Leakage Locating Technology Of Low Voltage Cable Based On Signal Tracing Principle

Low-voltage power distribution lines are distributed in densely populated areas,with wide coverage,harsh environments,and more potential leakage hazards.Contact with the leakage point of the human body can easily cause electric shock,endangering life and safety;long-term operation of the leakage point may cause electrical fire.Moreover,when the residual current is large,the residual current protector or the leakage protector operates to remove the fault,which will cause a long-term power outage and affect the reliability of the power supply.However,the commonly used methods for finding the leakage location are to use a clamp-on ammeter to measure the leakage current of the cable online,to use a Rogowski coil fully enclosed detector to measure the leakage current,or to use a shaker with a megohmmeter to measure the insulation resistance to ground.For hidden cables in walls and underground,if you want to measure the leakage current on the cables,you must excavate the wall and the ground.These types of leakage detection methods are constrained by space and need to be solved urgently.First,three-level residual protection,existing clamp-on ammeters and other leakage detection devices can be used to determine the line section where the fault point is located,and the faulty phase line can be determined according to the characteristics of the large current after the signal is connected.In order to locate the leakage point,a non-contact leakage fault location method based on the principle of signal tracing is proposed,and a feasibility analysis is carried out.A specific frequency current signal is applied to the fault cable through a signal generating device,and the signal acquisition device is used The magnetic rod coil sensor more accurately collects the magnetic field around the cable to obtain the current signal,and judge the location of the fault point based on the current mutation characteristics.Secondly,analyze the changes of the current path before and after the leakage and the characteristics of the change of the current at the leakage point.A low-voltage cable simulation model is established in the Ansoft Maxwell simulation software to provide a theoretical basis for the measurement of the current on the existing cable;establish a magnetic rod coil detection The finite element model of the sensor changes the length and cross-sectional area of the magnetic rod of the magnetic rod coil sensor,as well as the diameter and number of turns of the enameled wire.Design a non-contact sensor that meets the measurement requirements;establish a joint model of rebar-cable-detector to analyze the influence of rebar material on the signal received by the sensor.Furthermore,the software and hardware design schemes of the signal generating device and the signal collecting device are given,and the key parameters such as the frequency and amplitude of the injected signal and the frequency characteristics of the sensor are optimized.The signal generating device is mainly designed based on Direct Digital Frequency Synthesis(DDS)to generate a sine signal of a specific frequency.It has a current detection module.Under the action of automatic gain control,the gear can be adjusted according to the size of the grounding resistance.The signal acquisition device system mainly includes: STM32F407high-performance embedded microcontroller,filter circuit,signal gain regulator,Bluetooth wireless communication module,display module,non-contact sensor,etc.Finally,a leakage fault detection experiment platform was established,and sensor characteristic experiments,detection device anti-interference experiments,and simulated leakage fault experiments were carried out.Through the simulated leakage experiment,the specific range of the circuit and the leakage point is detected,and the error range is within an acceptable range between 25 cm.The correctness of the conclusions obtained from the analysis in this paper and the effectiveness of the non-contact sensor used in determining the leakage point are verified,which indicates that the leakage detection system has good reliability.