Author: Noyafa–Cable Tester Suppliers
Before 1970, the power cable fault location usually used the bridge method and the low-voltage pulse reflection method to test the power cable fault: 1. The bridge method short-circuits the faulty phase of the tested power cable with a non-faulty phase at the cable terminal, At the beginning of the power cable, use a single-arm bridge to connect the faulty phase and the short-circuited non-faulty phase, and measure the ratio of the resistance of the non-faulty phase plus the resistance after the fault point of the faulty phase to the resistance before the fault point of the faulty phase, The distance from the terminal to the fault point can be calculated according to the length of the cable. 2. In the low-voltage pulse reflection method, a low-voltage pulse is injected into the faulty phase of the power cable. When the pulse propagates along the cable to the impedance mismatch point, that is, the fault point, a reflected echo is generated and sent to the test point to be recorded by the instrument. The difference between the round-trip time of the pulse and the wave speed of the pulse in the cable makes it possible to calculate the distance from the fault point to the test point. Both cable fault location methods are accurate for low-resistance faults, but not suitable for high-resistance faults.
Later, the DC flash test method and the shock flash test method appeared, which test intermittent faults and high resistance faults respectively, both of which can be divided into current and voltage flash test methods. The voltage method has a high measurable rate, the waveform is clear and easy to judge, and the blind area is twice as small as that of the current method, but the wiring is complicated, and it is dangerous to people and instruments when the partial voltage is too large: the current law is opposite. At present, these two methods are the mainstream methods of domestic high-resistance cable fault testers, which basically solve the problem of cable high-resistance fault test.
However, the instrument has a blind spot, and the waveform is sometimes not obvious enough, and the error of the instrument is relatively large depending on human judgment. In 1990, the secondary pulse method of cable fault location was invented abroad, that is, combined with the high-voltage generator impact flashover technology, at the moment of arcing at the fault point, it was triggered by an internal device to emit a low-voltage pulse. This pulse is at the fault point flashover ( The resistance value of the arc is very low) short-circuit reflection occurs, and it is stored in the instrument. After the arc is extinguished, a recurring measurement pulse passes through the fault and reaches the end of the cable and an open-circuit reflection occurs. Comparing the waveforms of the two low-voltage pulses can easily determine the fault point ( Breakdown point) position is the most advanced basic test method at present. Based on the secondary pulse method, there are DL series cable fault testers from SHENZHEN NOYAFA TECHNOLOGY CO., LIMITED.
DL series cable fault tester is a secondary pulse cable fault tester developed and produced by Noyafa Electric according to the market demand and the test specifications of power cables. Device and external signal sensor receiving device, the secondary pulse cable fault tester can accurately test the high and low resistance faults of all cables below 35KV, and use different data sampling rates to provide fast and accurate technical indicators.
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