Direct current system transformation method

Abstract

The invention discloses a direct-current system transformation method, which comprises the following steps of: connecting a new direct-current bus of a new direct-current system with a cable of a storage battery pack connected with an old direct-current system, connecting a first load cable of the new direct-current system into target direct-current load equipment connected with a second load cable of the old direct-current system, and then dismounting the second load cable; all direct current load equipment is switched from the old direct current system to the new direct current system through a plurality of cycles, so that the new direct current system charger is connected to the new direct current bus, the old direct current system charger is disconnected from the old direct current bus, and the new direct current system insulation monitoring device is connected to the new direct current bus; and disconnecting the old direct current system insulation monitoring device from the old direct current bus to complete the transformation of the direct current system, so that the complete transformation of the direct current system can be realized on the premise of ensuring high safety and low complexity, the transformation period is greatly shortened, and the requirements of current power grid upgrading on efficiency and reliability are met.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and specifically provides a method for retrofitting a DC system. Background Technology

[0002] DC systems are an indispensable core component of power systems, providing a continuous and reliable DC power supply for many critical devices. The continuity and stability of DC system operation are directly related to the safe and stable operation of the entire power grid.

[0003] When the DC system in a substation has been in operation for a long time, problems such as equipment aging, frequent defects, increased failure rates, and maintenance difficulties are common, necessitating a systemic upgrade. Currently, common DC system upgrade methods mainly include the following: 1) Power outage load transfer method: After the new DC system is built, power outages are implemented in turn for each bay to complete the load transfer. This method is highly safe, has low complexity, and can achieve a complete transformation, but its transformation cycle is too long.

[0004] 2) Replacing the original charging module and insulation monitoring device: This method only replaces the charging module and insulation monitoring device in the original cabinet. It has moderate safety and complexity, and a short modification cycle, but it cannot achieve a complete overhaul of the DC system.

[0005] 3) Temporary power supply method: Using a temporary power supply to power the load of the main feeder or sub-feeder, thereby replacing the charger. This method has low safety, high complexity, medium transformation cycle, and also cannot achieve a complete transformation.

[0006] 4) Single-segment DC load-two-segment segmented upgrade method: By repeatedly connecting, transferring, and segmenting the newly built sub-panel with the original main panel, the replacement of the old system with the new system is gradually completed. Although this method can achieve a complete upgrade of the DC system, it has low security, high complexity, and a moderate upgrade cycle.

[0007] In summary, existing DC system retrofit technologies all have significant limitations. They cannot simultaneously achieve a complete system retrofit and a significant reduction in the retrofit cycle while ensuring high safety and low complexity, making it difficult to meet the current power grid upgrade's dual requirements for efficiency and reliability. Summary of the Invention

[0008] This invention provides a method for upgrading a DC system, which can achieve a complete upgrade of the DC system while ensuring high safety and low complexity, and significantly shorten the upgrade cycle, thus meeting the current power grid upgrade requirements for efficiency and reliability.

[0009] The DC system retrofit method provided by this invention includes: S1. Install and complete the commissioning of the first DC system; S2. Connect the first DC bus of the first DC system to the battery pack connected to the second DC system via a cable, and connect the first load cable of the first DC system to the target DC load device connected to the second load cable of the second DC system. The target DC load device is one of the DC load devices connected to the second DC system. The first DC system includes the first DC bus, the first load cable, the first charger, and the first insulation monitoring device. The second DC system includes the second load cable, the second DC bus, the second charger, and the second insulation monitoring device. S3. Disconnect the second load cable; S4. Repeat steps S2 to S3 until all DC load devices are switched to the first DC system; S5. Connect the first charger to the first DC bus and disconnect the second charger from the second DC bus; S6. Connect the first insulation monitoring device to the first DC bus and disconnect the second insulation monitoring device from the second DC bus.

[0010] Further, step S1 includes: Install and debug the first DC system; Once the commissioning of the first DC system is confirmed to be complete, disconnect the first charger and the first insulation monitoring device from the first DC bus.

[0011] Further, step S4 includes: Connect the first charger to the first DC bus and detect the operating status of the first charger; After confirming that the first charger is working properly, disconnect the second charger from the second DC bus.

[0012] Further, step S5 includes: Connect the first insulation monitoring device to the first DC bus but do not put it into operation; Disconnect the second insulation monitoring device from the second DC bus; Once it is confirmed that the second insulation monitoring device has stopped working, the first insulation monitoring device is put into operation.

