Automatic Cable Fault Location Based On Impulse Current Method

Impulse current fault location method(Impulse current method,ICM)is a kind of cable fault location method with safe test,high success rate and wide application range,but the current waveforms generated by ICM are complex,and the reflection pulses from the fault point are difficult to identify,up to now,it still mainly relies on manual identification of the reflected pulses from the fault point for cable fault location,which requires high professional experience of the operators.Realizing the automatic fault location is the future of the ICM,due to the inaccurate model of impulse current location system(ICLM),there is a lack of in-depth research on the signal characteristics and the reason for the complexity of the waveforms,the existing methods only can focus on the detection of wave heads,which can’t adapt to the complex waveforms.Therefore,the existing methods are still unsatisfactory.This paper introduced the structure and principle of ICLM,then established the model of it.For the surge generator,a series circuit model of RLC was established,and used the two methods of underdamped discharge characteristics and series resonance characteristics of the RLC circuit to quantify its parameters.For the linear coupler,a series circuit model of coil mutual inductance,self-inductance,self-resistance and sampling resistance was established,and the parameters were quantified by measuring the frequency response characteristics of the coil and the identification method of sub-band parameters.Aiming at the problem that the transfer function of the linear coupler isn’t convergent,a method of using the modified transfer function to realize the secondary loop calculation and simulation was proposed,which realized the quantitative analysis of ICM.Based on this model,the fault traveling wave process of ICM was analyzed and the following results were obtained: the traveling waves(forward traveling waves)moving toward the fault point is similar to its reflection waves from fault point(reverse traveling waves),and their polarity are opposite,what’s more,the delay is the time it takes for the traveling wave to propagate back and forth between the measuring end and the fault point.According to it,an automatic fault location method was proposed to detect the reflected wave of the fault point on the directional traveling wave by using the correlation coefficient.Since the length of the sound phase in three-phase cable is always longer than or equal to the fault distance(the fault is located at the end of the line),if high-voltage pulses are applied to the sound phase and the faulty phase,the arrival time of the first reflected pulse on the sound phase is always later than or equal to the faulty phase.Because of it,a method about constructing the fault phase direction traveling wave using only the current signal was proposed.The article also analyzed the influence of the linear coupler’s transfer characteristics,line loss and dispersion,the reflection coefficient change of the measuring end after paralleling the sound phase on the ICM.It proved that the secondary voltage signal output by the linear coupler still meets the characteristics obtained by the primary current;the accuracy of the correlation method is mainly affected by the dispersion of the traveling wave in the propagation process.The higher the signal frequency,the smaller the effect.The paper given the ideal frequency band used for location of medium voltage cables commonly used in engineering;the parallel sound phase mainly affects the reflection when the stray inductance of the measuring end is in effect,and there is still enough energy at the measuring terminal,so it has little effect on the method proposed in this paper.The conclusions were verified by the simulation data of ATP-EMTP and the test data of the actual system.It proved the accuracy and feasibility of the ICLM model,the impulse current characteristic analysis conclusion,the fault location method proposed in this paper.This method was based on effectively solving the problem that the waveforms of ICM are complex.It’s expected to reduce the requirements on the experience of operators and improve the efficiency of cable maintenance.