1. The test delivery method primarily focuses on checking the residual current device (RCD) itself. Here's how it works: first, turn off the power supply, then remove all the load-side leads of the zero-sequence transformer connected to the RCD (for secondary or third-stage RCDs, simply disconnect the outgoing lines). After that, re-connect the RCD. If the device still fails to operate, it indicates a fault within the RCD itself, and it should be repaired or replaced. However, if the RCD operates normally, the problem is not with the device but with the switchboard or the wiring. To locate the issue, start by cutting off the output of each line or AC contactor. If the RCD doesn’t trip, there may be a fault in the switchboard. Check whether the insulation of the electrical and instrumentation equipment on each circuit is intact and if the wiring is correct. If the RCD functions properly, the switchboard is likely fine. When the fault is confirmed to be in the external wiring, you can use the branch-line search method to identify the exact location of the fault.
2. Intuitive Inspection Method
The intuitive inspection method involves visually examining and analyzing the fault symptoms, including the RCD and the equipment it protects, to locate the problem. During this process, special attention should be given to complex areas such as corners, branches, and crossover points in the wiring. This method is straightforward and practical, making it ideal for identifying issues like broken wires, short circuits between conductors, or incorrect wiring configurations.
3. Numerical Comparison Method
This approach involves using instruments to measure the line or equipment and comparing the readings to the original values to pinpoint the fault. It’s important to note that when the neutral wire’s insulation deteriorates or the neutral wire is repeatedly grounded, it can lead to frequent tripping of the main protection system, while the secondary protector remains unaffected. When dealing with tripping of the secondary protector, avoid switching the phase and neutral wires to restore the secondary protection. Instead, consider removing the repeated grounding connection to resolve the issue.
4. Line Elimination Method
When troubleshooting a line fault, start by disconnecting the branch lines of the low-voltage power grid in the order of “main line first, then sub-branches, and finally the end.†Test only the main line initially. If no faults are found, the main line can run normally. Then, gradually reconnect the sub-branches and end lines one by one. If the RCD trips upon reactivating a specific line, the fault is likely located on that particular line. This step-by-step elimination helps efficiently identify the exact point of failure.
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