Abstract: This paper introduces a typical 400V low-voltage cable ground fault in a steel plant, analyzes the fault finding process, and provides a reference for troubleshooting similar faults.
For current measurement of the faulty cable, when the injected current cannot be measured, it can be determined that the ground fault point is before this measurement point. Considering safety issues and the limitation of equipment, maintenance personnel used a 12V portable lamp transformer as a power source, connected a resistance wire of 10Ω in series between the 12V output terminal of the transformer and the faulty cable of the 2# electric heater group B, injecting a current of 1A into the faulty cable. To reduce workload and improve efficiency, maintenance personnel adopted the 1/2 method, that is, first set a measurement point at half of the total cable length, determine whether the fault point is in the first half or the second half of the cable length, and then search accordingly. After taking safety measures, maintenance personnel dug up the cement board of the cable trench at about half of the total length of the faulty cable (250m) and measured the current of the cable. Due to the irregular laying of cables in the trench and the fact that there are 32 cables for the 5# oxygen generator unit purifier electric heater, it was impossible to identify which one was the faulty cable at the halfway point. Therefore, maintenance personnel measured all 32 cables, but none of them showed the injected 1A current, so it was determined that the grounding point was in the first 250m near the distribution cabinet side. Using the same method to search the first 250m, the ground fault point of the faulty cable was finally found at about 200m from the distribution cabinet side.
4. Fault cause analysis and handling: By observing the cable grounding point, the direct cause of the fault was that the cable insulation layer was worn by the grinder and directly contacted the angle steel support of the cable trench, causing a ground fault. The indirect cause was that the construction personnel did not pay attention to the friction between the cable and the support during cable laying, resulting in damage to the cable protective layer. After laying, no insulation pad was added between the cable and the angle steel support. After long-term operation, affected by the electromagnetic force of large current, the cable insulation layer was worn through and grounded. Maintenance personnel spliced the faulty cable with copper tubes and heat-shrinkable insulation tubes, and added insulation pads between the cable and the support to prevent similar faults from happening again. Conclusion: Through the search for this cable ground fault, it is summarized that the current method has the characteristics of simplicity, speed, economy, and practicality in finding such cable ground faults, accumulating valuable experience for low-voltage cable ground fault finding. Author biography: Zhang Long, male, born in 1985, engineer, bachelor's degree,