[0013] Furthermore, prior to step S2, the DC system modification method further includes: Determine whether the connection between the first DC bus and the target DC load device is normal; If so, proceed to step S2.

[0014] Furthermore, determining whether the connection between the first DC bus and the target DC load device is normal includes: Detect whether there is current in the first load cable; If yes, the connection between the first DC bus and the target DC load device is normal; if no, the connection between the first DC bus and the target DC load device is abnormal.

[0015] Furthermore, a clamp meter is used to detect whether there is current in the first load cable.

[0016] Furthermore, after step S5, the DC system modification method further includes: Detect the operating status of the first DC system; After confirming that the first DC system is operating normally, the second charger, the second insulation monitoring device, and the second DC bus are removed.

[0017] Furthermore, the detection of the operating status of the first DC system includes: The working status of the first charger and the working status of the first insulation monitoring device are detected.

[0018] Furthermore, the detection of the operating status of the first DC system also includes: Check whether the voltage of the first DC bus is stable.

[0019] Beneficial effects The DC system retrofit method provided by this invention involves connecting the new DC bus (i.e., the first DC bus) of the new DC system (i.e., the first DC system) to the battery pack connected to the old DC system (i.e., the second DC system) via cables. The first load cable of the new DC system is then connected to the target DC load device connected to the second load cable of the old DC system. The second load cable is then disconnected, and through several cycles, all DC load devices are transferred from the old DC system to the new DC system. Finally, the charger of the new DC system (i.e., the first charger) is connected to the new DC bus, and the connection between the charger of the old DC system (i.e., the second charger) and the old DC bus (i.e., the second DC bus) is disconnected. This completes the process of upgrading the new DC system. The insulation monitoring device (i.e., the first insulation monitoring device) is connected to the new DC bus, and the old DC system insulation monitoring device (i.e., the second insulation monitoring device) is disconnected from the old DC bus, thus completing the DC system transformation. Therefore, this invention can achieve a complete transformation of the DC system while ensuring high safety and low complexity, without complicated transformation steps, greatly shortening the transformation cycle. Furthermore, during the transformation process, the DC load equipment always has at least one DC system (first the old system, then the new system) supplying it with power, achieving uninterrupted and zero-sensory switching of power supply, avoiding equipment outages caused by transformation, and greatly improving the reliability of the transformation process, meeting the current power grid upgrade requirements for efficiency and reliability. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0021] Figure 1 A flowchart illustrating the DC system retrofit method provided in an embodiment of the present invention; Figure 2 A schematic diagram of the structure after connecting the first DC bus to the battery cable in the DC system modification method provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure after the first load cable is connected to the target DC load device in the DC system modification method provided in this embodiment of the invention; Figure 4 This is a schematic diagram of the structure of the first DC system after commissioning in the DC system modification method provided in the embodiment of the present invention; Figure 5 This is a schematic diagram of the structure after removing the second load cable in the DC system modification method provided in this embodiment of the invention; Figure 6This is a schematic diagram of the structure for detecting whether there is current in the first load cable in the DC system modification method provided in this embodiment of the invention; Figure 7 This is a schematic diagram of the structure after power transfer is completed in the DC system transformation method provided in the embodiment of the present invention; Figure 8 This is a schematic diagram of the structure after the insulation monitoring device is transferred using the DC system retrofit method provided in this embodiment of the invention. Figure 9 This is a schematic diagram of the structure of the new DC system after the DC system transformation is completed in the DC system transformation method provided in the embodiment of the present invention. Detailed Implementation

[0022] To solve this problem, refer to Figure 1 This invention provides an embodiment of a DC system retrofit method, which may include the following steps: S1. Connect the cable of the first DC bus of the first DC system to the battery pack connected to the second DC system, and connect the first load cable of the first DC system to the target DC load equipment connected to the second load cable of the second DC system. S2. Dismantle the second load cable; S3. Repeat steps S1 to S2 until all DC load devices are switched to the first DC system; S4. Connect the first charger to the first DC bus and disconnect the second charger from the second DC bus; S5. Connect the first insulation monitoring device to the first DC bus and disconnect the second insulation monitoring device from the second DC bus.

