Research Of Underground Cable Fault Detection Equipment

With the wide application of underground cables,the normal operation of underground cables has a great influence on daily life of people and the economic development of the society.Quickly investigating the location of faults in the cable will greatly reduce the losses caused by cable faults.Therefore,the equipments for fast detecting faults in underground cables has a broad market application prospect.In this paper,the theory and implementation involved in the detection of faults in underground cables are studied in depth.Theoretically,the transmission characteristics of traveling wave signals in a single conductor system are studied using the basic transmission line equation.The principle of traveling wave fault location is explained.Because the underground cable is different from the aerial cable,the transmission characteristics of the traveling wave signal in the double conductor system are deduced by matrix.The elements of the underground cable impedance matrix and the admittance matrix are given as well.The characteristics of the traveling wave signal in the underground cable are obtained.Due to the non-linearity of traveling wave signal propagation,in order to obtain more accurate measurement results,PSCAD electromagnetic transient simulation software was used to analyze the impact of equipment-related parameters on measurement errors,including sampling frequency,amplitude,pulse width,rise time of the drive signal,and fault return waveform recognition threshold.The sensitivity of the equipment to the fault and the applicable range of the ranging under the relevant parameters are also given.Based on the theory of underground cable fault point detection,an equipment which driven by multi-band signal with visible waveform fault detection is designed.The equipment adopts alternating sampling method to achieve 200 MHz sampling frequency.A touch screen is used as human-machine interface to input test parameters.DSP and FPGA control the peripheral circuit to produce the designated driving signal according to the detection demands.As the result,the detection of the fault point in different scales is realized.The relevant waveform can be shownon the screen.For the signal integrity problems that may exist in high-speed circuits,the PCB design ideas for key network are given,including clock distribution network tree topology signal reflection suppression,parallel data transmission path routing rules and power transmission-based decoupling network design method.The design and manufacture of underground cable fault point detection equipment is completed.The equipment has been used for on-site underground cable fault detection.The experimental results show that the sampling circuit works normally and the fault waveform is clear and easy to identify.The location and features of the fault point could be accurately detected.