Discussion on the solution of low voltage cable fa

2022-09-19
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A brief discussion on the solution of low-voltage cable fault

the first step is to measure the distance with a distance meter. In fact, we should first judge whether the cable fault is high resistance, low resistance or grounding, and adopt different test methods according to this condition. If it is a ground fault, the low-voltage pulse method of the distance meter is directly used to measure the distance; If it is a high resistance fault, it is necessary to use the method of high-voltage impulse discharge to measure the distance. When using the method of high-voltage impulse discharge to measure the distance, there are many auxiliary equipment: such as high-voltage pulse capacitor, discharge ball, current limiting resistance, inductance coil and signal sampler, etc., which are troublesome and unsafe to operate, and have a certain danger. What is more cumbersome is to analyze the sampling waveform, which requires a higher knowledge of the tester

the second step is to find the path (if the path is clear, this step can be omitted). When looking for the path, we should find the practical materials of solar cells and thermoelectric conversion, add a signal (path signal generator) to the cable, and then the receiver receives the signal, and walk along the signal path once to determine the path of the cable. However, the range of this path is roughly between meters, which is not particularly accurate

the third step is to accurately locate according to the measured distance. It is based on the sound generated by spark discharge. When the place where the sound is the most heard from the headset of the pointing instrument, that is, the location of the fault point is found. However, due to listening to the sound, it takes a lot of time to find it due to the influence of environmental noise. Sometimes it takes until the evening. When cross-linked cables are encountered, it takes more time, because the cross-linked cables are generally internally discharged, and the sound is very small, which is almost inaudible. Finally, there is only measurement

therefore, this method can solve the power cable fault of most new materials, which is the most important emerging industry in the material industry. For the cable fault with cross-linked materials and polyethylene materials as insulating materials in recent years, the test effect is not ideal, because the sound generated by ignition and discharge is often very small (the cable sheath is not damaged, but the internal discharge of the cable), In this case, only other methods can be used to solve it

although there are such shortcomings, the cable fault tester designed based on the principle of "flash method" has solved many cable faults for enterprises for a long time, which is basically recognized by everyone, and its contribution is well-known. At present, it has been widely used in various industries. With the rapid development of all walks of life, the use of cables is more and more extensive, and the types of cables are also increasing, so it is inevitable that cable faults continue to occur. We know that all industries have different requirements for the grade, environment, wiring and distribution mode and insulation of cables used, and the cable fault characteristics of different cables are also very different. The reason is that there are many factors that cause cable faults, but at present, people always want to solve all cable faults in one way due to the habits they formed in the past,

therefore, the cable fault tester designed based on the principle of "flash method" is still dominant in the market. However, in some industries, the "flash method" is used to solve cable faults, which cannot detect the faults at all, and is likely to have serious consequences. For example, the cables for street lamps and underground cables for mines cannot reduce the waste generated by Chinese factories by 5.5% in fiscal 2017, and the "flash method" is directly used to test the faults. Similarly, cables used in other industries have their own characteristics, which we cannot introduce in detail here. However, with the continuous development of science and technology, we should be able to find a more simple test method, classify cable faults, apply the remedy to the case, and analyze specific problems. In this way, we will find that some cable faults do not need the principle of "flash method", and it is also very convenient and fast to solve

in many years of practical work, we have found that there are many differences between the faults of high-voltage cables and low-voltage cables. The faults of high-voltage cables are mainly operational faults, and most of them are high resistance faults, which can be divided into two types: leakage and flashover; However, there are only three cases of low-voltage cable fault: open circuit, short circuit and open circuit (when actively identifying and stopping the machine for disposal, the high-voltage cable also includes these three cases)

in addition, the low-voltage cable has the following characteristics in the actual use process:

1. The laying is random, and the path is not very clear

2. When laying, it is not buried deep after filling sand and bricks like high-voltage cables. On the contrary, it is buried shallowly and is vulnerable to external force damage and failure

3. Cables are generally short, ranging from tens of meters to hundreds of meters, unlike high-voltage cables, which often range from hundreds of meters to several kilometers

4. The insulation strength requirements are low, and the process is relatively simple when dealing with faults and making joints

⒌ most cables have obvious burning damage at the fault point. It is very rare for the fault point to leave no trace on the cable sheath

⒍ the load changes greatly, and the phases are often unbalanced, which is easy to heat up, and the resulting faults are mostly common

in view of the above characteristics of low-voltage cables, the suggestions put forward by the majority of users and our comprehensive consideration of the actual use of various places, our researchers have successfully developed DW type low-voltage cable fault testing and positioning system: the system includes two parts: distance measuring instrument and positioning instrument. DW system's distance meter is a completely intelligent and humanized design. It automatically completes the test of cable fault point, and directly reports the distance and nature of fault point without manual analysis of fault waveform. Battery powered, convenient for field work, small size, light weight, easy to carry, without any auxiliary equipment. The cable fault locator of DW system is an instrument for synchronously locating and testing the buried path, buried depth and fault location of directly buried low-voltage cables. Because it is a low-voltage cable fault location system designed based on the principle of electromagnetic induction and step voltage, it basically meets all the conditions of low-voltage cable fault testing. This test system has many advantages over the cable fault tester based on the principle of "flash method":/p>

1. A variety of test methods are integrated to mutually verify the results to determine the uniqueness of the fault point

2. Small size, light weight, easy operation by one person, no auxiliary equipment

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