[0023] For step S1, Figure 2 The cable connecting the first DC bus of the first DC system to the battery pack of the second DC system is shown. Figure 2 Cable 1) connection, Figure 3 It shows in Figure 2Based on this, the first load cable of the first DC system is connected to the target DC load device connected to the second load cable of the second DC system. Here, the first DC system refers to the new DC system, and the second DC system refers to the old DC system that needs modification. The target DC load device is one of the DC load devices connected to the second DC system. The first DC system includes a first DC bus, a first load cable, a first charger, and a first insulation monitoring device. The end of the first load cable furthest from the target DC load device is connected to the first DC bus. The second DC system includes a second load cable, a second DC bus, a second charger, and a second insulation monitoring device. The battery pack, the second charger, the second insulation monitoring device, and the end of the second load cable furthest from the target DC load device are all connected to the second DC bus.

[0024] Understandably, at this point, referring to Figure 2 and Figure 3 The charger of the old DC system (i.e., the second DC system) (i.e., the second charger) drives the new DC bus (i.e., the first DC bus) through the old DC bus (i.e., the second DC bus) and cables. Meanwhile, referring to... Figure 3 Since the new DC bus connects the new DC load cable (i.e. the first load cable) to the target DC load equipment, the new DC load cable and the old DC load cable (i.e. the second load cable) are connected in parallel to supply power to the target DC load equipment.

[0025] In some embodiments, prior to step S1, the DC system retrofit method may further include: Install and debug the first DC system; confirm that the debugging of the first DC system is complete, and disconnect the first charger and the first insulation monitoring device from the first DC bus.

[0026] Specifically, the first charger, the first load cable, and the first insulation monitoring device are installed and commissioned. After commissioning, the connection between the first charger, the first insulation monitoring device, and the first DC bus is disconnected to facilitate the modification of the old DC system. The first DC system after disconnecting the first charger and the first insulation monitoring device from the first DC bus is as follows: Figure 4 As shown.

[0027] It is understood that the present invention provides pre-modification preparation by installing and debugging the new DC system before modifying the old DC system, which improves the reliability of the new DC system and thus also improves the reliability of the modification process of the old DC system, avoiding problems such as power outages of DC load equipment during the modification process.

[0028] For step S2, it is understood that, referring to Figure 5 After the second load cable is removed, the power supply of the target DC load equipment that was originally connected to the second DC bus is transferred to the first DC bus.

[0029] To further improve the reliability of the modification process and avoid losses caused by power outages of DC load equipment, in some embodiments, before removing the second load cable in step S2, the DC system modification method may further include: Determine whether the connection between the first DC bus and the target DC load equipment is normal; if so, proceed to step S2.

[0030] Therefore, this embodiment of the invention verifies whether the connection between the first DC bus and the target DC load device is normal before disconnecting the second load cable, and only disconnects the second load cable when the connection is normal, thus avoiding the loss of power to the target DC load device caused by disconnecting the second load cable when the connection between the first DC bus and the target DC load device is abnormal.

[0031] Furthermore, in some embodiments, determining whether the connection between the first DC bus and the target DC load device is normal may include: Check if there is current in the first load cable; if yes, the connection between the first DC bus and the target DC load equipment is normal; if no, the connection between the first DC bus and the target DC load equipment is abnormal.

[0032] Furthermore, referring to Figure 6 In some embodiments of the present invention, a clamp meter is used to detect whether there is current in the first load cable.

[0033] For step S3, it can be understood that steps S1-S2 are repeated to transfer the DC load devices connected to the second DC bus in sequence until the power supply of all DC load devices originally connected to the second DC bus is transferred to the first DC bus, thus completing the load transfer.

[0034] For step S4, refer to Figure 7 After the aforementioned steps complete the transfer of all DC load devices, the first charger is connected to the first DC bus, and the second charger is disconnected from the second DC bus, thus completing the power transfer and putting the first charger into operation while the second charger is disconnected. It is understood that this embodiment of the invention operates on the principle of "parallel connection first, then disconnection" during the power transfer process in step S4. Before disconnecting the second charger from the second DC bus, the output terminal of the first charger is connected in parallel to the DC bus. At this time, the first and second chargers jointly supply power to the DC load devices and float charge the battery, thereby ensuring uninterrupted DC power supply during the power transfer process in step S4 and preventing losses caused by power outages in the DC load devices.

