Power cable fault detection is a worldwide topic. Cable fault detection equipment with advanced electronic technology

　　Born for appear. The development of cable fault detection technology has experienced a long process. Cable fault test method basically has the following categories:

　　One, low voltage pulse method

　　Low voltage pulse method is based on the theory of microwave transmission (radar principle), add a pulse signal on cable fault phase, when the waves transmit to the point of failure must be partially reflecting back, through the analysis of the difference of the incident wave and reflected wave, compute the distance of the point of failure. Due to the low voltage of the output signal (usually a 150 v) is safe, therefore, is called the low pressure

　　Pulse method. This method can be used to measure the low resistance of the cable fault, open circuit fault and cable length and the position of the part of the middle connector. The waveform pattern as shown in figure:

　　Cable only after full discharge, can use method of pulse measurement. Open circuit, the total length of reflection wave and starting wave with polarity. When low resistance fault waveform does not appear in the total length of reflection wave. The middle of the cable connector of reflected wave and transmitted wave are the same as the polarity, commonly occasionally appear negative, pulse amplitude than the point of failure or cable terminal reflection pulse amplitude is small; Tee joint reflected wave and transmitted wave reverse polarity, and the larger.

　　Second, the high voltage pulse method

　　High voltage pulse method can measure all types of faults, especially the leakage is more effective in high resistance. Impulse voltage size for cable should be at fault can be fully flashover discharge, the instrument can record to the ideal of blunt waveform is good, do not start the ball gap adjustment was great. If the fault point discharge is difficult, should as far as possible can increase storage capacitance or improve impulse voltage (increasing gap spacing). But don't pressure impact flash all the time. For high voltage pulse method measuring cable fault at the beginning of this wiring diagram

　　With the wave:

　　Three, multiple pulse method in the application of cable fault test

　　To sum up, the second pulse method and the concept of multiple pulse method is based on high voltage breakdown in high voltage flashover method and make the fault point discharge on the basis of this. Cable fault point by instantaneous short circuit breakdown would produce arc, the moment low resistance fault characteristics. In the arc stability phase (or instantaneous low resistivity zone) on the cable again add a low-pressure pulse signal, will appear a and low resistance was tested with low voltage pulse method of failure of the same waveform. Put this on the cable and high voltage pulse and low voltage pulse method called the second pulse method, if the low voltage pulse signal is sent cycle is called multiple pulse method. Multiple pulse method principle diagram is illustrated below:

　　Another advanced multiple pulse method is that it can launch the pulse signal, periodic ensures that in the fault point is in a state of short circuit arc there will be one or more of the reflected wave back, so as to show the test waveforms. Multiple pulse method basic principle of the test or the wave reflection principle of transmission line theory, only relative average high voltage pulse method, it makes with high pressure pulse form instantaneous short circuit arc fault point, low pressure pulse during arc again to the fault cable, at this point, you can get high impedance fault of low pressure pulse waveform, the waveform than the ordinary high voltage pulse waveform easy interpretation, completely as low voltage pulse waveform interpretation analysis, such as to low voltage waveform of pulse length measurement with the screen, according to the comparison is more easy to read. To sum up, multiple pulse method of cable tester advancement is to fundamentally solve the problem of difficult reading waveform, because it will impact all complex waveforms of high voltage flashover method became a kind of extremely simple waveform, namely, low voltage pulse method fault test waveforms, easy to identify easy to grasp, use staff a little theory training can achieve the goal of fast accurate measurement fault distance.　　

　　Henan jinshui cable group co., LTD

　　Technical department

　　2016/7/2