Research On Fault Location And Its Application For Hybrid Transmisson Line Consisit Of Overhead Transmission Line And Power Cable In Distributed Network

The hybrid transmission lines consist of overhead transmission line and power cable are more and more applied to distribution network because of urban planning.Once fault occurs on hybrid transmission lines due to natural factors such as bad weather and human factors like piling construction,it would cause significant economic losses.Therefore,it is necessary to study effective and precise fault location method to reduce the difficulty of finding fault point,so that vigorous action could be taken to restore power supply to ensure the safe and stable operation of the power system.In order to obtain the operating characteristics of hybrid transmission lines under typical operating conditions,this paper establishes a simulation model based on actual hybrid transmission line of distributed network in Shanghai,then the characteristics of voltage and current under normal and various fault conditions are simulated and analyzed in PSCAD.The results show that the three phase voltage and current waveforms of the hybrid transmission line are consistent with that of a single overhead line or a single cable line.However,due to the joint resistance at the hybrid line’s connection point,the sequence voltage along the transmission line is quite different,because a sudden voltage change occurs at the connection point,resulting in an unknown voltage difference between the left and right sides of the connection,which needs to be considered.To analyze the influence of joint resistance on fault location,considering the stochastic variation of the joint resistance,this paper simulate and analyses the fault location process based on Monte Carlo method.The results show that,joint resistance would cause fault location errors under each fault condition,especially for three phase to ground fault because the fault current is large.For the two-segment overhead cable hybrid line,the joint resistance will increase the fault location error to about 1%.For the complex structure multi-section hybrid transmission line,the greater the fault location error is caused by the joint resistance,and the greatest the error can reach 10% when the hybrid transmission line is divided to 10 segments.To improve fault location accuracy,this paper presents an improved two-terminal fault location method.It takes joint resistances and fault distance as unknowns to establish the fault location equations,then the equations are solved through the multi-scale quantum harmonic oscillator algorithm to locate the fault point.Simulation results show that this method is immune to joint resistance,fault location and fault type,and the simulation errors are lower than 0.5%,which shows that this method is more accurate than traditional methods.This paper also proposes a fault section location method based on binary wolf pack algorithm for distribution network of multi-branch complex structure.This method firstly establishes mathematical model of the fault location of for the distribution network based on fault information collected from FTUs,then the wolf pack algorithm is utilized to optimize the solution to achieve the fault section positioning.The simulation results show that the proposed method has good adaptability and can be applied to typical power distribution network like single power supply radiation and multi-power source open-loop operation.It has good accuracy and high calculation speed with good fault-tolerant ability.Finally,this paper present practical examples of both fault distance detection and fault section location of distribution network’s hybrid lines.The results show that the fault location error is about 0.46 km,which is basically the same as the inspection result.And the fault section location result of the actual multi-branch distribution network is consistent with the fault section position,even the fault information code is distorted because of some FTUs are invalid.The results of this paper can provide important theoretical and practical reference for the fault location of the hybrid line of distribution network overhead cable,which is significant for the safe and stable operation of the distribution network and the reduction of on-site operation and maintenance costs.