Several common faults of cables

Author: Noyafa–CCTV Monitor Tester

Several common faults of cables at fault point of cable fault tester Cable fault tester fault point cable faults are commonly divided into several common faults such as high-resistance short-circuit fault, interphase short-circuit fault, low-resistance fault, and flashover fault. 1. The low-voltage pulse reflection method is suitable for low-resistance (less than 10 times the wave impedance), grounding and open-circuit faults, and can test the full length of the cable and the propagation speed of radio waves in the cable. When the cable has a low-resistance or grounding fault, The equivalent impedance at the fault point of the cable shall be the parallel connection of the fault resistance and the characteristic impedance of the cable. The smaller the fault resistance of the cable, the more obvious the reflected waveform.

When the fault resistance of the cable is zero, it is total reflection. Since the equivalent impedance of the test end (input impedance of the test instrument) is greater than the characteristic impedance of the cable, the same polarity reflection pulse is generated at the test end. At the low resistance or ground fault, since the fault resistance is smaller than the characteristic impedance of the cable, the reverse polarity pulse is generated after the incident pulse reaches the fault point and transmitted to the test terminal. The falling edge of the received reverse polarity pulse corresponds to the cable fault. The reflected waveform of the point. When an open-circuit fault occurs in the cable, the equivalent impedance of the cable fault is the series connection of the fault resistance and the cable characteristic impedance. The open-circuit means that the fault resistance is infinite. In this case, the incident pulse will form a total reflection, and a reflection pulse of the same polarity will be generated at the test end. , the rising edge of the received pulse of the same polarity and the reflected waveform of the fault point correspond to the fault point of the cable fault tester. 2. First, apply a high-voltage pulse of a certain voltage level and a certain energy to the faulty cable at the test end of the cable, so that the cable's fault A breakdown arc occurs at the high resistance fault point.

At the same time, a low-voltage pulse for measurement is added to the test end. When the measurement pulse reaches the high-resistance fault point of the cable, it encounters an arc and reflects on the surface of the arc. Since the high-resistance fault becomes an instantaneous short-circuit fault during arcing, the low-voltage measurement pulse will have obvious impedance characteristic changes, so that the waveform of the flashover measurement becomes the low-voltage pulse short-circuit waveform, making the waveform identification particularly simple and clear. this is what we call“second pulse method”.

The reflected waveform of the received low-voltage pulse is equivalent to the waveform of a complete short circuit of a wire core to ground. The low-voltage pulse waveforms obtained when the high-voltage pulse is released and the low-voltage pulse obtained when the high-voltage pulse is not released are superimposed, and the two waveforms will have a divergence point, which is the reflected waveform point of the cable fault point. This method combines the low-voltage pulse method with the high-voltage flashover technique, making it easier for the tester to determine the location of the fault point of the cable.

Compared with the traditional cable fault testing method, the advanced point of the secondary pulse method is that the complex waveform in the shock high-voltage flashover method is simplified to the low-voltage pulse short-circuit fault waveform, so the interpretation is extremely simple, and the fault distance can be accurately calibrated. Cable fault tester fault point 3. The three-pulse method adopts the double-impact method to prolong the arcing time and stabilize the arc, which can easily locate high-resistance faults and flashover faults. The three-pulse method has advanced technology, simple operation, clear waveform, fast and accurate positioning, and has become the mainstream positioning method for high-resistance faults and flashover faults.

The three-pulse method is an upgrade of the two-pulse method. The method is to first measure the reflected waveform of the low-voltage pulse without penetrating the fault point of the cable under test, and then use the high-voltage pulse to break down the fault point of the cable to generate an arc. When the arc voltage drops to a certain value, the medium voltage pulse is triggered to stabilize and prolong the arc time, and then the low voltage pulse is sent out to obtain the reflected waveform of the fault point. It is easier to find the fault point waveform than the secondary pulse method due to the use of medium voltage pulses to stabilize and prolong the arc time. Cable fault tester fault point Shenzhen Noyafa Electronic Technology Co., Ltd. is a high-tech enterprise engaged in scientific research, production and sales, and provides technical services for cable fault detection.

At present, a variety of high-voltage test equipment and testing instruments have been widely used in the industry. At the same time, our company provides technical services such as cable fault detection and substation testing and testing to users across the country. The core engineer responsible for providing technical services has 20 years of on-site testing. Experience, can provide solutions according to different types of cables and site environment. Several common faults of cables Cable fault tester fault point Shenzhen Noyafa Electronic Technology Co., Ltd.