Analysis on Fault Location Mode of Power Cable

Cable faults also occur in the process of cable laying. Due to different cable laying methods, the difficulty of cable fault location increases gradually. Among them, the positioning of bridge, tunnel and groove is relatively simple, and the direct buried positioning is relatively difficult. Generally, a special cable fault location device (also known as cable fault tester) is used, which can be located in dozens of minutes, Special faults often take 4-5 days or even longer to locate. Now let's analyze the fault location mode of power cable. When using echo method to locate power cable fault, sometimes by transferring fault phase and wiring mode, complex fault will often be transformed into simple fault to quickly determine fault location. It is of great significance for the power supply user department to win time for the emergency repair of on-site lines. Low voltage power cables are generally multi-core cables. When faults occur in continuous use after laying, they generally show two core and multi-core phase to phase or phase to ground short circuit faults. Sometimes when it is detected that the fault waveform collected by one core is not ideal, it can be considered to convert the wiring to other fault cores for fault waveform detection, which often has unexpected effects, The collected and detected waveforms will become more typical and regular, so the specific location of cable fault point can be determined quickly. During the long-term on-site measurement of cable customers, it is found that the fault of small section copper core directly buried power cable (35mm2 and below) and aluminum core cable may be accompanied by short circuit and wire breakage at the same time. During on-site detection, converting short-circuit fault into broken line fault measurement according to the different fault nature of each fault core will often double everything with half the effort. For the medium voltage direct buried power cable with extruded armor as the inner lining, the fault is mostly caused by external mechanical damage. When the insulation core fails, the inner lining may have been damaged. When the cable insulation fault is special and it is difficult to collect the waveform with a professional cable fault tester, the acoustic method can be considered, When the high voltage pulse is directly applied between the steel strip and copper shielding layer of the cable, it will often be fixed quickly. In the field measurement process, we also found that when using the acoustic method to locate the fault point of low-voltage cable. When the high-voltage line and ground wire are connected between the bad phase and the metal shield or armor, due to the low resistance metal connection state of the insulation resistance of the two, the sound is very small, so the probe can not be used to listen to the fixed point, and the effect is not ideal. Through the actual listening side on the site for many times, it is found that the distance between the discharge ball gaps is appropriately increased. At the same time, if the high voltage and grounding wire are connected between the two faulty phases, the discharge sound will become louder and the fault point will be determined quickly.

Analysis on Fault Location Mode of Power Cable 1

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Power Cable Fault Location Method
Fault location method of power cable: Aiming at the problem that it is more difficult to determine the fault location of buried power cable than overhead line, this paper selects a representative example of fault location process of 10 kV cable in case of high resistance fault, and introduces the method of locating and locating the fault point by using secondary pulse method according to the fault nature. For the high resistance fault during cable operation, first consult the relevant data of the cable and master the detailed information of the cable; Use multimeter and insulation resistance meter to judge the cable fault type, and determine the corresponding test method according to the fault type; Use the fault tester to test the length of the cable, check whether the test results are consistent with the data, and preliminarily determine the distance of the fault point; Finally, the secondary pulse method is used to accurately locate the fault point, find out the fault point, peel off the cable and find out the cause of the cable fault, so as to take corresponding preventive measures. This method is easy to master, especially for short-distance faults, the test waveform is easier to analyze, and the fault distance can be determined quickly, which makes the cable test more efficient and the fixed-point positioning time shorter. Power cable faults are complex and diverse, which can be divided into open faults and closed faults according to fault surface phenomena; According to the grounding phenomenon, it is divided into grounding fault, phase to phase fault and mixed fault; According to the fault location, it is divided into joint fault and cable body fault; According to the nature of resistance, it is divided into broken line fault, mixed line fault and mixed fault. Among them, mixed line fault is divided into low resistance fault, high resistance fault and flashover fault. 1. Fault detection methods for different cable faults, the common detection methods include low voltage pulse method, pulse current method, secondary pulse method, bridge method, pulse voltage method, etc. [3]. This paper only introduces the three commonly used detection methods. 2. Low voltage pulse method low voltage pulse method is suitable for detecting low resistance fault (short circuit fault with fault resistance less than 200 & omega;) and open circuit fault. It can also be used to measure the length of cable and the propagation speed of electromagnetic wave in cable, and distinguish the middle head, T-joint and terminal head of cable. 3. Pulse current method pulse current method generally includes impulse flash method and direct flash method. The linear current coupler is used to collect the current traveling wave signal in the cable and generate the fault test waveform, so as to judge the fault condition and measure the distance between fault points through the waveform. The direct flash method is used to detect flashover breakdown faults, that is, the resistance at the fault point is very high, and flashover breakdown faults will occur when the voltage is raised to a certain value with high-voltage test equipment. The impulse flashover method is also suitable for testing most flashover faults. Because the waveform of the direct flashover method is relatively simple and it is easy to obtain more accurate results, the direct flashover method should be used as much as possible. 4. Secondary pulse method with the cooperation of high voltage signal generator and secondary pulse signal coupler, the secondary pulse method can be used to measure the fault distance of high resistance and flashover faults. The waveform measured by this method is simpler and easy to identify.
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