How many test methods are there in the cable fault tester?

Author: Noyafa–Cable Tester Manufacturer

Question: How many test methods are there for the cable fault tester? Answer: The bridge method of the cable fault tester The bridge method of the cable fault tester is to measure the DC resistance value of the cable core wire with a double-arm bridge, and then accurately measure the actual length of the cable. According to the electrical problem: the cable fault tester has How many test methods? Answer: The bridge method of the cable fault tester The bridge method of the cable fault tester is to measure the DC resistance value of the cable core wire with a double-arm bridge, and then accurately measure the actual length of the cable. According to the proportional relationship between the cable length and the resistance, Calculate the point of failure. This method is a traditional and effective method for low-resistance faults. The operation is relatively simple and the precision is high.

However, due to the limitation of bridge voltage and galvanometer sensitivity, the bridge method of cable fault tester is only suitable for DC resistance less than 100 kΩThe low resistance leakage fault, and it is required that at least one cable is fault-free. This method is not applicable to high-resistance faults, wire-break faults and faulty cables with three-phase leakage. The low-voltage pulse test method of the cable fault tester The low-voltage pulse test method of the 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.

The distance to fault is calculated using the observed time difference between the transmitted pulse and the reflected echo pulse and 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 fault point of the cable 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 does not apply to high-resistance leakage faults and high-resistance flashover faults.

High-voltage impulse flashover method of cable fault tester The high-voltage impulse flashover method of cable fault tester can test high-resistance leakage faults, high-resistance flashover faults, low-resistance short-circuit faults and disconnection faults of cables. A cable fault detection method with wide adaptability. The high-voltage shock flashover method is to apply a shock high voltage at the beginning of the faulty cable to break down the fault point with an arc. Use the voltage sudden jump at the moment of fault breakdown as the test signal.

Ranging is performed by observing the time that this signal travels once between the fault point and the beginning of the cable. The current sampling method is often used to take test signals. The current sampling method uses the principle of electromagnetic induction, and uses the current transformer to pick up the current signal on the grounding wire to obtain the reflected signal of the electric wave current in the cable.

There is no electrical relationship with the high-voltage generator and mains, so it is particularly safe. The waveform obtained by the current sampling method has a clear characteristic inflection point of the reflected waveform, which is especially beneficial to the analysis and location of fault distance. However, the test waveform of the current sampling method is more complicated; the waveforms obtained by different types, different lengths, different fault distances, and different impulse high voltages are ever-changing, and are often far from the standard waveforms.

Misjudgment and misjudgment often occur due to the inability to grasp the waveform law. The second pulse method of the cable fault tester Because of the shortcomings of the above-mentioned test methods, it is required to develop a new test method that is both accurate and practical. The second pulse method thus appeared.

The advanced point of the secondary pulse method is to transform the complex waveform in the impact high-voltage flashover method into an extremely simple and easy-to-master short-circuit fault test waveform of the low-voltage pulse method. Anyone with a little training can quickly and accurately detect failures. The basic test principle of the second pulse method of the cable fault tester The low-voltage pulse method cannot test the high resistance fault (no fault echo) of the cable.

However, if a low-voltage test pulse can be sent while the fault point is broken down by the arc under the action of a sufficiently high impulse voltage, a short-circuit reflected echo can be obtained at the short-circuit point. The polarity of this reflected echo is opposite to that of the transmitted pulse. When the short-circuit arc at the fault point is extinguished, a low-voltage test pulse (secondary pulse) is launched, and the full-length waveform of the open circuit of the cable can be measured.

The waveforms acquired two times before and after are displayed on one screen at the same time. The full-length waveform of the open circuit has the same polarity as the transmitted pulse, and the polarity of the fault reflection waveform is opposite to that of the transmitted pulse, and must be within the full-length distance. Therefore, the fault waveform can be distinguished and judged very well.