5) are connected to the DC power grid, wherein, -Pre-defined time window - And after a ground fault is detected, the ground fault is associated with the following load areas (3, 4, 5) that were connected to the DC power grid (1) within the time window prior to the detection of the ground fault, so that the location of the fault can be determined immediately after the fault occurs without additional switching operations. If multiple load areas (3, 4, 5) are connected to the DC power grid (1) within the time window before a ground fault is detected, then the ground fault is associated with the load area among these load areas (3, 4, 5) that was connected to the DC power grid (1) last within the time window.

2. The method of claim 1, wherein, The load areas (3, 4, 5) associated with the ground fault are isolated from the DC grid (1).

3. The method of claim 2, wherein, After disconnecting the load areas (3, 4, 5) from the DC grid (1), check whether the ground fault still exists. If the ground fault still exists in the DC grid (1) after disconnecting the load areas (3, 4, 5) from the DC grid (1), then disconnect the ground fault from the load areas (3, 4, 5) and reconnect the load areas (3, 4, 5) to the DC grid (1).

4. The method of claim 1, wherein, The evaluation unit (17) stores the detection time point and the time window when the ground fault is detected, and for each access to the load area (3, 4, 5), it stores the access time point and the association between the access time point and the access to the load area (3, 4, 5), and associates the ground fault with the load area (3, 4, 5) based on the stored data.

5. The method of claim 4, wherein, The evaluation unit (17) is a control unit (13), which controls the access of the load areas (3, 4, 5).

6. The method of claim 4, wherein, The evaluation unit (17) is a ground fault monitoring unit (15), which is configured to detect ground faults.

7. The method of claim 4, wherein, The control unit (13) that controls access to the load areas (3, 4, 5) reports each access time point and its access association to the evaluation unit (17).

8. The method according to claim 4, wherein, The ground fault is detected by the ground fault monitoring unit (15) and reported to the evaluation unit (17).

9. The method according to claim 1, wherein, The DC grid (1) has access units (10, 11, 12) associated with each load area (3, 4, 5), through which the load areas (3, 4, 5) can be connected to the DC grid (1), and each access unit (10, 11, 12) stores the time window, and for each access of the load area (3, 4, 5) associated with the access unit (10, 11, 12), it is determined whether the access was performed within the time window before a ground fault was detected.

10. The method according to claim 9, wherein, Ground faults are detected by the ground fault monitoring unit (15) and reported to each access unit (10, 11, 12).

11. The method according to claim 9, wherein, Each access switch unit (10, 11, 12) is configured to detect ground faults.

12. The method according to claim 1, wherein, After a ground fault is detected, since no load areas (3, 4, 5) are connected to the DC grid (1) within the time window prior to the detection of the ground fault, the ground fault cannot be associated with the load areas (3, 4, 5). The faulty load areas are determined by first separating all load areas (3, 4, 5) from the DC grid (1), and then connecting the load areas (3, 4, 5) to the DC grid (1) at different connection times, within a connection duration greater than the time window and not overlapping with the connection duration of other load areas (3, 4, 5). For each connection of the load areas (3, 4, 5), it is checked whether a ground fault occurs within the time window after the connection.

13. A DC power grid (1), the DC power grid comprising: Evaluation unit (17) is configured to store the detection time point of the ground fault and a pre-given time window, and for each access to load areas (3, 4, 5), store the access time point and the association between the access time point and the access to the accessed load area (3, 4, 5), and associate the ground fault with the load area by means of any one of claims 1 to 12 based on the stored data.

14. The DC power grid (1) according to claim 13, wherein, Multiple load areas (3, 4, 5) can be connected to the DC grid via corresponding access units (10, 11, 12), and the DC grid has a ground fault monitoring unit (15), wherein the ground fault monitoring unit (15) is configured to report detected ground faults to the evaluation unit (17).

15. A DC power grid (1) having an electrical main line (7, 9), a ground fault monitoring unit (15) connected to the electrical main line, and multiple load areas (3, 4, 5) that can be accessed, the DC power grid having an access unit (10, 11, 12) associated with each load area (3, 4, 5), through which the load areas (3, 4, 5) can be accessed to the DC power grid (1), and the access unit is configured to store a pre-given time window, and for each access of the load area (3, 4, 5) associated with the access unit, determine whether the access was performed within the time window before the ground fault monitoring unit (15) reports a ground fault.

16. A method for locating ground faults in a DC power grid (1), wherein multiple load areas (3, 4, 5) are connected to the DC power grid, wherein, -Pre-defined time window - And after a ground fault is detected, the ground fault is associated with the following load areas (3, 4, 5) that were connected to the DC grid (1) within the time window prior to the detection of the ground fault. - And the evaluation unit (17) stores the detection time point and the time window when the ground fault is detected, and for each access to the load area (3, 4, 5), it stores the access time point and the association between the access time point and the access to the load area (3, 4, 5), wherein, based on the stored data, the ground fault is associated with the load area (3, 4, 5).

17. The method according to claim 16, wherein, The evaluation unit (17) is a control unit (13), which controls the access of the load areas (3, 4, 5).

18. The method according to claim 16, wherein, The evaluation unit (17) is a ground fault monitoring unit (15), which is configured to detect ground faults.

19. The method of claim 16, wherein, The control unit (13) that controls access to the load areas (3, 4, 5) reports each access time point and its access association to the evaluation unit (17).

20. The method of claim 16, wherein, The ground fault is detected by the ground fault monitoring unit (15) and reported to the evaluation unit (17).

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