[0035] Specifically, during the process of disconnecting the second charger from the second DC bus, the second charger is smoothly shut down or deactivated, at which point the DC load equipment and the battery will be powered solely by the first charger. After disconnecting the second charger from the second DC bus, this embodiment of the invention closely monitors whether the DC bus voltage is stable to confirm that the first charger can independently handle the entire load.

[0036] Optionally, in some embodiments, step S4 may include: Connect the first charger to the first DC bus and detect the operating status of the first charger; After confirming that the first charger is working properly, disconnect the second charger from the second DC bus.

[0037] It is understood that, in this embodiment of the invention, the connection between the second charger and the second DC bus is disconnected only after verifying that the first charger is working normally, in order to further ensure uninterrupted power supply of DC power and prevent losses caused by power outages of DC load equipment.

[0038] For example, the normal operating status of the first charger may include confirming that the new DC system charger is operating normally, without any abnormal alarms, and that current sharing is good (if current sharing is supported).

[0039] For step S5, refer to Figure 8 The first insulation monitoring device is connected to the first DC bus, and the second insulation monitoring device is disconnected from the second DC bus, thus completing the transfer of the insulation monitoring devices. This puts the first insulation monitoring device into operation, while the second insulation monitoring device is disconnected. It should be noted that steps S4 and S5 are not sequential.

[0040] Specifically, in the embodiment of the present invention, the principle of "one-on-one" is adopted during the transfer of the insulation monitoring device in step S5 to avoid the parallel operation of the first insulation monitoring device and the second insulation monitoring device, which would have adverse effects.

[0041] Understandably, insulation monitoring devices typically inject a special low-frequency detection signal into the DC system and then calculate the insulation resistance by detecting the current magnitude of this signal in the positive and negative bus-to-ground circuits. If two insulation monitoring devices operate simultaneously, their injected detection signals will superimpose and interfere with each other, causing neither device to correctly detect and calculate the actual insulation resistance. The resulting measurements will be completely erroneous, potentially displaying a false "normal insulation" reading or falsely reporting a "reduced insulation" alarm. Therefore, this embodiment of the invention operates based on the principle of "one device activated, one device deactivated," avoiding parallel operation of the first and second insulation monitoring devices. This prevents signal conflicts between the two devices and the resulting measurement distortion, improving the safety and reliability of the DC system retrofit process.

[0042] Optionally, in some embodiments, step S5 may include: Connect the first insulation monitoring device to the first DC bus but do not put it into operation; Disconnect the second insulation monitoring device from the second DC bus; Once it is confirmed that the second insulation monitoring device has stopped working, the first insulation monitoring device will be put into operation.

[0043] Therefore, the embodiments of the present invention avoid the parallel operation of the first insulation monitoring device and the second insulation monitoring device, thereby avoiding signal conflict between the two sets of insulation monitoring devices and the resulting measurement distortion problem, and improving the safety and reliability of the DC system transformation process.

[0044] In some embodiments, after step S5, the DC system modification method may further include: Detect the operating status of the first DC system; After confirming that the first DC system is working properly, the second charger, the second insulation monitoring device, and the second DC bus are removed.

[0045] Therefore, in this embodiment of the invention, the physical removal of the old DC system charger, the old DC system insulation monitoring device, and the old DC bus is carried out only after confirming that all new equipment is operating stably and functions normally, thus improving the safety and reliability of the DC system renovation process.

[0046] Figure 9 The present invention illustrates a new DC system after removing the old DC system charger, the old DC system insulation monitoring device, and the old DC bus according to an embodiment of the present invention.

[0047] Optionally, in some embodiments, detecting the operating state of the first DC system may include: The working status of the first charger and the working status of the first insulation monitoring device are detected.

[0048] Specifically, detecting the operating status of the first charger may include detecting at least one of the following: whether the first charger is operating normally, whether there are any abnormal alarms, and whether the current sharing is good (if current sharing is supported). When detecting the operating status of the first insulation monitoring device, a dedicated insulation resistance tester can be used to simulate a known grounding fault on a branch of the first DC system, and observe whether the first insulation monitoring device can correctly monitor and alarm. It is understood that in this embodiment, when the operating status of the first charger and the first insulation monitoring device are normal, the operating status of the first DC system is considered normal; when the operating status of the first charger or the first insulation monitoring device is abnormal, the operating status of the first DC system is considered abnormal.

