Correct Opening Method of Cable Fault Tester

Why can't the fault point be found when using the cable fault tester? What is the correct opening method of cable fault tester? We need to understand some common problems of cable fault first, and then effectively solve the fault problems according to different problems. With the development of China's power system, the laying of high-voltage cables is becoming more and more common. Basically, the cables connected between distribution stations are very long. As long as the cables fail, it is very difficult to troubleshoot, and most of them are buried cables, which is difficult to judge. At this time, we need a cable fault tester to judge the correct fault point for us, So that we can quickly restore the power supply, we can analyze the problem according to several common cable faults. Cable faults are commonly divided into high resistance short circuit fault, phase to phase short circuit fault, low resistance fault, flashover fault and other common faults on site. 1. The low voltage pulse reflection method is applicable to low resistance (less than 10 times of wave impedance), grounding and open circuit faults, and can test the full length of the cable and the propagation speed of radio waves in the cable. In case of low resistance or grounding fault of the cable, the equivalent impedance at the cable fault point shall be the parallel connection of fault resistance and cable characteristic impedance. The smaller the cable fault resistance is, the more obvious the reflected waveform is. When the cable fault resistance is zero, it is total reflection. Because the equivalent impedance at the test end (input impedance of the test instrument) is greater than the characteristic impedance of the cable, the same polarity reflection pulse is generated at the test end. At the low resistance or ground fault, because the fault resistance is less than the cable characteristic impedance, the incident pulse generates the reverse polarity pulse after the fault point and transmits it to the test end. The falling edge of the received reverse polarity pulse corresponds to the reflected waveform of the cable fault point. In case of open circuit fault of cable, the equivalent impedance of cable fault is the series of fault resistance and cable characteristic impedance. Open circuit is equivalent to infinite fault resistance. In this case, the incident pulse will form total reflection, and the reflection pulse of the same polarity will be generated at the test end. The rising edge of the received pulse of the same polarity corresponds to the reflection waveform at the fault point. 2. First, use a certain voltage level The high voltage pulse with certain energy is applied to the faulty cable at the test end of the cable, causing breakdown and arcing at the high resistance fault point of the cable. At the same time, add the low-voltage pulse for measurement at the test end. When the measurement pulse reaches the high resistance fault point of the cable, it encounters an arc and reflects on the surface of the arc. When arcing, the high resistance fault becomes an instantaneous short-circuit fault, and the low-voltage measurement pulse will change obviously in impedance characteristics, so that the waveform of flashover measurement becomes a low-voltage pulse short-circuit waveform, making the waveform discrimination particularly simple and clear. This is what we call the "secondary pulse method". The received low-voltage pulse reflection waveform is equivalent to the waveform of a wire core completely short circuited to ground. Superimpose the low-voltage pulse waveform obtained when releasing the high-voltage pulse and when not releasing the high-voltage pulse. The two waveforms will have a divergence point, which is the reflected waveform point of the cable fault point. This method combines low-voltage pulse method with high-voltage flashover technology, which makes it easier for testers to judge the location of cable fault point. Compared with the traditional cable fault test method, the advantage of the secondary pulse method is to simplify the complex waveform in the impulse high-voltage flashover method into the low-voltage pulse short-circuit fault waveform, so the interpretation is very simple and the fault distance can be accurately calibrated. 3. The triple pulse method adopts the double impact method to prolong the arc burning time and stabilize the arc, which can easily locate the high resistance fault and flashover fault. The triple pulse method has advanced technology, simple operation, clear waveform and fast and accurate positioning. At present, it has become the mainstream positioning method of high resistance fault and flashover fault. The third pulse method is an upgrade of the second pulse method. The method is to first measure the reflected waveform of the low-voltage pulse without breaking through the fault point of the measured cable, then impact the fault point of the cable with the high-voltage pulse to generate an arc, trigger the medium voltage pulse when the arc voltage drops to a certain value to stabilize and prolong the arc time, and then send the low-voltage pulse, Thus, the reflected waveform of the fault point is obtained. After the superposition of the two waveforms, it can also be found that the divergence point is the corresponding position of the fault point. Because the medium voltage pulse is used to stabilize and prolong the arc time, it is easier to find the fault point waveform than the secondary pulse method. The cable fault tester often has to solve the following problems: 1. The diversity and complexity of cable faults determine that the cable fault tester needs complete functions and diverse test methods. 2. 2. To solve the fault, many instruments should be used together in order to achieve the result of solving the fault. 3. Different test methods are needed for cable insulation, fault location and different faults. 4. Sometimes the difficulty of cable fault test lies in the snow with a thickness of more than one meter and bad weather (the temperature is more than minus 20 degrees), which is also a test for underground cable detectors and testers to pass the above understanding. I believe you basically have some general and judgment on the cable fault problem and how to use the cable fault tester normally.

Correct Opening Method of Cable Fault Tester 1

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