From the analysis of the structural characteristics of the low, medium and high voltage cable faults that have been found this year, the single-phase grounding faults of the cables are relatively common, mostly because the cables are damaged by external forces. It is also not ruled out that the quality of the body is caused, but it is rare that such an internal short circuit does not show traces from the outside. There are few cable-phase short-circuit faults, because the phase-to-phase short circuit generally occurs during operation. When a fault occurs, a strong short-circuit current will be generated, causing the quick-break protection action to trip. The high temperature caused by the strong current will generally burn the cable and cause an open circuit failure. There is a short circuit inside the cable, and no traces can be seen on the outside. This kind of fault is generally caused by the quality of the cable and is relatively rare. From the perspective of the fault position of the cable, the weakest part of a cable is the intermediate joint. The general cable has one or several intermediate joints. When making the intermediate joint of the cable, due to environmental conditions, and the cable is laid without moisture-proof treatment. If the intermediate nozzle is not tightly crimped during production, it may cause moisture in the intermediate joint of the cable and process defects. In the long-term operation, corona and free discharge are generated under the action of high-voltage electric field, so that the insulating body forms a water tree until the insulation is aged and broken down. According to the nature of the cable fault, it can be divided into open circuit, low resistance, high resistance and flashover Four kinds of faults: open circuit fault is that the working voltage cannot be transmitted to the terminal, or although the terminal has voltage, the load capacity is poor. The low-resistance fault is that the insulation of the cable between phases or to the ground is damaged, and the insulation resistance is reduced to below 100KΩ. The high resistance fault is that the insulation resistance of the cable between phases or to the ground is greater than 100kΩ. A flashover fault is a fault that suddenly breaks down in the process of maintaining high voltage and can be maintained at this voltage. Different from high-resistance faults, faults that can definitely break down when the high voltage reaches a certain voltage. The purpose of the above classification is also to facilitate the selection of test methods. According to the current popular fault location technology, the low-voltage pulse reflection method can be used for open-circuit and low-resistance faults, the impulse flashover method can be used for high-resistance faults, and the DC flashover method can be used for flashover faults. Network test. The above-mentioned faults can be tested by the secondary pulse method, which is the most advanced fault testing technology in the world, and is represented by Germany and Austria abroad. The field personnel have the habit of Rf<100KΩ faults called low resistance faults, mainly because the traditional bridge method can measure such faults. Based on the above analysis, grasping the following points is the key for us to find cable faults: 1. Determine whether the cable fault is an open-circuit fault, a low-resistance fault or a high-resistance fault; 2. Understand the length and specific direction of the cable (there will be an error ranging from 0.5 meters to 2 meters when using the instrument to measure); 3. Determine the length of the cable and the approximate position of the middle head; 4. Whether the cable fault is related to the quick-break protection action of the substation; 5. Whether there is construction excavation around the cable, and whether there is any unknown sound; 6. Cable burial depth and site environment.
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