[0049] Furthermore, in some embodiments, detecting the operating state of the first DC system may further include: Check whether the voltage of the first DC bus is stable.

[0050] Specifically, in this embodiment of the invention, the stability of the first DC bus voltage is monitored to confirm whether the first charger can independently bear the entire load.

[0051] It is understood that in this embodiment, when the voltage of the first DC bus is stable and the working state of the first charger and the working state of the first insulation monitoring device are normal, the working state of the first DC system is considered to be normal; when any one of the following occurs: the voltage of the first DC bus is unstable, the working state of the first charger is abnormal, or the working state of the first insulation monitoring device is abnormal, the working state of the first DC system is considered to be abnormal.

[0052] In summary, the DC system retrofit method provided by this invention connects the new DC bus of the new DC system to the battery pack connected to the old DC system via cables, connects the first load cable of the new DC system to the target DC load device connected to the second load cable of the old DC system, then disconnects the second load cable, and through several cycles, transfers all DC load devices from the old DC system to the new DC system. Next, the charger of the new DC system is connected to the new DC bus, and the connection between the charger and the old DC system bus is disconnected. The insulation monitoring device of the new DC system is connected to the new DC bus, and the connection between the insulation monitoring device and the old DC system bus is disconnected. This completes the DC system retrofit. Therefore, this invention can achieve a thorough DC system retrofit while ensuring high safety and low complexity, significantly shortening the retrofit cycle and meeting the current power grid upgrade requirements for efficiency and reliability.

[0053] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for retrofitting a DC system, characterized in that, include: S1. Install and complete the commissioning of the first DC system; S2. Connect the first DC bus of the first DC system to the battery pack connected to the second DC system via a cable, and connect the first load cable of the first DC system to the target DC load device connected to the second load cable of the second DC system. The target DC load device is one of the DC load devices connected to the second DC system. The first DC system includes the first DC bus, the first load cable, the first charger, and the first insulation monitoring device. The second DC system includes the second load cable, the second DC bus, the second charger, and the second insulation monitoring device. S3. Disconnect the second load cable; S4. Repeat steps S2 to S3 until all DC load devices are switched to the first DC system; S5. Connect the first charger to the first DC bus and disconnect the second charger from the second DC bus; S6. Connect the first insulation monitoring device to the first DC bus and disconnect the second insulation monitoring device from the second DC bus.

2. The DC system retrofitting method according to claim 1, characterized in that, Step S1 includes: Install and debug the first DC system; Once the commissioning of the first DC system is confirmed to be complete, disconnect the first charger and the first insulation monitoring device from the first DC bus.

3. The DC system retrofitting method according to claim 1, characterized in that, Step S4 includes: Connect the first charger to the first DC bus and detect the operating status of the first charger; After confirming that the first charger is working properly, disconnect the second charger from the second DC bus.

4. The DC system retrofitting method according to claim 1, characterized in that, Step S5 includes: Connect the first insulation monitoring device to the first DC bus but do not put it into operation; Disconnect the second insulation monitoring device from the second DC bus; Once it is confirmed that the second insulation monitoring device has stopped working, the first insulation monitoring device is put into operation.

5. The DC system retrofitting method according to claim 1, characterized in that, Prior to step S2, the DC system modification method further includes: Determine whether the connection between the first DC bus and the target DC load device is normal; If so, proceed to step S2.

6. The DC system retrofitting method according to claim 5, characterized in that, The step of determining whether the connection between the first DC bus and the target DC load device is normal includes: Detect whether there is current in the first load cable; If yes, the connection between the first DC bus and the target DC load device is normal; if no, the connection between the first DC bus and the target DC load device is abnormal.

7. The DC system retrofitting method according to claim 6, characterized in that, A clamp meter is used to detect whether there is current in the first load cable.

8. The DC system retrofitting method according to claim 1, characterized in that, Following step S5, the DC system modification method further includes: Detect the operating status of the first DC system; After confirming that the first DC system is operating normally, the second charger, the second insulation monitoring device, and the second DC bus are removed.

9. The DC system retrofitting method according to claim 8, characterized in that, The detection of the operating status of the first DC system includes: The working status of the first charger and the working status of the first insulation monitoring device are detected.

10. The DC system retrofitting method according to claim 9, characterized in that, The detection of the operating status of the first DC system also includes: Check whether the voltage of the first DC bus is stable.

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