1. Causes of cable failure
Due to the large area and long time of cable laying, the cable has been in a variety of complex site environments. The insulation layer is easy to age or corrosion, the conductor is cracked, the insulation is dry, and the connector is affected by external forces, resulting in various failures.
2. Type of cable fault
The types of cable faults are generally divided into cable low resistance fault, cable high resistance fault, cable open circuit fault, cable flashover fault, breakdown fault and cable operation fault. Short circuit fault (refers to the short circuit between phases, mainly the hidden danger left over in the manufacturing process), grounding fault (refers to the cable core and grounding fault, the insulation resistance less than 10k Ω is low resistance grounding, and more than 10k Ω is high resistance grounding), and mixed fault (refers to more than two kinds of cable faults).
3. Classification by fault cable laying environment
The fault cables are classified according to the cable laying environment. The cable fault detector also uses different methods to find cable faults according to the fault cables in different environments. ① Buried cable fault refers to fault finding and detection of directly buried high-voltage cables, buried cables, cables laid in open trenches, and cables laid in pipelines; ② The purpose of conduit cable troubleshooting is to troubleshoot plastic conduit cable, metal conduit cable and conduit cable; ③ Overhead cable fault is mainly used for fault finding and detection of tower type high-voltage overhead cable and bridge type cable; ④ Street lamp cables are generally directly buried and can be repaired in case of failure.
4. Cable fault finding procedure
The cable fault finding is generally divided into four steps: fault nature diagnosis, fault location, path detection, fault location, etc. When power cables such as transmission lines and directly buried cables fail, cable fault finder can find cable faults according to the following methods. Specific troubleshooting steps are as follows:
Step 1: Determine the nature of the cable fault. First, use the digital insulation resistance meter to judge the faulty cable line, measure the insulation resistance between cable phases and between phases and the ground, and judge whether the cable is broken, short circuited or grounded according to the resistance value. The method to measure the broken line fault is to short circuit one end of the two-phase cable, and then measure the resistance value of the other end of the cable to get the result. If the short circuit fault and the grounding fault are non detection phase grounding, use a digital insulation resistance meter to measure the resistance of the detection phase, judge whether the cable is short circuit fault (generally the resistance value is zero), and judge whether it is low resistance fault or high resistance fault according to the resistance value. (Note: 2500V tramegger is used for high-voltage cables of pilot test holding company, and 500V tramegger is used for low-voltage cables to detect whether the cables are faulty)
Step 2: Find cable fault distance After determining the nature and internal type of cable fault, adopt the corresponding cable fault finding method. The high resistance pulse system is used to detect the cable high resistance fault, and the cable fault tester is directly used to detect the low resistance fault. (① For cable low resistance fault, use the cable fault tester to directly find out the cable fault distance; ② For cable fault location, use the high resistance pulse system)
Step 3: Find the cable fault distance through step 2, and then accurately locate the cable fault point. Use the cable fault tester to directly locate the fault point, with the error not exceeding half a meter.