Fault test procedure and test principle of the hot

2022-08-24
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Cable fault requires very high materials. The fault test procedure and test principle of the identification instrument

the cable fault identification instrument is suitable for measuring the low resistance fault, short circuit fault and open circuit fault of power cables, high-frequency coaxial cables, local telephone cables, street lamp cables and more than two parallel buried wires of various materials with different cross sections and different media. Although the size of the sample used is small line fault, And high resistance leakage fault and high resistance flashover fault. It is an important tool for maintaining various cables. The instrument adopts a variety of fault detection methods, applies the most advanced contemporary electronic technology achievements, adopts computer and special electronic technology, and is a new generation of high-tech products with full functions. It can test the high resistance flashover fault, high and low resistance grounding, short circuit, cable disconnection, poor contact and other faults of the cable. If equipped with the acoustic method pointing instrument, it can accurately determine the precise position of the fault point. It is especially suitable for testing power cables and communication cables of various models and voltages. The fault test procedure and principle are as follows:

I. fault test procedure of cable fault recognizer

when using this instrument to test cable faults, the following procedures should be followed:

1. Multimeter, megger or judge the nature of cable faults from the cable pre-test results

2. Select the appropriate test method according to the nature of cable fault: the pulse method is best used for low resistance fault and open circuit fault, and of course, the flashover method can also be used for low resistance fault. It is hoped that the leakage high resistance fault can be selected carefully when purchasing the experimental machine. It is best to use the flashover method (impulse l method). Some leakage high resistance faults can also use the direct flash method, but usually this is not done. The flashover high resistance fault is best to use the direct flash method, or both methods can be used to measure and compare each other to improve the accuracy of judgment

3. Select the working grounding point, and lead two grounding wires from the selected grounding point, one to the ground of the instrument and the other to the ground of the high-voltage equipment. The selection principle of working ground wire is to ensure that the test phase and it form a closed loop, so that the instrument can get the correct test waveform. It should also be noted that the working ground wire must be connected with the system to make people, instruments, high-voltage equipment and the tested cable in the same position. To ensure personal safety and integrity of instruments and equipment. If the cable is in interphase fault, the working ground wire must be one of the phase wires, and the phase wire as the ground wire must be connected with the system ground. For the cable with lead-free bushing, the vast majority of faults are discharged to the earth or space during the high-voltage flashover test. Theoretically, the fault also forms a closed loop relatively to ground or space, but in fact, the equivalent impedance in the loop is quite large, so the instrument cannot get the correct test waveform. In case of this situation during the test, the method of directly fixing the suspected fault point can be adopted to solve it. No matter what ground wire, its grounding point must be reliable

4. Test the total length of the cable with the pulse method to calibrate the radio wave transmission speed of the tested cable

5. Rough test the fault point according to the selected test method

6. After rough measurement, fix the fault point

II. Test principle of cable fault recognizer

1. Test principle of high voltage flashover method

when aiming at the high resistance fault of the cable, external equipment is used to apply high voltage to the cable. When the fault cable cannot bear the applied high voltage, the fault point will produce breakdown arc. The breakdown arc will produce an echo, so we can use the tester to record the whole breakdown process in the form of collected waveform at the test end, and analyze and calculate the distance between the breakdown point and the test end through this breakdown process. Similarly, this test method is not affected by cable laying, but only related to the transmission speed of radio waves in the cable

2. Principle of pulse method test

pulse method test is to generate a pulse wave inside the instrument, which is applied to electricity. 3. Tension experiment: when the pulse wave meets the point where the characteristic impedance of the cable changes, an echo signal will be generated (according to the principle of transmission line). The instrument collects and displays these two signals (transmitted wave and echo) at the test end of the cable, According to the time difference between the two waves, the distance between the fault point and the test end is calculated. Therefore, this test method is not affected by the cable laying rules, but only related to the transmission speed of radio waves in this cable

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