Author: Noyafa–Cable Tester Manufacturer
Question: What is cable fault point detection? Answer: For cable fault point detection, it generally goes through three main steps: fault type diagnosis, fault point distance measurement, and precise point determination. The fault type diagnosis is mainly to determine the fault difference of the cable fault point: what is the cable fault point detection? Answer: The fault point detection of the cable generally needs to go through three main steps: fault type diagnosis, fault point distance measurement, and precise point determination. . The fault type diagnosis is mainly to determine the fault phase of the fault point of the cable, which belongs to the high resistance grounding or the low resistance grounding, so that the tester can choose the appropriate detection method.
The fault point distance measurement is also called pre-positioning. The test signal is applied to the faulty cable core wire or the fault information is measured and analyzed online, the distance of the fault is initially determined, and the fault scope is minimized to facilitate the accurate point determination. Pre-positioning methods can generally be classified into two categories, namely classical methods, such as bridge method, etc.; modern methods, such as low-voltage pulse method, high-voltage flashover method, etc. Precise point determination is based on the pre-positioning distance to accurately determine the actual location of the fault point.
The precise point determination methods mainly include the acoustic determination point method, the induction fixed point method, the time difference fixed point method and the synchronous fixed point method. This paper mainly discusses the basic method of fault point pre-location. For low-resistance breakdown, short-circuit, and open-circuit faults, a pulse signal can be applied to the cable core.
The signal is transmitted and reflected in the cable, and the pulse waveform is measured with a digital oscilloscope or a laptop virtual oscilloscope to calculate the location of the fault point. The advantages of the low-voltage pulse reflection method are that it is simple and intuitive, does not require careful cable raw materials, and can distinguish the fault type according to the polarity of the reflected pulse. The disadvantage is that it cannot be used to detect high resistance and flashover faults.
Using the echo phenomenon when the characteristic impedance of the transmission line changes, a certain voltage is added to the cable core to prevent it from burning through and causing discharge. The discharge pulse is transmitted and reflected in the cable, the position ratio of the reflected pulse is measured with a digital oscilloscope, and the position of the fault point is calculated. This method is suitable for high resistance breakdown, but the operator's safety is threatened, and the waveform is difficult to distinguish.
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