Several testing methods for cable fault testers

talk aboutCable fault testerSeveral testing methods

The Bridge Method of Cable Fault Tester
The bridge method of cable fault tester is to use a double arm bridge to measure the DC resistance value of the cable core wire, accurately measure the actual length of the cable, and calculate the fault point according to the proportional relationship between the cable length and resistance. This method is a traditional and effective approach for low resistance faults. The operation is relatively simple and the accuracy is also high. However, due to the limitations of bridge voltage and galvanometer sensitivity, the bridge method of cable fault tester is only applicable to low resistance leakage faults with DC resistance less than 100 k Ω, and requires that the cable must have at least one *. This method is not applicable for high resistance faults, wire breakage faults, and cables with leakage in all three phases.
Low voltage pulse testing method for cable fault tester
The low voltage pulse testing method of cable fault tester is based on the low voltage pulse traveling in the cable, which will cause the reflection of the pulse wave when encountering the fault point. Calculate the fault distance by using the time difference between the observed emitted pulse and reflected echo pulse, as well as the transmission speed of the traveling wave in the cable. The bridge method of the cable fault tester can intuitively determine whether the fault at the cable fault point is an open circuit or a short circuit, and can directly measure the distance from the test end to the fault point. However, the low voltage pulse rule is not applicable for high resistance leakage faults and high resistance flashover faults.
Cable fault testerHigh voltage impact flashover method
The high-voltage impulse flashover method of the cable fault tester can test high resistance leakage faults, high resistance flashover faults, low resistance short circuit faults, and wire breakage faults of cables. It is a reliable and widely adaptable cable fault detection method. The high-voltage impulse flashover method is to apply an impulse high voltage at the beginning of the faulty cable, and break down the fault point with an arc. Use the voltage jump at the moment of fault breakdown as the test signal. Observe the time it takes for this signal to travel back and forth between the fault point and the beginning of the cable for distance measurement. Use current sampling method more often to obtain test signals. The current sampling method utilizes the principle of electromagnetic induction and uses a current transformer to pick up the current signal on the grounding wire to obtain the reflected signal of the electromagnetic current in the cable. It has no electrical relationship with the high-voltage generator or mains power, so it is particularly safe. The waveform obtained by current sampling method has clear inflection points in the reflected waveform characteristics, which is particularly beneficial for fault distance analysis and localization. However, the test waveform of current sampling method is relatively complex; The waveforms obtained from different types, lengths, fault distances, and impact high voltages are constantly changing and often far from the standard waveform. Due to the inability to grasp waveform patterns, misjudgments often occur.
Secondary pulse method of cable fault tester
Due to the shortcomings of the above-mentioned testing methods, it is required to develop a new testing method that is both accurate and practical. The secondary pulse method emerged as a result. The advantage of the secondary pulse method is that it transforms the complex waveform in the impulse high-voltage flashover method into an extremely simple and easy to master waveform for short-circuit fault testing in the low-voltage pulse method. Anyone with a little training can quickly and accurately detect faults.
Secondary pulse method of cable fault tester
The basic testing principle of the secondary pulse method
The low voltage pulse method cannot test for high impedance faults (* echo) in cables. However, if the fault point is broken down by the arc under sufficiently high impulse voltage, a low-voltage test pulse can be sent to obtain a short-circuit reflection echo at the short-circuit point. The polarity of the reflected echo is opposite to that of the transmitted pulse. After the short-circuit arc at the fault point is extinguished, a low-voltage test pulse (secondary pulse) is emitted to measure the waveform of the cable's open circuit throughout its entire length. The waveforms collected twice before and after are displayed on the same screen simultaneously. The open circuit full length waveform has the same polarity as the transmitted pulse, while the polarity of the fault reflection waveform is opposite to that of the transmitted pulse and must be within the full length distance. So the fault waveform * can be distinguished and judged.