(1) Traveling wave method: When an electric wave is transmitted in a transmission line, if the transmission line is uneven, that is, the characteristic impedance of a certain point in the transmission line changes, when the electric wave is transmitted to this point, in addition to continuing to transmit far away, the electric wave will also generate reverse transmission and return to the test end. We call this reverse transmission electric wave a reflected wave, and the phenomenon of electric wave generating reverse transmission is called electric wave reflection phenomenon. The so-called traveling wave refers to the general term for incident wave and reflected wave.
(2) When an electric wave is transmitted in a transmission line, the polarity of the echo at the short-circuit point is opposite to the polarity of the transmitted pulse, while the polarity of the echo at the break point (including the cable terminal) is the same as the polarity of the transmitted pulse. For general low-resistance and open-circuit faults, the low-voltage pulse method can be used to easily determine the distance between the fault point and the test end based on the polarity of the echo.
(3) For high-resistance faults, we use the high-voltage flashover method to test. For leakage high-resistance faults, we use a high-voltage pulse signal source to cause the cable fault point to flash over and discharge, so that the fault point generates a reflection signal, and the fault reflection wave is detected at the test end. For flashover high-resistance faults, we use a DC high-voltage power supply to cause the cable fault point to flash over and discharge, so that the fault point generates a reflection signal, and the fault reflection wave is detected at the test end.
(4) Signal processing process of the cable fault tester: The signal applied to the cable generates a reflection signal after encountering the fault point, and the reflection signal is given to the input circuit. These two signals pass through the high-speed A/D converter and the computer control system in turn, and the analog signal is converted into a digital signal for storage, and digital processing is performed, and the test waveform is sent to the display to display the test waveform, and waveform analysis is performed, that is, the rough measurement of the fault distance is completed.
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